CN117214271A - Extended gate field effect transistor electrochemical sensor testing system and application - Google Patents
Extended gate field effect transistor electrochemical sensor testing system and application Download PDFInfo
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Abstract
The invention discloses an extended gate field effect transistor electrochemical sensor testing system and application, the system comprises an electrochemical workstation, a field effect transistor MOSFET, an adjustable regulated power supply, a BDD electrode, a platinum sheet electrode and a 3D printing reaction cavity, wherein the drain electrode and the source electrode of the field effect transistor MOSFET are respectively connected with the anode and the cathode of the electrochemical workstation, the grid electrode of the field effect transistor MOSFET is connected with a two-electrode system through a lead wire, the two-electrode system consists of the BDD electrode and the platinum sheet electrode, the two-electrode system takes the adjustable regulated power supply as an input voltage source, and the BDD electrode and the platinum sheet electrode are placed in the 3D printing reaction cavity when in operation. According to the invention, the BDD electrode is used as an extension material of the grid electrode, and the EGFET prepared by combining the field effect transistor, the platinum counter electrode and the 3D printing reaction cavity form the EGFET electrochemical sensor, so that the measurement of low-concentration organic pollutants in water can be realized, and the core sensor and the technical support are provided for monitoring the water quality safety of tap water, so that the measurement of the low-concentration organic pollutants in water can be realized.
Description
Technical Field
The invention relates to the technical field of sensors and applications thereof, in particular to a test system and an application of an extended gate field effect transistor electrochemical sensor.
Background
The safe drinking of tap water is a non-negligible ring in global health management, and real-time online monitoring of the quality of tap water is an important measure for guaranteeing the drinking safety of common people. The chemical oxygen demand COD (chemical oxygen demand) is a key water quality index for representing the content of organic pollutants in tap water, is mainly measured by a method for detecting in a field sampling laboratory at present, has the defects of expensive equipment, complicated operation process, poor real-time performance and the like, and is difficult to meet the requirement of rapid in-situ detection of tap water. The invention develops an Extended Gate Field Effect Transistor (EGFET) electrochemical sensor which is used for accurately detecting the chemical oxygen demand in tap water and representing the content of organic pollutants in the water, has the remarkable advantages of microminiaturization, batch preparation, suitability for on-site real-time monitoring and the like, and realizes the high-sensitivity detection of the organic pollutants in the tap water.
Disclosure of Invention
According to the actual needs, the invention aims at taking BDD (boron doped diamond ) electrode as the extension material of the grid electrode, combining with the EGFET prepared by the field effect tube, and forming an EGFET electrochemical sensor with a platinum counter electrode and a 3D printing reaction cavity.
In order to achieve the above purpose, the present invention adopts the following technical scheme.
The utility model provides an extension gate field effect transistor electrochemical sensor test system, includes EGFET electrochemical sensor, EGFET electrochemical sensor comprises electrochemical workstation, field effect transistor MOSFET, adjustable constant voltage power supply, BDD electrode, platinum sheet electrode and 3D printing reaction chamber, the drain electrode and the source electrode of field effect transistor MOSFET are connected with the positive pole of electrochemical workstation respectively, the negative pole is connected with two electrode system through the wire, two electrode system comprises BDD electrode and platinum sheet electrode, two electrode system regard as the input voltage source with adjustable constant voltage power supply, the platinum sheet electrode is the counter electrode, BDD electrode and platinum sheet electrode are placed in when the during operation 3D prints the reaction chamber.
Specifically, the electrochemical workstation is a Gamry Reference 600 electrochemical workstation, the maximum test current is 700mA, and the workstation automatically stops working when the current exceeds 700 mA.
Specifically, the MOSFET is 2N7002 in type, the starting voltage is 1-2.5V, and the on-resistance is smaller than 2.5 omega when the gate voltage is 10V.
