Biofunctionalized upconverting CaF2:Yb,Tm nanoparticles for Candida albicans detection and imaging

Versatile optimization of the synthesis method and composition of Yb3+ and Tm3+ co-doped CaF2 nanoparticles as well as a novel biofunctionalization method were developed and evaluated. Through multistep synthesis, the luminescence intensity of the Tm3+ activator was enhanced by more than 10-fold compared to standard one-step synthesis. The proposed methods were used to homogenously distribute the doping ions within the nanoparticle’s volume and thus reduce luminescence quenching. Optimization of dopant ions concentration led to the selection of the most efficient visible and near-infrared up-converting nanoparticles, which were CaF2 doped with 10% Yb3+ 0.05% Tm3+ and 20% Yb3+ 0.5% Tm3+, respectively. To illustrate the suitability of the synthesized nanoparticles as bio-labels, a dedicated biofunctionalization method was used, and the nanoparticles were applied for labeling and imaging of Candida albicans cells. This method shows great promise because of extremely low background and high specificity because of the presence of the attached molecules.