A glucose sensor for intravascular measurement of glucose concentration wherein the sensor is arranged to measure glucose concentration by monitoring the lifetime of the fluorophore, the sensor comprising: - an indicator system comprising a receptor for selectively binding to glucose and a fluorophore associated with said receptor, wherein the fluorophore has a lifetime of less than 100ns; - a light source; - an optical fibre arranged to direct light from the light source onto the indicator system; - a detector arranged to receive fluorescent light emitted from the indicator system; and - a signal processor arranged to determine information related to a fluorescence lifetime of the fluorophore based on at least the output signal of the detector.