Specifically, the adjustable voltage-stabilized power supply is an IT6302 type adjustable voltage-stabilized power supply of the Edex ITECH type. Preferably, the BDD electrode manufacturing process is as follows:
after the silicon wafer is cleaned, cutting the silicon wafer into small pieces with the thickness of 0.8cm and the thickness of 2cm by a dicing saw, cleaning the silicon wafer again, then placing the silicon wafer into a reaction chamber of a chemical vapor deposition instrument, preparing a BDD film with the thickness of 3-4 mu m by adopting 2000W microwave plasma chemical vapor deposition, introducing a mixture of methane and hydrogen into the reaction chamber at the flow rate of 250sccm, wherein the hydrocarbon ratio is 2%, B2H6 is used as a boron doping agent, the concentration of the boron doping agent in hydrogen is 15ppm, the substrate temperature is 600 ℃, and the deposition time is 4 hours, thus obtaining the BDD electrode.
Preferably, the 3D printing chamber volume is 1.2mL.
Furthermore, the invention also provides an application of the extended gate field effect transistor electrochemical sensor testing system in detecting COD in tap water, which specifically comprises the following steps:
step 1, collecting a sufficient amount of water sample to be measured, standing the water sample for 5min, and adding 0.01mol of Na into 100mL of tap water 2 SO 4 Formulated to contain 0.1M Na 2 SO 4 A solution;
step 2, applying 2.5V voltage to the gate electrode of the MOSFET through an adjustable stabilized power supply, and measuring by using an electrochemical workstation to obtain a current output characteristic curve;
step 3, according to the obtained current output characteristic curve, obtaining the COD of tap water to be detected by using the following formula (1):
wherein, C (organic matters) represents COD of various organic matter solutions, and the unit is mg/L; i represents drain current, in mA.
Specifically, the deduction process of the formula (1) in the step 3 is as follows:
the voltage of the grid electrode of the MOSFET changes to cause the change of an electric channel so as to influence the magnitude of drain current, and the voltage applied to the grid electrode of the MOSFET has two parts, one is the potential generated in the 3D printing reaction cavity, and the other is the voltage between the grid electrode and the channel of the MOSFET, thus U is formed G The expression of (2) is:
U G ＝U r +U g-c (2)
wherein U is G U for applying voltage to MOSFET gate r Electrochemical potential generated on the surface of a BDD electrode in the 3D printing reaction cavity is given by Ug-c, which is the voltage at the grid and the channel of the MOSFET;
when the solution contains organic pollutants, under the condition that the BDD electrode is electrified, organic matters in the aqueous solution are digested by OH oxidation, and the organic matters are oxidized according to the stoichiometric amount, and the potential on the BDD working electrode is as follows according to the Nernst equation:
wherein,for the potential of the working electrode, k represents the Boltzmann constant, T is the thermodynamic temperature, n is the number of electrons transferred when a single reducing species is oxidized, C m Represents the molar concentration of organic matters in a water sample to be detected, A 1 Is a constant;
let the potential on the counter electrode beThe voltage in the 3D printing reaction chamber can be obtained as follows:
the voltage Ug-c developed between the field effect transistor MOSFET gate and the conductive channel can be expressed as:
wherein a and b are constants;
according to the definition of COD, the number n of electrons transferred when the organic matters are oxidized is introduced, and the molar concentration C of the organic matters in the solution is simultaneously m Converted into COD, the conversion relation is COD=8000 nC m 8000 is a dimension factor, then equation (5) may be further expressed as:
U g-c ＝alog 10 (COD)+c (6)
wherein c is a constant, according to the drain current i of the field effect transistor D The relationship with Ug-c can be derived:
preparing sample solutions with different COD, wherein each sample solution contains 0.1M Na 2 SO 4 Applied U G Performing oxidation digestion reaction in a 3D printing reaction cavity at constant voltage of 2.5V to obtain a corresponding drain current output characteristic curve, thereby obtaining values of constants a and c, and substituting the values into a formula (7) to obtain drain current i of a corresponding sample solution D A relation with COD;
