A portable and quantitative detection of xanthine and xanthine oxidase based on cascade enzymatic reactions of Fe3O4@MWCNTs/Hemin

Sensitive and effective detection of xanthine oxidase (XOD) is essential for assessing human health. Herein, a dual-enzyme-based cascaded reaction system was developed for xanthine and xanthine oxidase assay based on the peroxidase (POD)-like catalytic activity of Fe 3 O 4 @MWCNTs/Hemin nanocomposite. The XOD could catalyze xanthine to produce H 2 O 2 , which is subsequently converted by Fe 3 O 4 @MWCNTs/Hemin into hydroxyl radicals (·OH) to oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) to produce a light blue. Notably, it is demonstrated that the modification of MWCNTs and Hemin could significantly enhance the POD-like activity from 9.78 × 10 −8  M s −1 ( V max value of Fe 3 O 4 ) to 23.34 10 −8  M s −1 ( V max value of Fe 3 O 4 @MWCNTs/Hemin), which makes the detection of xanthine oxidase more sensitive. By using the smartphone to capture the colorimetric signal of oxidized TMB (oxTMB), the assay can detect xanthine and XOD as low as 0.250 µM and 0.216 mU mL −1 , respectively. The reliability of the method in human serum suggested satisfactory spiked recoveries in the range of 92.350–105%. This work provided a new insight for Fe 3 O 4 -based nanozyme design and monitoring XOD level in blood. Graphical Abstract