MXPA97007351A - Sensor arrangements to detect enflui analytes - Google Patents

Abstract

The present invention relates to a sensor array for detecting an analyte in a fluid comprising at least first and second chemically sensitive resistors electrically connected to an electrical measuring device, each of said chemically sensitive resistors comprising: a non-conductive organic polymer mixture and a compositionally different conductive material to said non-conductive organic polymer, wherein each resistor provides an electrical pattern through said non-conductive organic polymer mixture and said conductive material, a first electrical resistance when contacted with a first fluid comprising a chemical analyte at a first concentration, and a second electrical resistance when placed in contact with a second fluid comprising said chemical analyte at a second concentration different

Description

AREAS OF SENSORS TO DETECT ANALYTS IN FLUIDS I N T RO D U C I I N Field of the Invention The field of the invention is located in electrical sensors to detect analytes in fluids.

Background There is considerable interest in developing sensors that act in a manner analogous to the olfactory system of mammals (Lundstrom et al. (1991) Nature 352: 47-50; Shurmer and Gardner (1992) Sens. Act. B 8: 1 -1 1 ). This system is designed to use probabilistic repertoires of many different receptors to recognize a simple smell (Reed (1992) Neuron 8: 205-209, Lancet and Ben-Airie (1993) Curr. Biol. 3: 668-674). In a configuration of these types, the weight of recognition does not fall on highly specific receivers, as in the case of the traditional "lock-and-key" molecular recognition approach of chemical sensors, but instead lies in the processing of distributed design of the olfactory bulb and brain (Kauer (1991) TINS 14: 79-85; DeVries and Baylor (1993) Ce // 10 (S): 139-149). Preliminary attempts to produce a sensor array that is largely sensitive to the use of thin resist films of heated metal oxide (Gardner et al (1991) Sens. Act. ß 4: 117-121; Gardner et al (1991) Sens. Act. B 6 : 71-75; Corcoran ef al. (Í993) Sens. Act. B 15: 32-37), the polymer sorption layers on the surface of acoustic wave resonators (Grate and Abraham (1991) Sens. Act. B 3: 85-111; Graté ef al. (1993) Anal. Chem. 65: 1868-1881), arrangements of electrochemical detectors (Stetter et al. (1986) Anal. Chem. 58: 860-866; Stetter et al. 1990) Sens. Act. B 1: 43-47; Stetter et al. (1993) Anal. Chem. Acta 284: 1-11), or "conducting polymers (Pearce et al. (1993) Analyst 118: 371-377 Shurmer et al. (1991) Sens. Act. B 4: 29-33) Arrangements of thin resistive films of metal oxide, generally based on Sn02 films that have been coated with various catalysts, different yields, diagnostic responses for several vapors (Gardner et al. (199 1) Sens Act. B 4: 117-121; Gardner ef al. (1991) Sens. Act. B 6: 71 * 75; Corcoran ef al. (1993) Sens. Act, 15: 32-37). However, due to the lack of understanding of the catalytic functions, the Sn02 arrangement did not allow the deliberate chemical control of the response of the elements in the array nor the reproducibility of response from array to array. Surface acoustic wave resonators are extremely sensitive to mass and acoustic impedance changes of the coatings in the array elements, but the signal transduction mechanism involves somewhat complicated electronic circuits, requiring frequency measurements of 1 Hz while one remains Rayleigh wave of 100 Mhz in the crystal (Grate and Abraham (1991) Sens. Act. B 3: 85-111; Grate ef. (1993) Anal. Chem. 65: 1868-1881). Attempts have been made to construct conductive polymer elements grown electrochemically with films and coatings of nominally identical polymers (Pearce et al (1993) Analyst 118: 371-377; Shurmer et al. (1991) Sens. Act. 0 4: 29-33; Topart and Josowics (1992) J. Phys. Chem. 96: 7824-7830; Charlesworth et al. (1993) J. Phys. Chem. 9705418-5423).

An object of the present is to provide a wide response analyte detector array based on a variety of "chemical resistor" elements. Such elements are simply prepared and are easily chemically modified to respond in a wide range of analytes. In addition, these sensors present a rapid, low power electrical signal in response to the fluid of interest, and their signals are easily integrated with software or hardware in neural networks for the purpose of identifying analytes.

Relevant Literature Pearce ef al. (1993) Analyst 118: 371-377 and Gardner ef al. (1994) Sensors and Actuators B 18-19: 240-243 describe sensor arrays based on polypyrrole to monitor the taste of beer. Shurmer (1990) US Patent 4,907,441 describes arrangements of sensors with particular electrical circuitry.

DESCRIPTION OF THE INVENTION The invention provides methods, equipment and expert systems for detecting analytes in fluids. The apparatuses include a chemical sensor comprising first and second conductive elements (for example: lead wires) electrically coupled to a chemically sensitive resistor that provides an electrical path between the conductive elements. The resistors comprise a plurality of alternating non-conductive regions (comprising a non-conductive organic polymer) and conductive regions (comprising a conductive material). The electrical passage between the first and second conductive element is transverse to (eg, passing through) said plurality of alternating conductive and non-conducting regions. In its application, the resistor provides a difference in the resistance between the conductive elements when it is brought into contact with a fluid comprising a chemical analyte at a first concentration, which when contacted with a fluid comprising the chemical analyte at a second different concentration.

The electrical path through any given non-conductive region is typically in the order of 100 angstroms long, providing a resistance of the order of 100mO across the region. The variability in the chemical sensitivity between sensor and sensor is conveniently provided by qualitative and quantitative chemical variations of the composition of the conductive regions and non-conductive regions. For example, in one embodiment, the conductive material in each resistor is held constant (for example, the same conductive material such as polypyrrole) while the non-conductive organic polymer varies between resistors (for example different plastics such as polystyrenes).