when the sample solution is mixed by a plurality of organic matters, the obtained drain current i D The relation with COD is:
in the above technical scheme, in step 3, the COD of tap water to be detected is obtained by using the following formula (1), and according to practical experimental tests, the lowest detection limit of the COD of the EGFET electrochemical sensor provided by the invention is 0.03mg/L and the detection range is 0.05 mg/L-200 mg/L when the COD of tap water is detected. The beneficial effects of the invention are as follows:
1. according to the invention, the field effect transistor and the BDD sensing electrode are combined to prepare the EGFET electrochemical sensor, the EGFET electrochemical sensor is applied to detection of COD in tap water, the starting voltage of the device is 1.5V, the span is derived from a positive uGS part, and the characteristics of the nMOSFET are integrally shown; when a voltage of 2.5V is applied to the grid electrode, the device is arranged at 0.1M Na 2 SO 4 The supported electrolyte solution obtains a low detection limit of 0.03mg/L and a detection range of 0.05mg/L to 200mg/L, and the repeatability and consistency of the supported electrolyte solution are within 3 percent, so the accuracy is high. In addition, the effectiveness of the EGFET electrochemical sensor provided by the invention is verified in a standard water sample and tap water, and the sensitive and accurate detection performance of the EGFET electrochemical sensor is attributed to the efficient oxidative digestion capability of a BDD electrode and the amplification capability of an EGFET device on weak signals, so that the sensor has good sensing performance in-situ detection.
2. The method for measuring the output characteristic curve of the EGFET and the acidic potassium permanganate titration method provided by the invention show good consistency in analysis of tap water COD; the EGFET electrochemical sensor has good development prospect in the aspect of in-situ high-sensitivity detection of low-concentration organic pollutants.
Drawings
FIG. 1 is a circuit diagram of an extended gate field effect transistor electrochemical sensor testing system according to the present invention;
FIG. 2 is a schematic diagram of an extended gate FET electrochemical sensor test system according to the present invention;
FIG. 3 is a BDD electrode prepared by the method provided in an embodiment of the invention;
FIG. 4 shows the concentration of chloride ions and i when the interference of chloride ions in tap water is measured in this example D Relation of (2)A figure;
FIG. 5 shows the results of the measurement of COD and i D Is a relationship diagram of (1);
FIG. 6 is a graph showing the relationship between the gate voltage and the oxidation peak of the glucose sample solution in this example;
FIG. 7 is a graph showing the relationship between the concentration of different electrolytes and the response current of the glucose sample solution in this example;
FIG. 8 is a graph showing the results of the repeatability test of the present embodiment;
FIG. 9 is a diagram showing the evaluation results of the consistency test in the present embodiment;
fig. 10 is a schematic diagram of an evaluation structure of the stability test in the present embodiment.
In the figure, 1, an electrochemical workstation; 2. a field effect transistor; 3. an adjustable regulated power supply; 4. a BDD electrode; 5. a platinum sheet electrode; 6. and 3D prints the reaction chamber.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but the scope of the present invention is not limited to the above.
Examples
As shown in FIG. 1, the extended gate field effect transistor electrochemical sensor testing system comprises an EGFET electrochemical sensor, wherein 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 printing reaction cavity, as shown in FIG. 2, the drain electrode and the source electrode of the field effect transistor MOSFET are respectively connected with the anode and the cathode of the electrochemical workstation, the grid electrode of the field effect transistor MOSFET is connected with a two-electrode system through wires, the two-electrode system consists of the BDD electrode and the platinum sheet electrode, the two-electrode system takes the adjustable regulated power supply as an input voltage source, the platinum sheet electrode is a counter electrode, and the BDD electrode and the platinum sheet electrode are placed in the 3D printing reaction cavity during operation.
