A field-effect transistor sensor based on titanium carbide MXene / MIP, its fabrication method and application

Abstract

This invention discloses a field-effect transistor sensor based on titanium carbide MXene / MIP, its fabrication method, and its application, belonging to the field of chemical sensor technology. The sensor includes a substrate, a transistor, and a sensing electrode. The sensing electrode is connected to the transistor gate via a wire, and its surface is sequentially modified with a titanium carbide MXene layer and a molecularly imprinted polymer layer targeting perfluorooctanoic acid (PFOA). The fabrication method includes: preparing an MXene dispersion by etching using a LiF / HCl system, drop-coating it onto a conductive substrate, electropolymerizing it using PFOA as a template to form a MIP layer, and finally assembling it with the transistor. This invention utilizes the high conductivity of MXene and the specific recognition capability of MIP to convert the interfacial potential change caused by PFOA binding into a significant drain current change through a solution gate control mechanism. This sensor is simple to fabricate, low in cost, and has good stability, enabling highly sensitive and specific detection of trace amounts of PFOA in aqueous solutions, and is suitable for on-site environmental monitoring.

Description

Technical Field

[0001] This invention relates to the field of chemical sensors, specifically to a field-effect transistor sensor based on titanium carbide MXene / MIP, its fabrication method, and its application. Background Technology

[0002] Perfluorooctanoic acid (PFOA) and its salts are among the most prominent representatives of the perfluorinated and polyfluoroalkyl substances (PFAS) family. Their unique carbon-fluorine bond structure exhibits extremely strong chemical and thermal stability, as well as excellent hydrophobic and oleophobic properties. These properties have led to their widespread application in various fields of industrial production and daily life over the past few decades, including as a key processing aid in the production of fluoropolymers such as polytetrafluoroethylene (PTFE), and in the manufacture of non-stick cookware coatings, waterproof and breathable textiles, greaseproof paper packaging, leather protectants, floor waxes, and aqueous film-forming fire-fighting foams. However, it is precisely this chemical stability that makes PFOA extremely difficult to degrade in the natural environment through hydrolysis, photolysis, or biodegradation. Once PFOA enters the environment, it persists in the atmosphere, water bodies, soil, and sediments for extended periods, accumulating through the food chain and ultimately reaching humans and wild animals. Studies have shown that PFOA possesses significant biotoxicity, including potential carcinogenicity, reproductive and developmental toxicity, immunosuppressive effects, and liver and kidney damage, posing a serious threat to ecological security and human health. Given its persistence, bioaccumulation, long-distance migration ability and high toxicity, PFOA is recognized by the international community as a typical "new pollutant".

[0003] Currently, the detection of PFOA in environmental water bodies mainly relies on large-scale instrumental analytical techniques such as liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS). While these traditional methods offer high detection accuracy and qualitative precision, they suffer from significant drawbacks, including large and expensive equipment, complex and cumbersome sample preparation processes, long detection cycles, and heavy dependence on specialized laboratory environments. Especially in field environments such as aquaculture water bodies and surface water, where sample matrices are complex and variable, traditional methods struggle to achieve in-situ, real-time, and continuous monitoring, failing to meet the demands for rapid response to sudden pollution events and large-scale screening applications. Therefore, the development of new PFOA detection technologies that are easy to operate, have a rapid response time, are cost-effective, and suitable for field deployment is urgently needed.

[0004] Field-effect transistor (FET) sensors are considered ideal platforms for next-generation environmental monitoring due to their advantages such as high sensitivity, fast response, ease of miniaturization, and direct signal readout. FET sensors modulate channel current through the interaction between the target and the sensing interface, converting chemical signals into electrical signals. Their detection performance largely depends on the physicochemical reactions at the sensing interface. However, PFOA molecules are stable and often coexist with a large number of ions and organic matter in water bodies. Traditional FET sensors often lack specific recognition capabilities and are susceptible to interference, resulting in false positive signals. Meanwhile, existing high-performance FET sensors mostly rely on complex micro-nano fabrication processes, which are costly and hinder large-scale application. Summary of the Invention

[0005] This invention aims to address the technical challenges of existing perfluorooctanoic acid (PFOA) detection technologies, which rely on large instruments for real-time on-site monitoring, suffer from insufficient sensitivity and stability of commonly used sensing materials, exhibit poor specificity in complex water bodies, and face high costs for micro / nano fabrication, hindering widespread adoption. This invention provides a field-effect transistor sensor based on titanium carbide MXene / MIP, along with its fabrication method and applications. The sensing electrode surface is sequentially modified with a titanium carbide MXene layer and a molecularly imprinted polymer (MIP) layer specific to PFOA. Utilizing the high conductivity of MXene and the specific recognition capability of MIP, the interfacial potential change caused by PFOA binding is converted into a significant drain current change through a solution gate control mechanism. This sensor is simple to fabricate, low in cost, and exhibits good stability, enabling highly sensitive and specific detection of trace PFOA in aqueous solutions, making it suitable for on-site environmental monitoring.

