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A series of polycyclic aromatics, naphthalene, phenanthrene, perylene, pyrene, 1-pyrenebutyric acid N-hydroxysuccinimide ester (pyrene NHS) and coronene, were immobilized via π stacking on carbon nanotube (CNT) electrodes and electro-oxidized in aqueous solutions. The obtained quinones were characterized and evaluated for the mediated electron transfer with FAD dependent glucose dehydrogenase during catalytic glucose oxidation.

The non-covalent modification of carbon nanotube electrodes with pyrene derivatives is a versatile approach to enhance the electrical wiring of enzymes for biosensors and biofuel cells. We report here a comparative study of five pyrene derivatives adsorbed at multi-walled carbon nanotube electrodes to shed light on their ability to promote direct electron transfer with horseradish peroxidase (HRP) for H2O2 reduction. In all cases, pyrene-modified electrodes enhanced catalytic reduction compared to the unmodified electrodes. The pyrene N-hydroxysuccinimide (NHS) ester derivative provided access to the highest catalytic current of 1.4 mA cm−2 at 6 mmol L−1 H2O2, high onset potential of 0.61 V vs. Ag/AgCl, insensitivity to parasitic H2O2 oxidation, and a large linear dynamic range that benefits from insensitivity to HRP “suicide inactivation” at 4–6 mmol L−1 H2O2. Pyrene-aliphatic carboxylic acid groups offer better sensor sensitivity and higher catalytic currents at ≤ 1 mmol L−1 H2O2 concentrations. The butyric acid and NHS ester derivatives gave high analytical sensitivities of 5.63 A M−1 cm−2 and 2.96 A M−1 cm−2, respectively, over a wide range (0.25–4 mmol−1) compared to existing carbon-based HRP biosensor electrodes. A bacterial nanocellulose pyrene-NHS HRP bioelectrode was subsequently elaborated via “one-pot” and “layer-by-layer” strategies. The optimised bioelectrode exhibited slightly weaker voltage output, further enhanced catalytic currents, and a major enhancement in 1-week stability with 67% activity remaining compared to 39% at the equivalent electrode without nanocellulose, thus offering excellent prospects for biosensing and biofuel cell applications.

Metal-organic frameworks (MOFs) act as versatile coordinators for the subsequent synthesis of high-performance catalysts by providing dispersed metal-ion distribution, initial coordination condition, dopant atom ratios, and so on. In this work, a crystalline MOF trans-[Cu(NO3)2(Him)4] was synthesized as the novel precursor of a redox-alternating CuxO electrochemical catalyst. Through simple temperature modulation, the gradual transformation toward a highly active nanocomposite was characterized to ascertain the signal enhancing mechanism in H2O2 reduction. Owing to the proprietary structure of the transducer material and its ensuing high activity, a proof-of-principle sensor was able to provide an amplified sensitivity of 2330 μA mM-1 cm-2. The facile one-pot preparation and intrinsic nonenzymatic nature also suggests its wide potentials in medical settings.

International audience; A particularly efficient redox mediator for electron transfer between FAD‐dependent glucose dehydrogenase (FAD‐GDH) and carbon nanotube (CNT) based electrodes can be obtained via electrosynthetic oxidation of pyrene in aqueous buffer solution. 1H‐NMR spectroscopic studies reveal the formation of a 2 : 1 mixture of 1,6‐pyrenedione and 1,8‐pyrenedione at the electrode. The formed pyrenedione exhibits a well‐defined surface‐bound redox system at −0.1 V vs. SCE and provides excellent electron transfer kinetics with this enzyme. Furthermore, the π‐system of pyrenedione allows improved stacking behavior with the CNT walls, leading to enhanced stabilities compared to commonly used mediators like naphthoquinone. The electrosynthesis of pyrenedione for catalytic glucose oxidation is optimal at pH 2 using cyclic voltammetry or chronoamerometry. It is envisioned that the electrosynthetic methodology can be expanded to form different redox mediators for a series of enzymes.

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.

