CuMnO2 nanoflakes as pH-switchable catalysts with multiple enzyme-like activities for cysteine detection

As delafossite type of metal oxide materials, CuMnO2 nanoflakes show great promise for optoelectronics applications due to their excellent optical, electric and multiferroic properties. Here, we for the first time demonstrate that CuMnO2 nanoflakes possess intrinsic activity of mimicking enzymes of peroxidase, oxidase and catalase. Through modulating the pH value, CuMnO2 nanoflakes can catalyze the reduction of oxygen (O2) and hydrogen peroxide (H2O2) at acidic environment, and the decomposition of H2O2 to produce O2 at alkaline pH. The mechanism of their peroxidase-like activity has been proposed as the generation of hydroxyl radical (OH). Based on the colorimetric reaction of CuMnO2 nanoflakes and the hindrance of the peroxidase-like activity in the presence of H2O2 and l-cysteine, a simple platform for l-cysteine detection with low detection limit of 11.26 μM has been developed. Compared with other bimetallic oxides, CuMnO2 nanoflakes exhibit higher sensitivity and lower detection limit towards l-cysteine. Surprisingly, the proposed method for l-cysteine estimation can also be used in milk samples. These findings pave the way for further investigation about the catalytic activity of CuMnO2 nanoflakes and make them a promising candidate for biomedical applications.