Organic charge-transfer chemical sensor

Abstract

An electrochemical sensor for the detection of a selected analyte and methods of detecting the selected analyte. The sensor comprises an active layer containing a sensing material dispersed in a semiconducting and / or conducting polymer. The conductance of the active layer is responsive to the presence / amount of selected analyte in the active layer. The sensing material comprises a pi-conjugated moiety and at least one chemical functional group bonded to the pi- conjugated moiety, interaction of the sensing material with the selected analyte induces charge transfer into the active layer to change the conductance of the active layer. Example selected analytes are volatile bases, particularly ammonia, volatile amines, diamine or polyamines. Example sensing material is the N-Annulated perylene diamine NPDI-NH.

Description

ORGANIC CHARGE-TRANSFER CHEMICAL SENSORCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 560,336, filed March 1 , 2024, which is incorporated by reference herein in its entirety.BACKGROUND

[0002] The invention relates generally to chemical and biological sensors useful in a variety of applications. The invention relates to the detection and quantitation of one or more selected analytes employing an electrochemical chemical sensor implemented with organic semiconducting and conducting polymers. More specifically, the invention relates to the detection of amines and other basic chemical species and particularly to the detection of biogenic amines.

[0003] Chemical sensors based on organic semiconductors are employed in diverse applications because they are easy to manufacture and are mechanically flexible. Such sensors often rely for analyte detection and / or quantitation on an increase in resistance (i.e., chemiresistive sensors), or require implementation into a transistor configuration which increases device complexity and can limit sensitivity (e.g., Organic field-effect transistors (OFETs)). See: (Grant et al., 2023 and references cited therein)

[0004] The present invention, in contrast, provides a chemical sensor employing an organic semiconducting layer that relies for detection on an increase in conductivity of the active layer from an electron transfer reaction with a sensing material or molecule in the active layer. The sensor device can be implemented in a simple two-electrode configuration. Certain sensors herein are heterojunction sensors which rely on an interface between two layers or regions of dissimilar semiconductors having unequal electronic energy levels. In certain sensor device structures, the conductivity of the active layer is increased because of electron transfer induced by reaction with the analyte into an n-type semiconducting polymer of the active layer.

[0005] The chemical sensor of the invention is exemplified with the detection of bases and particularly amines and more particularly biogenic amines, which react, for example, with a selected sensing material or sensing molecule in the active layer by reversible deprotonation. The detection of amines is of particular importance for many applications including environmental monitoring, health diagnostics, and in assessing food quality or detecting food spoilage where microbes release a variety of volatile amines, including ammonia, histamine, cadaverine and putrescine, as they proliferate. (Danquah et al., 2012)

[0006] Detection of food spoilage and amine generation in food is important to human health. Foodborne contamination is responsible for the death of 420,000 people per yearworldwide. (World Health Organization, Food Safety, 2022) While commercially available sensing technologies can reliably detect ammonia at 100 ppb levels, improvements in detection limits and lower sensor costs are needed to expand applications of such sensors, particularly in the food industry.SUMMARY

[0007] The invention provides an electrochemical sensor for the detection of a selected analyte. The sensor comprises, consists essentially of, or consists of an active layer which comprises, consists essentially of, or consists of a semiconducting layer comprising, consisting essentially of, or consisting of semiconducting material including a semiconducting polymer, molecule, or inorganic layer, and a selected amount of a sensing material dispersed in, or deposited on the semiconducting material; and at least two electrodes each electrically connected to the active layer for measurement of a change in conductance of the active layer.

[0008] In embodiments, the semiconducting layer comprises a semiconducting polymer in which a selected amount of the sensing material is dispersed. In embodiments, the semiconducting layer comprises, consists essentially of, or consists of a mixture of a semiconducting polymer and a conducting polymer.

[0009] The sensing material comprises, consists essentially of, or consists of a pi- conjugated moiety and at least one chemical functional group bonded to the pi-conjugated moiety, wherein the at least one chemical functional group reacts with the selected analyte to induce charge transfer into the active layer to change the conductance of the active layer. A change in conductance of the active layer indicates the presence of the selected analyte in the active layer. In embodiments, the change in conductance of the active layer allows measurement of the quantity of the selected analyte in an environment being tested.

[0010] The invention provides a method for detecting a selected analyte which in embodiments comprises, consists essentially of, or consists of dispersing a sensing material in an active layer comprising, consisting essentially of, or consisting of a semiconducting polymer; and monitoring the conductance of the active layer when the active layer is exposed to an environment that may contain the selected analyte. In embodiments, the sensing material comprises, consists essentially of, or consists of a pi-conjugated moiety and at least one chemical functional group bonded to the pi-conjugated moiety, wherein the at least one chemical functional group reacts with the selected analyte to induce charge transfer into the active layer to change the conductance of the active layer. The increase in conductance of the active layer indicates the presence of the selected analyte the environment that is being tested or assessed for the presence of the selected analyte. In embodiments, the methods herein can be employed to quantitate the amount of a selected analyte in the environment being tested.

[0011] In embodiments of any sensors or method described herein, the selected analyte is a base. In embodiments of any sensors or method described herein, the selected analyte is an amine. In embodiments of any sensors or method described herein, the selected analyte is volatile, optionally a volatile base (e.g., hydrazine, an alkyl hydrazine, or other organic nitrogencontaining base). In embodiments of any sensor or method described herein, the selected analyte is selected from ammonia, a primary amine, a secondary amine, a diamine, a tertiary amine, pyrrole, indole, hydrazine or an alkyl hydrazine.

[0012] In embodiments of any sensor or method described herein, the selected analyte is one or more biogenic amine. In embodiments of any sensor or method herein, the senor or method is used to assess the freshness or detect the spoilage of a food product. In embodiments of any sensor herein the sensor is implemented within food packaging.

[0013] In embodiments of any sensor or method described herein, the pi-conjugated moiety is selected from a rylene moiety, optionally a perylene, terrylene or quaterrylene moiety; a perylene diimide moiety; an oligoacene moiety, a heteroacene moiety; a phthalocyanine moiety, and a napthalene diimide moiety. In embodiments of any sensor or method described herein, the chemical functional group is selected from an N-annulated (N-H) moiety, a pyrrole moiety (optionally a diketopyrrole), an indole moiety, a carbazole moiety, an azole moiety, an imidazole moiety and a benzoimidazole moiety.

[0014] In embodiments of any sensor or method described herein, the sensing material is a compound of Formula I:I wherein:Ri and R2are independently a substituted or unsubstituted C1 to C18 linear or branched alkyl group; andXi-X6are independently selected from the group H, a C1-C6 substituted or unsubstituted alkyl, a halogen, — NO2, and — CN orX2and X3together form — S — S — and Xi and X4are independently selected from the group H, a C1-C6 substituted or unsubstituted alkyl, a halogen, — NO2, and — CN; and wherein optional substitution of alkyl groups is substitution with one or more halogen, — CN, — NO2, — C(O)R', —COOR', — C(O)NH2, — NHC(O)R', — C(O)NR'R", — CF3, — SO3H, — SO2CF3, — SO2R', — SO2NR'R”, —OR', — OC(O)R', substituted or unsubstituted phenyl, substituted or unsubstituted benzyl, substituted or unsubstituted vinyl, — NHR' or — NR'R", wherein R' and R" are independently H, an unsubstituted C1 to C6 alkyl or a C1-C3 halogen-substituted C1-C6 alkyl.

[0015] In embodiments of any sensor or method described herein, the sensing material is a compound of Formula I where XrX4are selected from hydrogen, halogen or — CN and Ri and R2are C3-C11 alkyl groups. In embodiments of any sensor or method described herein the sensing molecule is NPDI-NH.

[0016] In embodiments of any sensor or method described herein, the semiconducting polymer comprises, consists essentially of, or consists of one or more pi-conjugated groups selected from thiophene or thiophene derivatives; fluorene or fluorene derivatives; benzothiadiazole or benzothiadiazole derivatives; indacenodithiophene (IDT) or indacenodithiophene derivatives; naphthalenediimide (NDI) or NDI derivatives; pyrrole or pyrrole derivatives; isoindigo or isoindigo derivatives; cyclopentadithiophene (CPDT) or CPDT derivatives; d i keto pyrro Io pyrrole (DPP) or DPP derivatives; and benzodithiophene (BDT) or BDT derivatives. In embodiments, the forgoing derivatives include substituted variants of the recited chemical group, where one or more hydrogens of the recited chemical group are substituted with a substituent selected from a halogen, — CN, — NO2, — C(O)R', — COOR', — C(O)NH2, — NHC(O)R', — C(O)NR'R", — CF3, — SO3H, — SO2CF3, — SO2R', — SO2NR'R”, — OR', — OC(O)R', substituted or unsubstituted phenyl, substituted or unsubstituted benzyl, substituted or unsubstituted vinyl, — NHR' or — NR'R", wherein R' and R" are independently H, an unsubstituted C1 to C6 alkyl or a C1-C3 halogen-substituted C1-C6 alkyl.

[0017] In embodiments of any sensor or method described herein the semiconducting polymer is a polymer illustrated in Scheme 2. In embodiments of any sensor or method described herein, the semiconducting polymer is a polymer illustrated in Scheme 3 or a mixture of polymers illustrated in Scheme 2 and Scheme 3. In embodiments of any sensor or method described herein, the semiconducting polymer is a polymer of structure P(ND12OT), wherein each R is selected from alkyl groups having 5-24 carbon atoms. In embodiments of any sensor or method described herein, the R groups of P(ND12OT) are independently selected from branched alkyl groups of formula -CH2-CH2(RI)(R2), where Ri and R2are independently alky groups having 6-12 carbon atoms. In embodiments of any sensor or method described herein the semiconducting polymer is P(NDI2OD-2T).

[0018] In embodiments of any sensor or method described herein, the active layer comprises a mixture of a semiconducting polymer and a conducting polymer, wherein the semiconducting polymer represents at least 10% of the weight of the mixture. In embodiments, the semiconducting polymer represents at least 50% of the weight of the mixture. In embodiments of any sensor or method described herein, the active layer contains a conducting polymer selected from polyacetylene, polythiophene, poly(p-phenylene) or poly(p-phenylene vinylene) or a substituted derivative thereof. Substituted derivatives include those in which one or more hydrogens are substituted with substituted with a substituent selected from a halogen, — CN, — NO2, — C(O)R', — COOR', — C(O)NH2, — NHC(O)R', — C(O)NR'R", — CF3, — SO3H, — SO2CF3, — SO2R', — SO2NR'R”, — OR', — OC(O)R', substituted or unsubstituted phenyl, substituted or unsubstituted benzyl, substituted or unsubstituted vinyl, — NHR' or — NR'R", wherein R' and R" are independently H, an unsubstituted C1 to C6 alkyl or a C1-C3 halogensubstituted C1-C6 alkyl.

[0019] In embodiments of any sensor or method described herein, the sensing material is PDI-NH and the semiconducting polymer is P(NDI2OD-2T). In these embodiments, the analyte is an organic or inorganic base and optionally is a volatile base. In these embodiments, the selected analyte is a volatile amine, volatile diamine or volatile polyamine.

[0020] In further embodiments of any method herein, the method employs any sensor embodiment or combination of sensor embodiments described herein. In further embodiments of any method herein, the amount of the selected analyte in the tested environment is quantitated using conductance measurement as described herein. In embodiments, any method as described herein is practiced with a sensor which can detect and optionally quantitate the selected analyte.

