Supramolecular assembly of water-soluble poly(ferrocenylsilanes): multilayer structures on flat interfaces and permeability of microcapsules

Polyferrocenylsilanes: synthesis, properties, and applications

This comprehensive review covers polyferrocenylsilanes (PFSs), a well-established, readily accessible class of main chain organosilicon metallopolymer. The focus is on the recent advances involving PFS homopolymers and block copolymers and the article covers the synthesis, properties, and applications of these fascinating materials.

Writing nanopatterns with electrochemical oxidation on redox responsive organometallic multilayers by AFM

Nanoelectrochemical patterning of redox responsive organometallic poly(ferrocenylsilane) (PFS) multilayers is demonstrated by electrochemical dip pen lithography (EDPN). Local electrochemical oxidation and Joule heating of PFS multilayers from the tip are considered as relevant mechanisms related to structure generation. The influence of applied bias potential, tip velocity, and multilayer thickness on the pattern height and width were investigated.

Recent Progress in Ferrocene-Modified Thin Films and Nanoparticles for Biosensors

This article reviews recent progress in the development of ferrocene (Fc)-modified thin films and nanoparticles in relation to their biosensor applications. Redox-active materials in enzyme biosensors commonly use Fc derivatives, which mediate electron transfer between the electrode and enzyme active site. Either voltammetric or amperometric signals originating from redox reactions of Fc are detected or modulated by the binding of analytes on the electrode. Fc-modified thin films have been prepared by a variety of protocols, including insitu polymerization, layer-by-layer (LbL) deposition, host-guest complexation and molecular recognitions. Insitu polymerization provides a facile way to form Fc thin films, because the Fc polymers are directly deposited onto the electrode surface. LbL deposition, which can modulate the film thickness and Fc content, is suitable for preparing well-organized thin films. Other techniques, such as host-guest complexation and protein-based molecular recognition, are useful for preparing Fc thin films. Fc-modified Au nanoparticles have been widely used as redox-active materials to fabricate electrochemical biosensors. Fc derivatives are often attached to Au nanoparticles through a thiol-Au linkage. Nanoparticles consisting of inorganic porous materials, such as zeolites and iron oxide, and nanoparticle-based composite materials have also been used to prepare Fc-modified nanoparticles. To construct biosensors, Fc-modified nanoparticles are immobilized on the electrode surface together with enzymes.

Covalent layer-by-layer assembly of redox-active polymer multilayers

Poly(ferrocenyl(3-bromopropyl)methylsilane) and poly(ethylene imine) are employed in a layer-by-layer deposition process to form covalently connected, redox-active multilayer thin films by means of an amine alkylation reaction. The stepwise buildup of these multilayers on silicon, ITO, and quartz substrates was monitored by UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), static contact angle measurements, surface plasmon resonance (SPR), atomic force microscopy, ellipsometry, and cyclic voltammetry, which provide evidence for a linear increase in multilayer thickness with the number of deposited bilayers. Upon oxidation and reduction, these covalently interconnected layers do not disassemble, in contrast to poly(ferrocenylsilane) (PFS) layers featuring similar backbone structures that are held together by electrostatic forces. The PFS/PEI multilayers are effective for the electrochemical sensing of ascorbic acid and hydrogen peroxide and show improved sensing performance at higher bilayer numbers. These covalently linked layers are readily derivatized further and can therefore be regarded as a versatile platform for creating robust, tailorable, redox-active interfaces with applications in sensing and biofuel cells.

pH- and sugar-sensitive layer-by-layer films and microcapsules for drug delivery

The present review provides an overview on the recent progress in the development of pH- and sugar-sensitive layer-by-layer (LbL) thin films and microcapsules in relation to their potential applications in drug delivery. pH-sensitive LbL films and microcapsules have been studied for the development of peptide and protein drug delivery systems to the gastrointestinal tract, anti-cancer drugs to tumor cells, anti-inflammatory drugs to inflamed tissues, and the intracellular delivery of DNA, where pH is shifted from neutral to acidic. pH-induced decomposition or permeability changes of LbL films and microcapsules form the basis for the pH-sensitive release of drugs. Sugar-sensitive LbL films and microcapsules have been studied mainly for the development of an artificial pancreas that can release insulin in response to the presence of glucose. Therefore, glucose oxidase, lectin, and phenylboronic acid have been used for the construction of glucose-sensitive LbL films and microcapsules. LbL film-coated islet cells are also candidates for an artificial pancreas. An artificial pancreas would make a significant contribution to improving the quality of life of diabetic patients by replacing repeated subcutaneous insulin injections.

Optical properties of poly(ferrocenylsilane) multilayer thin films

Spectroscopic ellipsometry has been used to investigate the optical properties of poly(ferrocenylsilane) polyion multilayer thin films in the visible and near-infrared range of the spectrum. The thin films were deposited using the layer-by-layer assembly process. Films with thicknesses of up to 55 nm were fabricated stepwise from polyelectrolyte solutions with a controlled ionic strength. These films allow an accurate characterization of the optical properties of poly(ferrocenylsilane) polyion layers. We show that the complex refractive index can be described by a simple Cauchy model. Refractive index values vary over the spectral range from 1.53 (near-infrared) to 1.8 (ultraviolet).

Functional polyelectrolytes

This perspective seeks to identify an area of soft materials research focused on the study of functional polyelectrolytes. These materials combine the useful properties intrinsic to polyelectrolyte chains, with added functionality provided by specific molecular (or polymeric) functional groups that are present in the polymer backbone or as a pendant functionality. Examples are provided to demonstrate how the combined functionality can be used to create films and assemblies with interesting and useful optical, electro-optical, and electronic properties.

Solvent-filled matrix polyelectrolyte capsules: preparation, structure and dynamics

Stable surfactant-free, water-dispersed, micron-sized organic solvent colloids have been a challenging subject of major interest both experimentally and theoretically in recent years. In this article, novel matrix capsules are introduced to carry an organic solvent ( toluene) into water and form a stable solvent dispersion in the aqueous phase without the addition of a surfactant. The structure and dynamics of the dispersion are investigated by confocal Raman microscopy, surface force microscopy, and pulsed field gradient nuclear magnetic resonance (PFG-NMR). The matrix capsules are fabricated according to a literature method using alternating layer-by-layer adsorption of oppositely charged polyelectrolytes onto porous calcium carbonate (CaCO) particles, followed by core removal. The highly rough surface and the inner cavities of CaCO particles result in a heavy matrix capsule, which can achieve a high solvent encapsulation efficiency and form a micron-sized carrier for the solvent in water that is stable for long times ( at least one week.) Two distinct diffusion coefficients are evidenced by PFG-NMR, which may indicate two distinct diffusion environments in the sample. This suggests that the toluene undergoes a partial exchange between environments within the 100 ms time frame of the NMR experiment.