JP5225981B2 - Self-excited and self-detecting piezoelectric cantilever sensor for direct detection of airborne analytes in air - Google Patents

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the priority of US patent application Ser. No. 11 / 625,919, filed Jan. 23, 2007, entitled "Self-Exciting, Self-Sensing Piezoelectric Cantilever Sensor ", which is hereby The entire document is incorporated by reference. U.S. Patent Application No. 11 / 625,919 is filed with U.S. Provisional Application No. 60 / 761,172, filed Jan. 23, 2006, entitled "Piezoelectric Cantilever Sensors" and U.S. Provisional Application No. 60/76, filed Jul. 11, 2006. 807,020, claiming the priority of the name “Piezoelectric Cantilever Sensors”; both of which are hereby incorporated by reference in their entirety. This application also claims priority of US Provisional Application No. 60 / 746,951, filed May 10, 2006, entitled “Detection of Airborne Pathogens Directly in Air”, which is also incorporated herein by reference in its entirety. Is incorporated.

TECHNICAL FIELD The technical field relates generally to sensors, and more specifically to piezoelectric cantilever sensors and detecting and measuring analytes using piezoelectric cantilever sensors.

Background cantilever sensors can be roughly classified into two types, microcantilevers and macrocantilevers, depending on the sensor dimensions. Microcantilever sensors can be used in both static (bending) and dynamic (resonant) modes. In static mode, the deformation of the cantilever arm is measured to determine whether the analyte (the substance being analyzed) is present. In the dynamic mode, the resonant frequency is measured to determine whether an analyte is present. Macrocantilever sensors are generally not used in static mode because the bending of the cantilever arm is often limited. The macro cantilever sensor can be used in a liquid immersion state or in a gas or under vacuum. In general, the sensitivity is higher when the cantilever sensor is used in gas / vacuum than in liquid. Wetting liquids tends to adversely affect sensitivity. However, there are many practical applications for measuring analytes in liquid media.

  One type of known microcantilever sensor is a silicon-based microcantilever sensor. A typical silicon-based microcantilever sensor includes a microcantilever that acts as a resonator. The micro-cantilever is driven by an external actuator at the base of the micro-cantilever to generate vibration in the resonator. In general, vibration is detected by an external optical detector. One drawback of typical silicon-based microcantilevers is the complex external optics required for detection. Furthermore, the optical detection means has the disadvantage of limiting the application of the microcantilever sensor to optically transparent samples. Another disadvantage is the weight and complexity added to the sensor by an external actuator. Yet another disadvantage is that the external actuator can only be placed on the base of the microcantilever, which limits its effectiveness in driving cantilever vibration. A further disadvantage of silicon-based microcantilever sensors is that they are mechanically fragile. Therefore, silicon-based microcantilever sensors cannot be used in environments with high liquid flow rates. In addition, typical silicon-based microcantilever sensors lose their detection sensitivity in liquid media due to viscous damping.

  Another type of known cantilever sensor is a quartz-based piezoelectric cantilever sensor. Quartz is weakly piezoelectric, and thus, like silicon-based cantilever sensors, quartz-based piezoelectric cantilever sensors have poor detection sensitivity due to viscous damping in liquid media. Furthermore, the detection sensitivity of quartz-based sensors is limited by the planar shape of the sensor.

  It is known that a conventional piezoelectric cantilever is manufactured by attaching a non-piezoelectric layer on a part or the entire surface of a piezoelectric layer. In some conventional piezoelectric cantilevers, the piezoelectric layer is fixed at one end so that when the piezoelectric material is excited, the non-piezoelectric layer bends to accommodate the strain produced in the piezoelectric material. Resonance occurs when the excitation frequency is equal to the natural frequency of the underlying mechanical structure. This type of piezoelectric cantilever sensor is known to operate at frequencies below about 100 kHz in millimeter size. Currently, higher frequencies can only be obtained by making the cantilever sensor very short (less than 1.0 mm in length), very narrow (less than 0.1 mm in width), and very thin (less than 100 μm in thickness). Can do. However, when the size of the cantilever sensor is reduced, especially when the width is reduced, the usability in the liquid medium is impaired due to viscous damping. Attenuation increases inversely proportional to the square of the cantilever width.

  Modern biosensing technologies rely on fluorescence, laser, optical fiber based methods, quartz crystal microbalance technology, electrochemical enzyme immunoassay, and / or binding to metal particles. Most of these techniques are neither straightforward nor quantitative. Many of these techniques are also very slow. Furthermore, most of the techniques are useless for measuring mass changes, which can provide a convenient way to measure a variety of different parameters.

  A mass sensor based on resonance frequency requires three types of elements: an actuator (driver), a resonator, and a detector. One example of a mass sensor is a silicon-based microcantilever, which can be easily integrated into existing silicon-based approaches. In a silicon-based microcantilever mass sensor, the microcantilever acts as a resonator and is driven by an external lead zirconate titanate (PZT) actuator at the base of the microcantilever to generate vibration in the resonator. It can be detected by an optical detector. In bio-related detection, the receptor is immobilized on the cantilever surface. Binding of the antigen to the receptor immobilized on the cantilever surface increases the mass of the cantilever and causes a decrease in the resonant frequency. Detection of the target molecule is realized by monitoring the mechanical resonance frequency. Silicon-based microcantilevers are popular, but they rely on complex external optics for detection. In addition, PZT vibration drivers add to the weight and complexity of the sensor. Furthermore, the external actuator can only be placed on the base of the micro-cantilever, which limits its effectiveness in driving cantilever vibration. Optical detection means also limit application to optically clear samples.

  In addition to mass detection, silicon-based microcantilevers are also used as sensors for small molecules, which detect the stress generated on the cantilever by adsorbing species onto the receptor associated with the cantilever. By doing. The surface of the microcantilever is coated with an antibody or DNA receptor and allowed to bind to the target biomolecule. The stress generated during the binding or separation of the target molecule to the receptor on the microcantilever surface causes the microcantilever to deflect, which is adsorbed by an external optical element or on the piezoresistive coating layer on the cantilever surface / Can be detected by stress-induced DC voltage.

Compared to silicon-based sensors, millimeter-sized piezoelectric cantilever sensors are less bulky and less complex. Piezoelectric devices are excellent conversion candidates because of their short response time and high piezoelectric coefficient. Since they are piezoelectric, the drive and detection of mechanical resonance can be conveniently performed electrically within the resonator. Currently, piezoelectric biosensors are based on a commercially available quartz crystal microbalance (QCM), which is a disk device that uses thickness mode resonance for detection. Although quartz is a weak piezoelectric material, it is widely used as a layer thickness monitor, partly because large single crystal quartz for film fabrication can be used. The typical mass detection sensitivity of a 5 MHz QCM with a minimum detectable mass density (DMD) of 10 ⁻⁹ g / cm ² is about 10 ⁻⁸ g / Hz, about 4 orders of magnitude over a millimeter size piezoelectric cantilever. The sensitivity is low.

  There are microcantilevers that are about 100 μm long, several tens μm wide, and several μm thick. Such a microcantilever is used for detection in a bending mode or a resonance mode. The disadvantage of these microcantilevers is that their resonance characteristics are significantly degraded due to viscous damping. Furthermore, use in these liquid media has been realized at very low flow rates of a few μl / min.

  DW Carr and HG Craighead's `` Fabrication of nanoelectromechanical systems in single crystal silicon using silicon on insulator substrates and electron beam lithography '' J. vac. Sci. Technology. B., 15 (6), 1997. pp 2760-2763 Manufacturing of beam sensors with a mesh structure on the order of several hundred nm and multiple beam sensors has been disclosed, and a high resonance frequency of 40 MHz has been achieved. US copending application No. 11 / 659,919, filed Jan. 23, 2007, entitled “Self-Exciting, Self-Sensing Piezoelectric Cantilever Sensor” Describes the structure and basic operation of the liquid sample environment.

  Accordingly, there is a need to improve the detection capabilities of currently existing sensors, and a need to provide sensors with improved capabilities for detecting airborne species.

Overview A self-exciting and self-detecting piezoelectric cantilever detection device includes a piezoelectric layer and a non-piezoelectric layer attached to the piezoelectric layer, the distal end of the non-piezoelectric layer extending beyond the distal end of the piezoelectric layer, or Said non-piezoelectric layer being attached in such a manner that the distal end of the piezoelectric layer extends beyond the distal end of the non-piezoelectric layer. That is, the piezoelectric layer is bonded to the non-piezoelectric layer in a manner that the piezoelectric layer and the non-piezoelectric layer do not have the same spread. In various configurations of the present piezoelectric cantilever detection device, the piezoelectric layer, the non-piezoelectric layer, or both are fixed to at least one base. An electrode is operably associated with the piezoelectric layer. A self-exciting / self-detecting piezoelectric cantilever sensor is used to detect a change in mass. In order to determine the mass of the analyte on the detection device, the resonance frequency of the mechanical element of the cantilever sensor is measured. The measured resonant frequency is compared with the baseline resonant frequency to determine the frequency difference. The difference in frequency indicates the mass of the analyte on the detection device.

  According to aspects of the present invention, airborne pathogen detection in air is performed without the need for sample collection in a liquid or solid matrix. According to one aspect, a method for air detection of a target analyte, such as a biological or chemical substance, is performed by exposing the detection device to an airborne analyte. Identification entities located on the detection device bind to the analyte and are detectable while the analyte is present in the gas. Examples of specific identifying entities include chemical coatings for detecting chemical substances and immobilized antibodies for detecting biological substances.

  In one aspect of the invention, the detection device includes a sensor that includes a piezoelectric layer, a non-piezoelectric layer, and an identifying entity located on either of these two layers. In the first aspect, the sensor is a cantilever assembly that is secured at only one end. Here, the piezoelectric layer is connected to the base and the non-piezoelectric layer is attached in an overlapping manner to the ends of the piezoelectric layer. The electrode is attached to the piezoelectric layer and is electrically driven to excite resonance in the piezoelectric layer. The identification region on the non-piezoelectric layer attracts the analyte when exposed to the air stream, causing a mass change in the cantilever formed by the combination of the piezoelectric layer and the non-piezoelectric layer and the identification region. The change in resonant frequency when the analyte is attached compared to the baseline resonant frequency is determined, and the frequency shift indicates the amount of analyte retained in the identifying entity.

  The sensor configuration may be varied to accommodate different frequency detection points. The second type of sensor involves the use of a beam-type sensor, where the non-piezoelectric layer is attached to the base structure at both ends. The piezoelectric layer is disposed on the non-piezoelectric layer and is excited by resonance as described above. Identification entities on either the non-piezoelectric layer or the piezoelectric layer cause a mass change upon exposure to the aerosolized analyte, resulting in a frequency shift of the resonant frequency of the beam sensor. In this way the analyte can be detected and its mass is determined. A third type of sensor is a variation of the beam sensor, where the piezoelectric layer is a beam and the non-piezoelectric layer is attached to the top of the beam.

  An apparatus for detecting airborne analytes includes an exposure tube that includes a cantilever sensor attached to a nebulizer that aerosolizes the analyte and causes the analyte to be present in an air stream across the sensor. The analyzer measures the resonant frequency of the sensor and determines whether and how much analyte is present in the air stream.

  These and various other advantages and novel features that characterize the present invention are pointed out with particularity in the claims appended hereto and form a part of this specification. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should also be made to the figures and accompanying descriptions that form a further part of this specification, including: There is a description and description of preferred embodiments of the invention.

This summary is provided to introduce a selection of concepts in a simplified form that are further described in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
The foregoing summary, as well as the following detailed description, is better understood when read in conjunction with the appended drawings. For illustration of the self-exciting and self-detecting piezoelectric cantilever sensor, an exemplary structure thereof is shown in the drawings; however, the self-exciting and self-detecting piezoelectric cantilever sensor is limited to the specific methods and means disclosed. Is not to be done.

