This review elucidates the technologies in the field of exhaled breath analysis. Exhaled breath gas analysis offers an inexpensive, noninvasive and rapid method for detecting a large number of compounds under various conditions for health and disease states. There are various techniques to analyze some exhaled breath gases, including spectrometry, gas chromatography and spectroscopy. This review places emphasis on some of the critical biomarkers present in exhaled human breath, and its related effects. Additionally, various medical monitoring techniques used for breath analysis have been discussed. It also includes the current scenario of breath analysis with nanotechnology-oriented techniques.
Novel nanograined ZnO/Au heterostructured nanofibers have been successfully prepared using two‐step process via electrospinning method followed by thermal oxidation and their surface bound NO2 sensing properties were analyzed. The ZnO/Au heterojunction nanofibers exhibited typical nanograined structure with 1D morphology consisting of two distinct lattice fringes with d spacing values of 0.14 ± 0.5 nm and 0.28 ± 0.5 nm corresponding to Au [111] and ZnO [101] respectively. Defects and surface bound properties were examined using Room temperature Photoluminescence (RTPL) spectroscopy, X‐ray photo‐electron spectroscopy (XPS) and X‐ray diffraction analysis. The existence of Au, Zn and O in 4 f, 2p and 1 s states and chemisorbed oxygen species on the surface were structurally confirmed after the careful evaluation and proves the purity of synthesis. NO2 gas sensor property analysis of ZnO/Au heterojunction nanofibers showed an extraordinary sensor response (S=98) and selectivity at a lower operating temperature of 350°C than pristine ZnO nanofibers (450 °C). The enhanced sensing behavior of the heterostructured nanofibers are ascribed to the synergetic effect of Au nanoclusters at the interface which act as spill‐over zone favoring physisorption and defect mediated sensing process.
An ultrasensitive and selective chemiresistive sensor interface based on Ag nanocluster integrated polyaniline functionalized multi-walled carbon nanotubes (AgNC@PANI/MWCNTs) has been developed for trace-level detection of NH 3 gas at room temperature. AgNC@PANI/MWCNTs was synthesized using surfactant-free, one-pot wet-chemical process, by controlled integration of active Ag sites onto MWCNTs. The structure and morphology of AgNC@PANI/MWCNTs nanocomposite have been extensively studied by various characterization techniques. The gas sensing properties of AgNC@PANI/MWCNTs nanocomposite towards trace-level concentrations NH 3 (2-10 ppm), an important biomarker in exhaled human breath, was systematically evaluated. The sensor exhibited dramatic enhancement in the sensor response (26 %), fast response (5 s) and recovery (~4 s) characteristics with good reproducibility and selectivity upon exposure to NH 3 gas. The excellent performance of the sensor towards NH 3 could be attributed to the rapid electronic sensitization of surface engineered active AgNC sites in the composite in which oxidized AgNC were found to play a critical role. Effect of humidity and the kinetics of the NH 3 gas adsorption on nanocomposite were analyzed. The possible interactions between NH 3 and AgNC@PANI/ MWCNTs nanocomposite were discussed. This investigation can pave the way to novel strategies for designing and fabricating low-cost, high performance NH 3 gas sensors for clinical breath analyzer application.[a] S.
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