Method for instability compensation and detection of ammonium in sweat via conformal electrolyte-gated field-effect transistors

The research interest towards wearable sensing devices has rapidly increased in recent years, due to the importance that personalized healthcare monitoring has gained in our everyday life. In this context, electrolyte-gated field-effect transistors (EG-FETs) for sensing applications are receiving increasing attention, owing to their intrinsic signal amplification and low operating voltages. Here, we report carbon nanotube EG-FETs (EG-CNTFET)-based sensors, functionalized with a nonactin-based ion-selective membrane for operation in an aqueous environment. In particular, we show a facile data analysis protocol to obtain a highly stable baseline response (i.e., 60 min) required for sensing applications. We successfully employ our EG-CNTFET-based sensors for the detection of ammonium (NH4+) in water, as well as in complex artificial sweat medium. Furthermore, we show how conditioning the membranes in artificial sweat significantly reduces the variability of the sensors. We achieve sensitivity as high as 1.797 μA/decade, with a linear range of the sensors entirely covering the physiological concentrations of NH4+ in sweat. We also show how increasing the nonactin concentration (from 0.2 to 1% wt) improves the sensors’ sensitivity by a factor of 2.