The Sers Analysis of the Interaction Between AG8 Cluster and Adenine for Optical Sensor Applications Using DFT Calculations

The Raman spectrum of adenine and the surface‐enhanced Raman spectrum (SERS) upon adsorption of adenine on an Ag₈ cluster in aqueous solution were calculated using the density functional theory method with the PBE0 hybrid functional and the Def2‐TZVP basis set, together with the integral equation formalism polarizable continuum model for the solvent (IEF‐PCM). TD‐DFT calculations were performed to determine the excitation wavelengths of adenine and the Ag₈•A complex, thereby selecting excitation wavelengths compatible with available experimental Raman spectroscopy instruments. In addition, excitation wavelengths with the maximum oscillator strength were chosen to propose characteristic spectra for experimental studies. The calculated Raman activities were converted into Raman scattering intensities, and the enhancement factor was determined. The results show that an excitation wavelength of 325 nm gives the strongest and most distinct SERS signal, 532 nm provides stable signals suitable for commercial instruments, while 442 nm significantly reduces several characteristic vibrational bands. The study also constructed Raman and SERS spectra corresponding to the excitation wavelength with the maximum oscillator strength. The findings indicate that the Ag₈ cluster greatly enhances the Raman signal of adenine. This study provides a basis for selecting excitation wavelengths and characteristic vibrational modes to identify adenine, supporting the development of label‐free biosensors based on silver clusters.