Arrays of such sensor types are constructed with at least two sensors that have chemically different sensitive resistors providing different differences in resistors. An electronic nose for detecting an analyte in a fluid can be constructed by using such arrangements in conjunction with an electrical measuring instrument electrically connected to the conductive elements of each sensor. Such electronic noses can incorporate a variety of additional components that include means to monitor the temporal response of each sensor, combining and analyzing sensor data to identify certain analytes, etc. The methods of manufacturing and uses of the disclosed sensors, arrangements and electronic noses are also proposed.

BRIEF DESCRIPTION OF THE FIGURES Figure 1A shows an overview of the sensor design; Figure 1 B shows a view of the operation of the sensor; Figure 1 C shows an overview of the operation system.

Figure 2 shows cyclic voltammograms of a poly (pyrrole) electrode coated with platinum. The electrolyte was 0.10 M [CIO -.] - in acetonitrile, with a ratio of 0 * 10 V s 1.

Figure 3A shows the optical spectrum of a spirally coated poly (pyrrole) film that has been washed with methanol to remove excess pyrrole and reduced phosphomolybdic acid. Figure 3B shows the optical spectrum of a poly (pyrrole) film spirally coated in Indian tin oxide after 10 cycles with potentials between +0.70 and -1.00 V vs. SCE at 0.10 M 0.10 M [(C H9) 4N] + [CIO4] - in acetonitrile at a ratio of 0.10 V s-1. The spectrum was obtained in 0.10 M Kcl - H20.

Figure 4A is a schematic of an array of sensors showing an amplification of one of the modified ceramic capacitors used as sensitive elements. The response pattern generated by the array of sensors described in Table 3 are displayed for acetone: Figure 4B; Benzene: Figure 4C and Ethanol: Figure 4D.

Figure 5 is an analysis of main components of autoscale data from individual sensors containing different plasticizers and flexibilizers. The numbers in the upper right corner of each square refer to the different sensor elements described in table 3.

Figures 6A and 6B analysis' of main data components obtained from all the sensors (table 3). Conditions and symbols are identical to those of Figures 5A-5D. Figure 6A shows the data represented in the first three main components pld, pc2 and pc3, while figure 6B shows the data when they are presented in pei, pc2 and pc4. A high degree of discrimination between some solvents can be obtained by considering the four main components as illustrated by the large separations between chloroform, tetrahydrofuran and isopropyl alcohol in Figure 6B.

Figure 7A is a graph of partial pressure acetone (O) as a function of the first major component; the least squares (-) adjustment between the acetone partial pressure and the first principal component (Pa = 8.26 »plc + 83.4, R2 = 0.989); the partial pressure of acetone (+) predicted from a multilinear least squares fit between the partial pressure of acetone and the first three main components (Pa = 8.26 »pc1 - 0.673» pc2 +6.25 «pc3 + 83.4, R2 = 0.998). Figure 7B is a graph of a mole fraction of methanol, xm. (0) in a methanol-ethanol mixture as a function of the major components; minimal linear quadratic fit () between? and the first principal component (xm = 0.112 »plc + 0.524, r2 = 0.979; xm predicted from a multilinear least squares adjustment (+) between xm and the first three principal components (xm = 0.112 * pc1 - 0.0300 * pc2 - 0.0444 * pc3 + 0.524, R2 = 0.987).

Figure 8 is the robust response of a poly (N-vinylpyrrolidone) sensor element: carbon black (20% w / w of carbon black), to methanol, acetone and benzene. The analyte was introduced at t = 60 s for 60 s. Each trace is normalized by the resistance of the sensor element (approx 125O) before each exposure.

Figure 9 is the first main component due to the response of a carbon based black array of sensors with 10 elements. The non-conductive components of the composite carbon black used are listed in Table 3, and the resistors were 20% weight / weight of carbon black.

DETAILED DESCRIPTION OF THE INVENTION The invention provides sensor array for detecting an analyte in a fluid for use in conjunction with an electrical measuring apparatus. These arrangements comprise a plurality of chemical sensors different in their composition. Each sensor comprises at least first and second conductor wires electrically coupled to and separated by chemically sensitive resistors. The conductors can be any suitable conductive material, usually a metal, and can be interdigitated to maximize the resistance of the signal to the noise.

The resistor comprises a plurality of conductive and non-conductive alternative regions traversing the electric paths between the conductor wires. Generally, the resistors are fabricated by bonding a conductive material with a non-conductive organic polymer such that the electrically conductive path between the conductors coupled to the resistor is interrupted by voids of non-conductive organic polymer material. For example, in a colloid, the suspension or dispersion of particulate conductive material in a matrix of non-conductive organic polymeric material, the matrix regions separating the particles provide the voids. The range of non-conductive gaps in the road measure from about 10 to about 1, 000 angstroms in length, usually in the order of 100 angstroms providing resistances l? Individuals from about 10 to about 1,000,000, usually in the order of 100 mO, through each gap. The length of the path and the strength of a given gap is not constant but is believed to change with the non-conductive organic polymer of the absorption region, absorbing an analyte. Consequently, the added dynamic resistance provided by these gaps in a given resistor is a function of the permeation of the analyte in the non-conductive regions. In some embodiments, the conductive material also contributes to the added dynamic strength as a function of analyte permeation (eg, when the conductive material is a conductive organic polymer such as polypyrrole).

A wide variety of conductive materials and non-conductive organic polymeric materials can be used. Table 1 provides examples of conductive materials for use in the manufacture of resistors; Mixtures, such as the listings, can also be used. Table 2 provides examples of non-conductive organic polymeric materials; Mixtures and copolymers, such as those of the polymers listed herein, may also be used. Combinations, concentrations, mixtures, percolation, etc., are easily empirically determined empirically by manufacturing and choosing resistors (quimoresistors) as described below.

