Synthesis Of Graphene Nanocomposites And Their Applications In Electrochemical Sensing

Nanomaterials have special structure, which results in series of interesting physical and chemical properties. The application of nanomaterials has involved in environmental controlling, biosensing, nanochemistry, catalysis, medicine, nanomachine, biotechnology and so on. Recently, Graphene nanosheet (GN), a "rising star" material, has received considerable interest due to its high surface areas, low cost, and high conductivity. Various graphene nanocomposites have been intensively investigated because of their hybrid properties of the involved graphene and other materials. In this dissertation, we prepared a series of graphene nanocomposites and construct novel electrochemical sensing. The details are given as follows:1. The composite materials which were responsive to pH have been synthesized by modified graphene nanosheets (rGO) surface with poly(acrylic acid)(PAA), a pH-sensitive polymer, with the method of in situ living free radical polymerization. The morphologies and electrochemistry of the composite materials were investigated by using scanning electron microscopy (SEM) and electrochemical techniques including electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), respectively. Surface wettability of the composite materials also has been explored by measuring the static contact angle using ultrapure water as the probe liquid. Results demonstrated the composite materials have the good stability and excellent electric conductivity due to the introduction of graphene. Real-time electrochemical measurements including EIS and CV, indicated that the interfacial electrochemicalproperties can be intelligently switched through varying external stimuli The stepwise change of the pH value between10.0and3.0resulted in the reversible switching off and on of the electrode redox activity, respectively. The composite materials modified electrode with the pH-controlled switchable redox activity was account as a "smart" interface for a new generation of electrochemical biosensors with a signal-controlled activity.2. A novel matrix based on Au-polydopamine-graphene (Au-PDA-rGO) nanocomposite for immobilization of protein was used to develop a highly sensitive acetylcholinesterase (AChE) biosensor for pesticides detection. The morphologies and characteristics of the as-prepared Au-PDA-rGO nanocomposite were investigated by using scanning electron microscope, UV-vis spectroscopy, drop shape analysis system and electrochemical techniques, respectively. The characteristics of the modified electrode at different stages of modification were studied by cyclic voltammetry. In addition, the performances of the resulting biosensor for pesticides detection were studied by differential pulse voltammetric. The as-prepared Au-PDA-rGO not only provides a favorable microenvironment to maintain the activity of the immobilized AChE, but also increases the loading capacity of the AChE due to the two-dimensional structure of the graphene, and the present of graphene and Au nanoparticles enhances the conductivity and charge-transport properties of the composite. As a result of these important enhancement factors, the proposed biosensor exhibited extreme sensitivity to OP pesticides. The influences of phosphate buffer pH, substrate concentration on the response of the fabricated biosensor were investigated. Under optimum conditions, the inhibition rates of Dimethoate were proportional to their concentrations in the range of0.3～1000ng mL-1with a low detection limit of0.15ng mL-1. Moreover, the studied biosensor exhibited high sensitivity, good reproducibility and long-term stability. The present method is simplified, economical and efficient, and the prepared biosensor exhibits high selectivity, low detection limit, long-term stability and good reproducibility.