Strategies To Achieve Control over the Surface Ratio of Two Different Components on Modified Electrodes Using Aryldiazonium Salts.

Controlling the composition of an interface is very important in tuning the chemical and physical properties of a surface in many applications including biosensors, biomaterials, and chemical catalysis. Frequently, this requires one molecular component to a minor component in a mixed layer. Such subtle control of composition has been difficult to achieve using aryldiazonium salts. Herein, aryldiazonium salts of carboxyphenyl (CP) and phenylphosphorylcholine (PPC), generated in situ from their corresponding anilines, are electrografted to form molecular platform that are available for further functionalization. These two components are chosen because CP provides a convenient functionality for further coupling of biorecognition species while PPC offers resistance to nonspecific adsorption of proteins to the surface. Mixed layers of CP and PPC were prepared by grafting them either simultaneously or consecutively. The latter strategy allows an interface to be developed in a controlled way where one component is at levels of less than 1% of the total layer.

A robust DNA interface on a silicon electrode.

Two different interfaces prepared via UV-hydrosilylation of undecylenic acid and 1,8-nonadiyne on silicon(111) have been explored to develop a robust electrochemical DNA sensor. Electrodes modified with undecylenic acid were found to stably immobilise DNA but could not resist the growth of insulating oxides, whereas 1,8-nonadiyne modified electrodes satisfy both requirements.

Evidence for a surface confined ion-to-electron transduction reaction in solid-contact ion-selective electrodes based on poly(3-octylthiophene).

The ion-to-electron transduction reaction mechanism at the buried interface of the electrosynthesized poly(3-octylthiophene) (POT) solid-contact (SC) ion-selective electrode (ISE) polymeric membrane has been studied using synchrotron radiation-X-ray photoelectron spectroscopy (SR-XPS), near edge X-ray absorption fine structure (NEXAFS), and electrochemical impedance spectroscopy (EIS)/neutron reflectometry (NR). The tetrakis[3,5-bis(triflouromethyl)phenyl]borate (TFPB(-)) membrane dopant in the polymer ISE was transferred from the polymeric membrane to the outer surface layer of the SC on oxidation of POT but did not migrate further into the oxidized POT SC. The TFPB(-) and oxidized POT species could only be detected at the outer surface layer (≤14 Ǻ) of the SC material, even after oxidation of the electropolymerized POT SC for an hour at high anodic potential demonstrating that the ion-to-electron transduction reaction is a surface confined process. Accordingly, this study provides the first direct structural evidence of ion-to-electron transduction in the electropolymerized POT SC ISE by proving TFPB(-) transport from the polymeric ISE membrane to the oxidized POT SC at the buried interface of the SC ISE. It is inferred that the performance of the POT SC ISE is independent of the thickness of the POT SC but is instead contingent on the POT SC surface reactivity and/or electrical capacitance of the POT SC. In particular, the results suggest that the electropolymerized POT conducting polymer may spontaneously form a mixed surface/bulk oxidation state, which may explain the unusually high potential stability of the resulting ISE. It is anticipated that this new understanding of ion-to-electron transduction with electropolymerized POT SC ISEs will enable the development of new and improved devices with enhanced analytical performance attributes.

Transport and accumulation of ferrocene tagged poly(vinyl chloride) at the buried interfaces of plasticized membrane electrodes.

Cyclic voltammetry (CV), synchrotron radiation-X-ray photoelectron spectroscopy (SR-XPS) and near edge X-ray absorption fine structure (NEXAFS) show that oxidation of ferrocene tagged PVC induces an accumulation of high molecular weight polymer at the buried interface between the substrate electrode and the plasticized membrane.

Is ballistic transportation or quantum confinement responsible for changes in the electrical properties of thin polymer films?

Resistivities of thin polymer films increase abruptly with decreasing thickness, although the corresponding decline in resistance plateaus below a certain thickness. One can jump to the incorrect conclusion that quantum confinement and surface scattering are responsible for this behaviour, and we highlight the pitfalls of committing such an error.

Sulfur-adlayer-coated gold electrode for the in vitro electrochemical detection of uric acid in urine.

The present article demonstrates the electrochemical oxidation of uric acid (UA) at sulfur-adlayer-coated gold (S-Au) electrode in alkaline media. At S-Au electrode, UA oxidized at a significantly lower overpotential with a higher current density as compared to the bare Au electrode. The oxidation of UA at the S-Au electrode is highly selective in the presence of the other commonly existing bio-molecules in urine. The proposed electrochemical sensor not only exhibited good reproducibility, but also showed a fast amperometric response to UA in the concentration range of 0.0025-5 mM with a low detection limit of 0.4 microM.

Nonlinear phenomena at mercury Hg electrode/room-temperature ionic liquid (RTIL) interfaces: polarographic streaming maxima and current oscillation.

The polarographic streaming maxima and cyclic voltammetric anodic current oscillation (CVACO) at a hanging mercury drop electrode (HMDE) in room-temperature ionic liquid (RTIL) have been studied for the first time using cyclic voltammetric, potential step chronoamperometric and pulse voltammetric techniques. The reversible redox reaction of the 2,1,3-benzothiadiazole (BTD)/BTD*- (an anion radical of BTD) couple with a formal potential (E0') of -1.36 V versus Ag/AgCl/NaCl(saturated) in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) RTIL was typically employed for this purpose. A maximum was observed at the rising part of the normal pulse voltammogram for the reduction of BTD to BTD*- as well as of the reversed pulse voltammogram for the reoxidation of BTD*- to BTD at the HMDE. The conditions of the initiation and control of the CVACO at the HMDE in EMIBF4 were extensively investigated. Generally, the CVACO was enhanced by increasing the concentration of BTD at a given potential scan rate (upsilon) and was attenuated by increasing upsilon. An electrocapillary curve was measured using a dropping mercury electrode in EMIBF4, and the potential of zero charge was determined to be -0.23 V. On the basis of the modern theory of the polarographic streaming maxima of the first kind, the observed streaming maxima and CVACO phenomena are successfully explained to originate from the macroscopic instability at the electrode/solution interface wherein the oscillating mode creates the CVACO.