采用溶剂热法合成了聚乙烯亚胺(PEI)修饰的NaYF4∶Yb3+,Tm3+纳米晶。产物具有良好的结晶性, 粒径分布均匀, 可稳定分散在水溶液中。通过微乳法制备了NaYF4∶Yb3+,Tm3+纳米晶负载壳聚糖微球。结果表明:纳米晶均匀地嵌在壳聚糖微球的表面壳层, 球核为纯壳聚糖的交联产物。粗糙的球体表面使微球具有较好的分散性。在980 nm近红外光激发下, 纳米晶负载壳聚糖微球具有良好的上转换发光特性, 发光强度随纳米晶负载量的增加而增大, 通过调控纳米晶的负载量可实现对纳米晶负载壳聚糖微球发光强度的调控。

Upconversion nanocrystals have caused much attention, due to their superior optical and chemical properties. In this study, upconversion nanocrystals loaded chitosan microshperes were designed to develop the applications in biomedicine. Polyethyleneimine (PEI) modified NaYF4∶Yb3+,Tm3+ upconversion nanocrystals were prepared by solvothermal method. XRD and TEM indicated that the particles crystallized very well and the size was about 20 nm. The dispersity was enhanced, both in water and in chitosan solution. NaYF4∶Yb3+,Tm3+ loaded chitosan microshperes were fabricated using microemulsion method. SEM pictures showed that the chitosan microspheres surface was rough and the NaYF4∶Yb3+,Tm3+ particles were embedded in the surface shell. For PEI and chitosan having the same positive charge, during the cross-linking process, PEI modified particles moved to the surface of the chitosan microshperes drived by repulsive force. The luminescence intensity of the NaYF4∶Yb3+, Tm3+ loaded chitosan microshperes increased with the increasing of nanopaticles. Due to the biocompatibility and biodegradability of the chitosan carrier, this material can improve the duration in vivo, avoid process release effect. This kind of nanocrystals loaded chitosan microshperes may have broad application prospects in photodynamic therapy, biological imaging, fluorescent identification, as controlled release materials.