UV-SERRS and SEIRAS study of adenine adsorption on cuprous oxide nanostructures

The adsorption of adenine on cuprous oxide was studied by two complementary surface-enhanced vibrational spectroscopy techniques: ultraviolet surface-enhanced resonance Raman spectroscopy (UV-SERRS) and surface-enhanced infrared absorption spectroscopy (SEIRAS). X-ray diffraction measurements confirmed that the electrochemically deposited surfaces used for adenine adsorption consisted of a pure Cu₂O phase, with no detectable metallic copper or CuO phases. Multiwavelength Raman spectroscopy confirmed the intact cuprous oxide structure and identified characteristic marker bands that differentiate Cu₂O and CuO phases across excitation wavelengths of 325, 442, 532, and 633 nm. Assignments of adenine vibrational bands were refined by using isotopically labeled adenine (Ade-¹³C8), analyzing spectral changes following H₂O/D₂O exchange, and applying DFT modeling. SEIRAS data indicated that the NH₂ group of adenine does not participate in surface bonding, as the marker band in the surface spectrum (1653 cm^-1) appeared at nearly the same frequency as in the solution phase. Surface vibrational spectra revealed that adenine adsorbs onto the Cu₂O surface via the N3 and N9 sites in a tilted orientation.