CN112578009B - Graphene transistor label-free DNA sensor and preparation method thereof - Google Patents
Graphene transistor label-free DNA sensor and preparation method thereof Download PDFInfo
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- G01N27/327—Biochemical electrodes, e.g. electrical or mechanical details for in vitro measurements
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Abstract
The invention provides a graphene transistor DNA sensor, which comprises a substrate, and a grid electrode, a source electrode and a drain electrode which are arranged on the substrate; a graphene channel is arranged between the source electrode and the drain electrode; carbon dots are fixed on the surface of the grid electrode. According to the invention, a carbon point is fixed on the surface of a gate electrode of a graphene transistor, then a single-stranded probe DNA is connected to the carbon point, and the single-stranded probe DNA can be complementarily paired with complementary DNA in a solution, so that the interface characteristic of an electric double layer between the transistor and a sample solution is changed, the current in a graphene channel is changed, and trace DNA in the solution can be detected by detecting the current change in the channel; the graphene transistor label-free DNA sensor provided by the invention has the advantages that the operation voltage is lower than 1V, and the minimum detection limit of DNA can reach 10 ‑12 M, and after changing DNA concentration, the current of the sensor changes immediately, and the sensitivity is very high.
Description
Technical Field
The invention relates to the technical field of biosensors, in particular to a graphene transistor label-free DNA sensor and a preparation method thereof.
Background
With the development of nanotechnology, many nanomaterial-based chemical and biological sensors or electronic devices are being extensively studied, and graphene is considered as a very promising material in chemical and biological sensors due to its unique physical properties.
Deoxyribonucleic acid (abbreviated as DNA) is one of the four biological macromolecules contained within a biological cell. DNA carries the genetic information necessary for the synthesis of RNA and proteins, and is a biological macromolecule essential for the development and normal functioning of organisms. DNA diagnostics has shown great scientific and economic value in many fields. The method has important application value in aspects of gene expression monitoring, clinical medicine, virus and bacteria identification, biological weapon and biological terrorist detection and the like. However, detection of nucleic acid molecules, especially short DNA strands, is challenging if time-consuming radiolabeled assays and non-portable confocal fluorescence microscopy are not used. Therefore, it is of great significance to design a biochemical sensor that can effectively detect DNA in an organism. In the device of the graphene transistor, the functionalization of the DNA probe and the nanomaterial facilitates the realization of high-sensitivity and selective DNA detection.
Disclosure of Invention
The invention aims to provide a deviceGraphene transistor copper DNA sensor and preparation method and application thereof. The graphene transistor copper DNA sensor provided by the invention is simple to operate and convenient to use, can be used for detecting DNA with extremely low concentration, has high sensitivity, and can reach 10 at the lowest detection limit of the DNA -14 M。
The invention provides a graphene transistor DNA sensor, which comprises a substrate, and a grid electrode, a source electrode and a drain electrode which are arranged on the substrate; a graphene channel is arranged between the source electrode and the drain electrode; carbon dots are fixed on the surface of the grid electrode.
Preferably, the width of the graphene channel is 0.2-0.3 mm, and the length of the graphene channel is 4-8 mm.
Preferably, the graphene channel is a single-layer graphene.
Preferably, the gate, source and drain independently include a chromium layer and a gold layer, the chromium layer being located between the substrate and the gold layer.
Preferably, the thickness of the chromium layer is 6-12 nm, and the thickness of the gold layer is 40-90 nm.
Preferably, the fixed amount of carbon points on the surface of the grid electrode is 10-30 mug/mm 2 。
The invention also provides a preparation method of the graphene transistor DNA sensor, which comprises the following steps:
(1) Preparing a grid electrode, a source electrode and a drain electrode on the surface of a substrate, so that a channel exists between the source electrode and the drain electrode;
(2) Tiling graphene on a channel between a source electrode and a drain electrode to obtain a graphene transistor;
(3) And (3) fixing carbon points on the surface of the grid electrode of the graphene transistor obtained in the step (2) to obtain the graphene transistor DNA sensor.
Preferably, the preparing of the gate electrode, the source electrode and the drain electrode in the step (1) includes: and sequentially evaporating a chromium layer and a gold layer on the surface of the substrate by adopting a thermal evaporation coating method.
