Researchers from Penn State have developed a sensor that can rapidly detect acetone in breath samples (1). The sensor could serve as a "surrogate" biomarker for diabetes – enabling early diagnostics and treatment evaluations.
“We have long been dreaming of directly measuring glucose from the breath or skin perspiration for diabetes patients to easily manage the condition since we published our first wearable gas sensor work” (2), says Huanyu “Larry” Cheng, Associate Professor and Dorothy Quiggle Career Development Professor in Engineering, who led the research group at Penn. “However, it has been extremely challenging due to the low concentration.”
This led the researchers to explore acetone – a byproduct of burning fat – which at levels above a threshold of about 1.8 parts per million in exhaled breath indicate diabetes.
When acetone gas is adsorped onto the sensor surface, the band structure of the sensing material changes, resulting in varied electrical resistance that correlates with the concentration of the acetone.
The sensor is based on a zinc oxide (ZnO)/laser-induced graphene (LIG) composite with heterostructures on interdigitated electrodes, prepared by one-step laser direct writing and simple drop casting. In lab tests, the sensor exhibited a “large” response of −24 percent to 1 ppm acetone, a “fast” response recovery time of 21/23 s, and an “ultralow” experimentally demonstrated (or theoretical) detection limit of 4 ppb (or 334 ppt).
Metal oxide-based gas sensors for acetone have been developed previously, but they often require high operating temperatures – impractical for clinical use. Gas sensors based on carbon nanomaterials, on the other hand, have a large specific surface area, which enables them to work at room temperature – and could be combined with metal oxides to improve sensing performance. But there are challenges here too.
“The lack of sufficient active functional groups and relatively weak chemical interactions with acetone molecules through van der Waals forces, or weak hydrogen bonding, lead to limited gas adsorption and weak electron transfer, and thus a low sensitivity,” says Cheng. This led the researchers to consider ZnO nanospheres with large adsorption sites and gas diffusion channels. “We combine ZnO with 3D porous graphene foams that exhibit high electron mobility and a large specific surface area to form heterojunctions and provide additional adsorption sites for accelerated response/recovery speed and lower gas detection temperature.”
Another key challenge the researchers faced was humidity: water molecules in breath can compete with the target gas at the sensor surface. The solution? A molecular sieve coating layer to block water molecules, while allowing the acetone to pass through.
Cheng and his colleagues are now considering other nanocomposites, which could open the door to other applications. “The ZnO/LIG nanocomposites provide highly selective detection of acetone, but replacing ZnO with other materials can result in different LIG nanocomposites,” he says. “Examples from the literature include: tungsten trioxide/LIG to detect hydrogen sulfide (for halitosis or even gut health (3), In2O3–ZnO/LIG to detect methane (4), PANI/LIG to detect ammonia (5), molecularly imprinted polymers/LIG to detect vitamin B6 and glucose (6), among others.”
For their ZnO/LIG acetone sensor, the next step is to make improvements so that it can be used directly under the nose or attached to the inside of a mask. “We also plan to investigate how an acetone-detecting breath sensor could be used to optimize health initiatives (e.g., diet and exercise) for individuals,” says Cheng. “We aim to provide non-invasive sensors to continuously monitor health-relevant biomarkers over a long time across a large population for early diagnosis of different disease conditions (which could be further combined with timely treatment options in a closed-loop system) and treatment evaluation.”
Newsletters
Receive the latest analytical science news, personalities, education, and career development – weekly to your inbox.
