Facile Green Synthesis of Gold Nanoparticles with Carboxymethyl Gum Karaya, Selective and Sensitive Colorimetric Detection of Copper (II) Ions

Herein, we developed a gold nanoparticles (AuNPs) based label free colorimetric probe for the sensitive and selective detection of Copper (II) ions (Cu2+). Fabrication of the detection system involves a single step in which plant derived, nontoxic polysaccharide carboxymethyl gum karaya (CMGK) acts as reducing, stabilizing and functionalizing agent. Synthetic conditions were optimized by using UV-Vis spectra, zeta potential and DLS analysis and as synthesized AuNPs were thoroughly characterized by TEM, FTIR, and XRD analysis. They exhibited excellent stability to conditions like pH, salt and have a longer shelf life. These CMGK capped AuNPs exhibited a selective colorimetric response to Cu2+ ions with a visible colour change from red to blue, which could be due to the Cu2+ induced aggregation and the same was confirmed by TEM and DLS analysis. The detection conditions such as pH, amount of nanoparticles used and incubation time were optimized. Under the optimal detection conditions, the present system exhibited a good linear correlation (R-2 = 0.998) in the range of 10-1000 nM of copper with a limit of detection 10 nM. Further the method was successfully applied for the detection of copper in real water samples and biological samples (human plasma and urine).