OPTICAL GAS SENSOR FABRICATION BASED ON PORPHYRIN-ANCHORED ELECTROSTATIC SELF-ASSEMBLY ONTO TAPERED OPTICAL FIBERS

Tapered optical fibers with nano-assembled coatings of thicknesses of order tens of nano-metres were used for the detection of ammonia gas. The film coating was composed of alternate layers of tetrakis-(4-sulfophenyl) porphine (TSPP) and poly(allylamine hydrochloride) (PAH), which were deposited using the electrostatic self-assembly process (ESA). Exposure of a PAH/TSPP nano-assembled non-adiabatic tapered optical fiber with a waist diameter of 10 mu m to ammonia induced significant optical changes in the transmission spectrum of the optical fiber. The fiber optic sensor showed a linear sensitivity to the concentration of ammonia in the range of 10-100 ppm, with response and recovery times less than 100 and 240 sec, respectively. The 3 sigma limit of detection (LOD) was estimated to be ca. 2 ppm.