Efficient Preparation Of CdTe Nanocrystals And Its Hybrid Microspheres

Semiconductor nanocrystals(NCs) have drawn considerable attention in the past few decades due to their unique optical properties,such as strong size-dependent emission wavelength,continuous excitation spectrum,excellent emission spectrum and high stability against photobleaching.To prepare semiconductor nanocrystals in aqueous media has a lot of advantages like low-cost,simplified device,and the product has better biocompatibility which can be directly used in biomedical applications.Semiconductor nanocrystals usually need to be incorperated with inert materials beacause of their high specific surface area and high sensitivity to the surrounding environment and also some extend of heavy metal ions release.In this context,our work is devoted to efficient preparation of CdTe nanocrystals(especially near-IR-emitting NCs) in aquous media and their incorperation into inert materials to obtain luminescent hybrid microspheres.The results are listed as follows:(1) We presented a facile one-pot method to fabricate water-dispersed CdTe nanocrystals(NCs) with high efficiency(the solid contend of as-prepared nanocrystal dispersion was up to 5 w.t.‰.) We also investigated conditions for preparing near-infrared-emitting(650 nm-800 nm) CdTe NCs with high photoluminescence quantum yields(PL QYs),such as effects of type of ligands,ligand-to-Cd molar ratio, and precursor concentration.We conclude that mercaptopropionic acid(MPA) is the best ligands,and a high MPA-to-Cd ratio and precursor concentration is also nessassary for the synthesis of high-quality near-IR-emitting CdTe NCs.The bio-imaging tests showed that the as-prepared nanocrystals can be uptaken by different cells without preference and were well distributed in the cytoplasm of the cells.The MTT assay showed that the cytotoxicity of the as prepared NCs were moderate when the CdTe NCs were cultured with the NCs for 4 hours(At this concentration,the relatively cell viability was 60%for HeLa cells and 74%for AD293 cells.).The water-dispersed CdTe NCs with excellent emissions in the near-IR spectrum window have great potential in the biological and medical applications especially in in vivo imaging.(2) We prepared hydrophilic fluorescent microspheres incorperated with CdTe nanocrystals.Firstly,Reverse miniemulsion polymerization was employed to fabricate CdTe@PAm hybrid microspheres.It was found that the nanocrystals have been extruded from the miniemulsion during the polymerization when we use MPA capped CdTe NCs.By using polyacrylic acid(PAA)-capped CdTe NCs instead,we fabricated CdTe@PAm hybrid microspheres successfully.Secondly,fluorescent CdTe@SiO₂ hybrid nanoparticles were successfully prepard by the reverse microemulsion method.We found that the use of ammonia aqueous solution as catalyst would cause a blue-shift of the fluorescent wavelength and the fall of the fluorescence intensity,while using NaOH of appropriate concentration as catalyst the fluorescent can be maintained much the same after the incorporation.Further more, by introducing poly(diallyldianethyl-ammonium chloride)(PDDA) into the waterpool of the microemulsion,the number of CdTe NCs incorporated in the hybrid microspheres can be largely increased.We found when the molar ratio of Quaternary amine in PDDA and mercaptopropionic acid(MPA) on the surface of the NCs was 5, the highest luminescence of the hybrid microspheres can be obtained.(3) Fluorescent CdTe@PSt-DVB hybrid nanoparticles were prepared by miniemulsion polymerization.In this process,firstly,we transferred the aqueous synthesized CdTe NCs into organic phase by partially exchange MPA ligand to dodecyl mercaptan (DTT).Secondly,the miniemulsion(CdTe/toluene dispersion minidroplet,with initiator AIBN in them) was formed by the ultrasonic emulsification.Thirdly, monomer Styrene and crosslinked agent DVB was added and the polymerization was initiated to form the hybrid microspheres.The formed fluorescent microspheres had a reasonably narrow size distribution and high luminescence.A high initiator concentration and high crosslinldng degree is necessary to inhibit the phase separation of polymer chains with nanocrystals.The optimum condition is.5%initiator concentration and 40%crosslinking degree.Further more,to make the hybrid microsphere with good dispersibility in aqueous media,we added 3-(Methacryloxy)propyltriethoxysilane(MPS) to copolymerize with St and DVB,and after hydrolization we obtained microspheres with silanol groups on the surface, which may coupled with biomoleculars conveniently.