Studies On Synthesis Of Fluorescent Carbon Dots With Glucose Carbon Source And Their Interactions With Bovine Serum Albumin

Fluorescent carbon dots（CDs）were a new type of fluorescent nanoparticles,which having important application value in biological medicine. Compared withother fluorescent nano-material, CDs not only have obvious superiority inbiocompatibility and easy for functionalization, but also have optical stability. As aresult, the research on the synthesis and applications of CDs has become a hot-pointarea in the field of luminescent materials.First, bare CDs and PEI modified CDs were synthesized. Secondly, experimentshas investigated the interaction between BSA and the two small molecule substances(CDs, PEI-CDs) including the action mechanism,the action characteristics and theimpact on the structure of BSA through using several spectroscopic techniques.The results are as follows:1、With glucose as the carbon source, bare CDs were synthesized solvothermalyin ethanol solution and then modified with branched polyethyleneimine (PEI) toimprove their, in order to synthesize PEI-CDs. The as-prepared CDs werecharacterized by transmission electron microcopy (TEM), X-Ray Diffraction(XRD),infrared spectrum (IR) and fluorescence spectrum (FL). The results indicated that thesynthesized PEI-CDs have small size about of7nm, the quantum yield was3.1%,and showing about5-fold enhancement in fluorescence emission.2、To study the interaction mechanism of BSA with CDs under physiologicalconditions by fluorescence quenching in combination with UV-Vis absorption, CDspectroscopy. The results showed that the quenching of BSA fluorescence by CDswas found to be a dynamic quenching process. Based on the experiments, the bindingconstants were calculated to be4.532,6.559L·mol-1at300and310K, respectively.Both of the binding sites about1. According to the van’t Hoff equation, thethermodynamic parameters were estimated, which indicated that CDs interacted withBSA mainly through hydrophobic forces and electrostatic force interactions. Theentropy increase and the free energy reducing in this combining process proved it is aspontaneous procedure. The binding distance between BSA and CDs was calculatedto be3.49nm according to the theory of F rster. The displacement experiments pointed out that CDs could bind to the Site I of BSA. The protein structure haven’talter in the presence of the CDs was confirmed by synchronous fluorescencespectroscopy,CD and3D fluorecence spectroscopy.3. To study the interaction mechanism of BSA with PEI-modified CDs underphysiological conditions by fluorescence quenching,UV-Vis absorption, CDspectroscopy. According to the formula of Stern-Volmer, the results showed that thequenching of BSA fluorescence by PEI-modified CDs was found to be a dynamicquenching procedure. Calculated the binding constants of the PEI-modified CDs-BSAsystem was7.1280,8.2457×103L·mol-1at290and310K, respectively. Their bindingsites n are about equal to1at two temperatures. According to the Van’t Hoff equation,the thermodynamic parameters were calculated, which indicated that PEI-modifiedCDs interacted with BSA mainly through hydrophobic forces The entropy increaseand the free energy reducing in this combining process proved it is a spontaneousprocedure. The binding distance between BSA and PEI-modified CDs was calculatedto be3.0nm according to the theory of F rster’s non-radiation energy transfer. Thedisplacement experiments suggested that PEI-modified CDs could bind to theSiteⅠof BSA. The protein structure haven’t alter in the presence of the CDs wasconfirmed by synchronous fluorescence spectroscopy,CD and3D fluorecencespectroscopy.