Polyphenolic compounds present in tea, red wine, and chocolate form thin adherent polyphenol films on substrates through spontaneous adsorption from solution. From this observation emerged a versatile and comprehensive approach to surface modification of a variety of solid, porous, and nanoparticulate substrates composed of metals, ceramics, and polymers (see picture; ROS=reactive oxygen species).

Natively unfolded phenylalanine-glycine (FG)-repeat domains are alleged to form the physical constituents of the selective barriergate in nuclear pore complexes during nucleocytoplasmic transport. Presently, the biophysical mechanism behind the selective gate remains speculative because of a lack of information regarding the nanomechanical properties of the FG domains. In this work, we have applied the atomic force microscope to measure the mechanical response of individual and clusters of FG molecules. Single-molecule force spectroscopy reveals that FG molecules are unfolded and highly flexible. To provide insight into the selective gating mechanism, an experimental platform has been constructed to study the collective behavior of surface-tethered FG molecules at the nanoscale. Measurements indicate that the collective behavior of such FG molecules gives rise to an exponentially decaying long-range steric repulsive force. This finding indicates that the molecules are thermally mobile in an extended polymer brush-like conformation. This assertion is confirmed by observing that the brush-like conformation undergoes a reversible collapse transition in less polar solvent conditions. These findings reveal how FGrepeat domains may simultaneously function as an entropic barrier and a selective trap in the near-field interaction zone of nuclear pore complexes; i.e., selective gate.force spectroscopy ͉ nanomechanics ͉ natively unfolded proteins ͉ nuclear pore complex ͉ selective gating N ucleocytoplasmic transport describes the exchange of molecular cargo between the nucleus and the cytoplasm across numerous perforations in the nuclear envelope called nuclear pore complexes (NPCs) (1). Each vertebrate NPC is an Ϸ120-MDa supramolecular complex consisting of Ϸ30 different proteins called nucleoporins (or Nups) that form an eightfold symmetric central framework embracing a central pore. The cross-section of the central pore reveals an hourglass-like channel that is Ϸ90 nm long and is narrowest (diameter of Ϸ40 nm) at the NPC's midplane (1). Whereas small molecules such as water and ions proceed freely by passive diffusion (2), the NPC poses a barrier to larger molecular cargo (Ͼ20 kDa) that do not harbor nuclear localization signals (NLSs) (3). Conversely, the barrier does not seem to hinder the passage of NLS cargo when in complex with a transport receptor (e.g., Karyopherin͞Importin) (4). Moreover, because receptormediated transport is rapid even for large NLS cargoes (5), it is apparent that the NPC-selective gating mechanism is not solely based on size exclusion.Presently, an unambiguous understanding of the gating mechanism remains elusive because of a lack of information regarding the mechanical aspects of the molecular components that make up the NPC. Emerging evidence indicates that gating is closely correlated with the interactions and spatial organization of nucleoporins containing phenylalanine-glycine (FG)-repeat domains (called FG domains) (1). Importantly, FG domains exhibit low overall hydrophobicity and are...

We have applied nanoporous anodic alumina films as planar optical waveguides and studied changes in the effective dielectric constants of these thin films due to various processes occurring in the pores. We demonstrate the potential of the porous anodic alumina waveguide for high sensitivity (bio-) chemical sensing with bovine serum albumin adsorption and desorption at various pH values, with subangstrom sensitivity in the effective thickness of protein adsorbed. We also monitored pore widening (alumina dissolution) with subangstrom sensitivity, which is conceptually the reverse of detecting conformal film deposition on pore surfaces. Furthermore, we monitored the exchange of pore-filling media between phosphate buffer solution and ethanol, which produces qualitatively the same response as complete pore filling with other materials by various deposition techniques. Thus porous anodic alumina films may be employed simultaneously as deposition templates and as highly sensitive detectors of processes within the pores.

