Right now, breath pattern recognition is still a futuristic diagnostic method. Being able to simplify the characterizing of target gas concentrations of human exhaled breath will lead to easier diagnosing of diseases as well as physical condition. A Korea Advanced Institute of Science and Technology in South Korea research group under Prof. Il-Doo Kim in the Department of Materials Science has developed diagnostic sensors using protein-encapsulated nanocatalysts, which can diagnose certain diseases by analyzing human exhaled breath.
This technology enables early monitoring of various diseases through pattern recognition of biomarker gases related to diseases in human exhalation. The prototype device features sixteen sensorsin all, each able to spot a specific chemical that is a signature of various health parameters. They rely on newly developed heterogeneous nanocatalysts, functionalized on metal oxide nanofiber sensing layers, that were build using protein templates that are 2 nanometers in size.
Gasses related to diseases
In human breath, components such as water vapor, hydrogen, acetone, toluene, ammonia, hydrogen sulfide, and carbon monoxide, are more excessively exhaled from patients. Some of these components are closely related to diseases such as asthma, lung cancer, type 1 diabetes mellitus, and halitosis.
Breath analysis for disease diagnosis started from capturing exhaled breaths in a Tedlar bag and inhecting captured breath gases into a miniaturized sensor system, similar to an alcohol detector. It is possible to analyze exhaled breath very rapidly with a simple analyzing process. The breath analysis can detect trace changes in exhaled breath components, which contribute to early diagnosis of diseases.
However, technological advances are needed to accurately analyze gases in the breath, which occur at very low levels, from 1 ppb to 1 ppm. In particular, it has been a critical challenge for chemiresistive type chemical sensors to selectively detect specific biomarkers in thousands of interfering gases including humid vapor.
Overcoming current limitations
Conventionally, noble metallic catalysts such as platinum and palladium have been functionalized onto metal oxide sensing layers. But the gas sensitivity was not enough to detect ppb-levels of biomarker species in exhaled breath. To overcome current limitations, the research team utilized nanoscale protein (apoferritin) in animals as sacrificial templates. The protein templates possess hollow nanocages at the core site and various alloy catalytic nanoparticles can be encapsulated inside the protein nanocages.
These protein nanocages are advantageous because a nearly unlimited number of material compositions in the periodic table can be assembled for the synthesis of heterogeneous catalytic nanoparticles. The research team developed outstanding sensing layers consisting of metal oxide nanofibers functionalized by the heterogeneous catalysts with large and highly-porous surface areas, which are especially optimized for selective detection of specific biomarkers.
The biomarker sensing performance was improved approximately 3~4-fold as compared to the conventional single component of platinum and palladium catalysts-loaded nanofiber sensors. In particular, 100-fold resistance transitions toward acetone (1 ppm) and hydrogen sulfide (1 ppm) were observed in exhaled breath sensors using the heterogeneous nanocatalysts, which is the best performance ever reported in literature.
The research team also developed a disease diagnosis platform that recognizes individual breathing patterns by using a multiple sensor array system with diverse sensing layers and heterogeneous catalysts, so that the people can easily identify health abnormalities. Using a 16-sensor array system, physical conditions can be continuously monitored by analyzing concentration changes of biomarkers in exhaled breath gases.
Prof. Kim explains that new types of heterogeneous nanocatalysts were synthesized using protein templates with sizes around 2 nm and functionalized on various metal oxide nanofiber sensing layers. The established sensing libraries can detect biomarker species with high sensitivity and selectivity. “The new and innovative breath gas analysis platform will be very helpful for reducing medical expenditures and continuous monitoring of physical conditions.”