A kind of extended gate field effect transistor electrochemical sensor test system and application

Abstract

The application discloses an extended gate field effect transistor electrochemical sensor test system and application, and the system comprises an electrochemical workstation, a field effect transistor MOSFET, an adjustable voltage stabilizing power supply, a BDD electrode, a platinum sheet electrode and a 3D printing reaction cavity; the drain and the source of the field effect transistor MOSFET are connected with the positive and negative poles of the electrochemical workstation respectively; the gate of the field effect transistor MOSFET is connected with a two-electrode system through a wire; the two-electrode system is composed of the BDD electrode and the platinum sheet electrode; the two-electrode system takes the adjustable voltage stabilizing power supply as an input voltage source; and the BDD electrode and the platinum sheet electrode are placed in the 3D printing reaction cavity during work. The application takes the BDD electrode as an extended material of the gate, combines the EGFET prepared by the field effect transistor, and forms the EGFET electrochemical sensor together with the platinum counter electrode and the 3D printing reaction cavity, so that the measurement of low-concentration organic pollutants in water bodies can be realized, and core sensors and technical supports are provided for tap water quality safety monitoring.

Description

Technical Field

[0001] This invention relates to the field of sensor and its application technology, specifically to an extended gate field-effect transistor electrochemical sensor testing system and its application. Background Technology

[0002] Safe drinking water is an indispensable part of global health management, and real-time online monitoring of tap water quality is a crucial measure to ensure the safety of drinking water for the public. Chemical oxygen demand (COD) is a key water quality indicator characterizing the content of organic pollutants in tap water. Currently, it is mainly measured using on-site sampling and laboratory testing methods, which suffer from drawbacks such as expensive equipment, cumbersome operation, and poor real-time performance, making it difficult to meet the need for rapid in-situ detection of tap water. This invention develops an extended gate field-effect transistor (EGFET) electrochemical sensor for accurately detecting COD in tap water and characterizing the content of organic pollutants. The sensor has significant advantages such as miniaturization, mass production capability, and suitability for real-time on-site monitoring, achieving highly sensitive detection of organic pollutants in tap water. Summary of the Invention

[0003] The purpose of this invention is to meet practical needs by using a BDD (boron-doped diamond) electrode as the gate extension material, combined with an EGFET fabricated from a field-effect transistor, and a platinum counter electrode and a 3D-printed reaction chamber to form an EGFET electrochemical sensor. The EGFET electrochemical sensor provided by this invention has the characteristics of mass production capability, miniaturization, and good stability. It can realize the measurement of low concentrations of organic pollutants in water, providing a core sensor and technical support for the safety monitoring of tap water quality.

[0004] To achieve the above objectives, the present invention adopts the following technical solution.

[0005] An extended gate field-effect transistor (EGFET) electrochemical sensor testing system includes an EGFET electrochemical sensor. The EGFET electrochemical sensor consists of an electrochemical workstation, a field-effect transistor (MOSFET), an adjustable regulated power supply, a BDD electrode, a platinum sheet electrode, and a 3D-printed reaction chamber. The drain and source of the MOSFET are connected to the positive and negative terminals of the electrochemical workstation, respectively. The gate of the MOSFET is connected to a two-electrode system via a wire. The two-electrode system consists of a BDD electrode and a platinum sheet electrode. The adjustable regulated power supply is used as the input voltage source for the two-electrode system, and the platinum sheet electrode is the counter electrode. The BDD electrode and the platinum sheet electrode are placed inside the 3D-printed reaction chamber during operation.

[0006] Specifically, the electrochemical workstation is a Gamry Reference 600 electrochemical workstation with a maximum test current of 700mA. The workstation will automatically stop working when the current exceeds 700mA.

[0007] Specifically, the MOSFET is model 2N7002, with a startup voltage of 1 to 2.5V and an on-resistance of less than 2.5Ω when the gate voltage is 10V.

