Co(OH)₂/MXene-Ti₃C₂ nanocomposites with triple-enzyme mimic activities as hydrogel sensing platform for on-site...

Novel Co(OH)₂/MXene-Ti₃C₂ 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-Ti₃C₂ 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-Ti₃C₂ nanocomposites were investigated. Subsequently, hypoxanthine (Hx) was catalyzed by xanthine oxidase (XOD) to form H₂O₂, which reacts with 3,3',5,5'-tetramethyl-benzidine (TMB) in the presence of Co(OH)₂/MXene-Ti₃C₂ 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-Ti₃C₂ nanocomposites hydrogel-assisted colorimetric biosensor is cost-effective, sensitive, and selective and has excellent application prospects for in-the-field determination of Hx.