Biophotonics technologies for the detection of VOCs in healthcare applications: Are we there yet?

The detection of volatile organic compounds (VOCs) has emerged as one of the most promising diagnostic approaches in the field of medicine. For example, human breath contains endogenous volatiles that could be potential biomarkers. The demand for the cost-effective, noninvasive, and sensitive detection of VOCs has increased significantly following the recent COVID-19 pandemic. Typically, VOCs are detected using the gold-standard technology of gas chromatography and mass spectrometry, but this equipment can be bulky and expensive outside of laboratory settings. In this context, biophotonics (or optical) technologies play a crucial role as they can provide highly sensitive detection of VOCs in a cost-effective manner and are suitable for developing point-of-care devices. This review critically and comprehensively analyzes the recent advancements (over the last decade) in biophotonics technologies for the detection of VOCs, such as surface-enhanced Raman spectroscopy, fluorescence spectroscopy, laser absorption spectroscopy, photoacoustic spectroscopy, and surface plasmon resonance, with a special focus on healthcare applications. Relative merits and demerits of these techniques are provided by comparing their sensitivity, limit of detection, and methodology in operation. Finally, the review highlights future perspectives on technical advancements and gaps in research that need to be addressed to translate these biophotonics technologies into a routine VOC-based disease diagnostic platform.