[0006] The first aspect of the present invention provides a field-effect transistor sensor based on titanium carbide MXene / MIP.

[0007] This includes the substrate, transistors, and sensing electrodes.

[0008] The transistor is disposed on a substrate and includes a source, a drain, and a gate.

[0009] The sensing electrode is electrically connected to the transistor. The sensing electrode includes a conductive substrate, a titanium carbide MXene layer modified on the surface of the conductive substrate, and a molecularly imprinted polymer (MIP) layer modified on the surface of the titanium carbide MXene layer.

[0010] The molecularly imprinted polymer layer has a specific recognition cavity for perfluorooctanoic acid (PFOA).

[0011] Furthermore, the sensing electrode is electrically connected to the transistor via a metal wire, with one end of the metal wire connected to a pin of the transistor gate and the other end connected to the conductive substrate of the sensing electrode.

[0012] Furthermore, the conductive substrate is indium tin oxide conductive glass (ITO); the titanium carbide MXene layer is formed by dropping and drying MXene dispersion; and the molecularly imprinted polymer layer is formed by polymerizing functional monomers using a template molecule-induced electropolymerization method.

[0013] Furthermore, the functional monomer is o-phenylenediamine, and the template molecule is perfluorooctanoic acid; the molar ratio of the template molecule to the functional monomer in the molecularly imprinted polymer layer is 1:5-1:15.

[0014] A second aspect of this invention provides a method for fabricating a field-effect transistor sensor based on titanium carbide MXene / MIP, comprising the following steps: Step S1: Prepare titanium carbide MXene dispersion.

[0015] Step S2: Load the titanium carbide MXene dispersion described in step S1 onto the surface of a conductive substrate and dry it to form a titanium carbide MXene layer.

[0016] Step S3: Electropolymerize the surface of the titanium carbide MXene layer to synthesize a molecularly imprinted polymer layer for perfluorooctanoic acid, thereby obtaining the sensing electrode.

[0017] Step S4: Connect the sensing electrode to the gate of the transistor to assemble the field-effect transistor sensor based on titanium carbide MXene / MIP.

[0018] Furthermore, in step S1, the titanium carbide MXene dispersion is prepared by using a mixed solution of lithium fluoride and hydrochloric acid as an etchant to etch Ti3AlC2 powder. After the reaction is completed, the upper dispersion is collected by centrifugation and washing. The molar ratio of LiF to HCl in the etchant is 1:3-4:3, and the etching time is 12-48 hours.

[0019] Furthermore, in step S3, the specific process of the electropolymerization synthesis is as follows: A polymerization solution containing functional monomers, template molecules, and supporting electrolytes was prepared. A conductive substrate loaded with a titanium carbide MXene layer was immersed in the polymerization solution as the working electrode. An Ag / AgCl electrode was used as the reference electrode, and a platinum wire electrode was used as the counter electrode. Cyclic voltammetry was used for scanning polymerization.

[0020] Furthermore, the functional monomer is o-phenylenediamine (oPD), the template molecule is perfluorooctanoic acid, and the molar ratio is 5:1-15:1; the supporting electrolyte is acetate buffer, with a pH of 5-6.

[0021] The cyclic voltammetry method has 5-15 scan cycles, a scan rate of 50 mV / s, and a potential range of 0 V to +1 V.

[0022] A third aspect of the present invention provides an application of a titanium carbide MXene / MIP-based field-effect transistor sensor in the detection of perfluorooctanoic acid in aqueous solution.

[0023] The detection methods include: A. The sensing electrode of the titanium carbide MXene / MIP-based field-effect transistor sensor is immersed in the aqueous solution to be tested, so that the perfluorooctanoic acid molecules in the aqueous solution to be tested bind to the specific recognition cavity of the molecularly imprinted polymer layer, wherein the detection concentration range of perfluorooctanoic acid in the aqueous solution to be tested is 121 pM-2420 pM.

[0024] B. Record the changes in the sensor's electrical signal, and quantitatively analyze the concentration of perfluorooctanoic acid in the aqueous solution based on the amount of change in the electrical signal.

