Non-covalent protein-based adhesives for transparent substrates-bovine serum albumin vs. recombinant spider silk

Protein-based adhesives could have several advantages over petroleum-derived alternatives, including substantially lower toxicity, smaller environmental footprint, and renewable sourcing. Here, we report that non-covalently crosslinked bovine serum albumin and recombinant spider silk proteins have high adhesive strength on glass (8.53 and 6.28 MPa, respectively) and other transparent substrates. Moreover, the adhesives have high visible transparency and showed no apparent degradation over a period of several months. The mechanism of adhesion was investigated and primarily attributed to dehydration-induced reorganization of protein secondary structure, resulting in the supramolecular association of β-sheets into a densely hydrogen-bonded network.

Colloid-probe AFM studies of the interaction forces of proteins adsorbed on colloidal crystals

In recent years, colloid-probe AFM has been used to measure the direct interaction forces between colloidal particles of different size or surface functionality in aqueous media, as one can study different forces in symmerical systems (i.e., sphere-sphere geometry). The present study investigates the interaction between protein coatings on colloid probes and hydrophilic surfaces decorated with hexagonally close packed single particle layers that are either uncoated or coated with proteins. Controlled solvent evaporation from aqueous suspensions of colloidal particles (coated with or without lysozyme and albumin) produces single layers of close-packed colloidal crystals over large areas on a solid support. The measurements have been carried out in an aqueous medium at different salt concentrations and pH values. The results show changes in the interaction forces as the surface charge of the unmodified or modified particles, and ionic strength or pH of the solution is altered. At high ionic strength or pH, electrostatic interactions are screened, and a strong repulsive force at short separation below 5 nm dominates, suggesting structural changes in the absorbed protein layer on the particles. We also study the force of adhesion, which decreases with an increment in the salt concentration, and the interaction between two different proteins indicating a repulsive interaction on approach and adhesion on retraction.

Bovine serum albumin film as a template for controlled nanopancake and nanobubble formation: in situ atomic force microscopy and nanolithography study

Air nanobubbles and nanopancakes were investigated in situ by both tapping mode atomic force microscopy (TM AFM) and atomic force nanolithography techniques employing bovine serum albumin (BSA) film supported by highly oriented pyrolytic graphite (HOPG). The BSA denaturation induced by the water-to-ethanol exchange served for conservation of nanobubble and nanopancake sites appearing as imprints in BSA film left by gaseous cavities formerly present on the interface in the aqueous environment. Once the BSA film was gently removed by the nanoshaving technique applied in ethanol, a clean basal plane HOPG area with well-defined dimensions was regenerated. The subsequent reverse ethanol-to-water exchange led to the re-formation of nanopancakes specifically at the nanoshaved area. Our approach paves the way for the study of gaseous nanostructures with defined dimensions, formed at solid-liquid interface under controlled conditions.

Nanoshaving of bovine serum albumin films adsorbed on monocrystalline surfaces and interfaces

We apply the ex situ and in situ atomic force microscopy (AFM) nanoshaving technique to investigate the bovine serum albumin (BSA) films on Au(111) and highly oriented pyrolytic graphite (HOPG) surfaces. The both substrates were found to support the BSA films. The section analysis performed before and after the AFM nanoshaving allowed the determination of the film thickness. On Au(111) surface, both ex situ and in situ nanoshaving revealed that the film is formed by strongly denatured BSA molecules, with the average thickness 2.3 ± 0.2 and 2.0 ± 0.2 nm, respectively. On the other hand, the HOPG substrate was found to support less denatured BSA films, with the average film thickness 4.7 ± 0.3 and 5.2 ± 0.3 nm, based on the ex situ and in situ measurements, respectively.