Microfluidic paper-based analytical device for colorimetric detection of fluoride ion with smartphone readout

Abstract

Fluoride contamination in water is a widespread environmental and public health issue, originating from both natural sources and industrial activities. Excess fluoride levels can lead to severe health problems, prompting the World Health Organization (WHO) to set a maximum permissible concentration of 1.5 mg/L in drinking water. In this work, we present a novel microfluidic paper-based analytical device (μPAD) for colorimetric detection of fluoride ions as a rapid and selective sensor. The μPAD incorporates a styryl-dihydropyranylidenemalononitrile derivative bearing a silyl ether group (DCMSi), which reacts with fluoride to form a fluorosilane, triggering a visible colour change due to donor–acceptor interactions in the fluoride ions. The developed method allows for straightforward sample handling and reagent minimization, with colorimetric responses captured and quantified via smartphone imaging. The device exhibits a linear response in the 0.04–0.25 mM range, with a detection limit of 5 μM, demonstrating high sensitivity. These results highlight the potential of this colorimetric μPAD as a practical tool for real-time fluoride monitoring, particularly in remote or resource-limited settings. Its combination of high sensitivity, and simplicity positions it as a valuable contribution to environmental water quality monitoring and public health protection.