[0008] Specifically, the adjustable regulated power supply is the ITECH IT6302 model adjustable regulated power supply. Preferably, the BDD electrode fabrication process is as follows:

[0009] After the silicon wafer is cleaned, it is cut into small pieces of 0.8cm*2cm using a dicing machine. After being cleaned again, it is placed in the reaction chamber of a chemical vapor deposition instrument. A BDD film with a thickness of 3μm-4μm is prepared by microwave plasma chemical vapor deposition using a 2000W microwave. A mixture of methane and hydrogen is introduced into the reaction chamber at a flow rate of 250sccm, with a carbon-to-hydrogen ratio of 2%. B2H6 is used as a boron dopant with a concentration of 15ppm in hydrogen. The substrate temperature is 600℃ and the deposition time is 4h to obtain the BDD electrode.

[0010] Preferably, the volume of the 3D printing cavity is 1.2 mL.

[0011] Furthermore, the present invention also provides an application of the extended gate field-effect transistor electrochemical sensor testing system described above in the detection of COD in tap water, specifically including the following steps:

[0012] Step 1: Collect a sufficient amount of water sample to be tested. After the water sample has been left to stand for 5 minutes, add 0.01 mol of Na2SO4 to every 100 mL of tap water to prepare a Na2SO4 solution containing 0.1 M.

[0013] Step 2: Apply a 2.5V voltage to the gate of the MOSFET using an adjustable regulated power supply, and measure the current output characteristic curve using an electrochemical workstation.

[0014] Step 3: Based on the obtained current output characteristic curve, use the following formula (1) to obtain the COD of the tap water to be tested:

[0015]

[0016] Where C (organic matter) represents the COD of various organic matter solutions, in mg / L; I represents the drain current, in mA.

[0017] Specifically, the derivation process of formula (1) in step 3 is as follows:

[0018] Changes in the gate voltage of a MOSFET will alter the electrical channel, thus affecting the magnitude of the drain current. The voltage applied to the MOSFET gate has two components: one is the potential generated in the 3D printing reaction chamber, and the other is the voltage between the MOSFET gate and the channel. Therefore, U G The expression is:

[0019] U G =U r +U g-c (2)

[0020] Among them, U G U is the voltage applied to the gate of the MOSFET. r Ug-c is the electrochemical potential generated on the surface of the BDD electrode in the 3D printing reaction chamber, and Ug-c is the voltage at the gate and channel of the MOSFET.

[0021] When the solution contains organic contaminants, under the condition of energization at the BDD electrode, ·OH will be generated to oxidize and dissolve the organic matter in the aqueous solution. When the organic matter is oxidized according to stoichiometry, according to the Nernst equation, the potential at the BDD working electrode is:

[0022]

[0023] in, The potential of the working electrode is given by k, where k represents the Boltzmann constant, T is the thermodynamic temperature, n is the number of electrons transferred when a single reducing agent is oxidized, and C is the temperature. m A1 represents the molar concentration of organic matter in the water sample to be tested, and is a constant.

[0024] Let the potential on the counter electrode be The voltage in the 3D printing reaction chamber can be obtained as follows:

[0025]

[0026] The voltage Ug-c formed between the gate and the conductive channel of a MOSFET can be expressed as:

[0027]

[0028] Where a and b are constants;

[0029] Based on the definition of COD, we introduce the number of electrons n transferred when organic matter is oxidized, and simultaneously introduce the molar concentration C of organic matter in the solution. m The conversion to COD is as follows: COD = 8000nC m If 8000 is a dimension factor, then formula (5) can be further expressed as:

[0030] U g-c =alog 10 (COD) + c (6)

[0031] Where c is a constant, based on the drain current i of the field-effect transistor. D From the relationship with Ug-c, we can conclude that:

[0032]

[0033] Sample solutions with different CODs were prepared, each containing 0.1M Na2SO4, and U was applied. G With a constant voltage of 2.5V, an oxidation-digestion reaction is carried out in the 3D printing reaction chamber to obtain the corresponding drain current output characteristic curve, thereby obtaining the values ​​of constants a and c. Substituting these values ​​into formula (7), the drain current i of the corresponding sample solution is obtained. D Relationship with COD;