Preferably, the preparation of the carbon dots in the step (3) includes: and carrying out hydrothermal reaction on sodium alginate, ethylenediamine and deionized water in a reaction kettle.
Preferably, the method for fixing carbon points in the step (3) includes: performing activation treatment after modifying carboxyl on the surface of the grid electrode in the graphene transistor obtained in the step (2); and coating the carbon dot dispersion liquid on the surface of the gate after the activation treatment.
The invention also provides the application of the graphene transistor DNA sensor in DNA detection or the graphene transistor DNA sensor prepared according to the technical scheme.
The invention provides a graphene transistor DNA sensor, which comprises electronic grade glass, and a grid electrode, a source electrode and a drain electrode which are arranged on the electronic grade glass; a graphene channel is arranged between the source electrode and the drain electrode; carbon dots are fixed on the surface of the grid electrode. According to the invention, carbon dots are fixed on the surface of the gate electrode of the graphene transistor, and the carbon dots can adsorb DNA in the solution, so that the interface characteristic of an electric double layer between the transistor and a sample solution is changed, the current in a graphene channel is changed, and trace DNA in the solution can be detected by detecting the current change in the channel; the graphene transistor DNA sensor provided by the invention can be directly immersed in electrolyte to detect DNA, and is a label-free detection method, simple in operation and low in cost; the three-electrode structure and the graphene channel of the graphene transistor DNA sensor provided by the invention have the advantages that the induction to the change of voltage is very strong, the corresponding current change can be caused by the small voltage change, and the sensitivity is high; and the voltage of the input grid electrode is used for controlling the current of the graphene channel, so that the operation voltage is reduced. Experimental results show that the operation voltage of the graphene transistor DNA sensor provided by the invention is lower than 1V, and the minimum detection limit of DNA can reach 10 -14 M, provided that the degree of change in the DNA concentration is greater than 10 -14 The current of the sensor changes immediately, and the sensitivity is very high.
Drawings
FIG. 1 is a schematic diagram of a graphene transistor DNA sensor in an embodiment of the present invention;
FIG. 2 is a schematic diagram of a preparation process of a graphene transistor DNA sensor in an embodiment of the present invention;
FIG. 3 is a schematic diagram of a three-electrode structure of a graphene transistor DNA sensor according to embodiment 1 of the present invention;
FIG. 4 is a graph showing the transfer characteristic of the graphene transistor DNA sensor of example 3 of the present invention when detecting the DNA concentration;
FIG. 5 is a graph showing the output characteristics of the graphene transistor DNA sensor of example 3 according to the present invention when detecting the DNA concentration;
Detailed Description
The invention provides a graphene transistor DNA sensor, which comprises a substrate, and a grid electrode, a source electrode and a drain electrode which are arranged on the substrate; a graphene channel is arranged between the source electrode and the drain electrode; carbon dots are fixed on the surface of the grid electrode; the carbon spot is connected with a single-stranded probe DNA.
The graphene transistor DNA sensor provided by the invention comprises a substrate. The kind and source of the substrate are not particularly limited, and a substrate for a sensor known to those skilled in the art may be used. In a specific embodiment of the present invention, the substrate is preferably electronic grade glass, silicon wafer or PET, more preferably electronic grade glass; in the present invention, the electronic grade glass is preferably GL-10173-1.1.
The invention has no special limitation on the size of the substrate, and the size of the substrate can be adjusted according to the size of the device. In the present invention, the length and width of the substrate are preferably independently preferably 10 to 15mm, more preferably 12mm; the thickness of the substrate is preferably 2mm.
The graphene transistor DNA sensor provided by the invention comprises a grid electrode, a source electrode and a drain electrode which are arranged on the substrate. In the present invention, the gate electrode, the source electrode, and the drain electrode are preferably sequentially arranged on the same surface of the substrate at intervals; the specific positions of the grid electrode, the source electrode and the drain electrode are not particularly required, and the positions are set according to the well-known positions in the art. In the present invention, a channel having a width of 0.25 to 0.35mm is preferably formed between the source electrode and the drain electrode. The shapes of the gate electrode, the source electrode and the drain electrode are not particularly limited, and the shapes of the electrodes known to those skilled in the art may be used.
