Preparation method of carbon nanotube sensor adopting low-cost evaporation process and method for detecting Hg < 2 + > by using sensor

Abstract

The invention discloses a preparation method of a carbon nanotube sensor adopting a low-cost evaporation process and a method for detecting Hg < 2 + > by using the sensor, and the preparation method of the carbon nanotube sensor adopting the low-cost evaporation process comprises the following steps: S1, cleaning and preparing a silicon oxide sheet; s2, growing and preparing a carbon nano tube; s3, copper net attachment and electrode evaporation; s4, preparing a nano gap; s5, carrying out functional modification on the sensor; the preparation cost is low, the process is simple and convenient, an evaporation process is adopted to prepare the electrode, traditional expensive micro-nano machining technologies such as EBL and FIB are replaced, and the preparation cost is greatly reduced; meanwhile, the process of forming the nano gap by triggering electric breakdown of the carbon nano tube through voltage stress is simple and convenient to operate, high in controllability and beneficial to large-scale production; the prepared sensor has high sensitivity and high selectivity when used for detecting Hg < 2 + >, the current tends to be stable after the sensor is soaked in ultrapure water and a 1 * PBS solution for 90 min, the stability is good, and the requirement for accurate detection of trace Hg < 2 + > can be met.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, specifically to a low-cost carbon nanotube sensor fabrication method using vapor deposition and the use of this sensor to detect Hg. 2+ The method. Background Technology

[0002] Mercury ions (Hg) 2+ Hg, as a highly toxic heavy metal ion, exhibits high toxicity, bioaccumulation, and persistence. Even at trace concentrations, it can cause serious harm to the human nervous, digestive, and respiratory systems, while also causing irreversible damage to the ecological environment. Therefore, it is necessary to develop a highly sensitive, highly selective, low-cost Hg ion suitable for detection in practical samples. 2+ The detection method has important practical significance.

[0003] Currently, Hg 2+ Detection methods mainly include atomic absorption spectrometry, atomic fluorescence spectrometry, and inductively coupled plasma mass spectrometry. While these methods offer high detection sensitivity, they typically require complex sample pretreatment processes, expensive instruments, and specialized operators, making rapid on-site detection difficult. Biosensor technology, with its advantages of high sensitivity, real-time response, and ease of operation, has attracted widespread attention in the field of heavy metal ion detection.

[0004] Carbon nanotubes (CNTs), as one-dimensional nanomaterials with excellent electrical properties, high specific surface area, and good biocompatibility, are widely used in the construction of biosensors. Field-effect transistor (FET) biosensors based on carbon nanotubes can achieve highly sensitive detection of target substances by converting biochemical signals into electrical signals. However, the fabrication of existing carbon nanotube FET sensors often relies on high-precision micro-nano fabrication techniques such as electron beam lithography (EBL) and focused ion beam (FIB). These techniques are time-consuming and costly, limiting their large-scale production and practical applications. Furthermore, some carbon nanotube sensors still need improvement in terms of detection selectivity and stability, making it difficult to meet the requirements for detecting Hg in complex real-world samples. 2+ The need for precise testing.

[0005] Based on this, a low-cost carbon nanotube sensor fabrication method using vapor deposition is designed, and the sensor is used to detect Hg. 2+ The method. Summary of the Invention

[0006] The purpose of this invention is to provide a low-cost carbon nanotube sensor fabrication method using vapor deposition and to utilize this sensor for Hg detection. 2+ The method is to solve the problems raised in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A low-cost carbon nanotube sensor fabrication method using vapor deposition technology includes the following steps:

[0009] S1. Preparation of cleaning silicon oxide wafers: Cut silicon wafers into 15mm×15mm silicon oxide wafers, immerse them in piranha solution at 90℃ for more than 3 hours to remove surface impurities, then transfer them to ultrapure water, shake them at 70r / min for 10 minutes on an orbital oscillator, repeat the water changing and shaking steps three times, and finally blow them dry with pure nitrogen and store them in an IPC vacuum desiccator.

[0010] S2. Growth and preparation of carbon nanotubes: Using chemical vapor deposition, a 4.5 mm stainless steel needle wiped with anhydrous ethanol was dipped into a CuCl2 solution catalyst and uniformly coated on the silicon oxide sheet treated in step S1 at a 30° angle along the same direction. The silicon oxide sheet coated with the catalyst was placed in a quartz boat and placed in a single-temperature-controlled tube furnace.

