DFT-Based Theoretical Study on Label-Free SERS Detection of Type B Fumonisins: New Insights into Molecular–Substrate Interactions and Quantification Strategies

In this study, we employed density functional theory to investigate the interactions between type B fumonisins (FB1, FB2, and FB3) and silver-enhancing substrates in the surface-enhanced Raman scattering effect. Theoretical calculations of the molecular electrostatic potential reveal that the oxygen atoms at the terminal of the tricarboxylic acid structure in all three molecules exhibit the strongest electronegativity, suggesting these sites as potential active sites for molecular-substrate interactions. Molecular-Ag20 vertex-binding/surface-binding complex models were constructed based on possible docking modes between the molecule and the substrate, and binding energies were calculated. The binding energy results confirm the stable existence of the complexes. By analyzing the frontier molecular orbitals and charge density difference maps of the molecules and complexes, charge transfer excitation near the active sites between the molecule and Ag20 was confirmed. Analysis of the theoretical Raman spectra of vertex-binding/surface-binding complexes revealed selective enhancement phenomena associated with different docking modes. These findings provide a feasible strategy for the simultaneous quantification of the overall content of type B fumonisins and the individual components of FB1, FB2, and FB3 in a single detection. Finally, based on the characteristic frequency variations of the three molecules, a theoretically reproducible, highly sensitive, and high-throughput label-free detection strategy is proposed for analyzing type B fumonisins in complex sample systems. This study not only enhances our understanding of the physical mechanisms underlying molecular-substrate interactions in the SERS effect but also demonstrates the theoretical feasibility of using SERS for simultaneous quantification of different type B fumonisins in complex sample systems. Moreover, it provides a promising and potentially effective label-free sensing strategy for detecting substances with similar molecular structures.本研究采用密度泛函理论，探究了B型伏马菌素（FB1、FB2与FB3）与表面增强拉曼散射（surface-enhanced Raman scattering, SERS）银增强基底之间的相互作用。分子静电势的理论计算结果显示，三种分子的三羧酸结构末端氧原子均表现出最强电负性，提示该位点可作为分子与基底相互作用的潜在活性位点。基于分子与基底的可能对接模式，本研究构建了分子-Ag20顶点结合/表面结合复合模型，并计算了结合能，结合能结果证实了该复合结构的稳定存在。通过分析分子及复合结构的前沿分子轨道与电荷密度差图，本研究证实了分子与Ag20活性位点附近存在电荷转移激发过程。对顶点结合/表面结合复合结构的理论拉曼光谱进行分析后发现，不同对接模式下存在选择性增强现象。上述发现为单次检测中同时定量B型伏马菌素总含量及FB1、FB2、FB3各组分含量提供了可行策略。最后，基于三种分子的特征频率变化，本研究提出了一种理论可复现、高灵敏度、高通量的无标记检测策略，用于复杂样品体系中的B型伏马菌素分析。本研究不仅加深了人们对SERS效应中分子与基底相互作用物理机制的理解，也证实了利用SERS技术在复杂样品体系中同时定量不同B型伏马菌素的理论可行性。此外，本研究还为分子结构相似物质的检测提供了一种极具潜力且切实有效的无标记传感策略。