In the future, the procedure of blowing into the tube will not just be used by police checking for alcohol intoxication, but it will also be applied for testing the condition of athletes and for people wanting to lose that extra bit of weight. ETH Researchers have developed a sensor that allows carrying out measurements when the body begins to burn fat with a convenient breathalyzer.
Sensitive measurement techniques allow over 800 molecules involved in human metabolism to be detected in a person’s exhalations. One of these molecules is acetone. (Visualisations: Güntner et al. J Mater Chem B 2016, 4: 5358. Published by the Royal Society of Chemistry)
According to experts, anyone looking to shed extra kilos must eat less and exercise more. One method is through endurance training, during which the body burns not just carbohydrates such as sugar, but also burns fat. It is now possible to determine when exactly the body starts burning fat by analyzing, for instance, biomarkers in the urine or blood. Scientists at ETH Zurich and the University Hospital Zurich have recently developed a method for the highly convenient, real-time monitoring of lipolysis by testing an individual’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 molecules – particularly the volatile ones – enter the air exhaled by the individual.
Acetone is considered to be the most volatile of these lipid metabolites. Güntner and his colleagues have created a small gas sensor capable of measuring the exisitence of this substance. When compared to previous sensors, this sensor is much more sensitive and can detect a single acetone molecule in hundred million molecules. It also has the potential to measure acetone entirely, so that the measurement is not affected by the more than 800 other known volatile components in exhalations.
Major individual differences
In collaboration with pulmonary specialists at the University Hospital Zurich headed by Malcolm Kohler, Professor and Director of the Department of Pulmonology, the Researchers tested the working of the sensor in volunteers while they were exercising. A one-and-a-half-hour session on a bicycle ergometer was completed by the test subjects with two short breaks. The test subjects were asked to blow into a tube that was attached to the acetone sensor at steady intervals.
We were able to show how the acetone concentration in the exhalations varies greatly from person to person.
Andreas Güntner, Postdoctoral Fellow, ETH Zurich
Scientific opinion used to state that athletes only start burning fat after a specific period of physical exertion and on reaching a particular heart rate, but this view has presently been outdated. The measurements taken by the Researchers in Zurich revealed that lipolysis in some test subjects actually started only towards the end of the one-and-a-half-hour training session. In the other volunteers, the measurements revealed that their bodies started to burn fat much sooner.
Control measurements demonstrated that the new measurement method linked well with the concentration of the biomarker beta-hydroxybutyrate in the blood of the test subjects. This blood analysis is considered to be one of the standard methods presently used for monitoring lipolysis.
Interaction with nanoparticles
A chip coated with a porous film of special semiconducting nanoparticles is used by the sensor developed by the Scientists. The particles include tungsten trioxide that has been implanted by the Researchers with single atoms of silicon.
Development of the chip commenced seven years ago when ETH Professor Pratsinis and his colleagues studied that tungsten trioxide nanoparticles interact with acetone when the atoms of the nanoparticles are aligned in a particular crystalline structure. The interaction results in a decrease of the electrical resistance of the chip coated with the nanoparticles, and then it is possible to measure this phenomenon.
The idea originally was to make use of the chip in order to diagnose diabetes, since the exhaled breath of patients with untreated type 1 diabetes comprises of high concentrations of acetone. However, since then, the Scientists have demonstrated that the sensor is in fact sensitive enough for detecting the extremely low acetone concentrations in an individual’s exhalations during exercise.
In this study, the chip that is used is the size of a 1-cent euro coin, however the Researchers are working to improve the measurement technology so that it will be possible with chips that are much smaller. The aim here is to offer the chip in a device that is manageably sized.
This would allow athletes and people who want to lose weight to check for themselves when their bodies begin to burn fat so that they can optimise their training regimen.
Andreas Güntner , Postdoctoral Fellow , ETH Zurich
Small, cheap and yet greatly sensitive
Highly sensitive acetone measurements were previously possible with other instruments, for example mass spectrometers, which are known to be large laboratory devices that cost several hundred thousand Swiss francs. The Researchers make use of these instruments in the present study in order to prove their measurements. Portable acetone breath tests also existed earlier, but it is possible to use them only once and these tests take several minutes before they reveal the results.
Our technology has the major benefit of being inexpensive, manageable and yet highly sensitive – plus it can take measurements in real time. This makes it suitable for everyday use, while working out at a fitness center or for people on a diet.
Andreas Güntner , Postdoctoral Fellow , ETH Zurich
Presently, the Scientists are planning to continue developing their measurement method so that they can ultimately commercialize it. The Scientists already have a prototype of the instrument. They are also working towards developing gas sensors for various other medically relevant molecules in exhalations, including ammonia for testing kidney function, isoprene for testing cholesterol metabolism and different aldehydes for detecting lung cancer in its early stage.