Saliva-Sensing Dental Floss: An Innovative Tool for Assessing Stress via On-Demand Salivary Cortisol Measurement with Molecularly Imprinted Polymer and Thread Microfluidics Integration

On-demand dental-floss-based point-of-care platform is developed for the noninvasive and real-time quantification of salivary cortisol utilizing redox-molecule embedded molecularly imprinted polymer structures and thread microfluidics. Herein, we explore the high-surface-area graphene-based electrode substrate for electrochemically synthesizing selective cortisol MIPs and integrate it with thread microfluidics to build a highly sensitive cortisol-sensing platform for stress monitoring. This platform uses flossing to collect and transport saliva to a flexible electrochemical sensor via capillary microfluidics, where cortisol, a stress biomarker, is measured. This strategy allowed us to detect cortisol as low as 0.048 pg mL-1 in real-time with a detection range of 0.10-10,000 pg mL-1 (R2 = 0.9916). The saliva-sensing dental floss provides results within 11-12 min. The thread-based microfluidic design minimizes interference and ensures consistent repeatability when testing both artificial and actual human saliva samples, yielding 98.64-102.4% recoveries with a relative standard deviation of 5.01%, demonstrating high accuracy and precision. For the human saliva sample (as part of the stress study), the platform showed a high correlation (r = 0.9910) against conventional ELISA assays. Combined with a wireless readout, this saliva floss offers a convenient way to monitor daily stress levels. It can be extended to detect other critical salivary biomarkers with high sensitivity and selectivity in complex environments.