KR102288710B1 - lactate sensor system using phase change - Google Patents

Abstract

The present invention provides a lactate sensor system using a phase change that includes a lactate sensing structure composed of crossed electrodes having a wide operating range, linear sensing performance, short response time, and short recovery time. A lactic acid sensor system according to an embodiment of the present invention includes a substrate; first electrode fingers disposed on the substrate and made of a conductor and extending in a first direction and extending in a second direction opposite to the first direction alternately without contacting the first electrode fingers a cross-type electrode comprising second electrode fingers arranged to and a capacitance-changing layer covering the cross-type electrode and including a solvent-chromic material; a signal generator electrically connected to the lactate detection structure including the cross-type electrodes and providing a first electrical signal to the lactate detection structure including the cross-type electrodes; and a signal processing unit electrically connected to the lactate sensing structure composed of the cross-type electrodes and processing a second electrical signal in which the first electric signal is changed due to a change in capacitance of the lactate sensing structure composed of the cross-type electrodes. do

Description

Lactate sensor system using phase change

The technical idea of the present invention relates to a lactate sensor, and more particularly, to a lactate sensor system using a phase change.

The lactic acid sensor is used to measure, detect, and determine the lactic acid concentration, and is widely used in many fields such as the food industry, the cosmetic industry, the sports medicine industry, the medical diagnosis industry, the chemical industry, and the pharmaceutical industry. Measurement of lactic acid concentration by lactic acid sensor is very important for quality and freshness evaluation of food in various food industry, nutrition industry and fermentation industry. For example, fermented products that require information on the content of lactic acid include wine, pickled vegetables, fermented dairy products, salted fish, and pickled meat. In addition, the concentration of lactic acid in the blood of unstressed patients ranges from 0.5 mmol/L to 1.5 mmol/L, but this concentration can be increased to 25 mmol/L with vigorous exercise. A lactate concentration in a patient's blood can be a warning signal of an outbreak, so a lactate sensor may be used in a medical diagnostic facility to monitor or determine the lactate concentration in the blood. Such a lactate sensor can appropriately improve the diagnosis or treatment of a wide range of diseases. In the sports medicine industry, lactate sensors may be used to determine lactate levels in sports medicines to determine physical fitness during exercise. The reason is that the concentration of lactate in the blood can be used as an auxiliary indicator during exercise for training and fitness.

Many researchers and research institutes are designing and developing various types of lactate sensors, and are working on various detection methods, device structures, and materials. For example, potentiometry, voltammetry, amperometric method, impedance method, electrochemical lactate biosensor, microneedle-based technology, wearable sensor, field effect transistor (FET), organic field effect transistor (OFET), carbon nanotubes (CNTs), optical fibers, and surface plasmon resonance (SPR).

Deni Chana et al. fabricated an impedance method lactate biosensor by depositing a lactate dehydrogenase (LDH)/pyruvate oxidase (PyrOx) bioselective membrane on screen-printed carbon ink electrodes in 2017, and the impedance L-lactic acid was detected in yogurt samples using a method lactic acid biosensor. The impedance method lactate biosensor has a simple structure, but has excellent operational stability and excellent linearity of sensing performance. However, the impedance method lactate biosensor has limitations in that it has a narrow operating range, a long recovery time, and low stability for sensor storage.

B.H. Meshram et al. proposed an electrochemical lactic acid biosensor having an operating range of 5 μM to 60 μM. In the electrochemical lactic acid biosensor, a PPy/c-MWCNT/LOD nano-biocomposite thin film was deposited on a stainless steel electrode to construct a working electrode. The electrochemical lactic acid biosensor has advantages of simple structure and operation, high sensitivity, and a fast reaction time of about 8 seconds. However, the electrochemical lactic acid biosensor has a limitation in that it has a relatively large volume and a narrow measuring operating range of about 5 μM to 60 μM.

Minamiki et al. improved an extension gate with an enzyme and an osmium-redox polymer for application to a flexible organic field-effect transistor-based lactate sensor for lactate detection. Although the design of the transistor-based lactate sensor is simple and can operate at a low voltage, the transistor-based lactate sensor has a limitation in having a narrow lactate detection range of about 0 to 10 mM.

Xiaojin Luo et al. developed a lactate sensor based on a printed wearable carbon nanotube in 2018. The carbon nanotube-based lactate sensor was operated using an amperometric principle. The carbon nanotube-based lactic acid sensor was formed by manually printing three electrodes on a glove worn by a person. The carbon nanotube-based lactic acid sensor has advantages in that it has a very simple structure and operation, can be manufactured at low manufacturing cost, and has a small size. However, the carbon nanotube-based lactic acid sensor has a limitation in providing a linear sensing response within a short operating range.

S. G. Ignatov et al. proposed an optical fiber lactate sensor formed using the principle of intensity modulation (IM). The optical fiber lactate sensor used an oxygen-sensitive thin film as a transduce and a bacterial cytoplasmic membrane as a biological recognition element. The membranes were placed on an optical fiber to form the optical fiber lactate sensor. The optical fiber lactate sensor has advantages in that it has a simple structure and operating principle, can be manufactured at low manufacturing cost, has high sensitivity, and enables remote sensing. However, the optical fiber lactate sensor has limitations in that it has a narrow operating range of about 0 to 5 mM, low linearity, long response time, and long recovery time.

