Human exhaled breath consists of more than 3000 volatile organic compounds, many of which are relevant biomarkers for various diseases. Although gas chromatography has been the gold standard for volatile organic compound (VOC) detection in exhaled breath, recent developments in mid-infrared (MIR) laser spectroscopy have led to the promise of compact point-of-care (POC) optical instruments enabling even single breath diagnostics. In this review, we discuss the evolution of MIR sensing technologies with a special focus on photoacoustic spectroscopy, and its application in exhaled breath biomarker detection. While mid-infrared point-of-care instrumentation promises high sensitivity and inherent molecular selectivity, the lack of standardization of the various techniques has to be overcome for translating these techniques into more widespread real-time clinical use.

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Materials with biomolecule-compatible functional groups are desirable for the fabrication of microdisk lasers used in bio-sensing applications. In this study, a microdisk laser was fabricated using a low-viscosity hyper branched polymer FC-V-50 using ink-jet printing, and was surface-modified at room temperature within a relatively short time compared to conventional methods. The carboxyl functional group of the FC-V-50 polymer was used for surface modification and biotinylation. The adsorption characteristics of the microdisk laser were evaluated using bovine serum albumin, avidin, and streptavidin. This study reports the first demonstration of label-free biosensing using the FC-V-50 polymer-based microdisk laser.