In the present invention, the gate electrode, the source electrode, and the drain electrode preferably independently include a chromium layer and a gold layer, the chromium layer being located between the substrate and the gold layer. In the present invention, the thickness of the chromium layer in the gate electrode, the source electrode, and the drain electrode is independently preferably 8 to 11nm, more preferably 8nm; the thickness of the gold layer in the gate, source and drain electrodes is independently preferably 40 to 70nm, more preferably 70nm. In the invention, the chromium layer enables the gold layer to be firmly attached to the surface of the substrate, and the gold layer is prevented from falling off in the later operation.
In the invention, the three-electrode structure of the grid electrode, the source electrode and the drain electrode can control the channel current by utilizing the voltage of the input grid electrode in the DNA detection process, so as to realize the operation voltage lower than 1V.
The graphene transistor DNA sensor provided by the invention comprises a graphene channel arranged between the source electrode and the drain electrode. In the invention, the channel formed between the source electrode and the drain electrode in the technical scheme is a graphene channel. In the invention, the width of the graphene channel is preferably 0.25-0.35 mm, more preferably 0.25mm; the length of the graphene channel is preferably 5-8 mm, more preferably 5mm. In the present invention, the graphene preferably fills the gap between the source electrode and the drain electrode. In the present invention, the graphene channel is preferably a single-layer graphene. In the invention, the graphene channel can increase the sensitivity of the sensor.
The graphene transistor DNA sensor provided by the invention comprises carbon points fixed on the surface of a grid electrode. In the invention, the carbon dots are carbon nano materials with monodispersion characteristic and similar to spheres; the fixed amount of carbon points on the surface of the grid electrode is preferably 10-15 mug/mm 2 More preferably 15. Mu.g/mm 2 。
The schematic diagram of the graphene transistor DNA sensor provided by the invention is shown in figure 1, the gate electrode and the graphene channel are conducted by electrolyte to form a double-capacitance structure, and the voltage applied between the gate electrode and the graphene channel is constant. Since the electric double layer interface characteristic of the probe DNA on the immobilized carbon point changes when the complementary DNA is adsorbed, the current on the graphene channel is changed, and trace DNA in the solution can be quantitatively detected by detecting the current change in the channel.
The invention also provides a preparation method of the graphene transistor DNA sensor, which comprises the following steps:
(1) Preparing a grid electrode, a source electrode and a drain electrode on the surface of a substrate, so that a channel exists between the source electrode and the drain electrode;
(2) Tiling graphene on a channel between a source electrode and a drain electrode to obtain a graphene transistor;
(3) And (3) fixing carbon points on the surface of the grid electrode of the graphene transistor obtained in the step (2) to obtain the graphene transistor DNA sensor.
The invention prepares a grid electrode, a source electrode and a drain electrode on the surface of a substrate, so that a channel exists between the source electrode and the drain electrode. In the present invention, the preparation of the gate electrode, the source electrode and the drain electrode preferably includes: and sequentially evaporating a chromium layer and a gold layer on the surface of the substrate by adopting a thermal evaporation coating method.
The specific parameters of the thermal evaporation coating method are not particularly limited, and the electrode with the required thickness can be prepared by adopting parameters well known to those skilled in the art. In the present invention, the thermal evaporation coating is preferably performed under vacuum conditions; the vacuum degree of the vacuum is preferably 8×10 -4 Pa or less, more preferably 4×10 -4 Pa. In the present invention, the evaporation temperature of the chromium layer is preferably 180 to 200 ℃, more preferably 185 to 190 ℃; the vapor deposition temperature of the gold layer is preferably 100 to 120 ℃, more preferably 105 to 110 ℃.
The invention preferably cleans and dries the substrate prior to use. In the present invention, the washing is preferably ultrasonic washing, and more preferably ultrasonic washing is performed using acetone, isopropyl alcohol, and ethanol in this order. In the present invention, the time of ultrasonic cleaning of the acetone, isopropyl alcohol and ethanol is independently preferably 8 to 30 minutes, more preferably 20 minutes. The frequency of the ultrasonic cleaning is not particularly limited, and may be any frequency known to those skilled in the art. In the present invention, the drying is preferably drying.
