The current status of the use of core–shell rare-earth-doped nanoparticles in biomedical applications is reviewed highlighting the most relevant advances.

Single-particle polarized spectroscopy reveals the spatial orientation of single NaYF₄:Er³⁺,Yb³⁺ upconverting nanorods inside single- and multiple-beam optical tweezers.

Optical trapping has been evidence as a very powerful tool for the manipulation and study of biological entities. This review explains the main concepts regarding the use of optical trapping for biosensing, focusing its attention to those applications involving the manipulation of particles which are used as handles, force transducers and sensors.