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

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 As ions, the brownish-coloured solution of AC-AgNPs became colourless. Moreover, the computational study revealed that among all the metal ions, only As was able to form a stable complex with AC-AgNPs, with a binding energy of 8.7 kcal mol. 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 As 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.