In this embodiment, the electrochemical workstation is a Gamry Reference 600 electrochemical workstation, the maximum test current is 700mA, and the workstation automatically stops working when the current exceeds 700 mA.
In this embodiment, the MOSFET is 2N7002, the start voltage is 1-2.5V, and the on-resistance is less than 2.5Ω when the gate voltage is 10V.
In this embodiment, the adjustable regulated power supply is an IT6302 model of the idex ITECH adjustable regulated power supply.
In this embodiment, the BDD electrode manufacturing process is as follows:
after the silicon wafer is cleaned, the silicon wafer is cut into small pieces with the thickness of 0.8cm and the thickness of 2cm by a dicing saw, the small pieces are cleaned again and then are placed into a reaction chamber of a chemical vapor deposition instrument, a BDD film with the thickness of 3-4 mu m is prepared by adopting 2000W microwave plasma chemical vapor deposition, a mixture of methane and hydrogen is introduced into the reaction chamber at the flow rate of 250sccm, the hydrocarbon ratio is 2%, B2H6 is used as a boron doping agent, the concentration of the boron doping agent in hydrogen is 15ppm, the substrate temperature is 600 ℃, the deposition time is 4 hours, and the BDD electrode is obtained as shown in a graph of fig. 3.
In this embodiment, the 3D printing chamber volume is 1.2mL.
Further, in this embodiment, an example of the extended gate field effect transistor electrochemical sensor testing system for detecting COD in tap water is provided, which specifically includes the following steps:
step 1, collecting a sufficient amount of water sample to be measured, standing the water sample for 5min, and adding 0.01mol of Na into 100mL of tap water 2 SO 4 Formulated to contain 0.1M Na 2 SO 4 A solution;
step 2, applying 2.5V voltage to the gate electrode of the MOSFET through an adjustable stabilized power supply, and measuring by using an electrochemical workstation to obtain a current output characteristic curve;
step 3, according to the obtained current output characteristic curve, obtaining the COD of tap water to be detected by using the following formula (1):
wherein, C (organic matters) represents COD of various organic matter solutions, and the unit is mg/L; i represents drain current, in mA.
Specifically, the deduction process of the formula (1) in the step 3 is as follows:
the voltage of the grid electrode of the MOSFET changes to cause the change of an electric channel so as to influence the magnitude of drain current, and the voltage applied to the grid electrode of the MOSFET has two parts, one is the potential generated in the 3D printing reaction cavity, and the other is the voltage between the grid electrode and the channel of the MOSFET, thus U is formed G The expression of (2) is:
U G ＝U r +U g-c (2)
wherein U is G U for applying voltage to MOSFET gate r Electrochemical potential generated on the surface of a BDD electrode in the 3D printing reaction cavity is given by Ug-c, which is the voltage at the grid and the channel of the MOSFET;
when the solution contains organic pollutants, under the condition that the BDD electrode is electrified, organic matters in the aqueous solution are digested by OH oxidation, and the organic matters are oxidized according to the stoichiometric amount, and the potential on the BDD working electrode is as follows according to the Nernst equation:
wherein,for the potential of the working electrode, k represents the Boltzmann constant, T is the thermodynamic temperature, n is the number of electrons transferred when a single reducing species is oxidized, C m Represents the molar concentration of organic matters in a water sample to be detected, A 1 Is a constant;
let the potential on the counter electrode beThe voltage in the 3D printing reaction chamber can be obtained as follows:
the voltage Ug-c developed between the field effect transistor MOSFET gate and the conductive channel can be expressed as:
wherein a and b are constants;
according to the definition of COD, the number n of electrons transferred when the organic matters are oxidized is introduced, and the molar concentration C of the organic matters in the solution is simultaneously m Converted into COD, the conversion relation is COD=8000 nC m 8000 is a dimension factor, then equation (5) may be further expressed as:
U g-c ＝alog 10 (COD)+c (6)
wherein c is a constant, according to the drain current i of the field effect transistor D The relationship with Ug-c can be derived:
preparing sample solutions with different COD, wherein each sample solution contains 0.1M Na 2 SO 4 Applied U G Performing oxidation digestion reaction in a 3D printing reaction cavity at constant voltage of 2.5V to obtain a corresponding drain current output characteristic curve, thereby obtaining values of constants a and c, and substituting the values into a formula (7) to obtain drain current i of a corresponding sample solution D A relation with COD;
