Interaction Mechanism Of Water-soluble Quantum Dots With HSA And Their Analytical Applications

In recent years, water-soluble quantum dots have been applied in biomedical applications widely due to their superior fluorescent properties and good biocompatibility. The level of the toxicity studies of water-soluble quantum dots are just in cells and vivo, the researches of molecular interaction mechanism between these QDs and HSA are little, and the molecular toxicity mechanisms of these QDs are not clearly. Therefore, the thermodynamic and kinetic information of molecular interaction between these QDs and human serum albumin?HSA? is very important and need to be elucidated deeply. In this thesis, the molecular interactions between Zn doped CdTe quantum dots(CdTe:Zn²⁺ QDs), InP/ZnS quantum dots?InP/ZnS QDs?, Carbon dots?CDs?, Graphene quantum dots?GQDs? and HSA was systematically investigated respectively. In addition, the water-soluble quantum dots have been applied in the analysis field.This thesis consists of six chapters:The first chapter, the overview of water-soluble quantum dots and human serum albumin?HSA?. This chapter introduced the properties, biological applications, biological effects of water-soluble quantum dots.The second chapter, the comparative study of the molecular interaction between HSA and CdTe:Zn²⁺ quantum dots with different particle sizes.In this chapter, the molecular interactions between CdTe:Zn²⁺ quantum dots(CdTe:Zn²⁺ QDs) with three different sizes and HSA were systematically investigated by spectroscopic techniques. Three CdTe:Zn²⁺ QDs with maximum emission of 514 nm?green QDs, GQDs?, 578 nm?yellow QDs, YQDs?, and 640 nm?red QDs, RQDs? were tested. The binding of CdTe:Zn²⁺ QDs with HSA was a result of the formation of HSA-QDs complex and electrostatic interactions played major roles in stabilizing the complex. The Stern–Volmer quenching constants, associative binding constants, and corresponding thermodynamic parameters were calculated. The site-specific probe competitive experiments revealed that the binding location of CdTe:Zn²⁺ QDs with HSA was around site I. As further revealed by FT-IR spectroscopy, circular dichroism technique and three-dimensional fluorescence spectra, the microenvironmental and conformational changes of HSA induced by CdTe:Zn²⁺ QDs were analyzed. These results suggested that the conformational change of HSA was dramatically at secondary structure level and the biological activity of HSA was weakened in the present of CdTe:Zn²⁺ QDs with bigger size.The third chapter, the systematical study of the molecular interaction between HSA and InP/ZnS quantum dots.In this chapter, the molecular interaction between InP/ZnS quantum dots?InP/ZnS QDs? and HSA were systematically investigated by spectroscopic techniques. The binding of InP/ZnS QDs with HSA was a result of the formation of HSA-QDs complex and electrostatic interactions played major roles in stabilizing the complex. The Stern–Volmer quenching constant, associative binding constant, and corresponding thermodynamic parameters were calculated. The site-specific probe competitive experiments revealed that the binding location of InP/ZnS QDs with HSA was around site I. As further revealed by FT-IR spectroscopy, circular dichroism technique and three-dimensional fluorescence spectra, the micro-environmental and conformational changes of HSA induced by InP/ZnS QDs were analyzed. These results suggested that the conformational change of HSA was dramatically at secondary structure level and the biological activity of HSA was weakened in the present of InP/ZnS QDs.The fourth chapter, the systematical investigation of molecular interaction in vitro between fluorescent carbon dots and HSA.In this chapter, Carbon dots?CDs? was synthesized by microwave technique through a one-pot process firstly. Then the molecular interaction in vitro between CDs and HSA was systematically investigated by spectroscopic techniques and electrochemical approaches, and the effects of CDs on the second structure and biological activity of HSA were discussed. The intrinsic fluorescence of HSA can be quenched by CDs, and the type of quenching was static. The binding interaction of CDs with HSA was resulted from the complex formation of HSA-CDs. Hydrogen bonding and van der Waals interactions played major roles during HSA-CDs complex stabilization. The primary binding site of CDs was mainly located within site I?subdomain IIA? of HSA. The micro-environmental and conformational changes of HSA induced by CDs were investigated by multi-spectroscopic methods. These data suggested that the conformational change of HSA was significantly at secondary structure level and the biological activity of HSA was weakened dramatically in the present of CDs.The fifth chapter, the study of the molecular interaction between graphene quantum dots and HSA.In this chapter, the molecular interaction between Graphene quantum dots?GQDs? and HSA was systematically characterized by the combination of multi-spectroscopic and electrochemical approaches, and the effects of GQDs on the second structure and biological activity of HSA were discussed. GQDs could quench the intrinsic fluorescence of HSA via static mode. The competitive binding fluorescence assay revealed that the binding site of GQDs was site I of HSA. Some thermodynamic parameters suggested that GQDs interacted with HSA mainly through van der Waals interactions and hydrogen bonding interactions. As further revealed by FT-IR spectroscopy and circular dichroism technique, GQDs could cause the global and local conformational change of HSA, which illustrated the potential toxicity of GQDs that resulted in the structural damage of HSA.The sixth chapter, an on-off-on fluorescence sensor for the detection of chromium??? and ascorbic acid based on graphene quantum dots.In this chapter, we report that graphene quantum dots?GQDs? are viable fluorescent probes for the determination of chromium??? and ascorbic acid in an on-off-on mode. The fluorescence of GQDs is strongly quenched by Cr??? mainly due to an inner filter effect and static quenching. This shifts the system to the “off ” status. The fluorescence of GQDs-Cr??? system is converted back to “on” by adding ascorbic acid which will reduce yellow Cr??? ion, thereby eliminating the inner filter effect and static quenching. Fluorescence intensity is inversely proportional to the concentration of Cr??? in the 0.05 to 500 ?mol/L, concentration range with a 3.7 nmol/L detection limit. The relative intensity of restored fluorescence is directly proportional to the concentration of ascorbic acid in the 1.0 to 500 ?mol/L range, and the limit of detection is 0.51 ?mol/L. The quenching mechanism of this fluorescent system was investigated in some detail. There are almost no interferences to commonly encountered other substances. The methods were applied to the determination of Cr??? in spiked tape water, lake water and river water, and of ascorbic acid in a tablet and human urine. Both gave satisfactory results.