[0021] In embodiments the invention provides a method for detection and optionally quantitation of a selected analyte which comprises, consists essentially of, or consists of: providing a sensor of any embodiment described herein and monitoring the conductance of the active layer when the active layer is exposed to an environment that may contain the selected analyte. In embodiments of any method herein, the selected analyte is one or more biogenic amine (e.g., amine, diamine or polyamine). In embodiments, the methods herein assess the freshness of a food product or the spoilage of a food product.

[0022] In a specific embodiment of sensors and methods herein, the analyte is of one or more biogenic amines associate with spoilage of food and the sensor is provided within packaging of a food product.

[0023] Other aspects and embodiments of sensors and methods will be apparent to one of ordinary skill in the art on review of the detailed description, drawings and non-limiting examples herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figures 1A -1 F illustrate example sensor device configurations of the invention.

[0025] Figure 2 is a graph of the profilometry thickness measurement of a PDI-NH dopedP(NDI2OD-2T) film deposited by spin-coating on a glass substrate as described in the Examples.

[0026] Figure 3 illustrates UV-Vis spectra of PDI-NH doped P(NDI2OD-2T) films for various active layer doping concentrations (1%, 5%, 19% and 25% by weight) and undoped PDI-NH (as indicated) deposited by spin-coating on a glass substrate as described in the Examples. Black vertical lines mark the peak positions in the spectrum of undoped PDI-NH. Peak structure in this wavelength region grows in with increasing concentration of PDI-NH in the active layer.

[0027] Figure 4 schematically illustrates an example electrochemical gas sensor testing setup (50). The sensor (10) is inserted into a sealed sample chamber (51). The sensor can be exposed to different analytes at varying concentrations by introduction of analyte optionally in a carrier gas or fluid into the chamber through an input line (52) or nozzle equipped with an entrance valve (53) that allows controlled diffusion (flow) of the analyte into the chamber and an exit line (54) equipped with an exit or release valve (55) to release gas / vapor from the chamber.

[0028] Figures 5A and 5B schematically illustrates functioning of a sensor (10) over time to detect and quantitate analyte (black dots). In FIG. 5A, time point I, the active layer (2) of the sensor (10) contains a selected amount of sensing material (3, light dots) in a polymer layer (4). At time point II, analyte (black dots) in the sensor environment begins to permeate into the active layer (2) to react with sensing material where reacted sensing material is indicated by striped dots (4). At time point III, analyte concentration in the sensor environment increases and increasing amounts of analyte permeate into the active layer. FIG. 5B is a graph showing the change in conductance as a function of illustrated time points in FIG. 5A. Reacted sensing material induces a charge transfer into the active layer which is measured as an increase in conductance in the sensor. Conductance increases as the concentration of analyte increases in the environment of the sensor. In embodiments, the reaction of analyte with the sensing material is reversible, so that conductance in the sensor decreases as the concentration of the analyte in the environment of the sensor decreases.

[0029] Figures 6A and 6B are illustrations of the sensing mechanism occurring between the targeted analyte (e.g., an amine) and an active layer containing example sensing material PDI-NH which has a pyrrolic NH functional group. In FIG. 6A, reaction with analyte, illustrated as a primary amine, results in formation of the anionic species PDI-N- by deprotonation of sensing material (PDI-NH) in the presence of analyte (Reaction 1). Charge transfer then proceeds from the anionic sensing material to the semiconducting polymer of the active layer (Reaction 2). FIG. 6B, further illustrates the sensing mechanism with an exemplarysemiconducting polymer of the active layer (P(NDI2OD- 2T)), where energy levels in eV of the LUMO (lowest unoccupied molecular orbital) energy levels of sensing material (e.g., PDINH) and active layer polymer (e.g., P(NDI2OD-2T)) are shown. Also shown is the energy level of the highest occupied molecular orbital (HOMO) of the reacted sensing material (e.g., PDIN anion). The relative energies of the HOMO of the reacted sensing material and the LUMO of the active layer polymer are important for electron transfer reactions. As illustrated, there is a charge transfer from the anionic species PDIN- into P(NDI2OD- 2T) which has a LUMO energy level lower (more negative) than the HOMO of the anionic species. In embodiments to ensure charge transfer, the difference between the LUMO of the polymer and the HOMO of the reacted sensing material is 0.1 eV or more (e.g., 0.15 eV or more, 0.2 eV or more, 0.25 eV or more, or 0.3 eV or more). In embodiments, to ensure efficient charge transfer, the difference between the LUMO of the polymer and the HOMO of the reacted sensing material is preferably equal to or more than 0.4 electron volts (eV). In embodiments, the difference between the LUMO of the polymer and the HOMO of the reacted sensing material is preferably equal to or more than 0.5 or optionally more than 0.6 electron volts (eV).

[0030] Figures 7A-7E show AFM images of the PDINH doped P(NDI2OD-2T) film surface (FIGs. 7A-7D) compared to undoped film (FIG. 7E).

[0031] Figures 8A and 8B: FIG. 8A is a graph of l-V curve response (Current (pA) vs. Voltage (V)) of P(NDI2OD-2T) active layer films with different doping concentration in PDI-NH (5% (dashed line) and 10% (dotted line) by weight) compared to that of P(NDI2OD-2T) (solid line). FIG. 8B is a graph of l-V curve response of P(NDI2OD-2T) films (Current (nA) vs. Voltage (V)) after exposure of the active layer film to different concentration (0.5 ppb — 100 ppm, as indicated) of n-butylamine vapor compared to initial device (thin solid line).

[0032] Figures 9A-9C: Conductance response of thin films on exposure to n-butylamine. FIG. 9A shows response of a 10% by weight PDINH doped P(NDI2OD-2T) film after exposure to different n-butylamine concentrations (0.5 ppb — 100 ppm). FIG. 9B shows conductance change as a function of exposure time of 10% be weight PDINH doped P(NDI2OD-2T) film to 0.05 ppm n-butylamine vapor. FIG. 9C shows peak conductance response as a function of analyte (n-butylamine) concentration for different PDINH doping levels (0% (thin soldi line), 1%, 5%, 10% and 25% (thick solid line)).

[0033] Figures 10A-10B: Response / recovery of active film exposed to analyte. FIG. 10A is a graph showing repeated response / recovery of the PDI-NH doped P(NDI2OD-2T) film exposed to 0.5 ppm of n-butylamine. FIG. 10B shows the stability of performance (response / recovery) of the PDI-NH doped P(NDI2OD-2T) film over days when exposed to 100 ppm of n-butylamine.

[0034] Figure 11 : Sensitivity response of a sensor with 10 wt% PDI-NH doped P(NDI2OD- 2T) active layer toward different solvents and amine vapors at indicated concentrations.Experiments were performed on the same device.

[0035] Figure 12: Time dependent response of a sensor with 10 wt% PDI-NH doped P(NDI2OD-2T) active layer to different concentrations of the diamine cadaverine. The sensor used is the same as that tested in FIG. 11 .

[0036] Figures 13A-13C illustrate properties of organic field-effect transistors (OFETs) based on PDINH doped P(NDI2OD-2T) films. FIG. 13A is an output curve of PDINH doped P(NDI2OD-2T) OFET. FIG. 13B is a transfer curve for undoped P(NDI2OD-2T) (solid) and PDINH doped P(NDI2OD-2T) (dotted) OFET. FIG. 13C is a transfer curve of PDI-NH doped P(NDI2OD-2T) OFET before (solid) and after exposure to 5 ppm butylamine (dotted).DETAILED DESCRIPTIONExample Device Configurations

[0037] FIGs. 1A-1 F illustrate various electrochemical sensor configurations of the invention. Each example has a two-electrode configuration and when implemented with the active layer described herein functions as sensors for a selected analyte, such as a base or more specifically ammonia or an amine. Contact of the active layer with analyte results in an increase in conductance of the active layer and measurement of this increase in conductance allows detection and quantitation of analyte.

[0038] FIG. 1 A and FIG. 1 D illustrate top views and FIG. 1 B and 1C) lateral views, respectively, of example embodiments of an electrochemical gas sensor of the invention. The electrochemical gas sensor (10) has two spaced-apart electrodes (1a. 1 b), an active layer (2) and a substrate (5). The active layer (also called an active film) is formed from a polymer film (4) and comprises one or more sensing materials or sensing molecules (3). The sensing material or molecule (3) is dispersed in the polymer film (4) to form the active layer (2). The polymer forming the active layer is a semiconducting polymer or certain mixtures of a semiconducting polymer and a conducting polymer.

[0039] In embodiments, the mixture of the semiconducting polymer and the conducting polymer comprises at least 10% by weight of the semiconducting polymer. In other embodiments, the mixture of the semiconducting polymer and the conducting polymer comprises 50% by weight or more of the conducting polymer. In other embodiments, the mixture of the semiconducting polymer and the conducting polymer comprises 20% or more, 30% or more, 40% or more, 60% or more, 70% or more, 80% or more or 90% or more by weight of the semiconducting polymer.

[0040] In the sensors of FIGs. 1 A, 1 B and 1 D the two electrodes are positioned on top of and in electrical contact with the active layer (2). In FIG. 1C, the electrodes (1a, 1 b) are positioned on the substrate (5) in electrical contact with the active film (2) which is layered over the electrodes (1a, 1 b) on the substrate (5). In these examples, the substrate is not conductive or is insulated from the active layer. In the sensor of FIG. 1C the electrodes (1a, 1 b) are embedded in the active layer (2). FIG. 1 D illustrates an interdigitated electrode configuration (1a, 1 b) positioned on top of the active film (2). In an alternative configuration, not shown, the interdigitated electrodes (1a, 1 b) are positioned in physical contact with the substrate (5) and embedded in and in electrical contact with the active layer (2) as in FIG. 1C.

[0041] In the sensors of FIG. 1 E and FIG. 1 F, the substrate forms one of the electrodes (1 b) of the device. The active layer is formed on the substrate and the substrate is conductive and is in electrical contact with the active layer. The second electrode (1a) is formed on the active layer, such as by deposition, and is in electrical contact with the active layer. The second electrode may be formed as a continuous element on the active layer or as illustrated in FIG. 1 F may be a grid or other patterned porous structure formed on the active layer.

[0042] In these sensors, at least a portion of the substrate is conductive and in electrical contact with the active layer. When the substrate or a portion of the substrate is electrically conductive, it may be beneficial to electrically insulate the conductive portion of the substrate from its surroundings to prevent shorting. For example, a conductive material, such as a metal foil may be mounted on a non-conductive support to form the electrically conducting substrate.

[0043] In sensing applications, at least a portion of the active layer is open to contact with analyte in the environment of the sensor. In embodiments, the analyte permeates into the active layer. In embodiments, the analyte contacts at least a surface of the active layer. Positioning of the electrodes in contact with the active layer is such that analyte in the vicinity or environment of the sensor can contact or enter into the active layer where analyte reacts with the sensing material or molecule. Electrodes can, for example, cover only a portion of the active layer, as show in FIGs 1A-1 E, and / or one or both electrodes may be provided with apertures, such as in the grid of FIG. 1 E, to allow analyte to contact or enter the active layer. In embodiments, one or both electrodes are formed in contact with the active layer by deposition of a conductive layer (e.g., a metal layer or metal oxide layer), which may be deposited in a selected pattern using an appropriately shaped mask.

