Cu-PyC MOF with oxidoreductase-like catalytic activity boosting colorimetric detection of Cr(VI) on paper

Abstract

Hexavalent chromium ions (Cr(VI)) are highly toxic and prone to bioaccumulation in the natural environment. This study sought to develop a facile and cost-effective approach to on-site monitoring Cr(VI) content in diverse environmental samples. We synthesized copper-based MOF nanozymes (Cu-PyC MOF) and developed a simple colorimetric method by which to detect Cr(VI) on paper-based devices. The colorimetric product is obtained using the MOF nanozyme as a catalyst, Cr(VI) as an oxidant, 3,3',5,5'-tetramethylbenzidine (TMB) as a chromogenic substrate to produce a bluish-green color observable by the naked eye or a UV-visible spectrophotometer. After Cu-PyC MOF was suspended in an acidic buffer, it remained stable and showed oxidoreductase-like catalytic activity, which in turn boosts Cr(VI) reduction. The proposed scheme enables the detection of Cr(VI) within 3 min over a linear range of 0.5-50 μM with a low detection limit of 0.051 μM. The proposed nanozyme-based colorimetric method exhibits excellent reusability and selectivity over other 27 interference ions and can be used in real sample analysis.

Keywords: Colorimetric biosensor; Hexavalent chromium; Metal-organic frameworks; Nanozyme; Oxidoreductase-like activity.