An immunoelectrochemical sensor for salivary cortisol measurement

An immunoelectrochemical sensor based on alkaline phosphatase (AP) enzyme for determination of salivary cortisol concentration is reported. Microfabricated Au electrodes encased in a microfluidic chamber were functionalized to immobilize the cortisol capture antibodies. The reaction product p-nitrophenol (pNP) generated by reacting the AP enzyme attached to the cortisol antigen via detector antibodies with the p-nitrophenyl phosphate (pNPP) solution. pNP was detected as an oxidative peak between 0.9 and 1.1 V (vs. Ag pseudo-reference electrode) using cyclic voltammetry (CV) at room temperature. The magnitude of the peak varies linearly with the cortisol concentration, and was used to quantify the concentration of cortisol in real saliva samples. This immunoelectrochemical detection method accurately measured cortisol in the collected saliva samples achieved to a concentration of 0.76 nmol/L with an incubation time of 10 min. We demonstrate successfully the approach for establishing diurnal cortisol concentration behavior for clinical purposes with numerous advantages: a much higher throughput capability, significantly lower amounts of the sample, sub-pmol/L range sensitivity, higher resolution at low mass ranges, and easy to use.