Upconverting nanoparticles as nanotransducers for photodynamic therapy in cancer cells

Background: Photodynamic therapy (PDT) involves killing of diseased cells by excitation of photosensitizer chemicals with high-energy light to produce cytotoxic oxygen species from surrounding dissolved oxygen. However, poor tissue penetration of high-energy light and hydrophobic photosensitizers limits the effectiveness to superficial pathologies. Upconversion phosphor nanoparticles convert low-energy radiation to higher-energy emissions. Aim: To create upconverting 'nanotransducers' to enable PDT in deep tissues. Results: Monodisperse, 50 nm PEI/NaYF4:Yb3+,Er3+ nanoparticles producing green/red emission on near-infrared (NIR) excitation were targeted to folate receptors on human colon cancer cells and imaged with high signal-to-background ratio. It was demonstrated that these particles could be excited after deep intramuscular injection in rats. On NIR excitation, the particles, modified with zinc phthalocyanin photosensitizer, released singlet oxygen and, after targeted binding to cancer cells, resulted in significant cell destruction. Conclusion: Potential clinical use of these nanoparticles includes imaging and PDT of cancer in deep tissues.