FIG. 1 is a diagram of an exemplary configuration of a self-exciting / self-detecting piezoelectric cantilever sensor. FIG. 2 is a cross-sectional view of an exemplary self-exciting and self-detecting piezoelectric cantilever sensor, showing electrode placement regions for electrodes operatively associated with the piezoelectric layer. FIG. 3 is a cross-sectional view of an exemplary self-exciting / self-detecting piezoelectric cantilever sensor, illustrating an exemplary electrode arrangement within the base of the self-exciting / self-detecting piezoelectric cantilever sensor. FIG. 4 is a cross-sectional view of an exemplary self-exciting / self-detecting piezoelectric cantilever sensor, showing an exemplary electrode arrangement outside the base of the self-exciting / self-detecting piezoelectric cantilever sensor. FIG. 5 is a diagram of an exemplary configuration of a self-exciting and self-sensing piezoelectric cantilever sensor in which the distal end of the piezoelectric layer is flush with the distal end of the non-piezoelectric layer. FIG. 6 shows a self-exciting and self-detecting piezoelectric cantilever in which the distal end of the piezoelectric layer extends beyond the distal end of the non-piezoelectric layer and the adjacent end of the piezoelectric layer extends beyond the adjacent end of the non-piezoelectric layer. FIG. 3 is a diagram of an example configuration of a sensor. FIG. 7 is a diagram of an exemplary configuration of a self-exciting and self-detecting piezoelectric cantilever sensor having two base portions. FIG. 8 is a diagram of another exemplary configuration of a self-exciting and self-detecting piezoelectric cantilever sensor with no piezoelectric layer attached to either base. FIG. 9 is a diagram of an exemplary configuration of a self-exciting and self-detecting piezoelectric cantilever sensor having a piezoelectric layer fixed at two ends. FIG. 10 is a diagram of an exemplary configuration of a self-exciting and self-detecting piezoelectric cantilever sensor in which the piezoelectric layer has two portions, one of which is fixed. FIG. 11 is another view of an exemplary configuration of a self-exciting and self-detecting piezoelectric cantilever sensor, in which the piezoelectric layer has two parts, one of which is fixed. FIG. 12 is a diagram of an exemplary configuration of a self-exciting and self-detecting piezoelectric cantilever sensor in which the piezoelectric layer has two portions, neither of which is fixed. FIG. 13 is a diagram of an exemplary configuration of a self-exciting / self-detecting piezoelectric cantilever sensor having a fixed non-piezoelectric portion and an unfixed piezoelectric portion. FIG. 14 is a diagram of another exemplary configuration of a self-exciting and self-detecting piezoelectric cantilever sensor with no non-piezoelectric layer attached to either base. FIG. 15 is a diagram of another exemplary configuration of a self-exciting / self-detecting piezoelectric cantilever sensor in which the piezoelectric portion has a width different from that of the piezoelectric portion. FIG. 16 is a diagram of an exemplary configuration of a self-exciting / self-detecting piezoelectric cantilever sensor including a piezoelectric layer and a non-piezoelectric layer, where the width of the piezoelectric layer is narrower than that of the non-piezoelectric layer 16. The distal end extends beyond the distal end of the non-piezoelectric layer, and the adjacent end of the piezoelectric layer extends beyond the adjacent end of the non-piezoelectric layer. FIG. 17 is a flow diagram of an exemplary method for detecting an analyte utilizing a self-exciting and self-detecting piezoelectric cantilever sensor. 18 is a plot of an exemplary resonance spectrum of the self-exciting and self-detecting piezoelectric cantilever sensor configuration shown in FIG. 1 operated in air. FIG. 19A is a perspective view of a piezoelectric cantilever sensor useful in the method of the present invention. FIG. 19B is a diagram of an embodiment of a fixed piezoelectric excited cantilever beam sensor useful in the method of the present invention. FIG. 19C is an illustration of an embodiment of a floating piezoelectric excitation cantilever beam sensor useful in the method of the present invention. FIG. 19D is an illustration of an embodiment of a fixed bimorph piezoelectric excited cantilever beam sensor useful in the method of the present invention. FIG. 19E is an illustration of an embodiment of an overhanging piezoelectric excited cantilever beam sensor useful in the method of the present invention. FIG. 19F is an illustration of an embodiment of a fixed lead zirconate titanate (PZT) piezoelectric excited cantilever beam sensor useful in the method of the present invention. FIG. 19G is a schematic diagram of an embodiment of a floating tip PEMC (ftPEMC) sensor according to the present invention. FIG. 20 is a resonance spectrum in air of the first embodiment of the overhang type piezoelectric cantilever sensor such as the one shown in FIG. 1 (see oPEMC # 1 in Table 1 in FIG. 47). FIG. 21 is a resonance spectrum in the air of the second embodiment of the overhang type piezoelectric cantilever sensor shown in FIG. 1 (see oPEMC # 2 in Table 1 in FIG. 47). FIG. 22 is a resonance spectrum in the air of the third embodiment of the overhang type piezoelectric cantilever sensor shown in FIG. 1 (see oPEMC # 3 in Table 1 in FIG. 47). FIG. 23 is a resonance spectrum in the air of the fourth embodiment of the overhanging cantilever sensor shown in FIG. 1 (see oPEMC # 4 in Table 1 in FIG. 47). FIG. 24 is a resonance spectrum of the fifth embodiment of the overhanging cantilever sensor shown in FIG. 1 (see oPEMC # 5 in Table 1 in FIG. 47). FIG. 25 is a resonance spectrum plot of phase angle versus excitation frequency in air for a fixed PEMCB sensor (aPEMCB, FIG. 19B) excited at 100 mV. FIG. 26 is a diagram illustrating resonance characteristics of the floating PEMCB (fPEMCB # 1, FIG. 19C) sensor using a phase angle versus excitation frequency plot at an excitation voltage of 100 mV in air. FIG. 27 is the resonance spectrum of a fixed bimorph PEMCB (abPEMCB # 1, FIG. 19D) sensor using a phase angle versus excitation frequency plot at an excitation voltage of 100 mV in air. FIG. 28 is a resonance spectrum when an overhanging PEMCB (oPEMCB # 1, FIG. 19E) sensor is excited with a voltage of 100 mV in the air. FIG. 29A is a diagram of an apparatus used to implement airborne anthrax detection. FIG. 29B is a diagram of an apparatus used to implement airborne anthrax detection. FIG. 30A is a diagram showing a result of a detection experiment for detecting anthrax in the air. FIG. 30B is a diagram showing the results of a detection experiment for detecting anthrax in the air using inorganic particles as a control. FIG. 31 is a diagram showing confirmation of detection for the experiment of FIG. 30A. FIG. 32 is a scanning electron micrograph of a sensor tested by the method of the present invention, showing anthrax spores immobilized on the sensor surface. FIG. 33 shows a side view of the humidity injector of the present invention. FIG. 34 is a flow diagram of the method of the present invention. FIG. 35 shows a notch structure of the sensor. FIG. 36 is a diagram showing a sensor sandwich structure. FIG. 37 shows an alternative sandwich structure for the sensor. FIG. 38 shows an alternative to FIG. 19A for sensor geometry. FIG. 39 illustrates another alternative configuration of the sensor of FIG. 19A. FIG. 40 is a diagram showing the beam-type structure of FIG. 19F. FIG. 41 is a diagram showing an alternative configuration of FIG. 19E. FIG. 42 shows an alternative configuration of FIG. 19G. FIG. 43 is a diagram showing an alternative configuration of FIG. FIG. 44 shows an alternative configuration of FIG. FIG. 45 is a diagram illustrating a multi-layer sensor configuration in which the layers are at least partially secured to the base. FIG. 46 is a diagram showing a configuration having a modified base. FIG. 47 is a diagram including Table 1. FIG. 48 is a diagram including Table 2. FIG. FIG. 49 includes Table 3. FIG. 50 is a diagram including Table 4. FIG.

Detailed Description of Exemplary Embodiments The self-exciting and self-detecting piezoelectric cantilever sensor described herein provides the ability to detect and measure very small amounts of analyte. Self-exciting and self-detecting piezoelectric cantilever sensors can be used to detect and measure analytes immersed in a liquid and analytes contained in a gas or vacuum. In various exemplary configurations, a self-exciting and self-detecting piezoelectric cantilever sensor includes at least one piezoelectric layer and at least one non-piezoelectric layer, wherein the piezoelectric layer is a non-piezoelectric layer, and the piezoelectric layer and the non-piezoelectric layer are They are combined in a manner that does not have the same spread. The piezoelectric layer, the non-piezoelectric layer, or both are fixed to at least one base. Piezoelectric and non-piezoelectric layers can be of various widths, lengths and thicknesses.

  A self-exciting and self-detecting piezoelectric cantilever sensor can be used to determine the mass of the analyte accumulated thereon. In one exemplary embodiment, a portion of the self-exciting and self-detecting piezoelectric cantilever sensor is disposed in the medium (eg, liquid, gas, vacuum). The resonance frequency of the self-excited / self-detecting piezoelectric cantilever sensor in the medium is measured and compared with the baseline resonance frequency. The difference between the measured resonant frequency and the baseline resonant frequency is indicative of the mass of analyte accumulated (eg, bound, adsorbed, absorbed) in the self-excited, self-detecting piezoelectric cantilever sensor.

  The analyte can be directly or indirectly coupled to the surface of the non-piezoelectric portion of the self-exciting and self-detecting piezoelectric cantilever sensor. The coupling of the analyte to the non-piezoelectric part of the self-exciting / self-detecting piezoelectric cantilever sensor can be achieved by changing the mass of the self-exciting / self-detecting piezoelectric cantilever sensor, changing the stiffness of the self-exciting / self-detecting piezoelectric cantilever sensor, Or cause a combination of these. The change in mass and / or stiffness can be measured as a change in resonance frequency and can be monitored and measured by a suitable analyzer, such as an operational amplifier, impedance analyzer, network analyzer, oscillator circuit, and the like. The change in resonance frequency when only at least a part of the self-exciting / self-detecting piezoelectric cantilever sensor is immersed in the liquid can be detected and measured. The change in the resonance frequency when only at least a part of the self-excited / self-detecting piezoelectric cantilever sensor is immersed in gas or vacuum can also be detected and measured.

  The self-exciting / self-detecting piezoelectric cantilever sensor can be operated even at a high frequency such as the order of 0.1 MHz to 6 MHz. At these high frequencies, values of the order of 10-100 can be obtained under liquid immersion in terms of the Q factor (ratio of the resonance peak frequency to the peak width at the midpoint of the resonance peak height). Self-exciting and self-detecting piezoelectric cantilever sensors can be operated at relatively high frequencies in liquid, gaseous and vacuum media. Thus, the self-exciting / self-detecting piezoelectric cantilever sensor provides extreme sensitivity to mass changes. Self-exciting and self-detecting piezoelectric cantilever sensors are particularly suitable for analytes present in very low concentrations in the medium, such as body fluids, water, and food materials.

The self-exciting and self-detecting piezoelectric cantilever sensor described in this specification has a mass accumulated in a small amount of 100 attogram / Hz (100 × 10 ⁻¹⁸ g / Hz) or less when immersed in a liquid medium. Provides the ability to detect changes. Therefore, the sensitivity of the self-excited and self-detecting piezoelectric cantilever sensor is about 1 million times that of the quartz crystal micro-cantilever sensor, about 100,000 times that of the standard analyzer, and the conventional three layers. About 10,000 times higher than the piezoelectric cantilever design.

  The self-exciting / self-detecting piezoelectric cantilever sensor enables detection of an analyte having a minimum concentration coupled to the non-piezoelectric portion. Using a self-excited, self-detecting piezoelectric cantilever sensor, pathogens and proteins are at concentrations up to several pathogens / mL and for proteins of average size (60 kDalton, kDa) at less than 1 pathogen / mL Detectable by concentration. Furthermore, any analyte that binds to the organic or inorganic functional group of the non-piezoelectric portion can be detected. The self-exciting / self-detecting piezoelectric cantilever sensor can operate in a medium having a relatively high flow rate. Piezoelectric cantilevers can operate in media with a flow rate of 0.5-10.0 mL / min, which is about 1000 times faster than the flow rates successfully used with known bending mode microcantilevers.

  Various exemplary uses of the present piezoelectric cantilevers include: detection of bioterrorism agents such as Bacillus anthracis, detection of foodborne pathogens such as E. coli, detection of pathogens in food and water, certain cell types in body fluids (eg, Detection of circulating tumor cells), biomarkers in body fluids (eg, proteins that mark specific pathophysiology, α-fetoprotein, β2-microglobulin, bladder cancer antigen, breast cancer marker CA-15-3, and others Detection of CAs (cancer antigens), calcitonin, carcinoembryonic antigen, etc., for example detection of explosive markers such as the presence of trinitrotoluene, dinitrotoluene, and detection of air-borne and water-borne toxins. Self-excited and self-detecting piezoelectric cantilever sensors can also be used to detect biological entities at the picogram level and to detect protein-protein interactions in both static and dynamic states.

