Development of evanescent field optical fiber sensor for pH measurement using sol-gel technology

Electrochemical sensors are sensitive to electromagnetic interference, and some require a laboratory structure to carry out measurements. This work proposes developing a fiber optic sensor to measure pH by absorbing light in the evanescent field using sol-gel technology with the purple bromocresol indicator. Due to the variation in the color of the sol-gel, which contains the imprisoned indicator, light is absorbed in the evanescent field region when it comes into contact with different pH values. In this way, we can correlate the optical power read by the spectrometer, which corresponds to the difference between the power transmitted by the LED and the power of the light absorbed in the evanescent field region with the pH values. This article reports the preparation of the claddingless multimode optical fiber. The experiment was carried out initially in the laboratory with pH values between 4 and 7, which obtained excellent results with a coefficient of linear regression (R²) of 0.95439 and an adjusted R-squared of 0.93159.