[0011] Use a high vacuum pump to evacuate the pressure inside the reaction tube to below 100 Pa, then fill it with high-purity argon gas to atmospheric pressure. The argon gas purity should be ≥99.99%. Repeat the evacuation-argon filling operation three times to completely replace the residual air inside the tube.

[0012] Set the tube furnace program as follows: heat to 950℃ at 10℃ / min, and maintain the argon gas flow rate at 212 sccm; at 950℃, first introduce H2 at a flow rate of 297 sccm for 10 min, and then simultaneously introduce anhydrous ethanol at a flow rate of 35 sccm for 25 min; stop introducing H2 and anhydrous ethanol, and cool down at 10℃ / min. Stop introducing argon gas when the temperature drops below 650℃.

[0013] Remove the silicon oxide wafers and use a scanning electron microscope to screen out those containing qualified single-walled carbon nanotubes;

[0014] S3, Copper mesh attachment and electrode evaporation: Stick Scotch tape to a clean glass plate, cut it into 1.5cm×1.5cm squares and cut out two 2mm×6mm window panes, turn the tape over so that the copper mesh is applied to the window panes in the opposite direction, and then stick the tape with the copper mesh onto the silicon oxide wafer on which carbon nanotubes have grown after screening in step S2.

[0015] A silicon oxide wafer is fixed on a evaporation machine plate. First, metallic chromium is deposited at 195℃ for 8 minutes, and then gold is deposited at 165℃ for more than 10 minutes to obtain a carbon nanotube field-effect transistor sensor. The initial electrical signal is measured using a semiconductor parameter instrument.

[0016] S4. Preparation of nano-gap: Connect the semiconductor parameter instrument to the sensor prepared in step S3, and set the electrical breakdown parameters: the gate voltage is +10V, the source-drain voltage increases from 0.05V to 20V, the step voltage is 0.1V, and monitor the changes in source-drain current in real time. When the current drops discontinuously to zero, stop applying the voltage, indicating that the carbon nanotubes have been electrically broken down and formed nano-gap. The sensor with a nano-gap size of about 10nm is selected by scanning electron microscopy. At this time, carboxylic acid groups -COOH are generated at the nano-gap due to oxidation functionalization.

[0017] S5. Functional modification of the sensor: Add 20 μL of NHS / EDC mixed solution (NHS:EDC volume ratio 1:10) to the surface of the sensor screened in step S4, and place it in a 4℃ refrigerator for 12 h to activate the carboxyl-COOH groups in the nano-gap; then add 20 μL of 40 nM DNA1, sequence: 5'-C6-NH2-CCACCACTTTTTTTTTCCTTTTTTTTTCGCGTCGTAA-NH2-C6-3', and react in a 4℃ refrigerator for 12 h to couple the amino-NH2 groups of DNA1 with the activated carboxyl-COOH groups. DNA1 acts as a "conductive bridge" connecting the carbon nanotubes at both ends of the nano-gap. Rinse the sensor surface three times with 1×PBS solution and air dry to remove unconnected DNA1. Remeasure the electrical signal using a semiconductor parameter analyzer and record the source-drain current to obtain a low-cost carbon nanotube sensor produced by vapor deposition.

[0018] Preferably, the piranha solution in S1 is prepared by mixing concentrated sulfuric acid and hydrogen peroxide in a volume ratio of 7:3.

[0019] Low-cost carbon nanotube sensor for Hg detection using vapor deposition process 2+ The method includes the following steps:

[0020] T1. Sensitivity Detection: 20 μL of Hg at different concentrations was added to the surface of the carbon nanotube sensor. 2+ Solutions with concentrations of 5 pM, 10 pM, 50 pM, 100 pM, 500 pM, 1 nM, 5 nM, and 10 nM were reacted at room temperature for 40 min, washed three times with ultrapure water, and then air-dried.

[0021] The gate voltage was set to -8V to +8V, the step voltage to 0.16V, and the source-drain voltage to +50mV using a semiconductor parameter analyzer. The current signal was measured, and the current change was recorded as I0 - I, where I0 is the value without Hg. 2+ The reference current at that time, I is the current when Hg is added. 2+ The current after;

[0022] T2. Selective Detection: 20 μL of 10 nM solutions of different metal salts were added to the surface of the carbon nanotube sensor, with the metal ions being Pb... 2+ Na + Mg 2+ Cu 2+ Mn 2+ K + Zn 2+ Ca 2+ Hg 2+ React at 4℃ for 40 minutes, wash three times with ultrapure water, and then air dry.

[0023] In step T1, set the parameters of the semiconductor parameter instrument to measure the current signal and compare the degree of current reduction corresponding to different metal ions.

