A fiber-optic pH sensor based on relative Fresnel reflection technique and biocompatible coating

A biocompatible fiber-optic pH sensor based on Fresnel reflection technique and a sensing coating is presented. Sodium alginate and polyethylenimine are alternatively deposited on the sensing fiber end to form the sensing coating via a layer-by-layer electrostatic self-assembly technique. An optical switch is added to the measurement system for the convenience of fast calibration. A linear, monotonic and fast response in a large pH range (from pH   5.87 to pH   10.55) is obtained with the resolution of 0.01   pH unit. The sensitivity of the pH sensor is 0.018   R.I.U/pH. It is not influenced by fluctuations of light source.