Description:BACKGROUND

FIELD OF THE DISCLOSURE
[0001] Various embodiments of the disclosure relate generally to a sensor for determining perchlorate ions in a sample. More specifically, various embodiments of the disclosure relate to an electrode assembly comprising diketopyrrolopyrrole-based polymers, the sensor incorporating the electrode assembly, and methods of making and using the same.
DESCRIPTION OF THE RELATED ART
[0002] Perchlorate salts are widely used in propellants, explosives, fireworks, and certain fertilizers. In aqueous environments, these salts readily dissociate to form perchlorate ions (ClO4⁻). Due to their high-water solubility, perchlorate ions leach easily into groundwater and surface water through agricultural runoff and industrial discharge. The combination of high solubility, chemical stability, and environmental persistence has led to widespread perchlorate ion contamination of water and soil. This contamination poses a significant environmental and public health concern globally, with increasing attention in India. The issue is particularly critical in rural and resource-constrained areas, where regular monitoring infrastructure is often unavailable or inadequate.
[0003] Perchlorates (perchlorate ions) pose a significant health risk by competitively inhibiting iodide uptake in the thyroid gland, thereby disrupting normal thyroid function. This disruption can lead to hypothyroidism and associated developmental disorders, with heightened vulnerability observed in pregnant women, infants, and children.
[0004] Despite its known toxicity, perchlorate is rarely included in routine water quality assessments due to the absence of affordable, rapid, and field-deployable detection technologies. Conventional analytical methods, such as ion chromatography and mass spectrometry, though highly accurate, are prohibitively expensive, time-intensive, and require centralized laboratory facilities and trained personnel. These limitations greatly hinder routine monitoring, particularly in decentralized and underserved areas where environmental contamination often goes undetected and unaddressed.
[0005] Limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of described systems with some aspects of the present disclosure, as set forth in the remainder of the present application and with reference to the drawings.
SUMMARY
[0006] According to embodiments of the present disclosure, an electrode assembly for a sensor for determining perchlorate ions in a sample is provided. The electrode assembly comprises a source electrode and a drain electrode disposed on a substrate. The electrode assembly further comprises an electrochemically active layer defining a channel between the source electrode and the drain electrode. The channel is in electrical communication with the source electrode and the drain electrode. The electrochemically active layer comprises a diketopyrrolopyrrole-based polymer having a general structure [I],

[I]
wherein, R1 and R2 are independently selected from hydrogen, C₁–C₁₂ alkoxy groups, halogen, cyano, amino groups, C₁–C₁₂ alkyl groups, C2–C₁₂ alkenyl groups, C2–C₁₂ alkynyl groups, C₁–C₁₂ haloalkyl groups, C3–C₁₂ cycloalkyl groups, C6–C₁₂ aryl groups, C2–C₁₂ heterocyclyl groups, and C3–C₁₂ heteroaryl groups, provided that, at least one of R1 and R2 is C₁–C₁₂ alkoxy groups; R3 is selected from linear or branched C4-C30 alkyl groups, C4-C30 cycloalkyl-substituted alkyl groups, C4-C30 aralkyl-substituted alkyl groups, C4-C30 fluorinated alkyl groups, and C8-C20 branched fluoroalkyl-substituted alkyl groups; and R4 is –(R’-O)m-R”, wherein, R’ is selected from C₂–C₄ alkylene groups, optionally substituted with alkyl, halo, or hydroxyl groups; and R” is selected from hydrogen, C₁–C₆ alkyl groups, C₁–C₆ alkoxy groups, carboxylic acid (–COOH) group, sulfonic acid (–SO₃H) group, phosphonic acid (–PO₃H₂) group, quaternary ammonium groups (–N⁺R₃), imidazolium cations, zwitterionic groups, and cleavable hydrophilic moieties; m is in a range of 1 to 10; and n is in a range of 15 to 30. The electrode assembly further comprises an electrolyte well comprising the sample. The sample is in electrochemical communication with the channel of the electrochemically active layer. The electrode assembly further comprises a gate electrode in electrochemical communication with the sample in the electrolyte well, wherein upon application of a voltage between the source electrode and the drain electrode, and between the gate electrode and the source electrode an electrical signal that correlates to a presence of perchlorate ions in the sample, or concentration of perchlorate ions in the sample, or both is generated.
[0007] In another embodiment of the present disclosure, a method of fabricating an electrode assembly for a sensor for detecting perchlorate ions in a sample is provided. The method comprises providing a source electrode and a drain electrode on a substrate. The method further comprises forming an electrochemically active layer to define a channel between the source electrode and the drain electrode, and in electrical communication with the source electrode and the drain electrode. The electrochemically active layer comprises a diketopyrrolopyrrole-based polymer having a general structure [I],

[I]
wherein, R1 and R2 are independently selected from hydrogen, C₁–C₁₂ alkoxy groups, halogen, cyano, amino groups, C₁–C₁₂ alkyl groups, C2–C₁₂ alkenyl groups, C2–C₁₂ alkynyl groups, C₁–C₁₂ haloalkyl groups, C3–C₁₂ cycloalkyl groups, C6–C₁₂ aryl groups, C2–C₁₂ heterocyclyl groups, and C3–C₁₂ heteroaryl groups, provided that, at least one of R1 and R2 is C₁–C₁₂ alkoxy groups; R3 is selected from linear or branched C4-C30 alkyl groups, C4-C30 cycloalkyl-substituted alkyl groups, C4-C30 aralkyl-substituted alkyl groups, C4-C30 fluorinated alkyl groups, and C8-C20 branched fluoroalkyl-substituted alkyl groups; and R4 is –(R’-O)m-R”, wherein, R’ is selected from C₂–C₄ alkylene groups, optionally substituted with alkyl, halo, or hydroxyl groups; and R” is selected from hydrogen, C₁–C₆ alkyl groups, C₁–C₆ alkoxy groups, carboxylic acid (–COOH) group, sulfonic acid (–SO₃H) group, phosphonic acid (–PO₃H₂) group, quaternary ammonium groups (–N⁺R₃), imidazolium cations, zwitterionic groups, and cleavable hydrophilic moieties; m is in a range of 1 to 10; and n is in a range of 15 to 30. The method further comprises providing an electrolyte well on the electrochemically active layer. The electrolyte well is configured to receive or comprise the sample. The method further comprises positioning a gate electrode in electrochemical communication with the sample in the electrolyte well, enabling sensor activation upon analyte interaction.
[0008] In another embodiment of the present disclosure, a sensor for determining perchlorate ions in a sample is provided. The sensor comprises a source electrode and a drain electrode disposed on a substrate. The sensor comprises an electrochemically active layer defining a channel between the source electrode and the drain electrode, wherein the channel is in electrical communication with the source electrode and the drain electrode. The electrochemically active layer comprises a diketopyrrolopyrrole-based polymer having a general structure [I],