TABLE 1 TABLE 2 The quimoresistors can be manufactured by many techniques such as, but not limited to, solution molding, suspension molding and mechanical mixing. In general, solution routes by molding are advantageous because they provide homogeneous structures and are easy to process. The molding routes in solution, the Resistor elements can be easily manufactured by coating by wrapping tape, spray or bath. Since all resistor elements must be soluble, however, the suspension molding path has a bit of limitation in its applicability. The suspension molding still provides still provides the possibility of coating by rolled tape, spray or bath but with more heterogeneous structures than in the case of solution molding. With mechanical mixing, there are no solubility restrictions since this means only the physical mixing of the resistor components, but the more difficult manufacturing device given that the wrapped tape, spray and bath coating is no longer possible. A more detailed discussion of each of these follows.

For systems where both conductive and non-conductive media and their reaction precursors are soluble in a common solvent, chemosorestores can be manufactured by solution molding. The oxidation of pyrroles by phosphomolybdic acid represents such system types. In this reaction, the phosphomolybdic acid and the pyrrole are dissolved in tetrahydrofuran (THF) and polymerization occurs in solvent evaporation. This takes into consideration that the THF solubilizes the non-conducting polymers to be dissolved within this reaction mixture allowing the mixing to be formed in a single step by evaporation of solvent. The choice of non-conducting polymers in this pathway is, of course, limited to those that are soluble in the reaction medium.

In the case of the polypyrrole described above, the preliminary reactions were carried out in THF, but this reaction could be generalizable to other non-aqueous solvents such as acetonitrile or ether. A variety of permutations in this scheme are possible for other conducting polymers. Any of these are listed above.

Certain conducting polymers, such as substituted poly (cyclooctatetraenes), are soluble in their non-conductive, undoped state, in solvents such as THF or acetonitrile. Consequently, the mixture between the non-doped polymer and the plasticized polymer can be formed from the solution molding. After which, the doping process (vapor exposure of I ?, for example, can be carried out in the mixing to provide the substituted poly (cyclooctatetraene) conductor.) Again, the choice of nonconductive polymers is limited to those They are soluble in the solvent in which the undoped conductive polymer is soluble and those which are stable in the doping reaction Certain conductive polymers can also be synthesized via a soluble precursor polymer.In these cases, the mixture between the precursor polymers and The non-conducting polymers can first be formed by chemical reaction to convert the precursor polymer into the desired conductive polymer, for example poly (p-phenylene vinylene) can be synthesized through a soluble sulfonium precursor.The mixtures between these sulfonium precursors and Non-conductive polymers can be formed by molding in solution. After which, the mixture can be subjected to thermal vacuum treatment to convert the sulfonium precursor to poly (p-phenylene vinylene).

In the suspension molding, one or more of the components of the resistors is suspended and the others dissolved in a common solvent. Suspension molding is a bit of a technique applicable in a wide range of species such as black carbon or colloidal metals, which can be suspended in solvents by vigorous mixing or sonication. In a suspension molding application, the non-conductive polymer is dissolved in an appropriate solvent (such as THF, acetonitrile, water, efe). Silver coloration is then suspended in this solution and the resulting mixture is used to bathe coated electrodes.

Mechanical mixing is desirable for all possible combinations of conductors / non-conductors. In this technique, the materials are physically mixed in a ball mill or other mixing device. For example, black carbon: non-compounding polymer compounds are easily made by ball milling. When non-conducting polymers can be melted or significantly softened without decomposition, mechanical mixing at elevated temperature can improve the mixing process. Alternatively, the composite fabrication can be improved by several sequential heating and mixing steps.

Once manufactured, the individual elements can be optimized for a particular application to vary its chemical aspect and its morphology. The chemical nature of the resistors determines which analytes will respond and their ability to distinguish the different analytes. The relative ratio of insulating components to conductors determines the magnitude of the response since the resistance of the elements becomes more sensitive to the molecules sorbed as percolate is approximate. The morphology of the film is also important in certain response characteristics. For example, thin films respond more quickly to analytes than coarse ones. Therefore, with an empirical catalog of information on different sensors chemically made with different ratios of conductive components to insulating components and by different ways of manufacturing, the sensors can be chosen that are suitable for the analysis experado in a particular application, their concentrations and the times of desired response. An additional optimization can then be carried out in an iterative manner as feedback on the operation of an array under particular conditions becomes available.

The resistor itself can form a substrate to join the conductor or resistor. For example, the structural rigidity of the resistors can be improved through a wide variety of techniques: degradation by radiation or by chemical means of polymer components (dicumil peroxide radicals) degraders, ultraviolet radiation degradation of poly (olefins), degradation by sulfur of rubbers, e-beam degraders of nylon, etc.) The incorporation of polymers or other materials within the resistors to improve the physical properties (for example, the incorporation of a polycarbonate of high transition metals, high molecular weight), the incorporation of the resistive elements in support matrices such as clays or polymeric networks (forming the resistive mixture with poly (methacrylate) or with the lamellae of montmorilonite, (for example) In another embodiment, the resistor is deposited as a surface layer in a solid matrix that provides means for supporting the conductors Typically, the matrix is a non-conductive, chemically inert sustrate, such as a glass or ceramic.

Well-adapted sensor arrays for scaling production are manufactured using integrated circuit design (IC) technology. For example, the chemosistors can easily be integrated into the front end of a simple amplifier connected by interface to an A / D converter to power. efficiently the flow of data directly within a neural network software or hardware analysis section. Micro-fabrication techniques can integrate the chemosystems directly into the micro-chip that contains the circuitry for processing / conditioning analog signals and therefore data analysis. This allows the production of millions of different elements incrementally in a single manufacturing step using technology from ink-jet. The controlled compositional gradients in the chemosistor elements of a sensor array can be induced in a similar method to a color inkjet printer reservoir and mix different colors. However, in this case, more than multiple colors, a plurality of different polymers in solution are used that can be deposited. A sensor array of one million different elements only requires a chip size of 1 cm x 1 cm, using lithography at the level of detail of 10 μm, which is within the capacity of conventional commercial processing and deposition methods. This technology allows the production of chemical sensors, of isolated shelf, of small size.

