Effects of the nature and charge of the topmost layer in layer by layer self assembled amperometric enzyme electrodes.

Organized layer-by-layer nanostructured amperometric enzyme electrodes with self-contained redox polyelectrolyte mediators have shown important effects depending on the nature and charge of the adsorbed topmost layer. Adsorption of PVS causes the drop of the catalytic responses to negligible values due to hindrance in electron hopping and enzyme wiring.

Wired-enzyme core-shell Au nanoparticle biosensor.

We report a fully integrated core-shell nanoparticle system responsive to glucose. The system is comprised of self-assembled glucose oxidase and an osmium molecular wire on core-shell Au nanoparticles. Characterization of the functional nanoparticles by spectroscopy, quartz crystal microbalance and electrochemical techniques has shown that the catalytically active shell has a structure as designed and all components are active in the self-assembled multilayer shell. Furthermore, amperometric reagentless detection of glucose and contactless photonic biosensing by the Os(II) resonant Raman signal have been demonstrated. The enzymatic reduction of FAD by glucose and further reduction of the Raman silent Os(III) by FADH 2 yields a characteristic enzyme-substrate calibration curve in the millimolar range. Furthermore, coupling of electronic resonant Raman of the osmium complex with the SERS amplification by Au NPs plasmon resonance has been demonstrated which leads to an extra enhancement of the biosensor signal. We present a proof of concept extending the work done with planar surfaces to core-shell NPs as an advance in the design of glucose-responsive chemistry detected by SERS-like methods.

Extracting kinetic parameters for homogeneous [Os(bpy)2ClPyCOOH]+ mediated enzyme reactions from cyclic voltammetry and simulations.

The homogeneous reaction between glucose oxidase and osmium bipyridine-pyridine carboxylic acid in the presence of glucose has been studied in detail by cyclic voltammetry and digital simulation. Combination of the analytical equations that describe the dependence of the amperometric response on enzyme, substrate and co-substrate concentrations for the limiting cases with digital simulation of the coupled enzyme reaction diffusion problem allows us to extract kinetic parameters for the substrate-enzyme reaction: K(MS)=10.8 mM, k(cat)=254 s(-1) and for the redox mediator-enzyme reaction, k=2.2x10(5) M(-1) s(-1). The accurate determination of the kinetic parameters at low substrate concentrations (<7 mM) is limited by depletion of the substrate close to the electrode surface. At high substrate concentrations (>20 mM) inactivation of the reduced form of glucose oxidase in the bulk solution must be taken into account in the analysis of the results.

Relaxation and Simplex mathematical algorithms applied to the study of steady-state electrochemical responses of immobilized enzyme biosensors: Comparison with experiments.

A description of the implementation of the relaxation method with automatic mesh point allocation for immobilized enzyme electrodes is presented. The advantages of this method for the solution of coupled reaction-diffusion problems are discussed. The relaxation numerical simulation technique is combined with the Simplex fitting algorithm to extract kinetic parameters from experimental data. The results of the simulations are compared to experimental data from self-assembled multilayered electrodes comprised of glucose oxidase (GOx) and an Os modified redox mediator and found to be in excellent agreement.