MOF-derived porous ZnO-CoO nanocages as peroxidase mimics for colorimetric detection of copper(ii) ions in serum.

Sensitive detection of copper ions (Cu) in biological samples is extremely important since an abnormal level of Cu is linked with many diseases. Herein, we demonstrated a novel turn-on colorimetric sensor for selective detection of Cu both in buffered solution and serum samples based on porous bimetallic transition metal oxide nanocages (ZnO-CoO NCs) as peroxidase mimics. The ZnO-CoO 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-CoO NCs can catalyze the oxidation of tetramethylbenzidine (TMB) in the presence of HO to form a blue colored product. The inhibition effect of cysteine (Cys) on the catalytic activity of ZnO-CoO NCs and its strong binding ability toward Cu enabled the ZnO-CoO NCs/Cys system to be utilized for sensitive detection of Cu, in which the catalytic activity of ZnO-CoO NCs/Cys can be recovered by the introduction of Cu with an obvious color change of the solution. The linear range for Cu 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 Cu in serum without pretreatment. Our findings are expected to expand the scope of application of nanozyme and shed light on early disease diagnosis.