Stick-Shaped Multilayer Sensors Containing Fluorescent Imprinted Polymers: Promising Devices for Portable Fluoride Sensing in Water

Abstract

Fluoride offers both beneficial and harmful health effects depending on its concentration, highlighting the need for low-cost, portable sensors compatible with deployable technologies. Despite recent progress, achieving high anion selectivity and full water compatibility remains a major challenge in fluoride sensing. Here, we synthesized and evaluated three novel arene-containing urea/thiourea-based compounds as optical probes for fluoride detection in water. The most effective, a pyrene-derived chemosensor, showed high sensitivity but low selectivity toward chloride(2). To overcome this, it was embedded into a fluoride-imprinted polymer (2P), enhancing selectivity in aqueous suspension at the expense of sensitivity. To improve performance and enable sensor alignment within the optochemical system, 2P was incorporated into a stick-shaped multilayer device (2PS). A comparable device using a previously developed anthracene-based polymeric sensor (1PS) was also prepared. Both devices, mounted diagonally on a cuvette for fluorescence measurements, exhibited higher sensitivity (5242 and 3156 M^–1, respectively) than the polymers in suspension and showed excellent stability across multiple cycles. The 2PS device emerged as the top performer, combining very high fluoride selectivity, rapid response, excellent recovery in real samples (102 ± 6%), and a working range (164–942 μM) aligned with international guidelines, making it a promising tool for aqueous fluoride monitoring.