Surface Modification and (Bio)Functionalization of Upconverting Nanoparticles

Recent years have witnessed the surge of investigations in the field of nanomaterial development that aims to improve the efficiency and applications in new fields. One such nanomaterial is the upconverting nanophosphor material that yields bright emission in different parts of the electromagnetic spectrum under suitable low-energy excitation by optical sources. However, the limited performance of an individual material restricted the practical applications of the material. The performance of such materials may be modified by doping or dispersion of suitable active ions in the host. Nevertheless, the issue pertaining to the high-end concentration limits the multicomponent doping in the same lattice. Such problems are the real challenges to design the new materials and conceptualize the device accordingly. However, to meet the industry demand and international perquisites for efficient futuristic devices, a material emitting in the multiple spectral regions is required and accomplished by methods such as surface modification using a suitable functional group. Surface-decorated nanophosphors, specifically with molecules or groups of biomedical interest, have plenty of applications in various bioanalytical, diagnostic, and treatment applications such as tissue imaging, targeting, in vivo imaging, bioassays, biosensors, etc. The rational surface design of upconversion nanomaterials helps to improve the performance of biomedical and biophotonics devices. The present chapter describes the various upconverting optical processes and related materials of biomedical importance. A comprehensive review with recent advancements of the surface modification processes and methods with particular emphasis on biofunctionalization of upconverting nanomaterials is presented.