Effect of Contact Area and Shape of Anode Current Collectors on Bacterial Community Structure in Microbial Fuel Cells.

Low electrical conductivity of carbon materials is a source of potential loss for large carbonaceous electrode surfaces of MFCs due to the long distance traveled by electrons to the collector. In this paper, different configurations of titanium current collectors were used to connect large surfaces of carbon cloth anodes. The current collectors had different distances and contact areas to the anode. For the same anode surface (490 cm2), increasing the contact area from 28 cm2 to 70 cm2 enhanced power output from 58 mW·m-2 to 107 mW·m-2. For the same contact area (28 cm2), decreasing the maximal distance of current collectors to anodes from 16.5 cm to 7.75 cm slightly increased power output from 50 mW·m-2 to 58 mW·m-2. Molecular biology characterization (qPCR and 16S rRNA gene sequencing) of anodic bacterial communities indicated that the Geobacter number was not correlated with power. Moreover, Geobacter and Desulfuromonas abundance increased with the drop in potential on the anode and with the presence of fermentative microorganisms. Electrochemical impedance spectroscopy (EIS) showed that biofilm resistance decreased with the abundance of electroactive bacteria. All these results showed that the electrical gradient arising from collectors shapes microbial communities. Consequently, current collectors influence the performance of carbon-based anodes for full-scale MFC applications.

Microcapsule-based biosensor containing catechol for the reagent-free inhibitive detection of benzoic acid by tyrosinase.

A biosensor based on the release of the enzyme substrate from its structure was developed for the inhibitive detection of benzoic acid. A polyurethane support comprising two perforated microcapsules (800 µm in diameter) filled with methylene blue as a model compound and covered with a conductive deposit of multiwalled carbon nanotubes, continuously released this stored dye for 24 h. An increase in methylene blue concentration of 0.5-0.75 µmol L-1 h-1 and 1.5-2 µmol L-1 h-1, in the presence and absence of the multiwalled carbon nanotube coating, respectively, was demonstrated by UV-vis spectroscopy in a 2 mL UV cuvette. The same configuration with microcapsules filled with catechol was modified by a laponite clay coating containing tyrosinase enzyme. The resulting biosensor exhibits a constant cathodic current at -0.155 V vs AgCl/Ag, due to the reduction of the ortho-quinone produced enzymatically from the released catechol. The detection of benzoic acid was recorded from the decrease in cathodic current due to its inhibiting action on the tyrosinase activity. Reagentless biosensors based on different deposited quantity of tyrosinase (100, 200, 400 and 600 µg) were investigated for the detection of catechol and applied to the detection of benzoic acid as inhibitor. The best performance was obtained with the 400 µg-based configuration, namely a detection limit of 0.4 µmol L-1 and a sensitivity of 228 mA L mol-1. After the inhibition process, the biosensors recover 97-100% of their activity towards catechol, confirming a reversible inhibition by benzoic acid.

Voltammetric sensing of recombinant viral dengue virus 2 NS1 based on Au nanoparticle-decorated multiwalled carbon nanotube composites.

A homemade gold electrode is modified with a carbon nanotubes/gold nanoparticles nanocomposite to perform selective and sensitive electrochemical detection of dengue toxin. This nanostructured composite offers a large specific surface and a reactive interface allowing the immobilization of biological material. Dengue antibodies are immobilized on gold nanoparticles via covalent bonding for dengue toxin detection. The porous tridimensional network of carbon nanotubes and gold nanoparticles enhances the electrochemical signal and the overall performance of the sensor. After optimization, the system exhibits a high sensitivity of - 0.44 ± 0.01 µA per decade with wide linear range between 1 × 10-12 and 1 × 10-6 g/mL at a working potential of 0.22 V vs Ag/AgCl. The extremely low detection limit (3 × 10-13 g/mL) ranks this immunosensor as one of the most efficient reported in the literature for the detection of recombinant viral dengue virus 2 NS1. This biosensor also offers good selectivity, characterized by a low response to various non-specific targets and assays in human serum. The outstanding performances and the reproducibility of the system place the biosensor developed among the best candidates for future medical applications and for early diagnosis of dengue fever. Graphical abstract.

Long duration stabilization of porous silicon membranes in physiological media: Application for implantable reactors.

