Fluorescence Enhancement Effect Of CdSe Quantum Dots Assembled On Ag Nanoparticles And Its Application

Recently, due to the distinctive enhancement effect of surfacephotoelectric signals, noble metal nanoparticles (NPs) have been widelyused in scientific fields such as analytical chemistry, bio-medicine, etc..Among the researches on influence and mechanism of fluorescenceproperties affected by noble metal nanoparticles, the fluorescenceenhancement induced by surface plasmon resonance and fluorescencequenching resulted from fluorescence resonance energy transfer are twoimportant aspects. Quantum dots (QDs) or organic dyes, which often beused as fluorescence probes to detect particular objects including heavymetal ions and some essential substances in life, have been chosen asfluorescent materials to investigate the interactions between them. In thisthesis, novel complexes containing noble metal Ag nanoparticle andmercaptopropionic acid (MPA) capped CdSe QDs have been synthesized.Transmission electron microscopy (TEM), fluorescencespectrophotometer (FL), ultraviolet and visible spectrophotometer(UV-vis),1H nuclear magnetic resonance (1H-NMR) and fouriertransform infrared spectroscopy (FT-IR) have also been used tocharacterize their properties. The main results are as follows:1. A new assembled glucose sensor based on Ag nanoparticles(AgNPs)-enhanced fluorescence of CdSe QDs was developed. Themercaptoglycerol-modified AgNPs and aminophenyl boronic acid-functionalized CdSe QDs are assembled into AgNPs-CdSe QDscomplexes through the formation of boronate ester bond. As comparedwith that of bare CdSe QDs, up to9-fold fluorescence enhancement and aclear blue-shift of the emission peak for AgNPs-CdSe QDs complexes were observed, which are attributed to the surface plasmon resonance ofAgNPs. In addition, the as-formed complexes are gradually disassembledin the presence of glucose molecules because they can replace the AgNPsby competitive binding with boronic acid groups, resulting in theweakening of fluorescence enhancement. The decrease of fluorescenceintensity presents a linear relationship with glucose concentration in therange from2to52mM with a detection limit of1.86mM. Such ametal-enhanced QDs fluorescence system may have promisingapplications in chemical and biological sensors.2. Trace Cu2+ions in aqueous solution were detected by usingAgNPs-CdSe QDs complex with enhanced fluorescence properties asfluorescent probes. Upon addition of Cu2+ions, the fluorescence systemof AgNPs-CdSe QDs is weakened due to the formation of CuSe withlower solubility, which leads to fluorescence quenching. These complexeswith enhanced fluorescence properties exhibit ultra-sensitivity andexcellent selectivity toward Cu2+over other metal ions in aqueoussolution. The decrease of fluorescence intensity presents a linearrelationship with Cu2+ions concentration in the range from0to14μMwith a detection limit of0.077μM.3. We synthesized poly(N-isopropyl acrylamide)-b-poly(glycidylmethacrylate)(PNIPAM-b-PGMA) diblock copolymer by usingreversible addition fragmentation chain transfer radical polymerizationmethod. After that, the PNIPAM-b-PGMA modified-CdSe QDsnanocomposite was successfully prepared via ring-opening reactionbetween epoxy group of GMA and MPA-capped CdSe QDs. Laser lightscattering and fluorescence spectrometer were used to study the influenceof temperature on size and fluorescent properties of formednanocomposite. As the temperature increases, the compound particle sizeincreases. In addition, the fluorescence emission of CdSe QDs takes ared-shift to the near-infrared region, and become narrowed and symmetric.The stability of QDs is also increased. All of these are because PNIPAM chains aggregate with increasing of temperature, resulting in theassociation of CdSe QDs. Furthermore, the polymer forms a protectivelayer on the surface of CdSe QDs, leading to the high stability of CdSeQDs.