Theoretical study of laser-based phototherapies’ improvement via upconverting nanoparticles

The introduction of new upconverting nanoparticles (UPCNPs) in the tumor area is being investigated worldwide as a solution for deep tissue theranostics interventions. Moreover, as the development of biophotonics techniques permits bioimaging in nanoscale, both photodynamic and photothermal sensing should be achieved even at cellular level with minimum perturbation, i.e., in absence of any physical contact between cells and sensing units at a single-cell level via optical tweezers. In our work, we discuss the biophotonic upconversion mechanism of nanoparticles’ excitation/emission at cellular level, under laser trapping conditions, via considering laser radiation of NIR (specifically at λ = 808 nm) for optimal penetration in biological tissues. Moreover, a theoretical simulation model will be presented for evaluation of the electric field distribution in optically trapped particles. Water soluble UPCNPs with maximum absorbance wavelength at λ = 808 nm and emission at 545 nm and 660 nm will be studied. The photoluminescence of biocompatible UPCNPs could provide a promising powerful tool for PDT single-cell analysis and/or for photothermal enhancement and sensing in an optical tweezers’ platform.