[0044] In embodiments, one or more sensing materials or molecules (3) are dispersed in the active layer (4). In general embodiments, the active layer comprises, consists essentially of or consists of from 0.5% to 50% by weight of one or more sensing materials or molecules. In embodiments, the active layer comprises, consists essentially of or consists of from 0.5% to 25% by weight, or from 0.5 to 20% by weight, or from 1% to 20% by weight, or 0.5% to 15% by weight, or 1 % to 15% by weight, or 1 to 10% by weight of one or more sensing materials ormolecules. In embodiments, two different sensing materials or molecules are present in the active layer. In embodiments, only one sensing material or molecule is present in the active layer. In embodiments, the active layer can contain up to 5% by weight of other components that do not detrimentally affect the reaction of the analyte with the sensing materials or molecules or detrimentally affect charge transfer from the sensing materials or molecules into the polymer of the active layer. In embodiments, the sensing material or molecule is miscible in the active layer up to a concentration of at least 50% by weight. In embodiments, the sensing material or molecule is miscible in the active layer up to a concentration of at least 25% by weight. In embodiments, the sensing material or molecule is miscible in the active layer up to a concentration of at least 10% by weight.

[0045] The polymer (4) of the active layer comprises, consists essentially of, or comprises one or more semiconducting materials. In embodiments, the semiconducting material is a semiconducting molecule, a semiconducting polymer, or a semiconducting inorganic material. In embodiments, the semiconducting material is a semiconducting polymer. In embodiments, the semiconducting polymer of the active layer is a single semiconducting polymer. In embodiments, the semiconducting polymer of the active layer is a mixture of two or more semiconducting polymers. In embodiments, the polymer of the active layer is a mixture of two semiconducting polymers. In embodiments, the mixture of a semiconducting polymer and a conducting polymer comprises 10% by weight or more (e.g., 15%, 20%, 25%, 30%, 35%, 40%, 45% or more by weight) of the semiconducting polymer. In embodiments, the polymer of the active layer is a mixture of a semiconducting polymer and a conducting polymer. In embodiments, the mixture of a semiconducting polymer and a conducting polymer comprises 50% by weight or more (e.g., 55%, 60%, 65%, 70% or more) of the semiconducting polymer. In embodiments, the mixture of a semiconducting polymer and a conducting polymer comprises 75% by weight or more (e.g., 80%, 85% or more) of the semiconducting polymer. In embodiments, the mixture of a semiconducting polymer and a conducting polymer comprises 90% by weight or more (91%, 92%, 93%, 94% or more) of the semiconducting polymer. In embodiments, the mixture of a semiconducting polymer and a conducting polymer comprises 95% by weight or more (e.g., 96%, 97%, 98% or 99% or more) of the semiconducting polymer.

[0046] In embodiments, the active layer has a thickness from 10 nm to 1000 nm. More specifically, the thickness of the active layer ranges from 10 nm to 500 nm, or 10 nm to 250 nm, or 10 nm to 100 nm, or 10 nm to 50 nm, or 25 nm to 1000 nm, or 25 nm to 500 nm, or 25 nm to 250 nm, or 25 nm to 100 nm, or 50 nm to 1000 nm, or 50 nm to 500 nm, or 50 nm to 250 nm, or 50 nm to 100 nm, or 100 nm to 1000 nm, or 100 nm to 500 nm, or 100 nm to 250 nm, or 500nm to 1000 nm or 10 nm to 25 nm.

[0047] In embodiment, electrodes (1a, 1 b) are composed of any conductive material layer which is deposited in a lateral or interdigitated configuration directly on the substrate (5) or ontop of the active layer (2). In embodiments, one or both electrodes can be a metal foil in contact with the active layer. In embodiments, an inter-electrode channel (6) is formed between the spaced apart electrodes (1a, 1 b), such that the electrodes are in electrical contact with each other through contact with the active layer (2). In embodiments, at least one electrode is formed on the substrate or the substrate is itself electrically conductive. The electrodes provide for electrical connection of the sensor to a voltage source (not shown) and for measurement of electrical conductivity through the active layer (2). In embodiments, the electrodes range in thickness from 50 nm to 1000 nm. In embodiments, deposited electrodes range in thickness from 50 nm to 100 nm. In embodiments, at least one electrode is formed as a conductive grid. In embodiments, at least one electrode is formed with holes or apertures to allow analyte to contact or enter the active layer.

[0048] In embodiments, a channel is formed between the first and second electrodes. In embodiments, the channel contains at least a portion of the active layer. In embodiments, the length of the channel (L, FIG. 1A) between the two electrodes is in the range of 500 pm to 4 000 pm. In embodiments, the width of the channel between the two electrodes (W, FIG. 1A) is in the range 25 pm to 200 pm. The length (L) and width (W) of the inter-electrode channel formed can be adjusted as desired. The length and width of the inter-digital channel (L) can be varied using different electrode configurations. For example, in specific embodiments, the electrodes can be linear, lateral, circular, or cylindrical in shape. In embodiments, one or more electrode can be made from one or more metal (e.g., Au, Ag, and Al), one or more metal oxide, or carbon. In embodiments, one or more electrode can be made from highly conductive organic films, such as those made from polypyrrole (PPy), polyaniline (PANI), or poly(3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT / PSS).

[0049] In embodiments, the substrate can be made of any non-conductive or conductive material or materials that provides mechanical support for the active layer. In embodiments, the substrate can generally be any convenient size or shape upon which the active layer can be positioned. In embodiments, the substrate provides support for the active layer and electrodes. In embodiments, the substrate is rigid. In embodiments, the substrate is flexible. For example, the substrate may be made of paper, cardboard, glass, quartz, non-conductive plastic (e.g., polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polydimethylsiloxane (PDMS), or non-conductive ceramic. In embodiments, as illustrated in FIGs. 1 E and 1 F, the substrate is at least in part conductive and is in electrical contact with the active layer and also functions as an electrode. In embodiments, the substrate / electrode is a metal film or foil sufficiently thick to support the active layer. In embodiments, the substrate / electrode is a conductive electrode deposited or mounted on a non-conductive substrate.

[0050] A sensor herein can in embodiments be encapsulated to avoid contamination. However, analyte must contact or enter the active layer for detection and quantitation. Adiffusion barrier can be used as a protection layer to avoid mutual contamination. The primary function of the protective / diffusion layer is to prevent direct contact between the sensor and food or other components in the environment being tested (other than analyte), while allowing the diffusion of targeted analytes (e.g., biogenic amines) to the sensor. As an example, nonwoven high-density polyethylene (HDPE) has shown good permeability to gas vapor while blocking water or other liquids and seems a suitable candidate. HDPE can be used as a protective diffusion layer in sensors of this invention.

[0051] Standard two-electrode measurements are employed to assess the electrical properties of the active sensing layer. The device is connected to an external power supply via the electrodes. One electrode acts as the working electrode, while the second electrode provides a pathway for current to flow and complete the circuit. The current is then measured using either an electrometer or a source meter unit. Subsequently, the film conductivity is extracted (or film resistivity, as resistivity is the inverse of conductivity). Sensor devices herein optionally include a power supply, electrical connectors and circuitry for connection of electrodes to the power supply and to standard equipment for measurement of conductivity. In embodiments, the sensor device is provided with an appropriate battery or battery pack. In embodiments, the sensor optionally comprises a display device for displaying the results of conductivity measurements.

[0052] In use as a sensor, the active layer (2) is exposed to an environment, for example, a closed environment, for assessing the presence of a selected analyte in that environment. The sensing material or molecule (3) in the active layer is selected for its ability to react with the selected analyte. In particular, the sensing material or molecule reacts with the selected analyte to induce charge transfer and more specifically reacts with the selected analyte by protonation or deprotonation which ultimately results in a charge transfer into the semi-conducting or conducting polymer (4) in the active layer (2). On exposure of the active layer in which the selected sensing material or molecule is dispersed, the selected analyte contacts or permeates into the active layer, reacts with the selected sensing material or molecule therein and induces charge transfer from the sensing material or molecule into the active layer. With this reaction, the conductance of the active layer will change, e.g., will increase. Such an increase in conductance of the active layer indicates the presence of the selected analyte in the environment being tested.

[0053] Surface engineering techniques can optionally be applied to the substrate to enhance the adhesion of the active layer to the substrate. Various surface engineering techniques are known in the art that can be employed to enhance the adhesion of organic layers on a surface, including self-assembled monolayers (SAMs). Such techniques may significantly improve sensing performance and may be beneficially employed during the fabrication process of sensor devices of this invention. See, for example, Wang, (2022)“Surface adhesion engineering for robust organic semiconductor devices,” Journal of Materials Chemistry C, 2022, 7, available at pubs.rsc.org / en / content / articlehtml / 2022 / tc / d1tc05966a; Hu et al. “Self-assembled monolayers for interface engineering in polymer solar cells,” J of Polymer Science, 60 915):2175-2190, available at onlinelibrary.wiley.com / doi / full / 10.1002 / pol.20210938. In addition, adhesion can be improved through the use of polymeric materials not involved with the electronic functionality and / or sensing mechanism. See, for example, Kim et al. (2020) “Elastic conducting polymer composites in thermoelectric modules,” Nature Comm. 11 , article number 1424, 10 pages available at the web site www.nature.com / articles / s41467-020- 15135- w. Each reference cited in this paragraph is incorporated by reference herein in its entirety for any purpose, but particularly for descriptions of surface engineering techniques applicable to the devices herein.

[0054] The sensors of the invention can be fabricated by any appropriate methods known in the art. For example, the sensors can be fabricated using additive manufacturing techniques. In embodiments, the active layer is fabricated using solution coating and printing processes, such as inkjet printing or blade-coating. The fabrication of the sensor can follow standard processes, as reported in the following references: W02001046987A2 (US 7176040, US 7572651); W02005069403A2 (US2006159842A1); W02005024895A2 (US 7678857); or CN1639246A (US patent 7,351 ,357) each of which is incorporated by reference herein in its entirety for any purpose, but particularly for methods of making layered devices such as the sensors of this invention.

[0055] Electrodes, particularly for flexible devices, can be printed using methods known in the art. See: Li et al, 2019.Analytes, Sensing Materials and Polymers

[0056] In embodiments, the specific analyte is a base or an amine, and more specifically the analyte is a biogenic amine (an amine or mixture of amines inherent in an organism or biological tissue or generated in biological tissue or generated by an organism). In embodiments, the biogenic amine is generated on spoilage of a food product, for example on spoilage of a meat product.

[0057] In embodiments, the analyte is a base having a vapor pressure of 1 Pa or more, 2.5 Pa or more, or 5 Pa or more at about 20 °C (+ / -5 °C). In embodiments, the analyte is a volatile base. In embodiments, the volatile base is ammonia, an alkyl amine, an alkyl diamine, a polyamine, hydrazine, or a nitrogen heterocycle, such as pyrrole or indole.

[0058] The term volatile as used herein refers to a chemical compound that has a vapor pressure of 10 Pa or more at about 20 °C (+ / -5 °C).

[0059] In embodiments, the analyte is an amine, diamine or polyamine having a vapor pressure of 1 Pa or more, 2.5 Pa or more, or 5 Pa or more at about 20 °C (+ / -5 °C). In embodiments, the analyte is a volatile amine, diamine or polyamine having a vapor pressure of 10 Pa (Pascal) or more at about 20 °C (+ / -5 °C). In embodiments, the analyte is a liquid at about room temperature (25 °C + / - 5 °C). In embodiments, the analyte has a vapor pressure of 50 Pa (Pascal) or more at about 20 °C (+ / -5 °C). In embodiments, the analyte has a vapor pressure of 100 Pa (Pascal) or more at about 20 °C (+ / -5 °C). In embodiments, the analyte is an amine that is a liquid at about room temperature (25 °C + / -5 °C). In embodiments, the analyte is an amine that has a vapor pressure of 10 Pa (Pascal) or more at about 20 °C (+ / -5 °C). In specific embodiments, the analyte is ammonia, including gaseous ammonia or ammonia vapor. In specific embodiments, the analyte is a primary amine, a secondary amine or a tertiary amine. In embodiments, the amine is an alkyl amine or a dialkyl amine, wherein the alkyl group has one to eight carbon atoms. In specific embodiments, the amine is a alkyl diamine, such as propane-1 , 3-diamine, putrescine (butane-1 , 4-diamine) or cadaverine (pentane-1-5-diamine) or isomers thereof. In embodiments, the amine is histamine, or a related primary or secondary amine substituted with a nitrogen heterocyclic group, such as an imidazolyl group.

