Focusing scattered light with upconversion-nanoparticle-guided wavefront shaping

Optical scattering limits the formation of optical focus to approximately 1 mm within biological tissue, posing challenges for deep-tissue optical imaging, manipulation, and therapy. To address this limitation, wavefront shaping combined with suitable guide stars shows promise. Among existing guide stars, fluorescent particles are favored for their controllable size and biological compatibility. However, they are prone to photobleaching and exhibit a broadband emission spectrum. In this study, we propose using upconversion nanoparticles (UCNPs) as alternative guide stars to mitigate the drawbacks of fluorescent particles while retaining their advantages. Through numerical simulations and empirical experiments, we demonstrate that the UCNPs effectively assist wavefront shaping in focusing scattered light, achieving a spot size of 5 μm and an enhancement factor of 48. Due to their reduced photobleaching, excellent photochemical stability, and clean emission background, the UCNPs serve as valuable supplements to existing guide stars in wavefront shaping, particularly for biomedical imaging and optical manipulation.