Amplified electron transfer at poly-ethylene-glycol (PEG) grafted electrodes

Abstract

"Amplified" electron transfer is observed purely based on electron transfer kinetic effects at modified carbon surfaces. An anodic attachment methodology is employed to modify the surface of glassy carbon or boron doped diamond electrodes with poly-ethylene glycols (PEGs) for polymerisation degrees of n = 4.5 to 9.1 (PEG200 to PEG400). Voltammetry and impedance data for aqueous Fe(CN)6(3-/4-) suggest systematic PEG structure-dependent effects on the standard rate constant for heterogeneous electron transfer as a function of PEG deposition conditions and average polymer chain length. Tunnel distance coefficients are polymerisation degree dependent and estimated for shorter PEG chains, β = 0.17 Å(-1) for aqueous Fe(CN)6(3-/4-), consistent with a diffuse water-PEG interface. In contrast, electron transfer to 1,1'-ferrocene-dimethanol (at 1 mM concentration) appears un-impeded by PEG grafts. Mediated or "amplified" electron transfer to Fe(CN)6(3-/4-) based on the 1,1'-ferrocene-dimethanol redox shuttle is observed for both oxidation and reduction with estimated bimolecular rate constants for homogeneous electron transfer of kforward = 4 × 10(5) mol dm(3) s(-1) and kbackward = 1 × 10(5) mol dm(3) s(-1). Digital simulation analysis suggests an additional resistive component within the PEG graft double layer.

Amplified Charge Transfer for Anionic Redox Probes through Oriented Mesoporous Silica Thin Films

“…This explains the signal amplification for Fe(CN) 6 4− oxidation. The redox shuttling resembles that reported for amplified electron transfer at monolayer‐ or polymer‐grafted electrodes, but is nevertheless conceptually different in the sense that long‐range charge shuttling is involved here (film thickness=100 nm) whereas previously reported amplification was purely based on electron transfer kinetic effects.…”

“…anodic peak currents of 12.4, 16.5, and 49.8 μA, respectively, for Fe(CN) 6 4− concentrations of 0.5, 1.0, and 5.0 m m ). This is consistent with the diffusion‐limited mechanism suggested above, as a simple bimolecular mediation process would have resulted in a linear relationship . One can also notice from the voltammetric data in Figure that, once the signals become peak‐shaped (i.e.…”

“…This is consistent with the diffusion-limited mechanism suggested above, as as imple bimolecular mediation process would have resulted in al inear relationship. [62] One can also notice from the voltammetric data in Figure 5t hat, once the signals become peak-shaped( i.e. at sufficiently high mediator concentration), the mediated redox process is likely to operate in both oxidation and reduction modes, thanks to the close proximity of the standard potentials of the redoxs ystems [Fc(MeOH) 2 + /0 and Fe(CN) 6 3À/4À ].…”

Lubricin Antiadhesive Coatings Exhibit Size‐Selective Transport Properties that Inhibit Biofouling of Electrode Surfaces with Minimal Loss in Electrochemical Activity

“…Direct modification of electrode surfaces with self‐assembling antiadhesive molecules, typically polyethylene glycol (PEG), is an alternative approach that has been used with limited success. The main drawback of direct modification of electrode surfaces with antifouling agents is that they too often passivate the electrode with detrimental effects on amperometric or voltammetric sensing and are instead more suitable for optical or impedimetric approaches …”

Microporous La–Metal–Organic Framework (MOF) with Large Surface Area

“…“Protected” PEGs with alkylated terminal alcohol groups have been studied as electrolyte5 and can be applied in energy storage technologies6 or as gel electrolytes in solar cells 7. Surface immobilised PEGs have been employed in sensors8 and for controlling electrochemical surface reactivity 9. PEGs generally may be considered very benign and low‐cost, low‐volatility industrial solvent media with many interesting properties including 1) ability to absorb moisture,10 2) ability to bind carbon dioxide,11, 12 and 3) introducing resistance of surfaces to biofouling 13.…”