Metal Carbonyls for the Biointerference-Free Ratiometric Surface-Enhanced Raman Spectroscopy-Based Assay for Cell-Free Circulating DNA of Epstein-Barr Virus in Blood

By taking advantage of the spectral properties of metal carbonyls, we have designed a surface-enhanced Raman spectroscopy (SERS) ratiometric assay for measuring cell-free circulating DNA (cfDNA) from Epstein-Barr virus in blood for nasopharyngeal carcinoma (NPC). This assay consists of a rhenium carbonyl (<b>Re–CO</b>) to serve as a DNA probe, an osmium carbonyl (<b>Os–CO</b>) embedded within the SERS-active substrate as an internal reference, and a streptavidin layer on the surface of the substrate. Hybridization of cfDNA with biotinylated-capture sequence leads to immobilization of cfDNA on the substrate. The binding of <b>Re–CO</b> via daunorubicin (DNR) to cfDNA is accompanied by an appearance of a strong symmetry stretching vibrations peak at 2113 cm^–1, which has spectral overlap with <b>Os–CO</b> (2025 cm^–1). This results in an increase in the <i>I</i>₂₁₁₃/<i>I</i>₂₀₂₅ ratio and quantitatively correlates with cfDNA. This SERS assay can be readily used to detect cfDNA in blood samples from patients due to the intensity ratio of <i>I</i>₂₁₁₃/<i>I</i>₂₀₂₅ lying in a silent region (1780–2200 cm^–1) in the SERS spectrum of the biomolecules