The natural biodegradabilty of porous silicon (pSi) in physiological media limits its wider usage for implantable systems. We report the stabilization of porous silicon (pSi) membranes by chemical surface oxidation using RCA1 and RCA2 protocols, which was followed by a PEGylation process using a silane-PEG. These surface modifications stabilized the pSi to allow a long period of immersion in PBS, while leaving the pSi surface sufficiently hydrophilic for good filtration and diffusion of several biomolecules of different sizes without any blockage of the pSi structure. The pore sizes of the pSi membranes were between 5 and 20 nm, with the membrane thickness around 70 µm. The diffusion coefficient for fluorescein through the membrane was 2 × 10-10 cm2 s-1, and for glucose was 2.2 × 10-9 cm2 s-1. The pSi membrane maintained that level of glucose diffusion for one month of immersion in PBS. After 2 months immersion in PBS the pSi membrane continued to operate, but with a reduced glucose diffusion coefficient. The chemical stabilization of pSi membranes provided almost 1 week stable and functional biomolecule transport in blood plasma and opens the possibility for its short-term implantation as a diffusion membrane in biocompatible systems.

Functionalized tungsten disulfide nanotubes for dopamine and catechol detection in a tyrosinase-based amperometric biosensor design.

WS2 nanotubes functionalized with carboxylic acid functions (WS2-COOH) were used for improved immobilization of the enzyme tyrosinase in order to form an electrochemical biosensor towards catechol and dopamine. The nanotubes were deposited on glassy carbon electrodes using a dispersion-filtration-transfer procedure to assure the reproducibility of the deposits. After the electrochemical and morphological characterization of these WS2-COOH nanotube deposits, the formed biosensors showed very satisfying performance towards catechol detection with a linear range of 0.6-70 µmol L-1 and a sensitivity of 10.7 ± 0.2 mA L mol-1. The apparent Michaelis Menten constant of this system is slightly lower than the KM value of tyrosinase in solution, reflecting an excellent accessibility of the active site of the enzyme combined with a good mass transport of the target molecule through the deposit. For dopamine detection, we observed an accumulation of this substrate due to electrostatic interactions between the amine function of dopamine and the carboxylic acid groups of the nanotubes. This led to improved signal capture at low dopamine concentrations. With linear ranges of 0.5-10 µmol L-1 and 10-40 µmol L-1, and respective sensitivities of 6.2 ± 0.7 mA L mol-1 and 3.4 ± 0.4 mA L mol-1, the overall sensor performance is within the average of comparable results using carbon nanotubes. Nonetheless, the simplified handling of these nanotubes and their reduced environmental impact make these WS2-COOH nanotubes a promising nanomaterial for biosensing applications.

Controlled carbon nanotube layers for impedimetric immunosensors: High performance label free detection and quantification of anti-cholera toxin antibody.

An original impedimetric immunosensor was developed based on carbon nanotube (CNT) deposits with controlled thicknesses for enhanced electroactive surface areas leading to improved sensor performances. Cholera monitoring was chosen as the model immune system for this setup. These CNT deposits were characterized using confocal laser microscopy and electrochemical methods. To form the sensor device, the CNT deposits were functionalized via electrocoating of polypyrrole-nitrilotriacetic acid (poly(pyrrole-NTA)) followed by the formation of a Cu (II) complex with the NTA functions. The bioreceptor unit, cholera toxin B Subunit, modified with biotin, was then immobilized via coordination of the biotin groups with the NTA-Cu(II) complex. Each step of the formation of the immunosensor and the subsequent binding of the analyte antibody anti-cholera toxin were investigated with cyclic voltammetry and Electrochemical Impedance Spectroscopy. After optimization, the resulting impedimetric cholera sensor shows excellent reproducibility, increased sensitivities, a very satisfying detection limit of 10-13gmL-1 and an exceptional linear range for anti-cholera detection of 8 orders of magnitude (10-13-10-5gmL-1) and a sensitivity of 24.7 ± 0.4Ω per order of magnitude.

A synthetic redox biofilm made from metalloprotein-prion domain chimera nanowires.

