Abstract
Proteins represent complex biomolecules capable of wide-ranging but also highly specific functionalities. Their immobilization on material supports can enable broad applications from sensing and industrial biocatalysis to biomedical interfaces and materials. We demonstrate the advantages of using aqueous-processed cross-linked polyphenol coatings for immobilizing proteins, including IgG, avidin, and various single and multidomain enzymes on diverse materials, to enable active biofunctional structures (e.g., ca. 2.2, 1.7, 1.1, and 4.8 mg·m-2 active phosphatase on nanoporous cellulose and alumina, steel mesh, and polyester fabric, respectively). Enzyme assays, X-ray photoelectron spectroscopy, silver staining, supplemented with contact angle, solid-state 13C NMR, HPLC, and ESI-MS measurements were used to characterize the polyphenols, coatings, and protein layers. We show that the functionalization process may be advantageously optimized directly for protein activity rather than the traditional focus on the thickness of the coating layer. Higher activities (by more than an order of magnitude in some cases) and wider process pH and material compatibility are demonstrated with polyphenol coatings than other approaches such as polydopamine. Coatings formed from different plant polyphenol extracts, even at lowered purity (and cost), were also found to be highly functional. Chemically, our results indicate that polyphenol coatings differ from polydopamine mainly because of the elimination of amine groups, and that polyphenol layers with intermediate levels of reactivity may better lead to high immobilized protein activity. Overall, an improved understanding of simple-to-use polyphenol coatings has been obtained, which enabled a significant development in active protein surfaces that may be applied across diverse materials and nanostructured supports.
Highlights
Proteins are active biomolecules that perform many of the functions of life at mild pH and temperatures and can be exploited for practical applications.[1−3] Enzymatic proteins in particular catalyze chemical reactions with high specificity and high rates and may be useful for environmentally and economically attractive industrial biocatalysis,[4] tuneable biomaterials,[5−7] and molecular sensing.[8]
We focused on tannic acid (TA) and PG to form poly(tannic acid) (pTA) and pPG coatings, respectively, because these incorporate only trihydroxybenzene functional moieties and may be considered prototypical polyphenol coatings (Figure 1)
Initial experiments (Figure 2) used coatings formed at pH 7.8, by immersion of material supports in aqueous buffers containing TA and PG
Summary
Proteins are active biomolecules that perform many of the functions of life at mild pH and temperatures and can be exploited for practical applications.[1−3] Enzymatic proteins in particular catalyze chemical reactions with high specificity and high rates and may be useful for environmentally and economically attractive industrial biocatalysis,[4] tuneable biomaterials,[5−7] and molecular sensing.[8]. We previously reported a “universal” cross-linked polyphenol-coating approach for the surface modification of a great variety of materials without surface preparation and demonstrated polymer grafting, nanoparticle formation, and antibacterial applications.[25] Polyphenols such as tannic acid (TA) and catechins are highly abundant plant-based compounds characterized by dihydroxyphenyl (catechol) and/or trihydroxybenzoyl (galloyl) groups. Their coatings form by multiple cross-linkings between the precursor monomers and covalent and noncovalent interactions with a material surface. We showed that low-cost polyphenol extracts from different plant species of even intermediate purities could form effective coatings for immobilization, further demonstrating wide applicability of polyphenol coatings for biofunctionalization
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