Highly selective colorimetric assay for nickel ion using N-acetyl-L-cysteine-functionalized silver nanoparticles

A colorimetric assay based on silver nanoparticles (NAC-Ag NPs) capped with N-acetyl-L-cysteine (C5H9NO3S, NAC) has been developed which exhibits highly selectivity towards Ni2+ over other cations such as Al3+, Cr3+, Fe3+, Co2+, Pb2+, Ba2+, Cd2+, Fe2+, Cu2+, Hg2+, Zn2+, Mn2+, Ag+, Mg2+, Ca2+, Na+, and K+ under specified conditions. Silver nanoparticles were prepared by reducing AgNO3 with sodium borohydride (NaBH4) in the presence of NAC. The infrared spectra suggested that NAC was successfully capped on the surface of the silver nanoparticles. In the presence of Ni2+, rapid aggregation of NAC-AgNPs was induced along with color change from yellow to deep orange. The absorbance ratio (A(550)/A(390)) was linear with the concentration of Ni2+ in the wide range from 2 to 48 mu M with a detection limit of 0.23 mu M. The proposed method was applied successfully to the determination of Ni2+ in tap water samples, and the recoveries were from 92 to 106 %.