Synthesis of multicolor silver nanostructures for colorimetric sensing of metal ions (Cr, Hg and K) in industrial water and urine samples with different spectral characteristics.

In this work, we have synthesized four different color (yellow, orange, green, and blue (multicolor)) silver nanostructures (AgNSs) by chemical reduction method where silver nitrate, sodium borohydride and hydrogen peroxide were used as reagents. The as-synthesized multicolor AgNSs were successfully functionalized with bovine serum albumin (BSA) and applied as a colorimetric sensor for the assaying of metal cations (Cr, Hg, and K). The addition of metal ions (Cr, Hg, and K) into BSA functionalized AgNSs (BSA-AgNSs) causes the aggregation of BSA-AgNSs, and are accompanied by visual color changes with red or blue shift in the surface plasmon resonance (SPR) band of BSA-AgNSs. The BSA-AgNSs show different SPR characteristic for each metal ions (Cr, Hg, and K) with exhibiting different spectral shift and color change. The yellow color BSA-AgNSs (Y-BSA-AgNSs) act as a probe for sensing Cr, orange color BSA-AgNSs (O-BSA-AgNSs) act as probe for Hg ion assay, green color BSA-AgNSs (G-BSA-AgNSs) act as a probe for the assaying of both K and Hg, and blue color BSA-AgNSs (B-BSA-AgNSs) act as a sensor for colorimetric detection of K ion. The detection limits were found to be 0.26 μM for Cr (Y-BSA-AgNSs), 0.14 μM for Hg (O-BSA-AgNSs), 0.05 μM for K (G-BSA-AgNSs), 0.17 μM for Hg (G-BSA-AgNSs), and 0.08 μM for K (B-BSA-AgNSs), respectively. Furthermore, multicolor BSA-AgNSs were also applied for assaying of Cr, and Hg in industrial water samples and K in urine sample.