Enhanced Peroxidase-like Activity of Mo⁶⁺-Doped Co₃O₄ Nanotubes for Ultrasensitive and Colorimetric l-Cysteine Detection

Doping with transition metal ions has been regarded as one of the most effective means to optimize the catalytic efficiency of metal oxides. In this work, a general approach for the fabrication of Mo6+-doped Co3O4 (Mo–Co3O4) nanotubes for peroxidase mimicking has been demonstrated via an electrospinning method combined with a calcination process. The prepared Mo–Co3O4 nanotubes exhibited a higher peroxidase-like catalytic activity than pure Co3O4 nanotubes, and the highest catalytic activity is achieved when the molar fraction of Mo is 2.0%. The catalytic kinetic of Mo–Co3O4 nanotubes follows a typical Michaelis–Menten mechanism, representing a strong affinity to H2O2 and 3,3′,5,5′-tetramethylbenzidine (TMB) substrates. Because of the high catalytic efficiency of the Mo–Co3O4 nanotubes, we have developed a facile and efficient strategy for the sensitive colorimetric determination of l-cysteine with a low detection limit of 24.2 nM. This detection limit is superior to many previous reported enzyme-like detection systems. Furthermore, a favorable selectivity toward the determination of l-cysteine based on this approach is also achieved, showing bright prospects in environmental monitoring and biomedical analysis.