Paper-based colorimetric sensor for detection of chloride anions in water using an epoxy-silver nanocomposite

An epoxy-silver nanocomposite printed on paper was prepared for colorimetric detection of chloride anions (Cl − ) in aqueous solution. This paper-based sensor provides a promising platform with attractive advantages such as simple fabrication, intense colors, fast naked-eye response, and high specificity toward Cl − detection. The sensor undergoes a color change from yellow-orange to chestnut-brown in the presence of water and turns to green–brown in the presence of Cl − . A good linear relationship ( R 2 = 0.9754) between logarithmic Cl − concentration and the extinction intensity difference at 515 nm was observed at concentrations in the 20–400 mM range with a limit of detection (LOD) of 14 mM, far beyond the usual concentrations at which most of the Cl − colorimetric sensors are limited. It was also proposed a sensing mechanism based on the oxidative etching of anisotropic silver nanoparticles (from 20 to 250 nm) by Cl − and subsequent formation of chain-like aggregates, resulting in strong interparticle plasmonic coupling. This paper-based sensor can distinguish Cl − from other ions such as F − , OH − , NO 3 − , SO 4 2− , HPO 4 2− , H 2 PO 4 − , H + , K + , Na + , NH 4 + , Zn 2+ , and Co 2+ and from mixtures of these ions. The nanosensor was also tested to recognize Cl − in seawater and a commercial electrolyte solution, even using volumes as small as 4 µL, suggesting its easy inclusion in portable devices. This novel colorimetric platform is undoubtedly useful for recognizing Cl − in environmental and physiological systems. Graphical abstract Epoxy-silver nanocomposite printed on paper for colorimetric detection of chloride anions in water. The paper-based sensor shows intense colors, fast naked-eye response, and high specificity toward Cl − detection at high concentrations (mM)