Human stress monitoring through an organic cotton-fiber biosensor

Selective detection of bioanalytes in physiological fluids, such as blood, sweat or saliva, by means of low-cost and non-invasive devices, is of crucial importance to improve diagnosis and prevention in healthcare. To be really useful in everyday life a sensing system needs to be handy, non-invasive, easy to read and possibly wearable. Only a sensor that satisfies these requirements could be eligible for applications in healthcare and physiological condition monitoring. Herein an organic electrochemical transistor has been investigated as a simple, low-cost and e-textile biosensor, fully integrated on a single cotton yarn. The biosensor has been used for real-time detection of adrenaline, selectively compared to the saline content in human physiological fluids. The sensing mechanism is based on the oxidation of adrenaline at the Pt-gate electrode surface, with the formation of adrenaline-quinone and adrenochrome. Two independent organic electrochemical transistors, characterized by different gate-electrode materials, detect saline and adrenaline concentrations, respectively, in real human sweat. Measurements performed in real-time mode show the complete independence of adrenaline detection from NaCl and, hence, guarantee the simultaneous monitoring of both concentrations. The oxidation of adrenaline has been studied by means of absorption spectroscopy in air, with either silver or platinum working electrodes. Our results confirm that the oxidation reaction driven by the Pt-electrode leads to the formation of adrenochrome, while with the Ag-electrode the oxidation is similar to the spontaneous one occurring in air. The cotton-based biosensor shows the possibility of monitoring human performances (hydration and stress) in situ and using a non-invasive approach, opening new unexplored opportunities in healthcare, fitness and work safety.