Biosensor based on heterojunction field effect transistor and preparation method thereof

Abstract

The invention relates to the technical field of semiconductors, in particular to a heterojunction field effect transistor-based biosensor and a preparation method thereof, the biosensor comprises a substrate, a graphene / molybdenum disulfide heterojunction, a liquid metal electrode and a microfluidic module; a central liquid flow channel, a grid electrode pore channel and two groups of electrode channels are formed in the micro-fluidic module; each group of electrode channels comprises two electrode hole channels of which the bottoms are communicated, and the inlet end of one electrode hole channel is used for inserting a wire of external connecting equipment; and the inlet end of the other electrode hole channel is used for infusing liquid gallium-indium alloy to form a liquid metal electrode so as to connect the heterojunction with a wire. According to the invention, by introducing a modular heterojunction film construction method, the assembled preparation of each functional component of the biosensor is realized, the overall manufacturing complexity and time cost are remarkably reduced, the experimental repeatability and the feasibility of large-scale preparation are improved, and the high sensitivity and high specificity of extremely low concentration biomolecule detection are realized.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and in particular to a biosensor based on a heterojunction field-effect transistor and its fabrication method. Background Technology

[0002] In recent years, biosensors based on field-effect transistors (FETs) have become an important research direction for next-generation label-free biosensor platforms due to their advantages such as high sensitivity, low power consumption, real-time response, and ease of integration. Among them, FET devices constructed with two-dimensional materials as the core, such as graphene field-effect transistors (GFETs) and molybdenum disulfide field-effect transistors, have shown broad application prospects in the detection of biological targets such as nucleic acids, proteins, and peptides.

[0003] Graphene possesses ultra-high electron mobility, single-atom thickness, and highly tunable surface chemical activity, while its interface modifiability offers potential for biosensing. GFET-based biosensors are extremely sensitive to charge / potential changes occurring on graphene channels, precisely sensing minute charge changes caused by biomolecule binding or alteration, thus achieving highly efficient detection of minute amounts of biomolecules. Combined with its excellent surface functionalization capabilities and manufacturing process compatibility, GFET offers significant advantages in achieving label-free, highly selective detection, particularly suitable for rapid nucleic acid detection and real-time response applications.

[0004] Molybdenum disulfide (MoS2), another type of two-dimensional semiconductor material, possesses an intrinsic bandgap (~1.8 eV), good biocompatibility, high surface sensitivity, and excellent electrical stability. MoS2 field-effect transistors exhibit high carrier mobility, excellent current on / off ratio, and low dark current, significantly improving the on / off ratio and signal-to-noise ratio of FET devices. This makes MoS2 FETs highly responsive to changes in interface charge and electric field, suitable for detecting various target molecules. Therefore, the unique combination of tunable bandgap, stable electrical properties, two-dimensional layered structure, and biocompatibility makes MoS2 an excellent choice for biosensor channel materials based on field-effect transistors. These characteristics enable the development of highly sensitive, stable, and reliable biosensing devices, which can be widely applied in medical diagnostics, environmental monitoring, and other fields. Therefore, field-effect transistors developed using graphene and MoS2, namely GFETs and MoS2 FETs, are demonstrating unique advantages in the rapid detection of biomarkers.

[0005] Traditional graphene field-effect transistor (GFET) biosensors typically rely on micro-nano fabrication processes. These processes are complex, involve numerous steps, have long fabrication cycles, and are costly to produce. Furthermore, the fabrication process can easily cause secondary damage to the graphene, such as surface contamination, structural defects, or stress introduction, which in turn affects its electrical performance and interface stability. These problems severely limit the large-scale, low-cost manufacturing of GFET sensors and their widespread adoption in practical biological detection applications.

[0006] Meanwhile, current strategies for improving sensor sensitivity through material surface modification or heteroelement doping, while improving the sensing performance of biosensors to some extent, often involve irreversible damage to the intrinsic properties of the sensitive materials. Some chemical dopants exhibit environmental instability or have difficult-to-control doping concentrations, further exacerbating performance fluctuations during long-term operation, especially in practical sample detection where they can easily introduce non-specific background responses. Summary of the Invention

[0007] This application provides a biosensor based on a heterojunction field-effect transistor and its fabrication method. Based on integrated modular design, introduction of liquid metal electrodes and construction of heterojunction materials, it aims to achieve a low-cost, high-efficiency, low-material-damage, and high-sensitivity biosensor.

[0008] To address the aforementioned technical problems, in a first aspect, embodiments of this application provide a biosensor based on a heterojunction field-effect transistor, comprising: a substrate and a graphene / molybdenum disulfide heterojunction, a liquid metal electrode, and a microfluidic module disposed on the substrate; the microfluidic module is disposed on the side of the graphene / molybdenum disulfide heterojunction away from the substrate, and the microfluidic module has a central liquid channel, a gate electrode channel, and two sets of electrode channels respectively located on both sides of the central liquid channel; the central liquid channel is located inside the microfluidic module, and the extension direction of the central liquid channel is perpendicular to the thickness direction of the microfluidic module; the gate electrode channel is located in the middle of the central liquid channel; each set of electrode channels includes two electrode channels connected at the bottom, one of which has an inlet end for inserting a wire of an external connection device; the other electrode channel has an inlet end as a liquid electrode infusion end for infusing liquid gallium indium alloy to form a liquid metal electrode, thereby connecting the heterojunction to the wire.

[0009] In some exemplary embodiments, the central liquid channel has an inlet end and an outlet end, which are located on opposite sides of the length of the microfluidic module. A biomolecular solution is pumped in by inserting a hollow tube into the inlet end, and the solution flows through the reaction zone of the central liquid channel where the graphene / molybdenum disulfide heterojunction is located before flowing out from the outlet end.

[0010] In some exemplary embodiments, two sets of electrode channels are symmetrically distributed on both sides of the central liquid channel with the central liquid channel as the axis of symmetry. Liquid metal is injected into the electrode channels by external pressure and contacts the graphene / molybdenum disulfide heterojunction and the wire to form the source and drain of the field-effect transistor, respectively. A gate electrode channel is formed by drilling a hole in the middle of the central liquid channel, and a reference Ag / AgCl electrode is inserted into the gate electrode channel as the gate.

[0011] In some exemplary embodiments, with the flow direction of the biomolecular solution as the length direction, the length of the central liquid channel is 1 cm to 1.5 cm; the height of the central liquid channel in the thickness direction of the microfluidic module is 30 μm to 50 μm; and the width of the central liquid channel in the direction perpendicular to the thickness of the microfluidic module is 20 μm to 50 μm.

