由图5（a）可发现以超纯水为支持电解质时，所得修饰电极的循环伏安图响应

From Fig. 5(a), it can be found that when ultrapure water is used as the supporting electrolyte, the response current of the resulting modified electrode is 0 mA. This is because the ultrapure water (pH 6.88) removes the water during the treatment process. Almost all conductive media have deionized water, so there is no conductive effect, and electron transfer cannot be performed, resulting in a response current of 0 mA for the cyclic voltammogram. It was also found that the cyclic voltammogram of the modified electrode supported by 0.5 mol•L-1 Na2SO4 (pH 7.02) solution and 50 mmol•L-1PBS solution (pH 6.8, 7.2 respectively) does not have the characteristic redox peak of polyoxometalates, which may be The reason is that polyoxometalates are easily decomposed in a neutral solution, resulting in polyoxometalates ion concentration insufficient to respond to a sufficiently strong response current, so that there is no characteristic redox peak of polyoxometalates. While in 0.5mol•L-1 H2SO4 solution (pH 0.46), 0.1 mol•L-1 H2SO4 solution (pH 1.13), 0.5 mol•L-1 H2SO4 and 0.5 mol•L-1Na2SO4 mixed solution (pH is 0.73), the mixed electrode of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1Na2SO4 (pH 1.54) supported the cyclic voltammogram of the modified electrode (figure 5(b)), the characteristic redox of polyoxometalates appeared peak. And from Fig. 5(b), it can be seen that the modified electrode has the strongest response current under the support of 0.5 mol•L-1 H2SO4 solution (pH 0.46). However, considering that the target detection substance of the reaction system is tyrosinase, and the conditions required for tyrosinase to maintain activity are relatively mild and cannot be in a strong acid and alkali environment, so 0.1 mol•L-1 H2SO4 with a pH of 1.54 is selected The mixed solution with 0.5 mol•L-1Na2SO4 is used as a reference for the next experiment, and continue to study the electrochemistry of the modified electrode when the mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 at different pH is used as the supporting electrolyte. Behavior (Figure 6a). The pH of the mixed solution of 0.1 molL-1 H2SO4 and 0.5 molL-1 Na2SO4 in Figure 6a is 1.54, 2.62, 3.86, 5.29, 6. 51. The volume ratio of the corresponding 0.1 mol•L-1 H2SO4 solution and 0.5 mol•L-1 Na2SO4 solution in the mixed solution are respectively 1:1 (5:5), 4:6, 3:7, 2:8, 1:9. It can be seen from Figure 6(a) that as the pH of the 0.1 mol•L-1 H2SO4 solution and 0.5 mol•L-1 Na2SO4 solution changes from 1.54 to 6.51, that is, the acidity continues to weaken, it is found that the modified electrode is in the process of cyclic voltammetry scanning The response current in the middle decreases continuously, and the redox peak potential shifts negatively, indicating that protons participate in the electrochemical reaction process. Comparing the cyclic voltammograms of the modified electrode obtained when the mixed solutions of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 at pH 1.54 and 6.51 were used as the supporting electrolyte (Figure 6(b)), we can see that the modification The electrode in two different pH supporting electrolyte solutions, although the corresponding redox peak potential and response current have changed, but still have the characteristic redox peak of polyoxometalates. And when the pH of the mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 changes from 5.29 to 6.51, that is, 0.1 mol•L-1 H2SO4 solution and 0.5 mol•L-1 Na2SO4 solution in the mixed solution The volume ratio in the solution changes from 2:8 to 1:9, and the cyclic voltammograms under the corresponding conditions basically overlap, but when the ratio of 0.1 mol•L-1 H2SO4 solution to 0.5 mol•L-1 Na2SO4 solution is 0 : At 10 o'clock, that is, when 0.5 mol•L-1 Na2SO4 (pH 7.02) solution is used as the supporting electrolyte, its cyclic voltammogram does not have the characteristic redox peak of polyoxometalates. This