Preferred sensor arrays have a predetermined intersensor variation in the structure or composition of the non-conductive organic polymer regions. The variation can be quantitative and / or qualitative. For example, the concentration of the non-conductive organic polymer in the mixture can vary between sensors. Alternatively, a variety of different organic polymers can be used in different sensors. An electronic nose for detecting an analyte in a fluid is manufactured by electrical coupling of the sensor conductor of an array of sensors of different compositions to an electrical measuring device. The device measures changes e? as to resistivity to each sensor of the array, preferably simultaneously and preferably out of time. Frequently, the device includes processing means and is used in conjunction with a computer and data structure to compare a given response profile to a response profile database for qualitative and quantitative analysis. Typically such nose types comprise at least 10, usually at least 100, and often 1, 000 different sensors with mass deposition manufacturing techniques described herein or otherwise, known in the state of the art, arrangements of the order of Less than 10ß sensors are easily produced.

In operation, each resistor provides a first electrical resistance between its conducting wires when the resistor is contacted with a first fluid comprising and chemical analyte at a first concentration, and a second electrical resistance between its conducting wires when the resistor is contacted with a fluid comprising the same chemical analyte at a different second concentration. The fluids can be liquid or gaseous in nature. The first and second fluid may represent samples from two different media, a change in the concentration of an analyte in a fluid sample at two different times, a sample and a negative control, efe. The sensor array necessarily comprises sensors that respond differently to a change in analyte concentration, for example, the difference between the first and second electrical resistance of a sensor is different with respect to the difference between the first and second electrical resistance of a sensor. another sensor.

In a preferred embodiment, the temporal response of each sensor (resistance as a function of time) is stored. The temporal response of each sensor can be normalized to a maximum percentage increase and percentage decrease in resistance, which produces a response structure associated with the exposure of the analyte. By definition of iterative profiles of known analytes, correlation of the structure-function database and the response of the profiles is generated. Unknown analytes can then be characterized or identified using response design comparison and unknown algorithms. Consequently, analyte detection systems comprise arrays of sensors, an electrical measurement device to detect electrical resistance through each chemosistor, a computer, a data structure of response profiles of sensor arrays, and an algorithm. of comparison. In another embodiment, the electrical measuring instrument is an integrated circuit comprising a hardware based on a neural network and an analog-digital converter (CAD) multiplexed to each sensor, or a plurality of CAD's, each connected to different sensor (s) .

A wide variety of analytes and fluids can be analyzed with disclosed sensors, arrays and noses as coarse as analytes are capable of generating differential responses through a plurality of array sensors. Analyte applications include broad ranges of chemical classes such organic compounds, such as alkanes, alkenes, alkynes, dienes, alicyclic hydrocarbons, arenes, alcohols, ethers, ketones, aldehydes, carbonyls, carbanions, polynuclear aromatics and derivatives of such organics, for example, halide derivatives, etc., biomolecules such as sugars, isopropenes and isopropenoids, fatty acids and their derivatives, etc. Consequently, commercial applications of sensors, arrays and noses include environmental and pharmaceutical toxicology, biomedicine, quality control of materials, monitoring of food and agricultural products, etc. , The general method to be used by the disclosed sensors, arrays or electronic noses, to detect the presence of an analyte in a fluid takes into account the resistance that senses the presence of an analyte in a fluid with a chemical sensor comprising first and second conductors electrically coupled to a separate by a chemically sensitive resistor as already described to measure a first resistance between the conductors when the resistor is contacted with a first fluid comprising an analyte at a first concentration and a second resistance different when the resistor is placed in contact with a second fluid comprising the analyte to a second different composition.

The following examples are offered by way of illustration and are not by way of limitation.

EXAMPLES Synthesis of Polymers. Poly (pyrrole) films are used for their conductivity, electrochemical and optical measurements, prepared by injection of equal volumes of purged N2 solutions of pyrrole (1.50 mmoles in 4.0 ml of dry tetrahydrofuran) and phosphomolybdic acid (0.75 mmoles in 4.0 ml). of tetrahydrofuran) in a purged N-test tube. Once the solutions were mixed, the yellow solution of phosphomolybdic acid turned dark green, without observable precipitation for several hours. This solution was used for film preparation within one hour of mixing.

Sensor Manufacturing The plasticized poly (pyrrole) sensors were made by mixing two solutions, one of which contained 0.29 mmol of pyrrole in 5.0 ml of tetrahydrofuran, with the other containing 0.25 mmoles of phosphomolybdic acid and 30 mg. of plasticizer in 5.0 ml of tetrahydrofuran. The mixture of these two solutions resulted in a weight to weight ratio of pyrrole to plasticizer of 2: 3. A quick and easy method to encapsulate the chemosorptive elements of the array was complemented by performing a sectional cut through commercial 22 nF ceramic capacitors (Kemet Electronics Corporation). Mechanical slices through these capacitors revealed a series of metallic lines interdigitated (25% Ag: 75% Pt), separated by 15 μm, which could be quickly covered with conductive polymer. The monomer-plasticizer-oxidant solutions were then employed to coat the interdigitated electrodes in favor of providing the polymerized organic films with a robust electrical contact. After the polymerization was complete, the film became insoluble and was washed with solvent (tetrahydrofuran or methanol) to remove residual phosphomolybdic acid and unreacted monomer. The sensors were then connected to a commercial connection strip, with the resistances of the various "chemoscientist" elements easily supervised by the use of a multiplexing digital ohmmeter.

Instrumentation. The optical spectrum was obtained with a Hewlett Packard 8452A spectrophotometer, connected by an interface to an IBM XT. The electrochemical experiments are they performed using a universal Applied Research 173 potentiostat / 175 programmer. All electrochemical experiments were performed with an auxiliary flag of Pt and a reference electrode of saturated calomel (SCE). The spiral coating was performed on a photoresist spiral coater Headway Research Inc. The thickness of the film was determined with a Dektrak Model 3030 profile meter. Conductivity measurements were made with a four point probe with osmium tips (Alessi Instruments Inc., tip spacing = 0.050", tip radius = 0.010"). The measurements of Transient resistance was made with a conventional multimeter (Fluke Inc., "Hydra Data Logger" Meter).

