Adsorption of serum components on Ag colloids: on the biochemical interpretation of surface-enhanced Raman spectra of human serum

Surface-enhanced Raman scattering (SERS) spectra of human serum exhibit consistent features across studies from multiple research groups, while the biochemical interpretation of bands has not yet reached a consensus. By critically reviewing the recent literature, the methods commonly used to assign SERS bands in biofluids are re-evaluated. Data are presented from various experimental approaches to test band attribution. Analyses of serum samples spiked with various biomolecules, spectral changes induced by uricase treatment, correlation patterns among bands across a serum dataset, and spectral fitting all indicate that the primary contributors to the SERS spectrum of serum (at its unaltered physiological pH of 7.4), obtained on Ag substrates with near infrared excitation, are uric acid and hypoxanthine. Principal component analysis further reveals that most of the dataset variance—reflecting inter-individual biochemical differences—is associated with the bands of these two metabolites. Additionally, data from isotopically labeled uric acid demonstrate that both its albumin-bound and free forms, which exhibit distinct spectral signatures, contribute to the overall serum spectrum.