is because polyoxometalates are sensitive to acidity. When the acidity weakens and the pH increases to a certain value, polyoxometalates decompose and the redox peak decreases. Therefore, in order to ensure the detection sensitivity, a mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 with a pH of 6.51 was selected as the supporting electrolyte for subsequent experiments. The volume ratio of 5 mol•L-1 Na2SO4 solution in the mixed solution is 1:1 (5:5), 4:6, 3:7, 2:8, and 1:9, respectively. It can be seen from Figure 6(a) that as the pH of the 0.1 mol•L-1 H2SO4 solution and 0.5 mol•L-1 Na2SO4 solution changes from 1.54 to 6.51, that is, the acidity continues to weaken, it is found that the modified electrode is in the process of cyclic voltammetry scanning The response current in the middle decreases continuously, and the redox peak potential shifts negatively, indicating that protons participate in the electrochemical reaction process. Comparing the cyclic voltammograms of the modified electrode obtained when the mixed solutions of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 at pH 1.54 and 6.51 were used as the supporting electrolyte (Figure 6(b)), we can see that the modification The electrode in two different pH supporting electrolyte solutions, although the corresponding redox peak potential and response current have changed, but still have the characteristic redox peak of polyoxometalates. And when the pH of the mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 changes from 5.29 to 6.51, that is, 0.1 mol•L-1 H2SO4 solution and 0.5 mol•L-1 Na2SO4 solution in the mixed solution The volume ratio in the solution changes from 2:8 to 1:9, and the cyclic voltammograms under the corresponding conditions basically overlap, but when the ratio of 0.1 mol•L-1 H2SO4 solution to 0.5 mol•L-1 Na2SO4 solution is 0 : At 10 o'clock, that is, when 0.5 mol•L-1 Na2SO4 (pH 7.02) solution is used as the supporting electrolyte, its cyclic voltammogram does not have the characteristic redox peak of polyoxometalates. This is because polyoxometalates are sensitive to acidity. When the acidity weakens and the pH increases to a certain value, polyoxometalates decompose and the redox peak decreases. Therefore, in order to ensure the detection sensitivity, a mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 with a pH of 6.51 was selected as the supporting electrolyte for subsequent experiments. The volume ratio of 5 mol•L-1 Na2SO4 solution in the mixed solution is 1:1 (5:5), 4:6, 3:7, 2:8, and 1:9, respectively. It can be seen from Figure 6(a) that as the pH of the 0.1 mol•L-1 H2SO4 solution and 0.5 mol•L-1 Na2SO4 solution changes from 1.54 to 6.51, that is, the acidity continues to weaken, it is found that the modified electrode is in the process of cyclic voltammetry scanning The response current in the middle decreases continuously, and the redox peak potential shifts negatively, indicating that protons participate in the electrochemical reaction process. Comparing the cyclic voltammograms of the modified electrode obtained when the mixed solutions of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 at pH 1.54 and 6.51 were used as the supporting electrolyte (Figure 6(b)), we can see that the modification The electrode in two different pH supporting electrolyte solutions, although the corresponding redox peak potential and response current have changed, but still have the characteristic redox peak of polyoxometalates. And when the pH of the mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 changes from 5.29 to 6.51, that is, 0.1 mol•L-1 H2SO4 solution and 0.5 mol•L-1 Na2SO4 solution in the mixed solution The volume ratio in the solution changes from 2:8 to 1:9, and the cyclic voltammograms under the corresponding conditions basically overlap, but when the ratio of 0.1 mol•L-1 H2SO4 solution to 0.5 mol•L-1 Na2SO4 solution is 0 : At 10 o'clock, that is, when 0.5 mol•L-1 Na2SO4 (pH 7.02) solution is used as the supporting electrolyte, its cyclic voltammogram does not have the characteristic redox peak of polyoxometalates. This is because polyoxometalates are sensitive to acidity. When the acidity weakens and the pH increases to a certain value, polyoxometalates decompose and the redox peak decreases. Therefore, in order to ensure the detection sensitivity, a mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 with a pH of 6.51 was selected as the supporting electrolyte for subsequent experiments. 