Colorimetric assay for determination of Cu (II) ions using L-cysteine functionalized silver nanoplates

A L-cysteine-modified silver nanoplate (L-cys-AgNPI)-based colorimetric assay was developed for simple and rapid screening for copper (II) ions (Cu2+) in aqueous solution. The assay is based on the Cu2+-induced aggregation of L-cys-AgNPIs. In the presence of Cu2+, L-cys-AgNPls were aggregated immediately and the color of solution was distinctly changed from violet to blue within 5 min. This method enabled the quantitative measurement of Cu2+ with sample volumes as low as 5 mu L. Under optimized conditions, the limit of detection (LOD) was 1 ppm and 0.34 ppm by naked eye and smartphone with RGB application, respectively. For quantitative analysis, the calibration curve was constructed by plotting the differences in absorbance ratio at wavelengths of 620 nm and 570 nm (A620/A570) of sample and blank as a function of Cu2+ concentration. This assay detected Cu(2+ )in the range of 0.25 to 6 ppm (R-2 = 0.9951) and the LOD was 0.22 ppm. In addition, L-cys-AgNPls exhibited good selectivity for Cu2+. Additionally, the developed method was successfully applied for rapid screening of Cu2+ in real wastewater samples with % recovery in the range of 73.08 to 114.62 and 93.48 to 114.04 by UV-visible spectrometry and smartphone with RGB application, respectively. The results from the developed method were compared with those from atomic absorption spectrometry and no significant difference was found between the two methods. The developed colorimetric method is promising for on-site detection of Cu2+ with high accuracy, good selectivity, and minimal reagent consumption.