International audience; A series of new glyconanoparticles (GNPs) was obtained by self-assembly by direct nanoprecipitation of a mixture of two carbohydrate amphiphilic copolymers consisting of polystyrene-block-β-cyclodextrin and polystyrene-block-maltoheptaose with different mass ratios, respectively 0–100, 10–90, 50–50 and 0–100%. Characterizations for all these GNPs were achieved using dynamic light scattering, scanning and transmission electron microscopy techniques, highlighting their spherical morphology and their nanometric size (diameter range 20–40 nm). In addition, by using the inclusion properties of cyclodextrin, these glyconanoparticles were successfully post-functionalized using a water-soluble redox compound, such as anthraquinone sulfonate (AQS) and characterized by cyclic voltammetry. The resulting glyconanoparticles exhibit the classical electroactivity of free AQS in solution. The amount of AQS immobilized by host–guest interactions is proportional to the percentage of polystyrene-block-β-cyclodextrin entering into the composition of GNPs. The modulation of the surface density of the β-cyclodextrin at the shell of the GNPs may constitute an attractive way for the elaboration of different electroactive GNPs and even GNPs modified by biotinylated proteins

Electrochemical grafting is a suitable technology for fabricating electrode surfaces with new chemical functionalities whilst maintaining the bulk properties of the electrode, and electrochemical amine oxidation and diazonium salt reduction are two widely used techniques to achieve this end. Herein, we report the electrochemical reductive grafting of Azure A onto multiwalled carbon nanotube (MWCNT) electrodes for the efficient wiring of flavin adenine dinucleotide (FAD) dependent glucose dehydrogenase. The diazonium salt of Azure A is formed in situ and subsequently grafted onto the electrode surface through electrochemical reduction. The formal potential of the resultant Azure-A-modified electrode shifted to −0.05 V vs. Ag/AgCl upon radical coupling to the MWCNT electrode. Electron transfer from FAD buried in the protein shell to the electrode via Azure A was then observed in the presence of glucose in the buffer solution. This study focused on the important effect of CNT mass loading on Azure-A loading as well as bioelectrocatalytic activity and storage stability. The three-dimensional porous structure of the MWCNT electrode was determined to be favorable for the immobilization of flavin adenine dinucleotide dependent glucose dehydrogenase and efficient electron transfer via the Azure-A functionalities. The optimized 300 µg CNT-loaded modified electrode on glassy carbon (3 mm diameter) retains its initial activity for 3 d and 25% of its initial activity after 10 d. Furthermore, we show that grafted Azure A is stably immobilized on the MWCNTs for 1 month; therefore, the limiting stability factor is enzyme leaching and/or deactivation.

International audience; The fabrication of bioelectrocatalytic protein electrodes by the simple compression of carbon nanotube and protein powders was investigated using a series of proteins including bilirubin oxidase (BOx), bovine serum albumin (BSA), catalase, cytochrome C (Cyt C), diaphorase, FAD-dependent glucose dehydrogenase (FAD-GDH), galactose oxidase (GAOx), glucose oxidase (GOx), horseradish peroxidase (HRP), laccase and urease. The isoelectric points (pI) of the proteins ranged from 3.5 to 12 and the molecular weights ranged from 12.4 to 480 kDa. The compression of diaphorase, laccase, BOx, FAD-GDH, catalase and urease gave mechanically stable biopellets in 0.1 M phosphate buffer pH 7.4. For Cyt C, BSA, GAOx, GOx, and HRP, contact with buffer destabilised the biopellet and induced a fast destruction of the composite. In parallel, stable redox pellets were obtained with differently charged redox mediators: hexaammineruthenium (III) chloride, potassium hexacyanoferrate or 1,4-naphthoquinone. Several parameters were explored to shed new light on the factors that determine biopellet stability. Stable biopellets capable of direct and mediated electron transfer were subsequently elaborated, for O 2 reduction and glucose oxidation, respectively, based on the simplified procedure that does not require stabilising protection membranes or holders on the contrary to existing methods.

International audience; The electrochemical reduction of aryldiazonium salts is a versatile and direct route to obtain robust covalently-modified electrodes. We report here a comparative study of Azure-A modified carbon nanotube electrodes prepared by diazonium electrografting and by physical adsorption for bioelectrocatalytic glucose oxidation with fungal FAD-glucose dehydrogenase from Aspergillus sp. The electrografted and adsorbed electrodes exhibited different reversible electroactivity consistent with polymer-type and monomer-type phenothiazine surface assemblies, respectively. The electrografted Azure A electrodes exhibited superior mediated bioelectrocatalysis compared to the adsorbed Azure A electrodes. A more than 10-fold higher catalytic current up to 2 mA cm-2 at 0.2 V vs. Ag/AgCl together with a similarly low onset potential of-0.05 V vs. Ag/AgCl was observed at the electrografted electrodes. Faster estimated electron transfer kinetics and a +200 mV potential shift for the polymer-type redox couple vs. the adsorbed monomer-type couple underlines the favourable driving force for mediated electron transfer with the buried FAD active site for the diazonium-derived bioelectrode. Keywords: Phenothiazine redox mediator • FAD dependant glucose dehydrogenase • biofuel cell anode • enzymatic bioelectrode • bioelectrocatalysis 2

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.

