Synthesis And Analytical Application Of Several Fluorescent Nanomaterials

Fluorescent nanomaterials such as semiconductor quantum dots(QDs),metal nanoclusters,have attracted much interest due to their unique optical properties.In recent years,QDs-based optical sensors have become one of the most exciting forefront fields in analytical chemistry.With the development of their synthetic techniques,surface processability and functional applications,QDs play important roles in the fields of chemical and biological analysis.Our goal is aimed to construct optical sensors based on fluorescent nanomaterials for the detection of hazardous analytes(such as TNT and organophosphorus pesticide residues)in environment and biomarkers(such as dopamine).In this dissertation,several high quality fluorescent nanomaterials such as Mn-doped ZnS QDs,Silicon QDs and Au NCs have been prepared by the aqueous methods.QDs-based optical sensing method were designed and built.The main research results are summarized briefly as follows:1.Highly Luminescent Glutathione-Capped Mn:ZnS/ZnS Core/Shell Doped Quantum Dots for Targeted Mannosyl Groups Expression on the Cell SurfaceHigh-quality glutathione(GSH)capped Mn:ZnS/ZnS core/shell doped quantum dots(d-dots)with pure dopant emission band and excellent stability have been synthesized directly in aqueous media.The influences of experimental variables on the luminescent properties of the Mn:ZnS/ZnS nanocrystals have been investigated.The quantum yield of the dopant Mn photoluminescence in the as-prepared Mn:ZnS/ZnS core/shell d-dots can be up to 27.4%,which is the highest reported to date for Mn:ZnS d-dots via the direct aqueous synthetic method.Additionally,the stability study against UV irradiation indicated that the obtained d-dots possessed excellent photostability.Furthermore,the MTT assay demonstrated that the Mn:ZnS QDs exhibit ultra low cytotoxicity toward HeLa cells up to a concentration of 600 ?g mL-1.Using the ConA-mannose recognization system as a model,ConA functionalized Mn:ZnS/ZnS nanocrystals was prepared and successfully used to target the mannosyl groups over expressed on the HeLa cells surface.Our investigation clearly shows that the GSH capped Mn:ZnS QDs are promising candidate as biological fluorescent labels.2.Manganese-doped ZnS quantum Dots as a Phosphorescent Probe for Use in the Bi-enzymatic Determination of Organophosphorus PesticidesWe present a sensitive and selective method for the determination of organophosphorus pesticides(OPs)based on the inhibition of the enzyme acetylcholinesterase(AChE).It is making use of quantum dots QDs of the type Mn:ZnS that display long-lived phosphorescence emission and act as optical probes for hydrogen peroxide(H2O2).In this assay,acetylcholine(ACh)is firstly hydrolyzed by AChE,and the enzyme choline oxidase(ChOx)further oxidizes choline under the formation of H2O2 which quenches the phosphorescence of the QDs.If,however,OPs are added to the solution,the rate of enzymatic hydrolysis by AChE is retarded.This reduces the rate of production of H2O2 and results in a reduced quenching efficiency.The slow decay time of the phosphorescence of the QDs also allows time-resolved luminescence intensity to be measured.This can eliminate background fluorescence from the sample and therefore improve analytical accuracy and the signal-to-noise ratio.Under optimized conditions,there is a linear relationship between luminescence intensity and the concentration of paraoxon in the range of 1 pM to 1 ?M,with an?0.1 pM limit of detection which is much lower than that of most existing methods.The phosphorescent probe was applied to determine OPs in spiked real samples.3.A Highly Sensitive Fluorescence Assay for 2,4,6-trinitrotoluene Using Amine-capped Silicon Quantum Dots as a ProbeWe present a simple and effective fluorescence method for the detection of 2,4,6-trinitrotoluene(TNT),which is based on TNT recognition by amine-capped silicon quantum dots(SiQDs).The highly luminescent SiQDs were obtained by a one-step hydrothermal process,using 3-aminopropyltrimethoxysilane as precursor.The as-prepared SiQDs were used directly as a recognition probe for TNT detection because of strong interactions between the TNT molecule and the SiQDs with an amine group.The formation of Meisenheimer complexes(TNT-amine complexes)could quench the fluorescence of SiQDs by fluorescence resonance energy transfer.Such fluorescence responses could be used to quantify TNT from-5-500 nM with a detection limit down to 1 nM,and has been applied successfully for the assay of TNT in spiked tap water.The probe exhibited excellent selectivity.This method has great potential in TNT detection.4.?-Cyclodextrin Functionalized Gold Nanoclusters as a Luminescent Probe for Ultrasensitive Detection of DopamineA novel mono-6-amino-?-cyclodextrin(NH2-?-CD)functionalized gold nanoclusters(?-CD-AuNCs)fluorescence probe was designed for dopamine(DA)detection.NH2-?-CD molecules were conjugated onto the surface of 11-Mercaptoundecanoic acid capped AuNCs(11-MUA-AuNCs)via traditional EDC/NHS condensation reaction.The integrity of the ?-CD cavities was preserved on the surface of AuNCs and retained their capability of host-guest recognition for DA molecular.DA could be captured by the ?-CD cavities to form an inclusion complex,and the oxidized DA could quench the fluorescence of ?-CD-AuNCs probe via electron transfer.The probe could be used for well quantifying DA in the range of 5?1000 nM with detection limit down to 2 nM,and the analytical sensitivity was increased by 1?2 orders of magnitude in contrast to the reported methods.Particularly,the interference of both AA and UA,which usually appeared in electrochemical and electrogenerated chemiluminescence method,had no appearance.Therefore,the?-CD-AuNCs probe could be directly used to determine DA in biological samples without further separation.The analytical strategy had been successfully applied for the DA assay in spiked human serum samples and exhibited remarkable accuracy,sensitivity and selectivity for DA detection.