Accurate cortisol detection in human saliva by an extended-gate-type organic transistor functionalized with a molecularly imprinted polymer

Salivary cortisol, a stress hormone is used as a reliable biomarker to indicate a psychological disorders. Accounting for the requirement of highly sensitive detection at nM levels, we have employed a molecularly imprinted polymer (MIP) as the detection scaffold for salivary cortisol in this study. The electrochemically deposited MIP possesses a three-dimensional recognition network through hydrogen bonds constructed by five monomers (i.e., 1,2-diaminobenzene) against one cortisol. In this regard, an organic field-effect transistor (OFET) functionalized with MIP can be used as a chemical sensor for sensitive and selective detection, owing to its inherent amplification ability. An extended-gate-type OFET functionalized with the MIP (MIP-OFET) has exhibited appropriate detectability against cortisol with a limit of detection of 0.72 μg/L (i.e., 2.0 nM), implying the applicability of the MIP-OFET to the quantification of salivary cortisol. Moreover, the results of a selectivity test against similar structural steroids (i.e., progesterone and prednisolone) and interferents in human saliva (i.e., uric acid, creatinine, glucose, and lactic acid) revealed the discriminatory power of MIP-OFET. Finally, the demonstration of a spike-and-recovery test for salivary cortisol in non-diluted human saliva has clarified the possibility of using MIP-OFET to diagnose of salivary cortisol levels because of its accurate recovery rate (102 −110%).