Analysis of main components and adjustment of least squares Multi-linear. A set of data obtained from a single exposure of the arrangement to an odorant produces a set of descriptors (that is, resistances), d ,,. The data obtained from multiple exposures thus produces a data matrix D where each row, designated by j, consisted of n descriptors describing a single member of the set of data (ie, a simple exposure to an odor). Since the basic line of resistance and the relative changes in resistance varied between sensors, the data matrix was autoscalled before an additional procedure (Hecht (1990) Mathematics in Chemistry: An Introduction to Modern Methods (Prentice Hall, Englewood Cliffs, NJ)). In this preprocessing technique, all data associated with a single descriptor (that is, a column in the data matrix) were centered around zero with unit standard deviation. d ',, = (d "- ¡/,) / s, (1) where d, is the mean value for the descriptor i and s, is the corresponding standard deviation.

The principal component analysis (Hecht (1990)) was carried out to determine the linear combinations of the data such that the maximum variance [defined as the square of the standard deviation] between the data set members was obtained in n mutually orthogonal dimensions. The linear combinations of the data resulted in a greater variance [or separation] between the members of the data set in the first principal component (pei) and produced decreasing magnitudes of variance from the second to the nth major component (pc2-pcn). The coefficients required to transform the autoscalled data in the space of the main component (by linear combination) were determined by multiplying the data matrix, D, by its transpose, Dt (that is, diagonalizing the matrix) (Hecht (1990)) R = DT D (2) This operation produced the correlation matrix, R whose diagonal elements were unitary and those elements outside the diagonal were the correlation coefficients of the data. The total variance in the data was then given by the sum of the elements of the diagonal in R. The n eigenvalues, and the corresponding n eigenvectors, were then determined for R. Each eigenvector contained a set of n coefficients that were used to transform the data by linear combination in one of its n main components. The corresponding eigenvalue yielded the fraction of the total variance contained in the main component. This operation produced a main component matrix, P, which had the same dimensions as the original data matrix.

Under these conditions, each row of the matrix P was still associated with a particular smell and each column was associated with a particular main component.

Since the values in the space of the main component have no physical meaning, it was useful to express the results of the main component analysis in terms of physical parameters such as partial pressure and mol fraction. This was achieved via a multilinear least squares adjustment between the main component values and the corresponding parameter of interest. A multi-linear least squares adjustment resulted in a linear combination of the principal components that produced the best fit to the value of the corresponding parameter. The adjustments were achieved by attaching a column with each entry being the unit to the principal component matrix P, with each row-, j, corresponding to a different parameter value (for example, the partial pressure), v ,, contained in the vector V. The coefficients for the best multi-linear fit between the main components and the parameter of interest were obtained by the following matrix operation where C was a vector containing the coefficients for the linear combination.

A key to our ability to chemically manufacture various sensor elements was the preparation of air-stable, processable films of electrically conductive organic polymers. This was achieved through the controlled oxidation of pyrrole (PY) using phosphomolybdic acid (H3PM0.2O40) (2) in tetrahydrofuran: PY? PY * + e (4) 2p? *? PY2 + 2H + (5) H3PM012O40 + 2e + 2H * - > H5PM ?? 2O40 (6) The redox or electrochemically induced polymerization of pyrrole has been previously explored, but this process typically offers insoluble and intractable deposits of poly (pyrrole) as a product (Salmon et al. (1982) J. Polym. Sci., Polym. Lett. 187-193). Our approach was to use low concentrations of the oxidant H3PM012O40 (Eß = +0.36 V vs. SCE) (Pope (1983) Heteropoly and Isopoly Oxometalates (Springer-Verlag, New York), Chap.4). In virtue of the fact that the electrochemical potential of PY + / PY is more positive (Eß = +1.30 V vs SCE) (Andrieux ef al. (1990) J. Am. Chem. Soc. 112: 2439-2440 = than that of H3PM012O40 / HdPM? I2? 4o, the equilibrium concentration of PY +, and therefore the polymerization ratio, was relatively low in diluted solutions (0.19 M PY, 0.09 M H3PM012O.0) However, it has been shown that the oxidation potential of pyrrole oligomers decreases from +1.20 V to +0.55 to +0.26 V vs. SCE as the number of units increases from one to two or three, and the oxidation potential * of the total poly (pyrrole) occurs at -0.10 V vs. SCE (Díaz ef al. (1981) J. Electroanal, Chem. 121: 355-361) As a result, the oxidation of pyrrole trimers to phosphomolybdic acid is expected to be thermodynamically favorable. the processing of the monomer-oxidant solution (ie, spiral coating, bath coating, introduction of plasticizers, etc.), after which the polymerization time to form thin films was simply effected by evaporation of the solvent. The direct electrical conductivity of poly (pyrrole) films formed by this method on glass plates, then washing the films with methanol to remove excess phosphomolybdic acid and / or monomer, was in the order of 15-30 S- cm-1 for films in the range of 40 - 100 nm thick.

The poly (pyrrole) films produced in this work exhibited excellent electrochemical and optical properties. For example, Figure 2 shows the cyclic voltimetric behavior of a chemically polymerized poly (pyrrole) film following ten cycles from -1.00 V to +0.70 V vs. SCE. The cathodic wave at -0.40 V corresponded to the reduction of poly (pyrrole) to its natural, non-conductive state, and the anodic wave at -0.20 V corresponded to the reoxidation of poly (pyrrole) to its conductive state (Kanazawa et al. (1981) Synth, Met.4: 119-130 = The lack of additional faradic current, which could result from the oxidation and reduction of phosphomolybdic acid in the film, suggests that the Keggin structure of phosphomolybdic acid was not present in the anions. of the film (Bidan et al (1988) J. Electroanal, Chem. 251: 297-306) and implies that Mo042o or other anions, served as the counterions of poly (pyrrole) in the polymerized films.

