Magnetoplasmonic photonic arrays for rapid and selective colorimetric detection of chloride ions in water

The rapid and efficient detection of chloride (Cl − ) ions is crucial in a variety of fields, making the development of advanced sensing methods such as colorimetric sensors an imperative advancement in analytical chemistry. Herein, a novel, selective, and straightforward paper-based colorimetric sensing platform has been developed utilizing an amorphous photonic array (APA) of magnetoplasmonic Ag@Fe 3 O 4 nanoparticles (MagPlas NPs) for the detection of Cl − in water. Taking advantage of the highly responsive APA, the key principle of this sensing method is based on the chemical reaction between Ag + and Cl − , which results in the precipitation of high-refractive index (RI) AgCl. This assay, distinct from typical plasmonic sensors that rely heavily on nanoparticle aggregation/anti-aggregation, is premised on the precipitation reaction of Ag + and Cl − . In the presence of Cl − , a rapid, distinctive color alteration from royal purple to a dark sky blue is visually observable within a short time of a few minutes, eliminating the necessity for any surface modification procedures. Comprehensive assessments substantiated that these sensors display commendable sensitivity, selectivity, and stability, thereby establishing their effective applicability for Cl − analysis in various technological fields. Introducing a rapid, color-changing assay for Cl − detection in water, this study showcases high sensitivity, selectivity, and stability, suitable for both environmental and biomedical applications, and offers versatility in detecting various anions for on-site screening.