International audience; Enzymatic biofuel cells are ecofriendly power sources that can deliver μW−mW outputs from renewable substrates, but their stability is a major issue owing to enzyme fragility. The vast majority of reported biofuel cells can only generate power continuously for relatively short periods of time. Here we report a novel "solubilized enzymatic fuel cell (SEFC)" concept for continuous long-term operation. Avoiding surface immobilization techniques allows bio- catalytic activity to be easily restored or replenished. The biofuel cell exploits freely diffusing enzymes and β-cyclodextrin-coated glycona- noparticles with entrapped quinone and thiazoline redox mediators, for mediated glucose and oxygen conversion. The cell was designed with permselective membranes to enable substrate and proton diffusion while trapping the enzymes and glyconanoparticles in separate compartments. The SEFC exhibited a peak power loss of only 26.3% after 7 days of continuous charge−discharge cycling at 50 μA; thus, SEFCs may be envisaged to power lab-on-a-chip devices for periods of several weeks.

International audience; Enzymatic biofuel cells are emerging technologies which gain a lot of interest as a power source for implantable devices. Effective enzyme wiring and simplification of the cell architecture are the main limitations of the fuel cell development nowadays. In the present study, spray coating was used as a reliable process to produce flexible biocathodes. That was achieved through spray coating of a conductive ink formulated by surfactant assisted carbon nanotubes dispersion. A thin continuous layer of carbon nanotubes (CNTs) was successfully coated on top of a gas diffusion layer paper. The film thickness was modulated by varying the CNT load in the ink and the number of deposited layers. It varied between 1 and 7.8 μm for a number of deposited layers between 5 and 100. Laccase enzyme was then wired to printed CNT electrodes thanks to the host-guest interaction between the hydrophobic pocket of laccase and pyrene-adamantane. Electrochemical investigations showed that laccase was effectively wired to the CNTs and presented a favorable orientation toward oxygen reduction. The biocathode current density was dependent of the number of deposited CNT layers and reached an optimum at 170 μA cm−2 for 50 deposited layers.

International audience; A disposable ovulation test is operated using a flow stack of 5 in series connected glucose biofuel cells giving an open circuit voltage (OCV) of 3.5 V. Such tests consume at total around 60 μWh of energy and in average 1.7 mW of power during one run of around 12 min which are supplied by a CR1220 3 V lithium button battery in the commercialized device. We replaced this battery by the glucose biofuel cell stack and observed during the measurements and display steps peak currents up to 1.4 mA inducing a voltage drop down to 2.8 V during few seconds (4 mW of power consumption). Even such power peaks are supported by the presented biofuel cell stack assuring the necessary operational cell voltage and current. After the measurements towards Luteinizing Hormone (LH) detection the display remains turned on for 8 min and consumes just 2 μW which allows to reestablish the initial OCV and to run a further test. The presented results demonstrate as proof of concept the suitability of eco-friendly enzymatic glucose biofuel cells as alternative power source for disposable devices.

International audience; Bioelectrocatalytic carbon nanotube pellets comprising glucose oxidase (GOx) at the anode and horseradish peroxidase (HRP) at the cathode were integrated in a glucose/H2O2 flow-through fuel cell setup. The porous bioelectrodes, separated with a cellulose membrane, were assembled in a design allowing the fuel/electrolyte flow through the entire fuel cell with controlled direction. An air saturated 5 mmol L−1 glucose solution was directed through the anode where glucose is used for power conversion and for the enzymatic generation of hydrogen peroxide supplying the HRP biocathode with its substrate. This configuration showed an open circuit voltage (OCV) of 0.6 V and provided 0.7 ± 0.035 mW at 0.41 V. Furthermore, different charge/discharge cycles at 500 Ω and 3 kΩ were applied to show the long term stability of this setup producing 290 μW h (1.04 J) of energy after 48 h. The biofuel cell design further allows a convenient assembly of several glucose biofuel cells in reduced volumes and its connection in parallel or in series.