[0012] In some exemplary embodiments, the liquid metal electrode formed by pouring liquid gallium indium alloy into the inlet end of the electrode channel has a dimension of 200 μm to 300 μm along the length of the central liquid channel.

[0013] In some exemplary embodiments, chip cover clamps are provided at the bottom of the substrate and the top of the microfluidic module, and the two chip cover clamps are connected by fixing bolts to fix the biosensor.

[0014] Secondly, embodiments of this application also provide a method for fabricating a biosensor based on a heterojunction field-effect transistor. This method is used to fabricate the biosensor based on a heterojunction field-effect transistor as described in the above embodiments, and includes the following steps: providing a substrate and forming a graphene / molybdenum disulfide heterojunction on the substrate; fabricating a microfluidic module; the microfluidic module has a central liquid channel, a gate electrode channel, and two sets of electrode channels located on both sides of the central liquid channel; the central liquid channel is located inside the microfluidic module, and the extension direction of the central liquid channel is perpendicular to the thickness direction of the microfluidic module; the gate electrode channel is located in the middle of the central liquid channel; each set of electrode channels includes two electrode channels connected at the bottom; placing the microfluidic module on the side of the graphene / molybdenum disulfide heterojunction away from the substrate; fixing the microfluidic module and the substrate using a chip cover plate clamp; inserting a wire of an external connection device into the inlet end of one electrode channel, and pouring liquid gallium indium alloy into the inlet end of the other electrode channel to fabricate source and drain electrodes.

[0015] In some exemplary embodiments, a silicon oxide substrate is used as the substrate, and a graphene / molybdenum disulfide heterojunction is formed on the substrate, including: Step 1, providing a monolayer of molybdenum disulfide pre-grown on sapphire and covered with a layer of polymethyl methacrylate (PMMA) and a monolayer of graphene grown on copper foil and covered with a layer of PMMA; placing the PMMA / molybdenum disulfide / sapphire substrate in an etching solution to separate the material from the substrate, changing the solution to clean the molybdenum disulfide, and obtaining clean PMMA / molybdenum disulfide; Step 2, transferring the PMMA / molybdenum disulfide to silicon oxide and allowing it to air dry, then drying it at 80°C for 0.5 hours. h Remove residual moisture, place PMMA / molybdenum disulfide / silicon oxide in acetone solution to remove PMMA, obtain molybdenum disulfide / silicon oxide, and anneal; Step 3, place PMMA / graphene / copper foil substrate in etching solution to etch away copper foil substrate, clean and obtain PMMA / graphene; transfer PMMA / graphene to molybdenum disulfide / silicon oxide prepared in step 2, ensuring that graphene completely covers molybdenum disulfide, then remove PMMA with acetone, anneal, and obtain graphene / molybdenum disulfide / heterojunction formed on silicon oxide.

[0016] In some exemplary embodiments, the fabrication of a microfluidic module includes: First, drawing a microfluidic photomask layout with a central liquid channel and electrode channel structure using CAD software; then, using micro-nano fabrication technology, curing and stabilizing photoresist on a 4-inch silicon wafer to form a positive mold with raised microstructures, obtaining a positive mold with a microfluidic structure, which is used for subsequent PDMS casting to form the microfluidic structure; next, mixing polydimethylsiloxane (PDMS) monomer and crosslinking agent at a ratio of 9.5:1 and pouring the mixture onto the positive mold with the microfluidic structure, curing at 80°C for 40-60 min to obtain a PDMS module with a microfluidic structure; and then, drilling holes in the PDMS module with the microfluidic structure at the liquid inlet, outlet, and liquid electrode infusion ends to connect the electrode channels to the central liquid channel, facilitating liquid flow and electrode fabrication, and drilling holes in the middle of the central liquid channel to form a gate electrode channel, which is reserved as a reference Ag / AgCl electrode as the gate.

[0017] In some exemplary embodiments, a chip cover clamp is used to fix the microfluidic module and the substrate, including: attaching the microfluidic module to a graphene / molybdenum disulfide heterojunction formed on the substrate, setting chip cover clamps at the bottom of the substrate and the top of the microfluidic module respectively, and connecting the two chip cover clamps by fixing bolts.

[0018] The technical solution provided in this application has at least the following advantages: This application provides a biosensor based on a heterojunction field-effect transistor and its fabrication method. The biosensor includes: a substrate and a graphene / molybdenum disulfide heterojunction, a liquid metal electrode, and a microfluidic module disposed on the substrate. The microfluidic module is disposed on the side of the graphene / molybdenum disulfide heterojunction away from the substrate. The microfluidic module has a central liquid channel, a gate electrode channel, and two sets of electrode channels located on both sides of the central liquid channel. The central liquid channel is located inside the microfluidic module, and the extension direction of the central liquid channel is perpendicular to the thickness direction of the microfluidic module. The gate electrode channel is located in the middle of the central liquid channel. Each set of electrode channels includes two electrode channels connected at the bottom. The inlet end of one electrode channel is used to insert a wire of an external connection device. The inlet end of the other electrode channel serves as a liquid electrode infusion end, used to infuse liquid gallium indium alloy to form a liquid metal electrode, thereby connecting the heterojunction to the wire. This application introduces a modular heterojunction thin film construction method to achieve the assembly-type fabrication of various functional components of biosensors (such as sensitive areas, electrode areas, and channel structures), which significantly reduces the overall manufacturing complexity and time cost, improves experimental repeatability and the feasibility of large-scale preparation, and achieves high sensitivity and high specificity for the detection of extremely low concentrations of biomolecules. Attached Figure Description

[0019] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments, and unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0020] Figure 1 This is a schematic diagram illustrating the structure and fabrication design of a biosensor based on a heterojunction field-effect transistor, provided as an embodiment of this application.

[0021] Figure 2 This is a schematic diagram illustrating the insertion of an Ag / AgCl reference electrode as a gate conduction and sensing electrode in the middle portion of the central liquid flow channel of a biosensor, as provided in an embodiment of this application.

[0022] Figure 3 This is a schematic diagram of the microfluidic module provided in an embodiment of this application.

[0023] Figure 4 The microfluidic module mold mask layout provided in the embodiments of this application.

[0024] Figure 5 The image shows the Raman spectrum of the heterojunction in the embodiments of this application.

[0025] Figure 6 This is for leakage current testing of multiple devices in the embodiments of this application.

[0026] Figure 7This is the transfer curve of the heterojunction device in the embodiments of this application.

