Confocal Raman spectroscopy, label-free and label surface-enhanced Raman scattering for microorganism detection

Raman spectroscopy is a powerful tool for microbial detection and analysis, which is vital for public health and safety in areas like food/drug safety, quality control, and disease prevention. This review discusses recent advances in three Raman techniques for microbial detection: confocal Raman spectroscopy, label-free Surface-Enhanced Raman Scattering (SERS), and label-based SERS. Confocal Raman spectroscopy provides nondestructive, label-free chemical analysis with high spatial resolution, enabling the differentiation of microbial cells at the single-cell level. Label-free SERS relies on the direct adsorption of analyte molecules onto the surface of plasmonic nanostructures, where their intrinsic Raman signals are dramatically amplified. Label-based SERS, also called indirect SERS, uses a “sandwich” approach where plasmonic nanoparticles are functionalized with two key components: a targeting molecule for specificity and a Raman reporter molecule for signal generation. We discuss the essential techniques in two primary SERS approaches: the commonly used nanostructures in label-free SERS, ranging from colloidal nanoparticles, array-based substrates to flexible substrate; the typical targeting molecules, Raman reporter molecules and SERS substrates employed in label SERS. Additionally, the integration of artificial intelligence algorithms with Raman technology and future directions in the field is examined.