in this embodiment, the calculation formulas of the EGFET electrochemical sensor in detecting the COD of a single organic matter and multiple organic matters in tap water are given respectively, and specifically are as follows:
a. test calibration of interfering ions in tap water
Chlorine ions widely exist in tap water, in China, chlorine is used as a main additive for sterilizing bacteria and viruses in tap water, excessive chlorine addition can cause carcinogens such as chloroform and the like in the water, insufficient addition can not perform the function of sterilization, and the method is used in a tap water plantAnd the concentration of free chlorine in the tap water is required to be in the range of 0.6mg/L-0.8mg/L and 0.05mg/L-0.3mg/L at the end of the tap water pipe, and chlorine ions are also the main interference component of detection in tap water COD detection, in this embodiment, the interference ions are calibrated, and as shown in FIG. 4, the concentration of the chlorine ions and drain current i are obtained by analysis in the range of 10mg/L-350mg/L D The relation of (2) satisfies the equation:
wherein C is Cl- Represents the concentration of chloride ions (mg/L), I represents the drain current I D (mA), linearity R 2 0.98428, which shows that when chloride ions are between 10mg/L and 350mg/L, the test result needs to be corrected by a fitting equation so as to finish accurate measurement of tap water COD;
b. COD measurement in tap water in the presence of various organics
In a, only a single organic matter is tested, however, the organic pollutant type in tap water is not single, so that it is necessary to detect the response of the EGFET electrochemical sensor to a plurality of organic matters, glucose, glutamic acid, potassium hydrogen phthalate and the equivalent mixture thereof are selected as standard samples, an operating voltage of 2.5V is applied to the grid electrode, and a voltage of 0.1M Na is applied to the grid electrode 2 SO 4 As shown in FIG. 5, it can be seen from the graph that the output characteristic curves of the EGFET electrochemical sensor against various standards are tested in the background solution of (1), i of the EGFET electrochemical sensor is different even if the detected organic matters are different D Still can form fitting relation with COD, they satisfy:
wherein C (organic matter) represents COD (mg/L) of various organic matter solutions, and I represents drain current I D (mA) their linearity R 2 = 0.99819, which indicates that even facingThe EGFET electrochemical sensor provided by the invention can still accurately measure in tap water environment with complex organic matters.
In the preparation of the sample solutions, each sample solution contains 0.1M Na 2 SO 4 Applied U G The constant 2.5V voltage is for the following reasons:
(1) in order to make the performance of the EGFET more in line with the requirements of tap water COD detection, the influence of the gate voltage on the experimental result is studied before the detection is carried out. As shown in FIG. 6, redox peak tests were sequentially performed on glucose samples (0 mg/L, 0.1mg/L, 0.5mg/L, 1mg/L, 5mg/L, 10 mg/L) of different COD concentrations using cyclic voltammetry; for a glucose solution with COD of 10mg/L, the position of the oxidation peak is about 2.3V, and the oxidation peak gradually shifts to the right and tends to be about a fixed voltage value along with the decrease of the COD; when COD is reduced to 0.1mg/L, an oxidation peak appears when the voltage is increased to about 2.5V, the deviation of the position of the oxidation peak is small, the stability and the sensitivity of a response signal are key factors for accurately measuring the COD, and in order to optimize the stability test and the sensitivity of a device to a response signal of a low COD to-be-measured liquid, 2.5V is selected as the gate voltage of an EGFET in an experiment;
(2) based on Na 2 SO 4 Good solution conductivity was exhibited in various supporting electrolytes, so in this example it was used as background solution for the test and Na was studied 2 SO 4 Effect of concentration of solution on electrochemical signal, na of each concentration 2 SO 4 The solution was subjected to three chronoamperometric tests, each with a COD of the glucose solution of 1mg/L, and each response current was averaged over 4s-5s, as shown in FIG. 7, over a concentration range of 0.05M-0.1M, with Na 2 SO 4 The concentration increases, the response current reaches the maximum value at 0.1M, and Na is 2 SO 4 As the concentration continues to increase to 0.15M, the response current tends to be gentle and decreases, so in order to detect a weak response signal to a greater extent, i.e. to allow the EGFET device to detect COD at a lower concentration in the solution, na is selected in this embodiment 2 SO 4 Concentration of solution0.1M.
