Studies Of Novel Optical Biosensing Technology Based On Graphene Oxide

Biosensors have provided novel strategies for the research in biomedicine and clinical medicine for the high sensitivity and selecti vity. Fluorescent biosensing technology is widely used in the detection of small molecules, DNA and protein, due to the advantages such as rapid response and simple operation. Owing to the existence of surface oxygen group, GO could disperse well in water and be modified by other molecules. Furthermore, GO has the fluorescence quenching ability for fluorophores, which is superior to many other materials. Therefore, GO has become one of the most commonly used nanomaterials for fuorescent biosensing in the la st decade. These sensors mainly rely on the differential adsorbability of GO to fluo rophore-labelled ss DNA and ds DNA, which lead to the different quenching efficiency. In this thesis, we developed two novel optical sensing strategies based on GO for the de tection of small molecule, DNA and enzyme. We confirm the feasibility and practical ability through a series of experiments. The details are shown as follows:In chapter 2, we developed a novel label-free colorimetric biosensing strategy based on graphene-hemin hybrid nanosheets(GHs) for DNA and small molecule assays. The GHs were synthesized by a simple wet-chemical method and possessed excellent properties of both graphene and hemin.Significantly, it was found that the GHs showed a novel unique property. When being mixed with ss DNA, GHs exhibited enhanced catalytic activity in the presence of ABTS and H2O2. In contrast, the GHs mixed with ds DNA had lower catalytic activity than that mixed with ss DNA. On the basis of this property of GHs, a novel universal label-free colorimetric method was proposed. DNA and cocaine were chosen as model analytes to construct a sensor. In the absence of target, both catalytic activity and signal were high. However, in the presence of target, the probe became rigid through combining with the target, resulting in low colorimetric signal. This simple strategy owns the merits over conventional assays in its label-free design, extreme operation simplicity and low cost. Thus, it is expectd that the developed method has a potential of becoming a universal platform for detection of a wide range of analytes.In chapter 3, an enzyme-free amplified fluorescent biosensor for UDG detection was presented based on GO and hybridization chain reaction(HCR). We designed a hairpin probe containing four uracil bases on stem and two hairpins(H1 and H2) according to the rules of HCR. Additionally, the H2 was labeled with a fluorophore. In the presence of UDG, the uracil bases were cleaved and the probe was turned from hairpin to ss DNA, triggering the hybridization chain reaction and fluorophore-labelled long ds DNA product was obtained. After addition of GO, the long ds DNA was relatively far from the GO and the fluorescence intensity was weak. However, in the absence of UDG, no long ds DNA was obtained and the fluorophore was still labelled on H2. After introduction of GO, the H2 was close to the surface of GO, resulting in the strong fluorescence quenching and low fluorescence signal. The proposed method owns the merits such as simple design and oper ation, high sensitivity and quite wide linear range. Moreover, the sensor performed well in complicated system, indicating that it has a promising application in the field of biomedicine and clinical diagnosis.