[I]
wherein, R1 and R2 are independently selected from hydrogen, C₁–C₁₂ alkoxy groups, halogen, cyano, amino groups, C₁–C₁₂ alkyl groups, C2–C₁₂ alkenyl groups, C2–C₁₂ alkynyl groups, C₁–C₁₂ haloalkyl groups, C3–C₁₂ cycloalkyl groups, C6–C₁₂ aryl groups, C2–C₁₂ heterocyclyl groups, and C3–C₁₂ heteroaryl groups, provided that, at least one of R1 and R2 is C₁–C₁₂ alkoxy groups; R3 is selected from linear or branched C4-C30 alkyl groups, C4-C30 cycloalkyl-substituted alkyl groups, C4-C30 aralkyl-substituted alkyl groups, C4-C30 fluorinated alkyl groups, and C8-C20 branched fluoroalkyl-substituted alkyl groups; and R4 is –(R’-O)m-R”, wherein, R’ is selected from C₂–C₄ alkylene groups, optionally substituted with alkyl, halo, or hydroxyl groups; and R” is selected from hydrogen, C₁–C₆ alkyl groups, C₁–C₆ alkoxy groups, carboxylic acid (–COOH) group, sulfonic acid (–SO₃H) group, phosphonic acid (–PO₃H₂) group, quaternary ammonium groups (–N⁺R₃), imidazolium cations, zwitterionic groups, and cleavable hydrophilic moieties; m is in a range of 1 to 10; and n is in a range of 15 to 30. The sensor comprises an electrolyte well configured to receive, or comprising the sample. The sample is in electrochemical communication with the channel of the electrochemically active layer. The sensor further comprises a gate electrode in electrochemical communication with the sample in the electrolyte well. The sensor further comprises a power source to apply a voltage between the source electrode and the drain electrode, and between the gate electrode and the source electrode. The sensor further comprises a processing unit configured to measure an electrical signal generated upon application of the voltage and correlate the electrical signal to a presence of perchlorate ions in the sample, or concentration of perchlorate ions in the sample, or both.
[0009] In yet another embodiment of the present disclosure, a method for determining perchlorate ions in a sample is provided. The method comprises providing an electrode assembly. The method further comprises applying a voltage between the gate electrode and the source electrode, and between the source electrode and the drain electrode. The method further comprises measuring an electrical signal generated on application of the voltage. The method further comprises correlating a measured electrical signal to a presence of perchlorate ions in the sample, or concentration of perchlorate ions in the sample, or both.
BRIEF DESCRIPTION OF DRAWINGS

[0010] FIG. 1 is a schematic representation of an electrode assembly, in accordance with an exemplary embodiment of the disclosure;
[0011] FIG. 2 is a flow chart that illustrates a method of preparing an electrode assembly, in accordance with another exemplary embodiment of the disclosure;
[0012] FIG. 3 is a schematic representation of a sensor, in accordance with yet another exemplary embodiment of the disclosure;
[0013] FIG. 4 is a flow chart of a method for determining perchlorate ions, in accordance with yet another exemplary embodiment of the disclosure;
[0014] FIG. 5 shows representative transfer characteristics curves of various anions;
[0015] FIG. 6 is a plot of drain current as a function of perchlorate ion concentration;
[0016] FIG. 7 is a plot of drain current against concentration of perchlorate ions in a mixed-ion environment;
[0017] FIG. 8 shows current versus time plots of the sensor at varying perchlorate ion concentrations;
[0018] FIG. 9 shows current versus time plots of the sensor at varying perchlorate ion concentrations in the presence of interfering ions; and
[0019] FIG. 10 is a comparative bar chart illustrating the response times of various anions in comparison to perchlorate ions using the sensor.
[0020] Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description of exemplary embodiments is intended for illustration purposes only and is, therefore, not intended to necessarily limit the scope of the present disclosure.
DETAILED DESCRIPTION OF EMBODIMENTS

[0021] The following description illustrates some exemplary embodiments of the disclosed disclosure in detail. Those of skill in the art will recognize that there are numerous variations and modifications of this disclosure that are encompassed by its scope. Accordingly, the description of a certain exemplary embodiment should not be deemed to limit the scope of the present disclosure.
[0022] The term “comprising” as used herein is synonymous with “including,” or “containing,” and is inclusive or open-ended and does not exclude additional, unrecited elements, or process steps.
[0023] All numbers expressing quantities of ingredients, property measurements, and so forth used in the specification are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained.
[0024] These and other features and advantages of the present disclosure may be appreciated from a review of the following detailed description of the present disclosure, along with the accompanying figures in which like reference numerals refer to like parts throughout.
[0025] As used herein, the term “sample” refers to any substance or composition suspected of containing a target ion (for example, perchlorate ions), typically dissolved in a suitable solvent. The term “analyte”, as used herein, refers to chemical species of interest or target ion (for example, perchlorate ion in the present disclosure) that is being detected or quantified in a given sample.
[0026] The term “sensitivity” refers to rate of change in a sensor’s electrical output (e.g., drain current or transconductance) per unit change in analyte concentration. A higher sensitivity implies greater responsiveness of the sensor to small variations in analyte levels.
[0027] The term “signal strength” corresponds to a measured magnitude of an output signal (e.g., current or voltage) generated by a sensor in response to an analyte. The term “signal amplification” refers to a process or mechanism that increases the magnitude of a signal, often without increasing an analyte concentration.
[0028] The term “operational stability” as used herein, refers to a sensor’s ability to maintain its electrical characteristics (such as drain current, or transconductance) within acceptable limits over extended periods of use, repeated sensing cycles, or prolonged exposure to electrolytes, without significant degradation in sensitivity, selectivity, or response reproducibility.
[0029] FIG. 1 is a schematic representation of an electrode assembly 100 in accordance with embodiments of the present disclosure. The electrode assembly 100 may be utilized in a sensor for determining concentration of perchlorate ions in a sample. As used herein, the term “determining” refers to detecting a presence of the perchlorate ions in the sample, as in qualitative detection. The term “determining” also refers to quantitatively measuring a concentration of the perchlorate ions in the sample.
[0030] The electrode assembly 100 includes a source electrode 102, a drain electrode 104, a gate electrode 106, an electrochemically active layer 108, and an electrolyte well 110. The sample is provided in the electrolyte well 110.
[0031] Referring to FIG. 1, the source electrode 102 and the drain electrode 104 are disposed on a substrate (not shown). Examples of substrate materials include, but are not limited to, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide, polydimethylsiloxane (PDMS), polyethylene, polypropylene, polycarbonate, mica, glass, silicon, paper, coated paper, resin-coated paper, paper laminates, paperboard, corrugated board, or combinations thereof.
[0032] The source electrode 102 and the drain electrode 104 of the electrode assembly 100 are made of conducting materials. The source electrode 102 and the drain electrode 104 may be of same material, or of different materials. Examples of conducting materials include metals like silver, platinum, gold, or conductive polymers like Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), or combinations thereof.
[0033] The electrochemically active layer 108 is disposed between the source electrode 102 and the drain electrode 104 to define a channel 114. The electrochemically active layer 108 comprises a diketopyrrolopyrrole-based polymer (DPP-based polymer) having a general structure [I].