Sharma et al. proposed a fiber SPR-based lactate sensor in 2019. The optical fiber SPR-based lactic acid sensor coats the unclad region of a multimode optical fiber with silver and silicone, and laminates a mixture of hydrogel, lactate dehydrogenase (L-LDH) and nicotinamide adenine dinucleotide (NAD+) on a silicone layer. was formed by The optical fiber SPR-based lactic acid sensor has advantages of a simple structure, high sensitivity, stable response, and excellent reproducibility. However, the optical fiber SPR-based lactate sensor has an outdated structure, bulky by the basic optical fiber SPR structure, difficult to obtain a resonance wavelength, has a narrow operating range of about 0 to 10 mM, and has a non-linear sensing performance. , there is a limitation in that it takes a long time for a reaction time of about 2 minutes and a recovery time.

The technical problem to be achieved by the technical idea of the present invention is to provide a lactate sensor system using a phase change, comprising a lactate sensing structure composed of crossed electrodes having a wide operating range, linear sensing performance, short response time, and short recovery time will be.

However, these tasks are exemplary, and the technical spirit of the present invention is not limited thereto.

A lactic acid sensor system according to the technical idea of the present invention for achieving the above technical problem is a substrate; first electrode fingers disposed on the substrate and made of a conductor and extending in a first direction and extending in a second direction opposite to the first direction alternately without contacting the first electrode fingers a cross-type electrode comprising second electrode fingers arranged to and a capacitance-changing layer covering the cross-type electrode and including a solvent-chromic material; a signal generator electrically connected to the lactate detection structure including the cross-type electrodes and providing a first electrical signal to the lactate detection structure including the cross-type electrodes; and a signal processing unit electrically connected to the lactate sensing structure composed of the cross-type electrodes and processing a second electrical signal in which the first electric signal is changed due to a change in capacitance of the lactate sensing structure composed of the cross-type electrodes. do.

In some embodiments of the present invention, the signal processing unit may measure the lactate concentration by converting a change in capacitance of the lactate sensing structure including the cross-type electrode into a phase change.

In some embodiments of the present invention, the signal generator may generate a sine wave signal.

In some embodiments of the present invention, the signal processing unit is electrically connected to the lactate detection structure composed of the cross-type electrodes, and converts a change in capacitance of the lactate detection structure including the cross-type electrode into a change in phase angle. a capacitance-to-phase conversion circuit unit that forms a converted sinusoidal sensing signal; a sine-to-digital conversion circuit unit electrically connected to the capacitive-to-phase conversion circuit unit and converting the sine wave type sensing signal transmitted from the capacitive-to-phase conversion circuit unit into a digital sensing signal; a phase detection unit electrically connected to the sign-to-digital conversion circuit unit and configured to detect a phase difference signal between the digital sensing signal transmitted from the sign-to-digital conversion circuit unit and a digital reference signal for reference capacitance; a peak detection unit electrically connected to the phase detection unit and converting the phase difference signal transmitted from the phase detection unit into a DC voltage; and a data collection module electrically connected to the peak detection unit and configured to collect data regarding the DC voltage transmitted from the peak detection unit. In some embodiments of the present invention, the forming of the metal layer comprises: forming a chromium layer on the substrate; and forming a copper layer on the chromium layer.

In some embodiments of the present invention, after performing the step of forming the cross-type electrode, the method may further include forming an additional copper layer on the cross-type electrode by using electroplating.

In some embodiments of the present invention, after performing the step of forming the additional copper layer, the step of forming a tin layer on the additional copper layer by electroplating; may further include.

In some embodiments of the present invention, the forming of the capacitance changing layer includes 9-diethylamino-5-benzo[a]phenoxazinone, which is a solvent-chromic material, on the cross-type electrode. It may be made by applying a mixed solution containing polyvinyl chloride and N,N-dimethylacetamide and then drying.

In some embodiments of the present invention, the data collection module may be configured to include an analog-to-digital conversion circuit (ADC), a microcontroller, and a communication circuit.

In some embodiments of the present invention, the capacitance-to-phase output voltage of the signal output from the phase conversion circuit unit by sensing the lactate concentration of the lactate sensing structure composed of the cross-type electrode may be expressed by the following equation .

Here, Ψ is the phase shift, _F C is the feedback capacitance, C _S is the sense capacitance.

In some embodiments of the present invention, the capacitance-to-phase change of the signal output from the phase conversion circuit unit by sensing the lactate concentration of the lactate sensing structure composed of the cross-type electrode may be expressed by the following equation .

Here, Ψ is the phase shift, C _S is the capacitance detection.

The technical idea of the present invention is to provide a physical, chemical, and biological sensor, and specifically, to provide a lactate sensor system including a lactate sensing structure composed of crossed electrodes using a capacitor principle. The lactic acid sensor system according to the technical idea of the present invention operates based on the principle of converting capacitance into phase, has high sensitivity, excellent stability, and is economical.

The lactic acid sensor system according to the technical concept of the present invention includes 9-diethylamino-5-benzo [a] phenoxazinone in order to detect the lactic acid concentration of a lactic acid-containing solution having a concentration in the range of 100 nM to 1 M. A lactate sensing structure composed of cross-shaped electrodes is proposed. When the lactic acid sensing structure composed of the crossed electrodes comes into contact with the lactic acid-containing solutions, it operates based on a change in capacitance. The lactate sensing structure composed of the crossed electrodes exhibits a high sensing capability of about 11.28 ns/decade over a wide operating range of lactate measurement, a fast response time of about 1 second, and a fast recovery time of 1.3 seconds. In addition, the sensing performance is linear with a correlation coefficient of 0.998, and has stable sensing characteristics.