51, that is, the acidity continues to weaken, and it is found that the modified electrode responds to a continuous weakening of the current during the cyclic voltammetry scan, and the redox peak potential shifts negatively, indicating that the electrochemical reaction process involves protons. Comparing the cyclic voltammograms of the modified electrode obtained when the mixed solutions of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 at pH 1.54 and 6.51 were used as the supporting electrolyte (Figure 6(b)), we can see that the modification The electrode in two different pH supporting electrolyte solutions, although the corresponding redox peak potential and response current have changed, but still have the characteristic redox peak of polyoxometalates. And when the pH of the mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 changes from 5.29 to 6.51, that is, 0.1 mol•L-1 H2SO4 solution and 0.5 mol•L-1 Na2SO4 solution in the mixed solution The volume ratio in the solution changes from 2:8 to 1:9, and the cyclic voltammograms under the corresponding conditions basically overlap, but when the ratio of 0.1 mol•L-1 H2SO4 solution to 0.5 mol•L-1 Na2SO4 solution is 0 : At 10 o'clock, that is, when 0.5 mol•L-1 Na2SO4 (pH 7.02) solution is used as the supporting electrolyte, its cyclic voltammogram does not have the characteristic redox peak of polyoxometalates. This is because polyoxometalates are sensitive to acidity. When the acidity weakens and the pH increases to a certain value, polyoxometalates decompose and the redox peak decreases. Therefore, in order to ensure the detection sensitivity, a mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 with a pH of 6.51 was selected as the supporting electrolyte for subsequent experiments. 51, that is, the acidity continues to weaken, and it is found that the modified electrode responds to a continuous weakening of the current during the cyclic voltammetry scan, and the redox peak potential shifts negatively, indicating that the electrochemical reaction process involves protons. Comparing the cyclic voltammograms of the modified electrode obtained when the mixed solutions of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 at pH 1.54 and 6.51 were used as the supporting electrolyte (Figure 6(b)), we can see that the modification The electrode in two different pH supporting electrolyte solutions, although the corresponding redox peak potential and response current have changed, but still have the characteristic redox peak of polyoxometalates. And when the pH of the mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 changes from 5.29 to 6.51, that is, 0.1 mol•L-1 H2SO4 solution and 0.5 mol•L-1 Na2SO4 solution in the mixed solution The volume ratio in the solution changes from 2:8 to 1:9, and the cyclic voltammograms under the corresponding conditions basically overlap, but when the ratio of 0.1 mol•L-1 H2SO4 solution to 0.5 mol•L-1 Na2SO4 solution is 0 : At 10 o'clock, that is, when 0.5 mol•L-1 Na2SO4 (pH 7.02) solution is used as the supporting electrolyte, its cyclic voltammogram does not have the characteristic redox peak of polyoxometalates. This is because polyoxometalates are sensitive to acidity. When the acidity weakens and the pH increases to a certain value, polyoxometalates decompose and the redox peak decreases. Therefore, in order to ensure the detection sensitivity, a mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 