[0025] The beneficial effects of this invention are as follows: 1. This invention utilizes titanium carbide (Ti3C2T) x The excellent metallic conductivity and unique two-dimensional layered structure of MXene material significantly improve the charge transport efficiency of field-effect transistors. The high specific surface area and abundant surface functional groups of MXene not only reduce the internal noise of the device but also greatly increase the effective sensing area. Combined with the inherent high transconductance characteristics and signal amplification mechanism of the field-effect transistor structure, weak interfacial potential changes can be converted into significant drain current changes, thereby achieving highly sensitive detection of trace PFOA and solving the problem of traditional sensors' inability to detect extremely low concentrations of new pollutants.

[0026] 2. To address the challenges posed by complex matrices such as aquaculture water bodies containing numerous coexisting ions and organic matter, this invention introduces a PFOA-specific MIP layer at the sensing interface. Through electrochemical polymerization using PFOA as a template molecule and o-phenylenediamine as a functional monomer, a structure with specific three-dimensional cavities and recognition sites is constructed on the MXene surface. This specific recognition mechanism ensures that the sensor responds only to PFOA molecules, effectively eliminating interference from structural analogs and other environmental factors, significantly improving the accuracy and reliability of detection.

[0027] 3. Thanks to the specific surface area of ​​MXene, it can immobilize more specific recognition sites as a loading substrate for MIPs. Compared with traditional materials such as graphene, MXene significantly improves the sensor's binding capacity for target molecules. When a large number of PFOA molecules are captured simultaneously, the resulting change in the interfacial electric double layer potential is more significant, thereby further amplifying the sensor's response signal.

[0028] 4. The titanium carbide MXene selected in this invention exhibits excellent chemical stability in an aqueous environment, overcoming the instability of materials such as black phosphorus in water. Simultaneously, the MIP layer, synthesized in situ via electrochemical methods, bonds firmly to the MXene / ITO substrate and is not easily detached. This enables the sensor to maintain stable performance in actual water sample detection, making it suitable for long-term monitoring or repeated use, thus meeting the durability requirements of environmental monitoring devices.

[0029] 5. This invention avoids the problem of traditional high-performance sensors relying on expensive photolithography equipment and complex micro / nano fabrication processes. It employs an improved MILD etching method to prepare MXene, avoiding the direct use of hazardous hydrofluoric acid, resulting in safer operation and higher product quality. Sensors can be constructed simply by connecting sensing electrodes with wires, eliminating the need for customized semiconductor production lines. The drop-coating drying and MIP electropolymerization steps for MXene are few, time-consuming, and low-cost. This modular design significantly lowers the manufacturing threshold and cost, facilitating mass production and widespread application of sensors.

[0030] 6. This invention is based on the working principle of FET. The change in electrical signal caused by the binding of the target molecule to the MIP is instantaneous, eliminating the need for complex labeling or lengthy incubation and color development processes. Combined with a portable digital source meter, the entire detection system is small in size, low in power consumption, and easy to operate. It can be easily carried to farms, rivers, and other locations for in-situ, real-time detection, solving the problem that existing large instruments cannot operate outside of laboratory environments. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the field-effect transistor sensor based on titanium carbide MXene / MIP in Example 1.

[0032] Figure 2 This is a graph showing the transfer curves of PFOA aqueous solutions at different concentrations in Example 2.

[0033] In the figure: 1. Substrate; 2. Source; 3. Drain; 4. Gate; 5. Conductive substrate; 6. Titanium carbide MXene layer; 7. Molecularly imprinted polymer layer; 8. Conductor. Detailed Implementation

[0034] The following specific embodiments further illustrate the technical solution and effects of the present invention. These embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Simple modifications made to the present invention based on the concept of the present invention are all within the scope of protection claimed by the present invention.

[0035] The equipment used in the preparation method of this invention can all be equipment known in the art. Unless otherwise specified, all raw materials used in this invention are commercially available.

[0036] The first aspect of the present invention provides a field-effect transistor sensor based on titanium carbide MXene / MIP.

[0037] Includes substrate 1, transistors, and sensing electrodes; The transistor is disposed on the substrate 1, and the transistor includes a source 2, a drain 3 and a gate 4; The sensing electrode is electrically connected to the transistor. The sensing electrode includes a conductive substrate 5, a titanium carbide MXene layer 6 modified on the surface of the conductive substrate 5, and a molecularly imprinted polymer layer 7 modified on the surface of the titanium carbide MXene layer 6. The molecularly imprinted polymer layer 7 has a specific recognition cavity for perfluorooctanoic acid (PFOA).