The lactic acid sensor system according to the technical idea of the present invention has advantages such as low price, very stable detection performance, and real-time lactate measurement possibility. The lactic acid sensor system as a whole has superior sensing performance compared to conventional lactic acid sensors.

The above-described effects of the present invention have been described by way of example, and the scope of the present invention is not limited by these effects.

1 is a schematic diagram showing a lactate sensing structure composed of a cross-type electrode according to an embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating a method of manufacturing a lactate sensing structure configured with the cross-type electrode of FIG. 1 according to an embodiment of the present invention.
3 is a schematic diagram illustrating a lactic acid sensor system according to an embodiment of the present invention.
4 is a view illustrating the characteristics of a solvent-chromic material as a lactic acid sensing method applied to a lactic acid sensor system according to an embodiment of the present invention.
5 is a circuit diagram illustrating a signal change according to the detection of lactic acid in the lactate sensor system according to an embodiment of the present invention.
6 is a graph showing the waveform change according to whether or not lactic acid is contained in the lactic acid sensor system according to an embodiment of the present invention.
7 is a graph showing the detection performance according to the lactic acid concentration of the lactic acid-containing solution of the lactic acid sensor system according to an embodiment of the present invention.
8 is a graph showing characteristics for lactate detection of a lactate sensor system according to an embodiment of the present invention.
9 is a graph showing the response time and recovery time characteristics of the lactic acid sensor system according to an embodiment of the present invention for detecting lactic acid.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments of the present invention are provided to more completely explain the technical idea of the present invention to those of ordinary skill in the art, and the following examples may be modified in various other forms, The scope of the technical idea is not limited to the following examples. Rather, these embodiments are provided so as to more fully and complete the present disclosure, and to fully convey the technical spirit of the present invention to those skilled in the art. In the present specification, the same reference numerals refer to the same elements throughout. Furthermore, various elements and regions in the drawings are schematically drawn. Accordingly, the technical spirit of the present invention is not limited by the relative size or spacing drawn in the accompanying drawings.

1 is a schematic diagram illustrating a lactate sensing structure 100 configured with cross-type electrodes according to an embodiment of the present invention.

In FIG. 1 , (a) shows a state in which the capacitance change layer 130 is not present, and (b) shows a state in which the capacitance change layer 130 is present.

Referring to FIG. 1 , the lactic acid sensing structure 100 configured as a cross-type electrode includes a substrate 110 , a cross-type electrode 120 , and a capacitance change layer 130 .

The substrate 110 may include a material having balanced chemical properties, physical properties, and electrical properties over a wide temperature range, and may include, for example, glass or polymer, and for example, polyimide.

The cross-type electrode 120 may be disposed on the substrate 110 . The cross-type electrode 120 extends in a second direction opposite to the first electrode fingers 122 and the first electrode fingers 122 extending in the first direction, and does not come into contact with the first electrode fingers 122 . and alternately disposed second electrode fingers 124 . In addition, the cross-type electrode 120 may further include an electrode terminal portion 129 to which an anode (+) and a cathode (-) are electrically connected to each other.

The cross-type electrode 120 may be formed of a conductor, for example, a metal. For example, the cross-type electrode 120 may have a structure in which a chromium layer, a copper layer, and a tin layer are stacked from the substrate 110 .

The capacitance change layer 130 may cover the cross-type electrode 120 . The capacitance change layer 130 may be disposed to fill a space between the first electrode fingers 122 and the second electrode fingers 124 . The capacitance change layer 130 may include a material whose capacitance changes according to the lactic acid concentration. The capacitance change layer 130 may include a dielectric material which is a solvatochromism material, and 9-diethylamino which is a solvatochromism material as a lactic acid sensitive material. It may be 5-benzo [a] phenoxazinone ( 9-diethylamino-5-benzo [a] phenoxazinone). In addition, the capacitance change layer 130 is composed of polyvinyl chloride (PVC) and N,N-dimethylacetamide (N,N-dimethylacetamide, DMAC), the specific mixing ratio is N,N- dimethyl It may contain 2 to 10 parts by weight of 9-diethylamino-5-benzo[a]phenoxazinone and 20 to 30 parts by weight of polyvinyl chloride based on 100 weight of acetamide. In this range, excellent lactic acid detection ability can be secured. On the other hand, if the content of 9-diethylamino-5-benzo [a] phenoxazinone is too small, the ability to detect lactic acid may be reduced, and the content of 9-diethylamino-5-benzo [a] phenoxazinone may decrease. If there is too much, the relative content of polyvinyl chloride may be too small, and the adhesive force may be deteriorated.

FIG. 2 is a schematic diagram illustrating a manufacturing method of the lactate sensing structure 100 configured with the cross-type electrode of FIG. 1 according to an embodiment of the present invention.

Referring to FIG. 2 , a method for manufacturing a lactic acid sensing structure configured with cross-type electrodes includes: providing a substrate; forming a metal layer on the substrate; forming a photomask pattern on the metal layer; forming a cross-type electrode by removing the metal layer exposed from the photomask pattern; and covering the crossed electrode on the crossed electrode and forming a capacitance changing layer including a material whose capacitance changes according to the lactic acid concentration.

