Inkjet-printed CMOS-integrated graphene metal oxide sensors for breath analysis

Early diagnosis in exhaled breath is a key technology for next-generation personal healthcare monitoring. Current chemiresistive sensors, primarily based on metal oxide (MOx) thin films, have limited applicability in such portable systems due to their high power consumption, long recovery time, poor device-to-device consistency, and baseline drifts. To address these challenges for ammonia (NH3) detection in exhaled breath, a critical biomarker for a variety of kidney and liver problems, we present a formulation of a graphene-MOx functional ink-based sensing platform. We integrate our sensing layer directly onto miniaturized CMOS microhotplates (IMP) via inkjet printing, potentially enabling scalability and device-to-device performance repeatability. Using stage-by-stage temporal analysis, and a temperature-pulsed modulation (TM) strategy, we achieve ultrahigh responsivity (1500% at 10 ppm pure NH3), fast response and recovery time (28 and 43 s), ultralow power consumption (similar to 6 mW), negligible baseline drift (<0.67%), excellent cross-device and cross-cycle consistency (<0.5% and <0.41% variation in responsivity) and long-term stability (<1% variation) in our graphene-zinc oxide (ZnO) formulation, outperforming conventional MOx chemiresistive sensors. We further mitigate the effect of humidity through our measurement protocols, while interference from acetone is compensated through the parallel deployment of an additional inkjet printed graphene-tungsten oxide (WO3) device as part of the sensor array. Our dual graphene-MOx formulations and their integration with ultralow power CMOS through inkjet printing represent a significant step towards reliable and portable multi-analyte breath diagnostics.