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UBC Theses and Dissertations

A raman cell based on hollow core photonic crystal fibre for human breath analysis Chow, Kam Kong


Lung cancer is the top cancer killer in Canada and North America. Current lung cancer detection tools involving X-ray, CT and bronchoscopy are relatively time-consuming and costly. Breath analyses done by mass spectrometry have shown that certain endogenous volatile organic compounds (VOCs) are related to lung cancer and revealed the potential of breath analysis for lung cancer detection. But mass spectrometry is costly and has slow turnaround times. Raman spectroscopy is a promising candidate for breath analysis because it can offer unique fingerprint-type signals for molecular identification. Hollow core-photonic crystal fibre (HC-PCF) is a novel light guide which allows light to be guided in a small hollow core and it can be filled with a gaseous sample (i.e., human breath) for spectral analysis. Our objective is to develop a simple, cost-effective and non-invasive tool based on Raman spectroscopy for breath analysis and potentially lung cancer screening. A Raman-gas analyzer was designed, based on photonics technology. A gas supply system was built to provide a sealed environment for the loading and unloading of gaseous samples. A laser source at 785 nm was used as the pump for molecular excitation. Stokes Raman signals generated in the hollow core of the HC-PCF can be guided by collection optics and analyzed by a Raman spectrometer. Raman spectra have been obtained successfully from air, reference gases (hydrogen gas, oxygen gas, carbon dioxide gas), and human breath. The limit of detection of the system was found to be approximately 15 parts per million by CO² concentration in the ambient air, characterized by the Raman peaks at 1286 cm₋¹ and 1388 cm-1. This is more than a 100-fold improvement over the recently reported detection limit with a reflective capillary fibre-based Raman cell. Furthermore the detection limit can be further improved by changes to the optical configurations, optimizing the interaction length of the HC-PCF and possible pre-concentration method to enhance signal-to-noise ratio. This work demonstrated a working prototype of a simple, compact, and cost-effective Raman-gas analyzer based on hollow core photonic crystal fibre, which could potentially be used for lung cancer screening through breath analysis.

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