High-stability liquid-gate graphene field-effect transistor and its fabrication method

Abstract

This invention provides a highly stable liquid-gate graphene field-effect transistor and its fabrication method, comprising: S1: hydrophobicating the substrate; S2: growing graphene by vapor deposition; S3: transferring the graphene onto the substrate; S4: drying, removing adhesive, cleaning, and removing impurities; S5: setting up a reaction tank and attaching the reaction tank above the graphene; S6: curing in an ultraviolet chamber to obtain the graphene field-effect transistor. This invention utilizes octadecyltrichlorosilane (OTS) to self-assemble on a glass substrate to form a hydrophobic film, effectively preventing the diffusion of liquid from the graphene surface to the space between the graphene and the substrate, thus overcoming the formation of a water film.

Description

[Technical Field]

[0001] This invention relates to the field of new biomaterials technology, and in particular to a highly stable liquid-gate graphene field-effect transistor and its preparation method. [Background Technology]

[0002] The limitations of traditional medicine have spurred the emergence of precision medicine. Utilizing nucleic acid information for disease diagnosis and treatment is a powerful tool in precision medicine, bringing disease diagnosis and treatment to the molecular level, thus attracting widespread attention both domestically and internationally. Comprehensive analysis of nucleic acid sequences can yield valuable medical information, enabling the design of optimal solutions tailored to individuals, achieving early prevention, accurate diagnosis, and precise treatment of diseases.

[0003] Nucleic acid types and sequences are crucial carriers of biological genetic information, containing a wide range of life information and genetic instructions. In recent years, by analyzing relevant nucleic acid detection information, the challenges of rapid and precise detection of Salmonella, swine influenza virus, COVID-19, Alzheimer's disease, Down syndrome, and various cancers have been successively overcome by graphene-based field-effect transistor (FET) biosensors. This series of innovative breakthroughs has shown researchers that graphene FET-based biosensors offer a new, reliable, and highly promising pathway for rapid and precise detection of various diseases at the molecular level through nucleic acid analysis.

[0004] Field-effect transistor (FET) biosensors typically consist of a source, drain, gate, sensing material, and dielectric layer. Common FET biosensors are classified into two types: back-gate and liquid-gate. Early FET biosensors were based on back-gate designs. However, back-gate FET biosensors generally require a high gate voltage to modulate the sensing material and cannot meet the requirements of solution environment monitoring, thus becoming unsuitable for the increasingly demanding and complex biomolecular detection requirements. In recent years, liquid-gate FET biosensors have attracted increasing attention due to their advantage of allowing direct contact between the gate and the solution medium, easily creating a solution detection environment. Liquid-gate FET biosensors consist of a source, drain, gate, sensing material, and a solution dielectric. When nucleic acid molecules adsorb onto the surface of the sensing material, these biomolecules can affect some electrical properties of the sensing material through electron scattering, electrostatic gating, electron transfer, the Guillauschsmann effect, or the Donan effect. These effects can increase or decrease carrier concentration and mobility, significantly altering the resistance or current of the FET. Researchers can qualitatively or quantitatively detect biomolecules by examining the output and transfer characteristic curves of such field-effect transistor biosensors.

[0005] Experimental studies and literature reviews have revealed that liquid-gate field-effect transistors exhibit significant instability in liquid environments over time. Water molecules can penetrate graphene and form a nanometer-thick intermediate water film between the graphene and the substrate, which modulates charge transfer from graphene to the substrate. More importantly, the thickness of this water film varies with the gate voltage. This means that the signal obtained at the scanning gate voltage may be noise caused by the water film, rather than by charged target molecules. Several research groups have reported similar instability behaviors and proposed methods to overcome the adverse effects of the water layer, such as multiple Vg scans (20 times) and thermo-electrostatic bonding under high temperature and strong electric fields. While these methods improve stability, they still suffer from long testing cycles and extreme fabrication conditions.