The providing of the substrate may include cleaning the substrate. For example, providing the substrate may include cleaning the substrate with ethanol, methanol, and deionized water, respectively, and drying the substrate by spraying nitrogen gas. The substrate may be a polyimide substrate. In a specific experimental example, a polyimide (Kapton® HN-type) substrate having a size of 4 cm x 2 cm and a thickness of 5 mm was used. The polyimide has the advantage of having highly balanced chemical, physical and electrical properties over a wide temperature range. However, this is only an example, and a case of using various types and various sizes of substrates is also included in the technical spirit of the present invention.

The forming of the metal layer on the substrate may include: forming a chromium layer on the substrate; and forming a copper layer on the chromium layer. In the step of forming the chromium layer, the chromium layer is formed to a thickness of about 10 nm on the substrate using a vacuum vaporizer. In the step of forming the copper layer, a copper layer is formed to a thickness of about 10 nm using a vacuum vaporizer on the chromium layer. However, the thickness of the chromium layer and the copper layer is exemplary, and can be formed in various thicknesses, chromium and copper constituting the metal layer are exemplary, and the case including various materials is also included in the technical concept of the present invention. .

The forming of the photomask pattern on the metal layer may include: forming a photoresist layer containing SU-8 25 or AZ-4620 on the copper layer using a spin coater; and exposing the photoresist layer using a mask aligner (Karl Suss MJB3 UV300) to form a photomask pattern. The photoresist layer may include SU-8 25 or AZ-4620.

In the step of forming the cross-type electrode by removing the metal layer exposed from the photomask pattern, the metal layer may be removed using a chemical etchant. The alternating electrode may include electrode fingers alternately disposed with each other, for example, 40 pairs of electrode fingers.

In addition, the manufacturing method may further include, after performing the forming of the cross-type electrode, forming an additional copper layer on the cross-type electrode by using electroplating. The thickness of the cross-type electrode may be increased by forming the additional copper layer.

In addition, the manufacturing method may further include, after performing the step of forming the additional copper layer, forming a tin layer on the additional copper layer by using electroplating. Accordingly, the cross-type electrode may have a stacked structure including a chromium layer, a copper layer, and a chromium layer.

Further, the manufacturing method may further include, after performing the step of forming the cross-type electrode, removing an unused outer region of the substrate to obtain a desired shape of the cross-type electrode.

As a result of measuring the experimental example using a scanning electron microscope, the width (W) of the cross-type electrode is 100 µm, the space (S) between adjacent electrode fingers is 100 µm, and the thickness of the cross-type electrode ( t) was 25 μm. However, these dimensions are exemplary, and the case where the cross-type electrode has various dimensions is also included in the technical spirit of the present invention.

In the forming of the capacitance change layer, a mixed solution containing 9-diethylamino-5-benzo[a]phenoxazinone, polyvinyl chloride, and N,N-dimethylacetamide on the crossed electrode It can be made by drying after coating.

In the experimental example, the capacitance change layer was formed as follows. First, 0.08 g of 9-diethylamino-5-benzo [a] phenoxazinone powder was mixed in 2 ml of DMAC solvent and ultrasonically stirred for 10 minutes, 9-diethylamino-5-benzo [a] A phenoxazinone solution was formed. Then, the 9-diethylamino-5-benzo [a] phenoxazinone solution and 0.5 g of PVC powder were mixed and ultrasonically stirred for 10 minutes. The mixed solution was homogenized by treatment on an orbital shaker (SHO-1D) for 4 days. In order to form the capacitance change layer, the mixed solution was again ultrasonically stirred before use. All compounds used to prepare the mixed solution were obtained commercially from Sigma-Aldrich.

Then, the cross-shaped electrode prepared by the above-described method was washed with ethanol, methanol, and deionized water, respectively, and dried by spraying nitrogen gas. Then, 0.25 ml of the mixed solution was applied on the cross-type electrode using a spin coater, and dried at room temperature to form a lactic acid sensing structure composed of the cross-type electrode.

3 is a schematic diagram showing a lactic acid sensor system 1 according to an embodiment of the present invention.

Referring to FIG. 3 , the lactic acid sensor system 1 includes: a lactic acid detection structure 100 configured with cross-type electrodes whose capacitance varies according to lactic acid concentration; a signal generating unit 200 electrically connected to the lactate sensing structure 100 composed of cross-type electrodes and providing a first electrical signal to the lactic acid sensing structure 100 composed of cross-shaped electrodes; and a signal for processing a second electrical signal in which the first electrical signal is changed by a change in capacitance of the lactate detection structure 100 including the cross-type electrode and electrically connected to the lactic acid detection structure 100 including the cross-type electrode processing unit 300;

As described with reference to FIG. 1 , the lactic acid sensing structure 100 including the cross-type electrodes may include the substrate 110 , the cross-type electrodes 120 , and the capacitance change layer 130 . The lactic acid sensing structure 100 composed of the cross-type electrode may be arranged to be accommodated in a test chamber. The lactic acid sensing structure 100 composed of the cross-type electrode has a capacitance changed by the lactic acid concentration, so that the first electrical signal provided from the signal generating unit 200 is converted into a second electrical signal to be provided to the signal processing unit 300 . can

The signal generator unit 200 may generate a first electrical signal of a sinusoidal waveform, for example, may generate various sinusoidal signals having the same frequency but various amplitudes and various phases. The frequency may be, for example, in the range of 1 Hz to 1 MHz, and may be, for example, 10 kHz.

