A novel electrochemical immunosensor based on SnS/NiCo metal-organic frameworks loaded with gold nanoparticles for cortisol detection.

In this work, a label-free electrochemical immunosensor using tin sulfide/nickel cobalt metal-organic frameworks (SnS/NiCo MOFs) was established for the sensitive detection of cortisol. First, SnS/NiCo MOFs were synthesized by doping SnS with NiCo MOF nanocubes by a hydrothermal method. Then, gold nanoparticles (AuNPs) were grown in situ on SnS/NiCo MOFs for electrochemical detection. The use of SnS/NiCo MOFs promoted the electron transfer rate of AuNPs and enhanced the electrochemical sensing performance of AuNPs@SnS/NiCo MOFs-modified electrodes. The large specific surface area of AuNPs@SnS/NiCo MOFs provides more active sites for antibody loading. After the prepared immunosensor was incubated with the target analyte, cortisol, the electron transfer impedance increased and the amperometric response decreased, thus establishing a highly sensitive immunosensing method. The sensor had a linear range of 100 fg/mL to 100 ng/mL and a low detection limit of 29 fg/mL. The sensor showed good accuracy and practicability and could be used for the determination of cortisol in saliva.