Preparation Of Several Functionalized Graphene Nanocomposites And Their Application In Electrochemical Sensing

Electrochemical sensors have been widely applied in analytical chemistry because of their advantages such as fast detection speed, simple operation, high sensitivity, no complicated pretreatment, low cost etc. Due to the unique and excellent properties of the nanomaterial, it has attracted widespread attention and plays important role in the industry, biology, physics, chemistry and material fields. When the nanocomposite materials are used in electrochemical biosensors, the response rate can be improved, the linear range can be broaden, the detection limit will be dropped, the stability can be enhanced. Owing to its unique electrical, mechanical, optical and thermal properties, graphene was widely studied by many researchers. In this thesis, on the basis of graphene, several functionalized graphene nanocomposites were synthesized and the structure and properties were thoroughly characterized. And the application of these composites in electrochemistry sensing were studied. The main contents are summarized as follows:1. A novel electroactive graphene oxide （GO） was firstly prepared by covalently grafted （4-ferrocenylethyne） phenylamine （Fc-NH₂） onto the surface of GO. The synthesized hybridized nanocomposite GO-Fc-NH₂ coupled with HAuCl₄ simultaneously electrodeposited on the glassy carbon electrodes （GCE） to obtain rGO-Fc-NH₂/AuNPs/GCE. The rGO-Fc-NH₂/AuNPs film has highly enhanced conductivity and can effectively prevent the electron mediator leaking from the electrode surface, which have the advantage of both the nanomaterials and electron mediators. Owing to the catalysis effect of nanomaterial and electron mediator as well as the large active surface area and high accumulation efficiency of the rGO-Fc-NH₂/AuNPs/GCE, a synergetic signal amplification platform for ultra-sensitive detection of bisphenol A （BPA） was successfully established. Modification of electron mediators on nanomaterials hold great promise to enhance the electrochemical performance of the sensors and will provide a new concept for fabricating more newly electroactive nanomaterials-based electrochemical biosensors.2. A new electrochemical sensor based on a novel probe N-（2-（1-（p-tolyl）-1H-phenenanthro[9,10-d]imidazol-2-yl）phenyl） picolinamide （Pi-A） functionalized reduced graphene （RGO） composite modified glassy carbon electrode （GCE） was constructed for highly selective detection of copper （II） ion using square wave anodic stripping voltammetric （SWASV）. Fluorescent probes Pi-A was immobilized on the reduced graphene （Pi-A/RGO） via Ï€-Ï€ stacking and the as prepared Pi-A/RGO is able to selectively capture the copper （II） ion with high efficiency. Under the optimal conditions, the sensor based on modified Pi-A/RGO has been successfully applied in the detection of copper （Ⅱ） ion in tap water, river water lake water, and mountain spring samples. Additionally, several transition metal ions did not show interference in the detection of copper （II） ion. The combination of probe molecules with graphene can expand the application of fluorescence probes in biological and electrochemical sensing areas.3. Inspired by the mussel adhesion proteins,3,4-dihydroxyphenylalanine （DA） was selected as a reducing agent to simultaneously reduce graphene oxide and selfzpolymerize to obtain the polydopamine-reduced graphene oxide （PDA-rGO）. The PDA-rGO was then functionalized with thiols and amines by the reaction of thiol/amino groups with quinine groups of PDA-rGO via the Michael addition/Schiff base reaction. Several typical compounds containing thiol and/or amino groups such as 1-[（4-amino） phenylethynyl] ferrocene （Fc-NH₂）, cysteine （cys）, and glucose oxidase （GOX） were selected as the model molecules to anchor on the surface of PDA-rGO using the strategy for construction of multifunctional electrochemical platforms. The composite grafted with ferrocene derivative shows excellent catalysis activity toward many electroactive molecules and could be used for individual or simultaneous detection of dopamine hydrochloride （DA） and uric acid （UA）, or hydroquinone （HQ） and catechol （CC）, while, after grafting of cysteine on PDA-rGO, simultaneous discrimination detection of Pb²⁺ and Cd²⁺ was realized on the composite modified electrode. In addition, direct electron transfer of GO_x can be observed when GO_x-PDA-rGO was immobilized on glassy carbon electrode （GCE）. When glucose was added into the system, the modified electrode showed excellent electric current response toward glucose. These results inferred that the proposed multifunctional electrochemical platforms could be simply, conveniently, and effectively regulated through changing the anchored recognition or reaction groups. This study would provide a versatile method to design more detection or biosensing platforms through a chemical reaction strategy in the future.