Surface-enhanced Raman scattering spectroscopy of human cerebrospinal fluid: protocol selection and biomolecular...

Surface-enhanced Raman scattering (SERS) of human cerebrospinal fluid (CSF) is a promising tool for identifying possible small-molecule pathological biomarkers in neurodegenerative and neuroinflammatory diseases. However, the biochemical interpretation of CSF SERS spectra remains incomplete and lacks consensus. By critically reviewing the available literature, and by using various experimental approaches, the spectral band interpretation of this biofluid is evaluated. The suitability of different SERS protocols and CSF preprocessing strategies, including analysis performed with and without deproteinization, was also critically evaluated through the comparison of six procedures employing both Ag and Au substrates. Analyses of CSF spiked with selected biomolecules, spectral changes induced by sequential enzymatic depletion treatments, spectral fitting, and reconstruction of an artificial CSF sample all indicate that the primary contributors to the SERS spectrum of CSF obtained from Au substrates with a near-infrared excitation (785 nm) are creatinine, hypoxanthine, xanthine, uric acid and guanine. Additionally, results from linear combination fitting by using pure components spectra and other experimental observations strongly emphasize the importance of considering competition for binding sites, spectral overlapping, and matrix effects when interpreting SERS spectra of complex biological fluids.