[0027] Figure 8 The output characteristic curve of the heterojunction device in the embodiments of this application is tested.

[0028] Figure 9 This is a comparison of the impact of modular and photolithography processes on the quality of graphene in the embodiments of this application.

[0029] Figure 10 The figures show the charge transfer characteristic curves of heterojunction device biosensors with different target concentrations for hybridization detection in the embodiments of this application.

[0030] Figure 11 This is a statistical diagram of the Dirac point offset of heterojunction device biosensors for hybridization detection at different target concentrations in the embodiments of this application.

[0031] Figure 12 This is to highlight the specificity of the heterojunction device biosensor in the embodiments of this application. Detailed Implementation

[0032] As the background technology shows, traditional graphene field-effect transistor (GFET) biosensors suffer from problems such as cumbersome processes, numerous steps, long preparation cycles, and high production costs. Moreover, the processing can easily cause secondary damage to graphene, thus affecting its electrical performance and interface stability. Currently, common methods such as material surface modification or heteroelement doping have improved the sensing performance of biosensors to some extent, but these often come at the cost of irreversible damage to the intrinsic properties of the sensitive material.

[0033] Modular systems, flexible and easy-to-assemble and maintain functional integration platforms, have demonstrated significant advantages in the design and fabrication of biosensor devices in recent years. By dividing complex biosensor systems into multiple standardized, interchangeable functional modules (such as substrate materials, signal transmission modules, and fluid control modules), modular design significantly simplifies the device manufacturing process, reduces process complexity, and improves system maintainability and scalability. This system not only possesses high adaptability and compatibility but also effectively enhances the standardization level and experimental flexibility of devices. Applying the modular concept to biosensors can further promote the realization of "lab-on-a-chip" systems, integrating sample processing, reaction, and detection steps into a small platform, providing a portable, efficient, and low-cost solution for point-of-care testing (POCT). Furthermore, liquid metal materials (such as GaIn), with their reversible rheological properties at room temperature and excellent conductivity, exhibit unique application potential in modular systems. Liquid metal can be directly injected into predefined channels or cavities within a modular structure, forming flexible electrodes in situ at room temperature. This not only achieves conformal bonding with the channel structure, avoiding the high-temperature deposition or complex encapsulation processes required for traditional rigid electrodes, but also effectively reduces mechanical or chemical damage to sensitive two-dimensional materials (such as graphene and molybdenum disulfide). Therefore, the combination of field-effect transistor biosensors based on graphene or molybdenum disulfide with modular systems not only integrates the advantages of highly sensitive electrical detection and reconfigurable structural integration, but also significantly enhances the device's application potential in portability, high-throughput detection, and automation, becoming one of the important directions for the development of current biosensor technology.

[0034] Among the developed GFET biosensors, biosensors based on different principles and applications have achieved high-sensitivity detection by regulating and constructing graphene-based materials, but they still face many technical challenges. For example, in patent CN118425499A, the GFET biosensor based on wrinkled graphene improves the sensitivity and detection limit of the graphene field-effect transistor by constructing a wrinkled graphene sensing layer. However, the material preparation stage suffers from uncontrollable processing of graphene properties, complex material preparation that easily damages the intrinsic properties of the material, and the use of micro-nano fabrication processes, i.e., photolithography, for device fabrication. The fabrication process is cumbersome, time-consuming, and costly. Secondary damage to the material is inevitable during the fabrication process, leading to reduced performance of the biosensor and making low-cost mass production difficult. In addition, there are application cases that combine microfluidics with GFETs, such as CN118090865A, which combines microfluidic structures with GFETs to achieve low-concentration detection of biomolecules in trace liquids. However, it still relies on micro-nano fabrication strategies for processing, which is time-consuming and easily damages materials. At the same time, the Debye shielding effect in the solution limits the detection of extremely low target biomolecules by the biosensor.

[0035] To address the problems existing in the prior art, this application proposes a biosensor based on a heterojunction field-effect transistor and its fabrication method, based on integrated modular design, the introduction of liquid metal electrodes, and the construction of heterojunction materials. This application introduces liquid metal electrodes to optimize device fabrication and reduce material damage on the basis of the previously established modular graphene field-effect transistor platform. Furthermore, by utilizing the synergistic effect of interfacial charge transfer in the graphene / molybdenum disulfide heterojunction, the charge response to the target biological sample is significantly enhanced, thereby achieving higher sensitivity detection.

[0036] Therefore, to solve the above-mentioned technical problems, this application provides a biosensor based on a heterojunction field-effect transistor and its fabrication method. The biosensor includes: a substrate and a graphene / molybdenum disulfide heterojunction, a liquid metal electrode, and a microfluidic module disposed on the substrate. The microfluidic module is disposed on the side of the graphene / molybdenum disulfide heterojunction away from the substrate. The microfluidic module has a central liquid channel, a gate electrode channel, and two sets of electrode channels located on both sides of the central liquid channel. The central liquid channel is located inside the microfluidic module, and the extension direction of the central liquid channel is perpendicular to the thickness direction of the microfluidic module. The gate electrode channel is located in the middle of the central liquid channel. Each set of electrode channels includes two electrode channels connected at the bottom. The inlet end of one electrode channel is used to insert a wire of an external connection device. The inlet end of the other electrode channel serves as a liquid electrode infusion end, used to infuse liquid gallium indium alloy to form a liquid metal electrode, thereby connecting the heterojunction to the wire. This application provides a biosensor based on a heterojunction field-effect transistor and its fabrication method. Based on integrated modular design, introduction of liquid metal electrodes and construction of heterojunction materials, it aims to achieve a low-cost, high-efficiency, low-material-damage, and high-sensitivity biosensor.

[0037] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0038] See Figure 1 This application provides a biosensor based on a heterojunction field-effect transistor, comprising: a substrate and a graphene / molybdenum disulfide heterojunction, a liquid metal electrode, and a microfluidic module disposed on the substrate; the microfluidic module is disposed on the side of the graphene / molybdenum disulfide heterojunction away from the substrate, and the microfluidic module has a central liquid channel, a gate electrode channel, and two sets of electrode channels respectively located on both sides of the central liquid channel; the central liquid channel is located inside the microfluidic module, and the extension direction of the central liquid channel is perpendicular to the thickness direction of the microfluidic module; the gate electrode channel is located in the middle of the central liquid channel; each set of electrode channels includes two electrode channels connected at the bottom, the inlet end of one electrode channel is used to insert a wire of an external connection device; the inlet end of the other electrode channel serves as a liquid electrode infusion end, used to infuse liquid gallium indium alloy to form a liquid metal electrode, thereby connecting the heterojunction to the wire.