[0034] When the sample solution is a mixture of multiple organic compounds, the resulting drain current i D The relationship with COD is:

[0035]

[0036] In the above technical solution, step 3 uses the following formula (1) to obtain the COD of the tap water to be tested. According to actual experimental tests, the EGFET electrochemical sensor provided by this invention has a minimum detection limit of 0.03 mg / L and a detection range of 0.05 mg / L to 200 mg / L when detecting COD in tap water. The beneficial effects of this invention are:

[0037] 1. This invention combines a field-effect transistor (FET) with a BDD sensing electrode to fabricate an EGFET electrochemical sensor, which is then applied to the detection of COD in tap water. The device has a turn-on voltage of 1.5V, with transduction occurring in the positive uGS region, exhibiting overall nMOSFET characteristics. When a gate voltage of 2.5V is applied, the device achieves a low detection limit of 0.03 mg / L and a detection range of 0.05 mg / L to 200 mg / L in a 0.1M Na2SO4 supporting electrolyte solution. Simultaneously, its repeatability and consistency RSD are both within 3%, demonstrating high accuracy. Furthermore, the effectiveness of the EGFET electrochemical sensor provided by this invention has been verified in standard water samples and tap water. Its sensitive and accurate detection performance is attributed to the efficient oxidation and digestion capability of the BDD electrode and the amplification capability of the EGFET device for weak signals, indicating that this sensor has excellent sensing performance for in-situ detection.

[0038] 2. The method for measuring the output characteristic curve of EGFET proposed in this invention shows good consistency with the acidic potassium permanganate titration method in the analysis of COD in tap water; indicating that the EGFET electrochemical sensor has good prospects for in-situ high-sensitivity detection of low concentrations of organic pollutants. Attached Figure Description

[0039] Figure 1 This is a circuit diagram of an extended gate field-effect transistor electrochemical sensor testing system according to the present invention;

[0040] Figure 2 This is a schematic diagram of the structure of an extended gate field-effect transistor electrochemical sensor testing system according to the present invention;

[0041] Figure 3 The BDD electrode prepared using the method provided in the embodiments of the present invention;

[0042] Figure 4 In this embodiment, the concentration of chloride ions and i are used to calibrate the chloride ion interference in tap water. D Relationship diagram;

[0043] Figure 5 This embodiment measures the organic matter COD and i when measuring the COD of various organic substances in tap water. D Relationship diagram;

[0044] Figure 6 This is the curve showing the relationship between the boronic electrode voltage and the oxidation peak of the glucose sample solution in this embodiment;

[0045] Figure 7 This is a curve showing the relationship between different electrolyte concentrations and the response current of the glucose sample solution in this embodiment;

[0046] Figure 8 This is a schematic diagram of the repeatability test results in this embodiment;

[0047] Figure 9 This is a schematic diagram illustrating the evaluation results of the consistency test in this embodiment;

[0048] Figure 10 This is a schematic diagram of the evaluation structure for stability testing in this embodiment.

[0049] In the diagram, 1. Electrochemical workstation; 2. Field-effect transistor; 3. Adjustable regulated power supply; 4. BDD electrode; 5. Platinum electrode; 6. 3D printed reaction chamber. Detailed Implementation

[0050] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0051] Example

[0052] like Figure 1 As shown, an extended gate field-effect transistor (EGFET) electrochemical sensor testing system includes an EGFET electrochemical sensor, which comprises an electrochemical workstation, a MOSFET, an adjustable regulated power supply, a BDD electrode, a platinum electrode, and a 3D-printed reaction chamber. Figure 2 As shown, the drain and source of the MOSFET are connected to the positive and negative terminals of the electrochemical workstation, respectively. The gate of the MOSFET is connected to the two-electrode system via a wire. The two-electrode system consists of a BDD electrode and a platinum plate electrode. The two-electrode system uses an adjustable regulated power supply as the input voltage source. The platinum plate electrode is the counter electrode. The BDD electrode and the platinum plate electrode are placed inside the 3D printing reaction chamber during operation.