In the above technical scheme, in step 3, the COD of tap water to be detected is obtained by using the following formula (1), and according to practical experimental tests, the lowest detection limit of the COD of the EGFET electrochemical sensor provided by the invention is 0.03mg/L and the detection range is 0.05 mg/L-200 mg/L when the COD of tap water is detected.
The repeatability, consistency and stability of the extended gate field effect transistor electrochemical sensor test system provided by the invention will be tested by specific experiments.
1) Repeatability test
To test the repeatability of a single EGFET electrochemical sensor, the sensor was tested on 0.1M Na 2 SO 4 The solutions were subjected to reproducibility tests of glucose solutions having COD of 0.5mg/L, 1mg/L and 3 mg/L. As shown in fig. 8, the EGFET electrochemical sensor provided in this example was used to test the solution with the same COD value 5 times, and the output characteristic curves of the tests were compared, and as a result, the RSDs of the iD were 2.113%, 2.327% and 1.876%, respectively, which indicates that the detection performance of the device was reliable, and the device was applicable to multiple measurements of COD in tap water.
2) Consistency test
The 5 EGFET electrochemical sensors prepared in the same batch in this example were selected and tested for i to 0.1mg/L, 0.3mg/L, 0.5mg/L, 1mg/L and 3mg/L glucose solutions D As shown in fig. 9, the results show that the EGFET electrochemical sensor has RSD within 3% for all of the 5 different COD glucose solutions, which demonstrates that the EGFET electrochemical sensor provided by the present invention has satisfactory consistency.
3) Stability test
Selecting 0.1M Na 2 SO 4 Solution as supporting electrolyte solution, 1mg/L glucose solution was subjected to i for 15 days D Stability test, one water sample was tested every two days, and each water sample was tested repeatedly three times. As shown in fig. 10, over time, i of an EGFET electrochemical sensor D The drop was slow, 122.42mA on the first day, and 116.87mA was still present by day 15, which was 95.47% of the first day. This indicates that EGFE provided by the inventionThe T electrochemical sensor has stable test performance with time and great potential in long-term stability when testing COD in water body.
Finally, in order to verify the feasibility of the EGFET electrochemical sensor provided by the invention in measuring COD in actual tap water, a sufficient amount of tap water sample is collected for detection in the embodiment.
The COD of tap water is measured by respectively adopting an acidic potassium permanganate titration method and the EGFET electrochemical sensor provided by the invention. Tap water is taken from Jiangxi university, and after a water sample is kept stand for 5min, 0.01mol of Na is added into each 100ml of tap water 2 SO 4 Formulated to contain 0.1M Na 2 SO 4 And (3) applying a grid voltage of 2.5V to the solution, measuring an output characteristic curve of the EGFET, and obtaining the COD of tap water according to a formula (9). Another water sample was sent to Zhejiang, detection technologies, inc., and the concentration of organics was measured by acidic potassium permanganate titration with the results shown in Table 1 below. The results in the table show that the error of the COD values obtained by the two methods is within 4.5%, which shows that compared with the acidic potassium permanganate titration method, the drain current method used by the EGFET electrochemical sensor has good consistency in the aspect of testing tap water COD, and also shows that the EGFET electrochemical sensor has good potential in the aspect of testing tap water COD.
