Simple smartphone merged rapid colorimetric platform for the environmental monitoring of toxic sulfide ions by cysteine functionalized silver nanoparticles

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Herein, we have proposed a new, highly specific and simple colorimetric assay for the chemosensing of sulfide ions (S2−) in environmental water samples, by using cysteine-functionalized colloidal silver nanoparticles (Cys-AgNPs). As prepared Cys-AgNPs and their interface with S2− ions were demonstrated using absorption, high resolution transmission electron microscopy (HR-TEM), dynamic light scattering (DLS) and Zeta potential measurements. The colour of Cys-AgNPs altered from vivid-yellow to colourless in two minutes after the mixing of S2− ions, resulting the suppression of surface plasmon resonance (SPR) band. The relative absorption intensity was inversely proportional to the concentrations of S2− ions in the ranges from 4 × 10−7 mol dm−3 to 48 × 10−7 mol dm−3 and lowest detection limit was computed as 28 × 10−9 mol dm−3. Furthermore, the current tactic illustrates a highly specific towards S2− ions over fifteen other potentially interfering inorganic anions investigated. Furthermore, visually measurable colour changes of Cys-AgNPs have been well incorporated with a RGB colour value of smartphone to construct it consistent indicator for immediate testing of S2− ions with the limit of detection attributable to 90 × 10−9 mol dm−3. An analytical practicability of the present approaches were (colorimetric and RGB colour value based tactics) applied for the chemosensing of S2− ions in real samples including drinking, tap and sea water samples with reasonable recoveries (90.1–101.4%). Finally, the current colorimetric method is rapid, very simple, very sensitive with highly specific and this effortless nanosensor was practicable for environmental screening of toxic S2− ions.