[0006] Therefore, it is necessary to study a highly stable liquid-gate graphene field-effect transistor and its fabrication method to address the shortcomings of existing technologies and solve or mitigate one or more of the aforementioned problems. [Summary of the Invention]

[0007] In view of this, the present invention provides a high-stability liquid-gate graphene field-effect transistor and its fabrication method, which utilizes octadecyltrichlorosilane (OTS) to self-assemble on a glass substrate to form a hydrophobic film, effectively preventing the diffusion of liquid from the graphene surface to the graphene and substrate in the solution environment, thus overcoming the formation of a water film.

[0008] On one hand, the present invention provides a method for fabricating a highly stable liquid-gate graphene field-effect transistor on a hydrophobic substrate, the method comprising:

[0009] S1: The substrate is hydrophobically treated;

[0010] S2: Graphene is grown by vapor deposition.

[0011] S3: Transfer graphene onto the substrate;

[0012] S4: Perform drying, degumming, cleaning and impurity removal;

[0013] S5: Set up a reaction groove on the substrate and attach the reaction groove to the graphene to form a graphene field-effect transistor with a reaction groove;

[0014] S6: The graphene field-effect transistor with the reaction tank in S5 is cured in an ultraviolet box.

[0015] In addition to the aspects and any possible implementations described above, an implementation is further provided, wherein S1 specifically includes:

[0016] S11: Dry the substrate, test tubes, and tweezers;

[0017] S12: Protect the test tube from light;

[0018] S13: Prepare a hydrophobic agent solution;

[0019] S14: Place the substrate in a hydrophobic agent solution for reaction;

[0020] S15: Rinse the substrate sequentially with toluene, acetone, ethanol and deionized water, then dry.

[0021] In addition to the aspects and any possible implementations described above, an implementation is further provided in which the hydrophobic agent solution in S13 includes, but is not limited to, a 1% concentration of toluene solution of n-octadecyltrichlorosilane.

[0022] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the reaction time in S14 is 20 minutes.

[0023] In addition to the aspects described above and any possible implementation, a further implementation is provided in which the drying temperature in S15 is 120°C and the drying time is 2 hours.

[0024] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the transfer method in S3 is to transfer graphene by wet transfer, during which the graphene is kept to completely cover the glass channel and uniformly placed on the ITO electrodes at both ends.

[0025] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the drying, desmearing and cleaning in S4 specifically involve drying until the graphene adheres tightly to the surface of the channel and electrode at a temperature of 100°C for 1 hour; desmearing overnight with acetone; and thorough cleaning with ethanol and deionized water.

[0026] In addition to the aspects described above and any possible implementation, a further implementation is provided in which the curing time in S6 is half an hour.

[0027] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the reaction tank in S5 is a polymethyl methacrylate reaction tank, and the bonding method is to attach it to the graphene using a methacrylate adhesive.

[0028] In accordance with the aspects and any possible implementations described above, a highly stable liquid-gate graphene field-effect transistor with a hydrophobic substrate is further provided. The graphene field-effect transistor is prepared by the aforementioned method and is a highly sensitive biosensor for detecting nucleic acid molecules.

[0029] Compared with the prior art, the present invention can achieve the following technical effects:

[0030] 1. This invention can fabricate graphene field-effect transistors with high stability in liquid environments;

[0031] 2. This invention provides a simple, fast, and economical processing method;

[0032] 3. The overall device method of the present invention is simple and controllable, low in cost, and has high application value.

[0033] Of course, any product implementing this invention does not necessarily need to achieve all of the technical effects described above at the same time. [Attached Image Description]

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 Image a is a characterization diagram of the hydrophobicity of a normal graphene field-effect transistor glass substrate provided in an embodiment of the present invention; image b is a characterization diagram of the hydrophobicity of a graphene field-effect transistor glass substrate after hydrophobic treatment provided in an embodiment of the present invention.