[0053] In this embodiment, the electrochemical workstation is a Gamry Reference 600 electrochemical workstation with a maximum test current of 700mA. The workstation will automatically stop working when the current exceeds 700mA.

[0054] In this embodiment, the MOSFET is model 2N7002, with a startup voltage of 1 to 2.5V and an on-resistance of less than 2.5Ω when the gate voltage is 10V.

[0055] In this embodiment, the adjustable voltage regulator is the ITECH IT6302 adjustable voltage regulator.

[0056] In this embodiment, the BDD electrode fabrication process is as follows:

[0057] After cleaning, the silicon wafers were cut into 0.8cm*2cm pieces using a dicing machine. After further cleaning, they were placed in the reaction chamber of a chemical vapor deposition (CVD) instrument. A 3μm-4μm thick BDD film was prepared using 2000W microwave plasma CVD. A mixture of methane and hydrogen was introduced into the reaction chamber at a flow rate of 250 sccm, with a carbon-to-hydrogen ratio of 2%. B₂H₆ was used as a boron dopant at a concentration of 15 ppm in hydrogen. The substrate temperature was 600℃, and the deposition time was 4 hours. The resulting BDD electrode was as follows: Figure 3 As shown.

[0058] In this embodiment, the volume of the 3D printing cavity is 1.2 mL.

[0059] Furthermore, this embodiment also provides an example of using the above-mentioned extended gate field-effect transistor electrochemical sensor testing system for COD detection in tap water, specifically including the following steps:

[0060] Step 1: Collect a sufficient amount of water sample to be tested. After the water sample has been left to stand for 5 minutes, add 0.01 mol of Na2SO4 to every 100 mL of tap water to prepare a Na2SO4 solution containing 0.1 M.

[0061] Step 2: Apply a 2.5V voltage to the gate of the MOSFET using an adjustable regulated power supply, and measure the current output characteristic curve using an electrochemical workstation.

[0062] Step 3: Based on the obtained current output characteristic curve, use the following formula (1) to obtain the COD of the tap water to be tested:

[0063]

[0064] Where C (organic matter) represents the COD of various organic matter solutions, in mg / L; I represents the drain current, in mA.

[0065] Specifically, the derivation process of formula (1) in step 3 is as follows:

[0066] Changes in the gate voltage of a MOSFET will alter the electrical channel, thus affecting the magnitude of the drain current. The voltage applied to the MOSFET gate has two components: one is the potential generated in the 3D printing reaction chamber, and the other is the voltage between the MOSFET gate and the channel. Therefore, U G The expression is:

[0067] U G =U r +U g-c (2)

[0068] Among them, U G U is the voltage applied to the gate of the MOSFET. r Ug-c is the electrochemical potential generated on the surface of the BDD electrode in the 3D printing reaction chamber, and Ug-c is the voltage at the gate and channel of the MOSFET.

[0069] When the solution contains organic contaminants, under the condition of energization at the BDD electrode, ·OH will be generated to oxidize and dissolve the organic matter in the aqueous solution. When the organic matter is oxidized according to stoichiometry, according to the Nernst equation, the potential at the BDD working electrode is:

[0070]

[0071] in, The potential of the working electrode is given by k, where k represents the Boltzmann constant, T is the thermodynamic temperature, n is the number of electrons transferred when a single reducing agent is oxidized, and C is the temperature. m A1 represents the molar concentration of organic matter in the water sample to be tested, and is a constant.

