Preparations And Applications Of Carbon And Silicon Quantum Dots

Carbon and silicon quantum dots(denoted with CQDs and SiQDs respectively)have performances of photo-fluorescence, which are very similar to some fluorescent dyes. In addition, they possess well biocompatibility, lower toxicity, wonderful stability against photo-bleaching and easily chemical surface-modification. These forecast that CQDs and SiQDs are the ideal fluorescent materials and therefore they are promised to be applied as fluorescent labelings on biomolecules.The work described in this dissertation includes the following four aspects.(1)The up-conversion fluorescence of the CQDs, prepared with aqueous glucose solution, was researched.(2) The CQDs, obtained by pyrolysis of citric acid, were chemically modified with N-hydroxysuccinimide(NHS) and successively were applied in fluorescent labeling on bovine serum albumin(BSA).(3) The CQDs with a high quantum dots, derived from mixture of citric acid and glycine, were prepared and utilized in labeling BSA.(4) The SiQDs, made from electrolyzing a silicon slice,were suffered stepwise chemical modifications and ultimately the covalent binding between SiQDs and BSA was realized. The detailed contents were stated in the following.1) The CQDs were synthesized by the dehydration of aqueous glucoses under hydrothermal treatment of 180°C for 60 min. The produced CQDs were characterized by infrared(IR) spectrum, ultraviolet and visible(UV-vis) spectra,images of atomic force microscopy(AFM) and transmission electron microscopy(TEM). The size of CQDs was about 5 nm. The down-conversion photoluminescence and up-conversion photoluminescence(UCPL) were measured with fluorescent spectroscope respectively. The UCPL emission of the obtained CQDs locates at about 517 nm(2.4 eV), which matches with the band gap of CdS semiconductor. The experiments proved that the system of CQDs-CdS performed well catalyses on both degradation of Rhodamine B and methylene blue. And the degenerating rate was fast than that of the bare CdS powders. However, CQDs-CdS system did not exhibit the catalytic effect on degradation of Rhodamine B and methylene blue under a dark environment. Those demonstrated the UCPL of the obtained CQDs.2) The CQDs manufactured facilely from cheap citric acids and their chemical modification with N-hydroxysuccinimide(NHS) as well as their covalent bondage with bovine serum albumin(BSA) for fluorescent labeling on BSA were described in detai. The carboxyl groups of the CQDs were easily to be esterified by NHS in very mild conditions for introducing active NHS esters(denoted with CQDs-NHS), which could be extracted by ethyl acetate from the mixture. Thus isolation and purification of the CQDs-NHS were then realized. The NHS-ester moieties of the CQDs-NHS performed high reactively with primary amino of BSA which was used as an example of biomolecules. This was confirmed by an experiment of gel electrophoresis and the fluorescence imaging. Experimental results also demonstrated the low cytotoxicity and the high stability against photo-bleaching of the CQDs-NHS. The CQDs were witnessed with transmission electron and atomic force microscopes. The structural information of the CQDs and CQDs-NHS were disclosed with infrared(IR) and X-ray photoelectron spectra(XPS).Photoluminescence of the CQDs and the CQDs-NHS were revealed with fluorescence spectra.3) The CQDs were prepared by pyrolysing the mixture of citric acid and glycine in drying oven. The product was immersed in tetrahydrofuran for 8 h. High quantum yield CQDs(HQY-CQDs) were obtained by removing tetrahydrofuran from the supernate. The experiments demonstrated that they possessed a much higher quantum yield compared with that without dealing with tetrahydrofuran and a wonderful photo-bleaching resistance. Such HQY-CQDs could be functionalized by NHS and successively combined with BSA covalently. Thus fluorescent labeling on BSA was realized. The HQY-CQDs were demonstrated with TEM images and the chemical modification with NHS was proved by IR and XPS spectra. Labeling BSA with the HQY-CQDs was confirmed by gel electrophoresis and fluorescence imaging.4) The SiQDs were prepared on surface of a silicon slice(denoted as SiQDs/Si)by electrolying the silicon slice which is as an anode in solutions of hydrofluoric acid and hydrogen peroxide. The morphology of the obtained chip of SiQDs/Si was exhibited by scanning electron microscopy. The resulted SiQDs received by ultrasonication were proved by the images of TEM and fluorescence spectra. The produced SiQDs/PSi chip was modified with propenoic acid firstly and with NHS successively. The terminal NHS esters were so active in combining with primary amino groups of biomolecules. The successes of stepwise modifications were proved by both IR and XPS spectra. BSA was chosen as a model compound to imitate thereaction of surface NHS esters of SiQDs and biomolecules. Such an approach provided an easy way of labeling biomolecues with SiQDs.