  Direct monitoring of singlet oxygen (1O2) luminescence is a particularly
challenging infrared photodetection problem. 1O2, an excited state of the
oxygen molecule, is a crucial intermediate in many biological processes. We
employ a low noise superconducting nanowire single-photon detector to record
1O2 luminescence at 1270 nm wavelength from a model photosensitizer (Rose
Bengal) in solution. Narrow band spectral filtering and chemical quenching is
used to verify the 1O2 signal, and lifetime evolution with the addition of
protein is studied. Furthermore, we demonstrate the detection of 1O2
luminescence through a single optical fiber, a marked advance for dose
monitoring in clinical treatments such as photodynamic therapy.