TABLE 1 correlation of drain amperometric and acidic Potassium permanganate titrations to measure the chemical oxygen demand of real samples
According to the invention, the field effect transistor and the BDD sensing electrode are combined to prepare the EGFET electrochemical sensor, the EGFET electrochemical sensor is applied to detection of COD in tap water, the starting voltage of the device is 1.5V, the span is derived from a positive uGS part, and the characteristics of the nMOSFET are integrally shown; when a voltage of 2.5V is applied to the grid electrode, the device is arranged at 0.1M Na 2 SO 4 A low detection limit of 0.03mg/L and a detection range of 0.05mg/L to 200mg/L are obtained in the supporting electrolyte solution while it is repeatedThe RSD of the consistency and the consistency is within 3 percent, and the precision is high. In addition, the effectiveness of the EGFET electrochemical sensor provided by the invention is verified in a standard water sample and tap water, and the sensitive and accurate detection performance of the EGFET electrochemical sensor is attributed to the efficient oxidative digestion capability of a BDD electrode and the amplification capability of an EGFET device on weak signals, so that the sensor has good sensing performance in-situ detection. The drain current method and the acidic potassium permanganate titration method provided by the invention show good consistency in analysis of tap water COD; the EGFET electrochemical sensor has good development prospect in the aspect of in-situ high-sensitivity detection of low-concentration organic pollutants.
The foregoing is only a preferred embodiment of the present invention, and the present invention is not limited thereto, and any simple modification, variation and imitation of the foregoing embodiments for the technical content of the present invention falls within the scope of the technical solution of the present invention.
Claims (9)
1. The utility model provides an extension gate field effect transistor electrochemical sensor test system, its characterized in that includes EGFET electrochemical sensor, EGFET electrochemical sensor comprises electrochemical workstation, field effect transistor MOSFET, adjustable regulated power supply, BDD electrode, platinum electrode and 3D print reaction chamber, the drain electrode and the source electrode of field effect transistor MOSFET are connected with the positive pole of electrochemical workstation, negative pole respectively, the grid of field effect transistor MOSFET passes through the wire and is connected with two electrode systems, two electrode systems comprise BDD electrode and platinum electrode, two electrode systems regard adjustable regulated power supply as the input voltage source, platinum electrode is the counter electrode, BDD electrode and platinum electrode are placed in during operation 3D print reaction chamber.
2. The extended gate field effect transistor electrochemical sensor test system of claim 1, wherein the electrochemical workstation is a Gamry Reference 600 electrochemical workstation, the maximum test current is 700mA, and the workstation automatically stops when the current exceeds 700 mA.
3. The extended gate field effect transistor electrochemical sensor test system of claim 1, wherein the field effect transistor MOSFET is model 2N7002, the starting voltage is 1-2.5V, and the on-resistance is less than 2.5 Ω when the gate voltage is 10V.
4. The extended gate field effect transistor electrochemical sensor test system of claim 1, wherein the adjustable regulated power supply is an IT6302 model edx ITECH adjustable regulated power supply.
5. An extended gate field effect transistor electrochemical sensor testing system according to claim 1, wherein said BDD electrode is fabricated as follows:
after the silicon wafer is cleaned, cutting the silicon wafer into small pieces with the thickness of 0.8cm and the thickness of 2cm by a dicing saw, cleaning the silicon wafer again, then placing the silicon wafer into a reaction chamber of a chemical vapor deposition instrument, preparing a BDD film with the thickness of 3-4 mu m by adopting 2000W microwave plasma chemical vapor deposition, introducing a mixture of methane and hydrogen into the reaction chamber at the flow rate of 250sccm, wherein the hydrocarbon ratio is 2%, B2H6 is used as a boron doping agent, the concentration of the boron doping agent in hydrogen is 15ppm, the substrate temperature is 600 ℃, and the deposition time is 4 hours, thus obtaining the BDD electrode.
