MOF-derived porous ZnO-Co3O4 nanocages as peroxidase mimics for colorimetric detection of copper(II) ions in serum

Sensitive detection of copper ions (Cu2+) in biological samples is extremely important since an abnormal level of Cu2+ is linked with many diseases. Herein, we demonstrated a novel turn-on colorimetric sensor for selective detection of Cu2+ both in buffered solution and serum samples based on porous bimetallic transition metal oxide nanocages (ZnO-Co3O4 NCs) as peroxidase mimics. The ZnO-Co3O4 NCs were prepared by using ZnCo-zeolitic-imidazolate-framework (ZnCo-ZIF) as precursors via direct calcination. With the high peroxidase-like activity, the obtained ZnO-Co3O4 NCs can catalyze the oxidation of tetramethylbenzidine (TMB) in the presence of H2O2 to form a blue colored product. The inhibition effect of cysteine (Cys) on the catalytic activity of ZnO-Co3O4 NCs and its strong binding ability toward Cu2+ enabled the ZnO-Co3O4 NCs/Cys system to be utilized for sensitive detection of Cu2+, in which the catalytic activity of ZnO-Co3O4 NCs/Cys can be recovered by the introduction of Cu2+ with an obvious color change of the solution. The linear range for Cu2+ determination was 2 to 100 nM with a detection limit of 1.08 nM. More importantly, this colorimetric sensor has been successfully applied to detect Cu2+ in serum without pretreatment. Our findings are expected to expand the scope of application of nanozyme and shed light on early disease diagnosis.