Design And Application Of Quantum Dot Fluorescent Probes

Colloidal semiconductor nanocrystals, which are also known as fluorescent quantum dots (QDs), have attracted increasing interest in fundamental studies as well as technical applications, owing to their size-dependent optoelectronic properties that are distinct from those of the corresponding bulk materials. Because of superior properties to traditional organic fluorophores, such as higher quantum yield, much sharper emission spectra etc., the QD based fluorescent probes have been extensively applied to the detection of metal ions, small molecules and substances which have close relationship with human being. In this thesis, home-made QDs are used to build fluorescent probe. A zinc ion probe has been successfully built based on QDs. At the same time, the exploration of building a probe for the detection of hydrogen sulfide has been discussed. The main contents are as follows:(1) A dithiolcarbamate capped quantum dots-based fluorescent probe for the detection of zinc ions.Since zinc ions play important roles in various physiological activities, developing a facile detection method for Zn2+is highly desirable. Dithiolcarbamate is a very good modifying ligand for quantum dots. In this study, water soluble di-2-picolylamine-dithiolcarbamate (DPA-DTC)/prolinedithiolcarbamate (P-DTC) co-capped CdSe/ZnS quantum dots as a sensitive and selective "turn-on" fluorescence probe for Zn2+was reported. The probe was easily obtained via ligand exchange from the initial oil-soluble QDs. The initial bright fluorescence of QDs was effectively quenched by DPA-DTC that acted as an effective hole trapper. Upon complexation with Zn+, the formation of Zn2+-DPA-DTC complex altered the energetic position of the HOMO for DPA-DTC, which rendered it unfavorable for the hole transfer. Thus the fluorescence of quantum dots was switched on again. Under optimal conditions, a good linear relationship between the fluorescence response and Zn2+concentration could be obtained in the range from0.9to16μM. The limit of detection for Zn2+was found to be0.7μM. Compared to other zinc ion probes, our reported probe shows distinct strengths. Furthermore, the present probe exhibited a high selectivity for Zn2+over other common metal ions and was successfully used in the detection of Zn2+in simulated biological fluids.(2) The attempt to build a quantum dots-based ratiometric fluorescent probe for the detection of hydrogen sulfide.Hydrogen sulfide has close relationship with environment and organism. In this study, we have tried to obtain a derivative of rhodamine which contains azide group. Also, we tried to combine the ligand with quantum dots and make them into practice. Although the ligand had fluorescence response to hydrogen sulfide, we couldn’t obtain an effective synthetic and purification approach for the production of this ligand in high yield. At the same time, we couldn’t combine the quantum dots with the ligand. As a result, a lot of efforts need to be conducted in the future study.