Breath instead of a blood test

Experts advise anyone looking to shed extra kilos to eat less and exercise more. One way is with endurance training, during which the body burns not only carbohydrates such as sugar, but also fat. When exactly the body begins burning fat can now be determined by analysing, for example, biomarkers in the blood or urine. Scientists at ETH Zurich and the University Hospital Zurich have now developed a method for the highly convenient, real-time monitoring of lipolysis by testing a person’s exhalations during exercise.
“When burning fat, the body produces by-products that find their way into the blood,” explains Andreas Güntner, a postdoc in the group of ETH Professor Sotiris Pratsinis. In the pulmonary alveoli, these volatile molecules, acetone, enter the air the person exhaled. Güntner and his colleagues have developed a small gas sensor that measures the presence of this substance.
The researchers tested the functioning of the sensor in volunteers while they exercised. The test subjects completed a one-and-a-half-hour session on a bicycle ergometer with two short breaks. Researchers asked test subjects to blow into a tube that was connected to the acetone sensor at regular intervals.
“We were able to show how acetone concentration in the exhalations varies greatly from person to person,” says Güntner. The measurements taken by the researchers in Zurich showed that lipolysis in some test subjects did only start towards the end of the one-and-a-half-hour training session. In others, the measurements showed they began burning fat much sooner.
Control measurements showed that the new measurement method correlated well with the concentration of the biomarker beta-hydroxybutyrate in the blood of the test subjects. This blood analysis is one of today’s standard methods for monitoring lipolysis.
The sensor uses a chip coated with a porous film of special semiconducting nanoparticles. The particles are tungsten trioxide that researchers have implanted with single atoms of silicon.
The chip used is the size of a 1-cent euro coin, but the researchers' goal is to offer the chip in a manageably sized device.
The scientists plan to continue developing measurement method so that they can eventually market it. They already have a prototype of the instrument. The scientists are also working on developing gas sensors for other medically relevant molecules in exhalations, including ammonia to test kidney function, isoprene to test cholesterol metabolism and various aldehydes for the early detection of lung cancer.