RESUMO
Cortisol, a steroid hormone mostly known as "the stress hormone," plays many essential functions in humans due its involvement in several metabolic pathways. It is well-known that cortisol dysregulation is implied in evolution and progression of several chronic pathologies, including cardiac diseases such as heart failure (HF). However, although several sensors have been proposed to date for the determination of cortisol, none of them has been designed for its determination in saliva in order to monitor HF progression. In this work, a silicon nitride based Immuno field-effect transistor (ImmunoFET) has been proposed to quantify salivary cortisol for HF monitoring. Sensitive biological element was represented by anti-cortisol antibody bound onto the ISFET gate via 11-triethoxysilyl undecanal (TESUD) by vapor-phase method. Potentiometric and electrochemical impedance spectroscopy (EIS) measurements were carried out for preliminary investigations on device responsiveness. Subsequently, a more sensitive detection was obtained using electrochemical EIS. The proposed device has proven to have a linear response (R2 always >0.99), to be sensitive (with a limit of detection, LoD, of 0.005 ± 0.002 ng/mL), selective in case of other HF biomarkers (e.g. N-terminal pro B-type natriuretic peptide (NT-proBNP), tumor necrosis factor-alpha (TNF-α), and interleukin 10 (IL-10)), and accurate in cortisol quantification in saliva sample by performing the standard addition method.