Silver-capped silicon nanopillar platforms for adsorption studies of folic acid using surface enhanced Raman spectroscopy and density functional theory

The study of the interactions of folic acid (FA) with surface enhanced Raman scattering substrates is relevant for understanding its adsorption mechanism and for fabricating analytical devices for detection of malignant cells over-expressing folate receptors. This paper presents a study of the adsorption of FA on silver-capped silicon nanopillar substrates employing surface enhanced Raman scattering spectroscopy and density functional theory calculations. The experimentally observed vibrations from free FA and FA bound to the Ag surface display different vibrational spectra indicating chemical interaction of the molecule with the metal surface. Density functional theory calculations show that the Ag-FA interaction is primarily through the nitrogen from the pteridine ring anchoring to the Ag metal surface. To investigate the Ag-FA binding behavior further, the adsorption isotherm of FA on the silver-capped silicon nanopillar surface is estimated. The results show a positive cooperative Ag-FA binding mechanism. That is, adsorbed FA increases the affinity of new incoming FA molecules.