Catalysis and Mass Transport in Spatially Ordered Enzyme Assemblies on Electrodes

Bourdillon, Christian; Demaille, Christophe; Moiroux, Jacques; Savéant, Jean‐Michel

doi:10.1021/ja00151a013

Cited by 110 publications

(94 citation statements)

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“…The reversible behavior is consistent with a large standard rate constant of ferrocene derivatives at carbon electrodes, e.g., k 0 = 0.19 cm/s for ferrocenemethanol at a glassy carbon electrode. 41 The geometrical parameters of b/a and RG in the best fits are consistent with those determined by optical microscopy. The current approach curve obtained with the 25 μm-diameter probe also fits with a theoretical curve for an insulating substrate, indicating that the unbiased substrate is too small in comparison with the probe diameter to regenerate the mediator.…”

Section: Finite Substrate Effectsupporting

confidence: 75%

Probing Heterogeneous Electron Transfer at an Unbiased Conductor by Scanning Electrochemical Microscopy in the Feedback Mode

2007

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The theory of the feedback mode of scanning electrochemical microscopy is extended for probing heterogeneous electron transfer at an unbiased conductor. A steady-state SECM diffusion problem with a pair of disk ultramicroelectrodes as a tip and a substrate is solved numerically. The potential of the unbiased substrate is such that the net current flow across the substrate/solution interface is zero. For a reversible substrate reaction, the potential and the corresponding tip current depend on SECM geometries with respective to the tip radius including not only the tip-substrate distance and the substrate radius but also the thickness of the insulating sheath surrounding the tip. A larger feedback current is obtained using a probe with a thinner insulating sheath, enabling identification of a smaller unbiased substrate with a radius that is approximately as small as the tip radius. An intrinsically slow reaction at an unbiased substrate as driven by a SECM probe can be quasireversible. The standard rate constant of the substrate reaction can be determined from the feedback tip current when the SECM geometries are known. The numerical simulations are extended to an SECM line scan above an unbiased substrate to demonstrate a "dip" in the steady-state tip current above the substrate center. The theoretical predictions are confirmed experimentally for reversible and quasi-reversible reactions at an unbiased disk substrate using disk probes with different tip radii and outer radii.Scanning electrochemical microscopy (SECM) is a powerful electroanalytical technique for probing interfacial reactions at a variety of substrates. 1-3 SECM is versatile partially because the substrates do not require an electrical connection to an external circuit, 4 which is in contrast to traditional electroanalytical techniques. 5 SECM measurement of unbiased substrates is advantageous when the substrates can not be conveniently connected to an external circuit or when the application of a potential causes an undesirable effect on the substrates. In particular, SECM feedback mode has been used in recent studies of charge transport at unbiased nanostructured systems such as metal nanoparticle arrays/films, 6-13 carbon nanotube network, 14 individual nanobands, 15 an array of protein nanopores, 16 and nanometer-thick polymer films. 17-20 A heterogeneous electron transfer process at an unbiased conductor can be studied by SECM in the feedback mode, where the process is driven and monitored using an ultramicroelectrode (UME) probe. Consider a disk UME positioned within a short distance (usually within about the tip diameter) of a disk-shaped conductive substrate (Figure 1). The UME tip is biased for electrolysis of a redox-active mediator, O, in the electrolyte solution (O + ne − → R; process 1 in Figure 1). The tip-generated species, R, diffuses to and reacts at the surface of the conductive

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Section: Finite Substrate Effectsupporting

confidence: 75%

Probing Heterogeneous Electron Transfer at an Unbiased Conductor by Scanning Electrochemical Microscopy in the Feedback Mode

2007

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“…Such high enzyme loadings of glucose oxidase could be achieved with SAM enzyme electrodes if a number of single molecule thick enzyme layers are deposited by exploiting some of the recently developed step-by-step immobilization techniques. [3][4][5][6][7][8][9][10][11][12][13][14] Such an approach could then lead to a transport limited enzyme electrode being fabricated in a highly controlled manner, thus exploiting the highly controlled immobilization virtues of the SAM approach with the advantages of transport limitation.…”

