Singlet oxygen luminescence detection with a fibre-coupled superconducting nanowire single-photon detector

We report the first demonstration of superconducting nanowire single-photon detectors (SNSPDs) for ¹O₂ luminescence detection. We employed a fibre-coupled cavity-enhanced SNSPD with >20% practical detection efficiency at ~1300 nm, representing a 20-fold improvement in efficiency over NIR PMTs used to date for singlet oxygen luminescence dosimetry (SOLD). The singlet oxygen signature was isolated via time-resolved and spectrally-filtered measurements performed on Rose Bengal (RB) in solution as a model photosensitizer. Quenching of the ¹O₂ luminescence was demonstrated using sodium azide. Bovine serum albumen (BSA) was employed to simulate a proteinaceous biological environment; the evolution of the RB triplet and ¹O₂ singlet-state lifetimes was successfully observed as the BSA concentration was increased. Finally, and most compellingly, an optical fibre delivery and collection scheme is demonstrated as a breakthrough advance in SOLD for in vivo preclinical and clinical applications.