After the preparation of the grid electrode, the source electrode and the drain electrode is completed, graphene is tiled on a channel between the source electrode and the drain electrode, and the graphene transistor is obtained. In the present invention, tiling of the graphene preferably includes: and transferring the metal substrate single-layer graphene onto a channel between the source electrode and the drain electrode by adopting wet transfer. In the present invention, the metal-based single-layer graphene is preferably copper-based CVD single-layer graphene. The source of the metal substrate single-layer graphene is not particularly limited, and the metal substrate single-layer graphene can be prepared by using commercial products well known to the skilled person or according to a preparation method well known to the skilled person. In the invention, the redundant grapheme on the two sides of the channel is preferably removed after the transfer, the method for removing the redundant grapheme is not particularly required, and in the specific embodiment of the invention, the redundant grapheme is preferably removed by using a toothpick.
The wet transfer operation is not particularly limited, and a technical scheme of wet transfer of single-layer graphene, which is well known to those skilled in the art, is adopted. In the invention, the technical scheme of the wet transfer single-layer graphene is preferably shown by Chen Mu, yan Yue, zhang Xiaofeng, and the like, the large-area graphene film transfer technology research progress [ J ]. Aviation materials journal, 2015, 35 (2): 1-11. The technical scheme disclosed in the specification.
After the transfer of the graphene is completed, the transferred product is preferably annealed to obtain the graphene transistor. In the present invention, the annealing temperature is preferably 110 to 130 ℃, more preferably 120 ℃; the annealing time is preferably 20 to 30 minutes, more preferably 25 minutes. In the invention, the annealing can remove the moisture on the surface of the sample, and can enable the graphene to be combined with the substrate more tightly.
After the graphene transistor is obtained, carbon points are preferably fixed on the surface of a grid electrode of the graphene transistor, so that the graphene transistor DNA sensor is obtained. In the present invention, the fixing of the carbon dots in the step (3) includes: performing activation treatment after modifying carboxyl on the surface of the grid electrode of the graphene transistor obtained in the step (2); and coating the carbon dot dispersion liquid on the surface of the gate after the activation treatment.
According to the invention, the activation treatment is carried out after the surface of the grid electrode of the graphene transistor obtained in the step (2) is modified with carboxyl. The invention preferably uses the thioglycollic acidCoating the aqueous solution on the surface of the grid, and then preserving the aqueous solution in a dark place, so that carboxyl groups are modified on the surface of the grid; the present invention preferably uses no particular requirement for the type of the thioglycollic acid, and the thioglycollic acid known to those skilled in the art is used, and is preferably n-thioglycollic acid. In the present invention, the concentration of the aqueous solution of mercaptoethanol is preferably 40 to 60mmol/L, more preferably 50mmol/L; the invention preferably drops the aqueous solution of the mercaptoethanol acid on the surface of the grid, and the drop-coating amount of the aqueous solution of the mercaptoethanol acid is preferably 5-20 mu L/mm 2 More preferably 10. Mu.L/mm 2 The method comprises the steps of carrying out a first treatment on the surface of the The time for the light-shielding preservation is preferably 10 to 15 hours, more preferably 12 hours. In the present invention, the hydrophobic interaction in the gold gate and the hydrophobic glycolic acid generates an S-Au bond, thereby modifying the carboxyl group at the gate surface.
After the carboxyl is modified on the surface of the gate of the graphene transistor, the carboxyl on the surface of the gate is activated. In the present invention, a mixed solution of 1- (3-dimethylaminopropyl) -3-Ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) is preferably applied to the gate surface to activate the carboxyl group. In the present invention, the concentration of EDC in the mixed solution is preferably 0.15 to 0.25mmol/L, more preferably 0.2mmol/L; the concentration of NHS in the mixed solution is preferably 0.4 to 0.6mmol/L, more preferably 0.5mmol/L; the solvent of the mixed solution is preferably Phosphate Buffer (PBS) with pH of 5.5; the invention preferably drops a mixed solution of 1- (3-dimethylaminopropyl) -3-Ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) onto the gate surface, the drop of the mixed solution preferably being 5 to 20. Mu.L/mm 2 More preferably 10. Mu.L/mm 2 The method comprises the steps of carrying out a first treatment on the surface of the After the dripping is finished, the graphene transistor with the mixed solution dripped on the grid is preferably kept stand for 4-6 hours, preferably kept stand for 5 hours, so that carboxyl is fully activated; the invention improves the activity of carboxyl connected to the surface of the grid electrode through the activation treatment, and is convenient for fixing carbon points.
