Autofluorescence insensitive imaging using upconverting nanocrystals in scattering media

Autofluorescence is a nuisance in the field of fluorescence imaging and tomography of exogenous molecular markers in tissue, degrading the quality of the collected data. In this letter, we report autofluorescence insensitive imaging using highly efficient upconverting nanocrystals (NaY F₄: Yb³⁺ Tm³⁺) in a tissue phantom illuminated with near-infrared radiation of 85 mW cm². It was found that imaging with such nanocrystals leads to an exceptionally high contrast compared to traditional downconverting fluorophores due to the absence of autofluorescence. Upconverting nanocrystals may be envisaged as important biological markers for tissue imaging purposes.