Antioxidant identification using a colorimetric sensor array based on Co-N-C nanozyme

• We developed a sensor array based on Co-N-C single-atom nanozymes for colorimetric discrimination of antioxidants. • Under two pH conditions, Co-N-C nanozymes produce different catalytic effects on the reaction between H 2 O 2 and TMB. • Linear discriminant analysis (LDA) was used to successfully analyze the 7 antioxidants. • The sensing strategy had excellent specificity and good application in human serum samples. Here we develop a simple and effective nose/tongue sensor array based on Co-N-C single-atom nanozymes-3,3′,5,5′-tetramethylbenzidine (TMB)-H 2 O 2 for colorimetric discrimination of antioxidants, which makes use of the color reaction of TMB oxidation by H 2 O 2 in two different pH (3.8 and 4.6) environments under the catalysis of Co-N-C nanoenzyme with peroxidase-like activity. Different antioxidants have varying reducing ability to the oxidation products of TMB (oxTMB), thus resulting in differential absorbance and color changes. Linear discriminant analysis (LDA) results indicate that the sensor array successfully identified 7 antioxidants, i.e., glutathione (GSH), ascorbic acid (AA), cysteine (Cys), tannin (TA), Catechin (C), dopamine (DA), and uric acid (UA) in both buffer and even serum samples. Additionally, the performance of the sensor array was validated with antioxidant mixtures, individual antioxidants with different concentrations, and target antioxidants and interfering substances. In general, the versatile sensor array based on Co-N-C single-atom nanozymes provides an excellent strategy for identifying a variety of antioxidants, which exhibits a broad application prospect in medical diagnosis.