with a pH of 6.51 was selected as the supporting electrolyte for subsequent experiments. The cyclic voltammogram of the modified electrode obtained when the 5 mol•L-1 Na2SO4 mixed solution was used as the supporting electrolyte (Figure 6(b)) shows that the modified electrode is in two different pH supporting electrolyte solutions, although the corresponding redox peaks The potential and its response current have changed, but they still have the characteristic redox peaks of polyoxometalates. And when the pH of the mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 changes from 5.29 to 6.51, that is, 0.1 mol•L-1 H2SO4 solution and 0.5 mol•L-1 Na2SO4 solution in the mixed solution The volume ratio in the solution changes from 2:8 to 1:9, and the cyclic voltammograms under the corresponding conditions basically overlap, but when the ratio of 0.1 mol•L-1 H2SO4 solution to 0.5 mol•L-1 Na2SO4 solution is 0 : At 10 o'clock, that is, when 0.5 mol•L-1 Na2SO4 (pH 7.02) solution is used as the supporting electrolyte, its cyclic voltammogram does not have the characteristic redox peak of polyoxometalates. This is because polyoxometalates are sensitive to acidity. When the acidity weakens and the pH increases to a certain value, polyoxometalates decompose and the redox peak decreases. Therefore, in order to ensure the detection sensitivity, a mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 with a pH of 6.51 was selected as the supporting electrolyte for subsequent experiments. The cyclic voltammogram of the modified electrode obtained when the 5 mol•L-1 Na2SO4 mixed solution was used as the supporting electrolyte (Figure 6(b)) shows that the modified electrode is in two different pH supporting electrolyte solutions, although the corresponding redox peaks The potential and its response current have changed, but they still have the characteristic redox peaks of polyoxometalates. And when the pH of the mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 changes from 5.29 to 6.51, that is, 0.1 mol•L-1 H2SO4 solution and 0.5 mol•L-1 Na2SO4 solution in the mixed solution The volume ratio in the solution changes from 2:8 to 1:9, and the cyclic voltammograms under the corresponding conditions basically overlap, but when the ratio of 0.1 mol•L-1 H2SO4 solution to 0.5 mol•L-1 Na2SO4 solution is 0 : At 10 o'clock, that is, when 0.5 mol•L-1 Na2SO4 (pH 7.02) solution is used as the supporting electrolyte, its cyclic voltammogram does not have the characteristic redox peak of polyoxometalates. This is because polyoxometalates are sensitive to acidity. When the acidity weakens and the pH increases to a certain value, polyoxometalates decompose and the redox peak decreases. Therefore, in order to ensure the detection sensitivity, a mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 with a pH of 6.51 was selected as the supporting electrolyte for subsequent experiments. 02) When the solution is a supporting electrolyte, its cyclic voltammogram does not have the characteristic redox peak of polyoxometalates. This is because polyoxometalates are sensitive to acidity. When the acidity weakens and the pH increases to a certain value, polyoxometalates decompose and the redox peak decreases. Therefore, in order to ensure the detection sensitivity, a mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 with a pH of 6.51 was selected as the supporting electrolyte for subsequent experiments. 02) When the solution is a supporting electrolyte, its cyclic voltammogram does not have the characteristic redox peak of polyoxometalates. This is because polyoxometalates are sensitive to acidity. When the acidity weakens and the pH increases to a certain value, polyoxometalates decompose and the redox peak decreases. Therefore, in order to ensure the detection sensitivity, a mixed solution of 0.1 mol•L-1 H2SO4 and 0.5 mol•L-1 Na2SO4 with a pH of 6.51 was selected as the supporting electrolyte for subsequent experiments.

