| Nowadays, chemically modified electrodes have developed the most widely studied frontier of electrochemistry and electroanalytical chemistry from the middle of1970s. Due to the fact that chemically modified electrodes push the limitation which only studies on bare electrodes/electrolyte interface in the traditional electrochemistry, they open a new frontier which human design surface structure of electrodes. By molecular tailoring on electrode surfaces, it purposefully fixes functional groups that have excellent chemical properties on surface of electrodes, which endow electrodes with some specific characters including chemical, electrical, electrochemical, optical and transmission and so on, so that they can carry on the wanted reactions with high selectivity. Due to the facts that chemically modified electrodes can combine separation, enrichment and determination in quantitative analysis and embody unique superiority in improving selectivity and sensitivity, they have wide application in the field of electroanalytical chemistry. In this paper, some chemically modified electrodes have been fabricated and they have been applied to the determination of thrombin, cadmium(II), and4-nitrophenol. We explored the formation conditions of electrodes, optimum reaction conditions, and influence factors and preliminarily discussed the reaction mechanism. The main researches are as follows:1. Study on the chronocoulometric aptasensor based on gold nanoparticles as signal amplification strategy and its applicationA chronocoulometric aptasensor for the determination of thrombin has been developed based on gold nanoparticles amplification. The functional gold nanoparticles were immobilized on the gold electrode by thrombin aptamers performing as a recognition element and capture probe. The incorporation of gold nanoparticles in the chronocoulometric aptasensor significantly enhanced the sensitivity.[Ru(NH3)6]3+served as the electrochemical signaling molecules, which quantitatively bound to the negatively charged phosphate backbone of DNA via electrostatic interactions. The surface density of thrombin aptamers has been optimized. Under optimum conditions, the chronocoulometric aptasensor exhibited a wide linear response range of0.1x10’9to18.5×10-9mol L-1with a detection limit of3.0×10-11mol L-1. The results demonstrated that the nanoparticles-based amplification strategy offered a simple and effective approach to detect thrombin.2. Fabrication of bismuth-tin composite film modified carbon paste electrode and its application for determination of Cd(Ⅱ)A bismuth-tin composite film modified carbon paste electrode, which was prepared by in situ depositing bismuth and tin on the carbon paste electrode, was employed for the determination of cadmium(Ⅱ). The parameters including the pH of measurement solution, the proper concentration ratio of Bi(Ⅲ) to Sn(Ⅱ), the preconcentration time, and the preconcentration potential have been studied and optimized. Under the optimized working conditions, the electrode displayed excellent linear behavior in the examined concentration range from0.4to50.0μg L-4Cd(Ⅱ), with a detection limit of0.02μg L-1for Cd(Ⅱ). The modified electrode showed high selectivity, sensitivity, and wide linear range in the repeated detection of Cd(Ⅱ). The promising results obtained here, coupled with the low-toxic nature of bismuth and tin, offered great promise in analysis of trace heavy metals.3. Fabrication of graphene-gold nanocomposite film modified glassy carbon electrode and its electrocatalytic activity toward4-nitrophenol oxidationA mixture of graphene oxide and tetrachloroauric acid were electrochemically co-reduced on a glassy carbon electrode (GCE) through cyclic voltammetry (CV) to fabricate a graphene-gold nanocomposite film modified GCE. The modified GCE was used to investigate the electrochemical behavior of4-nitrophenol by CV, electrochemical impedance spectroscopy, chronocoulometry, and linear sweep voltammetry. Compared with the bare GCE and the gold nanoparticles modified GCE, it was found that the oxidation signal of4-nitrophenol was remarkably improved at the graphene-gold nanocomposite film modified GCE. The experimental parameters such as the types of buffer solutions, the pH of supporting electrolyte, the amounts of deposits, and the accumulation time and potential were optimized. Under the optimum experimental conditions, the oxidation peak currents were proportional to the4-nitrophenol concentration in the range of3.6×10-8to9.0×10-5mol L-1with a detection limit of1.0×10-8mol L-1. The modified electrode presented high sensitivity, good repeatability and stability. |
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