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

Fluorosis is a worldwide public health problem induced by excess fluoride content in soft and hard tissues in the body, necessitating the development of fluoride sensors. This work demonstrated the development of a flexible, cost-effective, quantitative, and selective fluoride (
$\text{F}^{-}{)}$
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 three-electrode system comprises a working electrode with chemically modified LIG with electropolymerized polymer, LIG coated with Ag/AgCl conductive ink as a reference, and a bare LIG as a counter electrode. The surface chemistry and the morphology of the sensor were analyzed by physicochemical characterization. The electrocatalytic activity of the
$\text{F}^{-}$
ions on the electrode surface was studied using cyclic voltammetry (CV) and chronoamperometry (CA) techniques. The
$\text{F}^{-}$
ions concentration of the proposed sensor was found to be in the linear range from 5 to 130
$\mu \text{M}$
. The limit of detection (LoD) and limit of quantification (LoQ) were obtained as 2.218
$\mu \text{M}$
(0.093 ppm) and 6.723
$\mu \text{M}$
(0.282 ppm), which are much lesser than the permissible safe limit. The sensitivity was found to be
$0.0168 \mu \text{A}/\mu \text{M}\cdot $
cm
²
. Subsequently, the impact of various parameters, such as scan rate, pH influence, interference, and reproducibility, were analyzed. To further comprehend the sensor usability in real time, a lake water sample was used for testing and analysis. 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.