[0060] The sensing material or molecule comprises at least one chemical functional group that interacts with the selected analyte to induce charge transfer in the active layer. In embodiments, the sensing material or molecule comprises a pi-conjugated backbone to which the one or more chemical functional group that interacts with the selected analyte is bonded. In embodiments, the pi-conjugated backbone of the sensing material or molecule is not a polymer. In embodiments, the pi-conjugated backbone of the sensing material or molecule is a dimer or trimer. In embodiments at least one chemical functional group bonded to the pi-conjugated backbone is deprotonated on interaction with the analyte. In embodiments, the analyte is a volatile base or amine. In embodiments, the amine is a C1-C8 alkyl amine, a C1-C6 alkyl diamine or a C1-C3 alkyl amine substituted with a nitrogen heterocyclic group.

[0061] A base is a chemical species that donates electrons, accepts protons, or releases hydroxide (OH-) ions in aqueous solution. In embodiments, the base analyte is a chemical species that can deprotonate a functional group of a sensing molecule herein. In embodiments, the base is an organic base. In embodiments, the base is a nitrogen-containing organic base. In embodiments, the base is an inorganic nitrogen-containing base, such as ammonia or hydrazine. In embodiments, the base is an amine, a diamine, a polyamine (e.g., spermidine), a heterocyclic compound (e.g., pyrrole, indole), or an alkyl hydrazine (e.g., methylhydrazine).

[0062] In embodiments, the pi-conjugated backbone of the sensing material or molecule contains one or more pi-conjugated moiety selected from a rylene moiety, particularly a perylene, terrylene or quaterrylene moiety and more specifically a perylene diimide moiety; anoligoacene moiety, a heteroacene moiety, a phthalocyanine moiety, and a a napthalene diimide moiety.

[0063] A rylene is a dye having a pi-conjugated backbone of one or more naphthalene moieties and includes perylene, terrylenes and quaterrylenes. See: Zhan et al., 2011. Additional small molecule acceptors based on perylene diimides are described in Liu et al., 2016. Additional description of PDI small molecules with pyrrolic NH bonds is provide is US published application 20230189637. Each of these references is incorporated by reference herein in its entirety for any purpose. These references are of particular interest with respect to pi- conjugated backbones useful in the sensing materials of this invention.

[0064] The at least one chemical functional group that interacts with the analyte to induce charge transfer into the conductive or semi-conductive polymer of the active layer. In embodiments, the at least one chemical functional group reacts with one or more bases, particularly one or more amines, to induce the charge transfer. In embodiments, the at least one chemical functional group reacts with the analyte (particularly the base or amine) and is deprotronated forming an anionic species which can charge transfer into the active layer polymer. In embodiments, the at least one chemical functional group is an N-annulated (N-H) group as in the illustrated compounds of Formula 1 or as in US 20230189637. In embodiments, the at least one chemical functional group is a moiety selected from a pyrrole moiety (e.g., a diketopyrrole), an indole moiety, a carbazole moiety, an azole moiety, an imidazole moiety and a bezoimidazole moiety. In embodiments, the at least one chemical functional group is a primary or secondary amine group >NH or -RNH (where R is generally any organic group, alky, aryl or the like).

[0065] In embodiments, the at least one chemical functional group of the sensing material or molecule is bonded directly into the pi-conjugated backbone or indirectly bonded to the pi- conjugated backbone through a pi-conjugated linker group. The at least one chemical group of the sensing material can be formed as a part of the pi-conjugated backbone of the sensing material. Bonding of the at least one chemical functional group to the backbone (directly or indirectly) allows the delocalization of the free electron generate on interaction with the base or amine analyte (e.g., on deprotonation of the chemical functional group) through the pi- conjugated backbone.

[0066] In embodiments, the pi-conjugated backbone of the sensing material or molecule is an oligoacene of formula:where n is 1-10. Oligoacenes and heteroacenes are known in the art and readily available for use in the invention (See: Functionalized Acenes and Heteroacenes for Organic Electronics https: / / pubs.acs.org / doi / 10.1021 / cr050966z). This reference is incorporated by reference herein in its entirety for any purpose and particularly for descriptions of pi-conjugated backbones useful for sensing materials of this invention.

[0067] Scheme 1 provides examples of sensing materials composed of different pi- conjugated backbones. In Scheme 1 , Ri and R2are independently a substituted or unsubstituted C1 to C18 linear or branched alkyl, a halogen, — CN, — NO2, — C(O)R', — COOR', — C(O)NH2, — NHC(O)R', — C(O)NR'R", — CF3, — SO3H, — SO2CF3, — SO2R', — SO2NR'R”, — OR', — OC(O)R', substituted or unsubstituted phenyl, substituted or unsubstituted benzyl, substituted or unsubstituted vinyl, wherein R' and R" are independently H, an unsubstituted C1 to C6 alkyl or a C1-C3 halogen-substituted C1-C6 alkyl.

[0068] In embodiments, the sensing molecule is one or more of an N-annulated PDI compound each having a pyrrole N-H group. More specifically, the N-annulated PDI compound is a compound of Formula I:I wherein:Ri and R2are independently a substituted or unsubstituted C1 to C18 linear or branched alkyl group; andXi-X6are independently selected from the group H, a C1-C6 substituted or unsubstituted alkyl, a halogen, — NO2, and — CN orX2and X3together form — S — S — and Xi and X4are independently selected from the group H, a C1-C6 substituted or unsubstituted alkyl, a halogen, — NO2, and — CN; wherein optional substitution of alkyl groups is substitution with one or more halogens, — CN, — NO2, — C(O)R', — COOR', — C(O)NH2, — NHC(O)R', — C(O)NR'R", — CF3, — SO3H, — SO2CF3, — SO2R', — SO2NR'R”, —OR', — OC(O)R', substituted or unsubstituted phenyl, substituted or unsubstituted benzyl, substituted or unsubstituted vinyl, — NHR' or — NR'R", wherein R' and R" are independently H, an unsubstituted C1 to C6 alkyl or a C1-C3 halogen-substituted C1-C6 alkyl.

[0069] In specific embodiments, the sensing molecule is a compound of Formula I which has no amino, alkyl amino or dialkyl amino groups. In embodiments, the sensing molecule is not a polymer. A polymer herein has six or more repeating units and typically has greater than 10, 20, 50 or 100 repeating units. In embodiments, the sensing molecule is an oligomer having 2-5 or 2-3 repeating units.

[0070] In a specific embodiment, the sensing molecule is a compound of Formula I where X1-X4 are all hydrogens. In specific embodiments, R1 and R2are C3-C11 alkyl groups. In specific embodiments, R1 and R2are C5-C11 alkyl groups. In specific embodiments, R1 and R2are branched C5-C11 alkyl groups. In embodiments, R1 and R2are the same alky group. In embodiments, R1 and R2are pentan-3-yl groups or hepany-4-yl groups. In embodiments, the NPDI compounds is a compound of Formula 1 , wherein one or more of Xi, X2, X5or X6is a halogen, for example Cl or Br. In embodiments, the NPDI compound is a compound of Formula I, wherein one or two of Xi, X2, X5 or X6are -CN or a halogen and the remaining Xi-X6are hydrogens. In any such embodiments, R-i and R2are independently branched alkyl groups having 5-11 carbon atoms. In embodiments, the NPDI compound is a compound of Formula I, wherein Xi, and / or 3 are -CN or halogen and the remaining Xi-X6are hydrogens. In any such embodiment, R1 and R2are independently branched alkyl groups having 5-11 carbon atoms.Scheme 1

[0072] In a specific embodiment, the sensing molecule is NPDI-NH:NPDI-NH

[0073] Additional description of NPDI molecules useful as sensing material in this invention is found in published PCT application WO2023021488. This reference is incorporated by reference herein in its entirety for any use and in particular for its descriptions of NPDI molecules and methods of making them.

[0074] In embodiments, the active layer comprises one or more semiconducting polymers or a mixture of one or more semiconducting polymer with one or more conducting polymer. Preferably the polymer or polymer mixtures in the active layer have optimal conductivity, stability and printability.

[0075] In embodiments, the semiconducting and conducting polymers of the active layer are selected from classes of polymer containing pi-conjugated groups (i.e., one or more monomers of the polymer are pi-conducting groups.) Pi-conjugated groups include among others, thiophene and thiophene derivatives (e.g., thiophene, bithiophene, terthiophene); fluorene and fluorene derivatives (e.g., 9,9-dioctylfluorene, 9, 9-dialkyfluorene, where the alkyl group is a linear or branched C1-C10 alkyl group, or fluorenone); benzothiadiazole and benzothiadiazole derivatives (e.g., benzothiadiazole, dithieno[3,2-b:2',3'-d]thiophene); indacenodithiophene (IDT) and indacenodithiophene derivatives; naphthalenediimide (NDI) and NDI derivatives; pyrrole derivatives , Isoindigo derivatives; cyclopentadithiophene (CPDT) derivatives, d i keto pyrro Io pyrrole (DPP) derivatives, Benzodithiophene (BDT) derivatives. Derivatives of the forgoing pi-conjugated groups include one or more groups selected from C1- C10 alkyl groups (also C1-C6 and C1-C3 alkyl groups), halogens (particularly Cl or Br), aryl groups (particularly benzyl or phenyl groups), -CN, and -NO2. In embodiments, semiconducting and conducting polymers useful herein can comprise electron-deficient moieties, such as fullerene derivatives (e.g., PCBM, PC61BM), perylene derivatives, naphthalene derivatives, fluorinated aromatic / heteroaromatic moieties (e.g., fluorinatedthiophenes), quinoidal moieties, indene moieties and derivatives, pyridine moieties and derivatives, thiazole moieties or derivatives.

[0076] The term moiety (moieties) is used herein to refer to a portion of a molecule, for example, a monomer unit of a polymer, a backbone to which chemical groups can be bonded, or more simply a chemical group or a functional chemical group. The moiety is described as having certain function and / or structure and optionally is derivatized with one or more chemical group including among others to those listed above in Formula I. More specifically derivatives include those having one or more groups including an alkyl group (e.g., C1-C6 alky or C1-C3 alkyl), an aryl group (e.g., optionally substituted phenyl or benzyl), a halogen, — CN, — NO2, a halogenated alkyl group (e.g., — CF3), or thioalkyl (e.g., — S-alkyl). In embodiments, derivatives are backbone moieties, such as a pi-conjugated backbone, in which one or more hydrogens of the backbone are substituted with one or more derivative / substituent groups as described herein. In embodiments, the pi-conjugation of such derivatives is retained on derivatization or substitution.

