The Design And Imaging Application Of Cadmium-free Semiconductor Quantum Dots-based Fluorescence Probe

Quantum dots?QDs?,which possess the merits of wide spectral range,high quantum yield,excellent biocompatibility and easy surface modification,are considered as the ideal nano-materials for constructing novel fluorescent probes and biosensors.Nevertheless,conventional semiconduct quantum dots?SQDs?are synthesized in oil phase and usually comprise of elements with high levels of toxicity such as Cd and Pb.In order to overcome these shortcomings,cadmium-free ternary quantum dots have attracted more and more researchers'attention.The cadmium-free quantum dots not only avoid utilizing highly toxic heavy metal eliments,but also own fantastic biocompatibility.It can be directly employed for environmental detection,immunoassay,bioimaging,drug tracing,biomolecular marking,and so on.Therefore,to improve detection specificity and sensitivity,designing and exploring novel,water-soluble and green quantum dots-fluorescent probes based on different analytes is of great significance.In this dissertation,we briefly summarize the properties and synthesis methods of SQDs,as well as the mechanisms of quantum dots nano-fluorescent probes.And several high-performance water-soluble quantum dots nano-fluorescent probes were constructed by fluorescent quenching mechanisms.The primary research works in this dissertation contain the following four parts:?1?Detection and fluorescence imaging analysis of tyrosinase in serum by dopamine functionalized Mn-doped ZnS quantum dots.Herein,a facile aqueous fluorescence probe based on dopamine-functionalized-Mn-doped ZnS quantum dots?Dopa-Mn:ZnS QDs?was fabricated to detect tyrosinase?TYR?activity.TYR catalyzes the oxidation of dopamine to dopaquinone derivative,which annihilates the fluorescence of nanoprobes due to photoinduced electron transfer?PET?between Dopa-Mn:ZnS QDs and dopaquinone moiety.Quantitative evaluation of TYR activity was studied in terms of the relationship between fluorescence quenching efficiency and TYR activity.The probe could detect TYR in a broad linear range of up to 360 U L^-1 with a low detection limit of 1.82 U L^-1.It was then applied to detect TYR in chicken serum samples,in which,TYR could be recovered by 88.0–99.9%.Finally,the probe was evaluated by MTT assay to show low cytotoxicity and was successfully applied to intracellular imaging of A549 cells.This study has indicated potential applications of Dopa-Mn:ZnS QDs probe in monitoring TYR-associated diseases,clinical diagnostics,and drug discovery.?2?A novel ratiometric fluorescence probe based on dual-emitting Mn-doped ZnS quantum dots?Mn:ZnS QDs?was established for to achieve rapid detection of Pb²⁺and methyl parathion?MP?.The dual-emitting Mn:ZnS QDs was aqueous synthesised in one-pot and played as a ratiometric fluorescence probe for high sensitivity detection of Pb²⁺.Good linearity between the fluorescence intensity ratio(F₄₅₀ nm/F₅₈₅ nm)and Pb²⁺concentration in the concentration range of 10 nmol L^-1 to 60 nmol L^-1 was observed,and the detection limit of Pb²⁺is 0.5 nmol L^-1.Furthermore,a“turn-on”fluorescence sensing system based on the Mn:ZnS QDs/Pb²⁺system was established to quantitative measure the MP concentration.The fluorescence intensity at 450 nm exhibited a good linear response to the MP concentration range from 0.19 to 0.95mmol L^-1 with a detection limit of about 0.02mmol L^-1.It also had a satisfying performance in fruit and environmental water samples.Therefore,the prepared Mn:ZnS QDs-based sensor has been established as a ratiometric fluorescence probe and turn-on method for quantitative detection of lead ion and MP,respectively.The detection limit of this method is much lower than that in the US Environmental Protection Agency and China National Food Standards.?3?Enzymatic determination of uric acid using a fluorescent probe based on water-soluble CuInS/ZnS QDs?CIS QDs?.Glutathione-capped water-soluble CIS QDs were prepared by a microwave-assisted method.The fluorescence at its excitation/emission peak at 380/570 nm was found to be quenched by hydrogen peroxide?H₂O₂?,which is produced by the oxidation of uric acid?UA?and oxygen catalyzed by uricase.Moreover,horseradish peroxidase?HRP?can catalyze H₂O₂ to produce more hydroxyl radicals which can quench CIS/ZnS QDs fluorescent probes as well.Due to the interaction of uricase and horseradish peroxidase,the sensitivity of the method can be improved greatly,owing to the more pronounced fluorescence quenching of CIS/ZnS QDs.The findings are used in a quenchometric method for the determination of UA.The effects of different ligands on the QDs,of pH value,buffers,enzyme ratio and reaction time were optimized.The detection limit for UA is 50 nmol L^-1 which is lower than other QD-based method,and the detection ranges extends from0.25-4.0mmol L^-1.The assay is simple and sensitive,and no further modification of the QDs is required.?4?Using the principle of inner filter effect?IFE?,we constructed a highly selective CIS/ZnS QDs fluorescent probe based on mercaptopropionic acid modification for alkaline phosphatase?ALP?detection and cell imaging studies.It is well known that the key to maximize the sensitivity of an IFE-based fluorescence assays is to broaden the overlap between the absorption of an absorber and the excitation/emission of a fluorophore.We employed CIS/ZnS QDs and p-nitrophenylphosphate?PNPP?as the fluorescent indicator and the substrate,respectively,for ALP activity assessment.Due to the CIS/ZnS QDs have an efficient excitation at 405 nm,and a large Stokes shift emission at 588 nm,meanwhile p-nitrophenol?PNP?has an absorption peak at 405 nm,the hydrolyzed production of PNPP and ALP,can act as a competitive absorber to absorb the excitation light of CIS/ZnS QDs which resulting in noticeable quenching of CIS/ZnS QDs.The proposed sensor can be applied to detect ALP activity in human serum samples?sample consumption:20?L?with detection limit of 0.01 U L^-1.Excellent biocompatibility of CIS/ZnS QDs enables the sensor to monitor endogenous ALP in living cells.Furthermore,because the surface modification or the linking between the receptor and the fluorophore is no longer required,this fluorescent sensing system exhibits great potential to simplify ALP clinical measurement,thereby improving diagnostics of relevant diseases.