A silver-releasing antibacterial hydrogel was developed that simultaneously allowed for silver nanoparticle formation and gel curing. Water-soluble polyethylene glycol (PEG) polymers were synthesized that contain reactive catechol moieties, inspired by mussel adhesive proteins, where the catechol containing amino acid 3,4-dihydroxyphenylalanine (DOPA) plays an important role in the ability of the mussel to adhere to almost any surface in an aqueous environment. We utilized silver nitrate to oxidize polymer catechols, leading to covalent cross-linking and hydrogel formation with simultaneous reduction of Ag(I). Silver release was sustained for periods of at least two weeks in PBS solution. Hydrogels were found to inhibit bacterial growth, consistent with the well-known antibacterial properties of silver, while not significantly affecting mammalian cell viability. In addition, thin hydrogel films were found to resist bacterial and mammalian cell attachment, consistent with the antifouling properties of PEG. We believe these materials have a strong potential for antibacterial biomaterial coatings and tissue adhesives, due to the material-independent adhesive properties of catechols.

Poly(N-substituted glycine) “peptoids” are a class of peptidomimetic molecules receiving significant interest as engineered biomolecules. Sarcosine (i.e. poly(N-methyl glycine)) has the simplest sidechain chemical structure of this family. In this contribution, we demonstrate that surface-grafted polysarcosine (PSAR) brushes exhibit excellent resistance to non-specific protein adsorption and cell attachment. Polysarcosine was coupled to a mussel adhesive protein inspired DOPA-Lys pentapeptide, which enabled solution grafting and control of the surface chain density of the PSAR brushes. Protein adsorption was found to decrease monotonically with increasing grafted chain densities, and protein adsorption could be completely inhibited above certain critical chain densities specific to different polysarcosine chain-lengths. The dependence of protein adsorption on chain length and density was also investigated by a molecular theory. PSAR brushes at high chain length and density were shown to resist fibroblast cell attachment over a 7 wk period, as well as resist the attachment of some clinically relevant bacteria strains. The excellent antifouling performance of PSAR may be related to the highly hydrophilic character of polysarcosine, which was evident from high-pressure liquid chromatography measurements of polysarcosine and water contact angle measurements of the PSAR brushes. Peptoids have been shown to resist proteolytic degradation and polysarcosine could be produced in large quantities by N-carboxy anhydride polymerization. In summary, surface grafted polysarcosine peptoid brushes hold great promise for antifouling applications.

Surface-grafted water soluble polymer brushes are being intensely investigated for preventing protein adsorption to improve biomedical device function, prevent marine fouling, and enable applications in biosensing and tissue engineering. In this contribution, we present an experimental-theoretical analysis of a peptidomimetic polymer brush system with regard to the critical brush density required for preventing protein adsorption at varying chain lengths. A mussel adhesive-inspired DOPA-Lys pentapeptide surface grafting motif enabled aqueous deposition of our peptidomimetic polypeptoid brushes over a wide range of chain densities. Critical densities of 0.88 nm−2 for a relatively short polypeptoid 10-mer to 0.42 nm−2 for a 50-mer were identified from measurements of protein adsorption. The experiments were also compared with the protein adsorption isotherms predicted by a molecular theory. Excellent agreements in terms of both the polymer brush structure and the critical chain density were obtained. Furthermore, atomic force microscopy (AFM) imaging is shown to be useful in verifying the critical brush density for preventing protein adsorption. The present co-analysis of experimental and theoretical results demonstrates the significance of characterizing the critical brush density in evaluating the performance of an anti-fouling polymer brush system. The high fidelity of the agreement between the experiments and molecular theory also indicate that the theoretical approach presented can aid in the practical design of antifouling polymer brush systems.

Simple immersion of noble metals, oxides, semiconductors, and synthetic polymer substrates in a mussel‐mimetic catecholamine polymer solution p(DOMA‐AEMA) leads to formation of a thin film on the substrate. The resulting coated substrates can bind DNA without further surface treatment. This approach provides a new entrance to DNA microarray fabrication.

Polyphenolverbindungen, die in Tee, Rotwein und Schokolade vorkommen, bilden auf Trägermaterialien dünne haftende Polyphenolfilme durch spontane Adsorption aus einer Lösung. Auf der Grundlage dieser Beobachtung wurde ein allgemein anwendbarer Prozess zur Oberflächenmodifizierung von festen, porösen und nanopartikulären Metall‐, Keramik‐ und Polymermaterialien entwickelt (siehe Bild; ROS=reaktive Sauerstoffspezies).