[I]
wherein, R1 and R2 are independently selected from hydrogen, C₁–C₁₂ alkoxy groups, halogen, cyano, amino groups, C₁–C₁₂ alkyl groups, C2–C₁₂ alkenyl groups, C2–C₁₂ alkynyl groups, C₁–C₁₂ haloalkyl groups, C3–C₁₂ cycloalkyl groups, C6–C₁₂ aryl groups, C2–C₁₂ heterocyclyl groups, and C3–C₁₂ heteroaryl groups, provided that, at least one of R1 and R2 is C₁–C₁₂ alkoxy groups; R3 is independently selected from linear or branched C4-C30 alkyl groups, C4-C30 cycloalkyl-substituted alkyl groups, C4-C30 aralkyl-substituted alkyl groups, C4-C30 fluorinated alkyl groups, and C8-C20 branched fluoroalkyl-substituted alkyl groups; and R4 is –(R’-O)m-R”, wherein, R’ is selected from C₂–C₄ alkylene groups, optionally substituted with alkyl, halo, or hydroxyl groups; and R” is selected from hydrogen, C₁–C₆ alkyl groups; C₁–C₆ alkoxy groups, carboxylic acid (–COOH) group, sulfonic acid (–SO₃H) group, phosphonic acid (–PO₃H₂) group, quaternary ammonium groups (–N⁺R₃), imidazolium cations, zwitterionic groups, and cleavable hydrophilic moieties; m is in a range of 1 to 10; and n is in a range of 15 to 30.
[0034] As used herein, "C₁–C₁₂ alkoxy group" refers to an alkoxy group containing from 1 to 12 carbon atoms. That is, the alkyl portion of the alkoxy group may be a linear or branched chain containing between one and twelve carbon atoms, such as methoxy, ethoxy, propoxy, butoxy, etc. Similarly, the notation Cn–Cm preceding a group (e.g., alkyl, heterocyclyl, alkylene) refers to the number of carbon atoms present in that group, ranging from n to m carbon atoms. The preparation of the DPP-based polymer used in the present disclosure is disclosed in Indian Patent Application No. 202341047655, which is incorporated herein by reference in its entirety.
[0035] In the diketopyrrolopyrrole-based polymer (DPP), the core nitrogen atoms are substituted with the side chains R3 and R4, where R3 is a hydrophobic side chain while R4 is a hydrophilic side chain.
[0036] In some embodiments, R3 is a linear or branched alkyl group containing 4 to 30 carbon atoms, such as n-hexyl, n-octyl, n-decyl, 2-ethylhexyl, 2-butyloctyl, 3,7-dimethyloctyl, or 2-octyldodecyl. Examples of cycloalkyl-substituted alkyls include, but are not limited to, cyclopentylmethyl, cyclododecyl, or cyclohexylethyl. Examples of aralkyl-substituted alkyl groups include, but are not limited to, biphenylalkyl, phenylcyclohexylpropyl, or benzylhexyl. Examples of fluorinated alkyl groups include, but are not limited to, perfluoroalkyl chains, fluorodecyl, or branched fluoroalkyl-substituted C₈–C₂₀ groups.
[0037] In some embodiments, R4 is a linear or branched oligo(ethylene glycol) (OEG) side chain comprising 2 to 8 ethylene glycol repeating units, optionally terminated with hydroxy(–OH), methyl (–CH₃), or alkyl (–CH₂CH₃) groups. In some embodiments, R4 is a methoxy-terminated poly(ethylene glycol) (PEG) group, including but not limited to, 2-(2-methoxyethoxy)ethyl, 2-[2-(2-methoxyethoxy)ethoxy]ethyl, or methoxytriethylene glycol. In certain embodiments, R4 is a PEG chain terminated with a functional group, including but not limited to carboxyl (–COOH), sulphonic (–SO₃H), phosphonic (–PO₃H₂), quaternary ammonium groups (–N⁺R₃), imidazolium cations, cleavable hydrophilic side chains. or any combination thereof. As used herein, the term "cleavable hydrophilic side chains" refers to side chains that may impart water solubility and contain cleavable linkages that can be selectively broken. The cleavable hydrophilic side chains include, but are not limited to, ester linkages, and disulfide bonds.
[0038] In a preferred embodiment, the DPP-based polymer comprises alternating R3 and R4 side chains on the DPP core to modulate the spatial arrangement and microenvironment around the polymer backbone. The alternating side-chain architecture is believed to enhance the accessibility of perchlorate ions and promote efficient interaction between key components of the electrode assembly, such as the channel and the electrolyte well. The substitution pattern facilitates selective and specific response toward perchlorate ions over other anions, potentially by forming well-defined ionic access channels and controlled hydration domains. The asymmetry introduced by the alternating R3 and R4 groups also enables fine control over polymer aggregation, charge transport characteristics, and ion selectivity. Additionally, the combination of hydrophilic and hydrophobic side chains contributes to solubility in solvents while maintaining the morphological stability of a polymer film during operation of the electrode assembly. In one embodiment, a molar ratio of hydrophilic (R4) to hydrophobic (R3) side chains is between 1:3.
[0039] In some embodiments of the present disclosure, R1 and R2 are independently selected from hydrogen, and C1-C6 alkoxy groups, provided that, at least one of R1 and R2 is C1-C6 alkoxy. R3 is selected from hydrogen, and C12-C25 alkyl groups; and R4 is –(R’-O)m-R”, where R’ and R” are independently selected from C1-C12 alkyl groups, m is in a range of 1 to 10, and n is in a range of 15 to 30.
[0040] In some embodiments of the present disclosure, the DPP-based polymer has the structure [II]

[II]