[0072] Let the potential on the counter electrode be The voltage in the 3D printing reaction chamber can be obtained as follows:

[0073]

[0074] The voltage Ug-c formed between the gate and the conductive channel of a MOSFET can be expressed as:

[0075]

[0076] Where a and b are constants;

[0077] Based on the definition of COD, we introduce the number of electrons n transferred when organic matter is oxidized, and simultaneously introduce the molar concentration C of organic matter in the solution. m The conversion to COD is as follows: COD = 8000nC m If 8000 is a dimension factor, then formula (5) can be further expressed as:

[0078] U g-c =alog 10 (COD) + c (6)

[0079] Where c is a constant, based on the drain current i of the field-effect transistor. D From the relationship with Ug-c, we can conclude that:

[0080]

[0081] Sample solutions with different CODs were prepared, each containing 0.1M Na2SO4, and U was applied. G With a constant voltage of 2.5V, an oxidation-digestion reaction is carried out in the 3D printing reaction chamber to obtain the corresponding drain current output characteristic curve, thereby obtaining the values ​​of constants a and c. Substituting these values ​​into formula (7), the drain current i of the corresponding sample solution is obtained. D Relationship with COD;

[0082] In this embodiment, the calculation formulas for detecting COD of single organic matter and multiple organic matter in tap water using the EGFET electrochemical sensor are given respectively, as follows:

[0083] a. Calibration of interfering ions in tap water

[0084] Chloride ions are widely present in tap water. In my country, chlorine is used as a major additive for disinfection of bacteria and viruses in tap water. Excessive chlorine addition can lead to the formation of carcinogenic substances such as chloroform, while insufficient addition will not achieve disinfection. At water treatment plants and the end of water pipes, the concentration of free chlorine in the water is required to be within the ranges of 0.6 mg / L-0.8 mg / L and 0.05 mg / L-0.3 mg / L. In tap water COD testing, chloride ions become a major interfering component. This embodiment calibrates this interfering ion, such as... Figure 4 As shown, analysis revealed that within the concentration range of 10 mg / L to 350 mg / L, the concentration of chloride ions was related to the drain current i. D The relationship satisfies the following equation:

[0085]

[0086] Among them, C Cl- The concentration of chloride ions is expressed in mg / L, and I represents the drain current i. D (mA), linearity R 2 =0.98428, which indicates that when chloride ion concentrations are between 10 mg / L and 350 mg / L, the test results need to be corrected by fitting the equation in order to achieve accurate measurement of COD in tap water.

[0087] b. COD measurement when multiple organic substances are present in tap water

[0088] In step a, only a single organic compound was tested. However, tap water contains various organic pollutants. Therefore, it is essential to detect the response of the EGFET electrochemical sensor to multiple organic compounds. Thus, in this embodiment, glucose, glutamic acid, potassium hydrogen phthalate, and their equal mixtures were selected as standard samples. A working voltage of 2.5V was applied to the gate, and the output characteristic curves of the EGFET electrochemical sensor to various standard samples were tested in a 0.1M Na₂SO₄ background solution. Figure 5 As shown in the figure, the curves reveal that even with different types of organic compounds detected, the i of the EGFET electrochemical sensor... D They can still form a fitting relationship with COD, and they satisfy:

[0089]

[0090] Where C (organic matter) represents the COD (mg / L) of various organic matter solutions, and I represents the drain current i D (mA), their linearity R 2 =0.99819, which indicates that even in tap water environments with complex organic compositions, the EGFET electrochemical sensor provided by this invention can still perform accurate measurements.

[0091] In the preparation of the above sample solutions, each sample solution contained 0.1M Na2SO4, and the applied U G The voltage is a constant 2.5V, for the following reasons:

[0092] ① To ensure that the performance of the EGFET better meets the requirements for COD detection in tap water, the influence of the gate voltage on the experimental results was studied before the detection was performed. For example... Figure 6 As shown, cyclic voltammetry was used to sequentially test the redox peaks of glucose samples with different COD concentrations (0 mg / L, 0.1 mg / L, 0.5 mg / L, 1 mg / L, 5 mg / L, and 10 mg / L). For a glucose solution with a COD of 10 mg / L, the oxidation peak appeared around 2.3 V. As the COD decreased, the oxidation peak gradually shifted to the right and tended to be near a fixed voltage value. When the COD decreased to 0.1 mg / L, the oxidation peak only appeared when the voltage increased to about 2.5 V, and the position of the oxidation peak had a very small left-right deviation. The stability and sensitivity of the response signal are key factors for accurate COD measurement. In order to optimize the stability and sensitivity of the device's response signal to low COD test solutions, 2.5 V was selected as the gate voltage of the EGFET in the experiment.

