Label-Free Surface-Enhanced Raman Scattering in Liquid Biopsy for Cancer Detection: Promise, Pitfalls, and the Need for Biological Grounding

Surface-enhanced Raman spectroscopy (SERS) has emerged as a promising label-free liquid biopsy approach for cancer detection because of its ability to generate molecular fingerprints from complex biofluids. Although numerous studies report high diagnostic accuracies, the analytical and biological origins of the measured spectral signatures remain poorly understood. Most label-free SERS liquid biopsy studies employ colloidal silver nanoparticles (AgNPs) or gold nanoparticles (AuNPs), whereas nanostructured SERS-active surfaces are used less frequently. Accordingly, this perspective focuses on colloidal NP-based SERS platforms, in which biomolecules interact dynamically with NP surfaces and SERS-active sites formed during NP aggregation. The resulting spectra represent only a chemically and spatially selected subset of the biofluid constituents rather than their bulk molecular composition. This interfacial molecular ensemble is governed by NP physicochemical properties, aggregation and formation of SERS-active sites, biomolecular corona development, competitive bio−nano interface interactions, and sample preparation conditions. Furthermore, many studies rely on relatively small and clinically narrow cohorts, heterogeneous experimental protocols, and limited independent validation, raising concerns regarding reproducibility, molecular attribution, and clinical generalizability. This perspective argues that successful clinical translation of label-free, colloidal NP-based SERS liquid biopsy requires a stronger mechanistic understanding of nano−bio interfacial processes, standardized methodologies, rigorous reproducibility assessment, and robust molecular attribution.