Figure 3A shows the optical spectrum of a processed polypyrrole film that has been spirally coated on glass and then washed with methanol. The single absorption peak was characteristic of a highly oxidized poly (pyrrole) (Kaufman et al (1984) Phys. Rev. Lett 53: 1005-1008), and the absorption band at 4.0 eV was characteristic of an interband of transition between the conduction and valence bands. The lack of other bands in this energy range was evidence for the presence of bipolar states (see Figure 3A), as has been observed in highly oxidized poly (pyrrole) (Id). Cycling the film in 0.10 M [(C4H9) 4N] + [Cl? 4] -acetontromile and then recording the optical spectrum in 0.10; KCl-H20, it was possible to observe optical transitions of polar states in the oxidized poly (pyrrole) (See Figure 3B). The polar states that have been reported to produce three optical transitions (Id) were observed at 2.0, 2.9, and 4.1 eV in Figure 3B. After the reduction of the film (c.f. Fig. 3B), an increased intensity and a blue change in the 2.9 eV band were observed, as expected for the transition p? p \ associated with the pyrrole units contained in the polymer backbone (Yakushi ef al (1983) J. Chem. Phys. 79: 4774-4778).

As described in the experimental section, various plasticizers were introduced into the polymer films (Table 3).

Table 3. Plasticizers used in arrays of elements * plasticizer sensor 1 none 2 none ** 3 polystyrene 4 polystyrene 5 polystyrene 6 poly (a methyl styrene) 7 poly (styrene-acrylonitrile) 8 poly (styrene-maleic anhydride) 9 poly ( styrene-allyl alcohol) 10 poly (vinyl pyrrolidone) 11 poly (vinyl phenol) 12 poly (vinyl butral) 13 poly (vinyl acetate) 14 polycarbonate * Sensors containing a 2: 3 ratio (weight: w, w: w) of pyrrole to plasticizer ** Film not washed to remove excess phosphomolybdic acid These inclusions allowed chemical control over the bonding properties and electrical conductivity of the resulting plasticized polymers. The sensor arrays consisted of as many as 14 elements, with each element synthesized to produce a different chemical composition, and therefore a different sensor response, for this polymer film. The resistance, R, of each sensor covered individually with film was recorded automatically before, during and after exposure to several odorants. A typical trial consisted of a rest period of 60 seconds in which the sensors were exposed to running air (3.0 liters-min 1), a 60 second exposure to a mixture of air (3.0 liters-min-1), and air which had been saturated with solvent (0.5 - 3.5 liters-min 1), and then an exposure of 240 seconds to air (3.0 liters-min 1).

In an initial processing of the data, presented in this document, the only information used was the maximum amplitude of the resistance change divided by the initial resistance,? Rma < / R ?, of each individual sensor element. Many of the sensors exhibited either increases or decreases in the. resistance to exposure to different vapors, as expected by changes in the properties of polymers by exposure to different types of chemicals (Topart and Josowicz (1992) J. Phys. Chem. 97: 5418-5423). However, in some cases, the sensors showed an initial decrease followed by an increase in resistance in response to a test odor. In view of the fact that the resistance of each sensor could increase and / or decrease with respect to its initial value, two values of? Rma? / R, for each sensor. The source of bidirectional behavior of some sensor / odor pairs has not been studied in detail yet, but in many cases this behavior arises from the presence of water (which itself induces rapid decreases in film strength) in the solvents of Reactive grade used to generate the test odors from this study. The behavior observed in response to these test solvents exposed to air and containing water was reproducible and reversible in a given sensor array, and the environment was representative of many practical odor detection applications in which air and water might not be easily excluded.

Figures 4B-4D describe representative examples of an amplitude of sensor responses of a sensor array (see, Table 3). In this experiment, data were recorded for three separate exposures to vapors of acetone, benzene, and ethanol flowing in the air. The response patterns generated by the sensor array described in Table 3 are shown for: (B) acetone; (C) benzene; and (D) ethanol. The response of the sensor was defined as the maximum percentage increase and decrease of the resistance divided by the initial resistance (gray bar and black bar, respectively) of each sensor to the exposure to solvent vapor. In many cases the sensors exhibited reproducible increments and decrements of resistance. An exhibition consisted from; (i) a rest period of 60 seconds in which the sensors were exposed to running air (3.0 liters / min 1); (ii) a 60-second exposure to a mixture of air (3.0 liters / min 1) and air that had been saturated with solvent (0.5-3.5 liters / min 1); and (iii) an exposure of 240 seconds to air (3.0 liters / min-1). It is readily apparent that these odorants each produced a distinctive response on the sensor array. In additional experiments, a total of 8 separate vapors (acetone, benzene, chloroform, ethanol, isopropyl alcohol, methanol, tetrahydrofuran and ethyl acetate), selected to cover a range of physical and chemical characteristics, were evaluated over a period of 5 days in a sensor arrangement of 14 elements (Table 3). As discussed above, each odorant could be clearly and reproducibly identified from the others using this sensor device.

Principal component analysis (Hecht (1990) Mathematics in Chemistry: An Introduction to Modern Methods (Prentice Hall, Englewood Cliffs, NJ)), was used to simplify the presentation of data and to quantify the distinguishing capabilities of individual sensors and of the arrangement as a whole. In this approximation, the linear combinations of the data? Rma? / R¡ for the elements in the array were constructed in such a way that the maximum variance (defined as the square of the standard deviation) was contained in the minimum of mutually orthogonal dimensions. This allowed the representation of much of the information contained in the data sets shown in the Figures 4B-4D in two (or three) dimensions. The resulting grouping, or the lack of it, of the exposure data in the new dimensional space was used as a measure of the capacity of distinction, and of the reproducibility, of the sensor array.

