Surface-Enhanced\nRaman Scattering Analysis of Iron\nGall Inks

Surface-enhanced Raman scattering (SERS) spectra of Iron\nGall Inks\nare reported here for the first time. These inks were prepared by\ndifferent methods varying their basic ingredients: tannic acid (TA),\niron(II) sulfate, and gum Arabic. SERS spectra were acquired on different\nmetallic substrates of Ag and Au prepared by chemical reduction using\ncitrate and hydroxylamine as reducers. The high intensification of\nthe signal detected on citrate-reduced nanoparticles indicates that\nthe adsorption of the ferric complexes of tannic acid is produced\nthrough the interaction of iron with citrate, approaching the complex\nto the interface and leading to a great enhancement in SERS. Different\nmodels are proposed for such an adsorption. The effect of pH is important\nin this analysis since citrate protonation can be modulated at different\npH values. The high sensitivity of the SERS signals, with the limit\nof detection reaching the ppb order, makes the SERS technique very\nsuitable for the analysis of Iron Gall Inks in materials related to\nthe Cultural Heritage, while the adsorption of TA-Fe mediated by citrate\ncan be an attractive and promising way for plasmonic nanomaterial\nfunctionalization in the design of powerful and robust molecular sensing\ndevices.