[0039] In some embodiments, please refer to Figure 2The central liquid channel is located inside the microfluidic module and extends along the length of the microfluidic module. The central liquid channel has an inlet end (input) and an outlet end (output), which are located on both sides of the length of the microfluidic module. The biomolecule solution is pumped in by inserting a hollow tube into the inlet end. The solution flows through the reaction zone of the central liquid channel where the graphene / molybdenum disulfide heterojunction is located and then flows out from the outlet end.

[0040] In some embodiments, please refer to Figure 3 Two sets of electrode channels are symmetrically distributed on both sides of the central liquid channel with the central liquid channel as the axis of symmetry. Liquid metal is injected into the electrode channels by external pressure and forms the source and drain of the field-effect transistor by contacting the graphene / molybdenum disulfide heterojunction and the wire, respectively.

[0041] In some embodiments, please continue reading Figure 3 The gate electrode channel is located in the middle of the central liquid flow channel. The gate electrode channel is formed by drilling a hole in the middle of the central liquid flow channel. A reference Ag / AgCl electrode is inserted into the gate electrode channel as the gate.

[0042] In some embodiments, with the flow direction of the biomolecular solution as the length direction, the length of the central liquid channel is 1 cm to 1.5 cm; optionally, the length of the central liquid channel can be 1 cm, 1.2 cm, or 1.5 cm; as an example, Figure 3 A schematic diagram showing a central liquid flow channel with a length of 1.5 cm is shown.

[0043] In some embodiments, the height of the central liquid channel in the thickness direction of the microfluidic module is 30 μm to 50 μm; optionally, the height of the central liquid channel can be 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm; as an example, Figure 1 A schematic diagram showing the central liquid flow channel with a height of 40 μm is shown.

[0044] In some embodiments, the width of the central liquid channel in the direction perpendicular to the thickness of the microfluidic module is 20 μm to 50 μm. Optionally, the width of the central liquid channel can be 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm; as an example, Figure 3 A schematic diagram showing the central liquid flow channel with a width of 40 μm is shown.

[0045] In some embodiments, the liquid metal electrode formed by pouring liquid gallium-indium alloy into the inlet end of the electrode channel has a dimension of 200 μm to 300 μm along the length of the central liquid flow channel. Optionally, the width of the liquid metal electrode (electrode region) can be 200 μm, 220 μm, 240 μm, 260 μm, or 300 μm; as an example, Figure 3 A schematic diagram of a liquid metal electrode with a width of 300 μm is shown.

[0046] In some embodiments, chip cover clamps are provided at the bottom of the substrate and the top of the microfluidic module, and the two chip cover clamps are connected by fixing bolts to fix the biosensor.

[0047] For details, please refer to Figure 1 The modular device structure of this application includes: a substrate (silicon oxide / silicon substrate) with a transferred graphene / molybdenum disulfide heterojunction, a gallium-indium alloy liquid metal electrode (composition ratio: 75% gallium, 25% indium), a microfluidic module (including a central liquid channel and electrode channels for injecting liquid metal), and upper and lower clamps for fixing the microfluidic module to the material substrate; in addition, the operation of the entire system also includes an external pressure-driven liquid delivery pump connected to the liquid pump inlet and performance testing instruments. During assembly, the microfluidic module is attached to the substrate with the transferred graphene / molybdenum disulfide heterojunction, using, for example... Figure 1 The chip cover plate is firmly clamped in place, and liquid metal is introduced into the electrode channel to prepare the source and drain electrodes. The graphene / molybdenum disulfide heterojunction field-effect transistor is now fabricated.

[0048] Optionally, this application uses a 2-inch Si / SiO2 substrate with a 285 nm thick silicon oxide layer on the front side of the silicon wafer. The molybdenum disulfide film has a size of 1 cm × 1 cm, and the graphene film has a size of 1.2 cm × 1.2 cm. The graphene is stacked on the molybdenum disulfide and laid flat in the center of the silicon oxide substrate.

[0049] The principle of heterojunction field-effect transistors is to use graphene / molybdenum disulfide transferred onto silicon oxide as the semiconductor material. The source and drain electrodes are made of liquid metal in the microfluidic module, and the gate is made of Ag / AgCl reference electrode. A hollow tube is inserted into the central liquid flow channel (i.e., the inlet) to pump in liquid. The liquid flows through the heterojunction and modifies and detects the surface of the graphene / molybdenum disulfide heterojunction. On the other hand, it contacts the Ag / AgCl reference electrode to act as a liquid gate to realize the electrical performance test.

[0050] This application also provides a method for fabricating a biosensor based on a heterojunction field-effect transistor. This method is used to fabricate the biosensor based on a heterojunction field-effect transistor as described in the above embodiments, and includes the following steps: providing a substrate; forming a graphene / molybdenum disulfide heterojunction on the substrate; fabricating a microfluidic module; the microfluidic module having a central liquid channel, a gate electrode channel, and two sets of electrode channels located on either side of the central liquid channel; the central liquid channel being located inside the microfluidic module, and its extension direction being perpendicular to the thickness direction of the microfluidic module; the gate electrode channel being located in the middle of the central liquid channel; each set of electrode channels including two bottom-connected electrode channels; placing the microfluidic module on the side of the graphene / molybdenum disulfide heterojunction away from the substrate; fixing the microfluidic module and the substrate using a chip cover clamp; inserting a wire of an external connection device into the inlet end of one electrode channel, and injecting liquid gallium-indium alloy into the inlet end of the other electrode channel to fabricate source and drain electrodes.

[0051] In some embodiments, a silicon oxide substrate is used as the substrate, and a graphene / molybdenum disulfide heterojunction is formed on the substrate, including: Step 1, providing a monolayer of molybdenum disulfide grown on sapphire and covered with a layer of polymethyl methacrylate (PMMA) and a monolayer of graphene grown on copper foil and covered with a layer of PMMA; placing the PMMA / molybdenum disulfide / sapphire substrate in an etching solution to separate the material from the substrate, changing the solution to clean the molybdenum disulfide, and obtaining clean PMMA / molybdenum disulfide; Step 2, transferring the PMMA / molybdenum disulfide to silicon oxide and allowing it to air dry, then drying it at 80°C for 0.5 hours. h Remove residual moisture, place PMMA / molybdenum disulfide / silicon oxide in acetone solution to remove PMMA, obtain molybdenum disulfide / silicon oxide, and anneal; Step 3, place PMMA / graphene / copper foil substrate in etching solution to etch away copper foil substrate, clean and obtain PMMA / graphene; transfer PMMA / graphene to molybdenum disulfide / silicon oxide prepared in step 2, ensuring that graphene completely covers molybdenum disulfide, then remove PMMA with acetone, anneal, and obtain graphene / molybdenum disulfide / heterojunction formed on silicon oxide.