Pathogens such as E. coli can be detected using a self-exciting / self-detecting piezoelectric cantilever sensor. Detection of model protein, lipoprotein, DNA and / or RNA at a concentration of 1.0 femtogram / mL ( ^10-15 g) and pathogen at 1 pathogen / mL, respectively, directly in the liquid, This can be realized by measuring at a frequency of about 1 to 2 MHz using a self-exciting / self-detecting piezoelectric cantilever sensor immobilized with an antibody specific to the target analyte. Self-exciting and self-detecting piezoelectric cantilever sensors can detect target analytes without false positives or false negatives even in the presence of contaminants. The self-exciting and self-sensing piezoelectric cantilever sensor described herein is particularly advantageous when used with raw samples without processing, without preparation, without a concentration step, and / or without any kind of concentration. Analyte detection using a self-exciting and self-detecting piezoelectric cantilever sensor can be performed directly in a raw sample, for example, at 0.5-10.0 mL / min under flowing conditions. When a clean sample is available, for example, in a laboratory environment, detection at 1 femtogram / mL is possible. This sensitivity is about 100 times higher than the sensitivity associated with known optical techniques.

  As described below, the sensitivity of a self-exciting, self-detecting piezoelectric cantilever sensor depends in part on its own geometric design. The relative length and width of the piezoelectric and non-piezoelectric layers of a self-exciting / self-detecting piezoelectric cantilever sensor determine the sensitivity, and the peak shape of the frequency spectrum provided by the self-exciting / self-detecting piezoelectric cantilever sensor To do. As described in more detail below, a self-exciting and self-detecting piezoelectric cantilever sensor includes a piezoelectric layer and a non-piezoelectric layer coupled together, such that a portion of the piezoelectric layer extends beyond the non-piezoelectric layer. Stretched or bonded in such a way that a portion of the non-piezoelectric layer extends beyond the piezoelectric layer, or a combination thereof. Therefore, the piezoelectric layer and the non-piezoelectric layer do not have the same spread. That is, the self-exciting / self-detecting piezoelectric cantilever sensor is configured in such a manner that the entire surface of the non-piezoelectric layer is not coupled to the entire surface of the piezoelectric layer.

  The sensitivity of the self-excited / self-detecting piezoelectric cantilever sensor is, in part, the use of the piezoelectric layer of the cantilever sensor for both operation and detection, and the electrical machine of the piezoelectric layer of the self-exciting / self-detecting piezoelectric cantilever sensor. Depends on specific characteristics. In resonance, the vibrating cantilever concentrates the stress of the piezoelectric layer on the base portion of the self-excited / self-detecting piezoelectric cantilever sensor. This causes an amplified change in the resistance component of the piezoelectric layer, resulting in a large shift in the resonant frequency. By directing this stress to a part of the piezoelectric layer with a low bending coefficient (for example, a more flexible part), it is possible to search for a shift associated with the resonance frequency, and the mass of the self-excited and self-detecting piezoelectric cantilever sensor. A very small change in is detected. For example, if both the piezoelectric and non-piezoelectric layers of a piezoelectric cantilever sensor are fixed at the same end (for example, when placed in an epoxy), the sensor is less sensitive to mass changes, which is fixed This is because the bending stress of the detection piezoelectric layer close to the end is smaller than when only the piezoelectric layer is fixed. This is because the bending coefficient of the combined two layers is higher than when only the piezoelectric layer is fixed. The bending modulus is the product of the elastic modulus and the moment of inertia around the neutral axis. The moment of inertia is proportional to the cube of the thickness.

  FIG. 1 is a diagram of a self-exciting / self-detecting piezoelectric cantilever sensor 12 that includes a piezoelectric portion 14 and a non-piezoelectric portion 16. The piezoelectric part is indicated by a capital letter P, and the non-piezoelectric part is indicated by a capital letter NP. The self-exciting / self-detecting type piezoelectric cantilever sensor 12 is an unfixed and overhanging type self-exciting / self-detecting type piezoelectric cantilever sensor. The reason why the self-exciting / self-detecting piezoelectric cantilever sensor 12 is called “non-fixed” is because the non-piezoelectric layer 16 is not attached to the base portion 20. The self-exciting and self-detecting piezoelectric cantilever sensor 12 is referred to as “overhanging” because the non-piezoelectric layer 16 extends beyond the distal end 24 of the piezoelectric layer 14 and creates an overhanging portion 22 of the non-piezoelectric layer 16. Because. The piezoelectric portion 14 is coupled to the non-piezoelectric portion 16 via an adhesive portion 18. The piezoelectric portion 14 and the non-piezoelectric portion overlap in the region 23. The bonding portion 18 is located between the overlapping portions of the piezoelectric portion 14 and the non-piezoelectric portion 16. The piezoelectric portion 14 is coupled to the base portion 20.

  The piezoelectric portion 14 may be any suitable material, such as lead zirconate titanate, lead magnesium niobate-lead titanate solid solution, lead strontium titanate, quartz silica, piezoelectric ceramic lead zirconate titanate (PZT), and piezoelectric ceramic. -Polymer fiber composites can be included. The non-piezoelectric portion 16 can include any suitable material such as glass, ceramic, metal, polymer, and one or more ceramic and polymer composites such as silicon dioxide, copper, stainless steel, titanium, and the like. .

The self-exciting and self-detecting piezoelectric cantilever sensor can include portions having any suitable combination of dimensions. Furthermore, the physical dimensions may not be constant. Accordingly, the piezoelectric layer and / or the non-piezoelectric layer can be tapered. For example, the length (eg, L _{P in} FIG. 1) of the piezoelectric portion (eg, piezoelectric portion 14) can range from about 0.1 to about 10 mm. The length (eg, L _{NP of} FIG. 1) of the non-piezoelectric portion (eg, non-piezoelectric portion 16) can range from about 0.1 to about 10 mm. The overlap region (eg, overlap region 23) can have a length in the range of about 0.1 to about 10 mm. The width (for example, W _{P in} FIG. 1) of the piezoelectric portion (for example, the piezoelectric portion 14) and the width (for example, W _{NP in} FIG. 1) of the non-piezoelectric portion (for example, the non-piezoelectric portion 16) are about 0.1 mm to about 4. It can be in the range of 0 mm. The width of the piezoelectric portion (for example, W _{P in} FIG. 1) may be different from the width of the non-piezoelectric portion (for example, W _{NP in} FIG. 1). The thickness of the piezoelectric portion (eg, piezoelectric portion 14) (eg, T _{P in} FIG. 1) and the thickness of the non-piezoelectric portion (eg, non-piezoelectric portion 16) (eg, T _{NP in} FIG. 1) are about 0.1 mm to about It can be in the range of 4.0 mm. The thickness of the piezoelectric portion (eg, T _{P in} FIG. 1) can also be different from the thickness of the non-piezoelectric portion (eg, T _{NP in} FIG. 1).

  FIG. 2 is a cross-sectional view of the self-exciting and self-detecting piezoelectric cantilever sensor 12 showing an electrode placement region 26 for electrodes operatively associated with the piezoelectric portion 14. The electrodes can be placed at any suitable location on the piezoelectric portion of the self-exciting / self-detecting piezoelectric cantilever sensor, as indicated by brackets 26. For example, as shown in FIG. 3, the electrode 28 can be coupled to the piezoelectric portion 14 in the base portion 20. Alternatively, as shown in FIG. 4, the electrode 32 can be coupled to an arbitrary position of the piezoelectric portion 14 other than the inside of the base portion 20 and a position where the non-piezoelectric portion 16 does not overlap. The electrodes need not be arranged symmetrically with respect to the piezoelectric portion 14. In the illustrated embodiment, one electrode can be coupled to the base portion 20 of the piezoelectric portion 14 and the other electrode can be coupled to a position other than the base portion 20 of the piezoelectric portion 14. An electrical signal can be provided to or received from the piezoelectric portion 14 using electrodes, or any suitable means (eg, dielectric means, wireless means). In one exemplary embodiment, the electrode can be coupled to the piezoelectric portion 14 via an adhesive pad or the like (element 30 in FIG. 3 and element 34 in FIG. 4). Exemplary adhesive pads include any suitable material (eg, gold, silicon dioxide) that can immobilize receptor and / or absorbent materials suitable for use in chemical or biological sensing. it can.

  The electrodes can be placed at any suitable location. In one exemplary embodiment, the electrodes are operably disposed near the location of stress concentration in the piezoelectric layer 14. As described above, the sensitivity of the self-exciting and self-detecting piezoelectric cantilever sensor is partly due to the advantageous introduction (concentration) of stress to the piezoelectric layer 14 and the placement of electrodes in the vicinity thereof. The configuration of the self-exciting and self-detecting piezoelectric cantilever sensor (and variations thereof) described herein tends to concentrate vibration-related stress on the piezoelectric layer 14. In resonance, in some configurations of the self-exciting / self-detecting piezoelectric cantilever sensor, the vibrating cantilever concentrates stress on a portion near the base portion 20 of the piezoelectric layer 14. As a result, an amplified change is caused in the resistance component of the piezoelectric layer 14, and a large shift of the resonance frequency occurs in a portion where the stress is high. By directing this stress to a portion of the piezoelectric layer 14 having a low bending modulus (eg, more flexible), it is possible to search for a shift associated with the resonant frequency, and a self-excited and self-detecting piezoelectric cantilever sensor. A very small change in the mass of is detected. Therefore, in the exemplary configuration of the self-exciting / self-detecting piezoelectric cantilever sensor, the thickness of the piezoelectric layer 14 located near the base portion 20 is thinner than the piezoelectric layer 14 at a portion far from the base portion 20. As a result, the stress tends to be concentrated toward a thinner portion of the piezoelectric layer 14. In the illustrated configuration, the electrodes are placed near or at the location of the vibration-related concentrated stress near the base of the self-exciting and self-detecting piezoelectric cantilever sensor. In another exemplary configuration of a self-exciting and self-detecting piezoelectric cantilever sensor, the electrode is positioned at a concentration stress in the piezoelectric layer regardless of the proximity of the concentrated stress to the base of the self-exciting and self-detecting piezoelectric cantilever sensor. Place in close proximity to.

  The self-exciting / self-detecting piezoelectric cantilever sensor can be configured according to a plurality of configurations, some of which are shown in FIGS. However, it is understood that the configurations shown herein do not represent all possible configurations, but rather represent representative examples of configurations of self-exciting and self-detecting piezoelectric cantilever sensors. . FIG. 5 is an illustration of an exemplary configuration 36 of a non-fixed self-exciting and self-detecting piezoelectric cantilever sensor, wherein the distal end 40 of the piezoelectric portion 14 is flush with the distal end 38 of the non-piezoelectric portion 16. ing. The reason why the self-exciting / self-detecting piezoelectric cantilever sensor 36 is referred to as “unfixed” is because the non-piezoelectric portion 16 is not attached to the base portion 20. The piezoelectric part 14 is coupled to the non-piezoelectric part 16 via an adhesive part 18. The bonding portion 18 is located between the overlapping portions of the piezoelectric portion 14 and the non-piezoelectric portion 16. The piezoelectric part 14 is coupled to the base part 20.

  FIG. 6 is an illustration of an exemplary configuration 42 of a non-fixed self-exciting and self-detecting piezoelectric cantilever sensor, where the distal end 44 of the piezoelectric portion 14 extends beyond the distal end 46 of the non-piezoelectric portion 16. The adjacent end 43 of the piezoelectric portion 14 extends beyond the adjacent end 45 of the non-piezoelectric portion 16. The piezoelectric part 14 is coupled to the non-piezoelectric part 16 via an adhesive part 18. The bonding portion 18 is located between the overlapping portions of the piezoelectric portion 14 and the non-piezoelectric portion 16. The piezoelectric part 14 is coupled to the base part 20.

  The self-exciting / self-detecting piezoelectric cantilever sensor can also be configured to include a plurality of base portions. Exemplary configurations of a self-exciting / self-detecting piezoelectric cantilever sensor including a plurality of base portions are shown in FIGS. Although it is difficult to intuitively understand that a self-exciting / self-detecting type piezoelectric cantilever sensor includes a plurality of base portions, this is a self-exciting / self-detecting type piezoelectric cantilever sensor that is expected from those skilled in the art. By fixing both ends of the self-excited / self-detecting piezoelectric cantilever sensor to multiple bases, the displacement of the self-exciting / self-detecting piezoelectric cantilever sensor is limited, resulting in degraded response. is there. Regarding the configuration of the self-exciting / self-detecting piezoelectric cantilever sensor including two base portions, in one exemplary embodiment, the stress of the piezoelectric portion is measured instead of the displacement of the piezoelectric portion. A self-exciting, self-detecting piezoelectric cantilever sensor that is configured to include two bases can operate under relatively high media flow conditions and provide excellent mass change sensitivity that is stable and robust. A sensor is provided. A mechanically robust self-exciting and self-detecting piezoelectric cantilever sensor that provides the sensor with a minimum deterministic performance for a relatively wide range of media flow conditions, as well as self-exciting and self-detecting By configuring the piezoelectric cantilever sensor to include two base portions, it provides a fundamental frequency that is 3-4 times higher (eg, higher than 100 kHz) as compared to a similarly sized cantilever sensor having one base portion.