Engineering bioelectronic components and set-ups that mimic natural systems is extremely challenging. Here we report the design of a protein-only redox film inspired by the architecture of bacterial electroactive biofilms. The nanowire scaffold is formed using a chimeric protein that results from the attachment of a prion domain to a rubredoxin (Rd) that acts as an electron carrier. The prion domain self-assembles into stable fibres and provides a suitable arrangement of redox metal centres in Rd to permit electron transport. This results in highly organized films, able to transport electrons over several micrometres through a network of bionanowires. We demonstrate that our bionanowires can be used as electron-transfer mediators to build a bioelectrode for the electrocatalytic oxygen reduction by laccase. This approach opens opportunities for the engineering of protein-only electron mediators (with tunable redox potentials and optimized interactions with enzymes) and applications in the field of protein-only bioelectrodes.

Highly Sensitive Bisphenol-A Electrochemical Aptasensor Based on Poly(Pyrrole-Nitrilotriacetic Acid)-Aptamer Film.

An electrochemical highly sensitive aptasensor was developed based on electropolymerized poly(pyrrole-nitrilotriacetic) acid film and a new aptamer functionalized by a pentahistidine peptide for the quantification of bisphenol A. A surface coverage of antibisphenol A aptamer of 1.84 × 10(-10) mol cm(-2) was estimated from the electrochemical signal of the [Ru(III)(NH3)6](3+) complex bound by electrostatic interactions onto the aptamer-modified electrode. The binding of bisphenol A onto the polymer film was successfully characterized by electrochemical methods as square wave voltammetry and electrochemical impedance spectroscopy measurements. The designed label-free impedimetric aptasensor displayed a wide linear range from 10(-11) to 10(-6) mol L(-1) with a sensitivity of 372 Ω per unit of log of concentration and an excellent specificity toward interfering agents such as 4,4'-dihydroxybiphenyl and bisphenol P.

Label-free photoelectrochemical detection of double-stranded HIV DNA by means of a metallointercalator-functionalized electrogenerated polymer.

The design of photoactive functionalized electrodes for the sensitive transduction of double-stranded DNA hybridization is reported. Multifunctional complex [Ru(bpy-pyrrole)2 (dppn)](2+) (bpy-pyrrole=4-methyl-4'-butylpyrrole-2,2'-bipyridine, dppn=benzo[i]dipyrido[3,2-a:2',3'-c]phenazine) exhibiting photosensitive, DNA-intercalating, and electropolymerizable properties was synthesized and characterized. The pyrrole groups undergo oxidative electropolymerization on planar electrodes forming a metallopolymer layer on the electrode. Thanks to the photoelectrochemical and intercalating properties of the immobilized Ru(II) complex, the binding of a double-stranded HIV DNA target was photoelectrochemically detected on planar electrodes. Photocurrent generation through visible irradiation was correlated to the interaction between double-stranded DNA and the metallointercalator polymer. These interactions were well fitted by using a Langmuir isotherm, which allowed a dissociation constant of 2×10(6)  L mol(-1) to be estimated. The low detection limit of 1 fmol L(-1) and sensitivity of 0.01 units per decade demonstrate excellent suitability of these modified electrodes for detection of duplex DNA.

High power enzymatic biofuel cell based on naphthoquinone-mediated oxidation of glucose by glucose oxidase in a carbon nanotube 3D matrix.

We report the design of a novel glucose/O2 biofuel cell (GBFC) integrating carbon nanotube-based 3D bioelectrodes and using naphthoquinone-mediated oxidation of glucose by glucose oxidase and direct oxygen reduction by laccase. The GBFCs exhibit high open circuit voltages of 0.76 V, high current densities of 4.47 mA cm(-2), and maximum power output of 1.54 mW cm(-2), 1.92 mW mL(-1) and 2.67 mW g(-1). The GBFC is able to constantly deliver 0.56 mW h cm(-2) under discharge at 0.5 V, showing among the best in vitro performances for a GBFC. Using a charge pump, the GBFC finally powered a Light Emitting Diode (LED), demonstrating its ability to amplify micro watts to power mW-demanding electronic devices.

Label-free impedimetric thrombin sensor based on poly(pyrrole-nitrilotriacetic acid)-aptamer film.

