Breath analysis for the screening and diagnosis of diseases

Exhaled breath contains small molecules and complex volatile organic compounds (VOCs) such as H2O, CO2, NO, NH3, ketones, aldehydes, alcohols, and hydrocarbons. Analysis of VOCs can provide valuable information about health status, especially in several disorders and disease conditions. In view of pandemics like the recent COVID-19 incidences, Breath Analysis, which is totally noninvasive and can be adapted for Remote/In Situ Point-Of-Care (POC) use, require special attention in current health-care technology. A variety of techniques have been used for the detection of VOCs for decades. Mass spectrometry, laser spectroscopy and more recently e-noses (made up of nano-particle and metal oxide sensors) are the most popular methods. Most VOCs are present in exhaled breath at parts per million (ppm), parts per billion (ppb) and parts per trillion (ppt) levels only. Detection of VOCs even at such low-levels can be correlated with certain diseases, and they can be regarded as biomarkers of such ailments. A review of the various studies that have been carried out in breath analysis, together with a comparison of the different techniques available today, with their advantages and disadvantages, are presented in this article. The challenges and future prospects of the various techniques in providing viable technology for screening and early detection of various disease conditions are also discussed in brief.