Surface-enhanced Raman Scattering of Aflatoxin B₁ on Silver by DFT Method

The structure, electrostatic properties, and Raman spectra of aflatoxin B₁ (AFB₁) and AFB₁-Ag complex are studied by density functional theory with B3LYP/6-311G(d,p)/Lanl2dz basis set. The results show that the surface-enhanced Raman scattering (SERS) and pre-resonance Raman spectra of AFB₁-Ag complex strongly depend on the adsorption site and the excitation wavelength of the incident light. The SERS factors are found to enhance 10²-10³ order compared to normal Raman spectrum of AFB₁ molecule due to the larger static polarizabilities of the AFB₁-Ag complex, which directly results in the stronger chemical enhancement in SERS spectra. The pre-resonance Raman spectra of AFB₁-Ag complex are explored at 266, 482, 785, and 1064 nm incident light wavelength, in which the enhancement factors are about 10²-10⁴, mainly caused by the charge-transfer ex-citation resonance. The vibrational modes are analyzed to explain the relationship between the vibrational direction and the enhanced Raman intensities.