[0052] In some embodiments, the fabrication of a microfluidic module includes: First, drawing a microfluidic photomask layout with a central liquid channel and electrode channel structure using CAD software; then, using micro-nano fabrication technology, curing and stabilizing photoresist on a 4-inch silicon wafer to form a positive mold with raised microstructures, resulting in a positive mold with a microfluidic structure. This positive mold is used for subsequent PDMS casting to form the microfluidic structure. Next, mixing polydimethylsiloxane (PDMS) monomer and crosslinking agent at a ratio of 9.5:1 and pouring the mixture onto the positive mold with the microfluidic structure, curing at 80°C for 40-60 min, to obtain a PDMS module with a microfluidic structure. Finally, perforations are made at the liquid inlet, outlet, and liquid electrode infusion ends of the PDMS module with the microfluidic structure to connect the electrode channel to the central liquid channel, facilitating liquid flow and electrode fabrication. A hole is also made in the middle of the central liquid channel to form a gate electrode channel, which is reserved as a reference Ag / AgCl electrode for use as the gate.

[0053] In some embodiments, a chip cover clamp is used to fix the microfluidic module and the substrate, including: attaching the microfluidic module to a graphene / molybdenum disulfide heterojunction formed on the substrate, setting chip cover clamps at the bottom of the substrate and the top of the microfluidic module respectively, and connecting the two chip cover clamps by fixing bolts.

[0054] The following detailed description, with reference to the accompanying drawings, describes the biosensor based on heterojunction field-effect transistors and its fabrication method provided in the embodiments of this application.

[0055] Specifically, a typical implementation method provided in this application is shown below. Figure 1 This application provides a fabrication design for a graphene / molybdenum disulfide heterojunction thin film modular field-effect transistor biosensor, including a graphene / molybdenum disulfide substrate (silicon oxide) with transferred heterojunction thin film material, a microfluidic module above the substrate, a liquid metal module, and a chip cover clamp. Figure 1 (Related structure in the middle). The microfluidic module is pre-attached to a substrate with transferred graphene / molybdenum disulfide, then fixed by a chip cover plate fixture, and finally liquid metal is poured into the electrode channels to complete the device fabrication. The microfluidic module includes: a central liquid channel, a gate electrode channel, and two sets of electrode channels located on both sides of the central liquid channel. Each set of electrode channels includes two electrode channels connected at the bottom. The gate electrode channel is formed by drilling a hole in the center of the central liquid channel, and an Ag / AgCl reference electrode is inserted into the gate electrode channel to form the gate.

[0056] Example 1 The fabrication and design process of a modular field-effect transistor biosensor based on graphene / molybdenum disulfide heterojunction thin film is as follows: Figure 1As shown, the process is completed in three steps, with step S1 being the fabrication of the microfluidic module, and the steps are as follows: Step S1: Fabrication of PDMS microfluidic module.

[0057] 1) Use CAD software to draw the target structure mask layout (see attached image for microfluidic module mold mask layout). Figure 4 See attached diagram for microstructure schematic. Figure 3 And prepare a mask.

[0058] 2) Select a 4-inch silicon wafer as the substrate and ultrasonically clean it with acetone, isopropanol and deionized water for 15 min in sequence to remove surface contaminants; fix the clean silicon wafer in the center of the vacuum chuck of the spin coater and deposit SU-8 3050 negative photoresist using a two-step spin coating method: the first step is to spin coat at 500 rpm for 20 s to achieve photoresist spreading on the silicon wafer, and the second step is to spin coat at 3000 rpm for 30 s to control the uniformity of the photoresist thickness.

[0059] 3) After spin-coating the photoresist, the silicon wafer is placed on a hot plate and preheated at 95°C for 25 minutes to remove the solvent and enhance the adhesion of the photoresist film. Subsequently, in the photolithography machine, a hard contact mode is used to precisely align the mask and the silicon wafer, and the pattern transfer is completed by exposure to ultraviolet light (wavelength 365 nm) for 12 seconds.

[0060] 4) After exposure, the silicon wafer is baked at 95°C on a hot plate for 30 min to promote the crosslinking reaction. During development, the unexposed areas are dissolved by immersion in SU-8 special negative adhesive developer for 20 s; finally, the wafer is hardened at 150°C on a hot plate for 30 min to improve structural mechanical stability and etching resistance. (Through the above operations, the microfluidic module positive mold is fabricated, resulting in a silicon wafer with a central flow channel and electrode patterned protrusions, with an average protrusion height of 40 μm. Then, PDMS monomer and crosslinking agent are mixed and poured onto the flow channel and electrode patterned silicon wafer mold to solidify into a recessed PDMS microfluidic module for use in the fabrication of biosensors. This patterned silicon wafer mold is a PDMS positive mold and can be reused, avoiding the need for photolithography for each fabrication of field-effect transistors.)

[0061] 5) Mixing the PDMS monomer and crosslinking agent evenly at a mass ratio of 9.5:1, and stir thoroughly to ensure uniform mixing of the colloid. Then pour the PDMS mixture evenly and smoothly onto the surface of the silicon wafer positive mold.

[0062] 6) Defoaming: Place the positive mold containing the PDMS mixture in the vacuum extraction chamber, turn on the vacuum pump to create negative pressure for 30 minutes to remove air bubbles formed by stirring. After defoaming, place the PDMS adhesive in an 80℃ oven and bake for 40-60 minutes to cure and shape.

[0063] 7) Demolding: Slowly separate the PDMS modules from the silicon wafer male mold, taking care to avoid damaging the PDMS colloid to ensure the accuracy of the flow channels. Then use a spatula to cut each microchannel module along the dividing line for later use, ensuring the bottom surface is flat to prevent the PDMS colloid from sticking together.

[0064] 8) Drilling: Use a 0.8 mm drill to drill the central liquid flow channel through hole; use a 1.1 mm drill to drill the two sets of electrode channel holes; during the drilling process, ensure that there is no residual core in each hole and that the holes are as vertical as possible to ensure unobstructed fluid flow.

[0065] Step S2: Transfer of graphene / molybdenum disulfide heterojunction film.

