Mark Pritzker

Ionic-Complementary Peptide Matrix for Enzyme Immobilization and Biomolecular Sensing

A novel electrochemical biosensing platform is described using biocompatible, self-assembled ionic-complementary peptide nanofibers. The compatibility of a graphite electrode modified by these peptide nanofibers with enzymes is demonstrated using a model enzyme glucose oxidase (GOx). A glucose biosensor has been successfully fabricated by incorporating this enzyme into the modified electrode. From measurement of its electrode response and sensitivity, this nanofiber-modified electrode shows promise as an enzyme-based biosensor. The findings presented here demonstrate excellent potential of the use of ionic-complementary peptides to modify electrode surfaces for biomolecular sensing and diagnostics.

Low- and High-Frequency Pulse Current and Pulse Reverse Plating of Copper

A model for galvanostatic pulse plating via pulse current (PC) and pulse reverse (PR) modes has been developed and compared with experimentally obtained electrode responses during copper deposition from a CuSO 4 -H 2 SO 4 solution onto a rotating disk electrode. In addition to all forms of mass transport, electrode kinetics, and homogeneous reactions, the model incorporates capacitance effects due to double-layer charging and adsorption of an intermediate. Two important modifications from our previous model have been made: fully transient rather than steady-state electrode kinetics and a series rather than parallel connection between the adsorption pseudocapacitance and faradaic reactions. The model provides excellent quantitative agreement with the experimental results for both PR and PC plating for the entire range of conditions studied and shows considerable improvement over the previous version, particularly for PR plating. Fitting the model to some of the experimental data reveals that the double-layer capacity varies inversely with the square root of frequency for pulses of 500 Hz or more. Electrode responses do not totally become dc-like at frequencies as high as 50 kHz. Furthermore, at high enough frequencies (≥5 kHz) during PR plating, the electrode potentials do not rise above the open-circuit potential during the reverse-time, indicating that copper dissolution does not occur and leading to a response similar to that observed during high-frequency PC plating.

Aspects of copper electrodeposition from acidic sulphate solutions in presence of thiourea

Abstract This study focuses on clarifying certain aspects of copper electrodeposition from acidic sulphate solutions containing thiourea (TU). Examination by X-ray photoelectron spectroscopy (XPS) confirms the presence of TU on the deposit and reveals that the additive is incorporated in the coating throughout the course of plating. Polarisation experiments conducted in 0·1M CuSO4− 1·0M H2SO4 solutions at numerous TU concentrations particularly below 20 μM show that the electrode response during copper deposition changes qualitatively as the additive level is increased above 6 μM. These electrode responses are discussed in light of the knowledge of this system and used to propose a mechanism that is more consistent with the observed behaviour than previous explanations. In the presence of 20 μM TU, the coating remains bright as it grows to at least 10 μm thick, but then roughens with further growth to 25 μm. This trend is linked to the early stage formation of needle like protrusions or nodules that receive higher current than surrounding areas and eventually coarsen. Estimates of the maximum amount of TU depleted from solution during plating indicate that this alone cannot explain the loss of its levelling capability in later stages.

Electropolymerized poly(2-vinylpyridine) coatings as ion-exchange polymer modified electrodes

The effects of pH and of the nature and concentration of the electrolyte on the electrochemical behaviour of the Fe(CN)3−/4−6 charge-transfer reaction at a poly(2-vinylpyridine)-coated electrode formed by electropolymerization have been studied. Cyclic voltammetry during the Fe(CN)3−6 incorporation process was combined with measurement of the saturated concentration of the Fe(CN)3−6 confined in the films to investigate the electrochemical behaviour and the fundamental nature of the ion-exchange polymers. The poly(2-vinylpyridine) films formed by electropolymerization were found to have better properties (i.e., larger amount of Fe(CN)3−6 can be incorporated at various pH values and films are more chemically stable under acidic conditions) as polymer-modified electrodes than those formed by solvent evaporation. Of the various anions studied, ClO−4 was found to be distinct from the others (Cl−, NO−3, Br− and SO2−4). On the one hand, the polymer films exposed to ClO−4 are more dense and rigid than those exposed to other anions and show relatively little electroactivity. On the other hand, when the films are exposed to increasing concentrations of Cl−, the films become more swollen, thereby reducing the resistance within the film and enhancing the rate of charge-transfer from the outer film surface to the electrode surface.

Modified shrinking core model for uptake of water soluble species onto sorbent particles

Abstract The commonly used shrinking core model (SCM) envisages a sorbing species to diffuse through a particle as a sharp inward-moving front separating a completely untouched core ahead of the front from a completely saturated shell behind the front. However, in many situations involving the uptake of water soluble species onto sorbent particles and ion exchange resins, the assumption of a completely saturated shell may not be justified. The objective of this communication is to derive a model that generalizes the SCM to allow for an incompletely saturated shell. As with the SCM, the advance of the sorbate into the particle is marked by a distinct interface moving inward with a velocity dictated by the interplay between the rates of diffusion and uptake onto the solid matrix. Local equilibrium is considered to exist between the diffusing sorbing species in the pore space and the form bound to the matrix, as with many homogeneous models such as the linear absorption model (LAM). The model is general enough to accommodate any function describing this local equilibrium. We show that this model simplifies to the conventional SCM as a special limiting case. As an example, the model is applied to previously reported data for the uptake of Cu2+ ions onto calcium alginate gel beads and shown to fit well, comparable to that obtained previously using the SCM and LAM. However, the predicted concentration profiles within a particle during sorption are shown to vary markedly depending on the model.