Improving the dielectric properties of ethylene-glycol alkanethiol self-assembled monolayers.

Self-assembled monolayers (SAMs) can be formed at the interface between solids and fluids, and are often used to modify the surface properties of the solid. One of the most widely employed SAM systems is exploiting thiol-gold chemistry, which, together with alkane-chain-based molecules, provides a reliable way of SAM formation to modify the surface properties of electrodes. Oligo ethylene-glycol (OEG) terminated alkanethiol monolayers have shown excellent antifouling properties and have been used extensively for the coating of biosensor electrodes to minimize nonspecific binding. Here, we report the investigation of the dielectric properties of COOH-capped OEG monolayers and demonstrate a strategy to improve the dielectric properties significantly by mixing the OEG SAM with small concentrations of 11-mercaptoundecanol (MUD). The monolayer properties and composition were characterized by means of impedance spectroscopy, water contact angle, ellipsometry and X-ray photoelectron spectroscopy. An equivalent circuit model is proposed to interpret the EIS data and to determine the conductivity of the monolayer. We find that for increasing MUD concentrations up to about 5% the resistivity of the SAM steadily increases, which together with a considerable decrease of the phase of the impedance, demonstrates significantly improved dielectric properties of the monolayer. Such monolayers will find widespread use in applications which depend critically on good dielectric properties such as capacitive biosensor

Probable Immunoglobulin Subtype-G4-Related Disease in the Head and Neck from Foreign Body Injection: A Case Report

Introduction Immunoglobulin subtype G4-related disease (IgG4-RD) is a fibroinflammatory disease of unknown etiology, with manifestations involving nearly every organ system. Its association with foreign bodies is not established. Here, we present a novel case of IgG4-RD in response to foreign body injection. Case Description A 58-year-old woman presented with history of persistent left facial pain, xerophthalmia, blurred vision, and trismus. The patient\u27s medical history was significant for left-sided temporomandibular joint (TMJ) reconstruction with silicone injection into the joint. Magnetic resonance imaging revealed a lesion in the left skull base. Biopsies demonstrated the cardinal histopathological features of IgG4-RD. The patient was treated with a tapering dose of prednisolone followed by rituximab, resulting in tumor shrinkage and resolution of her symptoms. Discussion This is the first reported case of IgG4-RD potentially precipitated by a foreign body, in this case injected silicone into the TMJ. The pathogenesis and etiology of IgG4-RD is still not fully elucidated, but allergic and reactive inflammatory reactions have been implicated in the disease process. This case report should raise the idea of reactive foreign bodies as a causative agent for IgG4-RD

Mechanisms of Charge Transport through Monolayer-Modified Polycrystalline Gold Electrodes in the Absence of Redox-Active Moieties

The charge transport processes in thin insulating films separating a gold electrode and an electrolyte solution are characterized using a constitutive admittance expression that accounts for conduction, diffusion, and polarization of charge within the films. We specifically investigate cases in which the electrolyte solution does not contain electroactive ions. The general impedance response of all gold-monolayer-electrolyte systems to an applied potential, for systems in which the electrolyte does not contain any redox-active species, suggests the existence of a potential regime where the current is limited by the rate of charge transport through the monolayer phase and a regime limited by the rate of charge transfer at the monolayer-electrolyte interface. The monolayer free charge density that appears as a parameter in the admittance expression is evaluated from the measured admittance in both regimes. This calculated parameter describes two field-dependent mechanisms of charge transport in the monolayer phase, for potentials where charge transport limits the flow of charge through the insulating films. These charge transport mechanisms follow well-characterized solid-state mechanistic models of charge conduction; namely, Ohmic conduction at low electric fields and space-charge-limited transport at higher electric fields. Quantum mechanical tunneling effects are also observed at large (similar to 10(9) V/m) electric fields in the monolayer. For potential regimes in which the charge transfer is rate-limiting, the evaluation of the monolayer free charge density from the impedance response results in current densities that are described by the thermal activation of reacting species over a free energy barrier at the monolayer-electrolyte interface. At low electric fields, the rate-limiting process involves the thermally activated reorganization of the solvent molecules, in accordance with the Marcus theory, and for higher fields, the observed current is limited by the thermal hopping of transferring electrons over an electrostatic potential energy barrier within the monolayer phase. The charge transport and charge transfer mechanisms are also shown to be dependent on physical and chemical interactions between the monolayer functional group and the electrolyte constituents at the Stern layer. These interactions are described using empirical parameters obtained from the mechanistic expressions for these charge transport and transfer processes, and the effect of varying electrolyte properties on these parameters is examined in detail here