SERS spectroscopy for bioaerosol analysis and characterisation: challenges and future perspectives

Bioaerosols are microscopic airborne biological particles such as bacteria, fungal spores, pollen, viruses, and their derivatives. The global spread of the COVID-19 pandemic as well as the rise of antibiotic resistance in healthcare settings demonstrate how bioaerosols have become serious public health concerns in both outdoor and indoor settings. Identifying and quantifying bioaerosol components is critical for assessing risks and setting appropriate exposure limits. Specifically, new research opportunities have arisen thanks to the proliferation of real-time (RT) methods for autonomous, online detection and characterization of bioaerosols features [1]. However, effective online bioaerosol monitoring is hindered by the complexity, diversity, and great spatiotemporal variability of bioaerosols, as well as their mixing with abiotic components, both internally and externally. Though they are effective, traditional methods for bioaerosol analysis—such as culture-based and molecular approaches—are not always portable, have long processing periods, and can't always handle real-time analysis. Because of its high sensitivity and specificity, and ability to be performed in complex biological mixtures, using portable and relatively inexpensive devices, surface enhanced Raman scattering (SERS) spectroscopy has attracted interest as a feasible method for detecting airborne pathogens at environmentally relevant concentrations and sensing trace environmental contaminants, among many other potential applications [2]. Unlike spontaneous Raman scattering, SERS spectroscopy has a short assay time and requires far smaller concentrations of analytes, making it particularly suited for bioaerosol studies. The possibility of a direct (also known as “label free”) detection can reduce the need for complex sample preparation, while the availability of portable instrumentation can facilitate on-site and RT monitoring. However, the difficulty of standardising procedures to ensure consistent and comparable results, however, grows with the development of new technologies. Because of the lack of standardised methodologies, SERS sensing of bioaerosols remains challenging. Here we present state of the art in the use of SERS spectroscopy to examine bioaerosols. A critical evaluation of the experimental aspects involved in the collection of SERS spectra is presented, and the potential applicability and weaknesses of various experimental setups are highlighted, helping to provide a solid foundation for further research and the practical implementation of SERS spectroscopy for bioaerosol analysis and characterisation in various environmental and clinical settings.