Erica S. Forzani

Gravimetric and viscoelastic changes during the oxidation–reduction of layer-by-layer self assembled enzyme multilayers wired by an Os-containing poly(allylamine) polymer

The ellipsometric and mass increase during the oxidation � /reduction cycles of self-assembled layer-by-layer osmium complex derivatized poly(allylamine) and glucose oxidase multilayers due to the exchange of anions and solvent with the electrolyte and viscoelastic changes of the surface layer have been studied using the electrochemical quartz crystal microbalance (EQCM) technique. From the measurement of the quartz crystal impedance spectrum of films deposited on a thiolate Au-quartz crystal immersed in viscous aqueous electrolyte, simultaneously with cyclic voltammetry and potential steps, the real (RS) and imaginary components (XLS � /vLS) of the quartz complex impedance load have been derived. It has been shown that the quartz crystal impedance of the composite resonator (film and liquid) increases with the number of deposited layers due to increase of both the film thickness and the shear modulus. The reduced polymer multilayers, with ellipsometric thickness ranging from 200 to 600 nm behave as acoustically thin films, while in the oxidized Os(III) films viscoelastic characteristics are apparent at 10 MHz. Using a viscoelastic model for the enzyme/polymer film we conclude that the film acoustic impedance increases with the number of self-assembled layers due to the thickness increase, and also to the increase of the shear modulus due to oxidation. The values of the shear modulus and loss tangent were estimated from the acoustic impedance, the film density and the ellipsometric thickness; the latter follows a linear dependence with the degree of oxidation. The increase of loss modulus, and hence loss tangent, is more pronounced, the larger the degree of polymer oxidation. # 2002 Elsevier Science B.V. All rights reserved.

New bimetallic porphyrin film: An electrocatalytic transducer for hydrogen peroxide reduction, applicable to first-generation oxidase-based biosensors

Abstract A bimetallic porphyrin film was studied as electrode modifier with catalytic activity for molecular oxygen reduction and hydrogen peroxide reduction. Molecular oxygen reduction is catalyzed by both polyFePPIX or polyCuPPIX. Peroxidase activity at−200xa0mV versus Ag/AgCl is only performed by polyFePPIX in absence of oxidative agents, and the deposit polyCuPPIX is required to perform peroxidase activity in the presence of oxygen. Copper substitution by other metals in the porphyrin was not effective. It has been found that metalloporphyrin immobilization order acquire particular relevance. However, the mass of porphyrin deposit is always 1.5–1.6xa0μg of polyFePPIX and 7.3–9.1xa0μg of polyCuPPIX, indicating that polymer growth rate is not affected by immobilization order. polyCuPPIX deposited on polyFePPIX preserves catalytic properties over a wide pH range, and acts as a molecular sieve. The use of this bimetallic electrode in a first-generation oxidase biosensors is discussed.

Probe beam deflection study of ion exchange in self-assembled redox polyelectrolyte thin films

Probe beam deflection during chronoamperometric oxidation-reduction of osmium complex in layer-by-layer self-assembled redox active polyelectrolyte multilayers has shown that the nature of the charge in the topmost layer determines the ion flux that balances the redox charge.

Measurement of hydrolysis decay time constants of monoarylimino derivatives of β-lapachone through cyclic voltammetry

Abstract The stability of monoarylimino o-quinones derived from β-lapachone (1) was studied by cyclic voltammetry in buffer solutions of different pH values. Experiments performed on glassy carbon electrodes demonstrated not only that β-lapachone derivatives (2–6) are electroactive compounds but also that β-lapachone is one of the hydrolysis products. Decreasing concentrations of β-lapachone derivatives and increasing concentrations of β-lapachone were electrochemically evaluated and decay time constants were determined. All the studied compounds showed hydrolysis kinetics more rapid in acidic media than in neutral solutions, resulting the p-nitrophenylimine (5) and p-bromophenylimine (6) the most stable compounds at pH 4.5 and 7.4, respectively. Stability of the monoarylimino derivatives and their correlation with biological activity tests were analysed in order to propose some of the studied compounds as prodrugs of cancer therapy.