[0038] This invention physically separates the signal amplification unit (transistor) from the signal sensing unit (sensing electrode). The transistor processes the electrical signal, while the sensing electrode specifically captures the target substance in a liquid environment. The transistor itself does not directly contact corrosive or complex water samples; it is connected only by wire 8, significantly improving the device's lifespan and stability. The conductive substrate 5 is modified with MXene / MIP; this layered structure ensures efficient transmission from chemical bonding to electrical signal output. Furthermore, the modular design offers high flexibility, allowing for independent optimization of the sensing electrode material without redesigning the transistor circuitry, facilitating rapid adaptation to different contaminants.

[0039] The sensing electrode and the transistor are electrically connected via a metal wire 8. One end of the metal wire 8 is connected to a pin of the transistor gate 4, and the other end is connected to the conductive substrate 5 of the sensing electrode. The potential change of the sensing electrode is directly coupled to the transistor gate 4 using the wire 8. The metal wire 8 has extremely low resistance, ensuring that weak potential changes generated at the interface can be transmitted to the gate 4 with almost no loss. This avoids complex microfluidic integration or expensive waterproof packaging of the transistor chip, reducing manufacturing costs.

[0040] The conductive substrate 5 is indium tin oxide (ITO) conductive glass; the titanium carbide MXene layer 6 is formed by drop-drying an MXene dispersion. The ITO substrate serves as an adhesion platform for MXene and also as the working electrode for electrochemical polymerization, providing a smooth, transparent, and highly conductive surface. The MXene layer acts as a high-speed channel for electron transport, reducing the electrode's internal resistance. Its two-dimensional layered structure provides a considerable loading area, enhancing the adhesion of the MIP layer. The high carrier mobility of MXene reduces thermal noise and improves the signal-to-noise ratio. Compared to traditional gold or carbon paste electrodes, MXene can load more MIP recognition sites, significantly increasing the binding capacity and thus amplifying the response signal. The drop-coating process used in this invention is simple, requires no expensive equipment such as vacuum deposition, and is suitable for large-scale production.

[0041] Molecularly imprinted polymer layer 7 is formed by the polymerization of functional monomers using a template-induced electropolymerization method. The functional monomer is o-phenylenediamine, and the template molecule is perfluorooctanoic acid (PFOA); the molar ratio of template molecule to functional monomer in molecularly imprinted polymer layer 7 is 1:5. Using PFOA as a template and o-phenylenediamine as a monomer, the template is eluted after polymerization, leaving a cavity whose shape, size, and functional group positions are completely complementary to those of the PFOA molecule. The poly(o-phenylenediamine) film formed by oPD electropolymerization is dense and has good electrochemical activity, remaining stable at neutral pH. It can effectively distinguish PFOA from its structural analogs, solving interference problems in complex water bodies. Compared with antibodies or aptamers, MIP has lower synthesis costs, is resistant to high temperatures and acids / alkalis, and has a long shelf life.

[0042] A second aspect of this invention provides a method for fabricating a field-effect transistor sensor based on titanium carbide MXene / MIP, comprising the following steps: Step S1: Preparation of titanium carbide MXene dispersion. The aluminum layer in Ti3AlC2 is removed by chemical etching to obtain a two-dimensional layered Ti3C2T. x This yielded MXene materials with high conductivity, hydrophilicity, and abundant surface functional groups, providing a high-quality base material for the subsequent construction of high-performance sensing interfaces.

[0043] Step S2: Load the titanium carbide MXene dispersion from step S1 onto the surface of the conductive substrate 5 and dry it to form a titanium carbide MXene layer 6. Solvent evaporation induces the self-assembly and stacking of MXene nanosheets on the ITO surface, forming a continuous conductive film. This method is simple, produces uniform films, and significantly increases the effective specific surface area of ​​the electrode, providing a favorable foundation for the growth of the MIP layer and thus increasing the number of recognition sites per unit area.

[0044] Step S3: Electropolymerization is performed on the surface of the titanium carbide MXene layer 6 to synthesize a molecularly imprinted polymer layer 7 for perfluorooctanoic acid (PFOA), thus obtaining the sensing electrode. Using MXene / ITO as the working electrode, a voltage is applied in an electrolyte containing template molecules to initiate monomer polymerization, locking the template molecules within the polymer network. This achieves in-situ tight bonding between the MIP layer and the MXene layer, resulting in low interfacial contact resistance. Furthermore, the film thickness and porosity can be precisely controlled through electrochemical parameters, optimizing mass transfer efficiency.

[0045] Step S4: Electrically connect the sensing electrode to the gate 4 of the transistor to assemble a field-effect transistor sensor based on titanium carbide MXene / MIP. This completes the physical connection of the link. The assembly process is simple and quick, requiring no complex photolithography or micro / nano fabrication processes, greatly reducing the manufacturing threshold and facilitating rapid field deployment.