After the activation treatment is completed, the activated grid is preferably washed three times by using PBS buffer solution, and residual thioglycollic acid, EDC and NHS on the surface of the grid are washed clean by washing.
After the cleaning is finished, the carbon dot dispersion liquid is coated on the surface of the grid after the activation treatment, and the graphene transistor DNA sensor is obtained.
In the present invention, the carbon dots are preferably prepared by the steps of:
and mixing sodium alginate, amine substances and a polar solvent, and performing hydrothermal reaction to obtain carbon dots.
In the invention, the amine substance is preferably a mixture of sodium alginate and ethylenediamine; the mass ratio of the sodium alginate to the amine substances is preferably 1 to 20-80, more preferably 1 to 60; the polar solvent is preferably water or ethanol; the mass ratio of the sodium alginate to the solvent is preferably 0.25g to 20-50 mL, more preferably 1g to 140mL. In the present invention, the temperature of the hydrothermal reaction is preferably 180 to 220 ℃, more preferably 200 ℃, and the time of the hydrothermal reaction is preferably 2 to 5 hours, more preferably 3 hours.
After the hydrothermal reaction is completed, the hydrothermal product is preferably subjected to centrifugation, dialysis, concentration and freeze drying in sequence to obtain carbon dots. In the present invention, the rotational speed for centrifugation is preferably 8000 to 12000rpm, more preferably 10000rpm, and the time is preferably 5 to 10min, more preferably 8min; the dialysis membrane for dialysis preferably has a molecular weight cut-off of 500 to 2000Da (daltons), more preferably 1000Da; the method of dialysis according to the invention is not particularly limited, and dialysis methods well known to those skilled in the art may be used.
After the dialysis is completed, the present invention preferably concentrates the dialysis product. In the present invention, the concentration is preferably evaporation concentration, and the temperature of the evaporation concentration is preferably 30-90 ℃, more preferably 80 ℃; the dialysis product is preferably concentrated to 1/3 to 1/5 of the original dialysis product volume.
After concentration is completed, the concentrated product is preferably subjected to freeze drying to obtain carbon dots. In the present invention, the temperature of the freeze-drying is preferably-45 ℃; the time for the freeze-drying is preferably 24 to 48 hours, more preferably 48 hours.
After obtaining the carbon dots, the present invention preferably disperses the carbon dots in water to obtain a carbon dot dispersion. In the present invention, the concentration of the carbon dot dispersion is preferably 1 to 3mg/mL, more preferably 2mg/mL; the method of the present invention is not particularly limited, and the carbon dots can be uniformly dispersed by using a dispersing method well known to those skilled in the art.
After the carbon dot dispersion liquid is obtained, the carbon dot dispersion liquid is coated on the surface of the grid after the activation treatment, and the graphene transistor DNA sensor is obtained. The invention preferably drops a carbon dot dispersion onto the gate surface, the drop of the carbon dot dispersion preferably being 10 to 30. Mu.g/mm 2 More preferably 15. Mu.g/mm 2 After the completion of the dropping, the graphene transistor dropped with the carbon dot dispersion is preferably left to stand for 1 to 3 hours, more preferably for 2 hours, to fix the carbon dots on the gate surface.
In the invention, the thioglycollic acid contains both a thiobase and a carboxyl, the gold grid and the sulfhydryl act to generate an S-Au bond, and the carboxyl on the surface of the carbon point are dehydrated and condensed to generate an ester bond, so that the carbon point is fixed on the surface of the grid.
Then 15. Mu.g/mm 2 The probe DNA of (2) was applied dropwise to the surface of the gate electrode and stored in a dark place for 12 hours.
The invention also provides the application of the graphene transistor DNA sensor in DNA detection or the graphene transistor DNA sensor prepared according to the technical scheme. In the invention, the grid electrode and the graphene channel part of the graphene transistor DNA sensor are immersed in a solution containing DNA to be detected, constant voltage is applied between the source electrode and the drain electrode of the graphene transistor DNA sensor in the detection process, and the grid voltage is applied to the grid electrode, so that trace DNA in the solution can be detected by detecting current change in the graphene channel. In the present invention, the gate voltage is preferably 0.5 to 1V, more preferably 0.8V, and the constant voltage between the source and the drain is preferably 0.1V.