  FIG. 7 is a diagram of an exemplary configuration 48 of a fixed self-exciting and self-detecting piezoelectric cantilever sensor that includes two base portions 20 and 50. The reason why the self-exciting / self-detecting piezoelectric cantilever sensor 48 is referred to as “fixed” is that the non-piezoelectric portion 16 is attached to the base portion 20. In the configuration shown in the self-exciting / self-detecting type piezoelectric cantilever sensor 48, both the adjacent end 52 of the piezoelectric portion 14 and the adjacent end 54 of the non-piezoelectric portion 16 are attached to the base portion 20. The piezoelectric part and the non-piezoelectric part can be attached to the base part via any suitable means. A distal end 58 of the non-piezoelectric portion 16 is also attached to the base portion 50. The distal end 58 of the non-piezoelectric portion 16 extends beyond the distal end 56 of the piezoelectric portion 14. The piezoelectric part 14 is coupled to the non-piezoelectric part 16 via an adhesive part 18. The bonding portion 18 is located between the overlapping portions of the piezoelectric portion 14 and the non-piezoelectric portion 16.

  FIG. 8 is a diagram of an exemplary configuration 60 of a fixed self-exciting and self-detecting piezoelectric cantilever sensor that includes two base portions 20, 50, where the piezoelectric portion 14 is the base portion 20 or the base portion 50. Neither is attached. In the configuration shown in the self-exciting / self-detecting piezoelectric cantilever sensor 60, the adjacent end 62 of the non-piezoelectric part 16 is attached to the base part 20, and the distal end 64 of the non-piezoelectric part 16 is attached to the base part 50. The adjacent end 62 of the non-piezoelectric portion 16 extends beyond the adjacent end 66 of the piezoelectric portion 14, and the distal end 64 of the non-piezoelectric portion 16 extends beyond the distal end 68 of the piezoelectric portion 14. The piezoelectric part 14 is coupled to the non-piezoelectric part 16 via an adhesive part 18. The bonding portion 18 is located between the overlapping portions of the piezoelectric portion 14 and the non-piezoelectric portion 16.

  FIG. 9 is a diagram of an exemplary configuration 70 of a fixed self-exciting and self-sensing piezoelectric cantilever sensor, which includes two base portions 20, 50, two piezoelectric portions 14, 72, and two Bonding portions 18 and 74 are included. In the configuration shown in the self-exciting / self-detecting piezoelectric cantilever sensor 70, the adjacent end 76 of the piezoelectric portion 14 and the adjacent end 78 of the non-piezoelectric portion 16 are attached to the base portion 20. The distal end 80 of the piezoelectric portion 72 and the distal end 82 of the non-piezoelectric portion 16 are attached to the base portion 50. The adjacent end 78 of the non-piezoelectric part 16 extends beyond the adjacent end 86 of the piezoelectric part 72. The distal end 82 of the non-piezoelectric portion 16 extends beyond the distal end 84 of the piezoelectric portion 14. A distal end 84 of the piezoelectric portion 14 and an adjacent end 86 of the piezoelectric portion 72 form a space 88 therebetween. The piezoelectric part 14 is coupled to the non-piezoelectric part 16 via an adhesive part 18. The piezoelectric part 72 is coupled to the non-piezoelectric part 16 via an adhesive part 74. The bonding portions 18 and 74 are located between the overlapping portions of the piezoelectric portion 14 and the non-piezoelectric portion 16 and between the piezoelectric portion 72 and the non-piezoelectric portion 16, respectively.

  In various alternative exemplary configurations for the configuration 70 shown in FIG. 9, only one of the piezoelectric portions 14, 72 is attached to the respective base portion 20, 50. For example, in one exemplary configuration shown in FIG. 10, the piezoelectric portion 14 is attached to the base portion 20, and the piezoelectric portion 72 is not attached to the base portion 50. In another exemplary configuration, as shown in FIG. 11, the piezoelectric portion 72 is attached to the base portion 50 and the piezoelectric portion 14 is not attached to the base portion 20. In yet another exemplary configuration, neither the piezoelectric part 14 nor the piezoelectric part 72 is attached to the respective base parts 20 and 50 as shown in FIG. In various exemplary configurations where the piezoelectric layer is comprised of multiple portions, the electrodes can be attached to any one or more piezoelectric portions. For example, in the exemplary configurations shown in FIGS. 9, 10, 11, and 12, the electrodes can be attached to the piezoelectric portion 14, the piezoelectric portion 72, or a combination thereof.

  FIG. 13 is a diagram of an exemplary configuration 90 of a fixed self-exciting and self-detecting piezoelectric cantilever sensor that includes two base portions 20, 50, where the piezoelectric portion 14 is attached to the base portion 20 and is non-piezoelectric. The part 16 is attached to the base part 50. The piezoelectric part 14 is coupled to the non-piezoelectric part 16 via an adhesive part 18. The bonding portion 18 is located between the overlapping portions of the piezoelectric portion 14 and the non-piezoelectric portion 16. The distal end 98 of the non-piezoelectric portion 16 extends beyond the distal end 96 of the piezoelectric portion 14. The adjacent end 92 of the piezoelectric portion 14 extends beyond the adjacent end 94 of the non-piezoelectric portion 16.

  FIG. 14 is a diagram of an exemplary configuration 100 of a fixed self-exciting and self-detecting piezoelectric cantilever sensor that includes two base portions 20, 50, where the non-piezoelectric portion 16 includes a base portion 20 and a base portion 50. Neither is attached. In the configuration shown in the self-exciting / self-detecting piezoelectric cantilever sensor 100, the adjacent end 102 of the piezoelectric portion 14 is attached to the base portion 20, and the distal end 104 of the piezoelectric portion 14 is attached to the base portion 50. Yes. The adjacent end 102 of the piezoelectric portion 14 extends beyond the adjacent end 106 of the non-piezoelectric portion 16, and the distal end 104 of the piezoelectric portion 14 extends beyond the distal end 108 of the non-piezoelectric portion 16. The piezoelectric part 14 is coupled to the non-piezoelectric part 16 via an adhesive part 18. The bonding portion 18 is located between the overlapping portions of the piezoelectric portion 14 and the non-piezoelectric portion 16.

Figure 15 includes a piezoelectric portion 14 and the non-piezoelectric portion 16 is a diagram of an exemplary configuration 110 of the non-fixed self-exciting, self-sensing piezoelectric cantilever sensor, width W _P Here piezoelectric unit, the non-piezoelectric portion _Less than the width _WNP . Structure 110 shown in FIG. 15 is similar to the arrangement 12 shown in FIG. 1, however, _{W P} is less than _{W NP.} Therefore, the self-exciting / self-detecting type piezoelectric cantilever sensor 110 shows an aspect of an unfixed overhanging type self-exciting / self-detecting type piezoelectric cantilever sensor. The piezoelectric part 14 is coupled to the non-piezoelectric part 16 via an adhesive part (the adhesive part is not shown in FIG. 15). The bonding portion is located between the overlapping portions of the piezoelectric portion 14 and the non-piezoelectric portion 16. The piezoelectric portion 14 is coupled to the base portion 20.

Figure 16 includes a piezoelectric portion 14 and the non-piezoelectric portion 16 is a diagram of an exemplary configuration 112 of the non-fixed self-exciting, self-sensing piezoelectric cantilever sensor, wherein the width W _P of the piezoelectric portion of the non-piezoelectric portion _Less than the width W _NP and the distal end 114 of the piezoelectric portion 14 extends beyond the distal end 116 of the non-piezoelectric portion 16, and the adjacent end 118 of the piezoelectric portion 14 is adjacent to the adjacent end 120 of the non-piezoelectric portion 16. It extends beyond. Structure 112 shown in FIG. 16 is similar to the arrangement 42 shown in FIG. 6, however, _{W P} is less than _{W NP.} The piezoelectric portion 14 is coupled to the non-piezoelectric portion 16 via an adhesive portion (the adhesive portion is not shown in FIG. 16). The bonding portion is located between the overlapping portions of the piezoelectric portion 14 and the non-piezoelectric portion 16. The piezoelectric portion 14 is coupled to the base portion 20.

  FIG. 17 is a flow diagram of an exemplary method for detecting an analyte using a self-exciting and self-detecting piezoelectric cantilever sensor. A self-exciting and self-detecting piezoelectric cantilever sensor is provided in step 120. The self-exciting and self-detecting piezoelectric cantilever sensor can be configured according to the above or according to any suitable variation thereof. The self-exciting and self-detecting piezoelectric cantilever sensor prepares to receive the analyte at step 122. In the illustrated embodiment, the analyte attractant is applied to a non-piezoelectric portion of a self-exciting and self-detecting piezoelectric cantilever sensor. The attractant is specific for the analyte. Thus, the attractant attracts the target analyte but not other substances. For example, the non-piezoelectric part of a self-excited, self-detecting piezoelectric cantilever sensor can include an attractant to attract: bioterrorism agents such as Bacillus anthracis, foodborne pathogens such as E. coli, food and aquatic pathogens Cell types in body fluids (eg circulating tumor cells), biomarkers in body fluids (eg proteins marking specific pathophysiology, α-fetoprotein, β2-microglobulin, bladder cancer antigen, breast cancer marker CA- 15-3, and other CAs (cancer antigens), calcitonin, carcinoembryonic antigen, etc.), eg explosive markers such as trinitrotoluene, dinitrotoluene, biological media such as air-borne and water-borne toxins, proteins, etc. Entities, and combinations thereof.

  A self-exciting and self-detecting piezoelectric cantilever sensor is exposed to the medium in step 124. The medium can include any suitable medium, such as a liquid, a gas, a combination of liquid and gas, or a vacuum. The medium can exhibit a wide range of flow conditions. When the target analyte is present in the medium, the target analyte accumulates in the non-piezoelectric portion of the self-excited, self-detecting piezoelectric cantilever sensor treated with the attractant. As described above, when the target analyte accumulates (for example, couples) in the non-piezoelectric portion of the self-excited / self-detecting piezoelectric cantilever sensor, a change in rigidity of the self-exciting / self-detecting piezoelectric cantilever sensor and / or self-exciting / This causes an increase in the mass of the self-detecting piezoelectric cantilever sensor, thereby reducing the resonant frequency of the self-exciting and self-detecting piezoelectric cantilever sensor.

  In step 126, the resonance frequency of the self-exciting / self-detecting piezoelectric cantilever sensor is measured. The resonance frequency can be measured by any appropriate means, such as an operational amplifier, an impedance analyzer, a network analyzer, an oscillation circuit, and the like. When the piezoelectric material of the piezoelectric portion of the self-exciting / self-detecting type piezoelectric cantilever sensor is excited, the non-piezoelectric portion of the self-exciting / self-detecting type piezoelectric cantilever sensor is bent to correspond to the strain generated in the piezoelectric material. Resonance occurs when the excitation frequency is equal to the natural frequency of the underlying mechanical structure.

  The measured resonance frequency is compared with the baseline resonance frequency in step 128. The baseline resonance frequency is the resonance frequency of a self-exciting / self-detecting piezoelectric cantilever sensor in which no analyte is accumulated. If the frequency difference (frequency shift) between the measured resonant frequency and the baseline resonant frequency is not measured (in step 130), it is determined in step 132 that no analyte has been detected. If a frequency difference between the measured resonant frequency and the baseline resonant frequency is measured (in step 130), then in step 134 it is determined that the analyte has been detected, ie that the analyte is present in the medium. decide. In step 136, the mass of the analyte accumulated in the non-piezoelectric part of the self-exciting / self-detecting piezoelectric cantilever sensor is determined according to the frequency shift measured in step 130.

Various experiments have been carried out using various configurations of self-excited / self-detecting piezoelectric cantilever sensors. FIG. 18 is an exemplary resonance spectrum plot 137 of the self-excited self-detecting piezoelectric cantilever sensor configuration 12 operated in air shown in FIG. The width _Wp and the width _WNP are each about 2 mm. Plot 137 shows the phase angle (between excitation voltage and excitation current) versus excitation frequency at an excitation voltage of 100 mV. The first resonant frequency mode 140 occurred between approximately 150-200 kHz, and the second resonant frequency mode 142 occurred between approximately 250-300 kHz. The resonance spectrum shows high order characteristic peaks at about 980 kHz, 2.90 MHz and 4.60 MHz.