[0093] ②Based on the good solution conductivity of Na2SO4 in various supporting electrolytes, it was used as the background solution in this embodiment. The effect of Na2SO4 solution concentration on the electrochemical signal was studied. Each concentration of Na2SO4 solution was tested three times using chronoamperometry. The COD of the glucose solution was 1 mg / L in each test. The average response current of each solution was taken as the average value over 4-5 seconds. Figure 7 As shown, within the concentration range of 0.05M-0.1M, the response current increases with the increase of Na2SO4 concentration, reaching its maximum value at 0.1M. When the Na2SO4 concentration continues to increase to 0.15M, the response current tends to level off and shows a decreasing trend. Therefore, in order to detect weak response signals to the greatest extent possible, that is, to allow the EGFET device to detect COD at lower concentrations in the solution, the concentration of Na2SO4 solution is selected as 0.1M in this embodiment.

[0094] In the above technical solution, the COD of the tap water to be tested is obtained by using the following formula (1) in step 3. According to actual experimental tests, the EGFET electrochemical sensor provided by the present invention has a minimum detection limit of 0.03 mg / L and a detection range of 0.05 mg / L to 200 mg / L when detecting COD in tap water.

[0095] The repeatability, consistency, and stability of the extended gate field-effect transistor electrochemical sensor testing system provided by this invention will be tested through specific experiments below.

[0096] 1) Repeatability test

[0097] To determine the repeatability of a single EGFET electrochemical sensor, repeatability tests were performed using glucose solutions with CODs of 0.5 mg / L, 1 mg / L, and 3 mg / L in 0.1 M Na₂SO₄ solution. Figure 8 As shown, the EGFET electrochemical sensor provided in this embodiment was used to perform five tests on a solution with the same COD value. The output characteristic curves of the multiple tests were compared, and the RSDs of the iD were 2.113%, 2.327%, and 1.876%, respectively. This shows that the detection performance of the device is reliable and can be applied to the multiple measurements of COD in tap water.

[0098] 2) Consistency Testing

[0099] Five EGFET electrochemical sensors prepared in the same batch were selected in this embodiment, and their performance on glucose solutions of 0.1 mg / L, 0.3 mg / L, 0.5 mg / L, 1 mg / L, and 3 mg / L was tested. D ,like Figure 9 As shown, the results indicate that the RSD of the EGFET electrochemical sensor for these five glucose solutions with different CODs is all within 3%, which demonstrates that the EGFET electrochemical sensor provided by this invention has satisfactory consistency.

[0100] 3) Stability test

[0101] 0.1M Na₂SO₄ solution was selected as the supporting electrolyte solution, and a 1 mg / L glucose solution was subjected to ibuprofen treatment for 15 days. D For stability testing, one water sample is tested every two days, and each sample is tested three times. Figure 10 As shown, over time, the i of the EGFET electrochemical sensor... D The decrease was slow; the value was 122.42 mA on the first day and remained at 116.87 mA on the 15th day, representing 95.47% of the first day's value. This indicates that the EGFET electrochemical sensor provided by this invention exhibits stable performance over time when testing COD in water, demonstrating significant potential for long-term stability.

[0102] Finally, to verify the feasibility of the EGFET electrochemical sensor provided by this invention in measuring COD in actual tap water, a sufficient amount of tap water samples were collected for testing in this embodiment.