where, m is in a range of 2 to 5, and n is in a range of 20 to 25.
[0041] The channel 114 is a critical functional element of the electrode assembly 100. The term “channel”, as used herein refers to a region of the electrochemically active layer 108, that electrically communicate with the source electrode 102 and the drain electrode 104, and electrochemically communicate with the sample in the electrolyte well 110.
[0042] As used herein, the term “electrically communicate” refers to exchange or transfer of electrical carriers such as electrons and/or holes.
[0043] As used herein, the term “electrochemically communicate” refers to exchange or transfer of electrochemical species, such as ions and electrical carriers such as electrons and/or holes.
[0044] The term “communicate”, as used herein, refers to an exchange or transfer of electrical or electrochemical carriers between components, such as the source electrode and the drain electrode, either through direct physical contact or via an intermediate medium.
[0045] In a typical sensor, an electrochemically active polymer within a channel undergoes reversible doping and de-doping in response to a gate voltage. When target anions (for example, perchlorate ions) are present in the sample and a gate voltage is applied, the anions selectively migrate into the polymer matrix from the electrolyte well and interact with the polymer’s positively charged (oxidized) backbone, stabilizing its doped state and enhancing electrical conductivity. Conversely, upon reversal or removal of the gate voltage, the anions are expelled from the polymer, resulting in de-doping and a corresponding decrease in conductivity. This reversible ion-mediated modulation of the channel's conductivity forms the basis of electrical signal generation in the sensor. The resulting changes in electrical signal, such as drain current or gate current, directly correlate with the presence and concentration of the target anions, enabling continuous, real-time sensing and monitoring of analyte levels in the sample.
[0046] The DPP-based polymer advantageously shows specificity and selectivity towards perchlorate ions. As used herein, the term “selectivity”, refers to the ability of a sensing material or system to preferentially interact with, or respond to a particular ion (e.g., perchlorate ions) in the presence of potentially interfering substances or ions. High selectivity ensures that the signal output is predominantly influenced by the target ion (analyte) rather than by structurally or chemically similar species. As used herein, the term “specificity” denotes the inherent molecular or chemical recognition capability of the sensing material toward the target ion, arising from unique interactions such as size exclusion, charge complementarity, binding affinity, or redox compatibility. It is proposed that perchlorate ions favorably interact with delocalized polarons (oxidized species) formed on the DPP-polymer structure, which is energetically more favorable than when compared to the interactions in the presence of other competing anions, for example, chloride or nitrate.
[0047] The performance of the electrode assembly 100 is influenced by the dimensions of the channel 114, including its length (L), width (W), and thickness (d). The channel length refers to the distance between the source electrode 102 and the drain electrode 104, while the width denotes the lateral dimension of the channel 114 perpendicular to the direction of ion transport. The thickness typically corresponds to a film thickness of the electrochemically active layer 108 forming the channel 114.
[0048] A shorter channel length facilitates efficient charge transport, resulting in reduced channel resistance and increased drain current. However, excessively short channels may lead to higher leakage currents and diminished modulation efficiency. The term “leakage current” refers to an unintended current, for example, a small current that flows through the electrolyte even when the gate is supposed to be electrically isolated. An increase in channel width enlarges the cross-sectional area available for charge carrier flow, thereby supporting higher current and improving sensitivity and signal strength. Channel thickness governs the volumetric capacity for ionic exchange during gate modulation. A thicker channel can support deeper ionic penetration and more substantial doping/de-doping, leading to pronounced modulation of conductivity. Nonetheless, increased thickness may also introduce ion diffusion limitations, potentially reducing the temporal response of the sensor (sensor response).
[0049] The channel 114 has a channel architecture depending on the intended application and fabrication requirement. In one embodiment, the channel 114 has a vertical configuration, where the source electrode 102 and the drain electrode 104 are arranged in a stacked format with the channel 114 positioned in between. The vertical configuration can reduce a lateral footprint of the electrode assembly 100, enabling higher density integration in miniaturized or multi-layered systems. Alternative configurations include, but are not limited to, lateral (horizontal) and interdigitated configurations. In lateral (horizontal) configuration, the source electrode 102 and the drain electrode 104 are placed on the same plane with the channel 114 extending laterally between them, while in interdigitated the electrodes (102 and 104) are patterned as interleaved fingers to maximize electrode-channel interface area and improve signal amplification. In FIG. 1, the channel 114 has a lateral configuration.
[0050] The sample is provided in the electrolyte well 110, which is disposed on the electrochemically active layer 108. The term “electrolyte well,” as used herein, refers to a physical compartment, cavity, or reservoir designed to hold the sample. In certain embodiments, the electrolyte well 110 is configured to receive the sample. In certain embodiments, the electrolyte well 110 may include an electrolyte in addition to the sample. The electrolyte may be in liquid, gel, or solid-state form, without limitation. The selection of electrolyte and form of the electrolyte is guided by sensor design and fabrication requirements, and the intended application. For example, when the sensor is used for biological sample detection, a biocompatible electrolyte is typically preferred. In applications where rapid sensor response is required, a liquid electrolyte such as potassium chloride (KCl), known for its high ionic conductivity (a 0.20 molar (M) solution of KCl at 298 K has a conductivity of 0.0248 Siemens per centimeter (S cm⁻¹)), may be used. A rapid or fast sensor response refers to a temporal response time of 1 to 10 milliseconds (ms). For portable or point-of-care applications, solid-state or gel-based electrolytes are advantageous due to their mechanical stability and ease of fabrication and use. The ionic conductivity of the electrolyte is governed by the size, mobility, and charge of the ionic species present. The ionic conductivity increases with increasing concentration and temperature.
[0051] Examples of electrolyte include, but are not limited to, phosphate-buffered saline (PBS), sodium chloride (NaCl), potassium chloride (KCl), potassium fluoride (KF), potassium perchlorate (KClO4), potassium nitrate (KNO3), Potassium Sulphate (K2SO4), Potassium bicarbonate (KHCO3), Potassium Carbonate (K2CO3), agarose or polyvinyl alcohol (PVA) gels containing dissolved salts, ionic liquids such as 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][TFSI], propylene carbonate with lithium salts, polyethylene oxide (PEO) doped with lithium salts and the like.
[0052] The sample may be in liquid, solid, or gaseous form. In the case of solid or gaseous samples, the sample should either dissolve in the electrolyte or release ionic species into the medium to interact with the electrochemically active layer 108. Such ionic interaction is essential for modulating the channel 114 properties and enabling effective detection using a sensor incorporating the electrode assembly 100.
[0053] It is essential that the sample be compatible with the electrochemically active layer 108. Compatibility ensures efficient ion exchange between the sample in the electrolyte well 110 and electrochemically active layer 108, stable ion doping and de-doping kinetics of the DPP-polymer, and long-term operational stability of the sensor. The sample comprising the perchlorate ions should facilitate ion transport into the channel 114 without inducing degradation, delamination, or irreversible chemical changes in the electrochemically active layer 108. In one embodiment, the electrolyte well 110 comprises sodium perchlorate having a concentration of 1μM to 0.1M.
[0054] The gate electrode 106 is in electrical contact with the source electrode 102 through an external circuit and in electrochemical communication with the sample in the electrolyte well 110.
[0055] The gate electrode 106 is made of a metal or conductive material that is inert in a given sample and/or electrolyte. Suitable gate electrode materials include, but are not limited to silver/silver chloride, platinum, gold, carbon-based materials such as graphite, glassy carbon, conducting polymers such as Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS).
[0056] The selection of the gate electrode material is governed by factors such as electrochemical stability, work function, compatibility with the sample, and intended application (for example, biocompatibility for a biosensor). Moreover, the gate electrode 106 should be capable of facilitating repeated redox interactions (dope-dedope) without significant degradation or potential drift. The term “work function” as used herein, refers to a minimum energy required to extract an electron from a surface of a material and move it to a point in vacuum immediately outside the material’s surface.
[0057] In one embodiment, a geometry and surface area of the gate electrode 106 are optimized based on the sensor design and intended application. A larger surface area of the gate electrode 106 can facilitate enhanced ionic exchange between the channel 114 and the sample in the electrolyte well 110, resulting in greater modulation of the channel conductivity and thereby enabling signal amplification. Alternately, a miniaturized gate design, or the use of multiple gate electrodes, may be advantageous for constructing high-density sensor arrays.
[0058] On application of a voltage between the gate electrode 106 and the source electrode 102, and between the source electrode 102 and the drain electrode 104, ionic species present in the sample migrate towards the electrochemically active layer 108. The DPP-based polymer undergoes reversible doping and de-doping in response to the ionic flux, thereby modulating electrical conductivity of the channel 114. The modulation generates an electrical signal, which may be measured as a change in drain current (amperometric mode), gate or channel potential (potentiometric mode), or impedance (impedimetric mode), depending on the mode of operation.
[0059] In the amperometric mode, a constant gate voltage is applied across the gate electrode 106 and the source electrode 102, and the resulting drain current (ID) is measured between the source electrode 102 and the drain electrode 104. The drain current is quantitatively correlated with the concentration of the perchlorate ions in the sample. In the potentiometric mode, under a current input, the potential (VG) between the gate electrode 106 and the source electrode 102 is monitored. The potential is altered due to the presence of perchlorate ions. In the impedimetric mode, an AC signal is applied, and the impedance across the gate electrode 106 and the source electrode 102, or drain electrode 104 is measured over a frequency range. Transconductance (GM) is defined as the change in drain current (ID) per unit change in gate voltage (VG).
[0060] Each mode provides a distinct electrical readout influenced by the doping/de-doping behavior of the DPP-based polymer in response to ionic flux, offering flexibility in sensor design and application.
[0061] According to embodiments of the present disclosure, a method of fabricating an electrode assembly (for example, electrode assembly 100) is provided. The electrode assembly may be fabricated by laying layers on top of one another. The layers may be prepared by methods known in the art, including solution coating techniques. The coating steps may be carried out in an inert atmosphere, for example, under nitrogen gas. Alternatively, some layers may be prepared by thermal evaporation or by vacuum deposition. Metallic layers may be prepared by known techniques, such as, for example, thermal or electron-beam evaporation, chemical-vapour deposition or sputtering, or printing conductive metal particle inks.
[0062] FIG.2 is a flowchart 200 of a method of fabricating the electrode assembly. At step 210, a source electrode and a drain electrode (for example, the source electrode 102 and the drain electrode 104) are provided on a substrate. The materials used for the source electrode, the drain electrode, and the substrate are as described previously with respect to FIG. 1. The source electrode and the drain electrode may be patterned over the substrate using conventional microfabrication techniques. Suitable fabrication methods include, but are not limited to, photolithography, inkjet printing, spray coating, roll-to-roll processing, spin coating, drop casting, doctor blade coating, electrodeposition, and electrospinning.
[0063] At step 220, an electrochemically active layer is formed to define a channel between the source electrode and the drain electrode. According to embodiments of the present disclosure, the electrochemically active layer comprises the DPP-based polymer, as described previously with reference to FIG. 1. In one embodiment, the DPP-based polymer is dispersed in a suitable solvent and cast or coated over the source electrode and the drain electrode, and a lateral space between the source electrode and the drain electrode to define the channel.
[0064] Non-limiting examples of solvents include dichloromethane, trichloroethane, chloroform, hexane, heptane, octane, toluene, ethylbenzene, xylene, ethylbenzoate, methylbenzoate, 1,1,2,2-tetrachloroethane, tetrahydrofuran (THF), dioxane, chlorobenzene, dichlorobenzenes, trichlorobenzene, mesitylene or combinations thereof.
[0065] Example casting or coating methods include, but are not limited to, spin coating, microgravure coating, gravure coating, bar coating, roll coating, wire bar coating, dip coating, spray coating, screen printing, flexo printing, micro-contact printing, inkjet printing, offset printing, blade coating or combinations thereof.
[0066] At step 230, an electrolyte well is provided on the electrochemically active layer. The electrolyte well is as described previously with respect to FIG. 1. The sample and/or the electrolyte is housed within the well on the electrochemically active layer. The electrolyte well, in some embodiments, is configured to receive a sample for analysis. In one embodiment, the electrode assembly comprises a microfluidic channel having an input port for introducing the sample. The microfluidic channel is in fluid communication with the electrolyte well, allowing the sample to be directed and drained into the electrolyte well for subsequent interaction with the electrochemically active layer.
[0067] At step 240, a gate electrode is positioned in electrochemical communication with the sample in the electrolyte well. The gate electrode may be integrated with the electrode assembly, or configured as a discrete component externally coupled to the electrode assembly. The gate electrode can be dipped in the electrolyte well, or cast and/or coated on top of the electrolyte well. The gate electrode is as described previously with respect to FIG. 1.
[0068] Encapsulation or passivation layers may be added to isolate electrical components and guide sample access, depending on the intended application, especially in biosensing or wearable applications.
[0069] In yet another embodiment of the present disclosure, a sensor for determining perchlorate ions in a sample is provided. FIG. 3 is a schematic representation of a sensor 300, in accordance with embodiments of the present disclosure. The sensor 300 comprises the electrode assembly 100 as illustrated in FIG. 1.
[0070] As will be appreciated by those skilled in the art, the detection limit and other performance parameters of the sensor 300 can be tuned by optimizing the geometry of the sensor and its components, such as the electrode assembly 100. This includes, but is not limited to, adjustments in channel length, channel width, film thickness, and electrode surface area. Such geometric optimization allows for improved sensitivity, signal strength, and adaptability of the sensor across various analytical conditions and target concentration ranges.
[0071] The sensor 300 includes a power source 310 and a processing unit 320. The power source 310 is operable to apply a voltage between the gate electrode and the source electrode, and between the source electrode and the drain electrode.
[0072] Upon application of voltage, a conductivity of the channel 114 is modulated due to electrochemical interaction with ions from the sample, resulting in the generation of an electrical signal. The electrical signal comprises one or more of drain current (ID), gate voltage (VG), drain voltage (VD), or impedance (Z). The term ‘one or more’ in this context refers to measuring either drain current, gate voltage, drain voltage, impedance, or a derived parameter such as transconductance (Gm). The term “transconductance (Gm)” is defined as the rate of change of drain current (ID) with respect to gate voltage (VG). It is measured in Siemens (S), and it indicates how effectively the gate voltage controls the channel current.
[0073] The processing unit 320 correlates the electrical signal generated to a presence of perchlorate ions in the sample, or concentration of perchlorate ions in the sample, or both. In embodiments where the sample does not contain perchlorate ions, there is no generation of an electrical signal, and the processing unit 320 correlates the absence of the electrical signal to the absence of perchlorate ions in the sample. The processing unit 320 may optionally include embedded calibration data. In some embodiments, the processing unit comprises a smartphone, a handheld reader, or a microcontroller-based circuit.
[0074] In yet another embodiment, the sensor 300 further includes a communication interface 330. The communication interface 330 is configured to receive user inputs to control the power source 310, communicate with the processing unit 320 to configure or monitor the electrical signal being measured, display a result from the processing unit 320, or any combination thereof.
[0075] The communication interface 330 is configured to indicate or display a presence of perchlorate ions when the sensor 300 is being used for detection. In another embodiment, the communication interface 330 displays a concentration of the perchlorate ions in the sample, in a quantitative determination. In certain other embodiments, the communication interface 330 indicate a presence of perchlorate ions as well as display a concentration of the perchlorate ions in the sample. For example, communication interface 330 may have a visual indicator such as colour change indicating presence of perchlorate and a numeric reading corresponding to concentration of the perchlorate ions in the sample. The communication interface 330 comprises a software application, or a visual indicator.
[0076] It is also envisaged to include a pre-screening assay (not shown) in the sensor 300 comprising the DPP-based polymer. The assay is configured to indicate the presence of perchlorate ions in the sample. The pre-screening assay is selected from a colorimetric method, or a chemical precipitation technique. Once the pre-screening assay confirms the presence of perchlorate ions, quantitative assessment may be performed.
[0077] In yet another embodiment, a method for determining perchlorate ions in a sample is provided. FIG. 4 is a flow chart 400 of a method for determining perchlorate ions in a sample. At step 402, an electrode assembly (for example, electrode assembly 100) is provided. At step 404, a voltage is applied between the gate electrode and the source electrode, and between the source electrode and the drain electrode. At step 406, an electrical signal generated on application of the voltage is measured. The perchlorate ions, if present in the sample modulate the conductivity of the channel, as described previously to generate the electrical signal. At step 408, the measured electrical signal is correlated to a presence of perchlorate ions in the sample, or concentration of perchlorate ions in the sample, or both.
[0078] A particular advantage of the present disclosure is that the electrode assembly 100, and the sensor 300 are reusable, allowing for multiple measurements without significant degradation in performance.
[0079] Another advantage is that the electrode assembly 100, and the sensor 300 can be readily manufactured using scalable and cost-effective fabrication techniques, enabling ease of manufacturing.
[0080] Furthermore, the electrode assembly 100, and the sensor 300 are suitable for mass production, supporting scalable deployment for widespread environmental monitoring.
[0081] The DPP-based polymer used in the electrochemically active layer exhibits high selectivity and specificity towards perchlorate ions, even in the presence of competing ionic species. Compared to existing methods for detection, the sensor demonstrates improved sensitivity and reliability in detecting perchlorates.
[0082] In some embodiments, the sensor has a limit of detection (LOD) for perchlorate ions of 6 × 10⁻⁷ M. As used herein, the term “limit of detection” refers to a minimum concentration or amount of an analyte that can be reliably distinguished from an absence of that analyte (i.e., background noise) with a defined level of statistical confidence.
[0083] In some embodiments, the sensor exhibits a linear dynamic range for perchlorate ion concentrations from 1 µM to 100 mM. As used herein, the term “linear dynamic range” refers to the range of analyte (for example, perchlorate ion) concentrations over which the sensor exhibits a linear relationship between the measured signal (e.g., drain current, voltage, impedance) and the analyte concentration. Within this range, changes in analyte concentration produce proportional and predictable changes in the electrical signal, thereby allowing accurate quantification. The linear dynamic range is typically expressed in terms of its lower and upper concentration limits.
[0084] Although the sensor exhibits a defined linear dynamic range and limit of detection (LOD), the effective concentration range of analysis can be extended or adjusted using standard dilution techniques. In cases where the analyte concentration in a sample exceeds the upper bound of the linear range, or falls below it but remains above the LOD upon concentration, the sample can be appropriately diluted or pre-concentrated. This classical analytical approach allows the measured signal to fall within the optimal operating window of the sensor. By extrapolating the sensor’s response curve, the original concentration of the analyte in the undiluted sample can be accurately back-calculated. Such preprocessing enables adaptation of the sensor for a wider range of applications, including samples with highly variable analyte concentrations, without compromising measurement fidelity.

