Co(OH) 2 /MXene-Ti 3 C 2 nanocomposites with triple-enzyme mimic activities as hydrogel sensing platform for on-site detection of hypoxanthine

Novel Co(OH) 2 /MXene-Ti 3 C 2 nanocomposites with oxidase (OXD)-mimic, peroxidase (POD)-mimic, and catalase (CAT)-mimic activities were prepared by a simple two-step method. The Co(OH) 2 /MXene-Ti 3 C 2 nanocomposites with triple-enzyme mimic activities were embedded into sodium alginate (SA) gels for the first time to fabricate a target-responsive hydrogel-assisted assay. The catalytic mechanism and steady-state kinetics of Co(OH) 2 /MXene-Ti 3 C 2 nanocomposites were investigated. Subsequently, hypoxanthine (Hx) was catalyzed by xanthine oxidase (XOD) to form H 2 O 2 , which reacts with 3,3′,5,5′-tetramethyl-benzidine (TMB) in the presence of Co(OH) 2 /MXene-Ti 3 C 2 nanocomposites to form a blue oxide (ox-TMB) in the hydrogel. The visible color change of the hydrogel with the increase of Hx concentration can be recognized through a smartphone App to transfer the red (R), green (G), and blue (B) values for the quantitative determination of Hx, with a detection range from 5 to 250 μM, and detection limit of 0.2 μM. The method was applied to the determination of Hx content in different aquatic products. The spiked recoveries of the aquatic products were from 94.1 to 106.4%, and the relative standard deviations (RSD) were less than 5.4%. Our results show that the Co(OH) 2 /MXene-Ti 3 C 2 nanocomposites hydrogel-assisted colorimetric biosensor is cost-effective, sensitive, and selective and has excellent application prospects for in-the-field determination of Hx. Graphical abstract