[0024] T3. Actual Sample Testing: Yangtze River water samples were collected and pretreated by vacuum filtration using a 0.22μm aquatic microporous membrane. 20μL of 1nM, 5nM, and 10nM Hg solutions were added to the pretreated Yangtze River water samples, respectively. 2+ Standard solutions were used to measure the current signal according to the parameters in step T1; simultaneously, 20 μL of Hg solutions with concentrations of 1 nM, 5 nM, and 10 nM were added to the sensor. 2+ The standard solution was used as a control group to measure the current signal; the recovery rate was calculated according to the formula "Recovery rate P = (Spiked sample decrease ratio - Sample decrease ratio) / Spiked sample decrease ratio × 100%" to determine the Hg concentration in the actual water sample. 2+ concentration.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention has low preparation cost and simple process. The electrode is prepared by vapor deposition process, which replaces the traditional expensive micro-nano processing technology such as EBL and FIB, which greatly reduces the preparation cost. At the same time, the process of voltage stress triggering carbon nanotube electrical breakdown to form nano gaps is simple to operate and highly controllable, which is conducive to large-scale production.

[0027] 2. The present invention has excellent detection performance, and the sensor prepared therefrom can detect Hg. 2+ It exhibits high sensitivity and selectivity, and the current tends to stabilize after immersion in ultrapure water and 1×PBS solution for 90 min, demonstrating good stability and meeting the requirements for trace Hg. 2+ The need for precise testing;

[0028] 3. This invention is highly practical; the sensor can be used to detect Hg in actual water bodies (such as the Yangtze River). 2+ The detection method is simple, the sample pretreatment is straightforward, and the detection results are reliable, providing a reliable method for detecting Hg in environmental water bodies. 2+ It provides a feasible solution for rapid on-site testing and has broad application prospects. Attached Figure Description

[0029] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0030] In the attached diagram:

[0031] Figure 1 For the detection of Hg by carbon nanotube nanoelectrode biosensor 2+ A schematic diagram of the principle;

[0032] Figure 2 Image of electrode deposition for an optical microscope;

[0033] Figure 3 Image of electrode evaporation under a scanning electron microscope;

[0034] Figure 4 The image shows an electron microscope image of carbon nanotubes grown using the CVD method. The carbon nanotubes appear as hollow fibers and are straight.

[0035] Figure 5 This is an electron microscope diagram showing the carbon nanotubes between the electrodes after gold electrodes have been deposited. The carbon nanotubes span between the two electrodes, forming a "conductive bridge".

[0036] Figure 6 This is the initial electrical signal for the CNT-FET sensor;

[0037] Figure 7 The effect of ultrapure water on the conductivity of carbon nanotube sensors;

[0038] Figure 8 The effect of 1×PBS water on the conductivity of carbon nanotube sensors;

[0039] Figure 9 The graph shows the change in current signal triggered by the semiconductor parameter meter to induce electrical breakdown of carbon nanotubes.

[0040] Figure 10 Electron microscopy image of the nano-gap of the carbon nanotube burned by electrical breakdown; 10.42 nm is a qualified nano-gap.

[0041] Figure 11 Electron microscopy image of the nano-gap of the carbon nanotube burned by electrical breakdown, showing an excessively large gap of 395.35 nm;

[0042] Figure 12 This is the current signal of the device after connecting DNA1;

[0043] Figure 13 For Hg 2+ Results of reaction time optimization;

[0044] Figure 14 To detect Hg based on carbon nanotube nanoelectrode biosensors 2+ Sensitivity analysis graph of the detection, relationship between current and concentration;

[0045] Figure 15 To detect Hg based on carbon nanotube nanoelectrode biosensors 2+ Sensitivity analysis plot of the detection, linear fitting curve (R) 2 =0.99);

[0046] Figure 16 This is a detection map of different metal salt ions based on a carbon nanotube nanoelectrode biosensor, showing Hg 2+ The current drop in this group was significantly higher than that in other ion groups;

[0047] Figure 17 For a known concentration of Hg 2+ The test results of the solution. Detailed Implementation

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to specific examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] This embodiment describes a low-cost carbon nanotube sensor fabrication method using a vapor deposition process, comprising the following steps:

[0050] S1. Preparation of cleaning silicon oxide wafers: Cut silicon wafers into 15mm×15mm silicon oxide wafers, immerse them in piranha solution at 90℃ for more than 3 hours to remove surface impurities, then transfer them to ultrapure water, shake them at 70r / min for 10 minutes on an orbital oscillator, repeat the water changing and shaking steps three times, and finally blow them dry with pure nitrogen and store them in an IPC vacuum desiccator.

