Authors: D.K. Chatterjee, Y. Zhang
Affilation: National University of Singapore, Singapore
Pages: 69 - 72
Keywords: photodynamic therapy, upconversion, cancer, nanoparticles
Photodynamic therapy 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 effectiveness to superficial pathologies. Fluorescent upconversion phosphor nanoparticles convert low energy radiation to higher energy emissions and can be used as ‘nanotransducers’ to activate photosensitizers in deep tissues. We synthesized monodisperse, 50 nm PEI/NaYF4:Yb3+,Er3+ nanoparticles producing green/red emission upon NIR excitation. These 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 intra-muscular injection in rats. Fluorescence emission enabled these particles to be simultaneously as molecular probes. Upon NIR excitation, the particles, modified with ZnPC photosensitizer, released singlet oxygen, and after targeted binding to cancer cells, resulted in significant cell destruction. Potential clinical use of these nanoparticles includes imaging and PDT of cancer in deep tissues.