Iridium Oxide-modified Reference Screen-printed Electrodes for Point-of-Care Portable Electrochemical Cortisol Detection

Cortisol is a well-known stress biomarker. This study focuses on using electrochemical
immuno-sensing to measure the concentration of cortisol selectively and sensitively in
artificial sample. Anti-cortisol antibody has been immobilised on polycrystalline Au
electrodes via strong covalent thiol bonds, fabricating an electrochemical bioimmunosensor
for cortisol detection. IrOx was anodically electrodeposited as a
reference electrode on a commercial screen-printed electrode. Electrochemical
impedance spectrometry (EIS) studies were used to correlate the electrochemical
response to cortisol concentration and the induced changes in charge transfer
resistance (Rct). A linear relationship between the Rct and the logarithm of cortisol
concentrations were found in the concentrations ranging from 1 ng/mL to 1 mg/mL. The
modification of reference electrode with iridium oxide has greatly improved the
reproducibility of the screen-printed electrode. The sensing system can provide a
reliable and sensitive detection approach for cortisol measurements.