The Design Of Quantum Dots Based Ratiometric Fluorescent Probes For The Detection Of Bioactive Molecules

Quantum dots?QDs?have been applied to many areas because of their special properties,such as high quantum yield,large surface-to-volume ratio,high photostability and size-tunable emission spectra.With the development of aqueous QDs,the aqueous QDs with good biocompatibility show potential applications in biomedicine.Compared with traditional organic fluorescent dyes,QDs exhibit superior optical properties and show remarkable potentials for sensing applications.This thesis first focuses on the synthesis of different II-VI QDs?Cd Te and doped ZnS QDs?,together with the studies of their optical properties.Then the as-prepared QDs were used to build different ratiometric fluorescent probes for the selective and sensitive detection of different bioactive molecules.The main research contents are as follows:?1?One major challenge of aqueous synthesis is to obtain QDs with narrow full width at half maximum?FWHM?and high photoluminescence quantum yields?PL QY?.To improve the optical properties of aqueous Cd Te QDs,the synthetic process was investigated systematically and the results indicated that low precursor concentration and separation of nucleation and growth process were advantageous to the formation of high-quality QDs with excellent optical properties.Based on the fact that different sizes?colors?of QDs vary considerably in sensing performance?fluorescence response?,the ratiometric fluorescent probes composed of QDs with green and red emission?GQDs and RQDs?were designed for H₂O₂ detection.The results indicated that the plot of F606/F510 versus DA concentration showed a good linear relationship in the range of 10¹25 ?mol/L with the square of correlation coefficient?R2?of 0.991 and the detection limit was 0.3 ?M.In addition,the designed ratiometric fluorescent probes show high selectivity for H₂O₂ and show good potential for detection of H₂O₂ in real biological samples.?2?The FRET systems composed of UCNPs and Cd Te QDs with different sizes?different emission wavelength?were obtained during the growth of Cd Te QDs,in which the UCNPs were energy donors and QDs acceptors.Under 980 nm excitation,the emissions of QDs were detected because of the non-radiation process?FRET?.Thus,the near-infrared?NIR?excitation of QDs was achieved.NIR excitation could not only avoid the noise and interference caused by the UV excitation,but also improve the photostability of QDs.Additionally,the FRET systems were used as fluorescent probes for dopamine?DA?detection.The results indicated that the plot of F630 versus DA concentration showed a good linear relationship in the range of 10³00 n M with the square of correlation coefficient?R2?of 0.994 and the detection limit was 8 n M.In addition,the selectivity of the probes was investigated and the results suggested the probes showed high selectivity for DA.?3?The doped ZnS QDs with long wavelength emission were synthesized by doping the ZnS QDs with different metal ions.By the control of the doping process,the Mn²⁺ and Eu³⁺ doped ZnS QDs were synthesized,respectively.Eu³⁺ dopant emissions at 590,618 and 695 nm were observed in the emission spectra of Eu-ZnS QDs,which were assigned to transitions from 5D0 to 7F1,7F2 and 7F4,respectively.The Mn-ZnS QDs showed dual emissions at ⁴20 nm and ⁵80 nm,which corresponded to ZnS intrinsic emission and 4T1?6A1 transition of Mn²⁺ dopant ions,respectively.In addition,the Mn-ZnS QDs were used as ratiometric fluorescent probes due to the simple synthesis process and high PL QYs and the sensing performance was also investigated.?4?The Cu-Mn codoped ZnS QDs?Cu-Mn-ZnS QDs?were synthesized by two-steps doping strategy,in which the Cu²⁺ and Mn²⁺ ions were doped in ZnS through nucleation-doping and growth-doping processes,respectively.The PL spectra showed that Cu-Mn-ZnS QDs had two emissions at ⁴90 nm and ⁵95 nm,which corresponded to the Cu²⁺ and Mn²⁺ dopant emissions,respectively.The Cu-Mn-ZnS QDs with large ?? and appropriate emission intensity were obtained by controlling the doping process.Therefore,the difference of the two emissions led to the different fluorescent response to target biomolecule.In view of this fact,the emission intensity ratios F595/F490 was set as output signal to design the Cu-Mn-ZnS QDs based ratiometric fluorescent probes for FA detection.The results indicated that the Cu dopant fluorescence intensity decreased gradually while the Mn dopant fluorescence intensity increased with increasing concentrations of FA.The intensity ratios?F595/F490?versus the FA concentrations could be fitted to a linear regression equation ranging from 0.01⁵ ?mol/L with the correlation coefficient?R2?of 0.995.In addition,the mechanism of ratiometric fluorescent sensing of FA was proposed based on the electron transfer process.