Cobalt-doped MnO2-decorated N-CNT hybrid electrodes for sensitive and selective electrochemical detection of tryptophan in biological matrices.

This work reports the development of a robust electrochemical sensing interface for the selective and sensitive quantification of tryptophan (Trp). The sensor architecture was constructed from a cobalt-doped manganese dioxide framework anchored onto nitrogen-doped carbon nanotubes (Co@MnO₂/N-CNTs). The 3-D composite, synthesized via a straightforward hydrothermal strategy, exhibited a highly porous and uniformly distributed morphology with intimate interfacial coupling between the components. Comprehensive structural and compositional analyses using SEM, HRTEM, and XPS confirmed the successful formation of the Co@MnO₂/N-CNT hybrid. The combination of redox-active Co, high-surface-area MnO2, and conductive N-CNTs improved the movement of electrons and made the sensor work better for detecting Trp. Electrochemical studies demonstrated excellent catalytic performance toward Trp oxidation, with a wide linear range of 0.5-300 μM and a low limit of detection 0.062 μM (S/N = 3). The sensor displayed high sensitivity, repeatability (RSD < 2.7%), and reproducibility (RSD < 4.1%). Furthermore, the developed sensor exhibited excellent anti-interference performance and was effectively employed for the quantification of Trp in human plasma samples, achieving satisfactory recovery rates between 93.0% and 105.5%. This work provides a promising approach for the design of multifunctional nanomaterials for bioanalytical applications.