Ultra-sensitive paper-based biosensor for cortisol sensing in human saliva with electrical impedance analyzer

Cortisol, a hormone commonly released upon increased stress level, is a biomarker for numerous diseases and plays an important role in the regulation of various physiological processes. Normally a cortisol level is elevated in oral saliva during the time of anxiety and depression. A portable biosensor device could provide an interesting digital instrument to the patients and people who desire precautionary onsite cortisol diagnosis without visiting psychiatrists and/or physicians. We have developed disposable paper-based biosensor chip to monitor cortisol with a wide range of detection (RoD) from 1pg/mL to 10ng/mL with regression R²=0.9777. Ultra-sensitivity of the sensor with limit of detection (LoD) of 1 pg/mL has been achieved using nanocomposite of graphene nanoplatelet and diblock-co-polymer (poly(styrene)-block-poly(acrylic acid)) (PS-b-PAA) coated on filter paper followed by deposition of micro-Au electrodes. Standard cortisol in aqueous solution and human saliva samples were successfully tested by interfacing the sensor chip with programmable handheld impedance based analyzer. Results are finally compared with the standard ELISA and are in good agreement with R²=0.9386. We anticipate that this handheld electrochemical sensing technology has promising application to monitor psychological stress in POC setting.