Supramolecular metal-phenolic thin films attract an increasing interest since they allow the design of new types of self-assembling materials, such as tunable electronics or biomaterials. In this study, a new electrotriggered self-assembly of tannic acid-Fe(III) (TA-Fe(III)) nanocoatings was developed using the morphogenic approach with Fe(III) ions as a morphogen. Morphogens are molecules or ions produced locally that diffuse into the solution and induce a chemical reaction or interaction in a confined space near a surface. Using a mixture of TA and Fe(II) ions in contact with an electrode, a confined electrogenerated gradient of Fe(III) was obtained by application of an anodic current to locally form TA-Fe(III) coordination complexes. TA-Fe(III) nanocoatings, based on di-and tri-coordinated complexes, were thus obtained. Both the film thickness and its self-assembly kinetic were tuned by controlling Fe(II)/TA molar ratio of the building solution, the intensity and the duration of the applied current. We showed that this strategy can be applied to two other polyphenols (gallic acid and rosmarinic acid). This new electrotriggered confined self-assembly of metalpolyphenol gives new perspectives in application such as anti-oxidant coating.

Macromolecular coatings play an important role in many technological areas, ranging from the car industry to biosensors. Among the different coating technologies, electrochemically triggered processes are extremely powerful because they allow in particular spatial confinement of the film buildup up to the micrometer scale on microelectrodes. Here, we review the latest advances in the field of electrochemically triggered macromolecular film buildup processes performed in aqueous solutions. All these processes will be discussed and related to their several applications such as corrosion prevention, biosensors, antimicrobial coatings, drug-release, barrier properties and cell encapsulation. Special emphasis will be put on applications in the rapidly growing field of biosensors. Using polymers or proteins, the electrochemical buildup of the films can result from a local change of macromolecules solubility, self-assembly of polyelectrolytes through electrostatic/ionic interactions or covalent cross-linking between different macromolecules. The assembly process can be in one step or performed step-by-step based on an electrical trigger affecting directly the interacting macromolecules or generating ionic species.