Polymer-Functionalized Laser-Induced Graphene Electrochemical Sensor for Selective and Sensitive Detection of Fluoride Ions in Real Water Samples

Abstract

Fluorosis is a worldwide public health problem induced by excess fluoride content in soft and hard tissues in body, necessitating the development of fluoride sensors. This work demonstrated a flexible, cost-effective, quantitative, and selective fluoride (F-) sensor for fluoride ion detection in water samples. The miniaturized sensor was realized on a polyimide sheet by laser ablation, forming a three-electrode system with laser-induced graphene (LIG). The 3-electrode system comprises a working electrode with chemically modified LIG with electropolymerized polymer, LIG coated with Ag/AgCl conductive ink as reference, and a bare LIG as a counter electrode. The surface chemistry and morphology of the sensor were analyzed by physicochemical characterization. The electrocatalytic activity of F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> ions on the electrode surface was studied using cyclic voltammetry (CV) and chronoamperometry (CA) techniques. The F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> ions concentration of the proposed sensor was found to be in the linear range from 5 μM to 130 μM. The limit of detection (LoD) and limit of quantification (LoQ) were obtained as 2.218 μM (0.093 ppm), 6.723 μM (0.282 ppm) which are much lesser than the permissible safe limit. The sensitivity was found to be 0.0168 μA/μM∙cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The impact of other parameters, like scan rate, pH influence, interference, and reproducibility, were analyzed and to comprehend the sensor usability in real-time, a lake water sample was also tested and analyzed. The proposed sensor was found to have consistent repeatability and a good recovery rate. Owing to its flexibility, the sensor can further be miniaturized by integrating it into a microfluidic platform.