Rapid and highly selective dipchecking for cyanide ions in aqueous media

This article reports a simple dipping method for the detection of cyanide ions in water and biological samples, such as blood, using chitosan-gold nanoparticle (CH-Au NP) composite films prepared using CH-Au NP colloids. Here, gold nanoparticles were generated by heating (to similar to 80 degrees C) a solution of chitosan and gold chloride, where chitosan plays the dual role of reducing and stabilizing agent. The well-known chemistry of leaching of gold by cyanide is exploited here to detect cyanide ions. The CH-Au films showed the localized surface plasmon resonance (LSPR) absorption, similar to the CH-Au colloidal solution, at 534 nm. Gold nanoparticles (Au NPs) in the films are found to be dissolved quantitatively, causing a proportional decrease in intensity of the LSPR peak. Color change was observable by the naked eye above a concentration of 2 mg L-1 of CN- in solution. We found a good correlation between the reduction in intensity of the absorption peak at 534 nm and concentrations of CN- ions as low as 0.06 mg L-1. Most of the previously reported methods for cyanide detection involve tedious chemistry, demand the use of sophisticated instruments and still are not suitable for on-site cyanide monitoring. Our reported approach is rapid, eco-friendly, low cost, easy to use, and highly selective for cyanide detection in aqueous solution. We feel that this simple, low cost, novel and portable method is suitable particularly for third world countries, where more sophisticated aids are not so common.