The signal processing unit 300 includes a capacitance-to-phase conversion circuit unit 310 (capacitance to phase conversion circuit); Sine-to-digital conversion circuit 320 (sine to digital conversion circuit), phase detector 330 (phase detector), peak detector 340 (peak detector), and data acquisition module 350 (microcontroller based data acquisition) module) can be included.

The capacitance-to-phase conversion circuit unit 310 is electrically connected to the lactate detection structure 100 composed of cross-type electrodes, and changes the capacitance of the lactate detection structure 100 including the cross-type electrodes to change the phase angle. It is possible to form a sinusoidal sensing signal converted to . The capacitance-to-phase conversion circuit unit 310 may function as a summing amplifier.

The sine-to-digital conversion circuit unit 320 is electrically connected to the capacitance-to-phase conversion circuit unit 310 , and digitally converts the sine wave detection signal transmitted from the capacitive-to-phase conversion circuit unit 310 . It can be converted into a sensing signal.

The phase detection unit 330 is electrically connected to the sign-to-digital conversion circuit unit 320, and between the digital sensing signal transmitted from the sign-to-digital conversion circuit unit 320 and the digital reference signal for reference capacitance. can detect a phase difference signal.

The peak detector 340 may be electrically connected to the phase detector 330 and convert the phase difference signal transmitted from the phase detector 330 into a DC voltage.

The data collection module 350 may be electrically connected to the peak detector 340 and collect data regarding the DC voltage transmitted from the peak detector 340 . The data acquisition module 350 may include an analog-to-digital conversion circuit (ADC), a PIC16F877A microcontroller, and an RS232 communication circuit. Specifically, the analog-to-digital conversion circuit (ADC) may convert the analog output voltage of the peak detection unit 340 into a digital code, and transmit the digital code or digital data to the microcontroller through the i2C bus.

In the experimental example of the present invention, the PIC16F877A microcontroller used had a 10-bit internal converter, so an external 18-bit ADC (MCP3421) was additionally used to obtain higher bit resolution. The microcontroller was configured to collect information about the lactate sensing structure composed of crossed electrodes and transmit the information to a computer through an RS232 communication circuit. The TX port of the microcontroller was connected to the RS232 module. In addition, a LabVIEW program was used to measure the real-time response in the lactic acid detection process and to store the acquired information in a computer. The phase difference with other waveforms of the sensing system was measured using an oscilloscope (TDS2012B, Tektronix, lsonville, OR, USA).

Hereinafter, a method for measuring the concentration of lactic acid in a solution using the lactic acid sensor system 1 shown in FIG. 3 will be described as an example.

The lactic acid sensing structure 100 composed of cross-shaped electrodes is vertically placed in the experimental chamber using a clamp. Deionized water solution or lactic acid-containing solution is injected into the experimental chamber using a syringe. While sensing the lactic acid concentration, the solution is stored by blocking the outlet of the experimental chamber, and after the sensing is completed, the outlet is opened for removal of the solution or cleaning of the experimental chamber. A deionized water solution as a reference solution is injected into the chamber using the syringe, and the lactate sensor system 1 is adjusted. Then, the lactic acid-containing solution is slowly injected into the experimental chamber using the syringe, and the detection performance of the lactic acid-containing solution is measured. When the lactic acid-containing solution comes into contact with the capacitance change layer 130 of the lactic acid sensing structure 100 composed of a cross-type electrode, the dielectric constant of the capacitance change layer 130 is changed, and accordingly, the cross-type electrode is formed. The capacitance of the lactic acid sensing structure 100 is changed. This change in capacitance causes a phase change between the reference signal detected in the reference solution and the detection signal detected in the lactic acid-containing solution by the signal processing unit 300, and also the output voltage is changed, resulting in the detection of lactic acid concentration can do. The lactic acid sensor system 1 can be manufactured at a very low cost, has the advantage that continuous inspection is possible, and the sensing response can have a linear behavior in a wide measurement range.

Hereinafter, the operating principle of the lactic acid sensor system according to the technical spirit of the present invention will be described in detail.

4 is a view illustrating the characteristics of a solvent-chromic material as a lactic acid sensing method applied to a lactic acid sensor system according to an embodiment of the present invention.

In FIG. 4, (a) is an energy band graph of the positive solvent-chromic material, (b) is a spectrum graph of the positive solvent-chromic material, and (c) is a 9- used as a solvent-chromic material. The molecular structure of diethylamino-5-benzo[a]phenoxazinone is shown.

Referring to FIGS. 4A and 4B , solvatochromism is an absorption spectrum of a molecule that occurs due to the difference in dipole moments between the ground state and the excited state when the compound is dissolved in other solvents. The color is changed by the change of the emission spectrum and there are positive solvent discoloration and negative solvent discoloration. In the positive solvent chromic property, the dipole moment of the excited state is large compared to the dipole moment of the ground state, and thus, as the solvent polarity increases, the transition energy between the two energy states decreases and becomes stable. These results appear as redshifts in the spectrum. On the other hand, in negative solvent discoloration, the opposite effect occurs. Such solvent discoloration may provide optical properties along with electrical properties.

