Boron doped diamond biotechnology: from sensors to neurointerfaces.

Boron doped nanocrystalline diamond is known as a remarkable material for the fabrication of sensors, taking advantage of its biocompatibility, electrochemical properties, and stability. Sensors can be fabricated to directly probe physiological species from biofluids (e.g. blood or urine), as will be presented. In collaboration with electrophysiologists and biologists, the technology was adapted to enable structured diamond devices such as microelectrode arrays (MEAs), i.e. common electrophysiology tools, to probe neuronal activity distributed over large populations of neurons or embryonic organs. Specific MEAs can also be used to build neural prostheses or implants to compensate function losses due to lesions or degeneration of parts of the central nervous system, such as retinal implants, which exhibit real promise as biocompatible neuroprostheses for in vivo neuronal stimulations. New electrode geometries enable high performance electrodes to surpass more conventional materials for such applications.

New acridone derivatives for the electrochemical DNA-hybridisation labelling.

In the field of DNA sensing, DNA hybridisation detection is generally performed by fluorescence microscopy. However, fluorescence instrumentation is difficult to miniaturise in order to produce fully integrated DNA chips. In this context, electrochemical detection of DNA hybridisation may avoid this limitation. Therefore, the use of DNA intercalators is particularly attractive due to their selectivity toward DNA double strand enabling DNA labelling without target chemical modification and, for most of them, to their electroactivity. We have synthesized a pyridoacridone derivative dedicated to DNA hybridisation electrochemical-sensing which presents good electrochemical reversibility, electroactivity at mild potentials and specificity toward DNA double strand. The electrochemical behaviour of this molecule has been assessed using cyclic voltammetry (CV). DNA/intercalator interactions were studied by differential pulse voltammetry (DPV) before application to hybridisation detection onto DNA sensors based on polypyrrole modified electrodes.

Biotinylated polypyrrole films: an easy electrochemical approach for the reagentless immobilization of bacteria on electrode surfaces.

Biotinylated bacteria were immobilized onto biotin/avidin modified electrode surfaces. Firstly, an electrospotting deposition method, followed by fluorescence microscopy, showed that bacteria were specifically grafted onto a gold surface. Fluorescence intensity versus the quantity of bacteria deposited on the surface was correlated, allowing determination of the microbial saturation point. Secondly, biotinylated bacteria were immobilized onto a glassy carbon macro-electrode in order to assess immobilized bacterial denitrification activity. During a 7-day trial, the modified electrode completely denitrified 5 mM nitrate, with a rate of 1.66 mM/day over the first 3 days. When the same electrode was placed in fresh nitrate solution, the denitrification rate dropped to 0.80 mM/day. Crucially, the immobilized bacteria did not become detached from the electrode during the study.

Composite carbon paste biosensor for phenolic derivatives based on in situ electrogenerated polypyrrole binder.

Amperometric biosensors based on new composite carbon paste (CPE) electrodes have been designed for the determination of phenolic compounds. The composite CPEs were prepared by in situ generation of polypyrrole (PPy) within a paste containing the enzyme polyphenol oxidase (PPO). The best paste composition (enzyme/pyrrole monomer/carbon particles/Nujol) was determined for a model enzyme, glucose oxidase, according to the enzymatic activity of the resulting electrodes and to the enzyme leakage from the paste during storage in phosphate buffer. The in situ electrogenerated PPy enables improvement in enzyme immobilization within the paste since practically no enzyme was lost in solution after 72 h of immersion. Moreover, the enzyme activity remains particularly stable under storage since the biocomposite structure maintains 80% of its activity after 1-month storage. Following the optimization of the paste composition, PPO-based carbon paste biosensors were prepared and presented excellent analytical properties toward catechol detection with a sensitivity of 4.7 A M(-1) cm(-2) and a response time lower than 20 s. The resulting biosensors were finally applied to the determination of epicatechin and ferulic acid as flavonol and polyphenol model, respectively.

Electropolymerisable pyrrole-oligonucleotide: synthesis and analysis of ODN hybridisation by fluorescence and QCM.