[0036] Figure 2 This is a flowchart of the fabrication process of a graphene field-effect transistor provided in one embodiment of the present invention; Figure 3 Figure a is a graph representing the transfer characteristics of a graphene field-effect transistor on a normal glass substrate according to an embodiment of the present invention; Figure b is a graph representing the transfer characteristics of a graphene field-effect transistor on a hydrophobic glass substrate according to an embodiment of the present invention.

Detailed Implementation Methods

[0037] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0038] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0039] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0040] This invention provides a highly stable liquid-gate graphene field-effect transistor with a hydrophobic substrate and a method for fabricating the same, the method comprising:

[0041] S1: The substrate is hydrophobically treated to make it hydrophobic and thus eliminate the water film.

[0042] S2: Graphene is grown by vapor deposition.

[0043] S3: Transfer graphene onto the substrate;

[0044] S4: Perform drying, degumming, cleaning and impurity removal;

[0045] S5: Set up a reaction groove on the substrate and attach the reaction groove to the graphene to form a graphene field-effect transistor with a reaction groove;

[0046] S6: The graphene field-effect transistor with the reaction tank in S5 is cured in an ultraviolet box.

[0047] S1 specifically includes:

[0048] S11: Dry the substrate, test tubes, and tweezers; the test tubes are 10mL tubes, placed in a 70°C drying oven for two hours;

[0049] S12: Protect the test tube from light;

[0050] S13: Prepare a hydrophobic agent solution;

[0051] S14: Place the substrate in a hydrophobic agent solution for reaction;

[0052] S15: Rinse the substrate sequentially with toluene, acetone, ethanol and deionized water, then dry.

[0053] The hydrophobic agent solution in S13 includes, but is not limited to, a 1% concentration of toluene solution of n-octadecyltrichlorosilane. Using n-octadecyltrichlorosilane as a modifier allows the glass substrate to effectively prevent the aqueous solution above the graphene from permeating through the graphene and forming a water film between the substrate and the graphene. n-Octadecyltrichlorosilane is only one of the hydrophobic options.

[0054] The reaction time in S14 is 20 minutes.

[0055] The drying temperature in S15 is 120℃, and the drying time is 2 hours.

[0056] The substrate in S1 includes, but is not limited to, a glass substrate. A glass substrate is only one type of substrate for graphene field-effect transistors; other substrates include high-purity silicon substrates, silicon dioxide substrates, and silicon / silicon dioxide substrates.

[0057] This invention emphasizes the role of hydrophobic substrates in the high stability of field-effect crystals in liquid environments. The types of substrates and hydrophobic agents are not limited to the single glass substrates and n-octadecyltrichlorosilane mentioned above.

[0058] The transfer method in S3 is to transfer graphene by wet transfer, during which the graphene is kept completely covering the glass channel and uniformly mounted on the ITO electrodes at both ends.

[0059] The drying, degumming, and cleaning in S4 specifically involve drying at 100°C for 1 hour until the graphene adheres tightly to the channel and electrode surfaces; degumming overnight with acetone; and thorough cleaning with ethanol and deionized water.

[0060] The curing time in S6 is half an hour.

[0061] The reaction tank in S5 is a polymethyl methacrylate reaction tank, which is attached to the graphene using a purple adhesive.

[0062] The present invention also provides a highly stable liquid-gate graphene field-effect transistor with a hydrophobic substrate, wherein the graphene field-effect transistor is prepared by the aforementioned preparation method, and the graphene field-effect transistor is a highly sensitive biosensor for detecting nucleic acid molecules.

[0063] Example 1:

[0064] like Figure 2 As shown in the figure, the English parts correspond to the explanations in parentheses in the steps. This invention discloses a highly stable liquid-gate graphene field-effect transistor with a hydrophobic substrate, comprising the following fabrication steps:

[0065] Step 1: Graphene is grown on a copper substrate using chemical vapor deposition;

[0066] Step 2: Wet transfer of graphene (using ferric chloride as the copper substrate etching solution and polymethyl methacrylate (PMMA) as the graphene support layer).

