Functionalized Graphene Nanocomposites And Their Real-time Electrochemical Sensing For Small Biological Molecules

Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS) are two types of vital active and functional small molecules in biological systems. They not only play important roles in signaling, mediatoring and defendering in various physiological process, but also can initiate or inhibit some fatal diseases and cancers. It’s very important to real-time in situ detect ROS and RNS released from living cells for us to better understand and study the related mechanism of the various physiological and pathological process and can also provide clinical diagnosis and treatments for fatal diseases such as cancers. Various methods have been reported for the real-time in situ detection of the ROS and RNS, including fluorescence, chemiluminescence, electron paramagnetic resonance and electrochemistry, among which the electrochemical method is very advantageous owing to its simple operation, low cost, high sensitivity, good selectivity, fast response and good stability. In addition, only electrochemical method can realize the real-time in situ detection. However, in living cells the target ROS or/and RNS often have very short half-life, while the measurements could be interfered by many kinds of other existing substances, making the real-time in situ detection extremely challenging. Hence, it is very critical to develop electrochemical sensor with high sensitivity, good selectivity and fast response time. The advances of nanoscience and nanoengineering offer great opportunities to tailor sensing materials for a transducer for highly sensitive and fast responsive electrochemical sensors. Graphene has risen up as a new superstar owing to its good conductivity, large surface area, high mechanical strength and good biocompatibility. Moreover, it has strong adorability and possesses many functional groups such as hydroxyl, carboxyl group on its surface. It is also easy to be functionalized through modifications with different materials such as inorganic noble metal nanoparticles, transition metal oxides and sulfide, organic conducting polymer and other carbon materials.The main contents of this thesis include:firstly, synthesized three-dimensional graphene hydrogel (3DGH) has been used as a good conductive substrate to recombine with noble metal and transition metal nanomaterials to realize functionalization through a simple chemical-precipitation process. Functionalized graphene not only offers a huge surface area and very good conductivity, but also aggrandized the special catalytic property of other materials. The electron transfer rate and the catalytic activity of the functionalized graphene nanocomposites can be significantly enhanced and their electroactive sites can be also boomed. Secondly, the physical properties and electrochemical performances of the as prepared materials have been characterized and tested in detail, and the catalytic mechanism of them has also been analyzed clearly. Finally, the functionalized graphene nanocomposites were used on the study of real-time electrochemical sensing toward the nitric oxide and hydrogen peroxide in vivo. The detail contents include:1. A nanocomposite of Au nanoparticles deposited on a three-dimensional graphene hydrogel (Au NPs-3DGH) was prepared through a facile one-step approach by in situ reduction of Au3+ on 3DGH to build a unique sensing platform for a strong synergistic effect, in which the highly porous 3DGH offers a large surface area while Au NPs uniformly deposited on 3DGH efficiently catalyze the electrochemical oxidation ofNO for sensitive detection with excellent selectivity, fast response, and low detected limit. The sensor was further used to in situ detect NO released from living cells under drug stimulation, showing significant difference between normal and tumor cells under drug stimulation.2. A novel nanocomposite of (Fe, Mn)3(PO4)2@3DGH was successfully synthesized through a facile coprecipitation under 60℃ water bath for the first time and its composition and the metal valence state were further analyzed. More importantly, the as-prepared nanocomposite was developed to detect hydrogen peroxide with high sensitivity, excellent selectivity and fast response. The sensing platform was used to in situ detect hydrogen peroxide released from living Aspergillus flavus under drug stimulation.3. Through the real-time electrochemically detect small biologic molecules, the electrocatalytic mechanism and the electrode kinetics process on graphene nanocomposite electrode were investigated.