Real-time detection of singlet-oxygen signatures using a single-photon avalanche diode detector.

Singlet-oxygen, the first excited state of molecular oxygen (O₂), is a reactive oxygen species that plays a key role as a cytotoxic agent in photodynamic therapy (PDT). In this work, we report a highly light-sensitive detection system based on a single-photon avalanche diode (SPAD) detector and time-correlated single-photon counting (TCPSC) for real-time detection of luminescence signatures from photosensitized singlet-oxygen. Dynamics of singlet-oxygen produced by the excitation of small-scale organic nitrobenzoselenadiazole photosensitizers were extracted with acquisition times as short as 1 second. In a clinical setting, the ability to detect singlet-oxygen production in short time frames could allow for real-time adjustments in light dosing, ensuring sufficient singlet-oxygen production and complete treatment of diseased tissue in applications such as PDT.