In a study in ACS Sensors, researchers report developing ultrasensitive, nanoscale sensors that in small-scale tests distinguished a key change in the chemistry of the breath of people with lung cancer.
People breathe out many gases, such as water vapor and carbon dioxide, as well as other airborne compounds. Researchers have determined that declines in one exhaled chemical — isoprene — can indicate the presence of lung cancer. However, to detect such small shifts, a sensor would need to be highly sensitive, capable of detecting isoprene levels in the parts-per-billion (ppb) range. It would also need to differentiate isoprene from other volatile chemicals and withstand breath’s natural humidity. Previous attempts to engineer gas sensors with characteristics like these have focused on metal oxides, including one particularly promising compound made with indium oxide. A team led by Pingwei Liu and Qingyue Wang set out to refine indium oxide-based sensors to detect isoprene at the level at which it naturally occurs in breath.
The researchers developed a series of indium(III) oxide (In2O3)-based nanoflake sensors. In experiments, they found one type, which they called Pt@InNiOx for the platinum (Pt), indium (In) and nickel (Ni) it contains, performed best. These Pt@InNiOx sensors:
- Detected isoprene levels as low as 2 ppb, a sensitivity that far surpassed earlier sensors.
- Responded to isoprene more than other volatile compounds commonly found in breath.
- Performed consistently during nine simulated uses.
More importantly, the authors' real-time analysis of the nanoflakes' structure and electrochemical properties revealed that Pt nanoclusters uniformly anchored on the nanoflakes catalyzed the activation of isoprene sensing, leading to the ultrasensitive performance.
Finally, to showcase the potential medical use of these sensors, the researchers incorporated the Pt@InNiOx nanoflakes into a portable sensing device. Into this device they introduced breath collected earlier from 13 people, five of whom had lung cancer. The device detected isoprene levels lower than 40 ppb in samples from participants with cancer and more than 60 ppb from cancer-free participants.
