Abstract
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 ({{rm{NH}}}_{3}) 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 (μHP) 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 {{rm{NH}}}_{3}), fast response and recovery time (28 and 43 s), ultralow power consumption (~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 ({{rm{WO}}}_{3}) 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.
Highlights
Increasing awareness of personal health conditions is rapidly promoting the development of point-of-care technologies for early diagnosis of diseases
By harnessing the location-specific, uniform material deposition through our inkjet technology, a sensor array comprising a variety of graphene–metal oxides (MOx) nanomaterials systems could be fabricated in a single multi-μHP CMOS die.[65]
We have developed an inkjet-printed graphene–MOx-based sensor system that has been integrated onto miniaturized CMOS compatible platforms to selectively measure NH3, a biomarker of kidney and liver problems, with fast and accurate performance
Summary
Increasing awareness of personal health conditions is rapidly promoting the development of point-of-care technologies for early diagnosis of diseases. After %1 s, the diameter of the droplet increases at a reduced speed, suggesting the contribution of Marangoni flow to suppress coffee-ring effect.[37,38] In addition, no sudden perturbation in the contact angle is observed during the drying process These indicate a good wetting of the substrate and uniformly deposited graphene/ ZnO after ink drying. We assess the cross-analyte selectivity with ethanol, acetone, and carbon monoxide (CO) which are the common interfering gas species in exhaled breath These species are measured at 2 ppm, which are above maximum levels a healthy human would exhale.[61,62] The cross-selectivity data in Fig. 5b indicates a relatively small amount of interference from ethanol and CO (0.91% and 0.75%, respectively) while the effect of acetone is more prominent (2.12%).
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