  The property factor was determined as the ratio of the resonant frequency to the peak width at the midpoint of the peak height. As a result, the property factor is a measure of the sharpness of the resonance peak. Experiments have shown that the property factor of self-excited and self-detecting piezoelectric cantilever sensors is not significantly reduced when the sensors are placed in different environments, from vacuum to liquid flow environments. Experiments have also shown that the Q value of various configurations of self-excited and self-detecting piezoelectric cantilever sensors is generally in the range of 10-70 depending on the respective frequency mode at the position where the peak is detected. It was. Various configurations of self-excited and self-detecting piezoelectric cantilever sensors generally did not reduce their Q value by more than 20% to 35% when used in viscous environments including vacuum, air and flow. . This relatively small loss in the overall value of the property factor is due to the ability of the self-excited and self-detecting piezoelectric cantilever sensor, ie chemicals and various biological items, in viscous environments including water and blood flow. It reflects the ability to detect accurately with.

  Experiments have shown that the sensitivity of a self-exciting and self-detecting piezoelectric cantilever sensor is a function of its dimensions. Certain changes in the geometry of a self-exciting, self-detecting piezoelectric cantilever sensor enhance the sensor's mass change sensitivity and thus enhance the response of the sensor to detect low concentrations of analyte. The plot of resonance spectrum, ie, phase angle in air versus excitation frequency, showed dominant bending mode resonance peaks at 102 ± 0.05, 970 ± 0.05, and 1810 ± 0.05 kHz, respectively. By changing the geometry of the self-excited and self-detecting piezoelectric cantilever sensor, the resonance characteristics of the sensor were enhanced. The corresponding bending resonance mode occurs at higher frequencies and has a larger phase angle, suggesting that the resonance peak of the self-excited and self-detecting piezoelectric cantilever sensor is more sensitive and less damped. .

In one exemplary experiment, the mass change sensitivity of a self-exciting and self-detecting piezoelectric cantilever sensor was measured. A known mass of paraffin wax was added to the glass surface of a self-excited and self-detecting piezoelectric cantilever sensor, and the mass sensitivity expressed in g / Hz was calculated using the change in resonance frequency. The mass change sensitivity in the liquid was measured directly; in addition, the ratio of the known mass to the change in resonant frequency before and after adding mass was also measured. The mass sensitivity of the resonance mode measured in the liquid was determined to be 1.5 × 10 ⁻¹⁵ g / Hz.

Application of piezoelectric cantilever sensors to airborne analyte detection Applicants failed to find published information regarding the detection of target analytes in the gas phase. The present invention relates to the detection of a target analyte in the gas phase by binding the analyte to an identifying entity in a sensor. The discriminating entity indicates affinity for the target analyte. Examples of biological identification entities include polyclonal and monoclonal antibodies, single chain antibodies (scFv), aptamers (synthetic DNA specifically developed to detect target molecules), recombinant and natural phages, and the like. In one embodiment, the detector uses an immobilized antibody as an identifying entity to detect the concentration of airborne analyte, for example when using frequency conversion methods as described herein. An immobilized antibody is an antibody attached to a sensor surface used for air detection as an identification entity. This type of airborne detection provides for rapid and accurate detection of biological materials such as pathogens including bacteria, viruses, oocysts, prions and spores, and non-biological materials such as chemicals. Biological threats such as bacteria, spores, and chemical threats such as explosive or toxic chemicals can be detected.

  In one aspect of the invention, analyte aerial detection using an identification entity such as described above is performed by exposing a sensor having an identification entity, such as a coated surface of the sensor, to an air stream. The airflow may or may not contain the analyte. If the airflow does not contain the analyte, detection is not expected. However, if an analyte is present in the air stream, the analyte will bind to the identifying entity and affect the characteristics of the sensor. The altered property can be detected using a transducer that detects the presence of the analyte currently bound to the sensor. In particular, the transducer mechanism can be operated via optics, frequency, capacitance, electrical conductivity, bending mode, or static mode cantilevers. The transducer mechanism can determine changes in sensor properties as a result of binding of the analyte to the identifying antibody. As a result, altered properties (ie, dimensions, frequency, mass, capacitance, electrical conductivity, bending mode, etc.) are detected and quantified. Once quantified, the amount of analyte bound to the identifying entity can be determined using computational means known in the art, such as a computer, an embedded processor, or a digital or analog circuit. One such transducer mechanism is frequency, where the mechanical resonance of the sensor changes as the analyte binds to the identification surface of the sensor. An example of an embodiment using frequency conversion is shown below. However, other conversion mechanisms are possible as noted above.

  In one aspect of frequency conversion for the detection of airborne analytes, we have found that piezoelectrically excited millimeter sized cantilevers (PEMC) sensors are useful for detecting airborne species due to their high sensitivity. It was issued. For example, a PEMC surface prepared with a recognition entity such as an antibody or DNA molecule responds to a target analyte, which can be a pathogen, protein or biomolecule. Such an event causes a change in the mass of the cantilever, which appears as a change in resonant frequency and can be monitored by a suitable analyzer. Suitable analyzers may include lock-in amplifiers, impedance analyzers, network analyzers or oscillator circuits.

  In this application, techniques for the detection of airborne pathogens are described. One aspect includes a method of contacting a target organism or molecule in air with a PEMC sensor that includes a discriminating molecule to detect the presence of the target organism or molecule. One advantage of the present invention is that it can be performed without collecting target organisms or molecules in a liquid medium for detection. Traditional approaches place the sensor in a liquid environment. Dynamic sensing surfaces such as oscillating surfaces are known to resist the deposition of unwanted particulate contaminants. Since the PEMC sensor vibrates while in contact with the gas stream, only chemical bond deposition can occur, thereby reducing false positives due to particulate contaminants carried by the gas in the airflow sample, or remove. This principle is an advantage of the present invention because the PEMC sensor can provide specificity for the exclusion of contaminants in its detection by its operation.

  In one aspect of the present invention, the position and / or orientation of the sensor surface is identified for airflow flowing in a low velocity region. Preferably, an air velocity of about 0.01 to about 30 m / s is used for detection. The low velocity basin provides increased contact time between the target species and the binding sensor surface. The contact time between the target species and the sensor surface can also be increased by the specific position and orientation of the sensor surface relative to the airflow. Preferably, the sensor surface is positioned substantially perpendicular to the airflow, although other orientations are possible. The binding affinity of the spore to the antigen on the sensor may depend on local humidity. Maintaining humidity in the range of 10-95% provides sufficient binding, and a value of 95% provides excellent binding affinity. Bonding is observed in the air velocity range of 0.01-30 m / s, but the lower limit of this range indicates a higher binding reaction rate. In some embodiments, an air velocity of 0.01-10 m / s was acceptable.

  The method of the present invention has been demonstrated to detect anthrax spores at concentrations as low as 40 spores per liter of air by directly measuring without the need to prepare liquid or gel matrix based samples.

19A-19G show various piezoelectric cantilever sensor embodiments that can be used in the method of the present invention. It is noted that the figures in this application are not to scale unless otherwise indicated, and that the figures represent a concept. 19A-19G, each sensor is a non-piezoelectric including a piezoelectric layer 14 (denoted P), an adhesive layer 18 (located between the overlapping portions of the piezoelectric and non-piezoelectric layers), and a portion extending as a tip. It consists of layer 16 (labeled NP). A piezoelectric layer 14 is attached to the base 20. The base 20 generally has an electrode (not shown) or some other similar means with a connection to the piezoelectric layer 14, provided that the electrode is connected to the piezoelectric layer 14, the electrode is the base 20. There is no need to link to The electrode can be disposed at any position on the piezoelectric layer 14. Further, gold, SiO _2, the material can be immobilized receptor material, and / or bond pads made of absorbent material may also be present which are suitable for use in chemical sensing or biosensing. Those skilled in the art will appreciate that the designs described in FIGS. 19A-19G are just some of the possible shapes. Accordingly, these design variations are within the scope of this application. For example, the non-piezoelectric portion of the sensor may be attached to the piezoelectric layer in one or many discrete numbers across the entire width of the piezoelectric layer or a portion thereof.

  The cantilever or beam (simple or compound) sensor is mechanically oscillated by AC electrical excitation of the PZT layer. If the excitation frequency matches the mechanical resonance frequency or its higher order mode, the magnitude of the vibration (deflection from equilibrium) will be greater than at lower or higher frequencies. Thus, at resonance, PZT experiences higher stress levels than those at non-resonant frequencies. The stress level of PZT varies along its length and depends on the mode shape. The mode shape also depends on the bending factor of the cantilever. For example, referring to FIG. 19A, the bending coefficient in the R portion is significantly larger than the bending coefficient in the S portion. It is advantageous that the location of the excitation electrode solder point is at or near a high stress location because this gives a larger signal in the measurement by electrical impedance. The sensitivity of the free end cantilever or beam sensor is higher at high resonance frequencies. The various exemplary structures depicted in FIGS. 19A-19G and FIGS. 35-46 are designed to achieve fundamental higher order resonant modes in the range of 60 kHz to 6 MHz. The positions of the discrete non-piezoelectric layers can be designed such that certain higher order modes are enhanced and the non-bending modes are reduced in strength.

  Piezoelectric layer 14 is composed of lead zirconate titanate, lead magnesium niobate-lead titanate solid solution, lead strontium titanate, quartz silica, piezoelectric ceramic lead zirconate titanate (PZT), or piezoelectric ceramic-polymer 1-3 fiber composite. It can consist of Non-piezoelectric layer 16 may be composed of ceramic, metal, polymer and one or more ceramic, metal and polymer composites, such as silicon dioxide, copper, stainless steel, and titanium. The non-piezoelectric layer can be constructed using any known material used to construct the non-piezoelectric layer of conventional piezoelectric cantilevers. The electrode may be any suitable conventional electrode. In one aspect, the electrodes may or may not be insulated based on the exposure environment of the various piezoelectric cantilever sensors.

  Detection is accomplished by measuring the oscillation (ie, resonant frequency) of the device and comparing the measured oscillation (resonant frequency) with the baseline oscillation (resonant frequency) to determine the frequency shift. The determined frequency shift is then used to determine the presence of an analyte attached to an identification entity welded to one of the piezoelectric or non-piezoelectric layers of the sensor. The combination of the piezoelectric layer, the non-piezoelectric layer, and the identifying entity constitutes a cantilever that vibrates when excited by an electrode attached to the piezoelectric layer.

  One aspect of the invention is an apparatus and method for measuring any analyte that can bind directly or indirectly to a surface. Analyte binding causes either or both mass or stiffness changes. These changes can be measured as changes in the resonant frequency and can be monitored by a suitable analyzer, such as a lock-in amplifier, impedance analyzer, network analyzer or oscillator circuit. Aspects of the invention include a novel shape design for piezoelectric cantilevers. Conventional piezoelectric cantilevers are manufactured by attaching the entire surface of a piezoelectric layer to a non-piezoelectric layer. In some conventional piezoelectric cantilevers, the piezoelectric layer is fixed at one end so that when the piezoelectric material is excited, the non-piezoelectric layer bends to accommodate the strain produced in the piezoelectric material. Resonance occurs when the excitation frequency is equal to the natural frequency of the underlying mechanical structure. This type of piezoelectric cantilever sensor is excellent in operation at frequencies below about 100 kHz in the millimeter size. Higher frequencies are only possible by making the cantilever sensor very short (less than 1 mm).

  Other types of conventional piezoelectric cantilevers include those where the piezoelectric material is not fixed at one end. This is a so-called “non-fixed piezoelectric cantilever”. Unfixed piezoelectric cantilevers exhibit their first bending mode resonance at values above 100 kHz, while conventional stationary cantilevers exhibit their first bending mode resonance at 2-60 kHz. The second bending mode resonance is generally in the 200 kHz range, with higher modes also present at 400 kHz, 800 kHz and potentially higher frequencies.

  Any mode that exhibits a Q value higher than 10 is practically convenient. The Q value is the ratio of the resonance peak frequency to the resonance peak width at the midpoint of the peak height. However, not all modes that exhibit high Q values provide sensitive detection. The difference in resonance frequency between air and water, and air and vacuum gives a measure of sensitivity because the difference in density causes a frequency shift at the resonance frequency. In many piezoelectric cantilever sensors, changing the medium from air to vacuum causes a resonant frequency change of 4-25 kHz due to the individual shape of the sensor.

  The relative lengths and widths of the piezoelectric and non-piezoelectric layers determine the sensitivity, and also determine the shape of the frequency spectrum peak provided by the sensor. This can be seen from the spectrum of various piezoelectric cantilever sensors included as diagrams in this specification.

  The present invention also allows for the detection of very low concentrations of analyte that bind to the piezoelectric cantilever surface. In the examples, detection of pathogens and proteins is shown at low concentrations in the air. In addition, any analyte that binds to organic or inorganic functional groups on the PEMC surface can be detected. Thus, both chemical and biological agents can be detected in the air environment using devices based on PEMC.