A label-free and highly sensitive impedimetric aptasensor was developed based on electropolymerized film for the determination of thrombin. The first step is the electrogeneration of a poly(pyrrole-nitrilotriacetic acid) (poly(pyrrole-NTA)) film onto the surface of electrodes followed by complexation of Cu(2+) ions. Then, the histidine labeled thrombin aptamer was immobilized onto the electrode through coordination of the histidine groups on the NTA-Cu(2+) complex. The aptamer sensor was applied for the detection and quantification of thrombin via impedimetric detection without a labeling step. A linear quantification of thrombin was obtained in the range 4.7×10(-12)-5.0×10(-10) mol L(-1) with a sensitivity of 2838 Ω/log unit (R(2)=0.9984). The impedance modulus at 0.3 Hz as a function of thrombin concentration was used to elaborate a similar linear relationship from 4.7×10(-12) to 5×10(-10) mol L(-1). In addition, aptamer-poly(pyrrole-NTA) electrodes incubated for 40 min in aqueous solutions of bovine serum albumin (BSA), lysozyme and IgG (5×10(-7) mol L(-1)) did not exhibit non-specific adsorption of proteins. Moreover, it has been demonstrated that the selective sensor can be regenerated several times with a good reproducibility.

Electrogenerated poly(pyrrole-lactosyl) and poly(pyrrole-3'-sialyllactosyl) interfaces: toward the impedimetric detection of lectins.

This paper reports on the impedimetric transduction of binding reaction between polymerized saccharides and target lectins. The controlled potential electro-oxidation of pyrrole-lactosyl and pyrrole-3'-sialyllactosyl at 0.95 V vs. Ag/AgCl, provides thin and reproducible poly(pyrrole-saccharide) films. The affinity binding of two lectins: Arachis hypogaea, (PNA) and Maackia amurensis (MAA) onto poly(pyrrole-lactosyl) and poly(pyrrole-3'-sialyllactosyl) electrodes, was demonstrated by cyclic voltammetry in presence of ruthenium hexamine and hydroquinone. In addition, rotating disk experiments were carried out to determine the permeability of both polypyrrole films and its evolution after incubating with lectin target. Finally, the possibility of using the poly(pyrrole-lactosyl) or poly(pyrrole-3'-siallyllactosyl) films for the impedimetric transduction of the lectin binding reaction, was investigated with hydroquinone (2 × 10(-3) mol L(-1)) as a redox probe in phosphate buffer. The resulting impedance spectra were interpreted and modeled as an equivalent circuit indicating that charge transfer resistance (R ct) and relaxation frequency (f°) parameters are sensitive to the lectin binding. R ct increases from 77 to 97 Ω cm(2) for PNA binding and from 93 to 131 Ω cm(2) for MAA binding. In parallel, f° decreases from 276 to 222 Hz for PNA binding and from 223 to 131 Hz for MAA binding. This evolution of both parameters reflects the steric hindrances generated by the immobilized lectins towards the permeation of the redox probe.

One-step vs stepwise immobilization of 1-D coordination-based Rh-Rh molecular wires on gold surfaces.

Reaction of dimeric [Rh(II)(2)(phen)(2)(µ-OAc)(2)(MeCN)(2)](BF(4))(2) (phen =1,10-phenanthroline) with pyrazine (pz) in a 1:2 ratio leads to the new 1-D metal-metal-bonded coordination oligomer {[Rh(II)(2)(phen)(2)(µ-OAc)(2)(pz)](BF(4))(2)}(n) (Rh-Rhpz)(n) (1), where each Rh atom of the dimeric unit (Rh-Rh) is coordinated in the equatorial plane to a nitrogen atom of a rigid and linear bifunctionalized organic linker (pz). Single X-ray diffraction analysis reveals the 1-D straight oligomeric chain structure (molecular wire, MW) consists of alternating (Rh-Rh) units and pz linking ligands with free BF(4)(-) as counteranions, and each metal center has a slightly distorted octahedral arrangement. The presence of accessible labile MeCN groups on both ends of these MWs ("free ends") enables functionalization of a 4-mercaptopyridine-gold coordinating platform (Au/MP) to form in one step a layer of coordination oligomer (Au/MP(Rh-Rhpz)(n); n ≈ 50). Furthermore (Rh-Rhpz)(n) (n = 1-6) MWs were grafted to Au/MP surfaces by a conventional step-by-step assembly construction involving coordination reactions between the Rh dimer ([Rh(2)(phen)(2)(µ-OAc)(2)(MeCN)(2)](BF(4))(2) (2)) and pz. A detailed physicochemical study (UV-vis, RAIR, QCM-D, ellipsometry, contact angle measurements, as well as impedance spectroscopy and cyclic voltammetry) has been made during both assembly methods to characterize the resulting surface-anchored coordination molecular wire (CMW) layers (Au/MP(Rh-Rhpz)(n)). The results indicate that the immobilized molecular assemblies (MAs) were successfully fabricated using both methods of assembly. The efficiency of the two methods is discussed.

