Tailoring the active sites in cobalt@nitrogen-doped carbon nanofibers for colorimetric and electrochemical assay of hydrogen peroxide

Regulating the valence states and composition of a catalyst surface allows a precise control of the electronic structure, enabling enhanced catalytic activity and improved detection sensitivity of sensors. Herein, an accurate quantification of hydrogen peroxide (H 2 O 2 ) has been achieved using a colorimetric and electrochemical sensing platform based on the catalytic activity of cobalt@nitrogen-doped carbon (Co@NC) nanocatalysts in acidic (pH 3.6) and neutral (pH 7.4) environment. A series of Co@NC samples were synthesized by electrospinning and subsequent calcination, where Co@NC-3 with a high Co 3+ /Co 2+ potential (1.92 V) facilitates the direct oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) under acidic conditions. In the presence of H 2 O 2 , TMB oxidation was inhibited due to cyclic reactions involving oxidized TMB and H 2 O 2 on the Co@NC-3 surface, with an associated loss of the blue coloration that is detectable by the naked eye and is quantified by UV–vis spectrometry with a detection limit of 40.5 μM. Moreover, the Co 3+ /Co 2+ redox cycle on the surface of the Co@NC-3 modified glassy carbon electrode resulted in enhanced electrocatalytic H 2 O 2 reduction in a neutral phosphate buffered saline, where the amperometric currents exhibited a linear response to H 2 O 2 concentration over the 0.05–27.6 mM range with a detection limit of 3.16 μM, and an enhanced sensor sensitivity (991 μA mM −1 cm −2 ). The proposed Co@NC-3 detection system has been applied to real-time measure the concentration of H 2 O 2 released from HeLa cells. The colorimetric and electrochemical sensing analysis delivers reliable detection efficiency with important practical applications in clinical analysis and diagnosis.