EXAMPLES
[0085] The present disclosure will now be described in greater detail by the
following non-limiting examples. It is understood that one skill in the art will envision additional embodiments consistent with the disclosure provided herein.
EXAMPLE 1
Fabrication of the sensor
[0086] A commercial interdigitated electrode (ED_IDE2-Pt, MicruX Technologies) was spray coated with a DPP-based polymer having structure [II], where n is 20 and m is 2 (denoted as 2OMe-2TDPP-OD-3G) to form the sensor. This polymer functions as a mixed ionic-electronic conductor (MIEC), i.e., electrochemical conductor, enabling efficient volumetric doping and strong ion-polymer interactions in aqueous environments. The spray coated interdigitated electrode had an optical absorbance of approximately ~0.4 ± 0.05 absorbance units (a.u.), corresponding to a film thickness of approximately 100 ± 10 nm. The sensor was operated in a standard three-terminal configuration, with an Ag/AgCl reference electrode serving as the gate and 0.1 M sodium perchlorate as the electrolyte.
Characterization of the sensor
[0087] The sensor’s response towards perchlorate was assessed by measuring the transfer characteristics of the sensor in the presence of different anions at identical concentrations (0.1 M). The term “transfer characteristics” as used herein refers to the relationship between the gate voltage (VG) and the drain current (ID) at a fixed drain voltage (VD). The transfer characteristics curve indicates the change in current flowing through the channel with varying gate voltage.
[0088] The different anions included halides such as chloride (Cl⁻) and fluoride (F⁻); oxyanions including nitrate (NO₃⁻) and sulfate (SO₄²⁻); and pH-sensitive species such as carbonate (CO₃²⁻) and bicarbonate (HCO₃⁻). FIG. 5 shows representative transfer characteristics curves 500 of the anions. The results revealed a pronounced and distinct sensitivity toward perchlorate (ClO₄⁻), while all other anions induced either negligible or significantly reduced current modulation in the polymer channel.
[0089] A concentration-dependent calibration was carried out using aqueous sodium perchlorate (NaClO₄) in the range of 10⁻⁶ to 10⁻² M. The sensor demonstrated a linear relationship between drain current (ID) modulation and perchlorate concentration across this range, with excellent reproducibility. FIG. 6 is a plot 600 of drain current against concentration of perchlorate ions. From the plot 600, the limit of detection (LoD) was estimated to be approximately 6 × 10⁻⁷ M, equivalent to around 60 parts per billion (ppb). This detection limit not only satisfied but surpassed the thresholds set by environmental monitoring agencies, reinforcing the sensor's utility for early-stage detection of perchlorate contamination in field-relevant conditions.
[0090] To validate the real-world applicability of the sensor, cross-interference tests were conducted to assess its specificity toward perchlorate (ClO₄⁻) in the presence of commonly encountered anions in environmental water sources. The commonly encountered anions included nitrates (NO₃⁻), sulfate (SO₄²⁻), chloride (Cl⁻), and fluoride (F⁻), selected for their prevalence in groundwater and industrial effluents. The evaluation involved both individual anion exposures under identical conditions and a mixed-ion environment simulating realistic groundwater composition.
[0091] A synthetic groundwater mimic consisting of 1 mM Cl⁻, NO₃⁻, and SO₄²⁻, along with 0.1 mM F⁻, was prepared. At this stage, carbonate (CO₃²⁻) and bicarbonate (HCO₃⁻) were intentionally excluded to avoid pH-induced alterations that could influence doping efficiency. Upon incremental spiking of ClO₄⁻ (ranging from 10⁻² to 10⁻⁶ M) into the background electrolyte, a calibration curve 700 representing drain current against concentration of perchlorate ions in mixed-ion environment was obtained as shown in FIG. 7. The resulting sensor output remained consistent and quantifiable, with a limit of detection (LoD) of ~60 ppb, closely matching the response observed in perchlorate-only environments, as shown in FIG. 6. Although a slight suppression in signal intensity and a marginal shift in threshold voltage was noted, these effects were primarily attributed to competitive ionic interactions within the mixed electrolyte. The results demonstrated that the sensor maintained both measurement accuracy and ion selectivity even in complex sample environments, indicating its suitability for real-world applications such as on-site detection of perchlorate ions in contaminated water sources.
[0092] A response time of the sensor at various concentrations of perchlorate ions in the sample was measured. The gate-source voltage (VG) was pulsed from 0 V to -0.6 V, keeping the drain-source voltage (VD) constant at -0.4 V. The current (I) versus time (t) plots (800) were then fitted using a monoexponential decay equation to estimate the response time of the sensor, as shown in FIG. 8. The pulsing duration was 6 seconds (s) for perchlorate concentrations of 0.1 mM, 1 mM, and 10 mM, while for 100 mM perchlorate concentration it was 3 s. Table 1 shows the response time of the sensor at varying concentrations of perchlorate ions.