6. The extended gate field effect transistor electrochemical sensor testing system of claim 1, wherein the 3D print chamber volume is 1.2mL.
7. Use of the extended gate field effect transistor electrochemical sensor testing system according to any of claims 1-6 for detecting COD of tap water, comprising the steps of:
step 1, collecting a sufficient amount of water sample to be measured, standing the water sample for 5min, and adding 0.01mol of Na into 100mL of tap water 2 SO 4 Formulated to contain 0.1M Na 2 SO 4 A solution;
step 2, applying 2.5V voltage to the gate electrode of the MOSFET through an adjustable stabilized power supply, and measuring by using an electrochemical workstation to obtain a current output characteristic curve;
step 3, according to the obtained current output characteristic curve, obtaining the COD of tap water to be detected by using the following formula (1):
wherein, C (organic matters) represents COD of various organic matter solutions, and the unit is mg/L; i represents drain current, in mA.
8. The use of the extended gate field effect transistor electrochemical sensor test system according to claim 7, wherein the derivation of the formula (1) in step 3 is as follows:
the voltage of the grid electrode of the MOSFET changes to cause the change of an electric channel so as to influence the magnitude of drain current, and the voltage applied to the grid electrode of the MOSFET has two parts, one is the potential generated in the 3D printing reaction cavity, and the other is the voltage between the grid electrode and the channel of the MOSFET, thus U is formed G The expression of (2) is:
U G ＝U r +U g-c (2)
wherein U is G U for applying voltage to MOSFET gate r Electrochemical potential generated on the surface of a BDD electrode in the 3D printing reaction cavity is given by Ug-c, which is the voltage at the grid and the channel of the MOSFET;
when the solution contains organic pollutants, under the condition that the BDD electrode is electrified, organic matters in the aqueous solution are digested by OH oxidation, and the organic matters are oxidized according to the stoichiometric amount, and the potential on the BDD working electrode is as follows according to the Nernst equation:
wherein,for the potential of the working electrode, k represents the Boltzmann constant, T is the thermodynamic temperature, n is the number of electrons transferred when a single reducing species is oxidized, C m Represents the molar concentration of organic matters in a water sample to be detected, A 1 Is a constant;
let the potential on the counter electrode beThe voltage in the 3D printing reaction chamber can be obtained as follows:
the voltage Ug-c developed between the field effect transistor MOSFET gate and the conductive channel can be expressed as:
wherein a and b are constants;
according to the definition of COD, the number n of electrons transferred when the organic matters are oxidized is introduced, and the molar concentration C of the organic matters in the solution is simultaneously m Converted into COD, the conversion relation is COD=8000 nC m 8000 is a dimension factor, then equation (5) may be further expressed as:
U g-c ＝alog 10 (COD)+c (6)
wherein c is a constant, according to the drain current i of the field effect transistor D The relationship with Ug-c can be derived:
preparing sample solutions with different COD, wherein each sample solution contains 0.1M Na 2 SO 4 Applied U G Performing oxidation digestion reaction in a 3D printing reaction cavity at constant voltage of 2.5V to obtain a corresponding drain current output characteristic curve, thereby obtaining values of constants a and c, and substituting the values into a formula (7) to obtain drain current i of a corresponding sample solution D A relation with COD;
when the sample solution is mixed by a plurality of organic matters, the obtained drain current i D The relation with COD is:
9. the application of the extended gate field effect transistor electrochemical sensor testing system according to claim 7, wherein in the step 3, the following formula (1) is used to obtain the COD of the tap water to be tested, the lowest detection limit of the COD is 0.03mg/L, and the detection range is 0.05mg/L to 200mg/L.
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