Assisted lipid deposition by reductive electrochemical aryldiazonium grafting and insertion of the antiport NhaA protein in this stable biomimetic membrane.

Quartz crystal microbalance studies have been carried out to monitor the fusion of lipid vesicles (pure 1,2-dimyristoyl-sn-glycero-3-phosphocholine, DMPC) and mixed vesicles (DMPC and 4-decylaniline). In order to increase the stability of the lipid deposits onto the electrodes, we have developed an original approach involving electrografting of adsorbed mixed vesicles. Aryldiazonium salts generated in situ from 4-decylaniline (4DA) present in adsorbed and fused mixed vesicles at the electrode surface allow their cathodic reduction and subsequent grafting. The stability of the supported lipid deposit has been shown to significantly increase from less than one day for pure DMPC to about two weeks with the lipid deposition assisted by electrochemical grafting. In this stable lipid deposit, the insertion of the sodium/proton antiporter membrane protein (NhaA) or its inactive mutant has been carried out by fusion of proteoliposomes. This has been followed by characterization of the inserted protein activity by cyclic voltammetry onto an electrode previously modified by an adsorbed pH sensor (2-anthraquinone sulfonate). Activation of the protein function by sodium ions leads to a shift of the interfacial pH and confirms the integrity of the immobilized NhaA.

High catalytic performance of laccase wired to naphthylated multiwall carbon nanotubes.

The direct electrical connection of laccase on the electrode surface is a key feature in the design of efficient and stable biocathodes. However, laccase can perform a direct electron transfer only when it is in the preferred orientation toward the electrode. Here we report the investigation of the orientation of laccase from white rot fungus on multi-walled carbon nanotube surface modified with a naphthalene group. Naphthylated multi wall carbon nanotubes were synthesized and the kinetics of laccase from white rot fungus adsorption and its direct electro-catalytic activity toward oxygen reduction was investigated by QCM and electrochemical techniques. Compared to pristine multi-walled carbon nanotubes laccase shows a high affinity to be adsorbed onto the surface of naphthylated carbon nanotubes at a very fast rate. The subsequent wiring to the naphthylated multi-walled carbon nanotubes is accompanied by a reorientation and arrangement of adsorbed laccase to create a composite biocathode that exhibits a high-performance for oxygen reduction by direct electron transfer with maximum current densities of 3 mA cm-2.

Laccase-based biocathodes: Comparison of chitosan and Nafion.

Chitosan and Nafion(®) are both reported as interesting polymers to be integrated into the structure of 3D electrodes for biofuel cells. Their advantage is mainly related to their chemical properties, which have a positive impact on the stability of electrodes such as the laccase-based biocathode. For optimal function in implantable applications the biocathode requires coating with a biocompatible semi-permeable membrane that is designed to prevent the loss of enzyme activity and to protect the structure of the biocathode. Since such membranes are integrated into the electrodes ultimately implanted, they must be fully characterized to demonstrate that there is no interference with the performance of the electrode. In the present study, we demonstrate that chitosan provides superior stability compared with Nafion(®) and should be considered as an optimum solution to enhance the biocompatibility and the stability of 3D bioelectrodes.

Single glucose biofuel cells implanted in rats power electronic devices.

We describe the first implanted glucose biofuel cell (GBFC) that is capable of generating sufficient power from a mammal's body fluids to act as the sole power source for electronic devices. This GBFC is based on carbon nanotube/enzyme electrodes, which utilize glucose oxidase for glucose oxidation and laccase for dioxygen reduction. The GBFC, implanted in the abdominal cavity of a rat, produces an average open-circuit voltage of 0.57 V. This implanted GBFC delivered a power output of 38.7 µW, which corresponded to a power density of 193.5 µW cm(-2) and a volumetric power of 161 µW mL(-1). We demonstrate that one single implanted enzymatic GBFC can power a light-emitting diode (LED), or a digital thermometer. In addition, no signs of rejection or inflammation were observed after 110 days implantation in the rat.

Metallic oxide CdIn2O4 films for the label free electrochemical detection of DNA hybridization.

DNA functionalised semiconductor metallic oxide electrodes have been developed for the direct electrochemical detection of DNA hybridization, without labelling or the introduction of a redox couple. Conductive CdIn(2)O(4) thin films with controlled properties were deposited on glass substrates using an aerosol pyrolysis technique. The films exhibit a polycrystalline microstructure with a surface roughness of 1.5 nm (r.m.s.) and an electrical resistivity ranging between 1 and 3 x 10(-3) Omega cm. These electrodes were functionalised using hydroxylation and silanisation steps, to allow the binding of DNA probe sequences (20 bases). The electrical detection of DNA hybridization with complementary sequences has been performed using electrochemical impedance spectrometry (EIS) measuring the variation of impedance before and after hybridization. Two set-ups were used, a standard set-up including three electrodes and a set-up including two symmetrical electrodes. In both configurations, a significant increase of the impedance modulus, more particularly of the real part of the impedance (160-225% according to the electrochemical cell used) has been obtained over a frequency range of 10-10(5)Hz. DNA hybridization has also been systematically confirmed using the fluorescence spectrometry. This study emphasizes the high sensitivity of the CdIn(2)O(4) as a working electrode for the detection of biological events occurring at the electrode surface.