[0077] In embodiments, the semiconducting polymers of the active layer include one or more of the following of Scheme 2:Polyacetylene MEH-PPV PTAAScheme 2: Examples Semi-Conducting Polymers

[0079] In embodiments, semiconducting polymers include those of Scheme 2 which are optionally derivatized as described herein. In Scheme 2, each R is an alkyl group having 5-24 carbon atoms, and optionally having 10-20 carbon atoms, optionally a branched alkyl group, optionally a branched alkyl group, wherein the branch is at the second carbon of the group and wherein each illustrated specific alkyl group can be replaced with an alkyl group having 5-24 carbon atoms, optionally 6-12 carbon atoms, optionally 10-20 carbon atoms, optionally a branched alkyl group, optionally a branched alkyl group wherein the branch is at the second carbon of the group. For each polymer of Scheme 2 n is an integer representing the number of repeating units in a polymer, i.e., the degree of polymerization, with higher n values associated with higher molecular weight polymers. As is known in the art polymers area mixture of polymer species of different n. A polymer material contains polymers having a range or distribution of molecular weights. Molecular weight of a polymer can be calculated again as is known in the art as the number average molecular weight (Mn) or as the weight average molecular weight (Mw). Methods are known in the art for calculating / determining Mn and Mw of a given polymer. The ratio of Mw / Mn is the polydispersity index (PDI). The higher the PDI the wider the molecular weight distribution in a polymer. The closer the PDI is to 1 the more uniform the polymer is in molecular weight. Mn, Mw and PDi (among other characteristics) affect physical and mechanical properties of polymers. One of ordinary skill in the art can select polymers of appropriate Mn, Mw and PDI for use in applications herein. In many cases, polymers as described herein are commercially available having known Mn, Mw and / or PDI. A commercially available polymer may be available having different molecular weight properties and one of ordinary skill in the art can select a polymer having molecular weight properties suitable for a given application. Similarly, methods are known in the art for varying (or determining) the Mn, Mw and PDI of a polymer material and such methods can be employed to obtain polymers having physical properties suitable for use in this invention. In specific embodiments, polymers useful in the invention have Mw equal to or grater than 100,000 dalton, particular as measured by gel permeation chromatography.

[0080] In embodiments, the semiconducting polymer is a polymer of structure P(ND12OT) as in Scheme 2, wherein each R is selected from alkyl group having 5-24 carbon atoms, optionally C10-C20 carbon atoms, optionally a branched alkyl group, optionally a branched alkyl group wherein the branch is at the second carbon of the group.

[0081] In embodiments, the R groups of P(ND12OT) are selected from branched alkyl groups of formula:-CH2-CH2(RI)(R2), where Ri and R2are independently alky groups having 6-12 carbon atoms. Ri and R2are preferably linear alkyl groups. In embodiments, Ri and R2are different alkyl groups. In embodiments, Ri and R2are linear alkyl groups having 7-11 carbon atoms. In embodiments, Ri is an alky group having 8-12 carbon atoms and R2is an alkyl group having 6-10 carbon atoms. In embodiments, Ri is an alkyl group having 10 carbon atoms (e.g., n-decyl) and R2is an alkyl group having 8 carbon atoms (e.g., n-octyl).

[0082] In embodiments, the semiconducting polymer is:P(NDI2OD-2T).

[0083] In specific embodiments, any one or more of the semiconducting polymers of Scheme 2 can be employed in an active layer with a sensing material as described herein and particularly with an N-annulated PDI molecule of Formula I. In specific embodiments, the semiconducting polymer is a copolymer of naphthalene diimide (NDI) and bithiophene. In specific embodiments, the polymer P(NDI2OD-2T) can be employed in an active layer with a sensing material as described herein and particularly with a N-annulated PDI molecule of Formula I. Such active layers are particularly useful for detection and quantitation of volatile bases, including volatile amines.

[0084] The active film is composed of a combination of at least two compounds (the sensing material and the semiconducting polymer or mixture of semiconducting and conducting polymers). To ensure good and reliable performance, the film preferably presents a homogenous and smooth morphology as shown in the AFM images of any one of FIGs. 7A -7C. Films with sensing material dispersed there preferably do not have surface morphology as illustrated in FIG. 7D. The sensing material is preferably miscible in the polymer of the active layer at the concentration of sensing material that is employed in the active layer. Miscibility can be assessed by reviewing AFM images of the surface morphology of films formed with different semiconducting polymers or polymer mixtures with varying amounts of sensing materialdispersed in the polymer. In embodiments, 50% or more by weight of the sensing material is miscible in the polymer or polymer mixture of the active layer. In embodiments, 30% or more by weight of the sensing material is miscible in the polymer or polymer mixture of the active layer. In embodiments, 25% or more by weight of the sensing material is miscible in the polymer or polymer mixture of the active layer. In embodiments, 15% or more by weight of the sensing material is miscible in the polymer or polymer mixture of the active layer. In embodiments, 10% or more by weight of the sensing material is miscible in the polymer or polymer mixture of the active layer. In embodiments, 5% or more by weight of the sensing material is miscible in the polymer or polymer mixture of the active layer.

[0085] Polyacetyiyne Polythiophene Poly(p-phenylene Poly(p-phenylenevinylene)Scheme 3

[0086] Scheme 3 illustrates example conducting polymers useful in the sensors herein. Polymers of Scheme 3 can be unsubstituted or derivatized with one or more non-hydrogen groups as described herein (e.g., in descriptions of Formula I). Polymers of Scheme 3 may be derivatized with one or more groups as described for optional substitution in Formula I and including alkyl, alkoxy, halogen, — CN, — NO2, or optionally substituted phenyl or benzyl. Optional substitution for phenyl and benzyl groups includes one or more halogens, one or more C1-C3 alkyl groups, one or more C1-C3 alkoxy groups, one or more C1-C3 haloalkyl groups (such as -CF3) or combinations of these substituents.Assessment of Sensors, Measurement of Conductance

[0087] FIG. 4 schematically illustrates an example electrochemical gas sensor testing setup (50). The sensor (10) is inserted into a sealed sample chamber (51). The sensor can be exposed to different analytes at varying concentrations by introduction of analyte into the sample chamber, for example as a gas, vapor or liquid. For example, an input nozzle (52) is provided. The analyte can be introduced into the testing chamber in a carrier gas, vapor or liquid. Any carrier employed must be assessed for inertness with respect to the sensing mechanism. The input conduit or nozzle can be equipped with an entrance valve (53) that allows controlled diffusion (flow) of the analyte into the chamber and an exit conduit (54) with a release valve (55) to release gas / vapor or evaporated liquid from the chamber. The testing set up is provided with circuitry (56) that allows measurement of conductance of the active layer.Optionally conductance can be measured as a function of time. In embodiments, the temperature of the testing setup can be selectively controlled at a selected testing temperature.

[0088] FIGs. 5A and 5B schematically illustrates functioning of a sensor (10) over time to detect and quantitate analyte. At time point I, the active layer of the sensor contains a selected amount of sensing material in the polymer layer. At time point II, analyte in the sensor environment begins to permeate into the active layer to react with sensing material. At time point III, analyte concentration in the sensor environment increases and increasing amounts of analyte permeate into the active layer. FIG. 5B is a graph showing the change in conductance of the active layer as a function of time points l-lll. Reacted sensing material induces a charge transfer into the active layer which is measured as an increase in conductance in the active layer. Conductance increased as the concentration of analyte increases in the environment of the sensor. In embodiments, the reaction of analyte with the sensing material is reversible so that conductance in the sensor decreases as the concentration of the analyte in the environment of the sensor decreases. In embodiments, on exposure to amines, a {PDI- NH / P(NDI-2OT)} based sensor exhibits an increase in conductivity for concentrations of the volatile diamine cadaverine as low as 0.5 ppb (see: Examples and FIG. 12).Sensing Mechanism

[0089] FIGs. 6A and 6B illustrate the sensing mechanism of the invention with an example active layer and selected targeted analyte (a primary amine). The example sensing material (PDI-NH) is dispersed in the semiconducting polymer (P(NDI2OD-2T) to form the active layer. Analyte permeates into the active layer and reacts with PDI-NH to deprotonate PDI-NH (reaction 1) to form the anionic species PDI-N . Subsequent charge transfer (reaction 2) from the anion to the semiconducting polymer occurs. FIG. 6B illustrates the same two processes and shows the LUMO (lowest unoccupied molecular orbital) energy levels of PDINH and P(NDI2OD-2T). Also shown is the energy level of the highest occupied molecular orbital (HOMO) of the reacted sensing material (PDIN anion). To ensure charge transfer, the LUMO of the semiconducting polymer is lower in energy than the HOMO of the reacted sensing material and more specifically is more than 0.1 electron volts (eV) lower in energy (e.g., 0.15 eV or more, 0.2 eV or more, 0,25 eV or more, or 0.3 eV or more. In embodiments, it is preferred that the LUMO of the semiconducting polymer is lower in energy than the HOMO of the reacted sensing material and preferably is 0.4 eV or more, or optionally 0.5 eV or more or optionally 0.6 eV or more.

[0090] In embodiments, employing the PDI-NH sensing material, the semiconducting polymer of the active layer is selected to have a LUMO energy level lower than the HOMO of PDIN and specifically 0.1 eV or more (optionally 0.15 or more, 0.2 eV or more, 0.25 or more or 0.3 eV or more) lower and preferably the LUMO of the semiconducting polymer is at least 0.4eV or more lower in energy and optionally is 0.5 eV or more or 0.6 eV or more lower in energy than the HOMO of the anion.

[0091] In aspect 1 , the invention provides an electrochemical sensor for detection of a selected analyte which comprises: an active layer which comprises a semiconducting material and a selected amount of a sensing material in contact with the semiconducting material; and at least two electrodes electrically each electrically connected to the active layer for measurement of a change in conductance of the active layer; wherein the sensing material comprises a pi-conjugated moiety and at least one chemical functional group bonded to the pi-conjugated moiety, wherein the at least one chemical functional group reacts with the selected analyte to induce charge transfer into the active layer to change the conductance of the active layer; and wherein a change in conductance of the active layer indicates the presence of the selected analyte in the active layer.

[0092] In aspect 2, the invention provides a chemical senor of aspect 1 , wherein the semiconducting material comprises a semiconducting polymer.

[0093] In aspect 3, the invention provides a chemical senor of aspect 2, wherein the sensing material is dispersed in the semiconducting polymer.

[0094] In aspect 4, the invention provides a method for detecting a selected analyte which comprises the steps of: generating an active layer comprising a semiconducting material and a sensing material or molecule; and monitoring the conductance of the active layer when the active layer is exposed to an environment that may contain the selected analyte; wherein the sensing material comprises a pi-conjugated moiety and at least one chemical functional group bonded to the pi-conjugated moiety, wherein the at least one chemical functional group reacts with the selected analyte to induce charge transfer into the active layer to change the conductance of the active layer; and wherein an increase in conductance of the active layer indicates the presence of the selected analyte the environment that may contain the selected analyte.

[0095] In embodiments of aspect 4, generating the active layer comprises dispersing the sensing material or molecule in the active layer or otherwise contacting the sensing material or molecule with the active layer.

[0096] In embodiments of aspect 4, generating the active layer comprises dispersing the sensing material or molecule in a semiconducting polymer or a mixture of a semiconducting polymer and a conducting polymer.

[0097] In embodiments of aspect 4, the pi-conjugated moiety is selected from a rylene moiety, optionally a perylene, terrylene or quaterrylene moiety, a perylene diimide moiety; anoligoacene moiety, a heteroacene moiety, a phthalocyanine moiety, and napthalene diimide moiety.

[0098] In embodiments of aspect 4, the chemical functional group is selected from an N- annulated (N-H) moiety, a pyrrole moiety (optionally a diketopyrrole), an indole moiety, a carbazole moiety, an azole moiety, an imidazole moiety and a benzoimidazole moiety.

