Study On Preparation And Application Of Electrochemical Sensors Based On Two Thiadiazole-Modified Electrode

In this paper, three kinds of electrodes modified by two thiadiazole compounds were prepared using self-assembly and electropolymerization methods, respectively. The preparation methods of the modified electrodes was studied and optimized, and their electrochemical properties were characterized. Based on electrochemical responses of three modified electrodes to 4-methylimidazole (4-MEI), dacarbazine, glucose and cholesterol, respectively, four new methods were developed for the determination of 4-methyl imidazole in Cola drinks and dacarbazine in injection by suing electrochemical impedance sensors, and the determination of glucose in drinks, cholesterol in milk by suing electrochemiluminescence sensors.The completed work in the paper is summarized as following four aspects:1. A water-soluble complex MnHL2(H2O)2 was prepared based on simple reaction in aqueous solution by using 2,5-dimercapto-1,3,4-thiadiazole, acetyl acetone and MnCl2 as raw material. The prepared MnHL2(H2O)2 was self-assembled on the gold electrode surface to fabricate a 4-MEI electrochemical impedance sensor. The water-soluble complex and modified electrode were investigated and characterized by using single crystal diffraction, UV-vis spectra, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy, and the preparation mechanism of the modified electrode was studied. Under the optimum conditions, the charge transfer resistances (Rct) of the sensor were proportional to concentration of 4-methylimidazole in 5.00×10-5～2.00×10-3 μg/L range with a linear correlation coefficient of 0.9992, and the detection limit was estimated to 8.00×10-6μg/L. The relative standard deviation (RSD) was less than 1.98 (n=5) and the recovery was in the range of 93.2%～95.2% for the determination of 4-MEI in Cola drinks.2. A complex AMT-P was synthetized based on the reaction under 90℃ for refluxing 12 h by using 2-amino-5-mercapto-1,3,4-thiodiazole (AMT), paraformaldehyde, phosphorous acid and the concentrated hydrochloric acid as raw material. And AMT-P-M(H2O)2 was prepared based on complex reaction between MnCl2 with AMT-P. Then AMT-P-M(H2O)2 was self-assembled on the gold electrode surface to fabricate an electrochemical impedance sensor. As basis of the selective response of the sensor to imidazole compounds, the dacarbazine was determined in two kinds of anti-cancer injections. Under the optimum conditions, Changes of Ret of the sensor were proportional to concentration of dacarbazine in 4.00×10-5 ～7.00×10-4g/mL g/mL range with a linear correlation coefficient of 0.9994, and the detection limit for dacarbazine was estimated to 8.00×10-6 g/mL. RSD was less than 2.21 (n=5) and the recovery was in the range of 98.1%～105% for the determination of actual samples.3. The glucose oxidase was bonded to the surface of MnHL2(H20)2-modified electrode bv 4-imidazole carbaldehvde as the working electrode of sensor, by way of the electrochemiluminescence (ECL) between luminol with H2O2, an enzymatic reaction product, developing a new analysis method of glucose. Under the optimum conditions, the ECL intensities of the sensor were proportional to concentrations of glucose in 0.20～5.00μmol/mL range’with a linear correlation coefficient of 0.9991, and the detection limit was estimated to 0.005 μmol/mL. The relative standard deviation was less than 2.90 (n=5) and the recovery was in the range of 97.6%～105.2% for the determination of glucose in two drinks.4. AMT-AuNPs was synthesized by simple reaction using H4AoCl4, NaBH4, AMT as materials, a thin film of three dimensional gold-AMT core-shell nanoparticles (p-AMT-AuNPs) was prepared on the glassy carbon electrode by using electrochemical method, and then cholesterol oxidase was bonded to the surface of film using glutaraldehyde for fabricating a functional electrode. The modified electrode were characterized by using cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy and the preparation mechanism of the sensor was studied. On the basis of the catalysis of the functionalized electrode for cholesterol and ECL system of luminol-H2O2, a highly sensitive and sensitive ECL method for determination of cholesterol has been developed. Under the optimized conditions, the ECL intensity showed a good linear relationship with cholesterol at concentration range of 0.08～11.0 μg/mL with correlation coefficient of 0.999, and the detection limit was estimated to be 0.02 μg/mL. The proposed method has been applied to the determination of cholesterol in dairy products with the relative standard deviations of less than 1.8% and the recovery rates of 98.1%～104%.