“…In the label-free approach, biomolecules in solution are freely adsorbed onto a nanostructured metal surface, and the observed SERS bands are associated with the analytes themselves . The disease-specific perturbation in biomolecules, such as proteins, nucleic acids, lipids, and their metabolites, can be discriminated by the fingerprint Raman spectra, making SERS capable to stratify between diseased patients and healthy controls. , Label-free SERS has also been increasingly employed to investigate the biochemical and metabolic properties of the tumor microenvironment for more fundamental studies. For instance, Xu and co-workers fabricated a SERS-microfluidic droplet platform to realize the simultaneous analysis of multiplexed metabolites secreted from single live cells .…”