Carbon nanotubes (CNTs) have been widely exploited for the development of enzymatic biofuel cells with sufficient power densities in the μW to mW range for operating low-power bioelectronic devices from renewable substrates. Buckypaper is a randomly oriented self-supporting film of carbon nanotubes, resembling an electronic paper, with excellent prospects for the construction of high performance enzymatic electrodes for use in biofuel cells. Attractive properties of buckypaper materials include large specific surface areas, high electrical conductivity, flexibility, biocompatibility, scalable production and the ability for efficient electron transfer with enzymes. Buckypapers are ideal self-supporting frameworks for enzymes and guest molecules such as metals, polymers and redox molecules, permitting the development of a wide range of catalytic bioelectrode interfaces. This review summarizes recent developments and advances of buckypaper bioelectrodes as an emerging component for body-integrated energy harvesting biodevices.

International audience; Enzyme mimetics have attracted wide interest due to their inherent enzyme-like activity and unique physicochemical properties, as well as promising applications in disease diagnosis, treatment and monitoring. Inspired by the attributes of nonheme iron enzymes, synthetic models were designed to mimic their capability and investigate the catalytic mechanisms. Herein, metal-organic gels (Fe-MOGs) with horseradish peroxidase (HRP) like Fe-NX structure were successfully synthesized though the coordination between iron and 1,10-phenanthroline-2,9-dicarboxylic acid (PDA) and exhibited excellent peroxidase-like activity. Its structure-activity relationship and the in-situ electrochemiluminescence (ECL) detection of H2O2 secreted by Hela cells were further investigated. The highly dispersed Fe-NX active sites inside Fe-MOGs were able to catalyze the decomposition of H2O2 into large amounts of reactive oxygen species (ROS) via a Fenton-like reaction under a low overpotential. Due to the accumulation of ROS free radicals, the luminol ECL emission was significantly amplified. A proof-ofconcept biosensor was constructed with a detection limit as low as 2.2 nM and a wide linear range from 0.01 to 40 μM. As a novel metal organic gels based enzyme mimetic, Fe-MOGs show great promises in early cancer detection and pathological process monitoring.

International audience; A novel water-soluble Ru complex bearing phenanthrolinequinone ligands, diethyleneglycol linkers and pyrene anchoring groups was synthesized. Electrical wiring of NAD-and FAD-dehydrogenases is demonstrated via NADH oxidation and mediated electron transfer respectively. Bioelectrocatalysis is facilitated by the flexible and hydrophilic PEG groups, and strong binding of pyrene groups with the carbon nanotubes (CNTs) of the electrodes. Furthermore, owing to the surfactant properties of the PEG-modified complex, high quality CNT dispersions were obtained for homogeneous buckypaper preparation.

We report the controlled orientation of bilirubin oxidases (BOD) from Myrothecium verrucaria on multiwalled carbon nanotubes (MWCNTs) functionalised by electrografting of 6-carboxynaphthalenediazonium and 4-(2-aminoethyl)benzenediazonium salts. On negatively charged naphthoate-modified MWCNTs, a high-potential (0.44 V vs. SCE) oxygen reduction electrocatalysis is observed, occurring via the T1 copper centre. On positively charged ammonium-modified MWCNTs, a low-potential (0.15 V) oxygen reduction electrocatalysis is observed, occurring through a partially oxidised state of the T2/T3 trinuclear copper cluster. Finally, chemically modified naphthoate MWCNTs exhibit high bioelectrocatalytic current densities of 3.9 mA cm(-2) under air at gas-diffusion electrode.

Strategies to maximize direct electron transfer (DET) between redox enzymes and electrodes include the oriented immobilization of enzymes onto an electroactive surface. Here, we present a strategy for achieving a controlled orientation of a fungal laccase on carbon nanotube-based electrodes. A homogeneous population of pyrene-modified laccase is obtained via the reductive amination of a unique surface accessible lysine residue engineered near the T1 copper center of the enzyme. Immobilization of the site-specific functionalized enzyme is achieved either via π-stacking of pyrene on pristine CNT electrodes or through pyrene/β-cyclodextrin host guest interactions on β-cyclodextrin-modified gold nanoparticles (β-CD-AuNPs). Contrasting with unmodified and nonspecifically modified (pyrene-NHS) laccase-electrodes, an efficient DET is obtained at these nanostructured assemblies. Modeling the direct bioelectrocatalysis of dioxygen reduction reveals a heterogeneity in ET rates on MWCNT electrodes wheras β-CD-AuNPs ...

