Design And Construction Of Graphene Quan Tum Dots-based Fluorescent Nanosensor For Biosensing

As the new member of carbon nanomaterials, graphene quantum dot（GQD） had received extensive attention due to its unique physical and chemical properties. However, complicated covalent modifications and one-photo excition still restrict their application in complex environment. To address these issues, a sersis of simple non-covalent assembly nanoplatforms were designed and constructed for biomolecules such as hydrogen peroxide（H₂O₂）, glucose, cyanide（CN-） and glutathione（GSH） sensing in this thesis.1) NA-mediated Ag NP and GQDs hybrid nanocomposite for sensitive fluorescent detection of H₂O₂ and glucose. Since a growing body of evidence suggests that H₂O₂ plays an active role in the regulation of various physiological processes, development of sensitive probes for H₂O₂ is an urgent work. In this charpter, we proposed a DNA-mediated silver nanoparticle（Ag NPs） and GQDs hybrid nanocomposite（Ag NP-DNA@GQDs） for sensitive fluorescent detection of H₂O₂. With optimal conditions, the approach achieves a low detection limit of 0.10 mM for H₂O₂. Moreover, this nanocomposite is further extended to the glucose sensing in human urine combining with glucose oxidase（GOx） for the ox idation of glucose and formation of H₂O₂. The glucose concentrations in human urine are detected with satisfactory recoveries of 94.6-98.8% which holds potential of ultrasensitive quantitative analysis of glucose and supply valuable information for diabetes mellitus research and clinical diagnosis.2) Two-photon sensing and imaging of endogenous biological CN- in plant tissues using GQDs/Au NPs conjugate. One of the main sources of CN- exposure for mammals is through the plant consumption and thus d evelopment of sensitive probes for CN- in plants tissue is an important and urgent work. Up to now, a number of fluorescence probes have been reported for sensing and imaging of CN- species in water and mammalian cells. However, the efficient fluorescent strategy f or endogenous biological CN- imaging in plant tissue appears to be rare. In this chapter, we fabricated a new GQDs/Au NPs conjugate through peptide linker for sensing and imaging of endogenous biological CN-. With optimal conditions, the approach achieves a low detection limit of 0.52 mM for CN-. Benefited from the excellent two-photon property of GQDs, our method can efficiently realize CN- sensing and imaging in different kinds of plant tissues and even monitor the removing of CN- in the field of food processing.3) Construction of GQDs-MnO₂ nanocomposite for intracellular two-photon imaging of glutathione. Biothiols are significant reductant in human body and the level of GSH in vivo is implicated in many diseases. Thus, monitor ing the GSH concentration with highly sensitive and selective is very important. In this chapter, the GQDs were synthesized with a facile solvothermal method using ammonia water as solvent and the in situ growth of manganese dioxide nanosheets（MnO₂） on GQDs can result in the quenching of two-photon fluorescence of GQDs through FRET. The results demonstrated that the limit of detection（LOD） for GSH was 0.31 mM. What’s more important, the GQDs-MnO₂ nanocomposite has been successfully applied to monitor GSH level in living cell and tissue benifited from the excellent propery of GQDs.4) H₂O₂ responsive multifunctional Ag NP@Chi-GQDs nanocomposite for cancer imaging and therapy. Tumor is one of the common malignant diseases. The in-depth research of Ag NP demonstrated its potential in cancer therapy. In this chapter, GQDs-modified chistoan were served as the scaffold to synthetize Ag NPs and thus form Ag NP@Chi-GQDs nanocomposite. Since tumor is found to have an elevated level of H₂O₂, this Ag NP@Chi-GQDs nanocomposite could be etched by the intracellular H₂O₂, and the released silver ions thus lead antitumor effect. In addition, the tumor imaging was able to realize by fluorescence recovery of GQDs.