When the graphene transistor DNA sensor provided by the invention is used for measuring DNA, a standard solution containing DNA is preferably prepared, a current change value and a standard curve of DNA concentration are measured, and the concentration of the DNA to be measured is determined according to the standard curve and the current change value obtained by testing.
The invention provides a stoneThe graphene transistor DNA sensor is directly immersed in a solution to be detected to detect the DNA concentration, so that the detection method is a label-free detection method; and can carry out high-sensitivity detection on the sample, and has good stability. The three-electrode structure and the graphene channel of the graphene transistor DNA sensor provided by the invention have the advantages that the induction to the change of voltage is very strong, the corresponding current change can be caused by the small voltage change, and the sensitivity is high; in addition, the graphene transistor DNA sensor provided by the invention can be used for carrying out concentration down to 10 in solution -12 Detection of very small amounts of DNA of M.
In order to further illustrate the present invention, the graphene transistor DNA sensor provided by the present invention, and the preparation method and application thereof are described in detail below with reference to examples, but they should not be construed as limiting the scope of the present invention.
A schematic diagram of a preparation process of the graphene transistor DNA sensor is shown in FIG. 2.
Example 1:
thermal evaporation coating:
cutting electronic grade glass into 12X 12mm, sequentially ultrasonic cleaning with acetone, isopropanol and ethanol for ten minutes, oven drying in a drying box, adhering the glass sheet on a mask plate with a specific shape by using high-temperature adhesive, weighing appropriate amount of chromium and gold, and putting into a tungsten boat for preparing vacuum thermal evaporation coating.
Chromium is firstly evaporated during evaporation: the thickness was 8nm.
And (3) steaming the gold plating layer: the thickness was 50nm.
The electrode shape, structure and dimensions obtained are shown in fig. 3. In fig. 3, G is gate, S is source, and D is drain, and a channel with a width of 0.25mm between the source and the drain is a graphene channel after transferring graphene.
Wet transfer of monolayer graphene:
250mg of methyl methacrylate (PMMA) having a molecular weight of 99600g/mol was dissolved in 5mL of anisole and stirred on a magnetic stirrer to give a clear and transparent PMMA/anisole solution having a concentration of 50 mg/mL.
Cutting single-layer copper-based graphene obtained by an electrochemical deposition method to a size of 12mm multiplied by 12mm, dropwise adding 10 mu L of PMMA/anisole solution prepared by spin coating on the surface of the graphene, setting the rotating speed of a spin coater to be 3000rpm, spin coating for 30s, and drying at room temperature for 30min after spin coating is finished to obtain the PMMA/graphene.
Preparing a copper chloride solution with the concentration of 0.1g/mL, and placing the dried PMMA/graphene in the copper chloride solution with the side of the PMMA/anisole solution coated by spin facing upwards to completely etch the copper substrate.
Transferring PMMA/graphene etched with a copper substrate into deionized water by using a glass slide, soaking for 10min, replacing the deionized water for 2 times, and washing residual copper chloride solution on the PMMA/graphene by using the deionized water; and taking an electrode slice manufactured by thermal evaporation coating, respectively carrying out ultrasonic cleaning by using acetone, isopropanol and deionized water, drying, and then treating the surface of the electrode slice by using oxygen plasma to improve the hydrophilicity of the electrode slice.
Transferring the cleaned PMMA/graphene onto a cleaned electrode, flatly laying the cleaned PMMA/graphene on a channel between a source electrode and a drain electrode on the surface of an electrode sheet, naturally airing until no surface moisture is observed by naked eyes, then placing the electrode sheet on a heat table for annealing at 120 ℃, and thoroughly removing the surface moisture of a sample to obtain the PMMA/graphene/electrode sheet.
And cooling to room temperature, and removing redundant PMMA/graphene on two sides of the channel by using a toothpick. And then, acetone is used for washing PMMA/graphene/electrode plates twice for 10min each time, then the PMMA/graphene/electrode plates are put into an acetone solution and heated for 3h at 65 ℃, and the surface PMMA is removed, so that the required graphene transistor is obtained. And after 3 hours, the graphene transistor is replaced by deionized water, and is naturally dried and then is annealed at 120 ℃ for 30 minutes in a glove box to remove moisture and impurities attached to the surface of the graphene transistor.
