Selective and sensitive determination of copper ions in soft drink based on high catalysis of hemin–graphene hybrid nanosheets coupled with enzyme inhibitions

A simple and selective colorimetric biosensor was presented based on high catalysis of hemin–graphene hybrid nanosheets coupled with enzyme inhibitions. Alcohol oxidase (AO) can catalyze the oxidations of methanol to produce hydrogen peroxide (H2O2). Subsequently, the resulting H2O2 could be catalyzed to oxidize 3,3,5,5-tetramethylbenzidine (TMB) and then produce a blue color reactions by using hemin–graphene hybrid nanosheets with intrinsic peroxidase-like activity. The activity of AO could be selectively inhibited by the copper ions, and therefore, the oxidase-catalyzed reactions of TMB was decreased. Fortunately, other metal ions even at 10 or 100 times copper ions concentrations showed no intensive inhibitions to the AO activity. Based on this functional materials-enzyme inhibitions system, a simple, selective and sensitive colorimetric biosensor was established to determine copper ions in soft drinks. The linear relationship was obtained from 5 nM to 1 μM, and the detections limit was 1.4 nM. The results were in good agreement with those obtained by the classic ICP-MS. It was demonstrated that the proposed method had an excellent practical perspective on the determinations of copper ions in foodstuff samples.