Referring to Figure 4 (c), 9-diethylamino-5-benzo [a] phenoxazinone used in the present invention has positive solvent discoloration properties. Thus, the solvent sensitivity of 9-diethylamino-5-benzo[a]phenoxazinone is due to the increase in the dipole moment from the ground state to the excited state. In the 9-diethylamino-5-benzo [a] phenoxazinone, a large charge between a donor composed of diethyl amino and an acceptor composed of carbonyl oxygen is the result of transition. As a result, when the solvent polarity increases, the energy bandgap between the ground state and the first excited state decreases, thereby increasing the mobility of the charge, causing a red shift, and also changing the relative permittivity and refractive index of the dye molecules. do. Accordingly, the dielectric constant of the capacitance change layer including 9-diethylamino-5-benzo[a]phenoxazinone in the lactic acid sensing structure composed of the cross-type electrode is changed.

The lactic acid sensor system according to the technical idea of the present invention is the same as applying the technology for converting the capacitance into a phase in order to measure the concentration of lactic acid. In order to measure very small changes in capacitance, a reliable and high-precision detection or readout circuit is essential. There are many techniques of interface circuits for measuring small capacitances, for example capacitance-to-frequency conversion, alternating current bridge methods, switched capacitor circuits, charging and discharging methods, and the like. However, these methods have disadvantages such as phase jitter and amplitude change since they include a main oscillator indicating the instability of the output system. Therefore, the lactic acid sensor system according to the technical concept of the present invention adopts a new detection method of acquiring the capacitance for the phase transformation in order to detect changes in the parameters of the crossed electrode for various concentrations of lactic acid solutions.

Referring back to FIG. 1 , the lactic acid sensing structure 100 composed of the cross-type electrode has a structure of a storage battery, and has a unit cell capacitance (C _uc ) of Equation 1 below.

<Equation 1>

where W is the width of the crossed electrode, S is the size of the space between the adjacent electrode fingers, t is the thickness of the crossed electrode, ε ₀ is the absolute dielectric constant of the capacitance change layer, and ε _r is The relative dielectric constant of the capacitance change layer.

_{The total capacitance (C s} ) of the lactic acid sensing structure 100 composed of the cross-type electrode is expressed in Equation 2 below.

<Equation 2>

Here, L is the length of the crossed electrode, S is the size of the space between the adjacent electrode fingers, t is the thickness of the crossed electrode, N is the number of electrode fingers of the crossed electrode, ε ₀ is the capacitance where the absolute dielectric constant of the changeable layer, and ε _r is the relative dielectric constant of the capacitive changeable layer, K(k) is the elliptic integral of the first kind of modulus k.

The modulus (k) is as shown in Equation 3 below.

<Equation 3>

The K(k) is the same as in Equation 4 below.

<Equation 4>

Therefore, the lactic acid-containing solution is in contact with the capacitance change layer 130 of the lactic acid sensing structure 100 composed of the cross-type electrode, and the dielectric constant of the capacitance change layer 130 is changed to the lactic acid sensing structure composed of the cross-type electrode. (100) will change the capacitance. The change in the capacitance (ΔC _s ) is expressed in Equation 5 below.

<Equation 5>

5 is a circuit diagram illustrating a signal change according to the detection of lactic acid in the lactate sensor system according to an embodiment of the present invention.

Referring to FIG. 5 , the signal generator 200 generates two compensation driving signals V ₁ and V ₂ having the same frequency but a phase difference. For example, "op-amp-1" causes a phase shift of about 180 degrees, and the output of "op-amp-2" is changed by an RC low pass filter. The compensation driving signals are shown in Equations 6 and 7 below.

<Equation 6>

<Equation 7>

where A is the amplitude of the signal and B is the amplitude of the compensation signal.

In this case, the phase change Ψ is expressed by Equation 8 below.

<Equation 8>

The capacitance-to-phase conversion circuit section 310 functions as a summing amplifier. _{Accordingly, the output voltage V 0} output from the capacitance-to-phase conversion circuit unit 310 is as shown in Equation 9 or 10 below.

<Equation 9>

where _CS is the sensing capacitance, C _C is the compensation capacitance, and C _F is the feedback capacitance. _S ΔC is the change in capacitance due to the change in concentration of the lactic acid-containing solution.

<Equation 10>

The output voltage V ₀ of Equation 10 may be converted as in Equation 11 or 12 below.

<Equation 11>

<Equation 12>

Here, "X" is the same as the following Equation 13, and C _C is the same as the following Equation 14.

<Equation 13>

<Equation 14>

Using Equations 12 and 14, the output voltage V ₀ is converted as shown in Equation 15 below.

<Equation 15>

In Equation 15, if the sine function and the cosine function are expanded and simplified in the first two terms of the geometrical properties and the power series, the following Equation 16 is obtained.

<Equation 16>

Here, θ is the same as in Equation 17 below.

<Equation 17>

Equation 16 represents the amplitude of the signal at the output, and Equation 17 represents the phase change at the output. In Equation 17, it can be seen that when the capacitance of the lactic acid sensing structure composed of the cross-type electrode changes, the phase change occurs.

Hereinafter, lactic acid detection results using the lactic acid sensor system according to the technical spirit of the present invention will be described.

6 is a graph showing the waveform change according to whether or not lactic acid is contained in the lactic acid sensor system according to an embodiment of the present invention.

In FIG. 6, (a) shows an analog signal of a reference signal with respect to a reference solution composed of deionized water, (b) shows a digital signal of the reference signal, (c) shows a phase change with respect to the reference signal In the case of no detection signal, (d) shows the detection signal with a phase change with respect to the reference signal in the case of a 10 mM lactic acid solution, (e) shows the DC output with and without phase change represents the voltage.

