Functionalized Graphene/Hydroxyapatite/Biopolymer Nanocomposite for Fluorescent and Electrical Sensing Coupled with Adsorptive Sequestration of Chlorpyrifos

Abstract Chlorpyrifos, an organophosphate pesticide, harbors serious environmental and health ramifications due to its persistence and toxicity. To mitigate potential risks to human safety, reliable and sensitive on-site quantification of this pesticide at trace levels is essential. In this work, the engineering of a multifunctional graphene-based nanocomposite capable of serving as both a multimodal sensor and an adsorbent was orchestrated for the detection and treatment of chlorpyrifos-contaminated water. The KOH-assisted gas exfoliation and graphitization of Adenanthera pavonina seeds yielded graphene nanosheets, whose subsequent functionalization and hydroxyapatite incorporation resulted in a fluorescent nanocomposite. The fluorescence intensity was systematically dissipated in the presence of chlorpyrifos via a Förster resonance energy transfer (FRET) mechanism, achieving a detection limit of 0.52 nM. Furthermore, an electrical sensing device was fabricated by integrating the nanocomposite onto a biopolymer-coated filter paper strip, which demonstrated a rapid current response toward chlorpyrifos with a detection limit of 0.67 nM. A cellular-phone-integrated system was also assembled for field applications, enabling visual monitoring of RGB intensity changes on probe solution-coated filter paper upon exposure to different concentrations of chlorpyrifos. The sensing system showed reliable performance in real cabbage extract, lake water, and tap water. For remediation, the solid fraction obtained during the synthesis exhibited a porous architecture with a surface area of 49.152 m2g–1. Under optimized conditions, the material demonstrated a monolayer adsorption capacity of 30.08 mg g–1, along with good reusability. This work provides a graphene-based platform that integrates multimodal chlorpyrifos sensing with adsorption-based remediation for safe and practical applications.