Ultrasensitive and selective colorimetric and smartphone-based detection of arsenic ions in aqueous solution using alliin–chitosan–AgNPs

Abstract

In this study, we developed a highly selective and sensitive colorimetric sensor for arsenic [As(III)] detection using alliin–chitosan-stabilized silver nanoparticles (AC–AgNPs). The AC–AgNPs were synthesized using a complex prepared by mixing aqueous garlic extract containing alliin and chitosan extracted from shrimp. The synthesis of AC–AgNPs was confirmed by UV-vis spectroscopy, which showed a surface plasmon resonance (SPR) band at 403 nm, and TEM analysis revealing spherical nanoparticles with a mean diameter of 7.57 ± 3.52 nm. Upon the addition of As³⁺ ions, the brownish-coloured solution of AC–AgNPs became colourless. Moreover, the computational study revealed that among all the metal ions, only As³⁺ was able to form a stable complex with AC–AgNPs, with a binding energy of 8.7 kcal mol⁻¹. The sensor exhibited a linear response to As(III) concentrations ranging from 0.02 to 1.4 fM, with a detection limit of 0.023 fM. The highest activity was observed at pH 7 and temperature 25 °C. Interference studies demonstrated high selectivity against common metal ions. The study also demonstrated that the concentration of As³⁺ ions can be estimated by the decrease in red intensity and increase in green intensity in smartphone optical transduction signals. These results indicate the potential of the AC–AgNP-based sensor for reliable and efficient arsenic detection in environmental monitoring.