Referring to FIG. 6C , digital waveforms of a reference signal and a detection signal for a reference solution of a deionized water solution are shown. It can be seen that there is no phase change in these signals. Since there is no phase change, the output voltage from the lactate sensor system is 0V.

When the lactic acid-containing solution of about 10 mM is injected into the experimental chamber, the capacitance-changing layer of the lactic acid sensing structure composed of the cross-type electrode comes into contact with the lactic acid-containing solution. Due to this contact, the dielectric constant of the capacitance change layer is changed, the capacitance of the lactic acid sensing structure composed of the cross-type electrode is changed, and thus a phase difference between the reference signal and the detection signal is generated.

Referring to (d) of FIG. 6 , in the case of a 10 mM lactic acid solution, the phase difference between the reference signal and the detection signal is about 60 ns.

Referring to FIG. 6E , a phase difference of about 0 ns between the signals corresponds to 0V, and a phase difference of 60 ns corresponds to 3.703 mV.

For reference, to measure the phase change, an oscilloscope (Tektronix, TDS2012B) was used, and to measure the output voltage change, a multimeter (HP 34401A) was used.

7 is a graph showing the detection performance according to the lactic acid concentration of the lactic acid-containing solution of the lactic acid sensor system according to an embodiment of the present invention.

In Figure 7, (a) shows the phase change according to the concentration of the lactic acid-containing solution, (b) shows the capacitance change according to the concentration of the lactic acid-containing solution, (c) shows the concentration of the lactic acid-containing solution The relationship between the change in capacitance and the change in phase is shown, and (d) shows the difference in voltage according to the concentration of the lactic acid-containing solution. Here, the lactic acid-containing solution was changed in the range of 100 nM to 1 M.

Referring to (a) of FIG. 7 , when the lactic acid concentration of the lactic acid-containing solution is increased, it can be seen that the phase change between the reference signal and the detection signal is linearly increased. The sensitivity of the lactate sensor system was about 11.28 ns/decade, and the linearity was 0.994. Therefore, the detection performance of the lactic acid sensor system according to the technical idea of the present invention is very good, and provides a linear detection performance in a wide lactic acid concentration range.

Referring to (b) of FIG. 7 , when the lactic acid concentration of the lactic acid-containing solution is increased, it can be seen that the change in capacitance of the lactate sensing structure composed of the cross-type electrode is linearly changed.

Referring to (c) of FIG. 7 , it can be seen that as the lactic acid concentration of the lactic acid-containing solution increases, the relationship between the capacitance change and the phase change is very linear.

Referring to (d) of FIG. 7 , it can be seen that the change in output voltage between the detection signal and the reference signal is linear at a lactate concentration ranging from 100 nM to 1M.

8 is a graph showing characteristics for lactate detection of a lactate sensor system according to an embodiment of the present invention.

In FIG. 8, (a) shows the reproducibility measured by changing the lactate sensing structure composed of crossed electrodes, (b) shows the repeatability measured by repeating the same sample using one lactate sensor system, (c) ) indicates stability as a result of repeated performance over a long period of time.

Referring to (a) of FIG. 8 , for the reproducibility test, lactate sensing structures composed of four cross-type electrodes were formed, and a lactic acid sensing structure composed of the cross-type electrodes using a lactic acid-containing solution having a concentration of 100 mM lactic acid. Their sensing ability was reviewed. The lactate sensing structures composed of these four alternating electrodes exhibited almost the same lactate sensing performance. The relative standard deviation of measurements using lactate sensing structures consisting of four alternating electrodes was about 0.020. Therefore, it can be seen that the lactic acid sensing structure composed of the cross-type electrode has very good accuracy and reproducibility performance.

Referring to (b) of FIG. 8 , a lactate sensing structure composed of one cross-type electrode was selected, and the output voltage was measured in a lactic acid-containing solution having a concentration of 1 mM lactic acid, and the above experiment was repeated three times. As a result, the output voltages appeared the same as 3.016 mV, 3.062 mV, and 3.047 mV with little change. The standard deviation of the output voltage was found to be 0.0203. Therefore, it can be seen that the lactic acid sensing structure composed of the crossed electrodes has very good repeatability.

Referring to (c) of FIG. 8 , in order to examine stability, a lactic acid-containing solution having a concentration of 10 mM lactic acid was measured for 3 months using a lactate sensing structure composed of the same cross-type electrode. As a result, the lactate sensing structure composed of the crossed electrodes showed almost the same sensing performance for 3 months, and the standard deviation was about 0.024. Therefore, it can be seen that the lactic acid sensing structure composed of the cross-type electrode has long-term stability, and in particular, the capacitance change layer does not deteriorate with time.

9 is a graph showing the response time and recovery time characteristics of the lactic acid sensor system according to an embodiment of the present invention for detecting lactic acid.

9, (a) shows the reaction time and recovery time, (b) shows the reaction time and recovery time for the lactic acid concentration of the lactic acid-containing solution in the range of 100 nM to 1 M, (c) shows the reaction time The relationship between recovery time for

Referring to FIG. 9 (a), in a lactic acid-containing solution having a concentration of 1 mM lactic acid, it can be seen that the reaction time of the lactate sensing structure composed of the cross-type electrode of the lactic acid sensor system is 1 second, and the recovery time is 1.3 seconds. there is.

Referring to (b) of FIG. 9 , it can be seen that the reaction time and the recovery time are proportionally increased as the lactic acid concentration of the lactic acid-containing solution is increased. When the lactic acid concentration is high, the surface response is gradually controlled, and the response and recovery processes are slowed down because the active sites on the sensor surface are saturated at high concentrations.

