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Hyaluronan (HA) represents an interesting polymer for nanoparticle coating due to its biocompatibility and enhanced cell interaction via CD44 receptor. Here, we describe incorporation of oleatecapped b-NaYF 4 :Yb 3? , Er 3? nanoparticles (UCNP-OA) into amphiphilic HA by microemulsion method. Resulting structures have a spherical, micelle-like appearance with a hydrodynamic diameter of 180 nm. UCNP-OA-loaded HA micelles show a good stability in PBS buffer and cell culture media. The intensity of green emission of UCNP-OA-loaded HA micelles in water is about five times higher than that of ligand-free UCNP, indicating that amphiphilic HA effectively protects UCNP luminescence from quenching by water molecules. We found that UCNP-OA-loaded HA micelles in concentrations up to 50 lg mL -1 increase cell viability of normal human dermal fibroblasts (NHDF), while viability of human breast adenocarcinoma cells MDA-MB-231 is reduced at these concentrations. The utility of UCNP-OA-loaded HA micelles as a bio-imaging probe was demonstrated in vitro by successful labelling of NHDF and MDA-MB-231 cells overexpressing the CD44 receptor. NHDF (d) incubated with UCNP-OA-loaded oleyl-HA micelles and excess of oleyl-HA (2 mg mL -1 ) served as controls. Green and blue colours represent upconversion emission and Hoechststained cell nuclei, respectively. (Color figure online)

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We describe a modification of epifluorescence microscopes that allows quantitative widefield imaging of samples labeled by upconverting nanoparticles (UCNP). A top-hat illumination profile on the sample was achieved with a 980-nm laser diode by using tandem microlens arrays, a moving diffuser and a telescope, which adjusts the top-hat area to the field of view. Illumination homogeneity is a critical factor for imaging of UCNP since the intensity of their luminescence typically scales with the second power of the excitation intensity. Our illuminator is combined with the epifluorescence attachment of the microscope, allowing easy switching between observation of UCNP and traditional fluorescent dyes. Illumination profile homogeneity of about 98% was measured for objectives with magnification from 4× to 100×, and the top-hat profile was also obtained with phase contrast objectives. We demonstrate capability of the illuminator by evaluating in vitro uptake of UCNP encapsulated in oleyl-hyaluronan micelles into breast cancer cells. Micelles bearing the targeting peptide were about an order of magnitude more efficient than nontargeted micelles.

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