| Graphene, a single layer of carbon atoms densely packed in a honeycomb two-dimensional lattice, has unique nanostructure and properties, such as large theoretical specific surface area, high thermal conductivity and good electrical conductivity merit. Owing to the synergy effect of graphene and different nanomaterial, the biocompatibility and electrochemical properties of graphene can be greatly improved leading to the expansion andenhancement of the electrochemical effects of graphene. Recently, graphene nanocomposites provide a novel and efficient electrochemical platform for the immobilization of nano bioprobe (such as enzymes, antibody, aptamer) in various biosensors. Aptamer, a novel nano bioprobe, exhibit a number of advantages over antibodies (such as simple synthesis, easy labeling and good stability). Accordingly, extensive activities have been directed to the application of aptamers for bioanalytical methods and the design of biosensors. Among various biosensors, the electrochemical biosensor has attracted particular attention because it provides a sensitive, selective, simple, and miniaturized platform. Increasing efforts have been recently devoted to design electrochemical aptamer-based detection systems, since they often achieve the merit of aptamer and electrochemical biosensor. This paper tried to study and design different signal amplification electrochemical aptasensors by using graphene nanocomposites as a sensitive platform for mobilizing aptamer. The research details are described as follows:1. A multi-amplification aptasensor for highly sensitive detection of thrombin based on high-quality hollow CoPt nanoparticles decorated graphene In this work, we have successfully designed a high sensitive electrochemical aptasensor based on high-quality hollow CoPt bimetal alloy nanoparticles (HCoPt) decorated graphene sheet (HCoPt-RGs). Firstly, an effective two step method to prepare high-quality HCoPt-RGs. The formed HCoPt-RGs provided large surface area for loading plentiful redox probe thionine (Thi), horseradish peroxidase (HRP) and secondary aptamer (Apt II), indicating its superior properties in electro-active mediator enrichment and biomolecule immobilization. Furthermore, activated by glutaraldehyde (GA), the chitosan-hollow CoPt alloy nanoparticles (CS-HCoPt) film on glass carbon electrode (GCE) can greatly facilitate the capture of primary aptamer (Apt I) and dramatically reduce the nonspecific binding. After sandwich reaction, excellent sensitivity was obtained by detecting the conspicuously enhanced electrochemical signal of Thi, which was amplified by HCoPt alloy nanoparticles and HRP towards the catalytic reduction of H2O2. The aptasensor displayed excellent performance for thrombin with a wide linearity in the range from1.0×10-12to5.0×10-8mol·L-1and a relatively low detection limit of3.4×10-13mol·L-1. Moreover, the resulted aptasensor also exhibited good specificity, acceptable reproducibility and stability, indicating that the present strategy could pave a promising way for the wide application of graphene in clinical research.2. In situ enzymatic silver enhancement based on functionalized graphene oxide and layer-by-layer assembled gold nanoparticles for ultrasensitive detection of thrombinA highly specific in situ amplification strategy was designed for ultrasensitive detection of thrombin by combining the layer-by-layer (LBL) assembled amplification with alkaline phosphatase (ALP) and gold nanoparticles (Au) mediated silver deposition. High-density carboxyl functionalized graphene oxide (FGO) was introduced as a nanocarrier for LBL assembling of alkaline phosphataseand gold nanoparticles to form (ALP-Au)n nanocomposites, which were further adopted to label thrombin aptamer Ⅱ. After sandwich-type reaction, numerous ALP were captured onto the aptasensor surface and catalyzed the hydrolysis of ascorbic acid2-phosphate (AAP), which in situ generated ascorbic acid (AA), reducing Ag+to Ag nanoparticles (AgNPs) for electrochemical readout. Inspiringly, the in situ amplification strategy with ethanolamine as an effective blocking agent showed very little nonspecific adsorption, and low background signal, which was favorable to enhance the sensitivity of aptasensor. Our novel dramatic signal amplification strategy, with a detection limit of2.7fmol·L-1, showed about2-3orders of magnitude improvement in the sensitivity for thrombin detection compared to other universal enzyme-based electrochemical assay.3. Direct growth of Pt@Ag nanochains on tailorable graphene oxide with a green, in situ, template-free method and its biosensing applicationWe herein for the first time investigated the efficacy of functionalized graphene oxide (CFG) in modulating the growth of Ag nanochains (AgNCs) based on in situ enzymatic metalization. The merit of this method is that the AgNCs could be produced directly on CFG in an general nature, environmentally friendly and sustainable way with a large-scale production. Specifically, the Pt nanoparticles wrapped AgNCs (Pt@AgNCs) manifested some superior functions, such as excellent electrical conductivity, well-defined electrochemical redox activity, which attracted great interest as a perfect candidate for biosensing. With the Pt@AgNCs as redox probe, we developed a redox probe-label-free electrochemical aptasensor for ultrasensitive detection of platelet-derived growth factor (PDGF-BB). A quasilinear response was obtained in a concentration scale within a three-order of magnitude concentration range from6pmol·L-1to40nmol·L-1, and a readily achieved detection limit of1.97pmol·L-1was also received. |
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