[0046] In step S1, the titanium carbide MXene dispersion was prepared by etching Ti3AlC2 powder with a mixed solution of lithium fluoride and hydrochloric acid as the etchant. After the reaction, the upper dispersion was collected by centrifugation and washing. The molar ratio of LiF to HCl in the etchant was 2:3-4:3, and the etching time was 12-48 hours. The in-situ generation of low-concentration hydrofluoric acid from LiF and HCl was used for gentle etching, which thoroughly removed the Al layer while preserving the integrity of the Ti3C2 framework. This avoided the direct use of highly hazardous concentrated hydrofluoric acid, making the experimental operation safer and the waste liquid treatment more environmentally friendly. The prepared MXene sheets had fewer defects, larger lateral dimensions, excellent conductivity, and abundant surface functional groups, which is beneficial for the subsequent strong bonding of MIPs.

[0047] In step S3, the specific process of electropolymerization synthesis is as follows: A polymerization solution containing functional monomers, template molecules, and supporting electrolytes was prepared. A conductive substrate 5 loaded with a titanium carbide MXene layer 6 was immersed in the polymerization solution as the working electrode. An Ag / AgCl electrode was used as the reference electrode, and a platinum wire electrode was used as the counter electrode. Cyclic voltammetry was employed for scanning polymerization. This process constructed a three-electrode electrochemical system. Cyclic voltammetry was used to control the redox state of the monomers by periodically scanning the potential, causing them to undergo free radical polymerization on the electrode surface. Cyclic voltammetry not only initiates polymerization but also removes unbound loose monomers during the scanning process, resulting in a denser and more uniform MIP film.

[0048] The functional monomer is o-phenylenediamine, and the template molecule is PFOA, with a molar ratio of 5:1 to 15:1. The supporting electrolyte is acetate buffer with a pH of 5-6. The acetate buffer environment at pH 5-6 is conducive to the protonation and oxidative polymerization of o-phenylenediamine, while keeping the PFOA molecule in a dissociated state, which is beneficial for its electrostatic interaction with the monomer, thereby forming a stable pre-aggregate. This ensures that the cavity left after elution has optimal shape memory and binding capacity, significantly improving the selectivity of the sensor.

[0049] The cyclic voltammetry scan consists of 5-15 cycles at a scan rate of 50 mV / s, with a potential range of 0 V to +1 V. This step ensures the sensor's rapid response characteristics in practical applications, preventing PFOA diffusion from being hindered by an excessively thick film or insufficient recognition sites from being too thin.

[0050] A third aspect of the present invention provides an application of a titanium carbide MXene / MIP-based field-effect transistor sensor in the detection of perfluorooctanoic acid in aqueous solution.

[0051] The detection methods include: A. The sensing electrode of the titanium carbide MXene / MIP-based field-effect transistor sensor is immersed in the aqueous solution to be tested, so that the perfluorooctanoic acid molecules in the aqueous solution to be tested bind to the specific recognition cavity of the molecularly imprinted polymer layer 7. The detection concentration range of perfluorooctanoic acid in the aqueous solution to be tested is 121 pM to 2420 pM.

[0052] B. Record the changes in the sensor's electrical signal, and quantitatively analyze the concentration of perfluorooctanoic acid in the aqueous solution based on the amount of change in the electrical signal.

[0053] The sensor is suitable for detecting water samples in conjunction with an external reference electrode. In detection mode, both the sensing electrode and the reference electrode are immersed in the aqueous solution, with the reference electrode connected to the digital source meter port. The sensor's working mechanism is based on the potential modulation principle of a field-effect transistor. First, a transfer curve is obtained using a digital source meter scan to characterize the effect of the transistor gate voltage on the drain current (Id). ds The sensor's modulation characteristics and transconductance properties were assessed. At the start of detection, the sensing electrode modified with the MXene / MIP composite layer was immersed in a blank buffer solution (0.02×PBS, pH 7.4) to establish a baseline state. At this point, the MIP recognition cavity was in an unbound state, and a stable double-layer potential was formed at the interface between the conductive substrate 5 and the solution. This potential was coupled to the transistor gate 4 through the wire 8, establishing the sensor's initial operating point and reference drain current (I0). ds，0 When a PFOA-containing sample is introduced into the system, PFOA molecules diffuse and embed themselves specifically within the three-dimensional imprinted cavity due to the specific recognition function of the MIP layer. This binding process alters the local dielectric constant and surface charge distribution of the MIP film, thereby perturbing the double-layer structure at the interface between the conductive substrate 5 and the solution, inducing a shift (Δφ) in the interfacial potential. This slight potential change Δφ is transmitted losslessly to the transistor gate 4 via the wire 8, equivalent to a modulation signal of the gate voltage; amplified by the high transconductance characteristics of the FET, the small Δφ is converted into a significant change in channel current (ΔI). ds Finally, by monitoring ΔI ds By adjusting the amplitude, highly sensitive quantitative detection of PFOA concentration can be achieved. Example

