Surface modification of carbon materials with biological molecules under ambient condition is desirable for construction of biosensor and bioelectronic devices. Some of the desirable factors for surface modification are (i) robust attachment of biomolecules for stable biosensor response, (ii) high surface coverage of biomolecules for good signal/noise ratio and wide dynamic range, and (iii) rapid modification under ambient condition for facile and scalable manufacturing. A new method to electrochemically modify carbon electrodes using a benzothiadiazole-based conjugated polymer will be discussed. The method provides rapid modification of carbon materials with biomolecules, robustly attached to the surface through the polymer. The usefulness of the method will be demonstrated by construction of an electrochemical cholesterol biosensor. The biosensor exhibits amperometric detection of cholesterol in buffer and serum samples in presence of a soluble mediator. Details regarding the preparation of biomolecule-coupled polymer, surface modification and sensor performance will be discussed.

La presente invention concerne de nouvelles matieres qui combinent les avantages de matieres de depart polymeres bien definies et la commodite de modification de surface par des procedes physiques en un conditionnement et, ainsi, offre une plateforme generale et puissante appropriee pour une utilisation dans de nombreuses applications.

A Cu-I complex of 3-ethynyl-phenanthroline covalently immobilized onto an azide-modified glassy carbon surface is an active electrocatalyst for the four-electron (4-e) reduction of O-2 to H2O. The rate of O-2 reduction is second-order in Cu coverage at moderate overpotential, suggesting that two Cu-I species are necessary for efficient 4-e reduction of O-2. Mechanisms for O-2 reduction are proposed that are consistent with the observations for this covalently immobilized system and previously reported results for a similar physisorbed Cu-I system.

In this report, we present a novel platform to study proton-coupled electron transfer (PCET) by controlling the proton flux using an electrode-supported hybrid bilayer membrane (HBM). Oxygen reduction by an iron porphyrin was used as a model PCET reaction. The proton flux was controlled by incorporating an aliphatic proton carrier, decanoic acid, into the lipid layer of the HBM. Using this system, we observed a different catalytic behavior than obtained by simply changing the pH of the solution in the absence of an HBM.

An electrode-supported system in which ferrocene molecules are embedded in a hybrid bilayer membrane (HBM) has been prepared and characterized. The redox properties of the ferrocene molecules were studied by varying the lipid and alkanethiol building blocks of the HBM. The midpoint potential and electron transfer rate of the embedded ferrocene were found to be dependent on the hydrophobic nature of the electrolyte and the distance at which the ferrocene was positioned in the HBM relative to the electrode and the solution. Additionally, the ability of the lipid-embedded ferrocenium ions to oxidize solution phase ascorbic acid was evaluated and found to be dependent on the nature of the counterion.

Cholesterol is a tightly regulated structural component of the cell plasma membrane. Dysfunctional intracellular cholesterol transport machinery causes disease states with altered plasma membrane cholesterol. This Communication reports microelectrode evaluation of plasma membrane cholesterol of single cells at physiological temperature. Electrochemical data indicate that transport of intracellular cholesterol to the plasma membrane is active in an atherosclerotic macrophage model.

Azide-modified graphitic surfaces were prepared by reaction with iodine azide. The surface-attached azides undergo the “click” reaction with alkyne-terminated molecules ethynylferrocene and 1-ethynyl-4-(trifluoromethyl)benzene. Voltammetric and XPS analyses show the surface coverage of both the azide and the subsequent triazole of 2 × 1013 molecules/cm2. The 1,2,3-triazole linker is stable in an aqueous 1 M HCl solution for at least 60 min at 55 °C.

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Platinum microelectrodes are modified with a lipid bilayer membrane incorporating cholesterol oxidase. Details for electrode surface modification are presented along with characterization studies of electrode response to cholesterol solution and to cholesterol contained in the lipid bilayer membrane of vesicles. Ferrocyanide voltammetric experiments are used to track deposition of a submonolayer of a thiol-functionalized lipid on the platinum electrode surface, vesicle fusion for bilayer formation on the thiolipid-modified surface, and incorporation of cholesterol oxidase in the electrode-supported thiolipid/lipid bilayer membrane. The data are consistent with formation of a lipid bilayer structure on the electrode surface that contains defects. Experiments for detection of cholesterol solubilized in cyclodextrin solution show steady-state current responses that correlate with cholesterol concentration. Direct contact between the electrode and a vesicle lipid bilayer membrane shows a response that correlates with vesicle membrane cholesterol content.

Cholesterol oxidase is immobilized in electrode-supported lipid bilayer membranes. Platinum electrodes are initially modified with a self-assembled monolayer of thiolipid. A vesicle fusion method is used to deposit an outer leaflet of phospholipids onto the thiolipid monolayer forming a thiolipid/lipid bilayer membrane on the electrode surface. Cholesterol oxidase spontaneously inserts into the electrode-supported lipid bilayer membrane from solution and is consequently immobilized to the electrode surface. Cholesterol partitions into the membrane from buffer solutions containing cyclodextrin. Cholesterol oxidase catalyzes the oxidation of cholesterol by molecular oxygen, forming hydrogen peroxide as a product. Amperometric detection of hydrogen peroxide for continuous solution flow experiments are presented, where flow was alternated between cholesterol solution and buffer containing no cholesterol. Steady-state anodic currents were observed during exposures of cholesterol solutions ranging in concentration from 10 to 1000μM. These data are consistent with the Michaelis–Menten kinetic model for oxidation of cholesterol as catalyzed by cholesterol oxidase immobilized in the lipid bilayer membrane. The cholesterol detection limit is below 1μM for cholesterol solution prepared in buffered cyclodextrin. The response of the electrodes to low density lipoprotein solutions is increased upon addition of cyclodextrin. Evidence for adsorption of low density lipoprotein to the electrode surface is presented.

Platinum microelectrodes modified with a lipid bilayer membrane incorporating cholesterol oxidase are used for detection of cholesterol contained in the plasma membrane of a single cell. Amperometric responses are consistent with enzymatic catalysis being rate limiting and cholesterol diffusing laterally in the plasma membrane to the electrode contact site. Importantly, electrode response appears to correlate with the cholesterol content of the cell plasma membrane. The electrodes should be useful for characterizing cellular cholesterol tracking pathways involved in pathogenesis of disease.

Cholesterol oxidase is immobilized in lipid bilayer membranes assembled on tin-doped indium oxide electrode surfaces to sequester cholesterol from solution and to follow cholesterol oxidation via electrochemical reduction of hydrogen peroxide. The inner leaflet of the bilayer is chemically bound to the electrode surface through a thiol functionality at the polar headgroup end of the lipid. The outer lipid leaflet, containing cholesterol oxidase, is formed using a deoxycholate dialysis procedure. Continuous solution flow experiments, where the flow is changed from buffer solution containing no cholesterol to a buffer solution containing cholesterol, show currents for the reduction of hydrogen peroxide generated by the enzyme. The data indicate that cholesterol oxidase is immobilized on the electrode in an active state. The data are also consistent with energetically favored collection of cholesterol from solution by the electrode-supported lipid bilayer membrane.

The energy-efficient removal of electrons is a key chemical step in an efficient electron economy. The objective of this project to develop efficient electrocatalysts for two important classes of oxidative chemical transformations. The first transformation is the oxidative conversion of methane to alcohols or higher hydrocarbons that would convert natural gas into valuable liquid fuels without the release of any carbon dioxide. The second transformation is the oxidation of water that is critical to any energy system that uses electrochemistry as an intermediary between electricity and stored fuels.