From Figure 5(a) can be found to ultrapure water to support electrolytes, the resulting modified electrode of the cycle volt-ampo-response current of 0 mA, this is due to ultra-pure water (pH is 6.88) in the process of removing almost all the conductive media in the water, water deionization, so there is no conductive effect, can not be transferred electrons, resulting in the reaction of the cycle fuampite response current of 0 mA. It was also found that the circulating voltu to the modified electrodes supported by 0.5 mol L-1 Na2SO4 (pH is 7.02) and 50mmol L-1PBS solution (pH 6.8, 7.2) did not have the characteristic oxidation reduction peak of polyoxometalates, possibly due to the easy decomposition of polyoxobites in neutral solution, The resulting polyoxometalates ion concentration is not sufficient to respond to a sufficiently strong response current, so that there is no polyoxometalates characteristic redox peak. In the 0.5mol L-1 H2SO4 solution (pH 0.46), 0.1 mol L-1 H2SO4 solution (pH 1.13), 0.5 mol L-1 H2SO4 and 0.5 mol-L-1Na2SO4 mixed solution (pH 0.73), 0.1 mol-L-1H2SO0.5 The circulating voltatu (Figure 5(b)) of the modified electrode supported by the mixed solution of L-1Na2SO4 (pH is 1.54) has a characteristic redox peak of polyoxometalates. And as can be seen from Figure 5(b), the modified electrode has the strongest response current supported by 0.5 mol-L-1 H2SO4 solution (pH is 0.46). However, considering that the target testing substance of the reaction system is tyrosine enzyme, and the condition syrosine enzyme to maintain activity requirements is mild, can not be in the environment of strong acid and alkali, so choose pH of 1.54 0.1 mol -L-1 H2SO4 and 0.5 mol-L-1Na2SO4 mixed solution as reference for the next step of the experiment, and continue to study the different pH 0.1 mol-L-L2-HSO4 and 1.5 The Na2SO4 mixing solution modifies the electrochemical behavior of the electrode when supporting the electrolyte (Figure 6a). Figure 6a in 0.1 mol.L-1 H2SO4 and 0.5 mol.L-1 Na2SO4 mixed solutionpH are 1.54, 2.62, 3.86, 5.29, 6.51, respectively. The volume ratio of the 0.1 mol-L-1 H2SO4 solution and the 0.5 mol-L-1 Na2SO4 solution in the mixed solution is 1:1 (5:5), 4:6, 3:7, 2:8, 1:9. From Figure 6(a), it can be seen that with 0.1 mol-L-L-1 H2SO4 solution and 0.5 mol-L-1 Na2SO4 solution pH from 1.54 to 6.51, i.e. the acidity is decreasing, it is found that the modified electrode in the cycle volta scan in response to the current is decreasing, the redox peak electroposition is negative shift, indicating that the electrochemical reaction process has the participation of protons. Comparing the circular voltuate (Figure 6(b)) of the modified electrodes obtained when the modified electrodes with pH of 1.54 and 6.51 of 1.54 and 6.51, respectively, have changed, but still have the characteristics of the reduced peak of the corresponding redox peak electroidization and its current. And when the pH of 0.1 mol.L-1 H2SO4 dissolved and 0.5 mol-L-1 Na2SO4 mixed solution varies from 5.29 to 6.51, i.e. 0.1 mol.L-1 H2SO4 solution and 0.5 The volume ratio of mol L-1 Na2SO4 solution in the mixed solution varies from 2:8 to 1:9, and the circulating vaantgraphy under corresponding conditions basically coincides, but when 0.1 mol L-1 H2SO4 solution is compared to 0.5 mol L-L-1 At 0:10, when the ratio of The Na2SO4 solution is 0:10, i.e. when the electrolyte is supported with 0.5 mol L-1 Na2SO4 (pH is 7.02), its circulating vooats do not have the characteristic redox reduction peak of polyoxometalates. This is due to polyoxometalates sensitivity to acidity, when acidity weakens, pH increases to a certain value, polyoxometalates decomposition, redox peak reduction. Therefore, in order to ensure the sensitivity of the detection, the 0.1 mol-L-1 H2SO4 and 0.5 mol-L-1 Na2SO4 mixture solution with pH of 6.51 are selected to support the electrolyte for subsequent experiments.

