The results of this study were compared to a previous study using HC-PCF to trap industrial gases and backward-scatter 514.5 nm light from them. The authors found that the method presented in this paper has an advantage to enhance the signal-to-noise ratio (SNR). This SNR advantage, coupled with the better transmission of HC-PCF in the near-IR than in the visible wavelengths led to an estimated seven times improvement in the detection sensitivity. The authors' prototype device also demonstrated a 100-fold improvement over a recently reported detection limit of a reflective capillary fiber-based Raman cell for breath analysis. Continued development is underway to increase the detection sensitivity further to reach practical clinical applications.

The analysis of human breath has been driven to new heights and has great potential to impact our society in the area of medical science. Breath analysis is promising as non-invasive, simple and point-of-care clinical measurements to reduce the medical burden caused by invasive, time-consuming and expensive clinical devices. Spectroscopic techniques for breath analysis can offer information to correlate its signals to exhaled substances for molecular identification and quantification to provide the pathophysiological status of the body. In this review paper, techniques such as mass spectrometry-based (gas chromatography-mass spectrometry, proton transfer reaction-mass spectrometry, selected ion flow tube-mass spectrometry), laser absorption spectroscopy-based (cavity ring down spectroscopy and tunable diode laser absorption spectroscopy) and other spectroscopic techniques for breath analysis applications are compared in terms of its advantages/disadvantages, versatilities and plausibility to be transformed in clinical applications.