Referring to Figure 9 (c), it can be seen that the reaction time and the recovery time at the same lactic acid concentration is almost the same.

Table 1 is a table showing specifications related to a lactate sensing structure composed of a cross-type electrode of a lactate sensor system according to an embodiment of the present invention.

measurement number Parameters/features specification One How it Works change in capacitance 2 sensing material 9-diethylamino-5-benzo
[a] phenoxazinone 3 Applications Lactic acid detection 4 operating range 100 nM to 1 M 5 responsiveness 11.28 ns/decade 6 linearity 0.998 7 reproducibility 0.020 8 repeatability 0.023 9 stability 0.024 10 reaction time 1.02 seconds 11 recovery time 1.3 seconds

Table 2 is a table comparing the parameters of the lactate measurement range, linearity, and response/recovery time of the lactate sensing structure composed of the cross-type electrode of the lactate sensor system according to the technical concept of the present invention and the comparative examples that are other systems. Referring to Table 2, it can be seen that the performance of the lactate sensing structure including the cross-type electrodes according to the technical idea of the present invention is superior to that of other lactic acid sensors selected as Comparative Examples.

detection system parameter Lactic acid measurement range linearity reaction/recovery time Example Lactic Acid Sensing Structure 100 nM to 1 M 0.998 1.02 sec / 1.3 sec Comparative Example 1 Potentiometric titration 0 to 250 mM 0.948 Less than 60 seconds/ - Comparative Example 2 impedance method 0.01 to 0.25 mM 0.996 15 minutes/ - Comparative Example 3 electrochemistry 5 to 60 μM 0.95 8 seconds/ - Comparative Example 4 Flexible OFET 0 to 10 mM 0.9865 - Comparative Example 5 fiber optic IM 0 to 5 mM 0.9387 3 min/1 min Comparative Example 6 Fiber SPR 0 to 10 mM lowness Less than 2 minutes/ -

The technical spirit of the present invention described above is not limited to the above-described embodiments and the accompanying drawings, and that various substitutions, modifications and changes are possible without departing from the technical spirit of the present invention. It will be clear to those of ordinary skill in the art to which this belongs.

Claims (7)

Board; first electrode fingers disposed on the substrate and made of a conductor and extending in a first direction and extending in a second direction opposite to the first direction alternately without contacting the first electrode fingers a cross-type electrode comprising second electrode fingers arranged to and a capacitance-changing layer covering the cross-type electrode and including a solvent-chromic material;
a signal generator electrically connected to the lactic acid detection structure including the cross-type electrodes and providing a first electrical signal to the lactate detection structure including the cross-type electrodes; and
A signal processing unit electrically connected to the lactate sensing structure composed of the cross-type electrodes and processing a second electrical signal in which the first electric signal is changed by a change in capacitance of the lactate sensing structure composed of the cross-type electrodes; and ,
The capacitance change layer is a phase comprising 2 to 10 parts by weight of 9-diethylamino-5-benzo [a] phenoxazinone and 20 to 30 parts by weight of polyvinyl chloride relative to 100 parts by weight of N,N-dimethylacetamide Lactate sensor system using change. The method of claim 1,
The signal processing unit converts a change in capacitance of the lactate sensing structure composed of the cross-type electrode into a phase change, thereby measuring the lactate concentration. The method of claim 1,
The signal generator generates a sinusoidal signal, a lactic acid sensor system using a phase change. The method of claim 1,
The signal processing unit,
Capacitance-to-phase which is electrically connected to the lactate sensing structure composed of the crossed electrodes and forms a sinusoidal sensing signal in which a change in capacitance of the lactate sensing structure composed of the crossed electrodes is converted into a change in phase angle conversion circuitry;
a sine-to-digital conversion circuit unit electrically connected to the capacitive-to-phase conversion circuit unit and converting the sine wave type sensing signal transmitted from the capacitive-to-phase conversion circuit unit into a digital sensing signal;
a phase detection unit electrically connected to the sign-to-digital conversion circuit unit and configured to detect a phase difference signal between the digital sensing signal transmitted from the sign-to-digital conversion circuit unit and a digital reference signal for reference capacitance;
a peak detection unit electrically connected to the phase detection unit and converting the phase difference signal transmitted from the phase detection unit into a DC voltage; and
a data collection module electrically connected to the peak detection unit and configured to collect data regarding the DC voltage transmitted from the peak detection unit;
Including, lactic acid sensor system using a phase change. 5. The method of claim 4,
The data collection module is configured to include an analog-to-digital conversion circuit (ADC), a microcontroller and a communication circuit, the lactic acid sensor system using a phase change. 5. The method of claim 4,
A lactate sensor system using a phase change, wherein an output voltage of a signal output from the capacitance-to-phase conversion circuit unit by sensing the lactate concentration of the lactate sensing structure composed of the cross-type electrode is expressed by the following equation.

Here, Ψ is the phase shift, _F C is the feedback capacitance, C _S is the sense capacitance. 5. The method of claim 4,
A lactic acid sensor system using a phase change, wherein a phase change of a signal output from the capacitive-to-phase conversion circuit unit by sensing the lactate concentration of the lactate sensing structure composed of the cross-type electrode is expressed by the following equation.

Here, Ψ is the phase shift, C _S is the capacitance detection.

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