Ultraviolet phototoxicity of upconversion nanoparticles illuminated with near-infrared light.

Recently introduced upconversion nanoparticles (UCNPs) have pushed the depth of photodynamic therapy (PDT) treatment to the centimetre range by converting deeply-penetrating near-infrared (NIR) radiation to visible radiation for photoexcitation of PDT drugs. Here we demonstrate that the direct exposure of the cancer tissue to phototoxic ultraviolet radiation generated by NIR-photoexcited UCNPs enabled successful PDT. To this aim, core/shell UCNPs of the formula NaYF4:Yb3+Tm3+/NaYF4 featuring an enhanced band in the ultraviolet UV-A and UV-B spectral bands were rationally designed and synthesised. Coupling UCNPs to the recombinant modules of the Designed Ankyrin Repeat Protein (DARPin) fused to a fluorescent protein mCherry allowed the target delivery of DARPin-mCherry/UCNP to human breast adenocarcinoma SK-BR-3 cells overexpressing HER2/neu receptors, as confirmed by fluorescence microscopy. DARPin-mCherry/UCNPs were demonstrated to be phototoxic to SK-BR-3 cells under 975 nm laser irradiation at a dose of 900 J cm-2 due to the UV photoexcitation of endogenous photosensitizers and concomitant generation of reactive oxygen species. The Lewis lung cancer mouse model was employed to demonstrate the feasibility of PDT using UCNP-mediated UV excitation of endogenous photosensitizers in the tumor tissue at a NIR dose of 1200 J cm-2. This study paves the way for exploring and harnessing UV photoexcitation processes in deep tissues in vivo.

Riboflavin photoactivation by upconversion nanoparticles for cancer treatment.

Riboflavin (Rf) is a vitamin and endogenous photosensitizer capable to generate reactive oxygen species (ROS) under UV-blue irradiation and kill cancer cells, which are characterized by the enhanced uptake of Rf. We confirmed its phototoxicity on human breast adenocarcinoma cells SK-BR-3 preincubated with 30-µM Rf and irradiated with ultraviolet light, and proved that such Rf concentrations (60 µM) are attainable in vivo in tumour site by systemic intravascular injection. In order to extend the Rf photosensitization depth in cancer tissue to 6 mm in depth, we purpose-designed core/shell upconversion nanoparticles (UCNPs, NaYF4:Yb3+:Tm3+/NaYF4) capable to convert 2% of the deeply-penetrating excitation at 975 nm to ultraviolet-blue power. This power was expended to photosensitise Rf and kill SK-BR-3 cells preincubated with UCNPs and Rf, where the UCNP-Rf energy transfer was photon-mediated with ~14% Förster process contribution. SK-BR-3 xenograft regression in mice was observed for 50 days, following the Rf-UCNPs peritumoural injection and near-infrared light photodynamic treatment of the lesions.

Submicron polyacrolein particles in situ embedded with upconversion nanoparticles for bioassay.

We report a new surface modification approach of upconversion nanoparticles (UCNPs) structured as inorganic hosts NaYF4 codoped with Yb(3+) and Er(3+) based on their encapsulation in a two-stage process of precipitation polymerization of acrolein under alkaline conditions in the presence of UCNPs. The use of tetramethylammonium hydroxide both as an initiator of acrolein polymerization and as an agent for UCNP hydrophilization made it possible to increase the polyacrolein yield up to 90%. This approach enabled the facile, lossless embedment of UCNPs into the polymer particles suitable for bioassay. These particles are readily dispersible in aqueous and physiological buffers, exhibiting excellent photoluminescence properties, chemical stability, and also allow the control of particle diameters. The feasibility of the as-produced photoluminescent polymer particles mean-sized 260 nm for in vivo optical whole-animal imaging was also demonstrated using a home-built epi-luminescence imaging system.

Visualization of upconverting nanoparticles in strongly scattering media.

Optical visualization systems are needed in medical applications for determining the localization of deep-seated luminescent markers in biotissues. The spatial resolution of such systems is limited by the scattering of the tissues. We present a novel epi-luminescent technique, which allows a 1.8-fold increase in the lateral spatial resolution in determining the localization of markers lying deep in a scattering medium compared to the traditional visualization techniques. This goal is attained by using NaYF4:Yb(3+)Tm(3+)@NaYF4 core/shell nanoparticles and special optical fiber probe with combined channels for the excitation and detection of anti-Stokes luminescence signals.