5,10,15,20-tetrakis (4-carboxylphenyl) porphyrin functionalized NiCo2S4 yolk-shell nanospheres: Excellent peroxidase-like activity, catalytic mechanism and fast cascade colorimetric biosensor for cholesterol

5,10,15,20-tetrakis (4-carboxylphenyl) porphyrin functionalized NiCo 2 S 4 yolk-shell nanospheres (Por-NiCo 2 S 4 ) were fabricated by a facile and efficient solvothermal strategy and demonstrated to possess excellent peroxidase-like activity. Compared with pure NiCo 2 S 4 nanospheres, Por-NiCo 2 S 4 exhibits the superior peroxidase activity, which was evaluated by the fast oxidation of 3,3′,5,5′-tetramethylbenzidine (a chromogenic substrate, TMB) by H 2 O 2 to form the blue product (oxTMB) only in 10 s. The systematic studies including radical scavenger, fluorescence probe, and electrochemical experiments confirm that superoxide free radicals ( O 2 − ) play a key role in catalytic reactions, in addition to the synergistic effect of holes (h + ). Based on the developed peroxidase activity of Por-NiCo 2 S 4 , and combined with cholesterol oxidase (Chox), a fast cascade reaction sensing platform has been constructed to quantitatively determination cholesterol in a wide linear range of 0.1−9.0 mM with the detection limit of 19.36 μM. The Por-NiCo 2 S 4 based colorimetric biosensing platform has been used for determining the levels of total cholesterol in serum samples, indicating Por-NiCo 2 S 4 is expected to be used as the promising materials for fast visual colorimetry in clinical medical detection.