[0067] Step 3: Clean the transferred graphene with acetone, ethanol, and deionized water to remove impurities, and set aside for later use;

[0068] Step 4: Dry the glass substrate coated with indium tin oxide (ITO) electrode, tweezers, and 10ml test tube at 70 degrees Celsius for 2 hours;

[0069] Step 5: Dissolve n-octadecyltrichlorosilane in toluene (the volume ratio of n-octadecyltrichlorosilane to toluene is 1:100) in a pre-dried 10ml test tube;

[0070] Step 6: Place the pre-dried glass substrate coated with ITO electrode in the solution and react for 20 minutes. Note that the test tube should be protected from light.

[0071] Step 7: After the reaction is complete, the glass substrate coated with the ITO electrode is cleaned sequentially with toluene, acetone, ethanol, and deionized water.

[0072] Step 8: Cure the glass substrate coated with ITO electrodes at 120 degrees Celsius for two hours;

[0073] Step 9: After cleaning and removing impurities, the graphene is placed onto the surface of the glass substrate coated with ITO electrodes. Note that the graphene should fully cover the glass channels and effectively overlap both ends of the ITO electrodes. After completion, cure at 100 degrees Celsius for two hours.

[0074] Step 10: Attach the custom-made polymethyl methacrylate reaction tank to the graphene using UV adhesive and place it in a UV chamber to cure for half an hour.

[0075] This invention addresses the shortcomings of poor stability in current liquid-gate field-effect transistors (FETs) used for nucleic acid detection. It proposes a method to rapidly, conveniently, and economically enhance the stability of FETs in liquid environments. By modifying a glass substrate with n-octadecyltrichlorosilane to give it hydrophobic properties, thereby eliminating the water film, a highly stable FET in liquid environments is prepared for nucleic acid analysis and detection.

[0076] The shift of the Dirac point in graphene has been widely chosen as a characteristic signal for detecting nucleic acid molecules in FET sensors. Recent reports increasingly indicate that in liquid-gate graphene field-effect transistors (FETs), the Dirac point spontaneously shifts to the left over time, a phenomenon consistent with the specificity observed when probe molecules on the graphene surface capture target molecules. The graphene Dirac point is the lowest point on the transfer characteristic curve of a graphene FET.

[0077] like Figure 3 As shown in (a), the experimental results show that within 4 hours, the Dirac point spontaneously shifts to the left over time without the addition of any target molecules to the test solution, with a maximum left shift of 75 mV. More data are shown in Table 1. In fact, liquid molecules can penetrate graphene and form a nanoscale intermediate water film between graphene and the substrate, which can regulate the charge transfer between graphene and the substrate, thereby causing fluctuations in the Dirac point.

[0078] Table 1: Statistics on the Changes in Dirac Point Before and After Hydrophobicity of Glass Substrate

[0079] Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 mean Minimum value Maximum value Before drainage (4 hours) 46 millivolts 61 millivolts 52 millivolts 75 millivolts 63 millivolts 59.4 millivolts 46 millivolts 75 millivolts After drainage (31 hours) 2 millivolts 3 millivolts 2 millivolts 2 millivolts 1 millivolt 2 millivolts 1 millivolt 3 millivolts

[0080] Additional notes: The above tests were based on 0.8cm x 1cm monolayer graphene; the source and drain bias voltage was 0.1V, the gate was a silver / silver chloride reference electrode, and the test solution was 0.1X phosphate buffer.

[0081] More importantly, some articles report that the thickness of the water film varies with the scanning gate voltage. The scanning gate voltage is a necessary condition for reading the Dirac points of graphene. The presence of the water film makes it impossible to definitively determine whether the signal obtained in SARS-CoV-2 RNA detection is due to the target molecule or spontaneously generated by the graphene in the aqueous solution, thus making the obtained detection signal unconvincing.