[0054] The fabrication method of the field-effect transistor sensor based on titanium carbide MXene / MIP is as follows: S1. Synthesis and preparation of titanium carbide MXene material: A modified MILD method was used. 37wt% HCl was diluted to 9MHCl, and 10 mL of the solution was placed in a polytetrafluoroethylene (PTFE) plastic beaker. Then, 0.8 g of LiF powder was added, and the mixture was magnetically stirred for five minutes to ensure complete dissolution, forming a 3M LiF / 9M HCl etching solution. Subsequently, 0.5 g of Ti3AlC2 powder was slowly added to the etching solution over 5 minutes while continuously stirring. The reaction was allowed to proceed at room temperature for 24 hours. After etching, the resulting reaction mixture was transferred to a 50 mL centrifuge tube and diluted with deionized water. The centrifugation speed was set to 3500 rpm, and the centrifugation time was 5 minutes. After seven centrifugations, the supernatant pH was >5 and it appeared dark green, indicating that MXene had begun to peel off. Ti3C2-rich Ti3AlC2T was collected. x The supernatant of MXene was further centrifuged at 3500 rpm for 1 h to obtain Ti3C2T. x MXene dispersion.

[0055] S2. The MXene dispersion obtained in S1 was dropped onto the surface of conductive glass ITO using a pipette. The conductive glass ITO had a size of 20 mm × 10 mm and the dropping volume was 0.5 μL. The mixture was then dried at room temperature.

[0056] S3. Synthesis and preparation of the molecularly imprinted polymer layer: The molecularly imprinted polymer (MIP) was prepared by electrochemical synthesis using a formulation of 5 mM oPD and 1 mM PFOA, with 0.1 M acetate buffer (pH 5.2) as the solvent. The conductive glass ITO electrode modified with the MXene layer obtained in step S1 was immersed in the prepared electrolyte. Cyclic voltammetry was performed with 5 cycles, a scan rate of 50 mV / s, a potential range of 0 V to +1 V, and a positive scan trend to obtain the final sensing electrode.

[0057] S4. Connect the sensing electrode obtained in S3 to the gate 4 of the 2N7000 MOSFET through the wire 8 to obtain a field-effect transistor sensor based on titanium carbide MXene / MIP.

[0058] The resulting field-effect transistor sensor based on titanium carbide MXene / MIP, such as Figure 1 As shown, it includes a substrate 1, a transistor, and a sensing electrode; the transistor is disposed on the substrate 1, and the transistor includes a source 2, a drain 3, and a gate 4; the sensing electrode is connected to the transistor via a wire 8, and the sensing electrode includes a conductive substrate 5, a titanium carbide MXene layer 6 modified on the surface of the conductive substrate 5, and a molecularly imprinted polymer layer 7 modified on the surface of the titanium carbide MXene layer 6; the molecularly imprinted polymer layer 7 has a specific recognition cavity for perfluorooctanoic acid; wherein the conductive substrate 5 is conductive glass ITO. Example

[0059] The fabrication method of the field-effect transistor sensor based on titanium carbide MXene / MIP is as follows: S1. Synthesis and preparation of titanium carbide MXene material: A modified MILD method was used. 37wt% HCl was diluted to 9MHCl, and 10 mL was placed in a polytetrafluoroethylene plastic beaker. Then, 1.6g of LiF powder was added, and the mixture was magnetically stirred for five minutes to fully dissolve it, forming a 6M LiF / 9M HCl etching solution. Subsequently, 0.5g of Ti3AlC2 powder was slowly added to the etching solution over 5 minutes while continuously stirring. The reaction was allowed to proceed at room temperature for 36 h. After etching, the resulting reaction mixture was transferred to a 50 mL centrifuge tube and diluted with deionized water. The centrifugation speed was set to 3500 rpm, and the centrifugation time was 5 min. After seven centrifugations, the supernatant pH was >5 and it appeared dark green, indicating that MXene had begun to peel off. Ti3C2-rich Ti3AlC2T was collected. x The supernatant of MXene was further centrifuged at 3500 rpm for 1 h to obtain Ti3C2T. x MXene dispersion.

