Evanescent field-fiber loop ringdown glucose sensor.

Evanescent field-fiber loop ringdown (EF-FLRD) is a relatively new hybrid sensing technique which combines a versatile sensing mechanism with a sensitivity-enhanced ringdown detection scheme. An array of low cost, fast response, and high sensitivity biosensors based on the EF-FLRD technique can be developed. In this work, new fiber loop ringdown glucose sensors using refractive index-difference evanescent field attenuation effect as a sensing mechanism are described. The sensor head consists of either a section of partially-etched bare single mode fiber or a section of the etched fiber with glucose oxidase (GOD) immobilized on the etched fiber surface. Effects of the sensor head, with and without the immobilized GOD, on the sensor's performance are comparatively examined. The sensors' responses to standard glucose solutions and synthetic urines in different glucose concentrations ranging from 50 mg/dl to 10 g/dl are studied. The sensors, with or without the immobilized GOD, showed a linear response to glucose concentrations in the range of 100 mg/dl to 1 g/dl, but a nonlinear response in the higher glucose concentration ranging from 1 to 10 g/dl. The detection sensitivities of the sensors for the glucose solutions and artificial urine samples are 75 and 50 mg/dl respectively, and the sampling rate of the sensors is 10 to 100 Hz. Estimated theoretical detection sensitivity of the EF-FLRD glucose sensors is 10 mg/dl, which is approximately 17 times lower than the glucose renal threshold concentration.