A polyvinyl alcohol/poly-acrylic acid (PVA/PAA) hydrogel coated optical fiber interferometer was been evaluated as a pH sensor. The interferometer, which comprises a waist-enlarged bitaper, a round tip and a tantalum pentoxide layer displays high refractive index (RI) sensitivity. With the hydrogel coated, the sensor's optical interference fringes shifted with exposure to varying pH solutions. High pH sensitivity of 1.58 nm/pH was achieved for pH 2.48â€?.47. The miniature sensor demonstrates little hysteresis, high repeatability and low cross-sensitivity to temperature. A rising/falling time of 10/11 s for the sensor time response was acquired, respectively.
A Mach Zehnder fiber interferometer is demonstrated for sensing of the heavy metal cation, Ni2+ using a responsive poly(vinyl alcohol) (PVA) based hydrogel. The presence of Ni2+ increases degree of cross linkages within the hydrogel and increases its refractive index, leading to phase shift in the interferogram. Ni2+ concentration is monitored by the shifting of interference dips with a sensitivity of 0.214 nm/μM and limit of detection of 1 nM. Design of the PVA hydrogel to optimize sensitivity is discussed and the capability of the gel to immobilize various receptors enables a flexible platform for sensing applications.