Eco-friendly Zn-based Quantum Dots As Fluorescent Probe Detecting Bisphenol A And Melamine

Quantumn dots (QDs) are fluorescent inorganic semiconductor nanoparticleswith high fluorescence brightness and photostability, thus they are widely used inbiology, environmental monitoring and food safety. In this thesis, two kinds ofwater-soluble Zn-based QDs were synthesized: ZnS QDs and ZnSe QDs, then theywere used as fluorescent probes to detect bisphenol A (BPA) and melaminerespectively. This study included the following two aspects:（1）Low toxic ZnS QDs were synthesized via an environmently-friendlymethod using chitosan as capping agent, which were served as fluorescent sensors fordetecting BPA. The as-prepared ZnS QDs exhibited characteristic absorption(absorbance edge at310nm) and emission (maxima at430nm) spectra with arelatively high fluorescence quantum yield of11.8%. Quantitative detection of BPAwas developed based on fluorescence quenching of chitosan-capped ZnS QDs withhigh sensitivity and selectivity. Under the optimal conditions, the fluorescenceresponse of ZnS QDs was linearly proportional to BPA concentration in a wide rangefrom0.50to300μg·L-1with a detection limit of0.08μg·L-1. Most of potentialcoexisting substances did not interfere with the BPA-induced quenching effect. Theproposed analytical method for BPA was successfully applied to water and plastic realsamples, and the possible quenching mechanism was also discussed.（2）In this part, eco-friendly ZnSe QDs were synthesized using L-glutathione ascapping agent. A very practical and competitive sensing strategy for melamine hasbeen developed based on the efficient inner filter effect (IFE) of Ag nanoparticles(AgNPs) on the fluorescence of ZnSe QDs. The fluorescence emission of ZnSe QDscould be quenched significantly by AgNPs via IFE, which resulted in a fluorescence“off-state”. The presence of melamine could induce the aggregation of AgNPs andmodulate the IFE process. Thus the IFE-decreased fluorescence could graduallyrecover in a melamine concentration-dependent way, thereby achieving the fluorescence “turn-on” sensing for melamine. Under the optimal conditions, a decentlinear relationship for melamine was obtained in the range from1.0to36μg L-1, andthe detection limit was as low as0.11μg L-1. The IFE-based strategy was successfullyapplied for melamine analysis in raw milk and egg samples and satisfactory resultshave been achieved. Therefore, it is very promising to use this simple, rapid, sensitiveand eco-friendly method for on-site and real-time screening of melamine.