[0060] S2. The MXene dispersion obtained in S1 was dropped onto the surface of conductive glass ITO using a pipette. The conductive glass ITO had a size of 20 mm × 10 mm and the dropping volume was 0.5 μL. The mixture was then dried at room temperature.

[0061] S3. Synthesis and preparation of the molecularly imprinted polymer layer: The molecularly imprinted polymer (MIP) was prepared by electrochemical synthesis using a formulation of 15 mM oPD and 1 mM PFOA, with 0.1 M acetate buffer (pH 5) as the solvent. The conductive glass ITO electrode modified with the MXene layer obtained in step S1 was immersed in the prepared electrolyte. Cyclic voltammetry was performed with 15 cycles, a scan rate of 50 mV / s, a potential range of 0 V to +1 V, and a positive scan trend, ultimately yielding the sensing electrode.

[0062] S4. Connect the sensing electrode obtained in S3 to the gate 4 of the 2N7000 MOSFET through the wire 8 to obtain a field-effect transistor sensor based on titanium carbide MXene / MIP. Example

[0063] The fabrication method of the field-effect transistor sensor based on titanium carbide MXene / MIP is as follows: S1. Synthesis and preparation of titanium carbide MXene material: A modified MILD method was used. 37wt% HCl was diluted to 9MHCl, and 10 mL of the solution was placed in a polytetrafluoroethylene (PTFE) plastic beaker. Then, 2.4 g of LiF powder was added, and the mixture was magnetically stirred for five minutes to ensure complete dissolution, forming a 9M LiF / 9M HCl etching solution. Subsequently, 0.5 g of Ti3AlC2 powder was slowly added to the etching solution over 5 minutes while continuously stirring. The reaction was allowed to proceed at room temperature for 18 hours. After etching, the resulting reaction mixture was transferred to a 50 mL centrifuge tube and diluted with deionized water. The centrifugation speed was set to 3500 rpm, and the centrifugation time was 5 minutes. After seven centrifugations, the supernatant pH was >5 and it appeared dark green, indicating that MXene had begun to peel off. Ti3C2-rich Ti3AlC2T was collected. x The supernatant of MXene was further centrifuged at 3500 rpm for 1 h to obtain Ti3C2T. x MXene dispersion.

[0064] S2. The MXene dispersion obtained in S1 was dropped onto the surface of conductive glass ITO using a pipette. The conductive glass ITO had a size of 20 mm × 10 mm and the dropping volume was 0.5 μL. The mixture was then dried at room temperature.

[0065] S3. Synthesis and preparation of the molecularly imprinted polymer layer: The molecularly imprinted polymer (MIP) was prepared by electrochemical synthesis using a formulation of 10 mM oPD and 1 mM PFOA, with 0.1 M acetate buffer (pH 6) as the solvent. The conductive glass ITO electrode modified with the MXene layer obtained in step S1 was immersed in the prepared electrolyte. Cyclic voltammetry was performed with 10 cycles, a scan rate of 50 mV / s, a potential range of 0 V to +1 V, and a positive scan trend to obtain the final sensing electrode.

[0066] S4. Connect the sensing electrode obtained in S3 to the gate 4 of the 2N7000 MOSFET through the wire 8 to obtain a field-effect transistor sensor based on titanium carbide MXene / MIP. Example

[0067] The application of a titanium carbide MXene / MIP-based field-effect transistor sensor in the detection of perfluorooctanoic acid in aqueous solution includes the following steps: A. Prepare PFOA solutions of different concentrations, including 121 pM, 242 pM, 483 pM, 1208 pM, and 2420 pM, as well as a blank buffer solution (0.02×PBS, pH 7.4). Immerse the sensing electrode of the titanium carbide MXene / MIP-based field-effect transistor sensor obtained in Example 1 into the test solution for a certain period of time. Simultaneously, insert an Ag / AgCl reference electrode and connect it to a digital source meter, so that the perfluorooctanoic acid molecules in the test aqueous solution bind to the specific recognition cavity of the molecularly imprinted polymer layer 7.

[0068] B. Set a fixed gate voltage of 3 V, a step voltage of 0.01 V, a scan voltage range of 0 V to +3 V, and a source-drain voltage of 0.5 V. Start measuring the transfer curve data at different concentrations, record the changes in the sensor's electrical signal, and quantitatively analyze the concentration of perfluorooctanoic acid in the aqueous solution based on the changes in the electrical signal.

[0069] Test results are as follows Figure 2 As shown, according to Figure 2 As shown in the transfer curves at different concentrations, the transfer curves shift to the right as the PFOA concentration increases. This indicates that the binding of PFOA introduces a negative charge at the MIP / solution interface, resulting in a decrease in the effective gate voltage. The transfer curves shift towards the positive gate voltage direction relative to the initial state without PFOA binding. The higher the concentration, the more negative charge is introduced, and the greater the curve shift.

