Colorimetric determination of sulfide using chitosan-capped silver nanoparticles

The article describes a simple method for the rapid photometric and visual detection of sulfide in water samples. Silver nanoparticles were capped with chitosan (chit-AgNPs) and then characterized by absorption spectroscopy, high resolution transmission electron microscopy and zeta potential measurements. Chit-AgNPs exhibit a strong surface plasmon resonance band at 404 nm which disappears in the presence of increasing concentrations of sulfide. This is accompanied by color change from yellow to colorless and attributed to the formation of silver sulfide on the surface of the chit-AgNPs. This was corroborated by HR-TEM and zeta potential measurements. The method is fairly selective for sulfide even in the presence of 100-fold higher concentrations of interferents such as common anions and thiol containing molecules. The method can be applied to quantify sulfide in the 0.80 to 6.40 x 10(-6) mol dm(-3) concentration range with a 0.35 x 10(-6) mol dm(-3) detection limit (at an S/N ratio of 3).