[0051] S2. Growth and preparation of carbon nanotubes: Using chemical vapor deposition, a 4.5 mm stainless steel needle wiped with anhydrous ethanol was dipped into a CuCl2 solution catalyst and uniformly coated on the silicon oxide sheet treated in step S1 at a 30° angle along the same direction. The silicon oxide sheet coated with the catalyst was placed in a quartz boat and placed in a single-temperature-controlled tube furnace.

[0052] Use a high vacuum pump to evacuate the pressure inside the reaction tube to below 100 Pa, then fill it with high-purity argon gas to atmospheric pressure. The argon gas purity should be ≥99.99%. Repeat the evacuation-argon filling operation three times to completely replace the residual air inside the tube.

[0053] Set the tube furnace program as follows: heat to 950℃ at 10℃ / min, and maintain the argon gas flow rate at 212 sccm; at 950℃, first introduce H2 at a flow rate of 297 sccm for 10 min, and then simultaneously introduce anhydrous ethanol at a flow rate of 35 sccm for 25 min; stop introducing H2 and anhydrous ethanol, and cool down at 10℃ / min. Stop introducing argon gas when the temperature drops below 650℃.

[0054] Remove the silicon oxide wafers and use a scanning electron microscope to screen out those containing qualified single-walled carbon nanotubes;

[0055] S3, Copper mesh attachment and electrode evaporation: Stick Scotch tape to a clean glass plate, cut it into 1.5cm×1.5cm squares and cut out two 2mm×6mm window panes, turn the tape over so that the copper mesh is applied to the window panes in the opposite direction, and then stick the tape with the copper mesh onto the silicon oxide wafer on which carbon nanotubes have grown after screening in step S2.

[0056] A silicon oxide wafer is fixed on a evaporation machine plate. First, metallic chromium is deposited at 195℃ for 8 minutes, and then gold is deposited at 165℃ for more than 10 minutes to obtain a carbon nanotube field-effect transistor sensor. The initial electrical signal is measured using a semiconductor parameter instrument.

[0057] S4. Preparation of nano-gap: Connect the semiconductor parameter instrument to the sensor prepared in step S3, and set the electrical breakdown parameters: the gate voltage is +10V, the source-drain voltage increases from 0.05V to 20V, the step voltage is 0.1V, and monitor the changes in source-drain current in real time. When the current drops discontinuously to zero, stop applying the voltage, indicating that the carbon nanotubes have been electrically broken down and formed nano-gap. The sensor with a nano-gap size of about 10nm is selected by scanning electron microscopy. At this time, carboxylic acid groups -COOH are generated at the nano-gap due to oxidation functionalization.

[0058] S5. Functional modification of the sensor: Add 20 μL of NHS / EDC mixed solution (NHS:EDC volume ratio 1:10) to the surface of the sensor screened in step S4, and place it in a 4℃ refrigerator for 12 h to activate the carboxyl-COOH groups in the nano-gap; then add 20 μL of 40 nM DNA1, sequence: 5'-C6-NH2-CCACCACTTTTTTTTTCCTTTTTTTTTCGCGTCGTAA-NH2-C6-3', and react in a 4℃ refrigerator for 12 h to couple the amino-NH2 groups of DNA1 with the activated carboxyl-COOH groups. DNA1 acts as a "conductive bridge" connecting the carbon nanotubes at both ends of the nano-gap. Rinse the sensor surface three times with 1×PBS solution and air dry to remove unconnected DNA1. Remeasure the electrical signal using a semiconductor parameter analyzer and record the source-drain current to obtain a low-cost carbon nanotube sensor produced by vapor deposition.

[0059] In this embodiment, the piranha solution in S1 is prepared by mixing concentrated sulfuric acid and hydrogen peroxide in a volume ratio of 7:3.

[0060] Low-cost carbon nanotube sensor for Hg detection using vapor deposition process 2+ The method includes the following steps:

[0061] T1. Sensitivity Detection: 20 μL of Hg at different concentrations was added to the surface of the carbon nanotube sensor. 2+ Solutions with concentrations of 5 pM, 10 pM, 50 pM, 100 pM, 500 pM, 1 nM, 5 nM, and 10 nM were reacted at room temperature for 40 min, washed three times with ultrapure water, and then air-dried.

