Metal Enhanced Fluorescence Effect Of CdSe Quantum Dots Assembled On Ag Nanoparticles And Ag@Intelligent Core-shell Composite Microgels

In recent years,noble metal nanoparticles with unique optical properties were widely used in biomedical,analytical,testing fields,in which the noble metal nanoparticles enhanced fluorescence of quantum dot has been a hotspot.Composites formed by quantum dots assembled on noble metal nanoparticles were used as fluorescent probes to detect heavy metal ions in solution.Recent studies show that the distance between metal nanoparticles and the fluorescent substance may be an important factor for metal-enhanced fluorescence.Intelligent polymers have become excellent barrier materials due to their special environmental stimuli responsive.Thus,core-shell noble metal@ smart polymer microgels are prepared and studied.In this thesis,CdSe QDs were assembled on tannic acid stabilized AuNPs,AgNPs and core-shell noble metal@smart polymer microgels surface,respectively.The influence of the distance between noble metal nanoparticles and QDs on the fluorescence enhancement of QDs was mainly discussed.The properties and structures of nanoparticles were investigated using UV-vis spectrophotometry,Transmission electron microscopy,Fourier transform infrared spectroscopy,Dynamic laser light scattering and Fluorescence spectra.The main results are as follows:1.AgNPs and AuNPs were prepared by reducing of AgNO₃ and HAuCl₄ at room temperature using tannic acid as reducing agent and stabilizer.Aminophenylboronic acid（APBA）modified CdSe QDs were assembled on AgNPs surface through the formation of boric acid ester bond between boronic acid and adjacent dihydroxy groups.Since the metal-enhanced fluorescence effect,AgNPs significantly enhanced the fluorescence of CdSe CDs by 3.5 times accompanied by a significant blue shift,while AuNPs lead fluorescence quenching of CdSe QDs.In optimal conditions,AgNPs-CdSe QDs system was used in detecting Cu²⁺.The fluorescence intensity of composites decreased upon the addition of Cu²⁺,which was caused by the formation of insoluble Cu Se particles.Experimental results show that the decrease in fluorescence intensity presents a linear relationship with Cu²⁺ concentration in the range of 0.04 to 2.0 mM with detection limit of 0.048 mM.2.AgNPs@poly（2-（dimethylamino）ethyl methacrylate-co-divinylbenzeneacid）（AgNPs@P（DMA-co-VPBA））core-shell microgels were successfully synthesized by radical copolymerization,where the size of AgNPs core was 28 nm and the thickness of the polymer shell were 35 nm and 55 nm,respectively.The prepared microgels were sensitive to glucose and D-fructose.As glucose concentration increased,the polymer chains became more hydrophilic due to the formation of boronic ester,which lead to the swelling of microgels and increase of the hydrodynamic radius.In pH 8.0 phosphate buffer solution,Alizarin Red（ARS）exhibited a strong fluorescence when they combined with VPBA group in the microgel.However,the complexed ARS molecules gradually dissociated from polymer chain due to the competitive complexation of D-fructose and VPBA,resulting in the reduction of fluorescence intensity.Under optimum conditions,the decrease in fluorescence intensity presented a linear relationship with D-fructose concentration in the range of 0 to 25 mM with detection limit of 0.64 m M,which illustrated the core-shell microgels can be used to detect D-fructose.In addition,the fluorescence of CdSe QDs was enhanced by adding AgNPs @ P（DMA-co-VPBA）.Compared to that of CdSe QDs in the absence of microgels,the maximum fluorescence enhancement was about 4.5-fold by microgels with 35 nm shell thickness,while the MEF effect of microgels with 55 nm shell thickness to CdSe QDs was weaker.These results indicated that the thickness of the spacer layer plays an important role on the MEF effect between AgNPs and CdSe QDs,which laid a foundation for further studying the effect of MEF and its practical detecting applications.