[0099] In embodiments of any preceding aspect or embodiment, the pi-conjugated moiety is selected from a rylene moiety, optionally a perylene, terrylene or quaterrylene moiety, a perylene diimide moiety; an oligoacene moiety, a heteroacene moiety, a phthalocyanine moiety, and napthalene diimide moiety.

[0100] In embodiments of any preceding aspect or embodiment, the chemical functional group is selected from an N-annulated (N-H) moiety, a pyrrole moiety (optionally a diketopyrrole), an indole moiety, a carbazole moiety, an azole moiety, an imidazole moiety and a benzoimidazole moiety.

[0101] In embodiments of any preceding aspect or embodiment, the sensing material or molecule is a compound of Formula I:l wherein:Ri and R2are independently a substituted or unsubstituted C1 to C18 linear or branched alkyl group; andXi-X6are independently selected from the group H, a C1-C6 substituted or unsubstituted alkyl, a halogen, — NO2, and — CN orX2and X3together form — S — S — and Xi and X4are independently selected from the group H, a C1-C6 substituted or unsubstituted alkyl, a halogen, — NO2, and — CN; wherein optional substitution of alkyl groups is substitution with one or more halogens, — CN, — NO2, — C(O)R', — COOR', — C(O)NH2, — NHC(O)R', — C(O)NR'R", — CF3, — SO3H, — SO2CF3, — SO2R', — SO2NR'R”, —OR', — OC(O)R', substituted or unsubstituted phenyl, substituted or unsubstituted benzyl, substituted or unsubstitutedvinyl, — NHR' or — NR'R", wherein R' and R" are independently H, an unsubstituted C1 to C6 alkyl or a C1-C3 halogen-substituted C1-C6 alkyl.

[0102] In embodiments of any preceding aspect or embodiment, the sensing material is a compound of Formula I where X1-X4 are independently selected from hydrogen, halogen or — CN and R1 and R2are C3-C11 alkyl groups.

[0103] In embodiments of any preceding aspect or embodiment, the sensing material is a compound of Formula I, where X1-X4 are hydrogen.

[0104] In embodiments of any preceding aspect or embodiment, the sensing material is a compound of Formula I where X1-X4 are hydrogen and R1 and R2are C3-C11 alkyl groups.

[0105] In embodiments of any preceding aspect or embodiment, the sensing molecule is NPDI-NH:NPDI-NH.

[0106] In embodiments of any preceding aspect or embodiment, the semiconducting polymer comprises one or more pi-conjugated groups selected from thiophene or thiophene derivatives; fluorene or fluorene derivatives; benzothiadiazole or benzothiadiazole derivatives; indacenodithiophene (IDT) or indacenodithiophene derivatives; naphthalenediimide (NDI) or NDI derivatives; pyrrole or pyrrole derivatives, isoindigo or isoindigo derivatives; cyclopentadithiophene (CPDT) or CPDT derivatives, diketopyrrolopyrrole (DPP) or DPP derivatives, or benzodithiophene (BDT) or BDT derivatives.

[0107] In embodiments of any preceding aspect or embodiment, the semiconducting polymer comprises one or more pi-conjugated groups selected from thiophene; fluorene; benzothiadiazole; indacenodithiophene (IDT); naphthalenediimide (NDI); pyrrole, isoindigo; cyclopentadithiophene (CPDT), diketopyrrolopyrrole (DPP), or benzodithiophene (BDT).

[0108] In embodiments of any preceding aspect or embodiment, the semiconducting polymer is a polymer illustrated in Scheme 2.

[0109] In embodiments of any preceding aspect or embodiment, the semiconducting polymer is a polymer of structure P(ND12OT):wherein each R is independently selected from alkyl groups having 5-24 carbon atoms n is an integer indicating the number of repeating units in the polymer and is 6 or more. In embodiments, Mw of the P(ND120T) polymer is equal to or greater than 100,000 Da as measure by GPC. In embodiments, the R groups of P(ND12OT) are independently selected from branched alkyl groups of formula -CH2-CH2(RI)(R2), where Ri and R2are independently alky groups having 6-12 carbon atoms. In embodiments, the R groups of the polymer are the same.

[0110] In embodiments of any preceding aspect or embodiment, the semiconducting polymer is P(NDI2OD-2T).

[0111] In embodiments of any preceding aspect or embodiment, the active layer comprises a mixture of a semiconducting polymer and a conducting polymer, wherein the semiconducting polymer represents 10% or more by weight of the mixture. In embodiments, the semiconducting polymer represents 50% or more by weight of the mixture. In embodiments, the semiconducting polymer represents 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 65% or more by weight of the mixture. In embodiments, the semiconducting polymer represents 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or more by weight of the mixture, but less than 100%, or less than 95%, or less than 90%, of the mixture.

[0112] In embodiments of any preceding aspect or embodiment, the active layer comprises a mixture of a semiconducting polymer and a conducting polymer, wherein the semiconducting polymer represents 10% or more of the weight of the mixture and optionally 50% by weight of the mixture and wherein the conducting polymer is selected from a conducting polymer selected from polyacetylene, polythiophene, poly(p-phenylene) or poly(p-phenylene vinylene) or a substituted derivative thereof.

[0113] In embodiments of any preceding aspect or embodiment, the sensing material is PDI-NH and the semiconducting polymer is P(NDI2OD-2T).

[0114] In embodiments of any preceding aspect or embodiment, the sensing material is PDI-NH and the semiconducting polymer is P(NDI2OD-2T) and the conducting polymer selected from polyacetylene, polythiophene, poly(p-phenylene) or poly(p-phenylene vinylene) or a substituted derivative thereof.

[0115] In embodiments of any preceding aspect or embodiment, the sensing material is PDI-NH and the semiconducting polymer is P(NDI2OD-2T) and the conducting polymer is polyacetylene, polythiophene, poly(p-phenylene) or poly(p-phenylene vinylene).

[0116] In embodiments of any preceding aspect or embodiment, the analyte is an organic or inorganic base and optionally is a volatile base.

[0117] In embodiments of any preceding aspect or embodiment, the selected analyte is a volatile amine, diamine or polyamine.

[0118] In embodiments of any preceding aspect or embodiment, the selected analyte is a base and optionally is a volatile base.

[0119] In embodiments of any preceding aspect or embodiment, the selected analyte is an amine or diamine and optionally is volatile.

[0120] In embodiments of any preceding aspect or embodiment, wherein the selected analyte is selected from ammonia, a primary amine, a secondary amine, a diamine, a tertiary amine, pyrrole, indole, hydrazine or an alkyl hydrazine.

[0121] In embodiments of any preceding aspect or embodiment, the selected analyte is one or more biogenic amine.

[0122] In embodiments of any preceding aspect or embodiment, the analyte is a biogenic amine.

[0123] In embodiments of any preceding aspect or embodiment, the analyte is ammonia, an amine, a diamine or a polyamine.

[0124] In embodiments of any preceding aspect or embodiment, the selected analyte is ammonia, a primary amine, a secondary amine, a diamine, a tertiary amine, pyrrole, indole, hydrazine or an alkyl hydrazine.

[0125] In an additional aspect 5, the invention provides a method employing the sensor of any preceding aspect or embodiment. In embodiments, the method of aspect 5 detects any analyte of a preceding aspect or embodiment.

[0126] In an additional aspect 6, the invention provides a method for detecting a selected analyte which comprises providing a sensor of any preceding aspect or embodiment; and monitoring the conductance of the active layer when the active layer is exposed to an environment that may contain the selected analyte. In embodiments, the selected analyte is a biogenic amine and the sensor is employed to assess the freshness of a food product or the spoilage of a food product. In embodiments, the method of aspect 5 detects any analyte of a preceding aspect or embodiment.

[0127] In an additional aspect 7, the invention provides an electrochemical sensor of previous aspect or embodiment, wherein the analyte is a biogenic amine and the sensor is provided within packaging of a food product.

[0128] In an additional aspect 8, the invention provides a method of any preceding aspect or embodiment, wherein the analyte is a biogenic amine and the sensor is provided within packaging of a food product.

[0129] Additional details of the synthesis, characterization and application of N-annulated PDI materials and films thereof are provided in references cited herein and any supporting information of each of these references, which is freely available on-line for the publisher. Each cited reference herein, including any electronic supplemental information thereof, providing such additional description is incorporated by reference herein in its entirety for descriptions of film making techniques and methods for fabrication electronic devices incorporating such films.

[0130] Additional details of processing of materials, such as N-annulated PDI materials and films thereof of the invention, and the preparation of devices, such as organic solar cells are provided in certain references cited herein and any supporting information of each of these references which is freely available on-line for the publisher. Each of the references cited herein and any corresponding supporting information is incorporated by reference herein in its entirety for such additional details including synthetic methods for starting materials, purification methods, characterization of compounds, processing of materials, components of devices employing these materials and methods for such characterization, construction and testing of organic solar cell, as well as structure and components of organic solar cells.

[0131] All references throughout this application, for example patent documents including issued or granted patents or equivalents; patent application publications; and non-patent literature documents or other source material; are hereby incorporated by reference herein in their entireties, as though individually incorporated by reference.

[0132] All patents and publications mentioned in the specification are indicative of the levels of skill of those skilled in the art to which the invention pertains. References cited herein are incorporated by reference herein in their entirety to indicate the state of the art, in some cases as of their filing date, and it is intended that this information can be employed herein, ifneeded, to provide art-known device configurations, methods and materials that can be employed in the devices and methods of this invention or to exclude (for example, to disclaim) specific embodiments that are in the prior art. For example, when a compound is claimed, it should be understood that compounds known in the prior art, including certain compounds disclosed in the references disclosed herein (particularly in referenced patent documents), are not intended to be included in the claim.

[0133] The description herein may refer to a color of a film, solution or liquid phase. When provided such color designations are based on visual observation of the item begin described or a photograph of such item by a person believed to have normal color vision. It will be appreciated that the color description given are subjective to the observer. This, designations including yellow, reddish orange, and purple among others should be considered approximations of the actual color of the item described. UV-vis spectra of films, solutions and liquid phases, which are provided in some cases herein, provide a quantitative method for assessment of the color of a given item. In visual colorimetric detection methods herein the color change indicative of the presence of amines is described as a change from reddish orange / red to purple. This color change may be described differently by different individual observers.

[0134] When a group of substituents is disclosed herein, it is understood that all individual members of those groups and all subgroups, including any isomers and enantiomers of the group members, and classes of compounds that can be formed using the substituents are disclosed separately. When a compound is claimed, it should be understood that compounds known in the art including the compounds disclosed in the references disclosed herein are not intended to be included. When a Markush group or other grouping is used herein, all individual members of the group and all combinations and subcombinations possible of the group are intended to be individually included in the invention.

[0135] Every formulation or combination of components described or exemplified can be used to practice the invention, unless otherwise stated. Specific names of compounds are intended to be exemplary, as it is known that one of ordinary skill in the art can name the same compounds differently. When a compound is described herein such that a particular isomer or enantiomer of the compound is not specified, for example, in a formula or in a chemical name, that description is intended to include each isomers and enantiomer of the compound described individual or in any combination.

[0136] One of ordinary skill in the art will appreciate that methods, process conditions, concentration, device elements, starting materials, and synthetic methods other than those specifically exemplified can be employed in the practice of the invention without resort to undue experimentation. All art-known functional equivalents, of any such methods, device elements, starting materials, and synthetic methods are intended to be included in this invention.Whenever a range is given in the specification, for example, a temperature range, a time range, or a composition range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the invention.