[0062] The gate voltage was set to -8V to +8V, the step voltage to 0.16V, and the source-drain voltage to +50mV using a semiconductor parameter analyzer. The current signal was measured, and the current change was recorded as I0 - I, where I0 is the value without Hg. 2+ The reference current at that time, I is the current when Hg is added. 2+ The current after;

[0063] T2. Selective Detection: 20 μL of 10 nM solutions of different metal salts were added to the surface of the carbon nanotube sensor, with the metal ions being Pb... 2+ Na + Mg 2+ Cu 2+ Mn 2+ K + Zn 2+ Ca 2+ Hg 2+ React at 4℃ for 40 minutes, wash three times with ultrapure water, and then air dry.

[0064] In step T1, set the parameters of the semiconductor parameter instrument to measure the current signal and compare the degree of current reduction corresponding to different metal ions.

[0065] T3. Actual Sample Testing: Yangtze River water samples were collected and pretreated by vacuum filtration using a 0.22μm aquatic microporous membrane. 20μL of 1nM, 5nM, and 10nM Hg solutions were added to the pretreated Yangtze River water samples, respectively. 2+ Standard solutions were used to measure the current signal according to the parameters in step T1; simultaneously, 20 μL of Hg solutions with concentrations of 1 nM, 5 nM, and 10 nM were added to the sensor. 2+ The standard solution was used as a control group to measure the current signal; the recovery rate was calculated according to the formula "Recovery rate P = (Spiked sample decrease ratio - Sample decrease ratio) / Spiked sample decrease ratio × 100%" to determine the Hg concentration in the actual water sample. 2+ concentration.

[0066] Example 1: Fabrication of a carbon nanotube sensor

[0067] S1. Preparation of silicon oxide wafers: The silicon wafer was cut into 15mm×15mm silicon oxide wafers using a scribe and steel measuring tool, and immersed in piranha solution (concentrated sulfuric acid: hydrogen peroxide = 7:3, both produced by Shanghai Sangon Biotech Co., Ltd.) at 90℃ for 3.5h; the silicon oxide wafers were transferred to ultrapure water (prepared by a laboratory ultrapure water system UPF-10L) and shaken at 70r / min for 10min on an orbital oscillator (TS-2) produced by Haimen Qilin Bell Instrument Manufacturing Co., Ltd., and the water was changed and the step was repeated three times; the silicon oxide wafers were dried with pure nitrogen and stored in an IPC vacuum desiccator produced by Baoding Fagge Instrument Manufacturing Co., Ltd.

[0068] S2. Carbon Nanotube Growth and Preparation: Using a 4.5mm stainless steel needle wiped with anhydrous ethanol (Shanghai Sangon Biotech Co., Ltd.), a CuCl2 solution (Sinopharm Chemical Reagent Co., Ltd.) catalyst was applied uniformly to the silicon oxide sheet treated in step S1 at a 30° angle along the same direction. The catalyst-coated silicon oxide sheet was placed in a quartz boat produced by Hefei Kejing Materials Technology Co., Ltd., and then placed in a vacuum tube high-temperature sintering furnace (OTF-1200X) produced by the same company. The pressure inside the reaction tube was evacuated to below 100Pa using a high vacuum pump, and then high-purity argon gas (purity ≥99.99%) produced by Nanjing Special Gases Co., Ltd. was introduced to atmospheric pressure. The vacuum-argon gas filling operation was repeated. Three times; set the tube furnace program: heat up to 950℃ at 10℃ / min, and control the argon gas flow rate to 212 sccm using a three-channel proton flow controller (SSL-3Z-LCD) produced by Hefei Kejing Materials Technology Co., Ltd.; at 950℃, first introduce H2 at a flow rate of 297 sccm for 10 min, and then simultaneously introduce anhydrous ethanol at a flow rate of 35 sccm for 25 min; stop introducing H2 and anhydrous ethanol, and cool down at 10℃ / min. Stop introducing argon gas when the temperature drops below 650℃; remove the silicon oxide sheet and observe it with a focused ion beam field emission scanning dual-beam electron microscope produced by Carl Zeiss AG, Germany, and screen out silicon oxide sheets containing straight hollow fibrous single-walled carbon nanotubes;

[0069] S3, Copper Mesh Attachment and Electrode Evaporation: Scotch tape (manufactured by Zhongyang Kaisheng E-commerce Co., Ltd.) is adhered to a clean glass plate and cut into 1.5cm x 1.5cm squares. Two 2mm x 6mm panes are cut into the square tape. The tape is flipped over so that the AG200F4 copper mesh (manufactured by Beijing Zhongjing Scientific Instrument Co., Ltd.) is applied to the panes. The tape with the copper mesh is then adhered to the silicon oxide wafer screened in step S2. The silicon oxide wafer is fixed onto the rotating plate of a high-vacuum resistance evaporation coating machine (ZHD300) (manufactured by Beijing Taikeno Technology Co., Ltd.). High-purity chromium (manufactured by Beijing Xingrongyuan Technology Co., Ltd.) is first deposited at 195℃ for 8 minutes, followed by high-purity gold wire (manufactured by Shanghai Lanshuang Electric Co., Ltd.) at 165℃ for 12 minutes. The initial electrical signal is measured using a semiconductor parameter meter (4155C) (manufactured by Dongguan Pengqing Electronics Technology Co., Ltd.). The source-drain current is 717nA, and the gate current is close to 0, indicating that the device is in good condition and does not leak current.

