Comparative Analysis of Two-Photon Absorption and Normal Absorption images of dispersions of β-NaYF4:Yb3+,Er3+ Nanoparticles using fluorescence and two-photon microscopes

Up-conversion nanoparticles (UCNPs) have emerged as one of the most promising nanomaterials for bioanalytical and biomedical applications. β-NaYF4:Yb3+,Er3+ nanoparticles, with a size less than 40 nm, are currently being studied for diagnostic applications, utilizing regular optical spectroscopies, exploiting their ability to absorb in the infrared (IR) and emit in the visible spectrum. In this study, we performed the first tests to explore the possibility of using them in emission microscopy. Fluorescence microscopy and imaging were employed as the first proof-of-concept to examine the detectability of these nanoparticles using different microscopes, using either normal absorption or two-photon absorption in the IR region, and to detect their emission in the visible spectrum.