Embodiments of the invention are directed to an optical sensor for detecting blood glucose. The sensor comprises a chemical indicator system disposed within a gap between the distal end of an optical fiber and an atraumatic tip portion, wherein the optical fiber and atraumatic tip portion are coupled by a coupling member, such as a rod or hypotube or cage that traverses the gap. The sensor further comprises a means for generating and detecting an optical reference signal unrelated to the blood glucose, such that ratiometric correction of blood glucose measurements for artifacts in the optical system is enabled.
