Infrared laser pulse triggers increased singlet oxygen production in tumour cells

Photodynamic therapy (PDT) is a technique developed to treat the ever-increasing global incidence of cancer. This technique utilises singlet oxygen (O-1(2)) generation via a laser excited photosensitiser (PS) to kill cancer cells. However, prolonged sensitivity to intensive light (6-8 weeks for lung cancer), relatively low tissue penetration by activating light (630 nm up to 4 mm), and the cost of PS administration can limit progressive PDT applications. The development of quantum-dot laser diodes emitting in the highest absorption region (1268 nm) of triplet oxygen (O-3(2)) presents the possibility of inducing apoptosis in tumour cells through direct O-3(2) -> O-1(2) transition. Here we demonstrate that a single laser pulse triggers dose-dependent O-1(2) generation in both normal keratinocytes and tumour cells and show that tumour cells yield the highest O-1(2) far beyond the initial laser pulse exposure. Our modelling and experimental results support the development of direct infrared (IR) laser-induced tumour treatment as a promising approach in tumour PDT.