[0137] As used herein, “comprising” is synonymous with "including," "containing," or "characterized by," and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, "consisting of' excludes any element, step, or ingredient not specified in the claim element. As used herein, "consisting essentially of' does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. For compositions as claimed herein, the term consisting essentially of excludes any component that detrimentally and materially affects the properties of that composition for use in a sensor application recited herein.

[0138] Any recitation herein of the term “comprising”, particularly in a description of components of a composition or in a description of elements of a device, is understood to encompass those compositions and methods consisting essentially of and consisting of the recited components or elements. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein.

[0139] Without wishing to be bound by any particular theory, there can be discussion herein of beliefs or understandings of underlying principles relating to the invention. It is recognized that regardless of the ultimate correctness of any mechanistic explanation or hypothesis, an embodiment of the invention can nonetheless be operative and useful.

[0140] The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention.THE EXAMPLES:EXAMPLE 1 : Construction and Testing of Sensors

[0141] The synthesis of the N-annulated perylene diimide, PDI-NH, has been reported previously. (Hendsbee et al., 2016.) PDI-NH doped Poly{[N,N'-bis(2-octyldodecyl)-naphthalene- 1 ,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-2T)) solutions having selected levels of PDI-NH doping were prepared inside a nitrogen-filled glovebox by mixing a 9 mg / mL solution of P(NDI2OD-2T) (Brilliant Matters, Quebec, Canada) in chlorobenzene (Sigma- Aldrich, anhydrous, 99.8%) with a selected amount of a 3 mg / mL PDI-NH solution in chlorobenzene and stirred at 70°C for 4h.

[0142] Glass substrates were cleaned by sonication for 10 minutes in ethanol, acetone and isopropyl alcohol (IPA) sequentially before being transferred into a glovebox. PDI-NH doped P(NDI2OD-2T) films were deposited by spin-coating at 3000 rpm for 60 seconds. Films containing 1-25% PDINH are prepared. The organic films undergo a post annealing at 130°C for 1 hour.

[0143] Film thickness was measured to be 140 nm (FIG. 2). UV-Vis spectroscopy of the films is a linear superposition of the PDI-NH and P(NDI2OD-2T) spectra, demonstrating no charge transfer reactions in the absence of amine vapor (analyte) (FIG. 3).

[0144] Finally, example 60 nm-thick gold layers were deposited by thermal evaporation through a shadow mask to form the two electrodes with a channel width W= 4000 pm and a channel length L=100 pm.

[0145] Following the same protocol, organic field-effect transistors were fabricated in a bottom gate / top contact electrode configuration on single sided p-type low resistivity (0.01-0.02 Q.cm-2) Si (100) wafer (UniversityWafer, Inc). The 300 nm SiO2layer grown by wet thermal process acts as the dielectric.

[0146] IV response and FET characteristics were recorded at room temperature under inert atmosphere using a probe station (Everbeing-EB06) and a dual channel source-meter (Keithley, Model 2634B). Gas sensing measurement were performed using a customized gas testing chamber of 34 cm3capacity. Diluted solutions of the test analytes (n-butylamine, hexylamine, octylamine, cadaverine, ethanol, water, pentane) were prepared using NovecTM7100 (3M Company, Delaware) an inert hydrofluoroether fluid (methoxy-nonafluorobutane, C4F9OCH3) with low boiling point (61 C).

[0147] No interaction of the Novec™7100 carrier with the sensor was observed. The sensor was placed inside a test chamber facing down toward the analyte while a fixed amount of analyte solution was introduced into a test chamber on a watch glass by using a micropipette. The concentration of analyte within the chamber has been determined using following equation:^■(chamber)(See: Kaneti et al., 2014; Kalita et al., 2015).

[0148] FIGs. 7A-E show AFM images of the PDINH doped P(NDI2OD-2T) film surface compared to undoped film. The morphology of the films at the lowest doping concentrations (1%, 5%, 10% by weight) are consistent with those of the undoped film (FIG. 7E). The films are relatively smooth, exhibiting a peak-to-peak roughness of approximately 5 nm. At the highest doping concentration (25% by weight), nodules, approximately 5-8 nm in height are observed on top of an underlying smooth film. We interpret these nodules as PDINH rich structures extruded from the film as part of a phase separation process. This observation validates the hypothesis that PDINH is not miscible with P(NDI2OD-2T) at the highest concentration measured and that the interior regions of the PDINH rich phases cannot contribute meaningfully to an increase in mobile charge carrier density. The observation also indicates the importance of nanomorphology in sensor device operation.

[0149] Using simple two terminal devices, as described above, the conductivity of thin films of P(NDI2OD-2T):PDINH (w:w) with and without exposure to butylamine vapors. The conductance of the film was extracted from a fit of the current voltage curves (FIG. 8A) which were highly linear, showing no evidence of rectification or contact resistance. The change in conductance was scaled to that of the film in the absence of amine vapors by the following formula:AG > G-GpGQ U GQ U(1)where Go and G represent the conductance of the organic film before and after exposure to the different analytes, respectively. In an inert atmosphere glove box, films were exposed to solutions of butylamine in methoxynonafluorobutane (NOVEC™ 7100 engineering fluid, see FIG. 8B in a closed vessel.

[0150] Sensor response is illustrated in FIGs. 9A-9C. Devices were tested using a probe station. FIG. 9A shows the conductivity response resulting from exposure to butylamine at varying concentrations for 5-minute intervals. At concentrations as low as 500 parts per trillion (ppt), a measurable increase and decay of the conductivity was observed (see figure inset), with a conductance increase 84 % times the baseline conductivity. This is 5 times more sensitive than the previous state of the art. (Grant et al., 2023; Wang et al., 2016; Gomes Muller et al., 2022.)

[0151] At higher butylamine concentrations, the conductance increased to 2,570 % times baseline for 100 ppm. The sensors exhibit a reproducible response when cycled with the same concentration of butylamine vapor. Performance for five cycles at 0.5 ppm and stability over several days are shown in FIGs. 10A and 10B, respectively.

[0152] As shown in FIG. 9A, the changes in conductivity are dynamic. FIG. 9B further investigates this behavior by measuring the change in conductivity as a function of exposure time. The response first increases sharply and begins to saturate at longer times. We expect that the transport of the analyte into the film bulk is diffusive, with a greater charge carrier concentration being induced in P(NDI2OD-2T) with increasing exposure time until equilibrium is reached.

[0153] FIG. 9C shows the peak conductance response as a function of butylamine concentration for several doping levels of PDINH (1%, 5%, 10%, 25% by weight). For doping concentration higher than 5% by weight, the sensing performances improve drastically, as compared to undoped films. When the doping level is further increased to 25% no further improvements are observed, indicating that the optimized responsivity with respect to concentration has been reached. PDINH is believed to not be miscible with P(NDI2OD-2T) at the highest concentrations tested (25 % by weight) and that the interior regions of the PDINH rich phases cannot contribute meaningfully to an increase in mobile charge carrier density.

[0154] To demonstrate the selectivity of PDINH doped P(NDI2OD-2T) thin films, a variety of analytes were tested (FIG. 11). For concentrations as high as 300 ppm of water, ethanol and pentane, the sensor showed negligible response. Conversely, the sensor exhibits a strong sensing response upon exposure to 5 ppm of primary amines like n-hexylamine and n- octylamine, showing a conductivity increase of 6,140 % and 7,530 %, respectively. Remarkably, the device shows high selectivity toward cadaverine with sensing response up to 66,500 % at 5 ppm. FIG. 12 illustrates the time dependent response of the sensor to cadaverine.

[0155] As noted above, the conductance changes of the PDINH doped P(NDI2OD-2T) active layer in response to amine vapor is believed to be the result of a two-step process. First, PDINH is deprotonated at the pyrrolic NH functional group by reaction with the amine to create the PDIN- anion. This deprotonation had been observed previously. (Harding et al., 2020.) Then because of the energy offset between the HOMO of PDIN- and the LUMO of P(NDI2OD-2T), electron transfer to the n-type polymer occurs, resulting in an increase in thin film conductivity (See FIG. 6B).

[0156] To examine this mechanism, field effect transistor measurements were performed. If the amine vapor changes the carrier concentration, this is expected to cause a shift in the threshold voltage of the filed effect transistor. In particular, a shift of the threshold voltage to negative values would indicate the presence of mobile carriers in the absence of an appliedgate voltage. FIG. 5 shows typical output and transfer characteristics of on bottom-gate / top- contact OFET devices using undoped P(NDI2OD-2T) and PDINH-doped P(NDI2OD-2T) layers . The devices show typical n-type behavior with a slightly higher electron mobility in PDINH doped devices (8x103cm2 / Vs) compared to undoped P(NDI2OD-2T) devices (5x10.3cm2 / Vs). In the presence of 5 ppm butylamine vapor, charge carrier mobilities change only slightly, with PDINH doped devices having a mobility of 1 xio2cm2 / Vs and undoped P(NDI2OD-2T) devices having a mobility of 7xio2cm2 / Vs). The greatest difference between the two devices is threshold voltage. Although PDI-NH shifts the threshold voltage from 21 .2 to 8.6 V, the threshold voltage is even more shifted in the presence of amine vapor, becoming negative. A summary of the transistor characteristics is available in Table S1. The shift of the threshold voltage to negative values is believed to be the device characteristic responsible for increasing conductivity in a two-terminal device.

[0157] The bulk of the thin active film becomes doped even in the absence of an applied gate voltage. The proposed mechanism is confirmed by UV-Vis absorption measurements conducted on PDINH doped P(NDI2OD-2T) thin films before and after exposure to amine vapor (not shown). Difference spectra show evidence of the presence of anionic P(NDI2OD-2T) upon exposure to butylamine vapor, as expected.

[0158] The sensor devices of this invention are a rare example of an n-type polymeric sensor. The sensor device is, in some sense, an amperometric sensor with very low current in the absence of analyte. However, unlike a traditional amperometric sensor (Stetter & Li, 2008) the sensing mechanism comes from a specific chemical interaction between the sensitizer and the analyte, as exemplified herein with deprotonation. Thus, the sensors have high specificity to amine functional groups in this case. More generally, the sensor device is expected to be sensitive to base. Amines are the most common volatile base. Further specificity can be obtained by placing a diffusion barrier on the device, for example.EXAMPLE 2: Example Application of Amine Sensors

[0159] Among many different fields of application, the sensor of this invention is used to monitor the real-time freshness condition of perishable food products. In an example application, the sensor is integrated with one or more electrical components (power supply, integrated circuit, RFID / NFC tag) to facilitate conductance measurement. The sensor is implemented, for example as a tag or label in food packaging material. In a specific embodiment, the sensor provides an indication, for example a change in color, associated with detection of compounds known to be associated with the degradation of a food product, such as meat. The sensor detects the compounds associated with degradation of the food product from suitable for consumption to expired over time. In an embodiment, the change in signal is associated with the release of one or more chemical compounds, e.g., amines associated with degradation or spoilage of the food product. In an embodiment, the signal(s) (expired or closeto expiration) are triggered on detection of such chemical compounds or detection of a selected amount of one or more of such compounds. In an embodiment, the sensor provides a detectible signal that a food product is no longer suitable for consumption, e.g., is expired. In an embodiment, the sensor can alternatively or in addition provide a detectible signal that a food product is near to expiration. In a specific embodiment, the sensor is implemented in association with an RFID (radio frequency identification) or NFC (near field communication) tags. Such tags and the use of such tags is well known in the art and a variety of RFID tags including NFC tags are commercially available. The tags typically have a radio transponder, a radio receiver and a transmitter. Active tags include a battery. Power is provided to passive tags through transmission from an RFID / NFC reader. The sensor of the invention can be combined with such active or preferably passive tags for food sensing applications.

