Visual detection of cyanide ions by membrane-based nanozyme assay

Abstract

In this paper, we report a simple one-step synthesis of well-dispersed amorphous cobalt hydroxide/oxide-modified graphene oxide (CoOxH-GO) possessing peroxidase-like catalytic activity, and its application for the detection of H2O2, glucose, and CN– ions. CoOxH 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 CoOxH-GO nanohybrid in detail via the H2O2-mediated oxidation of Amplex Red (AR) to form fluorescent resorufin. The peroxidase-like activity of CoOxH-GO is utilized herein for the quantitation of H2O2 in a wide concentration range, from 100nM to 100μM. When coupled with glucose oxidase (GOD), the AR/CoOxH-GO system can determine glucose level in blood samples. Interestingly, cyanide ions (CN–) significantly inhibit the catalytic activity of the CoOxH-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 CoOxH-GO probe for the visual detection of CN– by preparing a thin film of CoOxH-GO on a positively charged and porous nylon membrane (N+M). The CoOxH-GO/N+M operates on the principle that CN– inhibits the catalytic activity of CoOxH-GO towards the H2O2-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.