Hydrothermal Synthesis Of Water Soluable Quantum Dots And The Fabrication Multi-responsive Fluorescence Composite Nanospheres

Water-soluble quantum dots (QDs) have potential interest in the application in biological label and imaging due to their unique optical properties and biocompatibility. Hydrothermal synthesis of water-soluable QDs can accelerate the growth rate and result in high photoluminescence quantum yield (PL QY) products. In this paper, we presented the hydrothermal synthesis of water-soluble CdTe and ternary ZnCdSe alloyed quantum dots with different ligands to meet the need of the bio-applications, and the effects of the reaction variables on the growth and the PL QYs were systematically investigated. In addition, we also prepared the polysaccharide-based fluorescent CdTe QDs composite nanospheres (NP-CdTe), which were sensitive to the change of temperature and pH through the coupled reaction of water-soluble CdTe QDs capped with amino-group and hydropropylcellulose-co-polyacrylic acid nanospheres (HANP).Firstly, a modified hydrothermal synthesis of thioglycolic acid (TGA)-stabilized CdTe QDs was carried out, and the maximum PL QY of TGA-CdTe QDs was enhanced from reported 50% to 70%. Especially, the PL QY of TGA-CdTe QDs could be higher than 30% in the emission wavelength range of 490-600 nm because of the sufficient monomer supplied by the control of the pH and the molar ratio of TGA/Cd in the solution The photostability of TGA-CdTe QDs was also investigated, we found the TGA-CdTe QDs prepared under the condition of higher TGA/Cd molar ratio were of good resistivity against the UV illumination.Secondly, we first introduced the hydrothermal synthesis into the preparation of high quality cysteamine(CA)-stabilized CdTe QDs. Due to the unique structure of cysteamine and the (CdS3) structure of the CA-Cd complex, the QDs with fully decorated surface were obtained, and the PL QY of cysteamine-stabilized CdTe QDs could reach up to 20% by optimizing the reaction conditions such as temperature, CA/Cd molar ratio and monomer concentration. The PL QY of the asprepared CA-CdTe QDs in the emission wavelength range of 490nm-640nm could be enhanced to 15-20% under the proper illumination of Hg lamp without oxygen, which faciliated the surface ordering of CA-CdTe QDs. The optical stability of CA-CdTe QDs in aqueous solution was pH-dependent, which could be utilized to fabricate luminescent latex microspheres and showed potential application in multiplexed bioassays.Thirdly, glutathione(GSH)- stabilized Zn1-xCdxSe alloyed QDs with blue-emission window (430nm-500nm) and the maximum PL QY up to 34% were successfully prepared through hydrothermal route and their alloy mechanism was studied. High temperature accelated the growth rate of Zn1-xCdxSe QDs, and the spectra were dominated by band gap emission in 15-20 minutes. The emission wavelength was red-shifted and covered almost the whole blue-emission window with the addition of cadmium into the ZnSe QD during the growth procedure till the composition of Zn1-xCdxSe QDs reached constant value. The effects of the reaction variables on the growth and the optical properties of Zn1-xCdxSe QDs were investigated in detail. Because of the strong chelation of GSH with heavy metal ion, high quality GSH-capped ZnCdSe alloyed QDs were applied for the detection of Pb2+ ions through selective fluorescence quenching in aqueous solution, and the system was still sensitive at a low concentration of Pb2+ as 50nM , which suggest their promising application in ion detection. Finally, we synthesized polysaccharide-based HANP directly through the self-assembly assisted copolymerization of acrylic acid monomer, hydropropylcellulose and crosslinker. The size and zeta potential of HANP were found reversibly responsive to the variation of temperature between 40℃-50℃. The HANP nanospheres possessing carboxyl groups were coupled with the cysteamine-stabilized CdTe QDs through covalent bonds to obtain NP-CdTe nano-composites with high fluorescence quality. The emission wavelength and fluorescence intensity of NP-CdTe was found reversibly responsive to the variation of temperature between 25℃-50℃. Besides, we synthesized several NP-CdTe nano-composites with different emission colors which might be applied to bio-medical fields due to their characteristic fluorescence quality, temperature sensitivity and inner carboxyl groups.