  The cantilevers of the present invention have a variety of potential uses, such as detection of bioterrorism agents such as Bacillus anthracis, detection of airborne pathogens such as detection of explosive markers such as the presence of trinitrotoluene, dinitrotoluene, and airborne For example, detection of airborne toxins. The piezoelectric cantilevers of the present invention can also be used to detect biological entities at the picogram level and to detect protein-protein interactions in both static and dynamic states.

  Examples of applications include non-biological entities that have a high affinity for certain chemical coatings, and therefore airborne analyte sensors such as PEMC or PEMCB sensors, for detecting toxic or explosive chemicals, etc. It can also be used for non-biological applications. For example, using a polymer coating of aSXFA- [poly (1- (4-hydroxy-4-trifluoromethyl-5,5,5-trifluoro) pent-1-enyl) methylsiloxane] as an identifying entity, 4-dinitrotoluene (DNT) can be detected. Also, using molecularly imprinted polymers (MIP) as identification entities, explosives such as trinitrotoluene (TNT) and explosive traces such as 2,4-dilinitrotoluene (2,4-DNT) Can be detected.

  FIG. 19A shows an embodiment 710 of a non-fixed overhang type piezoelectric cantilever sensor (oPEMC). This sensor 710 is referred to as “unfixed” because the non-piezoelectric layer 16 is not attached to the base. This sensor is referred to as “overhanging” because the non-piezoelectric layer 16 extends beyond the distal end of the piezoelectric layer 14 and creates an overhanging portion of the non-piezoelectric layer 16. 16 is separated from the piezoelectric layer by an overlap region 18. The base 20 serves to hold the proximal end of the piezoelectric layer 14.

  The present invention encompasses sensors having all suitable dimensions. For example, each of the piezoelectric layer 14, the non-piezoelectric layer 16, and the overlap region 18 may range from 0.1 to 10 mm in length. The widths of the piezoelectric layer 14 and the non-piezoelectric layer 16 may be in the range of 0.1 mm to 4 mm with respect to the above length. The width of the piezoelectric layer 14 may be different from the width of the non-piezoelectric layer 16.

  Typically, the non-piezoelectric layer 16 of the overhanging piezoelectric cantilever sensor 710 is between about 0.1 mm and about 10.0 mm in length and between about 0.1 mm and about 4.0 mm in width. Piezoelectric layer 14 may have a length between about 0.1 mm and about 10.0 mm, or a width between about 0.25 mm and about 4.0 mm. Layer 18 corresponds to the overlap between layers 14 and 16 and is between about 0.1 mm and about 10 mm in length, or about length, depending on the particular construction of the overhanging piezoelectric cantilever sensor. It may be between 0.1 mm and about 5.0 mm.

  The width of the overhang type piezoelectric cantilever sensor 710 may be between about 0.1 mm and about 4.0 mm. The thickness of the piezoelectric cantilever 710 may be between about 0.1 mm and about 1.0 mm. Table 1 in FIG. 47 shows examples of some dimensions of the overhanging PEMC device corresponding to FIG. 19A. In Table 1 of FIG. 47, length dimensions a, b, and c correspond to the symbols in FIG. 19A.

  The overhang type piezoelectric cantilever sensor 710 of the present invention generally exhibits a first bending mode resonance frequency mode peak at 10 to 120 kHz and a second bending mode resonance frequency mode peak at 120 to 250 kHz.

  19B-19F illustrate various aspects of a piezoelectric excited cantilever beam sensor according to the present invention, which have been demonstrated to successfully provide a sensing response. The cantilever beam sensor includes all the same elements as the overhang type sensor of FIG. 19A, and additionally includes a second base 50, which includes at least one of the piezoelectric layer 14 and the non-piezoelectric layer 16. One is fixed. 19B-19D, the non-piezoelectric layer 16 is attached to both bases (20, 50) to form a "beam". In FIG. 19E, the beam is formed with the piezoelectric layer 14 attached to the base 20, the non-piezoelectric layer 16 attached to the piezoelectric layer 14 via the adhesive layer 18, and the non-piezoelectric layer 16 attached to the base 50. In configuration 717 of FIG. 19F, the beam is formed with the piezoelectric layer 14 attached to both bases (20, 50).

  The two ends of the piezoelectric layer and the non-piezoelectric layer were fixed using a 3 mm glass rod or tungsten rod. As long as the bending factor of the support rod is much larger than the sensor beam, a good peak shape is observed. Other suitable methods for fixation can also be used.

  The design of the cantilever beam sensor of FIGS. 19B-19F is not intuitive, because, as one skilled in the art expects, the attachment of both ends of the beam is a result of the attachment to the base (20, 50). This is because it provides a degraded response because of the limited displacement. In other words, in a conventional cantilever, one end of the cantilever is a free end, i.e. not attached to the base, thereby allowing greater displacement of the cantilever during sensing to increase the sensor response. .

  FIG. 19G shows an alternative embodiment 719 for the overhanging shape of FIG. 19A, referred to as a floating tip PEMC (ftPEMC) sensor. Unlike the sensors of FIGS. 19B-19F, the structure of FIG. 19G has only one base 20 attachment. The performance results of this configuration and other configurations are further described below.

  Returning to the “beam” structure of the two bases (20, 50) of FIGS. 19B-19F, stress measurement at the piezoelectric layer shows that both ends of the cantilever are at the base (20, 50) rather than measurement of the displacement of the piezoelectric layer. It has been found to allow the use of a fixed cantilever “beam” sensor. Furthermore, the cantilever beam sensor of the present invention provides higher fundamental mode (> 100 kHz), stable and robust performance under flow conditions, and excellent mass change sensitivity that allows detection of low sample concentrations. .

  One advantage of the present invention is that the designs of FIGS. 19A-19G above are mechanically robust and withstand minimal degradation in performance against flow conditions. The second advantage is that the fundamental frequency is 3 to 4 times higher than a similarly sized sensor with a cantilever structure.

  20-31, described below, show the results of various experiments performed using different embodiments of an overhanging piezoelectric excited millimeter size cantilever (oPEMC) sensor according to the present invention. Table 1 in FIG. 47 shows the dimensions and resonant frequencies of overhanging PEMC (oPEMC) devices. FIG. 2 shows a typical resonance spectrum of the first embodiment of an overhang type piezoelectric cantilever sensor such as that shown in FIG. 19A when operated in air (see oPEMC # 1 in Table 1 in FIG. 47). ). FIG. 2 shows a plot of phase angle versus excitation frequency at an excitation voltage of 100 mV. The first resonant frequency mode generally occurred at 150-200 kHz, and the second resonant frequency mode occurred at 250-300 kHz. The resonance spectrum shows higher order characteristic peaks for a composite PZT cantilever with a width of 2 mm at about 980 kHz, 2.90 MHz and 4.60 MHz. Compared to a similar unfixed piezoelectric cantilever structure without overhangs, the baseline up to 5 MHz was slightly more stable and many of the observed resonant frequencies were higher. Furthermore, the characteristic coefficient (Q) of the characteristic peak at 980 kHz was three times higher for the overhang type embodiment, and the characteristic coefficient (Q) of the characteristic peak at 4.60 MHz was low at a factor of two.

  FIG. 21 shows a typical resonance spectrum when the second embodiment of the overhang type piezoelectric cantilever sensor shown in FIG. 19A is operated in air (see oPEMC # 2 in Table 1 in FIG. 47). FIG. 21 shows a plot of phase angle versus excitation frequency at an excitation voltage of 100 mV. The first resonant frequency mode generally occurred at 150-200 kHz, and the second resonant frequency mode occurred at 250-300 kHz. The resonance spectrum of the second embodiment of this overhanging piezoelectric cantilever sensor shows higher order characteristic peaks at about 980 kHz, 2.90 MHz and 4.60 MHz for a composite PZT cantilever with a width of 2 mm. The portion 16 of FIG. 19A of this embodiment of the overhang, ie overhang type piezoelectric cantilever sensor, is three times larger than the overhang of oPEMC # 1, which is the resonance that occurred in the first resonant frequency mode and 850-900 kHz. It may have caused some attenuation in the frequency mode.

  FIG. 22 shows a resonance spectrum when the third embodiment of the overhang type piezoelectric cantilever sensor is operated in air (see oPEMC # 3 in Table 1 in FIG. 47). FIG. 22 shows a plot of phase angle versus excitation frequency at an excitation voltage of 100 mV. The first resonant frequency mode generally occurred at 150-200 kHz, and there was no obvious second resonant frequency mode. The resonance spectrum of this embodiment of the overhang piezoelectric cantilever sensor shows higher order characteristic peaks at about 1.81 MHz and 1.95 MHz for a composite PZT cantilever with a width of 1 mm. Compared to an unfixed structure without overhangs, the resonance peak at 1.81 MHz of the overhang structure is clearly shown, but all other peaks above 2.5 MHz are attenuated.

  FIG. 23 shows a resonance frequency spectrum of the fourth embodiment of the overhang type piezoelectric cantilever according to the present invention (see oPEMC # 4 in Table 1 in FIG. 47). The resonance frequency spectrum of FIG. 23 was obtained by using an overhang type cantilever having a width of 1 mm of a piezoelectric layer made of ceramic PZT. The spectrum was obtained by exciting the cantilever with a 100 mV signal in air. Characteristic peaks were obtained at 250 kHz, 650 kHz, 850 kHz, 1.65 MHz and 4.65 MHz.

  FIG. 24 shows the resonance frequency spectrum of the fifth embodiment of the overhang type piezoelectric cantilever according to the present invention (see oPEMC # 5 in Table 1 in FIG. 47). The resonance frequency spectrum of FIG. 24 was obtained by using an overhang type cantilever having a width of 1 mm and a piezoelectric layer made of ceramic PZT. By shortening the cantilever part (a), attenuated peaks were obtained for all listed frequencies. The spectrum was obtained by exciting the cantilever with a 100 mV signal in air. Characteristic peaks were obtained at 200 kHz, 1.0 MHz, 1.55 MHz, 1.90 MHz and 4.50 MHz. Further, with the dimensions of this aspect, a resonance mode with high sensitivity was obtained at 1.00 MHz by the overhang type piezoelectric cantilever.

  In one embodiment, a piezoelectric cantilever sensor was fabricated from quartz silica and either piezoelectric ceramic lead zirconate titanate (PZT) or piezoelectric ceramic-polymer 1-3 fiber composite. In one embodiment, the non-piezoelectric layer is from conventional materials such as ceramics, metals, polymers and composites of one or more ceramics, metals and polymers, such as silicon dioxide, copper, stainless steel, and titanium. Consists of.

  Table 2 of FIG. 48 shows the corresponding resonance peak quality factor (Q) for the different piezoelectric cantilever sensors listed in Table 1 of FIG. The quality factor was determined as the ratio of the resonant peak frequency to the peak width at the midpoint of the peak height. Thus, the quality factor is a measure of the sharpness of the resonance peak. In the above experiments, it has been shown that the quality factor of an overhanging piezoelectric cantilever sensor is not significantly reduced when the sensor is placed in a different environment, from a vacuum to an air flow environment.

  It is observed that the Q value of an overhang type piezoelectric cantilever sensor is generally in the range of 10 to 70, depending on the respective frequency mode in which the peak is detected. When an overhang type piezoelectric cantilever sensor is used in a viscous environment including vacuum, air, and flow, its Q value generally does not decrease by more than 20% to 35%.

  Now consider the performance of the configurations of FIGS. 19B-19F. FIG. 25 shows a plot of phase angle versus excitation frequency, ie, a typical resonance spectrum, when excited at 100 mV in air for the fixed piezoelectric excited millimeter size cantilever beam (aPEMCB) sensor 711 of FIG. 19B. The first peak is the fundamental resonance mode, which generally occurred at 200-300 kHz. The second peak is the second resonance mode, which is typically in the frequency range of 700 kHz to 1 MHz. The aPEMCB resonance spectrum was measured by connecting the electrodes to an impedance analyzer (Agilent, HP4192A); the impedance analyzer was used for continuous measurement of impedance, phase angle and amplitude ratio in the frequency range of interest with an excitation voltage of 100 mV. It is connected to a personal computer via an interface.

  FIG. 26 shows the resonance characteristics of the floating piezoelectric excited millimeter size cantilever beam (fPEMCB # 1) sensor 712 of FIG. 19C using a plot of phase angle versus excitation frequency when excited at 100 mV in air. In general, the fundamental resonance mode occurred at 200-250 kHz, and the frequency of the second mode occurred at 800 kHz-1 MHz. The quality factor for each resonance peak is listed in Table 4 in FIG.