[0160] Additionally, the sensing device can be encapsulated or coated with a protective layer to minimize or prevent contact between the food and the sensor, while allowing the diffusion of biogenic amines to the sensor. As an example, nonwoven high-density polyethylene (HDPE) has shown good permeability to gas vapor while blocking water.

[0161] Additional details with respect to making and using the senor devices of this invention can be found in Courte et al. 2024 which is incorporated by reference herein in its entirety for any purpose, but in particular for details of construction and application of sensors and materials suitable for making sensors.BIBLIOGRAPHY / REFERENCES

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Claims

WE CLAIM:1 . An electrochemical sensor for detection of a selected analyte which comprises: an active layer which comprises a semiconducting material and a selected amount of a sensing material in contact with the semiconducting material; and at least two electrodes electrically each electrically connected to the active layer for measurement of a change in conductance of the active layer; wherein the sensing material comprises a pi-conjugated moiety and at least one chemical functional group bonded to the pi-conjugated moiety, wherein the at least one chemical functional group reacts with the selected analyte to induce charge transfer into the active layer to change the conductance of the active layer; and wherein a change in conductance of the active layer indicates the presence of the selected analyte in the active layer.

2. The electrochemical sensor of claim 1 , wherein the semiconducting material comprises a semiconducting polymer and the sensing material is dispersed in the semiconducting polymer.

3. The electrochemical sensor of claim 1 , wherein the selected analyte is a base and optionally is a biogenic amine, or optionally is an amine, diamine or a polyamine.

4. The electrochemical sensor of claim 1 , wherein the select analyte is volatile.

5. The electrochemical sensor of claim 1 , wherein the selected analyte is selected from ammonia, a primary amine, a secondary amine, a diamine, a tertiary amine, pyrrole, indole, hydrazine or an alkyl hydrazine.

6. The electrochemical sensor of claim 1 , wherein the pi-conjugated moiety is selected from a rylene moiety, optionally a perylene, terrylene or quaterrylene moiety, a perylene diimide moiety; an oligoacene moiety, a heteroacene moiety, a phthalocyanine moiety, and napthalene diimide moiety.

7. The electrochemical sensor of claim 1 , wherein the chemical functional group is selected from an N-annulated (N-H) moiety, a pyrrole moiety (optionally a diketopyrrole), an indole moiety, a carbazole moiety, an azole moiety, an imidazole moiety and a benzoimidazole moiety.

8. The electrochemical sensor of claim 1 , wherein the sensing material is a compound of Formula I:wherein:Ri and R2are independently a substituted or unsubstituted C1 to C18 linear or branched alkyl group; andXi-X6are independently selected from the group H, a C1-C6 substituted or unsubstituted alkyl, a halogen, — NO2, and — CN orX2and X3 together form — S — S — and Xi and X4 are independently selected from the group H, a C1-C6 substituted or unsubstituted alkyl, a halogen, — NO2, and — CN; wherein optional substitution of alkyl groups is substitution with one or more halogens, — CN, — NO2, — C(O)R', — COOR', — C(O)NH2, — NHC(O)R', — C(O)NR'R", — CF3, — SO3H, — SO2CF3, — SO2R', — SO2NR'R", —OR', — OC(O)R', substituted or unsubstituted phenyl, substituted or unsubstituted benzyl, substituted or unsubstituted vinyl, — NHR' or — NR'R", wherein R' and R" are independently H, an unsubstituted C1 to C6 alkyl or a C1-C3 halogen-substituted C1-C6 alkyl.

9. The electrochemical sensor of claim 8, wherein the sensing material is a compound of Formula I where X1-X4 are selected from hydrogen, halogen or — CN and R1 and R2are C3-C11 alkyl groups.

10. The electrochemical sensor of claim 1 , wherein the sensing molecule is NPDI-NH:NPDI-NH.11 . The electrochemical sensor of claim 1 , wherein the semiconducting polymer comprises one or more pi-conjugated groups selected from thiophene or thiophene derivatives; fluorene or fluorene derivatives; benzothiadiazole and benzothiadiazole derivatives; indacenodithiophene (IDT) and indacenodithiophene derivatives; naphthalenediimide (NDI) and NDI derivatives; pyrrole and pyrrole derivatives, isoindigo and isoindigo derivatives; cyclopentadithiophene (CPDT) and CPDT derivatives, diketopyrrolopyrrole (DPP) or DPP derivatives, benzodithiophene (BDT) or BDT derivatives.

12. The electrochemical sensor of claim 1 , wherein the semiconducting polymer comprises one or more pi-conjugated groups selected from thiophene; fluorene; benzothiadiazole; indacenodithiophene (IDT); naphthalenediimide (NDI); pyrrole, isoindigo; cyclopentadithiophene (CPDT), diketopyrrolopyrrole (DPP), benzodithiophene (BDT) or BDT derivatives.

13. The electrochemical sensor of claim 1 , wherein the semiconducting polymer is a polymer of structure P(NDI2OT):wherein each R is independently selected from an alkyl group having 5-24 carbon atoms, and n is an integer greater than 6.

14. The electrochemical sensor of claim 13, wherein each R group is selected from branched alkyl groups of formula -CH2-CH2(RI)(R2), where Ri and R2are independently alky groups having 6-12 carbon atoms.

15. The electrochemical sensor of claim 1 , wherein the semiconducting polymer is P(NDI2OD-2T).

16. The electrochemical sensor of claim 1 , wherein the active layer comprises a mixture of a semiconducting polymer and a conducting polymer, wherein the semiconducting polymer represents 10% or more by weight of the mixture and optionally represents 50% or more by weight of the mixture.

17. The electrochemical sensor of claim 1 , wherein the active layer comprises a mixture of a semiconducting polymer and a conducting polymer, wherein the semiconducting polymer represents 10% or more of the weight of the mixture and optionally 50% by weight of the mixture and wherein the conducting polymer is a conducting polymer selected frompolyacetylene, polythiophene, poly(p-phenylene) or poly(p-phenylene vinylene) or a substituted derivative thereof.

18. The electrochemical sensor of claim 1 , wherein the sensing material is PDI-NH and the semiconducting polymer is P(NDI2OD-2T).

19. The electrochemical sensor of claim 1 or claim 18, wherein the analyte is an organic or inorganic base and optionally is a volatile base.

20. The electrochemical sensor of claim 1 or claim 18, wherein the selected analyte is a volatile amine, diamine or polyamine.21 . A method for detecting a selected analyte which comprises the steps of: generating an active layer comprising a semiconducting material and a sensing material or molecule; monitoring the conductance of the active layer when the active layer is exposed to an environment that may contain the selected analyte; wherein the sensing material comprises a pi-conjugated moiety and at least one chemical functional group bonded to the pi-conjugated moiety, wherein the at least one chemical functional group reacts with the selected analyte to induce charge transfer into the active layer to change the conductance of the active layer; and wherein an increase in conductance of the active layer indicates the presence of the selected analyte the environment that may contain the selected analyte.

22. The method of claim 21 , wherein generating the active layer comprises dispersing the sensing material or molecule in the active layer or otherwise contacting the sensing material or molecule with the active layer.

23. The method of claim 21 or 22, wherein generating the active layer comprises dispersing the sensing material or molecule in a semiconducting polymer or a mixture of a semiconducting polymer and a conducting polymer.

24. The method of claim 21 or 22, wherein the selected analyte is a base and optionally is a volatile base.

25. The method of claim 21 or 22, wherein the selected analyte is an amine or diamine and optionally is volatile.

26. The method of claim 21 or 22, wherein the selected analyte is ammonia, a primary amine, a secondary amine, a diamine, a tertiary amine, pyrrole, indole, hydrazine or an alkyl hydrazine.

27. The method of claim 21 or 22, wherein the selected analyte is one or more biogenic amine.

28. The method of claim 21 or 22, wherein the pi-conjugated moiety is selected from a rylene moiety, optionally a perylene, terrylene or quaterrylene moiety, a perylene diimide moiety; an oligoacene moiety, a heteroacene moiety, a phthalocyanine moiety, and napthalene diimide moiety.

29. The method of claim 21 or 22, wherein the chemical functional group is selected from an N-annulated (N-H) moiety, a pyrrole moiety (optionally a diketopyrrole), an indole moiety, a carbazole moiety, an azole moiety, an imidazole moiety and a benzoimidazole moiety.

30. The method of claim 21 or claim 22, wherein the sensing material is a compound of Formula I:I wherein:Ri and R2are independently a substituted or unsubstituted C1 to C18 linear or branched alkyl group; andXi-X6are independently selected from the group H, a C1-C6 substituted or unsubstituted alkyl, a halogen, — NO2, and — CN orX2and X3together form — S — S — and Xi and X4are independently selected from the group H, a C1-C6 substituted or unsubstituted alkyl, a halogen, — NO2, and — CN; wherein optional substitution of alkyl groups is substitution with one or more halogens, — CN, — NO2, — C(O)R', — COOR', — C(O)NH2, — NHC(O)R', — C(O)NR'R", — CF3, — SO3H, — SO2CF3, — SO2R', — SO2NR'R”, —OR', — OC(O)R', substituted or unsubstituted phenyl, substituted or unsubstituted benzyl, substituted or unsubstituted vinyl, — NHR' or — NR'R", wherein R' and R" are independently H, an unsubstituted C1 to C6 alkyl or a C1-C3 halogen-substituted C1-C6 alkyl.31 . The method of claim 21 or 22, wherein the sensing material is a compound of Formula I where X-i-X4are selected from hydrogen, halogen or — CN and R1 and R2are C3-C11 alkyl groups.

32. The method of claim 21 or 22, wherein the sensing molecule is NPDI-NH:NPDI-NH.

33. The method of claim 21 or 22, wherein the semiconducting polymer comprises one or more pi-conjugated groups selected from thiophene or thiophene derivatives; fluorene or fluorene derivatives; benzothiadiazole and benzothiadiazole derivatives; indacenodithiophene (IDT) or indacenodithiophene derivatives; naphthalenediimide (NDI) or NDI derivatives; pyrrole or pyrrole derivatives, isoindigo or isoindigo derivatives; cyclopentadithiophene (CPDT) or CPDT derivatives, diketopyrrolopyrrole (DPP) or DPP derivatives, and benzodithiophene (BDT) or BDT derivatives.

34. The method of claim 21 or 22, wherein the semiconducting polymer comprises one or more pi-conjugated groups selected from thiophene; fluorene; benzothiadiazole; indacenodithiophene (IDT); naphthalenediimide (NDI); pyrrole, isoindigo; cyclopentadithiophene (CPDT), diketopyrrolopyrrole (DPP), benzodithiophene (BDT).

35. The method of claim 21 or 22, wherein the semiconducting polymer is a polymer of structure P(ND12OT):wherein each R is independently selected from an alkyl having 5-24 carbon atoms and n is 6 or more.

36. The method of claim 35, wherein the R groups of P(ND12OT) are selected from branched alkyl groups of formula -CH2-CH2(RI)(R2), where Ri and R2are independently alky groups having 6-12 carbon atoms.

37. The method of claim 21 or 22, wherein the semiconducting polymer is P(NDI2OD-2T).

38. A method for detecting a selected analyte employing the sensor of any one of claims 1- 20.

49. A method for detecting a selected analyte which comprises: providing a sensor of any one of claims 1-20; and monitoring the conductance of the active layer when the active layer is exposed to an environment that may contain the selected analyte.

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