Amphipol mediated surface immobilization of FhuA: a platform for label-free detection of the bacteriophage protein pb5.

Biotinylated amphipol was used to entrap FhuA (an E. coli outer membrane protein) and immobilize the FhuA-amphipol complex on streptavidin surfaces. Using this assembly, we have successfully devised surface-based assays for studying the recognition of FhuA by pb5 (a bacteriophage T5 protein) and determination of the affinity constant.

Tethered bilayer lipid membranes on mixed self-assembled monolayers of a novel anchoring thiol: impact of the anchoring thiol density on bilayer formation.

Tethered bilayer lipid membranes (tBLMs) are designed on mixed self-assembled monolayers (SAMs) of a novel synthetic anchoring thiol, 2,3-di-o-palmitoylglycerol-1-tetraethylene glycol mercaptopropanoic acid ester (TEG-DP), and a new short dilution thiol molecule, tetraethylene glycol mercaptopropanoic acid ester (TEG). tBLM formation was accomplished by self-directed fusion of small unilamellar vesicles of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine. The influence of the dilution of the anchoring thiol molecule in the SAM on the vesicle fusion process and on the properties of the resulting tBLMs is studied. It is observed by quartz crystal microbalance that vesicle fusion is a one-step process for a pure TEG-DP SAM as well as for mixed SAMs containing a high concentration of the anchoring thiol. However, upon dilution of the anchoring thiol to moderate concentrations, this process is decelerated and possibly follows a pathway different from that observed on a pure TEG-DP SAM. Electrochemical impedance spectroscopy is used to qualitatively correlate the composition of the SAM to the electrical properties of the tBLM. In this paper we also delineate the necessity of a critical concentration of this anchoring TEG-DP thiol as a requisite for inducing the fusion of vesicles to form a tBLM.

Mediatorless high-power glucose biofuel cells based on compressed carbon nanotube-enzyme electrodes.

Enzymatic fuel cells use enzymes to produce energy from bioavailable substrates. However, such biofuel cells are limited by the difficult electrical wiring of enzymes to the electrode. Here we show the efficient wiring of enzymes in a conductive pure carbon nanotube matrix for the fabrication of a glucose biofuel cell (GBFC). Glucose oxidase and laccase were respectively incorporated in carbon nanotube disks by mechanical compression. The characterization of each bioelectrode shows an open circuit potential corresponding to the redox potential of the respective enzymes, and high current densities for glucose oxidation and oxygen reduction. The mediatorless GBFC delivers a high power density up to 1.3 mW cm(-2) and an open circuit voltage of 0.95 V. Moreover, the GBFC remains stable for 1 month and delivers 1 mW cm(-2) power density under physiological conditions (5×10(-3) mol l(-1) glucose, pH 7). To date, these values are the best performances obtained for a GBFC.

A glucose biofuel cell implanted in rats.