[0070] S4. Nanoscale Gap Fabrication: Using a semiconductor parametric analyzer (4155C), a voltage stress logic scheme was applied to the carbon nanotubes of the sensor prepared in step S3. The gate voltage was set to +10V, and the source-drain voltage was gradually increased from 0.05V to 20V with a step voltage of 0.1V. The current signal was monitored in real time. When the current signal showed a tortuous drop and returned to zero, it was determined that the carbon nanotubes had been electrically broken down. The electrically broken down carbon nanotube samples were observed and characterized under a focused ion beam field emission scanning dual-beam electron microscope (Carl Zeiss AG, Germany). Sensors with a nanoscale gap size of about 10.42 nm were selected (samples with excessively large gaps, such as 395.35 nm, were excluded to avoid affecting subsequent DNA1 ligation).

[0071] S5. Functional modification of the sensor: 20 μL of NHS / EDC mixed solution (volume ratio 1:10, both analytical grade reagents) was added to the surface of the sensor screened in step S4. The sensor was placed in a 4℃ refrigerator and allowed to react for 12 h to fully activate the carboxyl groups generated by oxidation in the nano-interstitial spaces. Then, the excess mixed solution was removed, and 20 μL of DNA1 solution with a concentration of 40 nM (sequence: 5'-C6-NH2-CCACCACTTTTTTTTTCCTTTTTTTTTCGCGTCGTAA-NH2-C6-3', synthesized by Sangon Biotech (Shanghai) Co., Ltd., purified by HPLC and verified by mass spectrometry) was added. The reaction was continued in a 4℃ refrigerator for 12 h to ensure that DNA1 was linked to both ends of the nano-interstitial spaces through the coupling effect of amino groups and activated carboxyl groups. After the reaction, the sensor surface was rinsed three times with 1×PBS buffer (Sinopharm Chemical Reagent Co., Ltd.). After each rinse, the surface was gently dried with nitrogen to remove unlinked free DNA1, thus completing the preparation of the carbon nanotube sensor.

[0072] Example 2: Hg based on carbon nanotube sensor 2+ Detection

[0073] T1, Sensitivity Detection

[0074] 1) Control group setup: Blank carbon nanotube sensor (functionalized but without Hg) 2+ Add 20 μL of ultrapure water to the surface, let stand at room temperature for 40 minutes, rinse three times with ultrapure water, and then blow dry. Set the following parameters using a semiconductor parameter analyzer (Dongguan Pengqing Electronics Technology Co., Ltd., model 4155C): gate voltage -8V to +8V, step voltage 0.16V, source-drain voltage +50mV. Measure and record the reference current I0 (measured at 516nA). Figure 12 Consistent);

[0075] 2) Experimental group detection: 20 μL of Hg at different concentrations was dropped onto the surface of each of the 8 functionalized sensor groups. 2+ Solutions (concentrations of 5 pM, 10 pM, 50 pM, 100 pM, 500 pM, 1 nM, 5 nM, and 10 nM, prepared by dissolving mercuric nitrate (Shandong Xiya Chemical Industry Co., Ltd.) in ultrapure water) were reacted at room temperature for 40 min (based on...) Figure 13 (Optimized optimal reaction time); After the reaction, rinse three times with ultrapure water and dry. Measure the current I of each sensor group according to the same parameters as the control group, and calculate the current change (I0-I).

[0076] 3) Results Analysis: With Hg 2+ As concentration increases, the change in current (I0-I) gradually increases and then tends to stabilize; within the concentration range of 1–10 nM, the rate of change in current (1-I / I0) is related to Hg. 2+ The concentrations showed a good linear relationship, with the linear equation being y = 0.00611x + 0.42071 (R²). 2 =0.99), the calculated detection limit is 2.34 pM, which is consistent with trace Hg. 2+ Testing needs.

