Evolution of Highly Biocompatible and Thermally Stable YVO:Er/Yb Upconversion Mesoporous Hollow Nanospheriods as Drug Carriers for Therapeutic Applications.

In recent times, upconversion nanomaterials with mesoporous hollow structures have gained significant interest as a prospective nano-platform for cancer imaging and therapeutic applications. In this study, we report a highly biocompatible YVO:1Er/10Yb upconversion mesoporous hollow nanospheriods (YVO:Er/Yb UC-MHNSPs) by a facile and rapid self-sacrificing template method. The Rietveld analysis confirmed their pure phase of tetragonal zircon structure. Nitrogen adsorption-desorption isotherms revealed the mesoporous nature of these UC-MHNSPs and the surface area is found to be ~87.46 m/g. Under near-infrared excitation (980 nm), YVO:Er/Yb UC-MHNSPs showed interesting color tunability from red to green emission. Initially (at 0.4 W), energy back transfer from Er to Yb ions leads to the strong red emission. Whereas at high pump powers (1 W), a fine green emission is observed due to the dominant three-photon excitation process and traditional energy transfer route from Er to Yb ions. The bright red light from the membrane of HeLa cells confirmed the effective cellular uptake of YVO:Er/Yb UC-MHNSPs. The resonant decrease in cell viability on increasing the concentration of curcumin conjugated YVO:Er/Yb UC-MHNSPs established their excellent antitumor activity. Therefore, the acquired results indicate that these YVO:Er/Yb UC-MHNSPs are promising drug carriers for bioimaging and various therapeutic applications.