Optical sensor for fluoride determination in tea sample based on evanescent-wave interaction and fiber-optic integration

In this work, a miniaturized optical sensor was developed for fluoride determination in tea samples to evaluate their specific risks of fluorosis for public health based on evanescent-wave interaction. The sensor design was integrated on the optical fiber by utilizing the evanescent wave produced on the fiber surface to react with sensing reagents. According to the absorption change at 575   nm, fluoride could be determined by colorimetric method and evaluated by Beer's law. With improved performances of small detection volume (1.2   μL), fast analysis (0.41   min), wide linear range (0.01–1.4   mg   L −1 ), low detection limit (3.5   μg   L −1 , 3σ) and excellent repeatability (2.34%), the sensor has been applied to fluoride determination in six different tea samples. Conventional spectrophotometry and ion chromatography were employed to validate the sensor's accuracy and potential application. Furthermore, this sensor fabrication provided a miniaturized colorimetric detection platform for other hazardous species monitoring based on evanescent wave interaction.