[0077] T2, selective detection

[0078] 1) Experimental design: Eight common interfering metal ions (Pb) were selected. 2+ Na + Mg 2+ Cu 2+ Mn 2+ K + Zn 2+ Ca 2+ ) and Hg 2+For comparison, the concentration of each metal ion solution was 10 nM (prepared by dissolving lead acetate, sodium nitrate, magnesium chloride, copper sulfate, manganese chloride, potassium chloride, zinc chloride, and calcium chloride (all products of Sinopharm Chemical Reagent Co., Ltd.) in ultrapure water).

[0079] 2) Detection process: 20 μL of the above 9 metal ion solutions were dropped onto the surface of each of the 9 functionalized sensors. After reacting at 4°C for 40 min, the sensors were rinsed three times with ultrapure water and dried. The current signal of each group was measured by a semiconductor parameter analyzer (parameters are the same as those for sensitivity detection), and the degree of current reduction was recorded.

[0080] 3) Result determination: such as Figure 16 As shown, only Hg 2+ The decrease in current in this group was significantly greater than that in other interfering ion groups (Hg). 2+ The current drop in the interfering ion group was approximately 3 to 5 times that of the interfering ion group. Statistical analysis showed a significant difference, proving that the sensor effectively controlled the Hg ion exchange. 2+ It has good selectivity;

[0081] T3, Actual Sample Testing

[0082] 1) Sample pretreatment: Yangtze River water samples were collected and vacuum filtered in a clean laboratory environment using a 0.22μm water filter (Changde Bickman Biotechnology Co., Ltd., model B-GLQ22S-13) to remove suspended particulate matter and insoluble impurities from the water samples. The clear filtrate was collected for later use.

[0083] 2) Spiking experiment: Three groups of spiked samples were set up, and 20 μL of Hg at concentrations of 1 nM, 5 nM, and 10 nM were added to the pretreated Yangtze River water samples, respectively. 2+ Standard solution; simultaneously set up 3 standard control groups, directly adding 20 μL of Hg²⁺ standard solution of the same concentration to the sensor; for all samples, the current signal was measured according to the sensitivity detection parameters, and the current drop ratio was calculated;

[0084] 3) Recovery rate and result calculation: The recovery rate was calculated using the formula "Recovery (P) = (Reduction ratio of spiked sample - Reduction ratio of spiked sample) / Reduction ratio of spiked sample × 100%". The results showed that the recovery rate was 102.741%–105.657%, and the relative standard deviation (RSD) was 2.269%–4.896% (e.g., ...). Figure 17 (As shown in the table below); Hg in the unspecified Yangtze River water sample was also measured. 2+ The concentration was 61.563 pM, proving that this method is applicable to Hg in actual water bodies. 2+ Accurate detection.

