Zinc oxide coated polymer optical fiber for measuring uric acid concentrations

Uric acid detection based on ZnO coated polymer optical fiber (POF) by using intensity modulation technique is proposed. Zinc oxide was prepared using sol-gel method and characterized using UV-Vis spectrometer in order to determine its optical properties such as transmittance, absorbance and refractive index. The POF cladding is removed by using acetone and the unclad length of 2 cm was coated with ZnO by using dip coating method. The unclad fiber without coating is tested under uric acid solutions for comparison purpose. As the uric acid concentration increases until 500 ppm, the power output increases for ZnO coated fiber and produces a sensitivity of 4x10(-6) mW/ppm with a slope linearity of more than 88.56 %. The refractive index of ZnO is changing due to the interaction with uric acid and allows more light to propagate inside the fiber. The sensitivity for 2 cm and 4 cm of uncoated fiber is 2x10(-6) mW/ppm and 7x10(-6) mW/ppm. The longer the length of unclad fiber, the higher the evanescent wave absorbanceas well as the number of reflections inside the fiber.