Highlights

• A simple, reagent-free, non-colourimetric method for detection of fluoride in water at drinking-water-relevant 0–5?mg?L^?1 concentration range.
• Optical fibre tip coated with aluminum by sputter deposition is degraded in the presence of fluoride, decreasing internal reflection of infrared light.
• Kinetics of coating degradation are correlated to fluoride concentration.

Abstract

Naturally occurring elevated levels of fluoride in drinking water pose a health hazard throughout the developing world, with over 200 million people potentially impacted. In some cases, treatment methods or safer alternative sources are available, but robust, simple, affordable technologies for measuring fluoride in drinking water are absent. In this work, a simple method for fluoride detection is presented comprising a 35?nm aluminum coating on the distal tip of a length of single mode optical fiber. Broadband light is launched into the proximal end of the optical fiber and a portion of this light is reflected by the distal tip of the fiber, which is immersed in water containing an unknown concentration of dissolved fluoride. The intensity of the reflected light is detected by a photodiode connected to the proximal end of the fiber. The aluminum coating is removed from the distal tip by reaction with the dissolved fluoride at a rate that depends on the fluoride concentration and the intensity of the light reflected from the distal tip depends upon the thickness of this coating. Therefore, the rate at which the intensity of light detected by the photodiode decreases is correlated with the concentration of fluoride. The fabricated sensor measures fluoride concentration within the range of 0–5?mg?L^?1.

*Original abstract online at https://www.sciencedirect.com/science/article/abs/pii/S0924424719311094

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