The detection of a single photon at 1270 nm wavelength allows the direct monitoring of Singlet Oxygen (1O2), making Singlet Oxygen Luminescence Detection (SOLD) a powerful dosimetry technique for photodynamic therapy in the treatment of cancer. However, the direct detection of 1O2 emission at 1270 nm wavelength is extremely challenging as the 1O2 → 3O2 transition in biological media has very low probability and short lifetime due to the high reactivity of singlet oxygen with biomolecules. Recent advances in single photon detection providing high detection efficiency, low noise single-photon detectors are an important innovation in the development of a practical SOLD system for eventual clinical use. In this thesis I present a compact fibre coupled SOLD system, using a supercontinuum pump source to precisely target exact photosensitizer absorption peak wavelengths and single-photon detectors for near-infrared detection by benchmarking a superconducting and a semiconductor photon counting detector. Both pump laser and detector are intrinsically fibre-coupled making them ideally suited for the development of practical singlet oxygen sensor head. The SOLD system was used to carry out a series of singlet oxygen time-resolved measurements in solution and in live cells. These measurements offer information on the photosensitized generation and deactivation of singlet oxygen generated by different photosensitizers and microenvironments at the 1270 nm wavelength and a first investigation of the 1590 nm singlet oxygen luminescence signal is presented
