Integrated Hydrogel Biosensor and Wireless Readout for Real-Time Salivary Cortisol Monitoring

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PROJECT SUMMARY Measurement of cortisol is a reliable approach to diagnosing psychological stress, as well as chronic diseases related to cortisol disorders. The hormone cortisol is released in the body during stressed and agitated status and has a high correlation with post-traumatic stress disorders and other related psychological diseases. Salivary cortisol level is an excellent index of the unbound plasma free cortisol. Cortisol level typically fluctuates throughout the day, and diagnosis of cortisol-related diseases and assessment of psychological stress level cannot rely on a single measurement; mapping cortisol levels over time through is necessary to identify trends indicative of psychological stress onset or diagnosis of disease. Current cortisol measurement techniques are lab-based and episodic, and cannot be used for continuous monitoring. We propose to create a wearable, in- mouth sensor that supports ambulatory monitoring of salivary cortisol in real time. The device leverages a new biosensor architecture consisting of a bioresponsive hydrogel and embedded conductive nanowire networks. The proposed biosensor is expected to achieve a detection limit of 0.2 nM with a response time of less than 5 minutes, as required for real-time detection applications. The proposed strategy enables sensitive, specific, and reversible detection of neutrally-charged cortisol without the addition of chemical reporters or redox reagents for signal transduction. Such capability overcomes the limits encountered in charge-based transistor/nanowire biosensors or electrochemical techniques. Integration with a custom amperometric read-out integrated circuit (IC) will provide high-resolution, quantitative sensor measurement in a mm-scale microchip and the addition of a Bluetooth low energy (BLE) wireless transceiver will provide real-time data transmission to a smartphone for processing, archiving, and upload to the cloud.