[0066] 1. Molybdenum disulfide transfer.

[0067] 1) Place 1×1 cm 2 The PMMA / molybdenum disulfide / sapphire substrate was immersed in a 2 mol / L potassium hydroxide solution for 2 h to separate the PMMA film and the substrate.

[0068] 2) After separation, wash with ultrapure water 3-4 times to remove residual potassium hydroxide solution. After the fourth wash, use silicon dioxide to retrieve PMMA / molybdenum disulfide. Then place the retrieved substrate vertically and let the residual water flow to one corner to air dry naturally.

[0069] 3) After air drying, heat the PMMA / molybdenum disulfide / silicon oxide on an 80℃ heating plate to improve the bonding between the molybdenum disulfide and the substrate, preventing the substrate from falling off in the next step.

[0070] 4) Immerse the annealed material in acetone to etch the PMMA. Replace the acetone 3-5 times during this process, immersing for about 30 minutes each time. After removing the PMMA, dry and package for storage.

[0071] 2. Graphene transfer.

[0072] 5) Cut out a 1.2 × 1.2 cm piece. 2 The PMMA / graphene / copper foil substrate was placed in a 7% ammonium persulfate solution to etch the copper foil for about 1.5 hours until the copper foil was completely etched. The ammonium persulfate solution was then removed using a pipette, and ultrapure water was injected into the petri dish. This washing process was repeated 3 to 4 times to ensure that any residual ammonium persulfate was completely removed.

[0073] 6) After the fourth filling with water, use the molybdenum disulfide / silicon oxide sheet from 1) to gently pull the PMMA / graphene film out of the deionized water, so that the graphene completely covers the molybdenum disulfide, and avoid the formation of air bubbles between the layers.

[0074] 7) Lean it against the petri dish and let it air dry naturally. Transfer the PMMA / graphene film / silicon oxide to a glove box and heat it on a hot plate at 90°C for 30 min, then at 130°C for 30 min (to stretch the PMMA).

[0075] 8) After drying, transfer the substrate from the glove box to a fume hood, place it in a glass petri dish, and soak it in acetone for 1.5 h, changing the solution 3 times during this period. Cover the petri dish with aluminum foil to prevent acetone evaporation. After dissolving PMMA, clean the silicon oxide wafer with isopropanol, and then anneal it in a vacuum chamber at 200°C for 0.5 h to prepare the graphene / molybdenum disulfide heterojunction for later use.

[0076] Further, in step S3, the graphene / molybdenum disulfide heterojunction film is assembled with the microfluidic module and liquid electrode into a field-effect transistor device. The assembly steps are as follows: 1) The interface of the microfluidic module with flow channels and electrode channels is attached to the surface of graphene / molybdenum disulfide, so that the central flow channel covers the graphene / molybdenum disulfide to form a PDMS / material structure.

[0077] 2) Next, use the chip cover clamp to sandwich the assembled PDMS / material structure (e.g., Figure 1 As shown in the figure, to ensure the airtightness of the structure and the stability of the test, only the electrode channels, liquid inlet and outlet holes and gate electrode channels that have been pre-drilled with a punch are exposed.

[0078] 3) Insert the external wire electrode into the electrode outlet, and then inject liquid gallium indium alloy from the electrode inlet to complete the electrode preparation.

[0079] 4) Simultaneously, an Ag / AgCl reference electrode was inserted in the middle part of the central flow channel to apply electric field modulation as a gate conduction (e.g., Figure 2 (As shown).

[0080] Example 2 like Figure 2 As shown, this application uses the prepared graphene / molybdenum disulfide heterojunction thin film modular field-effect transistor biosensor for sample introduction verification in biological detection.

[0081] (1) First, the sample to be injected is stored in the storage tube and inserted into the inlet hole of the central flow channel through the conduit. It is connected to the graphene / molybdenum disulfide heterojunction field effect transistor biosensor. An external peristaltic pump is used to pump the liquid containing modified biomolecules that have been modified on the graphene interface into the central flow channel, thereby biofunctionalizing the graphene and giving the device the ability to detect biosensing.

[0082] (2) The biodetection solution containing the target molecule is pumped into the biofunctionalized graphene / molybdenum disulfide heterojunction thin film modular field effect transistor biosensor. After the target molecule binds to the bioprobe, charge transfer or potential change occurs at the material interface. The signal is monitored by measuring the transfer characteristic curve of the G / MFET biosensor to obtain the Dirac point value and fit the standard curve.

[0083] The above operations enable biological detection of biological samples and verification of the sensing performance of the biosensor. This device avoids the multi-step operations of micro-nano fabrication, greatly improving the device fabrication efficiency. Furthermore, the construction of heterojunction materials can effectively amplify the charge and potential changes generated by the binding of biomolecules, thereby improving the sensitivity of the biosensor and reducing the detection limit.

[0084] Through the above technical solutions, this application achieves efficient and convenient fabrication and high-sensitivity detection of field-effect transistor (FET) biosensors by modularly designing the biosensor and introducing heterojunction materials. The modular design ensures that the various fabrication modules do not interfere with each other and can be fabricated in parallel, avoiding the continuous and time-consuming fabrication problems of existing FET biosensors that require micro-nano processing. Furthermore, the introduced heterojunction material significantly improves the detection sensitivity of the biosensor by enhancing charge transfer generated by hybridization between biomolecules. Moreover, it is not limited to the detection of a single biomarker; it can achieve the detection of multiple biomarkers through different sensing mechanisms.

[0085] Compared with existing technologies, the biosensor based on heterojunction field-effect transistors and its fabrication method provided in this application have the following advantages: First, this application implements a modular design for each component of the device: a heterojunction thin film is prepared by stacking graphene and molybdenum disulfide as a biosensing material. The graphene / molybdenum disulfide heterojunction material is applied to the field-effect transistor biosensor, which improves the device's ability to capture charge transfer generated by biomolecule hybridization compared to the graphene field-effect transistor, thereby increasing the detection limit of the graphene field-effect transistor biosensor and improving the sensing performance.

[0086] Secondly, the microfluidic module of this application constructs a central liquid flow channel and electrode channels. After these are assembled, they are fixed using a customized microfluidic fixture, and the source and drain electrodes are fabricated using liquid metal. The modular design and fabrication of each part of the device (material substrate, microfluidic module, liquid electrodes) simplifies the device fabrication process, improves fabrication efficiency, and introduces gallium-indium alloy liquid metal as electrodes. The modular assembly of the device reduces material damage and facilitates performance and detection stability.