  FIG. 27 is a representative resonance using a plot of phase angle versus excitation frequency for the fixed bimorph piezoelectric excited millimeter-sized cantilever beam (abPEMCB # 1) sensor 713 of FIG. 19D for an excitation voltage of 100 mV in air. The spectrum is shown. The fundamental resonant frequency occurred at 200 kHz and the second mode occurred at 700 kHz. The physical dimensions and quality factors for all sensor construction types are shown in Table 3 and Table 4, respectively.

  FIG. 28 shows the resonance spectrum of the overhanging beam PEMCB (oPEMCB # 1) sensor 715 of FIG. 19E when excited in air with a voltage of 100 mV. The dimensions and resonant frequencies of the fixed, floating, and solid bimorph and overhanging PEMC sensors of FIGS. 19B, 19C, 19D, and 19E are listed in Table 3 of FIG. 49, respectively. Here, it can be seen that by changing the shape of the PEMCB sensor, the peak position of the resonance frequency can be adjusted to specific requirements. Thus, biological and chemical detection decisions depend on the location of the piezoelectric layer 14 and non-piezoelectric layer 16, and whether they are fixed or non-fixed to the beam bases 20, 50, and which material comprises the beam. A wide range of resonance frequencies can be selected.

  Table 3 in FIG. 49 shows the physical dimensions in mm of the PEMCB sensor used in FIGS. 25-28 and the fundamental mode resonance frequencies in air. The lengths of PZT and glass are the dimensions of layers 14 and 16 in FIGS. 19B-19F, respectively. Width and thickness are the dimensions of each layer. The PEMCB sensor was made from piezoelectric ceramic lead zirconate titanate (PZT) and quartz silica.

Another type of PEMC sensor with different shapes from the two base cantilever beam devices described herein is shown in FIG. 19G and was also manufactured and tested. A new shape 719, a floating tip PEMC sensor (ftPEMC), was fabricated using a 127 μm thick PZT single sheet and a 180 μm thick quartz cover square. The PZT layer used is the same as that used for the base sensor platform of FIG. 19A. The free end of the cantilever consists of a glass layer of 1.50 ± 0.05 × 1 ± 0.05 mm ² (length × width), 4 ± 0.05 × 1 ± 0.05 mm ² (length × width) It was designed by bonding to one end of the PZT layer with a non-conductive adhesive. At the other end, a 1.70 ± 0.05 mm long PZT layer was epoxy-bonded into the glass tube. As a result, the free end of the cantilever has an exposed PZT layer of 0.8 mm. The top and bottom electrodes were made using 30 gauge copper wire soldered to a BNC coupler on a 1.7 mm long PZT layer prior to epoxy bonding. The PZT layer at the free end of the cantilever was insulated with a polyurethane layer having a thickness of 8 μm. A glass layer of 1.50 ± 0.05 × 1 ± 0.05 mm ² provides a surface for antibody immobilization and antigen detection.

  Any of the above PEMC or PEMCB devices can form a sensor when the PEMC or PEMCB device is coated with an identifying entity such as an antibody or DNA. With appropriate coating, the resulting sensor coating attracts and binds to the target analyte, such as airborne pathogens, airborne proteins or airborne biological agents. In one embodiment, direct detection of airborne Bacillus anthracis (BA) spores was investigated using a millimeter size PZT cantilever sensor (PEMC) coated with immobilized BA antigen. The adhesion of BA to the coated PEMC sensor is detected as a frequency change in the PEMC device due to the mass of the added BA, which affects the mass of the cantilever device, thus affecting the mass of the cantilever device. It is because it affects.

  In one embodiment, the experimental device includes a horizontal tube with a PEMC sensor suspended vertically with its glass surface directed toward the air stream. The quartz surface was silanylated and subsequently a rabbit anti-BA specific for pathogen BA was immobilized and exposed to a flowing air flow (11 cm / s) containing 42-278,000 spores / L in the air. . BA was introduced upstream of the sensor using an axial flow nebulizer. The concentration of the BA solution in the nebulizer was measured using a Coulter counter Multisizer II. The sensor was made from 2 × 5 mm PZT laminated with 2 × 5 mm borosilicate glass with a 0.5 mm offset and secured to a non-conductive epoxy base.

  FIG. 29A shows an apparatus 100 used to detect airborne BA by flowing airborne anthrax (BA) through a PEMC type sensor. Supply air 110 (A0) adjusted to a state of zero humidity is divided into two flows. One stream uses air valve 110 (A1) to supply atomizer 121 with a known concentration of BA in deionized water. The nebulizer 121 produces about 5 μm liquid particles. A low shear atomizer is used to prevent damage as the BA spores flow through the atomizer. The liquid particles are carried by the air created from the adjustable air valve 115 (A2) adjustable from about 1 to 200 lpm through a 2 ″ pipe. In the configuration of FIG. 29A, the two streams are mixed in a mixer 123 and aerosol A higher speed is possible, although the PEMC sensor is inserted in a “T-type” exposure tube assembly 125 in a vertical manner, as shown in FIG. The impedance analyzer 131 and a personal computer that collects resonance frequency data every 30 seconds are connected via an interface. The humidity and temperature of the flowing bioaerosol are continuously monitored. Periodically, the outlet stream is sampled using a commercially available SASS 2000 air collection device 140, which provides a 5 ml liquid sample. These samples are analyzed using a PEMC sensor from another device, or their particle size and distribution are determined using a Coulter counter. The SASS2000 air collection device monitors using the RS-232 interface and the personal computer 150.

  The flow cell 125 of FIG. 29B includes a gas flow input part 1251, an airflow body part 1252, an exhaust opening 1253, and a sensor mounting part 1253. The sensor 1254 in the sensor mounting portion can be arranged to be adjustable in the vertical direction, and the penetration depth of the sensor into the airflow passing through the body 1252 is adjusted. In one embodiment, the sensor is arranged to expose the identification entity of the cantilever sensor at right angles to the direction of airflow to maximize the exposure of the identification entity to elements in the airstream.

  Using the configuration of FIG. 29A, a steady state frequency response of the sensor is achieved by first flowing wet air (RH = 85 ± 3% and T = 23 ± 0.3 ° C.) at a flow rate of 2.4 lpm. did. The nebulizer fill is 10 million spores in 4 mL, which when sprayed for 15 minutes produces a gas phase concentration of 278,000 spores / liter of air. The frequency of a PZT cantilever is a function of its mass and temperature and the hydrodynamic properties of the surrounding gas. When exposed to airborne BA, the resonant frequency was reduced to 700 Hz due to spore attachment to the coated cantilever device. After detection, the sensor was immersed in PBS, and the attached BA was released using a low pH buffer solution, thereby confirming the BA attachment. The frequency change resulting from spore release was 350 kHz. Frequency changes due to temperature and humidity effects were 60 Hz per degree C and 2 Hz per 1% relative humidity (RH).

  The PEMC sensor can have a sensitivity of 10 femtograms depending on the structure and vibration mode used for detection. For the results in FIG. 30A, two sensors were used. Sensor 1 gave a response of 760 Hz when exposed to BA spores flowing at a concentration of 278,000 spores / liter of air (humidity 95%, 24C). Using the same spore concentration, sensor 2 gave a 760 Hz shift that was almost the same response. FIG. 30A also shows excellent reproducibility between different runs with different sensors of similar structure when the same mode is used for detection. Thus, successful quantitative and reproducible detection of BA spores was observed.

  FIG. 30B shows the results of exposing four sensors. Sensor 1 (1006) and sensor 2 (1008) were prepared using identification entities that detect BA spores. Control sensors 1002 and 1004 were similarly prepared using the same discriminating entity. FIG. 30B shows the consistency of the results when detecting spores between sensor 1 and sensor 2 in an environment of 278,000 spores per liter of gas. Sensor plot 1002 shows the sensor response of inorganic particles, 0.2-0.6 μm sized aluminum silicate particles, to a control injection. Sensor plot 1002 shows no substantial response, as expected. Sensor plot 1004 shows the sensor response to a clean air environment. Point out that there is no substantial response, as expected. This demonstrates that the detection of analytes using PEMC / PEMCB sensors is very specific to the discriminating entity used, and thus the so configured sensor is less sensitive to non-target substances. .

  PEMC sensors respond to changes in mass, temperature and fluid density. Variations in system temperature, humidity (mass and density effects) and pressure (density) can mask and mask pathogen detection. The PEMC sensor design minimizes these mask effects. It is noted that the frequency of the PEMC device responded during the time that the spores traveled from the nebulizer to the sensor. The time for detecting BA is on the order of 2 minutes.

  As stated above, confirmation of BA adhesion to the PEMC sensor was confirmed by release in a low pH buffer. Direct observation with a microscope was also used for confirmation. In confirmation with a low pH buffer, the 2: 1 ratio to release of adhesion is consistent with other reports for air to liquid mass change. Confirmation of aerosolization of BA was performed through analysis of the particle size supplied by the nebulizer and analysis of exhaust gas captured by the air collection device (SASS200) in the configuration of FIG. 29A. SASS2000 captures about 30% of the injected airborne BA. The confirmation result of the detection is shown in FIG.

  After performing the experiment shown in FIG. 30A, a sensor exposed to 278,000 spores per liter of air sample was inserted into the release buffer (pH 2.2) and the resonant frequency was measured. At this pH, the antigen was released from the sensor surface, and a decrease in mass increased the resonant frequency, confirming that the decrease in frequency was indeed due to BA adhesion. This confirmation is shown in FIG.

  Further confirmation of BA adhesion was performed by direct inspection with a microscope. The scanning electron micrograph of FIG. 32 shows a broken cantilever used in one of the airborne anthrax detection experiments. The sensor was broken to allow mounting on the pedestal of the SEM and then used for microscopic analysis. The upper diagram of FIG. 32 shows the presence of anthrax spores used for detection in the area of the sensor surface shown in the lower diagram. These micrographs show that the anthrax antigen binds to the antibody chemically immobilized on the sensor surface.

  As pointed out above, the PEMC sensor vibrates while in contact with the gas stream and can only adhere due to chemical bonding, thereby preventing contamination from particles carried by the gas in the airflow sample. Reduce or eliminate false positives. Vapor phase experiments were conducted using 0.2-6.0 micron clay particles as inert contaminants. No change in sensor output was observed from exposure to contaminants. This also confirms that inert contaminants do not adhere to the PEMC surface during its operation.

  Thus, the sensor of the present invention detects bioterrorism agents, detection of airborne pathogens, detection of markers of TNT such as DNT, detection of airborne toxins, and any other that binds to a suitably prepared PEMC or PEMCB surface. It can be understood and shown by way of example that it can be used for the detection of target analytes. The sensor of the present invention can also be implemented in a sensor array where multiple sensors are placed on a single device to detect multiple different analytes simultaneously. In this manner, the sensor of the present invention can be used, for example, to identify unknown species in a gas or to indicate the presence of multiple different analytes in a gas.

  As pointed out above, detection is sensitive to humidity. In particular, very low humidity adversely affects binding affinity. It is therefore advantageous to include humidification associated with an airborne analyte sensor. FIG. 33 shows a configuration using the air sensor of FIG. 29B. In this embodiment, the gas pump 305 has an air inlet, takes air from an air sample such as a chamber, container, or room and pumps the intake air into the humidifier 310. The humidifier 310 applies a certain amount of humidity to the pumped air so that the PEMC or PEMCB sensor of the flow cell 125 reacts well with the target analyte contained in the intake air. The PEMC / PEMCB flow cell 125 then exhausts the air 315 to a safe location. The sensor of the flow cell 125 is measured using an impedance analyzer 131 and a personal computer 135 that collects resonant frequency data from the flow cell. FIG. 33 is a simple application of the PEMC / PEMCB sensor in the flow cell for airborne detection of analytes.

  FIG. 34 shows a flow diagram of a method comprising aspects of the present invention. The method relates to the detection of airborne analytes using PEMC type sensors (including PEMC and PEMCB types). The method begins by providing a PEMC type sensor at step 2120. These sensors can include any type and variation shown in FIGS. These types include one base cantilever type as shown in FIGS. 19A and 19G, two base beam type sensors with non-piezoelectric beams as shown in FIGS. 19B-19D, beam type sensors with piezoelectric beams as shown in FIG. 19F, and The layered structure shown in FIG. 19E is included.

  Next, the aerosolized target analyte is passed to the sensor in airflow at step 2122. Here, it is preferable that the identification entity that draws the analyte is arranged at right angles to the airflow having the analyte. Upon exposure to the air stream, the identification entity can capture the target analyte. Next, the PEMC sensor is excited to oscillate through the electrodes in step 2124. The oscillation frequency of the cantilever assembly or beam assembly depends on the mass of the assembly, including the analyte collected by the identification entity. The oscillation frequency of the sensor (ie, the resonant frequency of the cantilever assembly) is measured at step 2126. The measured oscillation frequency of the cantilever assembly is then compared at step 2128 with the natural (resonant) baseline frequency of the cantilever assembly. Such a comparison can be made by a personal computer, a built-in processor, calculation means including analog or digital circuits, or by manual calculation.