Conducting polymer films, such as polypyrrole, appear particularly attractive for the immobilisation of biological molecules by entrapment or covalent grafting. We describe here a new pyrrole phosphorarnidite building block allowing the synthesis of oligonucleotide (ODN) bearing a pyrrole moiety. The electropolymerisable pyrrole moiety was then introduced on the 5' end of the oligonucleotide. The electrosynthesis of a copolymer, from solutions containing pyrrole and pyrrole-ODN, gives in one step strongly adhesive films containing ODN probes at electrode surfaces. In this contribution, we have used such a methodology to verify its feasibility for the modification of quartz crystal microbalance (QCM) electrodes. The obtained biosensors enable the detection of DNA hybridisation in real time by micro-gravimetric transduction. Finally, as DNA targets were previously modified by biotin, we have used the affinity between biotin and avidin to validate the effectiveness of QCM transduction by fluorescence microscopy and to amplify the recorded micro-gravimetric signal.

Inclusion of metal micro-particles into poly(pyrrolylalkylammonium) films containing an enzyme for bioelectrocatalysis: a preliminary study.

The electrocatalytic detection of products issued from enzymatic reactions occuring at biosensor interfaces can be improved owing to metal microparticle dispersions. This contribution describes the faesability of this concept for the modification poly(pyrrolylalkylammonium) films containing an enzyme through the inclusion of platinum. A model enzyme, glucose oxidase (GOx) was employed to demonstrate the reliability of this approach through the design of an amperometric glucose biosensors. The obtained composite assemblies were characterised regarding their sensing capabilities toward glucose. Platinum particles incorporation was operated within the biofilms to obtain a suitable sensitivity of the biosensor to glucose at a lower operational oxidation potential (eg 0.5 V/SCE) than the oxidation potential generally observed for hydrogen peroxide detection onto carbon electrodes. The incorporation procedure of platinum aggregates has been optimised to design biosensors exhibiting a sensitivity of about 8 mA. M(-1) cm(-2).

A comparison of amperometric screen-printed, carbon electrodes and their application to the analysis of phenolic compounds present in beers.

In this paper a comparison between three commercially-available, screen-printable graphite inks for the construction of phenolic biosensors is made. The enzyme tyrosinase was immobilised within a polymer matrix and the substrate catechol was used to characterise the bio-electroanalytical response of each electrode. Biosensors fabricated from Gwent graphite inks exhibited the greatest sensitivity (5740 mA mol cm(-2)) compared to Dupont and Acheson graphite-based inks. This difference in sensitivity was attributed to a combination of a larger electroactive surface area, and thus a greater number of immobilised enzyme molecules. However, the dynamic range was considerably smaller (0.025-14 muM) indicating that the enzyme molecules were easily accessible to the substrate catechol. The surface properties of the biosensors were characterised using ac impedance, which indicated that the presence of the polymer on the electrode surface not only increased the charge-transfer kinetics of the three biosensors, but also increased the surface roughness of biosensors fabricated from Gwent inks. On the basis of these results Gwent graphite-based inks were used for analysis of phenolic compounds in lager beers by flow-injection analysis. The biosensor displayed favourable response characteristics, but cannot differentiate between the various phenolic compounds present in the samples. Nevertheless, the biosensor maybe suitable for indicating the phenolic status of beer or brew samples compared to time-consuming traditional methods, e.g. colorimetric or chromatographic methods.

Swelling and delamination of multi-electrode sensor arrays studied by variable-pressure scanning electron microscopy.

Multi-electrode sensor arrays are made of soft and wet materials not easily examined by most microscopic techniques. In this paper, we have demonstrated that low-vacuum scanning electron microscopy (LVSEM) and energy-dispersive X-ray analysis (EDX) are adequate for studying the hydration, swelling, and possible delamination of multi-electrode sensor arrays. We found that the LVSEM environment had no detectable effect on the morphology of Na(+), K(+), and Ca(++) sensors, and EDX analysis indicated that all three membranes have similar compositions. However, once hydrated, the sensors exhibited different behaviors. The K(+) and Ca(++) sensors swelled more than the Na(+) sensor did. This swelling is due principally to water sorption in the membrane. We believe that the larger thickness of the K(+) and Ca(++) membrane is partly responsible for the observed swelling effect. A simple Griffith analysis of the interface rupture confirms the experimental evidence that these thicker membranes also are more prone to delamination failure.