[0087] Furthermore, this application employs a heterojunction material as the biosensing material. Graphene protects molybdenum disulfide, which is susceptible to water and oxygen. Molybdenum disulfide is charge-sensitive and can effectively enhance charge transfer between biomolecules and materials, leading to changes in the device's electrical properties and achieving high-sensitivity detection. In addition, the modular design allows for the parallel implementation of material preparation, microfluidic module fabrication, and electrode fabrication, greatly simplifying device fabrication. The microfluidic module can effectively encapsulate the device while minimizing material damage, preventing device failure due to solution or electrode leakage. Finally, the central channel of the microfluidic module allows for the injection of different types of biological solutions, which flow through the graphene to achieve functional modification of the graphene and enable the detection of biomarkers, including but not limited to DNA, RNA, and protein molecules.

[0088] It should be noted that the application scenarios of this application are not limited to graphene / molybdenum disulfide heterojunction materials, but can be other semiconductor materials, such as graphene / tungsten diselenide, organic thin film semiconductors, etc.

[0089] Based on this application, it can be integrated into different biosensor devices or microfluidic detection chips, serving as a simple modular solution that improves the high fabrication efficiency and low material damage rate of biosensors.

[0090] Based on the modular construction of this application, different sensing mechanisms can be used to detect different biomarkers, such as other viruses, DNA, RNA, protein molecules, etc.

[0091] The biosensor fabricated using the heterojunction field-effect transistor-based method provided in this application has been experimentally and simulated, with the specific results as follows: The substrate for transferring heterojunction materials is mainly silicon oxide / silicon substrate with a size of 1×1 cm. 2 A 1×1 cm layer completely covers a single layer of molybdenum disulfide. 2 A heterojunction film composed of a single layer of graphene. After Raman characterization of the material, such as... Figure 5 As shown, it appears at ~386.5 cm -1 (E 1 2g ) and 405.9 cm -1 (A 1g The characteristic peaks of molybdenum disulfide were observed, with a frequency difference (Δ) of ~19.4 cm⁻¹. -1 It exhibits good monolayer properties. And G~1585 cm -1 and 2D~2680 cm -1The characteristic peaks show those of graphene, and the 2D / G ratio is approximately 1.24, exhibiting good monolayer properties. Characteristic peaks of molybdenum disulfide and graphene were detected in both heterojunction materials, and both exhibited good monolayer characteristics, demonstrating the successful construction of the heterojunction material.

[0092] The fundamental electrical properties of field-effect transistors fabricated based on graphene / molybdenum disulfide heterojunction materials are as follows: Figure 6 , 7 As shown in Figure 8, Figure 6 The results showed that the leakage current of all ten devices was less than 100 nA, demonstrating the good electrode packaging of the devices by the modular system. Figure 7 Exhibiting excellent transfer characteristic curves, the heterojunction material exhibits good bipolar characteristics as the gate voltage changes. Figure 8 The transfer characteristic curves demonstrate a good ohmic contact between the liquid metal and the material. Similarly, compared to commercially available micro / nano-fabricated graphene transistor devices, Figure 9 The graphene in the modular device has fewer defects than that in the commercial device, demonstrating that the modular process causes less damage during device fabrication.

[0093] Implement material functionalization and bioassay, such as Figure 2 As shown, a liquid containing modified molecules is pumped into the central channel via an external wire using a peristaltic pump to contact the graphene / molybdenum disulfide and gradually modify the graphene / molybdenum disulfide surface, thus endowing the graphene / molybdenum disulfide heterojunction thin film modular field-effect transistor with biosensing detection capabilities.

[0094] Using the above method, this application utilizes a graphene / molybdenum disulfide heterojunction field-effect transistor biosensor for nucleic acid detection of the novel coronavirus. The novel coronavirus positive sample contains a complementary strand, which is a single strand of RNA that can pair complementaryly with a DNA probe. When nucleic acid molecules hybridize, it causes changes in the charge doping on the graphene surface, such as... Figure 10 As shown, the change in the Dirac point voltage value of the electrical signal is reflected in the continuous leftward shift of the Dirac point voltage value with the increase of target concentration. This is because the negatively charged nucleic acid target binds to the probe, producing n-type doping, which causes the Dirac point to shift to the left. Therefore, monitoring the change in this signal can achieve the sensing and identification of viruses. Meanwhile, as... Figure 11 As shown, through validation with multiple sets of data, high-sensitivity detection of the target molecule 1 aM was achieved. Specificity detection results are as follows: Figure 12 As shown, this application used multiple sets of non-complementary viral sequences as negative control samples, and repeated tests demonstrated that the biosensor has high specificity. In summary, this biosensor based on a graphene / molybdenum disulfide heterojunction thin-film modular field-effect transistor can effectively improve the sensitivity and specificity of biological detection.

[0095] Based on the above technical solutions, this application provides a biosensor based on a heterojunction field-effect transistor and its fabrication method. The biosensor includes: a substrate and a graphene / molybdenum disulfide heterojunction, a liquid metal electrode, and a microfluidic module disposed on the substrate. The microfluidic module is disposed on the side of the graphene / molybdenum disulfide heterojunction away from the substrate. The microfluidic module has a central liquid channel, a gate electrode channel, and two sets of electrode channels located on both sides of the central liquid channel. The central liquid channel is located inside the microfluidic module, and the extension direction of the central liquid channel is perpendicular to the thickness direction of the microfluidic module. The gate electrode channel is located in the middle of the central liquid channel. Each set of electrode channels includes two electrode channels connected at the bottom. The inlet end of one electrode channel is used to insert a wire of an external connection device. The inlet end of the other electrode channel serves as a liquid electrode infusion end, used to infuse liquid gallium indium alloy to form a liquid metal electrode, thereby connecting the heterojunction to the wire. This application introduces a modular heterojunction thin film construction method to achieve the assembly-type fabrication of various functional components of biosensors (such as sensitive areas, electrode areas, and channel structures), which significantly reduces the overall manufacturing complexity and time cost, and improves experimental repeatability and the feasibility of large-scale fabrication.

