Preparation and upconversion luminescence cell imaging of O-carboxymethyl chitosan-functionalized NaYF4:Yb3+/Tm3+/Er3+ nanoparticles

Upconversion luminescence nanoparticles (UCNPs) have shown promising applications in biomedical fields as luminescent probes because of their excellent advantages such as single excitation with multicolor emission, low autofluorescence, and deep penetration. But the biological applications of such nanomaterials are still restricted due to the unfavorable surface properties. In this work, we develop a facile one-pot hydrothermal route to obtain O-carboxymethyl chitosan (OCMC)-wrapped NaYF₄: Yb³⁺/Tm³⁺ /Er³⁺ red UCNPs which have been used for targeted cell luminescence imaging directly and efficiently. The successful coating of the UCNPs by OCMC has been confirmed by Fourier-transform infrared (FTIR) spectroscopy and dynamic light scattering (DLS) studies. Transmission electron microscopy (TEM), powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and photoluminescence (PL) spectra have been used to characterize the size, composition and emission color of the samples, respectively. Due to the good biocompatibility, water-solubility, and strong UC luminescence, these hydrophilic nanocrystals will open up new avenues in further bioapplications.