Preparing a carbon dot solution: 0.2g of sodium alginate, 15mL of ethylenediamine and 20mL of deionized water are subjected to hydrothermal treatment at 200 ℃ in a 50mL reaction kettle for 3 hours, and then are subjected to centrifugation, dialysis, evaporative concentration and freeze drying to obtain pure carbon dots; pure carbon dots were dispersed in water to give 1mg/mL carbon dot solution.
Fixed carbon point: 10 mu L of 50mM thioglycollic acid is dripped on the surface of the grid electrode, and the grid electrode is preserved in dark for overnight, so that carboxyl groups are modified on the surface of the grid electrode; then 10 μl of a mixture of EDC (0.2 mm, ph=5.5 PBS) and NHS (0.5 mm, ph=5.5 PBS) was dropped onto the electrode surface to activate the carboxyl groups, and after 5 hours, washed three times with PBS buffer; and (3) dripping 10 mu L of 1mg/mL carbon dot solution, fixing the carbon dot solution on the grid for 2 hours, washing the grid once by using PBS buffer solution, washing off unfixed carbon dots and other impurities on the grid, dripping probe single-stranded DNA, and keeping away from light for 12 hours to obtain the graphene transistor DNA sensor.
Example 2:
thermal evaporation coating:
cutting electronic grade glass into 12X 12mm, sequentially ultrasonic cleaning with acetone, isopropanol and ethanol for ten minutes, oven drying in a drying box, adhering the glass sheet on a mask plate with a specific shape by using high-temperature adhesive, weighing appropriate amount of chromium and gold, and putting into a tungsten boat for preparing vacuum thermal evaporation coating.
Chromium is firstly evaporated during evaporation: the thickness was 6nm.
And (3) steaming the gold plating layer: the thickness was 35nm.
The shape, structure and dimensions of the electrode obtained were the same as in example 1.
Wet transfer of monolayer graphene:
250mg of methyl methacrylate (PMMA) having a molecular weight of 99600g/mol was dissolved in 5mL of anisole and stirred on a magnetic stirrer to give a clear and transparent PMMA/anisole solution having a concentration of 50 mg/mL.
Cutting single-layer copper-based graphene obtained by an electrochemical deposition method to a size of 12 multiplied by 12mm, dropwise adding 10 mu L of PMMA/anisole solution prepared by spin coating on the surface of the graphene, setting the rotating speed of a spin coater to be 3000rpm, spin coating for 30s, and drying at room temperature for 30min after spin coating is finished to obtain the PMMA/graphene.
Preparing a 100mg/mL copper chloride solution, and placing the dried PMMA/graphene in the copper chloride solution with the side of the PMMA/anisole solution spin-coated upwards to completely etch the copper substrate.
Transferring PMMA/graphene etched with a copper substrate into deionized water by using a glass slide, soaking for 10min, replacing the deionized water for 2 times, and washing residual copper chloride solution on the PMMA/graphene by using the deionized water; and taking an electrode slice manufactured by thermal evaporation coating, respectively carrying out ultrasonic cleaning by using acetone, isopropanol and deionized water, drying, and then treating the surface of the electrode slice by using oxygen plasma to improve the hydrophilicity of the electrode slice.
Transferring the cleaned PMMA/graphene onto a cleaned electrode, flatly laying the cleaned PMMA/graphene on a channel between a source electrode and a drain electrode on the surface of an electrode sheet, naturally airing until no surface moisture is observed by naked eyes, then placing the electrode sheet on a heat table for annealing at 120 ℃, and thoroughly removing the surface moisture of a sample to obtain the PMMA/graphene/electrode sheet.
And cooling to room temperature, and removing redundant PMMA/graphene on two sides of the channel by using a toothpick. And then, acetone is used for exchanging and washing PMMA/graphene/electrode plates twice for 10 minutes each time, then the PMMA/graphene/electrode plates are put into an acetone solution and heated for 3 hours at 65 ℃, and the surface PMMA is removed, so that the required graphene transistor is obtained. And after 3 hours, the graphene transistor is replaced by deionized water, and is naturally dried and then is annealed for 30 minutes at 120 ℃ in a glove box to remove moisture and impurities attached to the surface of the graphene transistor.