[0082] Here, octadecyltrichlorosilane (OTS) is used to form a hydrophobic film on the surface of a graphene substrate via self-assembly to prevent the formation of a water film between the graphene and the graphene substrate (glass). Hydrophobic modification can be easily and quickly achieved by simply immersing the graphene substrate in a toluene solution of OTS for thirty minutes.

[0083] like Figure 1 As shown, comparison Figure 1 (a) and Figure 1 (b) It is clearly visible that after OTS hydrophobic modification, the liquid contact angle of the graphene substrate changed from 20-30 degrees to 100-110 degrees (more data are shown in Table 2). Figure 3 As shown in (b), thanks to the hydrophobic treatment of the GFET substrate, even when graphene is in a liquid environment for up to 31 hours, the maximum left shift of its Dirac point is less than 3 mV (more data are shown in Table 1). Solving the stability problem of graphene in solution environments is a necessary technological breakthrough to promote the reliable detection of COVID-19 nucleic acid using graphene field-effect transistors, and it also has significant guiding significance for biosensing using field-effect transistors based on other sensing materials. The signal instability caused by using a water-film liquid-gate field-effect transistor for nucleic acid detection has been effectively overcome.

[0084] Table 2: Contact Angle Statistics Before and After Hydrophobicity of Glass Substrate

[0085]

[0086] The above provides a detailed description of a highly stable liquid-gate graphene field-effect transistor and its fabrication method provided in the embodiments of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this application; furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

[0087] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0088] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0089] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0090] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A high-stability liquid-gate graphene field effect transistor, characterized by, The graphene field effect transistor is prepared by the following preparation method, which comprises the following steps: S1: hydrophobic treatment is performed on a substrate; S2: graphene is grown by a vapor deposition method; S3: the graphene is transferred to the substrate; S4: drying, glue removal, cleaning and impurity removal treatment are performed; S5: a reaction tank is arranged above the substrate, and the reaction tank is pasted above the graphene to form a graphene field effect transistor with a reaction tank; S6: the graphene field effect transistor with the reaction tank in S5 is subjected to curing treatment in an ultraviolet box. The S1 specifically comprises the following steps: S11: the substrate, a test tube and tweezers are subjected to drying treatment; S12: the test tube is subjected to light-proof treatment; S13: a hydrophobic agent solution is configured; S14: the substrate is placed in the hydrophobic agent solution for reaction; S15: the substrate is sequentially rinsed with toluene, acetone, ethanol and deionized water and then dried; The hydrophobic agent solution in S13 comprises but is not limited to a 1% concentration of n-octadecyltrichlorosilane toluene solution; The reaction time in S14 is 20-40 minutes; The drying temperature in S15 is 80-120 DEG C, and the drying time is 1-2 hours; The transfer method in S3 is wet transfer of the graphene, and the graphene is kept intact to cover the glass channel and uniformly rest on the ITO electrodes at both ends during the transfer process; The graphene field effect transistor is a high-sensitivity biosensor for detecting nucleic acid molecules, and after hydrophobic modification by n-octadecyltrichlorosilane, the liquid contact angle of the graphene substrate of the graphene field effect transistor changes from 20-30 degrees to 100-110 degrees, and the maximum left shift of the Dirac point is less than 3 mV.

2. The graphene field effect transistor of claim 1, wherein, The drying, glue removal and cleaning in S4 are specifically performed under the condition that the temperature is 100 DEG C and the time is 1 hour, the graphene is dried until the graphene is tightly attached to the channel and the electrode surface, glue is removed by acetone overnight, and the graphene is fully cleaned by ethanol and deionized water.

3. The graphene field effect transistor of claim 1, wherein, The curing time in S6 is half an hour.

4. The graphene field effect transistor of claim 1, wherein, The reaction tank in S5 comprises but is not limited to a polymethyl methacrylate reaction tank, and the pasting mode comprises but is not limited to sticking to the graphene by using a UV adhesive.

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