Engineers Solve Key Physical Hurdle in Exhaled Breath Diagnostics
Researchers at the University of Notre Dame discover that biomarker evaporation during droplet collection causes test variability.
Engineers at the University of Notre Dame have pinpointed why exhaled breath tests often produce inconsistent results, solving a problem that has stalled the diagnostic method for decades. The discovery provides the physical basis for a new invention in sample collectors, ensuring that noninvasive breath monitors can reliably detect pulmonary diseases without invasive procedures.
The search for reliable noninvasive monitoring
Chronic obstructive pulmonary disease, known as COPD, ranks as the third leading cause of death worldwide according to report details shared by MedicalXpress. Monitoring the condition typically requires costly computed tomography scans or blood tests that cause patient discomfort. Flare-ups can develop quickly, making portable point-of-care diagnostics an urgent clinical innovation for remote and under-resourced clinics. Exhaled breath condensate collection, an approach introduced in the 1970s, chills breath into liquid droplets to measure chemical biomarkers. Yet clinical adoption stalled because repeated tests from the same patient yielded conflicting data. For decades, researchers assumed biological fluctuations caused these disparities.
“This is a promising first step; demonstrating that there are concrete and measurable sources of error in EBC collection shows us that we have a shot at creating a standardization system that allows clinicians to reliably use EBC in disease diagnosis”
— Amio Ritwik, doctoral student at the University of Notre Dame
Tracking biomarker loss at the droplet level
A study published in Nano Letters by the team of Jingcheng Ma, an assistant professor at Notre Dame's Department of Aerospace and Mechanical Engineering, shifts the blame from human biology to physics. Using a custom fluorescence measurement system built at the Interfacial Thermofluids Laboratory, the researchers monitored droplet behavior in real time. They evaluated two physical mechanisms: co-condensation, which dictates how markers enter droplets, and evaporation, which allows volatile compounds to escape into surrounding air. The tests revealed that droplets lose significant biomarker concentrations to evaporation within a single breathing cycle, refuting long-standing assumptions that collected liquid samples remain stable.
Designing standardized collection hardware
The researchers demonstrated that droplet size directly dictates biomarker retention, while longer pauses between exhalations increase evaporative losses. Ambient air temperature, humidity, and the temperature of the condenser plate also affect sample integrity. By quantifying these variables, the team constructed a mathematical model that tracks fluid loss from individual droplets to entire condenser plates. Understanding these physical limits enables engineers to build a standardized medical device for clinical screening, transforming laboratory insights into a reliable diagnostic invention. The Notre Dame team is now planning partnerships with clinicians and diagnostic hardware developers to patent the design and transition these thermodynamic models into validated clinical collectors.
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