Preparing a carbon dot solution: 0.2g of sodium alginate, 15mL of ethylenediamine and 20mL of deionized water are subjected to hydrothermal treatment at 200 ℃ in a 50mL reaction kettle for 4 hours, and then are subjected to centrifugation, dialysis, evaporative concentration and freeze drying to obtain pure carbon dots; pure carbon dots were dispersed in water to give a 2mg/mL carbon dot solution.
Fixed carbon point: 10 mu L of 50mM of thioglycollic acid is dripped on the surface of the grid electrode, and the grid electrode is preserved in dark for overnight, so that carboxyl groups are modified on the surface of the grid electrode; then 10 μl of a mixture of EDC (0.2 mm, ph=5.5 PBS) and NHS (0.5 mm, ph=5.5 PBS) was dropped onto the electrode surface to activate the carboxyl groups, and after 6 hours, washed three times with PBS buffer; and (3) dripping 15 mu L of 1mg/mL carbon dot solution, fixing the carbon dot solution on the grid for 2.5 hours, washing the grid once by using PBS buffer solution, washing off unfixed carbon dots and other impurities on the grid, dripping probe single-stranded DNA, and keeping away from light for 12 hours to obtain the graphene transistor DNA sensor.
Example 3
DNA concentration was tested using the graphene transistor DNA sensor prepared in example 1:
the source, drain and gate electrodes of the graphene transistor are connected to two combined Keithley data source tables (Keithley 2400), gate voltage V G And source-drain voltage V DS Is controlled by a Labview program in the computer.
The modified gate electrode was thoroughly washed with PBS solution to remove residues left on the electrode. The test was performed in a beaker filled with 10mL of PBS solution. During the test, a specific concentration of DNA solution was added to the solution of PBS, thereby obtaining different DNA concentrations.
Transfer characteristic test: the source-drain voltage is set to a constant value (V DS =0.1v), the channel current I between the source and the drain is measured while the gate voltage is continuously changed from 0.5V to 1.1V DS Then changing the concentration of DNA in the solution for sequential measurement; the transfer characteristic obtained is shown in FIG. 4. The change in interface will change the potential at the surface of the device and thus shift the characteristic curve, and it can be seen from fig. 4 that as the DNA concentration increases, the curve shifts to the right, i.e. the current of the device increases with increasing DNA concentration at the same voltage.
Output characteristic test: the source-drain voltage and the gate voltage are set to a constant value (V DS =0.1v and V G =0.8v), the channel current versus time image was continuously measured. During which the DNA concentration was increased from 10 after the channel current was stabilized for about 300 seconds -12 M、10 -11 M、10 -10 M、10 -9 M、10 -8 M is changed in turn; the test results obtained are shown in FIG. 5; as can be seen from fig. 5, the change of the DNA concentration can cause the current to change significantly, the magnitude of the current change can reflect the magnitude of the concentration change, and the current of the sensor changes immediately after the DNA concentration is changed, so that the sensitivity is very high; the graphene transistor DNA sensor provided by the invention can be used for carrying out concentration down to 10% in solution -12 Detection of very small amounts of DNA of M.
The foregoing is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that modifications and adaptations to the present invention may occur to one skilled in the art without departing from the principles of the present invention and are intended to be comprehended within the scope of the present invention.
Claims (1)
1. A graphene transistor DNA sensor with a functionalized grid carbon point comprises a substrate, and a grid, a source electrode and a drain electrode which are arranged on the substrate; a graphene channel is arranged between the source electrode and the drain electrode; fixing a carbon point on the surface of the gold grid, connecting single-stranded probe DNA to the carbon point, and detecting complementary DNA; performing activation treatment after carboxyl is modified on the surface of the gold grid; coating carbon dot dispersion liquid on the surface of the gold grid after the activation treatment; the fixed quantity of carbon points on the surface of the gold grid is 8-15 mug/mm 2 The graphene channel is single-layer graphene, the width of the graphene channel is 0.25-0.35 mm, and the length of the graphene channel is 5-8 mm.
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