In order to illustrate the variation in sensor response of the individual sensors that resulted from the changes in the plasticizer polymer, the principal component analysis was performed on each individual response, isolated from each of the 14 individual sensor elements in an array typical (Figure 5). Data were obtained from multiple exposures to acetone (a), benzene (b), chloroform (c), ethanol (e), isopropyl alcohol (i), methanol (m), tetrahydrofuran (t) or ethyl acetate ( @) over a period of five days with the test vapors exposed to the arrangement in various sequences. The numbers of the figures refer to the sensor elements described in Table 3. The units along the axes indicate the amplitude of the main component that was used to describe the particular data set for an odor. The black regions indicate groupings corresponding to a single solvent that could be distinguished from the others; the gray regions highlight the data of solvents whose signals overlap with each other around them. The exposure conditions were identical to those in Figure 4.

Because each individual sensor produced two data values, the principal component analysis of these responses resulted in only two major orthogonal components; PD and PC2. As an example of the selectivity exhibited by an individual sensor element, the sensor designated as number 5 in Figure 5 (which was plasticized with polystyrene.) Confused acetone with chloroform, isopropyl alcohol and tetrahydrofuran, and also confused benzene with acetate. of ethyl, while easily distinguishing ethanol and methanol from all other solvents.Changing the plasticizer to poly (methyl styrene) (sensor number 6 in Figure 5) had little effect on the spatial distribution of responses one with respect to Therefore, as expected, a lighter chemical modification of the plasticizer had little effect on the relative variance of the eight test odorants.In contrast, the addition of a cyano group to the plasticizer, in the form of poly (styrene-acrylonitrile), (sensor number 7 in Figure 5), resulted in a greater contribution to the overall variance by benzene and chloroform, while decreasing the contribution of ethanol. Changing the substituent group in the plasticizer to a hydrogen-bonded acid (poly (styrene-allylic alcohol), sensor number 9 in Figure 5) increased the contribution of acetone to the total variance while having little effect on the others smells, with the exception of methanol and ethanol confusion. These results suggest that the behavior of the sensors can be systematically altered by the variation of the chemical composition of the plasticizer polymer.

Figures 6A and 6B show the principal component analysis for the 14 sensors described in Table 3 and Figures 4 and 5. When the solvents were projected in a three-dimensional odor space (Figure 6A or 6B), all eight solvents were easily distinguished with the specific arrangement discussed here. The detection of a particular test odor, based only on the criterion of observing 1% of the values of? Rma? / R. for all the elements in the arrangement, it was easily achieved at the level of parts per thousand with no control over the temperature or humidity of the current air. Additional increases in sensitivity are possible after the total use of the temporal components of the data? Rmax / R? as well as a more complete characterization of the noise in the arrangement.

We have also investigated the suitability of this sensor array to identify the components of certain test mixtures. This task is greatly simplified if the array exhibits a predictable response signal when the concentration of an odorant is varied, and if the responses of several individual odors are additive (that is, if the superposition is maintained). When a 19-element sensor array is exposed to a number, n, of different concentrations of acetone in air, the concentration of (CH 3) 2) CO was semiquantitatively predicted from the first major component. This was evident from a good linear least squares fit through the first three main components (see Figure 7A for the linear least squares fit for the first principal component).

The same sensor array was also able to resolve the components in several methanol-ethanol test mixtures (Morris et al. (1942) Can. J. Res. B 20: 207-211). As shown in Figure 7B, a linear relationship was observed between the first principal component and the mole fraction of methanol in the liquid phase, xm, in a mixture of CH3OH-C2H5OH, demonstrating that the overlap for this arrangement combination is maintained sensor / mixture. Moreover, although the components of the mixture could be predicted quite adequately from only the first principal component, an increase in accuracy could be achieved by using a multi-linear least squares fit through the first three major components. The ratio maintained for CH3OH / (CH3OH + C2H5OH) ratios from 0 to 1.0 in saturated air solutions of this vapor mixture. The sensing arrays based on conductive polymer could therefore not only distinguish between pure test vapors, but also allow analysis of odorant concentrations as well as binary vapor mixtures analysis.

In summary, the results presented here advance the area of analyte sensor design. A relatively simple array design, using only a multiplexed low power direct current electrical resistance output reading signal, has been shown to easily distinguish between several test odorants. Such arrays based on conducting polymers are simple to build and modify, and offer an opportunity to control chemical on the response pattern of a vapor. For example, by increasing the ratio of plasticizer to conductive polymer, it is possible to approximate the percolation threshold, to the point at which the conductivity exhibits a very sensitive response to the presence of sorbed molecules.

Moreover, producing thinner films will offer the opportunity to obtain decremented response times, and increasing the number of plasticizer polymers and polymer backbones will likely result in increased diversity among the sensors. This type of polymer-based arrays is chemically flexible, simple to manufacture, modify and analyze, and uses a low-power direct current resistance reading signal transduction signal pattern to convert chemical data into electrical signals. This provides a new approach to highly responsive odor sensors for fundamental and applied chemical imitation investigations for the sense of smell of mammals. Such systems are useful in evaluating the generality of algorithms of a neural network developed to understand how the olfactory system of mammals identifies the directionality, concentration and identity of various odors.

Manufacture and testing of Sensing Arrangements based on Carbon Black. Sensor manufacturing The individual sensor elements were manufactured in the following manner. Each non-conductive polymer (80 mg, see Table 4) was dissolved in 6 ml of THF.

Table 4. sensor # Non-conductive polymer 1 poly (4-vinyl phenol) 2 poly (styrene-allyl alcohol) 3 poly (methyl styrene) 4 poly (vinyl chloride-vinyl acetate) 5 poly (vinyl acetate) 6 poly (N-vinyl pyrrolidone) 7 poly (bisphenol A carbonate) 8 poly (styrene) 9 poly (styrene-maleic anhydride) 10 poly (sulfone) Then, 20 mg of carbon black (BP 2000, Cabot Corp.) was suspended with vigorous stirring. The interdigitated electrodes (the split capacitors previously described) were then submerged in this mixture and allowed to the evaporation of the solvent. A series of such sensing elements with different non-conductive polymers were manufactured and incorporated into a commercial connection strip that allowed the chemosorestores to be easily supervised with a multiplexing ohmmeter.