[0085] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0086] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a carbon nanotube sensor by a low-cost evaporation process, characterized by, The method comprises the following steps: S1, cleaning and preparing the silicon oxidation sheet: cutting the silicon wafer into a silicon oxidation sheet with a size of 15 mm x 15 mm, immersing the silicon oxidation sheet in a piranha solution at 90 DEG C for more than 3 hours to remove surface impurities, then transferring the silicon oxidation sheet to ultrapure water, shaking the silicon oxidation sheet on an orbital shaker at a speed of 70 r / min for 10 minutes, repeating the water changing and shaking step three times, finally blowing dry with pure nitrogen, and storing the silicon oxidation sheet in an IPC vacuum drying vessel; S2, growing and preparing carbon nanotubes: using a chemical vapor deposition method, using a 4.5 mm stainless steel needle wiped with anhydrous ethanol to dip a CuCl2 solution catalyst, and evenly applying the catalyst on the silicon oxidation sheet treated in step S1 at an inclination angle of 30 DEG in the same direction, placing the catalyst-coated silicon oxidation sheet in a quartz boat and placing it in a single-temperature control tube furnace; using a high vacuum pump to pump the pressure in the reaction tube to below 100 Pa, filling high-purity argon to normal pressure, the purity of argon is greater than or equal to 99.99%, repeating the vacuum pumping-argon filling operation three times to completely replace the residual air in the tube; setting the tube furnace program: increasing the temperature to 950 DEG C at a rate of 10 DEG C / min, and keeping the argon gas flow rate at 212 sccm; at 950 DEG C, first pass in H2 at a flow rate of 297 sccm for 10 minutes, then pass in anhydrous ethanol at a flow rate of 35 sccm for 25 minutes; stop passing in H2 and anhydrous ethanol, and reduce the temperature at a rate of 10 DEG C / min, stop passing in argon when the temperature drops below 650 DEG C; taking out the silicon oxidation sheet, and selecting the silicon oxidation sheet containing qualified single-walled carbon nanotubes through a scanning electron microscope; S3, attaching a copper mesh and electrode evaporation: sticking Scotch tape on a clean glass plate, cutting the tape into a 1.5 cm x 1.5 cm square and opening two 2 mm x 6 mm windows, turning the tape over to attach the copper mesh to the windows in reverse, and then sticking the copper mesh-attached tape on the silicon oxidation sheet grown with carbon nanotubes after screening in step S2; fixing the silicon oxidation sheet on a evaporation machine wafer, first evaporating metal chromium at 195 DEG C for 8 minutes, and then evaporating gold at 165 DEG C for more than 10 minutes to obtain a carbon nanotube field effect transistor sensor, and measuring the initial electrical signal using a semiconductor parameter instrument; S4, preparing a nanogap: connecting the semiconductor parameter instrument to the sensor prepared in step S3, setting the electrical breakdown parameters: the gate voltage is +10 V, the source-drain voltage rises from 0.05 V to 20 V, and the step voltage is 0.1 V, and the source-drain current change is monitored in real time, when the current appears fault-like drop to zero, stop applying voltage, indicating that the carbon nanotube is electrically broken down and forms a nanogap, and the sensor with a nanogap size of about 10 nm is selected through a scanning electron microscope, at this time, carboxylic acid groups -COOH are generated at the nanogap due to oxidation functionalization; S5, functional modification of the sensor: 20 μL of a mixture of NHS / EDC is added to the surface of the sensor screened in step S4, the volume ratio of NHS:EDC is 1:10, and the carboxyl-COOH at the nanogap is activated by being placed in a 4°C refrigerator for 12 hours; then 20 μL of 40 nM of DNA1 is added, the sequence is: 5'-C6-NH2-CCACCACTTTTTTTTTCCTTTTTTTTTCGCGTCGTAA-NH2-C6-3', and the amino group-NH2 of DNA1 is coupled with the activated carboxyl-COOH by being reacted in a 4°C refrigerator for 12 hours; DNA1 is used as a "conductive bridge" to connect the carbon nanotubes at both ends of the nanogap, the surface of the sensor is washed three times with a 1×PBS solution and dried to remove the unconnected DNA1, and the electrical signal is re-measured by using a semiconductor parameter instrument, and the source-drain current is recorded, thereby obtaining a carbon nanotube sensor of low-cost evaporation process.

2. The method of claim 1, wherein the carbon nanotube sensor is prepared by a low-cost evaporation process. The piranha solution in S1 is prepared by mixing concentrated sulfuric acid and hydrogen peroxide at a volume ratio of 7:

3.

3. A method for detecting Hg using a low cost carbon nanotube sensor prepared by the method of any one of claims 1-2. 2+ characterized in that, The method comprises the following steps: T1, sensitivity detection: 20 μL of different concentrations of Hg 2+ solution, the concentration is 5 pM, 10 pM, 50 pM, 100 pM, 500 pM, 1 nM, 5 nM, 10 nM, respectively, and the reaction is carried out at room temperature for 40 min, and then the carbon nanotube sensor surface is cleaned with ultrapure water for three times and dried. The gate voltage is set to -8V~+8V by semiconductor parameter instrument, the step voltage is 0.16V, the source-drain voltage is +50mV, the current signal is measured, and the current change amount I0-I is recorded, wherein I0 is the reference current without Hg, and I is the current after Hg is added. 2+ 2+ ​​ T2, selective detection: 20 μL of 10 nM different metal salt ion solution was added to the surface of the carbon nanotube sensor, and the metal ions were Pb 2+ , Na + , Mg 2+ , Cu 2+ , Mn 2+ , K + , Zn 2+ , Ca 2+ , Hg 2+ , respectively, reacted at 4°C for 40 min, and then washed with ultrapure water three times and dried. The current signal is measured by setting the parameters of the semiconductor parameter instrument according to step T1, and the current reduction degrees corresponding to different metal ions are compared. T3, actual sample detection: collect Yangtze River water samples, and pretreat them by vacuum filtration with 0.22 μm water system microporous filter membranes; add 20 μL of Hg 2+ standard solution to the pretreated Yangtze River water samples, and measure the current signals according to the parameters in step T1; at the same time, add 20 μL of Hg 2+ standard solution to the sensor, and measure the current signals; calculate the recovery rate according to the formula "recovery rate P = (decrease ratio of spiked sample - decrease ratio of sample) / decrease ratio of spiked sample x 100%" to determine the Hg 2+ concentration in the actual water sample.

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