Preparation And Characterization Of Quantum Dots Fluorescence Probes

Quantum dots (QDs), also known as semiconductor nanocrystals, have drawn significant attention for their potential as fluorescent probes in biological field. This study mainly focuses on two areas of QDs research.(1) Hydrophobic CdSe quantum dots with high crystallization were synthesized by colloid chemistry method. The influences of reaction time and temperature on granule size and optical property of QDs had been discussed. All the samples were characterized by ultraviolet visible spectra (UV-Vis), photoluminescence (PL) and transmission electron microscope (TEM). It was found that the size of CdSe nanocrystal increased from 2.85nm to 4.77nm when the reaction time extended from 4s to 600s at 250℃. The absorption and emission spectra were clearly red shifted. The CdSe QDs with highest photoluminescence (PL) quantum yield (QY) were obtained at 4s. With the increase of reaction temperature from 210℃to 260℃, the size of CdSe QDs increased from 3.35nm to 4.10nm. The absorption and emission spectra were red shifted similarly. The PLQY of as-prepared QDs was decreased with the increase of temperature. Comprehensively analyzing the influences of reaction time and temperature, we found that CdSe QDs in our system with the highest photoluminescence (PL) quantum yield (QY) could be achieved when the emission peak of as-prepared CdSe QDs was on 605.6nm.To improve the fluorescence intensity of CdSe core QDs, two shells of different composition were prepared using SILAR (successive ion layer adsorption and reaction) method: CdSe/CdS/CdS/CdS and CdSe/Cd0.5Zn0.5S/CdS core/shell QDs. It was found that the former one could enhance the PLOY to 8.4 times of core QDs. The later one could improve the PLQY to 10.6 times. The Cd0.5Zn0.5S/CdS shell acted more efficiently to protect the core QDs.(2) As synthesized in organic solvents, QDs were coated with a hydrophobic outer shell, which limited its application in biodetection. It was necessary to convert hydrophobic nanocrystals into hydrophilic particles. Here we encapsulate luminescent CdSe/Cd0.5Zn0.5S/CdS core/shell QDs into an amphiphilic polymer using ultrasonic emulsification (O/W) method. Thioglycolic acid modified QDs and silica modified QDs were also prepared as control groups. The results indicated that the hydrophilic QDs/polymer particles obtained by ultrasonic emulsification were more stable than QDs modified by thioglycolic acid and brighter in fluorescence emission than QDs coated with SiO2. The size of the particle as prepared was 100nm to 500nm. The size could be adjusted by changing the property of amphiphilic polymer, the ratio of O/W, the composition of oil phase and the ratio of QDs to polymer. This QDs fluorescence probe could identify the objective antibody in the immunoassay. It will have great potential for biodetection.