Powering future generations of implanted medical devices will require cumbersome transcutaneous energy transfer or harvesting energy from the human body. No functional solution that harvests power from the body is currently available, despite attempts to use the Seebeck thermoelectric effect, vibrations or body movements. Glucose fuel cells appear more promising, since they produce electrical energy from glucose and dioxygen, two substrates present in physiological fluids. The most powerful ones, Glucose BioFuel Cells (GBFCs), are based on enzymes electrically wired by redox mediators. However, GBFCs cannot be implanted in animals, mainly because the enzymes they rely on either require low pH or are inhibited by chloride or urate anions, present in the Extra Cellular Fluid (ECF). Here we present the first functional implantable GBFC, working in the retroperitoneal space of freely moving rats. The breakthrough relies on the design of a new family of GBFCs, characterized by an innovative and simple mechanical confinement of various enzymes and redox mediators: enzymes are no longer covalently bound to the surface of the electron collectors, which enables use of a wide variety of enzymes and redox mediators, augments the quantity of active enzymes, and simplifies GBFC construction. Our most efficient GBFC was based on composite graphite discs containing glucose oxidase and ubiquinone at the anode, polyphenol oxidase (PPO) and quinone at the cathode. PPO reduces dioxygen into water, at pH 7 and in the presence of chloride ions and urates at physiological concentrations. This GBFC, with electrodes of 0.133 mL, produced a peak specific power of 24.4 microW mL(-1), which is better than pacemakers' requirements and paves the way for the development of a new generation of implantable artificial organs, covering a wide range of medical applications.

Label-free femtomolar detection of target DNA by impedimetric DNA sensor based on poly(pyrrole-nitrilotriacetic acid) film.

An ultrahigh performance impedimetric DNA sensor is presented showing detection limits in the femtomolar range. This electrochemical setup was constructed initially by electrogeneration of poly(11-pyrrol-1-yl-undecanoic acid N(alpha'),N(alpha)-bis(carboxymethyl)-L-lysine amide) (poly(pyrrole-NTA)) film. The latter was then modified by the coordination of Cu(2+) ions onto the chelating NTA centers followed by the immobilization of the ssHIV-DNA previously modified by a polyhistidine tag by affinity binding. The immobilization of the DNA probe and hybridization with the complementary target ssHIV-DNA were investigated using fluorescence microscopy and quantified with quartz crystal microbalance experiments leading to DNA probe and duplex coverage of 1.7 x 10(-11) and 7.7 x 10(-12) mol cm(-2), respectively. The duplex formation was corroborated by amperometric measurements through the duplex labeling by a glucose oxidase. In the presence of hydroquinone as redox indicator, the DNA sensor was applied to the impedimetric detection of target DNA without a labeling step. A linear quantification of the HIV DNA target was carried out in the range 10(-15) to 10(-8) mol L(-1).

Impedimetric immunosensor based on a polypyrrole-antibiotic model film for the label-free picomolar detection of ciprofloxacin.

This paper describes the construction of an impedimetric immunosensor for the label-free detection of ciprofloxacin, an antibiotic belonging to synthetic fluoroquinolones. A poly(pyrrole-N-hydroxysuccinimide) film was electrogenerated onto electrodes and then used for the reagentless covalent binding of a fluoroquinolone model bearing an amino group. The resulting electrodes were utilized to immobilize a layer of anticiprofloxacin antibody onto the polymer surface by immunoreaction. In presence of ciprofloxacin, the antibody was displaced in solution inducing marked changes in the impedance of the sensor electrodes. These phenomena were detected and characterized by electrochemical impedance spectroscopy allowing the selective detection of extremely low ciprofloxacin concentration, namely, 1 x 10(-12) g mL(-1) or 3 pmol L(-1). Sensors exposed to ciprofloxacin showed a decrease in the sum of the interfacial resistances with the increase in ciprofloxacin concentration from 1 x 10(-12) to 1 x 10(-6) g mL(-1).

Detection of carbohydrate-binding proteins by oligosaccharide-modified polypyrrole interfaces using electrochemical surface plasmon resonance.

This paper reports on the use of electrochemical surface plasmon resonance (E-SPR) for the detection of carbohydrate-binding proteins. The generation of an SPR sensor specific to lectins Arachis hypogaea (PNA) and Maackia amurensis (MAA) is based on the electrochemical polymerization of oligosaccharide derivatives functionalized by pyrrole groups. The resulting thin conducting polymer films were characterized using E-SPR and atomic force microscopy (AFM). The specific binding of PNA to polypyrrole-lactosyl and of MAA to polypyrrole-3'-sialyllactosyl films was investigated using SPR. The detection limit was 41 nM for PNA and 83 nM for MAA. Through Scatchard analysis and linear transformation of the SPR sensorgram data, association (k(ass)) and dissociation rate constants (k(diss)) could be determined.