Visual detection of cyanide ions by membrane-based nanozyme assay.

In this paper, we report a simple one-step synthesis of well-dispersed amorphous cobalt hydroxide/oxide-modified graphene oxide (CoOx H-GO) possessing peroxidase-like catalytic activity, and its application for the detection of H2 O2 , glucose, and CN- ions. CoOx H is formed and deposited in situ on the GO surface through the reaction between GO (size ~ 240nm) and Co2+ in basic solution at room temperature. We investigated the enzyme-mimicking activity of the CoOx H-GO nanohybrid in detail via the H2 O2 -mediated oxidation of Amplex Red (AR) to form fluorescent resorufin. The peroxidase-like activity of CoOx H-GO is utilized herein for the quantitation of H2 O2 in a wide concentration range, from 100nM to 100μM. When coupled with glucose oxidase (GOD), the AR/CoOx H-GO system can determine glucose level in blood samples. Interestingly, cyanide ions (CN- ) significantly inhibit the catalytic activity of the CoOx H-GO nanohybrid, which allows for the construction of a probe for the detection of CN- in water samples and laboratory wastes. We fabricated a membrane-based CoOx H-GO probe for the visual detection of CN- by preparing a thin film of CoOx H-GO on a positively charged and porous nylon membrane (N+ M). The CoOx H-GO/N+ M operates on the principle that CN- inhibits the catalytic activity of CoOx H-GO towards the H2 O2 -mediated oxidation of AR to form reddish resorufin on the membrane. The intensity of the red color of the membrane decreases with increasing CN- concentration, which can be easily observed with the naked eye at the nanomolar level. This cost-effective sensing system allows for the rapid and simple determination of the concentrations of CN- in complicated wastewater samples.