Concentration (mM) Response Time (s)
0.1 4.04
1 3.27
10 0.88
100 0.51
Table 1
[0093] Response times of the sensor with varying perchlorate concentrations in the presence of interfering anions (1mM Cl-, NO3-, SO42- and 0.1mM F-) were measured. The interfering ions (IA) were taken at a concentration of 1 millimolar (mM) of chloride ions, 1 mM of nitrate ions, 1 mM of sulphate ions, and 0.1 mM of fluoride ions. The gate-source voltage (VG) was pulsed from 0V to -0.6V, keeping the drain-source voltage (VD) constant at -0.4V. The current (I) versus time (t) plots 900 were then fitted using a monoexponential decay equation to estimate the response time of the sensor, as shown in FIG. 9. The pulsing duration was 6 seconds (s) for perchlorate concentrations of 0.1 mM, 1 mM, and 10 mM, while for 100 mM perchlorate concentration it was 3 s. Table 2 shows the response time of the sensor at varying concentrations of perchlorate ions.
Concentration (mM) Response Time (s)
0.1 7.91
1 3.91
10 1.33
100 0.68
Table 2
[0094] FIG. 10 is a comparative bar chart 1000 of response times of various anions versus perchlorate ions. In bar chart 1000, IA refers to an interfering ion sample containing anions at a concentration of 1 millimolar (mM) of chloride ions, 1 mM of nitrate ions, 1 mM of sulphate ions, and 0.1 mM of fluoride ions. The fluoride (F⁻), chloride (Cl⁻), sulphate (SO₄²⁻), and nitrate (NO₃⁻) ions showed negligible response even at 100 mM concentrations. However, in the presence of ClO₄⁻, the sensor activates, demonstrating selective detection even in the presence of interfering ions underlining the selectivity and specificity of DPP-based polymer.
[0095] The characterization studies conclusively demonstrated that the sensor comprising the DPP-based polymer exhibited a clear preference for perchlorate uptake over other competing anions. The selectivity of the inventive sensor is believed to arise from a favorable ion–polymer interaction energetics, volumetric doping dynamics, and a redox potential window finely tuned to facilitate ClO₄⁻ interactions. The term “volumetric doping dynamics” refer to an ion-mediated modulation of the electrochemical state of the channel material throughout its entire bulk volume, enabling efficient and reversible changes in electrical conductivity in response to an applied gate potential. The term “redox potential window” refers to the operational voltage range within which the channel material undergoes reversible electrochemical transitions between doped and de-doped states, without undergoing irreversible chemical degradation or inducing parasitic reactions in the electrolyte. The term “parasitic reaction” as used herein refers to unwanted side electrochemical reactions that occur at electrodes or within the electrolyte that are not part of the intended sensing mechanism. When tested independently (FIG. 10), electrolytes containing Cl⁻, NO₃⁻, SO₄²⁻, or F⁻ induced negligible changes in the drain current, indicating minimal polymer interaction and no significant electrochemical response. In stark contrast, when the electrolyte was spiked with perchlorate, it resulted in a pronounced modulation of the channel conductivity, confirming strong and selective polymer doping.
[0096] It is to be understood that the above description is intended to be illustrative, and not restrictive. Furthermore, many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. Although the present disclosure has been described with reference to specific exemplary embodiments, it will be recognized that the disclosure is not limited to the embodiments described, but can be practiced with modification and alteration within the scope of the appended claims.
, Claims:CLAIMS
I/We claim,
1. An electrode assembly (100) for a sensor for determining perchlorate ions in a sample, the electrode assembly comprising:
a source electrode (102) and a drain electrode (104) disposed on a substrate;
an electrochemically active layer (108) defining a channel (114) between the source electrode (102) and the drain electrode (104), wherein the channel (114) is in electrical communication with the source electrode (102) and the drain electrode (104), and wherein the electrochemically active layer (108) comprises a diketopyrrolopyrrole-based polymer having a general structure [I],