[0103] The COD of tap water was measured using both the acidic potassium permanganate titration method and the EGFET electrochemical sensor provided in this invention. Tap water was taken from Jiangxi Normal University. After standing for 5 minutes, 0.01 mol of Na₂SO₄ was added to every 100 ml of tap water to prepare a 0.1 M Na₂SO₄ solution. A gate voltage of 2.5 V was applied, and the output characteristic curve of the EGFET was measured. The COD of the tap water was then calculated according to formula (9). Another water sample was sent to Zhejiang Zhongtong Testing Technology Co., Ltd., where the concentration of organic matter was detected using the acidic potassium permanganate titration method. The results are shown in Table 1 below. The results in the table show that the error in the COD values ​​obtained by both methods is within 4.5%, indicating that the drain current method used in this invention's EGFET electrochemical sensor has good consistency with the acidic potassium permanganate titration method in testing the COD of tap water. This also demonstrates the great potential of this invention's EGFET electrochemical sensor in testing the COD of tap water.

[0104] Table 1. Correlation between drain current method and acidic potassium permanganate titration method in measuring the chemical oxygen demand of real samples.

[0105]

[0106] This invention combines a field-effect transistor (FET) with a BDD sensing electrode to fabricate an EGFET electrochemical sensor, which is then applied to the detection of COD in tap water. The device has a turn-on voltage of 1.5V, with transduction occurring in the positive uGS region, exhibiting overall nMOSFET characteristics. When a gate voltage of 2.5V is applied, the device achieves a low detection limit of 0.03 mg / L and a detection range of 0.05 mg / L to 200 mg / L in a 0.1M Na2SO4 supporting electrolyte solution. Furthermore, its repeatability and consistency RSD are both within 3%, demonstrating high accuracy. The effectiveness of the EGFET electrochemical sensor provided by this invention has been verified in standard water samples and tap water. Its sensitive and accurate detection performance is attributed to the efficient oxidation and digestion capabilities of the BDD electrode and the amplification capability of the EGFET device for weak signals, indicating that this sensor has excellent sensing performance for in-situ detection. The drain current method and acidic potassium permanganate titration method proposed in this invention show good consistency in the analysis of COD in tap water; indicating that EGFET electrochemical sensors have good prospects for in-situ high-sensitivity detection of low concentrations of organic pollutants.

[0107] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or imitations made to the above embodiments based on the technical content of the present invention shall fall within the protection scope of the present invention.

Claims

1. A testing system for an extended gate field-effect transistor electrochemical sensor, characterized in that, The device includes an EGFET electrochemical sensor, which comprises an electrochemical workstation, a MOSFET, an adjustable regulated power supply, a BDD electrode, a platinum sheet electrode, and a 3D-printed reaction chamber. The drain and source of the MOSFET are connected to the positive and negative terminals of the electrochemical workstation, respectively. The gate of the MOSFET is connected to a two-electrode system via a wire. The two-electrode system consists of a BDD electrode and a platinum sheet electrode. The adjustable regulated power supply serves as the input voltage source for the two-electrode system, and the platinum sheet electrode acts as the counter electrode. The BDD electrode and the platinum sheet electrode are placed inside the 3D-printed reaction chamber during operation.

2. The extended gate field-effect transistor electrochemical sensor testing system according to claim 1, characterized in that, The electrochemical workstation is a Gamry Reference 600 electrochemical workstation with a maximum test current of 700mA. The workstation will automatically stop working when the current exceeds 700mA.

3. The extended gate field-effect transistor electrochemical sensor testing system according to claim 1, characterized in that, The MOSFET is model 2N7002, with a startup voltage of 1~2.5 V and an on-resistance of less than 2.5 Ω when the gate voltage is 10 V.

4. The extended gate field-effect transistor electrochemical sensor testing system according to claim 1, characterized in that, The adjustable voltage regulator is the ITECH IT6302 model adjustable voltage regulator.

5. The extended gate field-effect transistor electrochemical sensor testing system according to claim 1, characterized in that, The BDD electrode fabrication process is as follows: After the silicon wafer is cleaned, it is cut into small pieces of 0.8 cm * 2 cm using a dicing machine. After being cleaned again, it is placed in the reaction chamber of a chemical vapor deposition instrument. A BDD film with a thickness of 3 μm-4 μm is prepared by microwave plasma chemical vapor deposition at 2000 W. A mixture of methane and hydrogen is introduced into the reaction chamber at a flow rate of 250 sccm, with a carbon-to-hydrogen ratio of 2%. B2H6 is used as a boron dopant with a concentration of 15 ppm in hydrogen. The substrate temperature is 600 °C and the deposition time is 4 h to obtain the BDD electrode.

