Synthesis Of Composite Materials Based On Graphene For Biological Catalysis And Sensing Applications

Biosensors are becoming a critical part of modern life due to the advantages of high sensitivity, fast response, low cost and the potential for minituarization. Graphene oxide (GO),which is well known as a promising precursor for graphene, has great potential for use in biosensors because of its unique characteristics such as facile surface modification, high mechanical strength, good water dispersibility and photoluminescence. Thus, the main work of this paper is focus on the preparation of graphene oxide nanomaterials, construction of sensitive sensor interface and novel signal enhancement strategy of the electrochemical biosensors. The details are summarized as follows:1. In this study, we demonstrated an effective and facile in situ electroless deposition approach for controllably growing high-quality Prussian blue nanocubes (PBNCs) on the surface of graphene oxide (GO). It is found that the coverage and the average size of PBNCs on GO could be easily controlled via simply changing the synthetic parameters, where GO acts not only as a carrier of PB nanocrystallites but also as Fe(III)-reducer. Most importantly, the electrochemical data indicated that the stability of the PB nanocubes was greatly improved by the GO. PBNCs/GO nanocomposite exhibited a prominent electrocatalytic activity toward the reduction of hydrogen peroxide. The proposed approach allows simple and controllable preparation of transition metal hexacyanoferrate nanocrystals/graphene oxide and finds use in applications for electronic nanodevices.2. A novel electrochemical immunosensor for sensitive detection of cancer biomarker a-fetoprotein (AFP) is described that uses Fe3O4-PDA-Au sensor platform and graphene oxide labeled with prussian blue-secondary antibodies (PB-Ab2). Greatly enhanced sensitivity for the cancer biomarker is based on a dual signal amplification strategy:first, Fe3O4-PDA-Au used for the biosensor platform increased the surface area to capture a large amount of primary antibodies (Ab1), which resulted in amplification of the detection response. Second, graphene oxide allowed several binding events of PB-Ab2. Enhanced sensitivity was also achieved by introducing the multibioconjugates of Ab2-PB-GO onto the electrode surface through "sandwich" immunoreactions. The proposed method could respond to1pg/mL AFP ith a linear calibration range from0.005to1ng/mL and1to20ng/mL.3. A graphene oxide-Au NPs sensor platform combined with a multiple-enzyme labeled detection antibody-carbon sphere bioconjugate was used as the basis for an ultrasensitive electrochemical immunosensor to detect cancer biomarker a-fetoprotein (AFP) is described. Greatly enhanced sensitivity was achieved by using the bioconjugates featuring horseradish peroxidase (HRP) and Ab2linked to carbon nanospheres (Ab2-HRP-Au-PDA-carbon sphere) at a high ratio of HRP/Ab2. After a sandwich immunoreaction, the Ab2-HRP-Au-PDA-carbon sphere captured onto the electrode surface produced an amplified electrocatalytic response by the reduction of enzymatically oxidized thionine in the presence of hydrogen peroxide. The increase of response current was proportional to the AFP concentration in the range of0.01-20ng/mLwith the detection limit of3pg/mL. This amplification strategy is a promising platform for detection of other proteins and clinical applications.