Claims

1. A field-effect transistor sensor based on titanium carbide MXene / MIP, characterized in that: Includes a substrate (1), a transistor, and a sensing electrode; The transistor is disposed on a substrate (1), and the transistor includes a source (2), a drain (3) and a gate (4). The sensing electrode is electrically connected to the transistor. The sensing electrode includes a conductive substrate (5), a titanium carbide MXene layer (6) modified on the surface of the conductive substrate, and a molecularly imprinted polymer layer (7) modified on the surface of the titanium carbide MXene layer (6). The molecularly imprinted polymer layer (7) has a specific recognition cavity for perfluorooctanoic acid.

2. The field-effect transistor sensor based on titanium carbide MXene / MIP according to claim 1, characterized in that: The sensing electrode is electrically connected to the transistor via a metal wire (8), one end of which is connected to the pin of the transistor gate (4), and the other end is connected to the conductive substrate (5) of the sensing electrode.

3. The field-effect transistor sensor based on titanium carbide MXene / MIP according to claim 1 or 2, characterized in that: The conductive substrate (5) is indium tin oxide conductive glass; the titanium carbide MXene layer (6) is formed by dripping and drying MXene dispersion; the molecularly imprinted polymer layer (7) is formed by polymerizing functional monomers using a template molecule-induced electropolymerization method.

4. The field-effect transistor sensor based on titanium carbide MXene / MIP according to claim 3, characterized in that: The functional monomer is o-phenylenediamine, and the template molecule is perfluorooctanoic acid; the molar ratio of the template molecule to the functional monomer in the molecularly imprinted polymer layer (7) is 1:5-1:

15.

5. A method of fabricating a MXene / MIP-based field effect transistor sensor according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step S1: Prepare titanium carbide MXene dispersion; Step S2: Load the titanium carbide MXene dispersion described in step S1 onto the surface of the conductive substrate (5) and dry it to form a titanium carbide MXene layer (6). Step S3: Electropolymerization is performed on the surface of the titanium carbide MXene layer (6) to synthesize a molecularly imprinted polymer layer (7) for perfluorooctanoic acid, thereby obtaining a sensing electrode; Step S4: Connect the sensing electrode to the gate (4) of the transistor to assemble the field-effect transistor sensor based on titanium carbide MXene / MIP.

6. The method for fabricating a field-effect transistor sensor based on titanium carbide MXene / MIP according to claim 5, characterized in that: The preparation of the titanium carbide MXene dispersion in step S1 involves etching Ti3AlC2 powder with a mixed solution of lithium fluoride and hydrochloric acid as an etchant. After the reaction is completed, the upper dispersion is collected by centrifugation and washing. The molar ratio of LiF to HCl in the etchant is 1:3-4:3, and the etching time is 12-48 hours.

7. The method for fabricating a field-effect transistor sensor based on titanium carbide MXene / MIP according to claim 5, characterized in that: In step S3, the specific process of electropolymerization synthesis is as follows: A polymerization solution containing functional monomers, template molecules and supporting electrolytes was prepared; a conductive substrate (5) loaded with a titanium carbide MXene layer (6) was immersed in the polymerization solution as a working electrode, and a cyclic voltammetry method was used to perform scanning polymerization with an Ag / AgCl electrode as a reference electrode and a platinum wire electrode as a counter electrode.

8. The method for fabricating a field-effect transistor sensor based on titanium carbide MXene / MIP according to claim 7, characterized in that: The functional monomer is o-phenylenediamine, the template molecule is perfluorooctanoic acid, and the supporting electrolyte is acetate buffer with a pH of 5-6. The cyclic voltammetry method has 5-15 scan cycles, a scan rate of 50 mV / s, and a potential range of 0 V to +1 V.

9. The application of a field-effect transistor sensor based on titanium carbide MXene / MIP as described in any one of claims 1 to 4 in the detection of perfluorooctanoic acid in aqueous solution, characterized in that: The detection methods include: A. Immerse the sensing electrode of the field-effect transistor sensor based on titanium carbide MXene / MIP into the aqueous solution to be tested, so that the perfluorooctanoic acid molecules in the aqueous solution to be tested combine with the specific recognition cavity of the molecularly imprinted polymer layer (7), and the detection concentration range of perfluorooctanoic acid in the aqueous solution to be tested is 121 pM-2420 pM. B. Record the changes in the sensor's electrical signal, and quantitatively analyze the concentration of perfluorooctanoic acid in the aqueous solution based on the amount of change in the electrical signal.

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