6. The extended gate field-effect transistor electrochemical sensor testing system according to claim 1, characterized in that, The 3D printing reaction chamber has a volume of 1.2 mL.

7. An application of the extended gate field-effect transistor electrochemical sensor testing system as described in any one of claims 1-6, characterized in that, The steps for detecting COD in tap water include: Step 1: Collect a sufficient amount of water sample to be tested. After the water sample has been left to stand for 5 minutes, add 0.01 mol of Na2SO4 to every 100 mL of tap water to prepare a Na2SO4 solution containing 0.1 M. Step 2: Apply a 2.5V voltage to the gate of the MOSFET using an adjustable regulated power supply, and measure the current output characteristic curve using an electrochemical workstation. Step 3: Based on the obtained current output characteristic curve, use the following formula (1) to obtain the COD of the tap water to be tested: （1）； Where C (organic matter) represents the COD of various organic matter solutions, in mg / L; I represents the drain current, in mA.

8. The application of the extended gate field-effect transistor electrochemical sensor testing system according to claim 7, characterized in that, The derivation process of formula (1) in step 3 is as follows: Changes in the gate voltage of a MOSFET will alter the electrical channel, thus affecting the magnitude of the drain current. The voltage applied to the MOSFET gate has two components: one is the potential generated in the 3D printing reaction chamber, and the other is the voltage between the MOSFET gate and the channel. Therefore, U G The expression is: （2）； Among them, U G U is the voltage applied to the gate of the MOSFET. r Ug-c is the electrochemical potential generated on the surface of the BDD electrode in the 3D printing reaction chamber, and Ug-c is the voltage at the gate and channel of the MOSFET. When the solution contains organic contaminants, under the condition of energization at the BDD electrode, ·OH will be generated to oxidize and dissolve the organic matter in the aqueous solution. When the organic matter is oxidized according to stoichiometry, according to the Nernst equation, the potential at the BDD working electrode is: （3）； in, The potential of the working electrode is given by k, where k represents the Boltzmann constant, T is the thermodynamic temperature, n is the number of electrons transferred when a single reducing agent is oxidized, and C is the temperature. m A1 represents the molar concentration of organic matter in the water sample to be tested, and is a constant. Let the potential on the counter electrode be The voltage in the 3D printing reaction chamber can be obtained as follows: （4）； The voltage Ug-c formed between the gate and the conductive channel of a MOSFET can be expressed as: （5）； Where a and b are constants; Based on the definition of COD, we introduce the number of electrons n transferred when organic matter is oxidized, and simultaneously introduce the molar concentration C of organic matter in the solution. m The conversion relationship to COD is as follows: If 8000 is a dimension factor, then formula (5) can be further expressed as: （6）； Where c is a constant, based on the drain current i of the field-effect transistor. D From the relationship with Ug-c, we can conclude that: （7）； Sample solutions with different CODs were prepared, each containing 0.1 M Na2SO4, and U was applied. G With a constant voltage of 2.5V, an oxidation-digestion reaction is carried out in the 3D printing reaction chamber to obtain the corresponding drain current output characteristic curve, thereby obtaining the values ​​of constants a and c. Substituting these values ​​into formula (7), the drain current i of the corresponding sample solution is obtained. D Relationship with COD; When the sample solution is a mixture of multiple organic compounds, the resulting drain current i D The relationship with COD is: 。 9. The application of the extended gate field-effect transistor electrochemical sensor testing system according to claim 7, characterized in that, In step 3, the COD of the tap water to be tested is obtained using the following formula (1). The minimum detection limit for COD is 0.03 mg / L, and the detection range is 0.05 mg / L to 200 mg / L.

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