  The frequency shift is detected at decision step 2130. If no frequency shift is detected as in step 2132, then a determination is made that there is no analyte on the identity entity. This occurs when the airflow sample is pure or the discriminating entity is not compatible with any analyte in the airflow. If a frequency shift is detected, it is determined in step 2134 that the target analyte has been detected. In addition, a specific amount of analyte (ie, the mass of analyte deposited on the identifying entity) is determined at step 2136. This step is done by examining the magnitude of the frequency shift and correlating this magnitude with the mass of analyte required to change the resonant frequency of the PEMC sensor. It is pointed out that the special preparation required for liquid-based sampling of analytes was not performed. Also, the above method does not include a special concentration step or concentration step compared to liquid-based analyte detection.

  To provide quality control or additional accuracy in analyte detection, a comparison is made between a control sensor and a measurement sensor that detects the analyte, although not shown in FIG. For example, the control sensor is preferably the same as the measurement sensor except that it does not have an identifying entity for the target analyte. When exposed to the same airflow as the measurement sensor, the resonant frequency change of the control sensor can be distinguished from the resonant frequency of the measurement sensor, providing accurate results.

Additional Sensor Configurations All configurations in FIGS. 35-47 are useful for sensor configurations that can be used to detect analytes in gaseous or liquid media, as in FIGS. 19A-19G. Thus, the uses of the configuration of FIGS. 35-47 are similar to those described herein for detection of airborne chemicals or biologics. FIGS. 35-47 share some characteristics with those of FIGS. 19A-19G. For example, where indicated, a base element 20 is present, to which either a piezoelectric 14 (P) type element or a non-piezoelectric 16 type element is attached. The adhesive layer 18 separates the P-type layer 14 from the NP-type layer 16. In FIGS. 35-47, an electrode 28 is shown connected to various locations of a piezoelectric 14 type element at point 30 to excite a cantilever or beam structure. Figures 35-47 illustrate a wide range of configurations that can be implemented with PEMC and PEMCB devices. A brief description of each of them is below.

FIG. 35 shows a configuration of a PEMC or PEMCB sensor in which the NP unit 16 is in contact with the P unit 14. The thickness of the NP layer 16 (T _NP ) can be variable along the length of the NP layer 14 and the T _NP can be designed to support a sensitive sensor. In this configuration, the bending coefficient of the notch portion of the NP layer 14 is smaller than that of the thicker portion of the NP layer 14. Although only the free end cantilever arms including P and NP layers are shown, the configuration of FIG. 35 may be replicated in the form of a mirror image about the centerline AA. This mirror image replica of FIG. 35 shows the symmetry of the beam-type (PEMCB) sensor. There are several examples in FIGS. 35-47 in which the centerline is drawn, where the profiling can be either a free end cantilever or a beam-type sensor. Further, all basic information about the placement of electrode wires 28 and terminals 30 and the width of the notches applies to this and all other configurations.

  FIG. 36 shows a two-layer NP16: one can be used effectively if one is on top and one is on the bottom, and the bending modulus (EI) of NP1 is not the same as that of NP2. Here, the names NP1 and NP2 in FIG. 36 indicate that the two NP layers may differ in shape and material. For example, NP1 can be smaller than NP2 or have a different shape. NP1 can also be made of glass, while NP2 can be made of ceramic. Similar to the case of FIG. 35, the mirror image about the centerline A-A produces a beam structure. In this case, the distance X is equal to or greater than 0, meaning that P is continuous to the mirror image anchor, or is a part separated into two. If X> 0, one or both parts of P can be excited, but in the latter case the two excitations can be synchronized. FIG. 37 shows a configuration similar to FIG. 36 except for two side surfaces. In FIG. 37, having P1 and P2 creates an axis of symmetry, so NP1 = NP2. The mirror image for A-A creates the beam structure. In this case, X is 0 or more. This means that P is continuous with respect to the mirror image anchor, or is a two-part. If X> 0, one or both portions of P can be excited, but in the latter case, the two excitations are preferably synchronized.

  FIG. 38 shows a configuration similar to FIG. 19A except for the additional portion of NP16 type material. The advantage of this structure over FIG. 19A is that better control over the resonant frequency peak position can be achieved and the configuration can be effective in undesired mode attenuation. NP1 (16) can be the same or different from NP2 (16) depending on the desired properties. The free end cantilever structure of FIG. 38 can be converted to a beam structure by simply securing the distal end of NP2 to the base element. It is also pointed out that the part indicated as NP2 in FIG. 38 can be produced simply by removing the electrode from the part of the P-type material (laser cutting, chemical etching, etc.) and using the part where the P-type material cannot be excited.

  FIG. 39 shows the same configuration as FIG. 19A except for the addition of NP1. Here, NP1 is bonded to the base 20 instead of the P-type layer. This configuration results in an improved signal because, unlike the configuration of FIG. 19A, the proximal end of P is unconstrained and some of its signal energy is not dissipated, thus generating a larger signal. Because. In other words, some of the signal energy from FIG. 19A can be lost because the proximal end is constrained. The configuration of FIG. 39 shows an improvement over that of FIG. 19A. As in the configurations of FIGS. 35 to 37, a beam structure can be produced by adding a mirror image about the center line AA.

  FIG. 40 shows the same configuration as FIG. 19F except that the inverted P and NP regions are added and the P-type layer 14 is added. This configuration can result in an improved signal because the proximal end of P is not constrained so that some of its signal energy is not dissipated. Therefore, a larger signal is generated. FIG. 41 shows the same configuration as FIG. 19E except that NP1 is added. This configuration can result in an improved signal because the proximal end of P is not constrained so that some of its signal energy is not dissipated. Therefore, a larger signal is generated. FIG. 42 shows a configuration similar to FIG. 19G except that the bending coefficient (EI) of the NP layer varies as a function of length L. By changing this parameter, enhancement of sensitivity is achieved by increasing the stress concentrated at the electrode position. One practical way of accomplishing this is to construct the NP layer from a number of separate parts, as shown in FIG. 43, which are either empty spaces or adjacent parts that are low coefficient alternative materials. Along its width can vary. The beam structure is created by adding a mirror image of AA in either FIG. 42 or FIG.

  FIG. 44 is the same configuration as FIG. 36 except that the upper NP layer has a bending coefficient (EI) that varies as a function of length and a lower layer that varies as a function of length. This is an effective mirror image of FIG. 43, but the lower layer is different from the upper layer, creating a resonant structure. 44, the upper and lower layers can be the same only when the P layer has a sandwich structure as shown in FIG. FIG. 45 shows a configuration in which stress is sufficiently concentrated on the electrode points to generate a highly sensitive response. However, this gives a more stable response due to the position of NP16. The beam structure can be made by mirroring the AA centerline. FIG. 46 is a useful structure for manufacturability because of the shortened base 20. However, this provides more undesirable vibration modes. The beam structure can be made by mirroring the AA centerline.

  Although many features and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, this disclosure is illustrative only and, in particular, changes in the form, size and arrangement of parts may be made. It should be understood that, within the principles of the invention, the appended claims may be made in detail to the full extent indicated by the broad general meaning of the terms expressed.

Claims (21)

A method for detecting a target analyte comprising the following steps:
Mounting the sensor in the media stream , where the sensor
Piezoelectric layer having a first end and a second end, wherein the first end is attached to the base is the side close to the base over the scan,
A non-piezoelectric layer having a first end and a second end, wherein a portion of the non-piezoelectric layer overlaps and is attached to the piezoelectric layer, and the non-piezoelectric layer is not attached to the base ;
The identification entity associated with the non-piezoelectric layer, where the combination of the piezoelectric layer, the non-piezoelectric layer, and the identification entity comprises a cantilever portion and an electrode operably attached to the piezoelectric layer, where electrical stimulation from the electrode Vibrates the cantilever part,
Including:
Exposing the identity of the cantilever to the target analyte in the media stream;
Measuring the oscillation frequency of the cantilever; and comparing the measured oscillation frequency with a baseline oscillation frequency to determine a frequency shift indicative of the presence of the target analyte on the identifying entity. Piezoelectric layer is intended to include both piezoelectric portions and non-piezoelectric portions arranged in a straight line, The method of claim 1.   The method according to claim 1, wherein the non-piezoelectric layer includes a plurality of non-piezoelectric portions arranged in a straight line at intervals. Determining the amount of target analyte present on the identifying entity;
The method of claim 1, further comprising:   The identification entity is selected from one of the group consisting of antibodies, DNA molecules, aptamers, phages and biochemical reagents, and the selection is one of the group consisting of natural and synthetic constructs Item 2. The method according to Item 1.   6. The method of claim 5, wherein the identification entity is an antibody that identifies and binds to the target analyte.   7. The method of claim 6, wherein the target analyte is chemically immobilized on the cantilever sensor surface by binding to an antibody.   2. The method of claim 1, wherein exposing the cantilever identifying entity to the target analyte comprises exposing the identifying entity to one of the group of biological and chemical substances in the media stream. The use of multiple sensors as a sensor array, wherein each of the plurality of sensors in the array are exposed to the medium flow, detecting at least one analyte,
The method of claim 1, further comprising: The method according to claim 9, wherein at least one analyte is detected by measuring a plurality of frequency shifts, one frequency shift being for each of the sensors used . An apparatus for detecting a target analyte,
Including a sensor and an analyzer,
Wherein the sensor is,
A piezoelectric layer having a first end and a second end, wherein the first end is near the base and is attached to the base;
A non-piezoelectric layer having a first end and a second end, wherein a portion of the non-piezoelectric layer overlaps and is attached to the piezoelectric layer, the non-piezoelectric layer not attached to the base and associated with the non-piezoelectric layer The identification entity, where the combination of piezoelectric layer, non-piezoelectric layer and identification entity constitutes the cantilever part, and the electrode operably attached to the piezoelectric material, where electrical stimulation from the electrode vibrates the cantilever part Let
That there is in Dressings containing;
The analyzer is
An analyzer that collects resonant frequency data from a sensor, comparing the measured resonant frequency of the sensor with a baseline resonant frequency to determine a frequency change, the frequency change being a target collected on the sensor's identification entity The apparatus, which indicates the mass of an analyte.   The apparatus of claim 11, further comprising an array of sensors, wherein each sensor in the array provides frequency information to the analyzer to determine the presence and amount of at least one analyte. The method of claim 1, comprising:
Coating the surface of a cantilever detection device having a fundamental resonance frequency with an immobilized antibody;
Exposing the coated surface to the media stream, where if the media stream contains an analyte, an analyte compatible with the immobilized antibody binds to the coated surface;
Measuring the oscillation frequency of the cantilever detection device;
Determining the amount of analyte bound to an identifying entity. The identifying entity has one of the group consisting of immobilized antibodies, aptamers, recombinant phages, and DNA molecules;
14. The method of claim 13, further comprising determining the amount of analyte bound to the identifying entity using a transducer mechanism connected to the computing means.   The apparatus of claim 11, wherein the piezoelectric layer comprises two piezoelectric layers.   The apparatus according to claim 11, wherein the non-piezoelectric layer includes a plurality of non-piezoelectric parts arranged in a straight line at intervals. The electrical excitation of the electrodes causes mechanical vibrations in the piezoelectric layer, where vibrations at resonance apply a higher level of stress to the sensor than vibrations at non-resonance; and where the electrode's to the piezoelectric layer The attachment is close to the point where stress on the piezoelectric layer is concentrated , indicating an increase in electrical impedance in the piezoelectric layer compared to other points in the piezoelectric layer,
The apparatus of claim 11. Increase in electrical impedance, it is intended to display the corresponding increases in stress in the piezoelectric layer, according to claim 17. Enhancing the detection of the target analyte is achieved by changing the bending factor of the sensor to generate a stress concentration and enhancing the stress and electrical impedance at the electrode attachment point where the stress concentration occurred .
The apparatus of claim 11. Enhancing the detection of the target analyte selects the shape of the piezoelectric layer and the shape of the non-piezoelectric layer to generate a stress concentration, and at least one fundamental higher order mode of the sensor at the location of the electrode where the stress concentration occurs. Wherein at least one fundamental higher-order mode is a function of impedance and quality factor at resonance,
The apparatus of claim 11. The non-bending mode of the sensor is reduced in amplitude intensity compared to at least one higher order mode; and the non-bending mode does not provide a appreciable contribution to the impedance in the bending mode resonance at the electrode location;
The apparatus of claim 20.

Images