It can be seen from Fig. 5 (a) that when ultrapure water is used as the supporting electrolyte, the response current of the cyclic voltammetry of the modified electrode is 0 ma. This is because ultrapure water (pH 6.88) removes almost all the conductive media in the water and deionizes the water in the process of treatment, so there is no conductive effect and electronic transfer, resulting in the response current of the cyclic voltammetry is 0 mA。 And it was found that at 0.5 mol · L-1 The cyclic voltammograms of modified electrodes supported by Na2SO4 (pH 7.02) and 50mmol · l-1pbs (pH 6.8 and 7.2, respectively) do not have the characteristic redox peak of polyometalates. The possible reason is that polyometalates are easy to decompose in neutral solution, so the ionon concentration of polyometalates is not enough to respond to strong response current, so there is no characteristic oxidation of polyometalates Reduction peak. But in the mixed solution of 0.5mol · L-1 H2SO4 (pH 0.46), 0.1mol · L-1 H2SO4 (pH 1.13), 0.5mol · L-1 H2SO4 and 0.5mol · l-1na2so4 (pH 0.73), 0.1mol · L-1 H2SO4 and 0.5 The cyclic voltammograms (Fig. 5 (b)) of the modified electrode supported by the mixed solution of mol · l-1na2so4 (pH 1.54) all show the characteristic redox peaks of polyoxometalates. It can be seen from Fig. 5 (b) that the response current of the modified electrode is the strongest under the support of 0.5 mol · L-1 H2SO4 solution (pH 0.46). However, considering that the target substance of the reaction system is tyrosinase, and the conditions for keeping the activity of tyrosinase are relatively mild, and it can not be in the environment of strong acid and strong alkali, the mixed solution of 0.1 mol · L-1 H2SO4 and 0.5 mol · L-1 Na2SO4 with pH of 1.54 is selected as the reference for the next experiment, and the further research is to take 0.1 mol · L-1 H2SO4 and 0.5 mol · L-1 with different pH as the reference The electrochemical behavior of the modified electrode when Na2SO4 mixed solution is the supporting electrolyte (Fig. 6a). In Fig. 6a, the pH of 0.1 mol · L-1 H2SO4 and 0.5 mol · L-1 Na2SO4 mixed solution is 1.54, 2.62, 3.86, 5.29 and 6.51, respectively. The volume ratios of the corresponding 0.1 mol · L-1 H2SO4 solution and 0.5 mol · L-1 Na2SO4 solution in the mixed solution are 1:1 (5:5), 4:6, 3:7, 2:8 And 1:9, respectively. From Fig. 6 (a), it can be seen that with the pH of 0.1 mol · L-1 H2SO4 solution and 0.5 mol · L-1 Na2SO4 solution from 1.54 to 6.51, namely, the acidity is constantly weakened. It is found that the response current of the modified electrode is continuously weakened during the cyclic voltammetry scanning process, and the redox peak potential is negatively shifted, which indicates that the electrochemical reaction process involves the participation of protons. Compare 0.1 mol · L-1 H2SO4 and 0.5 mol · L-1 with pH of 1.54 and 6.51, respectively The cyclic voltammogram of the modified electrode obtained when Na2SO4 mixed solution is used as the supporting electrolyte (Fig. 6 (b)) shows that the modified electrode in two different pH supporting electrolyte solutions, although the corresponding redox peak potential and its response current have changed, still has the characteristic redox peak of polyoxyometalates. Moreover, when the pH of 0.1 mol · L-1 H2SO4 solution and 0.5 mol · L-1 Na2SO4 solution changes from 5.29 to 6.51, that is, the volume ratio of 0.1 mol · L-1 H2SO4 solution and 0.5 mol · L-1 Na2SO4 solution in the mixed solution changes from 2:8 to 1:9, the cyclic voltammograms under the corresponding conditions basically recombine, but when 0.1 mol · L-1 H2SO4 solution and 0.5 mol · L-1 When the ratio of Na2SO4 solution is 0:10, i.e. 0.5 mol · L-1 Na2SO4 (pH 7.02) solution is used as supporting electrolyte, there is no characteristic redox peak of polyoxyometalates in the cyclic voltammogram. This is because polyoxometalates are sensitive to acidity. When the acidity weakens and the pH increases to a certain value, polyoxometalates decomposes and the redox peak decreases. Therefore, in order to ensure the sensitivity of detection, the mixed solution of 0.1 mol · L-1 H2SO4 and 0.5 mol · L-1 Na2SO4 with pH of 6.51 was selected as the supporting electrolyte for subsequent experiments.<br>