Section: What Limits the Response Of The Sam Enzyme Electrode?mentioning

confidence: 99%

“…Using SAMs has the potential to provide enzyme electrodes with a high degree of reproducibility, 1,2 molecular level control over the spatial distribution of the immobilized enzymes [3][4][5][6][7][8][9][10][11][12][13][14] and the immobilization of the enzyme close to the electrode thus allowing direct electron transfer to be achieved. [15][16][17][18][19][20][21][22][23][24] These advantages have resulted in a recent surge in research into self-assembled monolayers for biosensor applications in general, and enzyme electrodes in particular.…”

mentioning

confidence: 99%

Parameters Important in Fabricating Enzyme Electrodes Using Self-Assembled Monolayers of Alkanethiols

et al. 2001

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The immobilization of enzymes on the surface of electrodes modified with self-assembled monolayers (SAMs) provides a number of advantages as a method for the fabrication of enzyme electrodes. Using SAMs has the potential to provide enzyme electrodes with a high degree of reproducibility, 1,2 molecular level control over the spatial distribution of the immobilized enzymes 3-14 and the immobilization of the enzyme close to the electrode thus allowing direct electron transfer to be achieved. [15][16][17][18][19][20][21][22][23][24] These advantages have resulted in a recent surge in research into self-assembled monolayers for biosensor applications in general, and enzyme electrodes in particular. [25][26][27] However, despite the plethora of biosensor research papers using self-assembled monolayers as the base onto which the biomolecule is immobilized, there has been very little fundamental research into what steps are important in the fabrication process or which parameters control the response of the resultant biosensor.Alkanethiols modifying gold are the most popular SAMs. 25,26 The interaction between the thiol groups and the gold results in a strong pseudocovalent bond 28 which is stable throughout the potential range of 0.8 V to -1.4 V versus Ag/AgCl before being oxidatively or reductively desorbed. 29,30 If the alkanethiol has appropriate chemical functionality, such as an amine or carboxylic acid moiety, then once the SAM is formed, enzymes and other biomolecules can be easily covalently bound to the SAM. In this way, a monolayer or submonolayer of enzyme is immobilized. For enzyme electrodes a short alkyl chain alkanethiol, usually three carbons long, is chosen so that the enzyme is as close as possible to the electrode. An additional advantage of the short alkyl chain is that a relatively disordered SAM is formed which means the underlying metal is still electrochemically accessible. In contrast, if a long chain alkanethiol is used the electrode is passivated unless defects are deliberately introduced into the SAM. 31 There are a number of steps in the fabrication of an enzyme electrode using an alkanethiol. First, the metal surface must be prepared and cleaned. The alkanethiol must self-assemble onto the metal, followed by activation of the chemical functionality of the SAM, leading finally to the exposure of the activated SAM to the enzyme which is when attachment occurs. There are however many unknowns in this fabrication process. Questions that needs answers are: what effect does the roughness of the gold surface have? How long should the metal be exposed to the alkanethiol solution to allow a stable SAM to be formed? What is the optimal procedure for activating the SAM for enzyme attachment? How long should the activated SAM be exposed to enzyme? What should the concentration of the enzyme solution be during enzyme immobilization? Does the buffer used have any effect on subsequent performance? Can the amount of enzyme immobilized be controlled and do different enzyme loadings lead to different electr...

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“…A larger peak separation, and a larger increase in the peak separation for a hexacyanoferrate (II/III) couple might be additionally due to the lower electron transfer rate (k 0 =0.03 cm/s [36,37]) than that for ferrocenemethanol (k 0 =0.2 cm/s [36,38]) because of the bridge transition state pathway in the electron transfer in the anion redox process and complex reorganization, where the rate of the bridge-assisted electron transfer is higher than that of the direct electron transfer. However, this three-body problem in electron transfer is not within the scope of the present work and may require further investigations [39][40][41].…”

mentioning

confidence: 99%

On “resistance overpotential” caused by a potential drop along the ultrathin high aspect ratio gold nanowire electrodes in cyclic voltammetry

Muratova

Mikhelson

Ermolenko

et al. 2016

J Solid State Electrochem

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High aspect ratio ultrathin (d10 nm) gold nanowires deposited on Si/SiO2 substrate are used as working electrodes for measuring cyclic voltammograms (CVs) in aqueous solutions of ferrocene methanol and potassium hexacyanoferrate(III). The broadening of the peak separation as compared with that at a solid working electrode is explained as a result of the potential drop ("resistance overpotential") along nanowires and nanowire network. The change in the CV shape over a sequence of scans is ascribed to a gradual breakup of individual nanowires and the respective transition of the linear diffusion to hemispherical diffusion regularities.

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Catalysis and Mass Transport in Spatially Ordered Enzyme Assemblies on Electrodes

Cited by 110 publications

References 0 publications

Probing Heterogeneous Electron Transfer at an Unbiased Conductor by Scanning Electrochemical Microscopy in the Feedback Mode

Probing Heterogeneous Electron Transfer at an Unbiased Conductor by Scanning Electrochemical Microscopy in the Feedback Mode

Parameters Important in Fabricating Enzyme Electrodes Using Self-Assembled Monolayers of Alkanethiols

On “resistance overpotential” caused by a potential drop along the ultrathin high aspect ratio gold nanowire electrodes in cyclic voltammetry

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