Sphere-like CoS with nanostructures as peroxidase mimics for colorimetric determination of H2O2 and mercury ions

CoS, which was prepared using a facile solvothermal method, and characterized using various analytical techniques, was demonstrated for the first time to exhibit intrinsic peroxidase-like activity. CoS catalyzed the oxidation of the peroxidase substrate 3,3',5,5'-tetramethylbenzidine in the presence of H2O2 rendering the reaction solution blue, which is the principle used for H2O2 sensing. The mechanism of the CoS catalysis was also investigated. Under optimal conditions, the linearity of H2O2 detection ranged from 0.05 to 0.8 mM (R-2 = 0.9965). More importantly, using the reducibility of glutathione and the strong affinity to thiol compounds exhibited by mercury ions (Hg2+), a novel "off-on" colorimetric sensor for Hg2+ determination was designed using CoS as a peroxidase mimics. The analytical platform for Hg2+ determination was developed, ranging from 0.25 to 3 mu M (R-2 = 0.9965). The limit of detection was 0.1 mu M. CoS exhibited several advantageous features including good chemical stability, ease of preparation, simple purification, and excellent reproducibility.