Highly luminescent and silica-coated upconversion nanoparticles by coprecipitation and sol-gel methods

Highly efficient bioimaging probes for monitoring biological functions in real time are currently under research. Upconversion nanoparticles (UCNPs) are considered as the next generation of fluorophores due to their excellent optical properties. UCNPs need to present a high fluorescence emission when excited by near infrared radiation while being long-term physicochemically stable and biocompatible to ensure the maintenance of the fluorescence and the absence of toxicity.

In this work, UCNPs were synthesized by a novel and simple coprecipitation method based on the synthesis of the lanthanide core and the formation of an extrathin silica layer by the sol-gel Stöber method. Different formulations were obtained depending on the selected drying procedure (oven or, alternatively, supercritical gel drying) and the moment when the silica layer shell was incorporated (before or after the drying step). Long-term fluorescence evaluation of UCNPs was also carried out by upconversion luminescence spectra and confocal microscopy regarding bioimaging applications. Biological characterization of the most promising formulation of UCNPs was also performed with excellent results.

The work entitled “Synthesis of highly luminescent silica-coated upconversion nanoparticles from lanthanide oxides or nitrates using coprecipitation and sol-gel methods” has been published in Gels journal (I.F. 4.6, December 2023). This work is the result of a collaboration between the University of Coimbra and the AerogelsLab.