ABSTRACT
Upconversion nanoparticles (UCNP), which utilize the sequential absorption and energy transfer steps to emit a higher energy photon after absorbing two or more low-energy excitation photons, have evoked great attention for bio-applications in areas such as biodetection and cancer imaging. This chapter focuses on the developments in the design and applications of hybrid UCNPs with emphasis on the fields of biodetection and cancer imaging. It summarizes the surface functionalization and discusses the strategies to sense biomolecules using the upconversion luminescence (UCL) signal of luminescence resonance energy transfer (LRET)- based UCNPs, such as LRET-on and LRET-off detection. The chapter discusses how to use hybrid UCNPs as an efficient nanoplatform to combine UCL imaging with other imaging modalities such as magnetic resonance imaging, computed tomography and radio-nuclear imaging for multimodality cancer imaging. Apart from the ligand engineering technique, coating processes like surface silanization and polymer self-assembly are other effective ways to obtain hydrophilic hybrid UCNPs.
