Sensor Detects Bad Breath

Bad breath (or halitosis) can be awkward, but it could also be a warning sign for dental health issues. Usually, people do not smell their own breath, and asking someone else can be embarrassing. The level of halitosis can generally be determined by measuring the H₂S concentration in a patient’s exhaled breath. Some devices can measure small amounts of hydrogen sulfide, but they require exhaled air to be collected and tested in a lab, which is not feasible for consumers. Thus, other selective detection methods for hydrogen sulfide are needed.

Kak Namkoong, Samsung Advanced Institute of Technology, Samsung Electronics Co., Ltd., Suwon-si, Republic of Korea, Il-Doo Kim, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Republic of Korea, and colleagues have constructed a portable device for the direct, reliable, and rapid detection of H₂S in human breath without the need for collection or filtering equipment. Some metal oxides can react with sulfur-containing gases, resulting in a change in their electrical conductivity. Pairing these metal oxides with other metal-based catalysts can improve both sensitivity and selectivity. The team co-functionalized WO₃ nanofibers with different amounts of an alkaline metal (Na) and a noble metal (Pt) as catalysts by adding sodium chloride (NaCl) and Pt nanoparticles (NPs) during the nanofiber production, followed by an electrospinning process.

The team drop-coated gold electrodes with the resulting nanofibers to obtain a gas sensor. A composite made using equal parts of Na and Pt had the largest reactivity to hydrogen sulfide, which led to a quick and large decrease in electrical resistance that can be measured. Although the nanofiber also reacted with other sulfur-containing gases, it was most sensitive to hydrogen sulfide, creating a response 9.5 and 2.7 times greater than for, e.g., dimethyl sulfide or methyl mercaptan, respectively.

The team combined the gas sensor with commercial humidity, temperature, and pressure sensors into a small prototype device. The device correctly identified H₂S-based bad breath with an accuracy of 86 % when people exhaled directly onto it, using gas chromatography as a reference. According to the team, the sensor could be incorporated into very small devices for the quick and easy self-diagnosis of bad breath.