The dynamics of complex formation between amylose brushes on gold and fatty acids by QCM-D.

Amylose brushes were synthesized by enzymatic polymerization with glucose-1-phosphate as monomer and rabbit muscle phosphorylase b as catalyst on gold-covered surfaces of a quartz crystal microbalance. Fourier transform infrared (FT-IR) spectra confirmed the presence of the characteristic absorption peaks of amylose between 3100 cm(-1) and 3500 cm(-1). The thickness of the amylose brushes-measured by Spectroscopic Ellipsometry--can be tailored from 4 to 20 nm, depending on the reaction time. The contour length of the stretched amylose chains on gold surfaces has been evaluated by single molecule force spectroscopy, and a total chain length of about 20 nm for 16.2 nm thick amylose brushes was estimated. X-ray photoelectron spectroscopy (XPS) was employed to characterize the amylose brushes before and after the adsorption of fatty acids. The dynamics of inclusion complex formation between amylose brushes and two fatty acids (octanoic acid and myristic acid) with different chain length was investigated as a function of time using a quartz crystal microbalance with dissipation monitoring (QCM-D) immersed in the liquid phase. QCM-D signals including the frequency and dissipation shifts elucidated the effects of the fatty acid concentration, the solvent types, the chain length of the fatty acids and the thickness of the amylose brushes on the dynamics of fatty acid molecule adsorption on the amylose brush-modified sensor surfaces.

Antibacterial polyelectrolyte micelles for coating stainless steel.

In this study, we report on the original synthesis and characterization of novel antimicrobial coatings for stainless steel by alternating the deposition of aqueous solutions of positively charged polyelectrolyte micelles doped with silver-based nanoparticles with a polyanion. The micelles are formed by electrostatic interaction between two oppositely charged polymers: a polycation bearing 3,4-dihydroxyphenylalanine units (DOPA, a major component of natural adhesives) and a polyanion (poly(styrene sulfonate), PSS) without using any block copolymer. DOPA units are exploited for their well-known ability to anchor to stainless steel and to form and stabilize biocidal silver nanoparticles (Ag(0)). The chlorine counteranion of the polycation forms and stabilizes biocidal silver chloride nanoparticles (AgCl). We demonstrate that two layers of micelles (alternated by PSS) doped with silver particles are enough to impart to the surface strong antibacterial activity against gram-negative E. coli. Moreover, micelles that are reservoirs of biocidal Ag(+) can be easily reactivated after depletion. This novel water-based approach is convenient, simple, and attractive for industrial applications.

Nanopatterning by protein unfolding.

Molecular layers patterned on the nanoscale, with long-range order properties extending over the microscopic scale, have been obtained upon adsorption of commonly available proteins onto the hydrophobic and long-range ordered surface of pyrolytic graphite (HOPG). Proteins lose their native folding and polypeptide chains re-assemble on the surface in a layered fashion, forming a molecular bilayer. This behaviour is rather general since it is observed for different proteins irrespective of their specific structural properties.

Mechanical properties of single living cells encapsulated in polyelectrolyte matrixes.

We have studied the mechanical properties of encapsulated Saccharomyces cerevisiae yeast cells by performing AFM force measurements. Single living cells have been coated through the alternate deposition of oppositely charged polyelectrolyte layers and mechanically trapped into a porous membrane. Coated and uncoated cells in presence/absence of bud scars, i.e. scars resulting from previous budding events, have been investigated. No significant differences between encapsulated and bare cells could be inferred from AFM topographs. On the other hand, investigation on the system elasticity through the acquisition and analysis of force curves allowed us to put in evidence the differences in the mechanical properties between the hybrid cell/polyelectrolyte system and the uncoated cells. Analysis of the curves contact region indicates that the polyelectrolyte coating increases the system rigidity. Quantitative evaluation of the cell rigidity through the Hertz-Sneddon model showed that coated cells are characterized by a Young's modulus higher than the value obtained for uncoated cells and similar to the value observed on the bud scar region of uncoated cells.

Biointerface multiparametric study of intraocular lens acrylic materials.

PURPOSE: To compare hydrophilic and hydrophobic acrylic materials designed for intraocular lenses in a multiparametric investigation in a liquid environment to highlight their properties in terms of adhesion forces, lens epithelial cell (LEC) adhesion, and tissue response as indicators of the risk for posterior capsule opacification (PCO) development. SETTING: University of Liège, Liège, Belgium. DESIGN: Experimental study. METHODS: The hydrophobicity and surface adhesion force were assessed using contact-angle and atomic force microscopy measurements. The bioadhesiveness of the disks and the tissue response were determined by in vitro experiments using bovine serum albumin and porcine LECs and by in vivo rabbit subcutaneous implantation, respectively. RESULTS: Increasing surface hydrophobicity led to a greater surface-adhesion force and greater LEC adhesion. After 1 month, the rabbit subcutaneous implants showed a similar thin layer of fibrous capsule surrounding the disks without extensive inflammation. A layer of rounded cells in contact with disks was detected on the hydrophobic samples only. CONCLUSIONS: Hydrophobic acrylic disks that have been associated with a reduced risk for PCO in clinical studies showed increased tackiness. FINANCIAL DISCLOSURES: Proprietary or commercial disclosures are listed after the references.

A single synthetic small molecule that generates force against a load.

Some biomolecules are able to generate directional forces by rectifying random thermal motions. This allows these molecular machines to perform mechanical tasks such as intracellular cargo transport or muscle contraction in plants and animals. Although some artificial molecular machines have been synthesized and used collectively to perform mechanical tasks, so far there have been no direct measurements of mechanical processes at the single-molecule level. Here we report measurements of the mechanical work performed by a synthetic molecule less than 5 nm long. We show that biased Brownian motion of the sub-molecular components in a hydrogen-bonded [2]rotaxane-a molecular ring threaded onto a molecular axle-can be harnessed to generate significant directional forces. We used the cantilever of an atomic force microscope to apply a mechanical load to the ring during single-molecule pulling-relaxing cycles. The ring was pulled along the axle, away from the thermodynamically favoured binding site, and was then found to travel back to this site against an external load of 30 pN. Using fluctuation theorems, we were able to relate measurements of the work done at the level of individual rotaxane molecules to the free-energy change as previously determined from ensemble measurements. The results show that individual rotaxanes can generate directional forces of similar magnitude to those generated by natural molecular machines.