With every breath, we intake and expel a complex mix of chemicals. The quality of the air that we inhale depends on our immediate environment, but what we exhale is based on the biochemical processes occurring in our bodies. Thus, our exhalation can be used as a health indicator, and should be especially sensitive to the state of our lungs. Over the years, scientists across multiple disciplines have worked on ways to use exhaled breath for detecting diseases and measuring chemical changes. The breathalyzer, which estimates blood alcohol content, is a popular example of success in the field; the method is simple, noninvasive, portable, and affordable.

Diagnosing diseases like lung cancer has proven to be more difficult. So far, all the methods based on examining the expelled breath require pretreatment of the air, which adds time, money, and complexity to the process. That has made current techniques too cumbersome for commercial use. By employing recent developments in nanotechnology, however, researchers from the Israel Institute of Technology have overcome the need to pre-treat exhaled breath for analysis.

The new work appears in the current issue of Nature Nanotechnology. Hossam Haick, the principal researcher, and his team collected breath samples from 56 healthy volunteers and 40 people who had been diagnosed with lung cancer, but have not received treatment yet. They analyzed the samples and identified 33 biomarkers, chemicals that were present at significantly distinct levels in the lung cancer patients.

The team devised a sensor system made from nine chemiresistors that could respond to the biomarkers by altering their electrical properties. The chemiresistors were assembled from gold nanoparticles that are 5nm in diameter and functionalized with different organic compounds that allowed them to sense the biomarkers.

When the researchers exposed the sensors to untreated breath samples, they obtained readings that clearly distinguished between the exhalations of healthy patients and those with lung cancer. Regardless of the humidity of the breath, the gender of its source, or their smoking habits, the sensors were able to detect the lung cancer biomarkers. The sensors were also capable of working with a wide range of concentrations, and the process was reversible, meaning the nanoparticles can be reused.

The researchers point out that they need to test their sensors on "a wider population of volunteers to thoroughly probe the influence of diet, alcohol consumption, metabolic state, and genetics.” Those experiments are already underway.

The authors neglect to mention if they will try to figure out how sensitive their sensors are to different stages of lung cancer. All of the cancer subjects in this study had primary stage-3 or stage-4 lung cancer, so the disease had already progressed significantly. It would be important to know if their sensors are useful in stages 1 and 2 of the disease, as being able to diagnose patients in earlier stages would vastly improve their chances of survival.

Haick and his colleagues have shown that it is possible to obtain reliable lung cancer diagnoses from analyzing the exhaled breath using portable equipment that doesn't require any pretreatment of the sample. That is a significant step forward, but as mentioned above, there is definitely room for further development.

Nature Nanotechnology, 2009. DOI: 10.1038/NNANO.2009.235

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