The Size Separation Of Graphene Oxide And Graphene Oxide-based DNA Aptamer Biosensor

Graphene oxide (GO) is a derivative of graphene with hydrophobic π electron plane structure and hydrophilic oxygen-containing groups. Due to the size-dependent effect, GO exhibits different physical and chemical properties in mechanical strength, cytotoxicity and photoluminescence. In addition, the special adsorption/desorption properties between GO and DNA aptamer have received much attention in the relevant fields of biosensor applications. Carbon dots (CDs) are a new class of carbon nanomaterials, which is expected to be a better fluorescence label reagent in the biological sensing fields. In this thesis, the size separation of GO, GO-based CDs labeled or rhodamine B label-free DNA aptamer biosensor was explored.In chapter one, graphene oxide was synthesized by improved Hummers method, and characterized by FT-IR, UV-vis, and X-ray diffraction. The results showed that GO possessed lots of oxygen groups on its surface, large layer space, small average size and a wide range of near-infrared emission photoluminescence. By adjusting the pH of the GO dispersion and taking different centrifugation, simple and convenient lateral dimension separation based on amphiphilic of GO sheets was achieved. Different sizes of GO calculated through X-ray diffraction were5.22nm,5.12nm,4.24nm and0.72nm, respectively. Furthermore, the GO sheets with smaller size and narrower distribution had shorter excitation and emission wavelengths, higher quantum yield.In chapter two, CDs with a high-quantum-yield were synthesized using citric acid and ethylenediamine by hydrothermal methods, and labeled on DNA aptamer. It was confirmed by FT-IR and UV-vis spectra that the carbon dots could be combined with DNA aptamer. The fluorescence of resultant CDs-labeled DNA aptamer was quenched by GO via fluorescence resonance energy transfer. In the presence of Hg2+, the fluorescence was recovered by the release of CDs-labeled DNA aptamer from GO due to the formation of T-Hg2+-T duplex. In the light of this theory, we designed a fluorometric Hg2+sensor based on CDs-labeled DNA aptamer and GO. Under optimal experimental conditions, standard curve and regression equation of Hg2+have been received. The present GO-based sensor system is highly selective toward Hg2+over a wide range of metal ions and has a detection limit of2.58nM. This method can be applied for the detection of Hg2+in practical samples, which was similar to the true value and detection data obtained by atomic fluorescence spectrometry. On the other hand, the label-free aptamer biosensor based on GO and rhodamine B (Rb) has been studied. We confirmed that the quenching efficiency of GO was reduced due to the adsorption of DNA aptamer. Rb+GO-mixture could response DNA aptamer, and be applied to detect DNA damaging agents, for example H2O2. In this work, by taking the change of fluorescence intensity, standard curve and regression equation of H2O2have been received, and the result is satisfactory.