Proteins voltammetry

Figure 4.39 Schematic representations of the various types of electrode surfaces for which protein voltammetry is commonly observed (a) a metal electrode modified with an XY SAM (b) a metal oxide electrode (c) an electrode modified with a surfactant layer in which protein molecules are embedded (d) a pyrolitic graphite edge electrode, often used in conjunction with mobile co-adsorbates such as aminocyclitols. Reprinted from Uectrochim. Acta, 45, F.A. Armstrong and G.S. Wilson, Recent developments in faradaic bioelectrochemistry, 2623-2645, Copyright (2000), with permission from Elsevier Science...

In Situ Imaging of Bio-related Molecules and Linker Molecules for Protein Voltammetry 97... 

The utility of direct protein voltammetry is enhanced when the molecules... 

Interfacial electrochemical electron transfer across thin dielectric films is, finally, a frequent environment in protein voltammetry (Fig. 8-2). 

Surface structures of ordered linker monolayers for protein voltammetry... 

Figure 8-12. Left Monolayer protein voltammetry of P. furiosus ferredoxin on an Au(lll)-electrode modified by a mercaptopropionic acid (MPA) SAM, cf, Fig. 8-lOC 5 mM phosphate buffer, pH 7.9. Scan rate 5 mV s . Middle In situ STM image of P. furiosus ferredoxin molecules in electron transport action on the same MPA-modified Au(lll)-electrode surface Ar-atmosphere. Working electrode potential -0.35 V (SCE), bias voltage -0.35 V. Tunneling current 0.10 nA. Right Schematic view of the P. furiosus ferredoxin molecule on the MPA-modified Au( 111 )-surface. From ref. 137 with permission.

Oven/iew Waters, Sediments, and Soils. Ion-Selective Electrodes Water Applications. Isotope Dilution Analysis. Liquid Chromatography Size-Exclusion Liquid Chromatography-Mass Spectrometry Mass Spectrometry Peptides and Proteins. Voltammetry Overview. 

Success in protein voltammetry depends critically upon the electrode and how it is prepared and modified. The current response may stem from protein molecules free in solution and undergoing a reaction upon diffusing to the electrode surface, or it may stem from molecules that are already bound tightly (adsorbed) to the electrode. Quasi-reversible diffusion-controlled electrochemistry has been documented for a wide range of proteins, mostly the smaller variety (molecular mass <15kDa) that function as mobile electron carriers [3], Diffusion-controlled electrochemistry requires that the protein interacts with the electrode in a transient manner, that is, weakly, so that the electrode does not become blocked. Increasingly, however, attention has turned to electrodes that bind protein molecules tightly, so that the sample is studied as a stable monolayer that typically comprises less than a picomole [1]. 

Fig. 1 Electrodes for protein voltammetry (a) noble metals (Au, Ag) modified with a SAM. Group X is typically sulfur, while Y is a functionality, such as —CH3, COO, CH2OH, the variety and mixture of which can be designed to optimize the interaction with the protein. Examples are described in Refs. [10-13] (b) a metal oxide electrode. Examples are described in Refs. [9, 15-lSj (c) a carbon electrode, typically pyrolytic graphite with the edge surface projected to the solution. Protein adsorption is often optimized by inclusion of polycations. Examples are described in Refs. [1,14) (d) An electrode coated with a surfactant layer within which the protein is confined. Examples are described in Refs. [19-21].

The success of protein voltammetry for DET measurements depends critically on the electrode material - how it is prepared and modified. The current response may come from (1) free diffusing molecules in solution or (2) tightly bound protein molecules. Diffusion-controlled electrochemistry (case 1) requires a transient interaction of the protein with the electrode so that the electrode is not blocked by reacted species. Nowadays the interest has turned more to electrode-bound protein molecules, allowing the study of redox proteins or redox enzymes as a stable monolayer or layer-by-layer assembly. Proteins can be immobilized by adsorpticm, electrostatic interaction, hydrophobic interaction or covalent bonds. 

Au nanoparticle (AuNP) electrodes prepared through various other deposition strategies have been extensively used for protein voltammetry and in electrochemical biosensing applica-tions. ° ° Electrodes with layers of HRP-modified AuNPs (prepared through covalent modification, self-assembly, or layer-by-layer techniques) have been shown to exhibit electrocatalytic activity toward the reduction of H2O2 through direct electron transfer between electrode and enzyme redox... 

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