A highly active nano-silver film is used as the surface enhanced Raman scattering (SERS) substrate, and a near-infrared laser (785nm) is used as the excitation light source, and the cytosine (cytidine) aqueous solution (10-2~10-8 mol· L-1) The near-infrared surface-enhanced Raman scattering (NIR-SERS) spectroscopy was performed. The experimental results show that when the concentration of cytidine aqueous solution is equal to or lower than 10-7 mol·L-1, the NIR-SERS spectrum with good signal-to-noise ratio can be obtained in the range of 300~2 000cm-1. The cytidine aqueous solution (10-2~10-5 mol·L-1) was dropped on 10 different nano-silver films for detection. The results showed that the nano-silver films showed good spectral reproducibility. By characterizing the surface morphology of the nano-silver film, it is found that the nano-silver particles coated with polyvinyl alcohol (PVA) form a "grass-like" structure on the surface of the aluminum sheet. And through ultraviolet-visible light reflectance spectroscopy detection of the nano silver film adsorbed with cytidine molecules, it was found that a plasmon resonance peak appeared at 800nm. Therefore, when a 785nm near-infrared laser is used as the excitation light, the system can exhibit strong surface plasmon resonance (SPR) characteristics. At the same time, DFTB3LYP/6-311G was used to calculate the Raman spectrum of the cytidine molecule, and the wavelength of the incident light used in the calculation was 785nm. In the range of 1, the two are matched well, and the vibration is assigned. Finally, by comparing the Raman spectrum and NIR-SERS spectrum of cytidine, the possible adsorption mode of cytidine molecule on the nano-silver film was analyzed. The analysis results show that the cytidine molecule is mainly the ribose part adsorbed on the silver nanoparticles, and the 17NH2 group of the molecule may be close to the local electromagnetic field enhancement area.
