Humic acid mediated self-signal molecularly imprinted electrochemical sensor for cortisol detection

Generally, it is essential to externally introduce redox probes for cortisol detection through molecularly imprinted electrochemical sensor. However, this approach complicates the detection process, hinders real-time monitoring and may cause significant interference during body fluid analysis. To address the issue, we innovatively proposed a self-signal sensor based on humic acid (HA)-mediated conductive redox nanoprobe. Amphiphilic HA can effectively coat multi-walled carbon nanotubes (MWCNT) through π-π interactions, providing exceptional dispersibility while retained conductivity. Additionally, due to its colloidal characteristics, the HA coated MWCNT exhibited remarkable adsorption capacity towards various types of redox molecules, particularly cationic redox species, thus acquiring a kind of conductive redox nanoprobe in a facile way. The nanoprobe could serve as a bottom layer to prepare an electrochemical sensor in combination with cortisol-imprinted polydopamine as the upper layer. Finally, a self-signal electrochemical sensor for cortisol was successfully fabricated, achieving a detection limit of 0.72 × 10 −9  M, a wide detection range from 1 nM to 1 mM and good recovery. Overall, we believe the HA-mediated strategy proposed in this study could inspire more innovation in the field of self-signal sensing.