[I]

wherein, R1 and R2 are independently selected from hydrogen, C₁–C₁₂ alkoxy groups, halogen, cyano, amino groups, C₁–C₁₂ alkyl groups, C2–C₁₂ alkenyl groups, C2–C₁₂ alkynyl groups, C₁–C₁₂ haloalkyl groups, C3–C₁₂ cycloalkyl groups, C6–C₁₂ aryl groups, C2–C₁₂ heterocyclyl groups, and C3–C₁₂ heteroaryl groups, provided that, at least one of R1 and R2 is C₁–C₁₂ alkoxy groups; R3 is selected from linear or branched C4-C30 alkyl groups, C4-C30 cycloalkyl-substituted alkyl groups, C4-C30 aralkyl-substituted alkyl groups, C4-C30 fluorinated alkyl groups, and C8-C20 branched fluoroalkyl-substituted alkyl groups; and R4 is –(R’-O)m-R”, wherein, R’ is selected from C₂–C₄ alkylene groups, optionally substituted with alkyl, halo, or hydroxyl groups; and R” is selected from hydrogen, C₁–C₆ alkyl groups, C₁–C₆ alkoxy groups, carboxylic acid (–COOH) group, sulfonic acid (–SO₃H) group, phosphonic acid (–PO₃H₂) group, quaternary ammonium groups (–N⁺R₃), imidazolium cations, zwitterionic groups, and cleavable hydrophilic moieties; m is in a range of 1 to 10; and n is in a range of 15 to 30;
an electrolyte well (110) comprising the sample, and in electrochemical communication with the channel (114) of the electrochemically active layer (108); and
a gate electrode (106) in electrochemical communication with the sample in the electrolyte well (110), wherein upon application of a voltage between the source electrode (102) and the drain electrode (104), and between the gate electrode (106) and the source electrode (102) an electrical signal that correlates to a presence of perchlorate ions in the sample, or concentration of perchlorate ions in the sample, or both is generated.

2. The electrode assembly (100) as claimed in claim 1, wherein R1 and R2 of the diketopyrrolopyrrole-based polymer are independently selected from hydrogen, or C₁–C6 alkoxy groups, provided that, at least one of R1 and R2 is C₁–C6 alkoxy groups, wherein R3 is C12-C25 alkyl groups and R4 is –(R’-O)m-R”, wherein, R’ is selected from C₂–C₄ alkylene groups, optionally substituted with alkyl, halo, or hydroxyl groups; and R” is selected from hydrogen, C₁–C₆ alkyl groups, C₁–C₆ alkoxy groups, carboxylic acid (–COOH) group, sulfonic acid (–SO₃H) group, phosphonic acid (–PO₃H₂) group, quaternary ammonium groups (–N⁺R₃), imidazolium cations, zwitterionic groups, and cleavable hydrophilic moieties; m is in a range of 1 to 10; and n is in a range of 15 to 30.

3. The electrode assembly (100) as claimed in claim 1, wherein the diketopyrrolopyrrole-based polymer has a structure [II],

[II]

where, m is in a range of 2 to 5; and n is in a range of 20 to 25.

4. The electrode assembly (100) as claimed in claim 1, wherein the substrate comprises polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide, polydimethylsiloxane (PDMS), polyethylene, polypropylene, polycarbonate, mica, glass, silicon, paper, coated paper, resin-coated paper, paper laminates, paperboard, corrugated board, or combinations thereof.

5. The electrode assembly (100) as claimed in claim 1, wherein the channel (114) has a channel architecture comprising lateral configuration, vertical configuration, or interdigitated configuration.

6. The electrode assembly (100) as claimed in claim 1, wherein the electrolyte well (110) is configured to receive the sample.

7. The electrode assembly (100) as claimed in claim 1, wherein the electrical signal comprises one or more of drain current (ID), gate voltage (VG), drain voltage (VD), or impedance (Z).