Test of the Sensor Arrangement. To evaluate the performance of the sensors based on carbon black, arrays with up to 20 elements were exposed to a series of analytes. A sensor exposure consisted of (1) a 60 second exposure to running air (6 liters / min 1), (2) a 60 second exposure to a mixture of air (6 liters / min 1) and air that had been saturated with the analyte (0.5 liters / min 1), (3) a recovery period of 5 minutes during which the sensor array was exposed to running air (6 liters / min 1). The resistance of the elements was monitored during the exposure, and depending on the thickness and chemical composition of the film, resistance changes as large as 250% could be observed in response to an analyte. In one experiment, a 10-element sensor array consisting of carbon black compositions formed with a series of nonconductive polymers (see Table 4) was exposed to acetone, benzene, chloroform, ethanol, hexane, methanol, and toluene by a two day period. A total of 58 exposures were made to these analytes in this period of time. In all cases, changes in resistance in response to analytes were positive, and with the exception of acetone, reversible (see Figure 8). The Maximum positive deviations were then subjected to a principal component analysis in a manner analogous to that described for the poly (pyrrole) based sensor. Figure 9 shows the results of the main component analysis for the complete array of 10 elements. With the exception of the overlap between toluene and benzene, the analytes were distinguished from one another. All the publications and patent applications cited in this specification are incorporated by reference as if each individual publication or patent application was specific and individually indicated its incorporation as a reference. Although the foregoing invention has been described in some detail, by way of illustration and example for purposes of clarity of understanding, it will be readily apparent that certain changes and modifications may be made thereto without departing from the spirit of the scope of the appended claims.

Claims (7)

R E I V I N D I C A C I O N S

1. A sensor arrangement for detecting an analyte in a fluid comprising at least first and second chemically sensitive resistors electrically connected to an electrical measuring device, each of said chemically sensitive resistors comprising: a non-conductive organic polymer mixture and a compositional material compositionally different from said non-conductive organic polymer, wherein each resistor provides an electrical pattern through said mixture of non-conductive organic polymer and said conductive material, a first electrical resistance when placed in contact with a first fluid comprising a chemical analyte at a first concentration, and a second electrical resistance when placed in contact with a second fluid comprising said chemical analyte at a second different concentration, wherein the difference between the first electrical resistance and the second electrical resistance of said first chemically sensitive resistor being different from the difference between the first electrical resistance and the second electrical resistance of said second chemically sensitive resistor under the same conditions.

2. A sensor array according to claim 1, wherein said non-conductive organic polymer of said first chemically sensitive resistor is different from said non-conductive organic polymer of said second chemically sensitive resistor.

3. A sensor arrangement according to claim 1, wherein said conductive material is an inorganic conductor.

4. A system for detecting an analyte in a fluid, said system comprising: a sensor arrangement comprising at least first and second chemically sensitive resistors, each chemically sensitive resistor comprising a mixture of non-conductive organic polymer and compositionally different conductive material than said non-conductive organic polymer, each resistor providing an electrical pattern through said polymer blend non-conductive organic and said conductive material, a first resistance electrical when contacted with a first fluid comprising a chemical analyte at a first concentration and a second different electrical resistance when it is contacted with a second fluid comprising said chemical analyte at a second different concentration, wherein the difference between the first electrical resistance and the second electrical resistance of said first chemically sensitive resistor being different from the difference between the first electrical resistance and the second electrical resistance of said second chemically sensitive resistor under the same conditions; an electrical measuring device electrically connected to said sensor array; Y a computer comprising a resident algorithm; said electrical measurement device detecting said first and second electrical resistors in each of said chemically sensitive resistors and said computer assembling said resistors in a response profile of the sensor array.

5. A system according to claim 4, wherein said non-conductive organic polymer of said first chemically sensitive resistor is different from said non-conductive organic polymer of said second chemically sensitive resistor.

6. A system according to claim 4, wherein said conductive material is an inorganic conductor.

7. A method for detecting the presence of an analyte in a fluid, said method comprising: resistively feeling the presence of an analyte in a fluid with a sensor arrangement comprising at least first and second chemically sensitive resistors each comprising a mixture of non-conductive organic polymer and a compositional material compositionally different from said non-conductive organic polymer, each resistor providing a electrical pattern through said non-conductive organic polymer mixture and said conductive material, a first electrical resistance when contacted with a first fluid comprising a chemical analyte at a first concentration and a second different electrical resistance when contacted with a second fluid comprising said chemical analyte at a second different concentration. A method according to claim 7, wherein said non-conductive organic polymer of said first chemically sensitive resistor is different from said non-conductive organic polymer of said second chemically sensitive resistor. A method according to claim 7, wherein said conductive material is an inorganic conductor. . A method according to claim 7, said first and second resistance each being a resistance over time. SUMMARY Chemical sensors for detecting analytes in fluids comprise first and second conductive elements (eg, electrical conductors) electrically coupled to and separated by a chemically sensitive resistor that provides an electrical pattern between the conductive elements. The resistor comprises a plurality of non-conductive regions (comprising a non-conductive organic polymer) and conductive regions (comprising a conductive material) alternating transverse to the electrical pattern. The resistor provides a difference in resistance between the conductive elements when placed in contact with a fluid comprising a chemical analyte at a first concentration, which when brought into contact with a fluid comprising the chemical analyte at a second different concentration. The arrangements of such sensors are constructed with at least two sensors having different chemically sensitive resistors providing such differences a dissimilarity in the resistance. The variability in the chemical sensitivity of sensor to sensor is provided by the quantitative and qualitative variation of the composition of the conductive and / or non-conductive regions. An electronic nose for the detection of an analyte in a fluid can be constructed using such arrangements in conjunction with an electrical measuring device electrically connected to the conductive elements of each sensor.