In this work, for the first time, an efficient carbon quantum dots/gold nanoclusters (CQDs/AuNCs) nanohybrid based ratiometric fluorescent probe for sensitive and selective sensing of cadmium (II) ions and l-ascorbic acid (AA) has been established. The blue emissive CQDs, prepared by a one-step hydrothermal treatment with alanine and histidine, play the role of reference fluorophore. The red emissive AuNCs, capped by 11-mercaptoundecanoic acid (MUA), serve as a specific recognition element. Different from MUA-capped AuNCs, the proposed CQDs/AuNCs nanohybrid exhibits high selectivity and sensitivity to cadmium (II) ions with a detection limit of 32.5 nM, which is attributed to the static quenching and the inner filter effect (IFE) of Cd2+ to CQDs/AuNCs nanohybrid. Unbelievable, in the presence of AA, the above-quenched sensor is recovered gradually. The proposed fluorescence sensor displays an enhanced performance for AA determination in the range from 0.15 to 15 μM (R = 0.995) with a detection limit down to 0.105 μM. More importantly, this fluorescent “on–off–on” method also offers the excellent performance to Cd2+ and AA detection in lake water and in human serum, respectively.

Cubic Pd nanoparticles (PdNPs) were synthesized using ascorbic acid as a reducing agent and were evaluated for the catalytic oxygen reduction reaction. PdNPs were confined with multiwalled carbon nanotube (MWCNT) dispersions to form black suspensions and these inks were dropcast onto glassy carbon electrodes. Different nanoparticle sizes were synthesized and investigated upon oxygen reduction capacities (onset potential and electrocatalytic current densities) under O2 saturated conditions at varying pH values. Strong evidence of O2 diffusion limitation was demonstrated. In order to overcome oxygen concentration and diffusion limitations in solution, we used a gas diffusion layer to create a PdNP-based air-breathing cathode, which delivered -1.5 mA cm(-2) at 0.0 V with an onset potential of 0.4 V. This air-breathing cathode was combined with a specially designed phenanthrolinequinone/glucose dehydrogenase-based anode to form a complete glucose/O2 hybrid bio-fuel cell providing an open circuit voltage of 0.554 V and delivering a maximal power output of 184 ± 21 μW cm(-2) at 0.19 V and pH 7.0.

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.

After a short comparison of biofuel cells based on enzymes and microorganisms, several important developments and applications of enzymatic fuel cells (EFCs) are discussed. This discussion emphasizes how to evaluate the performance of EFCs, and highlights the influence of temperature and how it must be carefully considered for practical use of EFCs as power sources. Some of the latest and most important innovations in EFC design using buckypapers and redox nanoparticles are briefly reviewed.

A high performance impedimetric immunosensor for the dengue virus antibody detection is presented. The setup profits from the formation of controlled and reproducible carbon nanotube (CNT) deposits on electrodes. Their easy functionalization via electrogeneration of a polypyrrole-NHS (N-hydroxysuccinimido 11-(pyrrol-1-yl) undecanoate) film enables the immobilization of the Dengue Virus 2 NS1 glycoprotein, the receptor unit, on the porous CNT layer via covalent amide coupling to provide the necessary selectivity towards Dengue NS1 antibody. All building steps of this immunosensor and the performance of this system were monitored by impedance spectroscopy and cyclic voltammetry. The resulting impedimetric dengue biosensor was tested in bovine blood plasma in addition to conventional measurements under controlled environment. After optimization, this immunosensor shows a good linearity in a wide concentration range (10−13–10−5 g mL−1).

International audience; We report the oriented immobilization of [NiFeSe] hydrogenases on both covalently and noncovalently modified carbon nanotubes (CNTs) electrodes. A specific interaction of the [NiFeSe] hydrogenase from Desulfomicrobium baculatum with hydrophobic organic molecules was probed by electrochemistry, quartz crystal microbalance with dissipation monitoring (QCM-D), and theoretical calculations. Taking advantage of these hydrophobic interactions, the enzyme was efficiently wired on anthraquinone and adamantane-modified CNTs. Because of rational immobilization onto functionalized CNTs, the O-2-tolerant [NiFeSe]-hydrogenase is able to efficiently operate in a H-2/air gas-diffusion enzymatic fuel cell.

