Abstract: 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 (R2=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-, NO3-, SO42-, HPO42-, H2PO4-, H+, K+, Na+, NH4+, Zn2+, and Co2+ 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.

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