[0096] Those skilled in the art will understand that the above-described embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail may be made without departing from the spirit and scope of this application. Any person skilled in the art can make their own modifications and alterations without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A biosensor based on a heterojunction field-effect transistor, characterized in that, include: The substrate and the graphene / molybdenum disulfide heterojunction, liquid metal electrode, and microfluidic module disposed on the substrate; The microfluidic module is disposed on the side of the graphene / molybdenum disulfide heterojunction away from the substrate. The microfluidic module has a central liquid channel, a gate electrode channel, and two sets of electrode channels located on both sides of the central liquid channel. The central liquid channel is located inside the microfluidic module, and the extension direction of the central liquid channel is perpendicular to the thickness direction of the microfluidic module; the gate electrode channel is located in the middle of the central liquid channel. Each set of electrode channels includes two bottom-connected electrode channels. The entrance end of one electrode channel is used to insert wires for external connection devices. The entrance end of the other electrode channel serves as a liquid electrode infusion end, used to infuse liquid gallium-indium alloy to form a liquid metal electrode, thereby connecting the heterojunction to the wires.

2. The biosensor based on a heterojunction field-effect transistor according to claim 1, characterized in that, The central liquid channel has an inlet end and an outlet end, which are located on opposite sides of the length of the microfluidic module. A biomolecular solution is pumped in by inserting a hollow tube at the inlet end. The solution flows through the central liquid flow channel reaction zone where the graphene / molybdenum disulfide heterojunction is located and then flows out from the outlet end.

3. The biosensor based on a heterojunction field-effect transistor according to claim 1, characterized in that, Two sets of electrode channels are symmetrically distributed on both sides of the central liquid flow channel with the central liquid flow channel as the axis of symmetry. Liquid metal is injected into the electrode channels by external pressure and forms the source and drain of the field-effect transistor by contacting the graphene / molybdenum disulfide heterojunction and the wire, respectively. A gate electrode channel is formed by drilling a hole in the middle of the central liquid flow channel, and a reference Ag / AgCl electrode is inserted into the gate electrode channel as a gate.

4. The biosensor based on a heterojunction field-effect transistor according to claim 1, characterized in that, With the flow direction of the biomolecular solution as the length direction, the length of the central liquid flow channel is 1 cm to 1.5 cm; The height of the central liquid channel in the thickness direction of the microfluidic module is 30 μm to 50 μm; The width of the central liquid channel in the direction perpendicular to the thickness of the microfluidic module is 20 μm to 50 μm.

5. The biosensor based on a heterojunction field-effect transistor according to claim 1, characterized in that, The liquid metal electrode, formed by injecting liquid gallium-indium alloy into the inlet end of the electrode channel, has a dimension of 200 μm to 300 μm along the length of the central liquid channel.

6. The biosensor based on a heterojunction field-effect transistor according to claim 1, characterized in that, Both the bottom of the substrate and the top of the microfluidic module are provided with chip cover clamps, and the two chip cover clamps are connected by fixing bolts to fix the biosensor.

7. A method for fabricating a biosensor based on a heterojunction field-effect transistor, the method being used to fabricate the biosensor based on a heterojunction field-effect transistor as described in any one of claims 1 to 6, characterized in that, Includes the following steps: A substrate is provided on which a graphene / molybdenum disulfide heterojunction is formed; A microfluidic module is fabricated; the microfluidic module has a central liquid channel, a gate electrode channel, and two sets of electrode channels located on both sides of the central liquid channel; the central liquid channel is located inside the microfluidic module, and the extension direction of the central liquid channel is perpendicular to the thickness direction of the microfluidic module; the gate electrode channel is located in the middle of the central liquid channel; each set of electrode channels includes two electrode channels connected at the bottom; The microfluidic module is placed on the side of the graphene / molybdenum disulfide heterojunction away from the substrate; The microfluidic module and the substrate are fixed using a chip cover plate clamp; A wire from an external connection device is inserted into the inlet of one electrode channel, and liquid gallium-indium alloy is poured into the inlet of another electrode channel to prepare the source and drain electrodes.

8. The method for fabricating a biosensor based on a heterojunction field-effect transistor according to claim 7, characterized in that, The substrate is a silicon oxide substrate, on which a graphene / molybdenum disulfide heterojunction is formed, including: Step 1: Provide a monolayer of molybdenum disulfide grown on sapphire and covered with a layer of polymethyl methacrylate (PMMA) and a monolayer of graphene grown on copper foil and covered with a layer of PMMA; place the PMMA / molybdenum disulfide / sapphire substrate in an etching solution to separate the material from the substrate, change the solution to clean the molybdenum disulfide, and obtain clean PMMA / molybdenum disulfide; Step 2: After transferring PMMA / molybdenum disulfide to silicon oxide, air dry naturally, then dry at 80℃ for 0.5 h to remove residual moisture. Place PMMA / molybdenum disulfide / silicon oxide in acetone solution to remove PMMA, and obtain molybdenum disulfide / silicon oxide. Anneal the mixture. Step 3: Place the PMMA / graphene / copper foil substrate in an etching solution to etch away the copper foil substrate. After cleaning, PMMA / graphene is obtained. Transfer the PMMA / graphene to the molybdenum disulfide / silicon oxide prepared in Step 2, ensuring that the graphene completely covers the molybdenum disulfide. Then remove the PMMA with acetone and anneal to obtain a graphene / molybdenum disulfide heterojunction formed on silicon oxide.

9. The method for fabricating a biosensor based on a heterojunction field-effect transistor according to claim 7, characterized in that, Fabrication of a microfluidic module, including: First, a microfluidic photomask layout with a central liquid channel and electrode channel structure is drawn using CAD software. Then, photoresist is cured and stabilized on a 4-inch silicon wafer using micro-nano fabrication technology to form a positive mold with raised microstructures, thus obtaining a positive mold with microfluidic structure. This positive mold is used for subsequent PDMS casting to form microfluidic structure. Then, the polydimethylsiloxane (PDMS) monomer and crosslinking agent are mixed in a ratio of 9.5:1 and poured onto a positive mold with a microfluidic structure. The mixture is then cured at 80°C for 40-60 min to obtain a PDMS module with a microfluidic structure. On the PDMS module with microfluidic structure, holes are drilled at the inlet end, outlet end and liquid electrode filling end of the liquid to conduct the electrode channel and the central liquid channel, respectively, to facilitate liquid flow and electrode preparation. In addition, a hole is drilled in the middle of the central liquid channel to form a gate electrode channel, which is reserved as a reference Ag / AgCl electrode as the gate.

10. The method for fabricating a biosensor based on a heterojunction field-effect transistor according to claim 7, characterized in that, The microfluidic module and the substrate are fixed using a chip cover clamp, including: The microfluidic module is bonded to the graphene / molybdenum disulfide heterojunction formed on the substrate. Chip cover plate fixtures are set at the bottom of the substrate and the top of the microfluidic module, respectively, and the two chip cover plate fixtures are connected by fixing bolts.

Images