The Layer-by-layer deposition of positively and negatively charged macromolecular species is an ideal method for constructing thin films incorporating biological molecules. We investigate the adsorption of fibronectin onto polyelectrolyte multilayer (PEM) films using optical waveguide lightmode spectroscopy (OWLS) and atomic force microscopy (AFM). PEM films are formed by adsorption onto Si(Ti)O2 from alternately introduced flowing solutions of anionic poly(sodium 4-styrenesulfonate) (PSS) and cationic poly(allylamine hydrochloride) (PAH). Using OWLS, we find the initial rate and overall extent of fibronectin adsorption to be greatest on PEM films terminated with a PAH layer. The polarizability density of the adsorbed protein layer, as measured by its refractive index, is virtually identical on both PAH- and PSS-terminated films; the higher adsorbed density on the PAH-terminated film is due to an adsorbed layer of roughly twice the thickness. The binding of monoclonal antibodies specific to the protein's cell binding site is considerably enhanced to fibronectin adsorbed to the PSS layer, indicating a more accessible adsorbed layer. With increased salt concentration, we find thicker PEM films but considerably thinner adsorbed fibronectin layers, owing to increased electrostatic screening. Using AFM, we find adsorbed fibronectin layers to contain clusters; these are more numerous and symmetric on the PSS-terminated film. By considering the electrostatic binding of a segmental model fibronectin molecule, we propose a picture of fibronectin adsorbed primarily in an end-on-oriented monolayer on a PAH-terminated film and as clusters plus side-on-oriented isolated molecules onto a PSS-terminated film.

Molecular aggregates formed by polymethine dyes in solutions, at surfaces, and in crystals can be used to modulate the intensity and wavelength of light absorption. 1 The applications for such dye aggregates are manifold: photography, xerography, photovoltaic, molecular photonic, and microelectronic devices. 2 The internal structure of such aggregates is widely perceived as arrays of tightly packed molecules with their molecular planes stacked against each other. Several packing models have been proposed based on the epitaxy match between dye crystalline layers and the lattice of a mica substrate: staircase, brickwork, and ladder structure. 3 A special case of the staircase packing in single crystals of polymethine dye 1,7-bis(dimethylamino)heptamethine perchlorate or BDH + ClO 4is illustrated in Figure 1. The aggregate structure has been quantitatively linked to its spectroscopic properties. 4 The strong coupling of molecular transition dipoles generates excitonic states 4 whose absorption energy is significantly shifted to shorter (Haggregates) or to longer (J-aggregates) wavelength with respect to the nonaggregated state. When there are two molecular orientations in the unit cell, the molecular transition dipoles, M 1 and M 2 , couple with each other as vectors, which results in two excitonic transitions: the Davydov sum, m + , and difference m -. These two components are perpendicular to each other. 5 In BDH + ClO 4crystals, the m + component parallels [201] and absorbs light at 639 nm, and the mcomponent parallels [010] and exhibits an absorption maximum at 592 nm. 6 Both transitions are red-shifted from the monomer absorption at 510 nm. In addition to the exciton propagation, the absorption behavior of three-dimensional dye arrays is also altered by polaritons. 7 The polaritons are generated by the coupling of the light wave with the polarization of the medium and lead to a splitting in the longitudinal and transverse exciton energy. The absorption wavelength of the dye crystal varies within the two energy boundaries according to the angle, , between the transition dipole moment and the crystal face normal. It is conceivable that the color of a transparent thin film of threedimensionally oriented J-aggregates can be tuned precisely if one finds a way to rotate the molecular axis in such thin films.A method called the thin layer aggregation (TLA) was recently developed to prepare dye films with various color patterns. 8 The TLA method exploits the aggregation of polymethine dyes in strongly undercooled amorphous layers. While the macroscopic properties of the dye layers have been investigated by the UV/vis spectroscopy and thermal analysis, almost nothing is known about the dye thin film surface coverage, roughness, morphology, and molecular packing at the nanoscale. Atomic force microscopy (AFM) 9 has been widely used to study the lattice structure of ordered self-assembled and Langmuir-Blodgett thin films as well as the microstructure of amorphous films and has recently been used to study J-aggregate st...

Langmuir–Blodgett films of metallosurfactants were used in Au|molecule|Au devices to investigate the mechanisms of current rectification.

The possibility of using surface topography for guidance of different biological molecules and cells is a relevant topic that can be applied to a wide research activity. This study investigated the adsorption of fibronectin to a diffraction grated silicon surface. The rectangular grating profile featured a controlled surface with 350 nm period and a corrugation depth of 90 nm. Results demonstrated that the controlled surface had a significantly positive effect on the fibronectin binding. Thus, nanoscale surface topography can enhance fibronectin binding.