Printable transistors for wearable sweat sensing

Human performance monitoring (HPM) devices for sweat sensing in both civilian and military uses necessitate chemical sensors with low limits of detection, rapid read out times, and ultra-low volumes. Electronic and electrochemical sensing mechanisms for biomarker identification and quantification are attractive for overall ease of use, including robust, portable, fast readout, and simple operation. Transistors have the high signal gain required to sense low concentrations (μM to pM) at low volumes (μL to nL) in real-time (<1 minute), metrics not achievable by benchtop analytical techniques. Two main challenges currently prohibit the realization of transistor-based biosensors: i) the need for printed devices for low-cost, disposable sensors; and ii) the need to overcome diminished sensitivity in high ionic strength solutions. In this proof-of-concept work, we demonstrate organic electrochemical transistors (OECT) as a promising low cost, printable device platform for electrochemical detection of biomarkers in high ionic strength environments. This work focuses on how the materials choice and functionality impacts the electrochemical and sensor and transducer performance and determining the feasibility of reducing the size of the sensor to nanoliter volume detection. Initial studies target dopamine. Detection limits for simple electrochemical approaches using platinum or glassy carbon electrodes remain relatively high (~ 1-10 ng/mL or 50 nM). Using an OECT, we demonstrate an initial detection level of dopamine at ~ 10 pg/mL achieved without any selective binding modifications to the gate electrode at gate voltages below 1 V.