8. The electrode assembly (100) as claimed in claim 1, wherein the voltage is applied through a power source.

9. A method (200) of fabricating an electrode assembly for a sensor for detecting perchlorate ions in a sample, the method comprising:
providing a source electrode and a drain electrode on a substrate (210);
forming an electrochemically active layer to define a channel between the source electrode and the drain electrode (220), wherein the channel is in electrical communication with the source electrode and the drain electrode, and wherein the electrochemically active layer comprises a diketopyrrolopyrrole-based polymer having a general structure [I],

[I]
wherein, R1 and R2 are independently selected from hydrogen, C₁–C₁₂ alkoxy groups, halogen, cyano, amino groups, C₁–C₁₂ alkyl groups, C2–C₁₂ alkenyl groups, C2–C₁₂ alkynyl groups, C₁–C₁₂ haloalkyl groups, C3–C₁₂ cycloalkyl groups, C6–C₁₂ aryl groups, C2–C₁₂ heterocyclyl groups, and C3–C₁₂ heteroaryl groups, provided that, at least one of R1 and R2 is C₁–C₁₂ alkoxy groups; R3 is independently selected from linear or branched C4-C30 alkyl groups, C4-C30 cycloalkyl-substituted alkyl groups, C4-C30 aralkyl-substituted alkyl groups, C4-C30 fluorinated alkyl groups, and C8-C20 branched fluoroalkyl-substituted alkyl groups; and R4 is –(R’-O)m-R”, wherein, R’ is selected from C₂–C₄ alkylene groups, optionally substituted with alkyl, halo, or hydroxyl groups; and R” is selected from hydrogen, C₁–C₆ alkyl groups; C₁–C₆ alkoxy groups, carboxylic acid (–COOH) group, sulfonic acid (–SO₃H) group, phosphonic acid (–PO₃H₂) group, quaternary ammonium groups (–N⁺R₃), imidazolium cations, zwitterionic groups, and cleavable hydrophilic moieties; m is in a range of 1 to 10; and n is in a range of 15 to 30;
providing an electrolyte well (230) on the electrochemically active layer, wherein the electrolyte well is configured to receive, or comprises, the sample; and
positioning a gate electrode in electrochemical communication with the sample in the electrolyte well (240).

10. The method (200) as claimed in claim 9, wherein forming the electrochemically active layer (220) comprises depositing a solution comprising the diketopyrrolopyrrole-based polymer by a technique comprising spin coating, microgravure coating, gravure coating, bar coating, roll coating, wire bar coating, slot-die coating, dip coating, spray coating, screen printing, flexo printing, micro-contact printing, inkjet printing, offset printing, blade coating or combinations thereof.

11. A sensor (300) for determining perchlorate ions in a sample comprising:
a source electrode (102) and a drain electrode (104) disposed on a substrate;
an electrochemically active layer (108) defining a channel (114) between the source electrode (102) and the drain electrode (104), wherein the channel (114) is in electrical communication with the source electrode (102) and the drain electrode (104), and wherein the electrochemically active layer (108) comprises a diketopyrrolopyrrole-based polymer having a general structure [I],

[I]
wherein, R1 and R2 are independently selected from hydrogen, C₁–C₁₂ alkoxy groups, halogen, cyano, amino groups, C₁–C₁₂ alkyl groups, C2–C₁₂ alkenyl groups, C2–C₁₂ alkynyl groups, C₁–C₁₂ haloalkyl groups, C3–C₁₂ cycloalkyl groups, C6–C₁₂ aryl groups, C2–C₁₂ heterocyclyl groups, and C3–C₁₂ heteroaryl groups, provided that, at least one of R1 and R2 is C₁–C₁₂ alkoxy groups; R3 is independently selected from linear or branched C4-C30 alkyl groups, C4-C30 cycloalkyl-substituted alkyl groups, C4-C30 aralkyl-substituted alkyl groups, C4-C30 fluorinated alkyl groups, and C8-C20 branched fluoroalkyl-substituted alkyl groups; and R4 is –(R’-O)m-R”, wherein, R’ is selected from C₂–C₄ alkylene groups, optionally substituted with alkyl, halo, or hydroxyl groups; and R” is selected from hydrogen, C₁–C₆ alkyl groups, C₁–C₆ alkoxy groups, carboxylic acid (–COOH) group, sulfonic acid (–SO₃H) group, phosphonic acid (–PO₃H₂) group, quaternary ammonium groups (–N⁺R₃), imidazolium cations, zwitterionic groups, and cleavable hydrophilic moieties; m is in a range of 1 to 10; and n is in a range of 15 to 30;
an electrolyte well (110) configured to receive, or comprising the sample, wherein the sample is in electrochemical communication with the channel (114) of the electrochemically active layer (108);
a gate electrode (106) in electrochemical communication with the sample in the electrolyte well (110);
a power source (310) to apply a voltage between the source electrode (102) and the drain electrode (104), and between the gate electrode (106) and the source electrode (102); and
a processing unit (320) configured to measure an electrical signal generated upon application of the voltage and correlate the electrical signal to a presence of perchlorate ions in the sample, or concentration of perchlorate ions in the sample, or both.

12. The sensor (300) as claimed in claim 11, wherein the processing unit (320) comprises a smartphone, a handheld reader, a microcontroller-based circuit, or combinations thereof.

13. The sensor (300) as claimed in claim 11, wherein the sensor (300) exhibits a linear dynamic range for perchlorate ion concentrations from 1 µM to 100 mM.

14. The sensor (300) as claimed in claim 11, wherein the sensor (300) has a limit of detection for perchlorate ions of 6 × 10⁻⁷ M.

15. The sensor (300) as claimed in claim 11, wherein the channel (114) has a channel architecture comprising lateral configuration, vertical configuration, or interdigitated configuration.

16. The sensor (300) as claimed in claim 11, wherein the electrical signal comprises one or more of drain current (ID), gate voltage (VG), drain voltage (VD), or impedance (Z).

17. The sensor (300) as claimed in claim 11, wherein the sensor (300) is operable in one or more modes comprising potentiometric, amperometric, or impedimetric.

18. The sensor (300) as claimed in claim 11, wherein the diketopyrrolopyrrole-based polymer has a structure [II],

[II]

where, m is in a range of 2 to 5; and n is in a range of 20 to 25.

19. The sensor (300) as claimed in claim 11, wherein the sensor (300) comprises a communication interface (330), wherein the communication interface (330) is configured to, receive user inputs to control the power source (310), communicate with the processing unit (320) to configure or monitor the electrical signal being measured, display a result from the processing unit (320), or any combination thereof.

20. The sensor (300) as claimed in claim 19, wherein the communication interface (330) comprises a software application or a visual indicator.

21. The sensor (300) as claimed in claim 19, further comprising a pre-screening assay configured to indicate the presence of perchlorate ions in the sample, wherein the pre-screening assay is selected from a colorimetric method or a chemical precipitation technique.

22. A method (400) for determining perchlorate ions in a sample, the method comprising:
providing an electrode assembly (402) as claimed in claim 1;
applying a voltage between the gate electrode and the source electrode, and between the source electrode and the drain electrode (404);
measuring an electrical signal generated on application of the voltage (406); and
correlating a measured electrical signal to a presence of perchlorate ions in the sample, or concentration of perchlorate ions in the sample, or both (408).