TiO2‐coated fluoride nanoparticles for dental multimodal optical imaging

Core‐shell nanostructures associated with photonics techniques have found innumerous applications in diagnostics and therapy. In this work, we introduce a novel core‐shell nanostructure design that serves as a multimodal optical imaging contrast agent for dental adhesion evaluation. This nanostructure consists of a rare‐earth‐doped (NaYF₄:Yb 60%, Tm 0.5%)/NaYF₄ particle as the core (hexagonal prism, ~51 nm base side length) and the highly refractive TiO₂ material as the shell (~thickness of 15 nm). We show that the TiO₂ shell provides enhanced contrast for optical coherence tomography (OCT), while the rare‐earth‐doped core upconverts excitation light from 975 nm to an emission peaked at 800 nm for photoluminescence imaging. The OCT and the photoluminescence wide‐field images of human tooth were demonstrated with this nanoparticle core‐shell contrast agent. In addition, the described core‐shell nanoparticles (CSNps) were dispersed in the primer of a commercially available dental bonding system, allowing clear identification of dental adhesive layers with OCT. We evaluated that the presence of the CSNp in the adhesive induced an enhancement of 67% scattering coefficient to significantly increase the OCT contrast. Moreover, our results highlight that the upconversion photoluminescence in the near‐infrared spectrum region is suitable for image of deep dental tissue.