In vivo measurement of dye concentration using an evanescent-wave optical sensor

A miniaturised evanescent-wave optical sensor is proposed for in vivo measurement of dye concentrations. It enables a continuous monitoring of the optical-dye attenuation or fluorescence spectra between 380 and 650 nm. The sensor is constructed with polished fibres: the cladding of a single-mode fibre is removed by longitudinal polishing. The proximity of the core to the medium favours penetration of the evanescent part of the modal field into the bio fluid. The dimensions of the probe permit several potential applications: for example, insertion into hypodermic needles for spectroscopic analysis of tissues and blood. In the paper, a gastro-enterologic application of the sensor introduced into a catheter is reported. In vivo tests demonstrate the feasibility of quantitative measurement of dye clearance in the gastro-oesophageal tract.