Highly sensitive, quantitative detection of singlet oxygen (1O2) is required for the evaluation of newly developed photosensitizers and the elucidation of the mechanisms of many processes in which singlet oxygen is known, or believed, to be involved. The direct detection of 1O2, via its intrinsic phosphorescence at 1270 nm, is challenging because of the extremely low intensity of this emission, coupled with the low quantum efficiency of currently available photodetectors at this wavelength. We introduce hollowcore photonic crystal fibre (HC-PCF) as a novel optofluidic modality for photosensitization and detection of 1O2. We report the use of this approach to achieve highly sensitive detection of the luminescence decay of 1O2, produced using two common photosensitizers, Rose Bengal and Hypericin, within the 60-m diameter core of a 15-cm length of HC-PCF. We demonstrate the feasibility of directly detecting sub-picomole quantities of 1O2 using this methodology, and identify some aspects of the HC-PCF technology that can be improved to yield even higher detection sensitivity.