Dual Activity of Rose Bengal Functionalized to Albumin-Coated Lanthanide-Doped Upconverting Nanoparticles: Targeting and Photodynamic Therapy.

A modified version of a desolvation method was used to render lanthanide-doped upconverting nanoparticles NaGdF4:Yb3+/Er3+ (Ln-UCNPs) water-dispersible and biocompatible for photodynamic therapy. Bovine serum albumin (BSA) was used as surface coating with a direct conjugation to NaGdF4:Yb3+/Er3+ nanoparticles forming a ∼2 nm thick shell. It was estimated that approximately 112 molecules of BSA were present and cross-linked per NaGdF4:Yb3+/Er3+ nanoparticle. Analysis of the BSA structural behavior on the Ln-UCNP surfaces displayed up to 80% loss of α-helical content. Modification of the Ln-UCNPs with a BSA shell prevents luminescence quenching from solvent molecules (H2O) with high energy vibrations that can interact with the excited states of the optically active ions Er3+ and Yb3+ via dipole-dipole interactions. Additionally, the photosensitizer rose bengal (RB) was conjugated to albumin on the surface of the Ln-UCNPs. Emission spectroscopy under 980 nm excitation was carried out, and an energy transfer efficiency of 63% was obtained. In vitro cell studies performed using human lung cancer cells (A549 cell line) showed that Ln-UCNPs coated with BSA were not taken by the cells. However, when RB was conjugated to BSA on the surface of the nanoparticles, cellular uptake was observed, and cytotoxicity was induced by the production of singlet oxygen under 980 nm irradiation.