Adsorption\nof Tannic Acid onto Gold Surfaces

Abstract

Thin\nfilm coatings are widely applicable in materials\nfor consumer\nproducts, electronics, optical coatings, and even biomedical applications.\nWet coating can be an effective method to obtain thin films of functional\nmaterials, and this technique has recently been studied in depth for\nthe formation of bioinspired polyphenolic films. Naturally occurring\npolyphenols such as tannic acid (TA) have garnered interest due to\ntheir roles in biological processes and their applicability as antioxidants,\nantibacterial agents, and corrosion inhibitors. Understanding the\nadsorption of polyphenols to surfaces is a core aspect in the fabrication\nprocesses of thin films of these materials. In this work, the adsorption\nof TA to gold surfaces is measured using a quartz crystal microbalance\nwith dissipation monitoring (QCMD) and surface plasmon resonance (SPR)\nfor a wide range of TA concentrations. The adsorption kinetics, aggregation,\nand stability of TA solutions in physiological-like conditions are\nstudied. Unexpectedly, it is found that the adsorption rates depend\nonly weakly on concentration because of the presence of TA aggregates\nthat do not adsorb. The mechanism of layer formation is also investigated,\nfinding that TA monolayers readily adsorb onto gold with flat or edge-on\nmolecular orientations dependent on the solution concentration. A\nmix of orientations in the intermediate case leads to slow multilayer\nadsorption.