Herein, the direct electrochemistry of bilirubin oxidase from Magnaporthe orizae (MoBOD) was studied on CNTs functionalized by electrografting several types of diazonium salts. The functionalization induces favorable or unfavorable orientation of MoBOD, the latter being compared to the well-known BOD from Myrothecium verrucaria (MvBOD). On the same nanostructured electrodes, MoBOD can surpass MvBOD in terms of both current densities and minimal overpotentials. Added to the fact that MoBOD is also highly active at the gas-diffusion electrode (GDE), these findings make MoBOD one of the MCOs with the highest catalytic activity towards the oxygen reduction reaction (ORR).

International audience

Owing to their conductivity, carbon nanotubes (CNTs) coatings are widely used for modifying electrode surfaces. In particular, the formation of bucky papers (BP) based on CNT assemblies obtained by filtration, represents an attractive way of creating a new kind of electrode. However, these BP are brittle and difficult to manipulate, hence their applications remain limited due to their fragility and lack of flexibility. Notably, their use for “in vivo” experiments is markedly hampered by the potential release of CNTs. The strengthening of the mechanical stability of BP has hereby been explored by the combination of BP and linear polymeric chains displaying non-covalent π-interactions with CNTs. These organic polymers act as a cross-linking agent throughout the BP assembly thus conferring stability and flexibility. Flexible BP electrodes were produced by simply mixing poly(norbornene) bearing pyrene groups and multi-walled CNTs, both dispersed in dimethylformamide followed by filtration through a PTFE membrane. The immobilization of laccase as a model protein was achieved on the resulting BP electrodes by adsorption or chemical grafting. These biocathodes displayed a direct electrical communication with laccase, allowing the reduction of oxygen in water (pH 5) with maximum current densities of ca 1.1 mA cm−2 at 0.4 V vs. SCE.

A new cyclodextrin-modified pyrrole monomer (Py-CD) was synthesized and used both as an aqueous surfactant for the stabilization of aqueous reduced graphene oxide (RGO) dispersion and as an electropolymerizable unit to generate a RGO-polypyrrole composite electrode. This nanocomposite was used in combination with amphiphilic pyrrole derivative for the entrapment of tyrosinase, an enzyme catalyzing the oxidation of phenols and diphenols. Compared to glassy carbon electrodes, these nanostructured electrodes exhibit enhanced electroactive surface area and electrochemical properties and achieve higher performances towards catechol and dopamine biosensing.

International audience; A biocathode was designed by the modification of a carbon nanotube (CNT) gas-diffusion electrode with bilirubin oxidase from Bacillus pumilus, achieving high current densities up to 3 mA cm−2 for the reduction of O2 from air. A membraneless air-breathing hydrogen biofuel cell was designed by combination of this cathode with a functionalized CNT-based hydrogenase anode.

We demonstrate self-assembly, characterization and bioelectrocatalysis of redox-active cyclodextrin-coated nanoparticles. The nanoparticles with host–guest functionality are easy to assemble and permit entrapment of hydrophobic redox molecules in aqueous solution. Bis-pyrene-ABTS encapsulated nanoparticles were investigated electrochemically and spectroscopically. Their use as electron shuttles is demonstrated via an intraelectron transfer chain between neighboring redox units of clustered particles (Dh,DLS = 195 nm) and the mono- and trinuclear Cu sites of bilirubin oxidases. Enhanced current densities for mediated O2 reduction are observed with the redox nanoparticle system compared to equivalent bioelectrode cells with dissolved mediator. Improved catalytic stability over 2 days was also observed with the redox nanoparticles, highlighting a stabilizing effect of the polymeric architecture. Bioinspired nanoparticles as mediators for bioelectrocatalysis promises to be valuable for future biofuel cells an...

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 10−13 g mL−1 and an exceptional linear range for anti-cholera detection of 8 orders of magnitude (10−13–10−5 g mL−1) and a sensitivity of 24.7 ± 0.4 Ω per order of magnitude.

For the efficient surface plasmon resonance (SPR)-based DNA assay researching, signal amplification tactics were absolutely necessary. In this work, a sensitive SPR-DNA sensor was developed by employing in situ synthesis of copper nanoparticles (CuNPs) templated by poly-T sequences DNA from terminal deoxynucleotidyl transferase (TdT)-mediated extension, and synergistically with nano-effect deposition as the mass relay. The objective of this strategy was manifold: firstly, tDNA hybridized with the optimal designed probes to active the TdT-mediated DNA extension onto the surface of SPR chip, resulted a long poly-T sequences ssDNA chain in dsDNA terminal onto surface of gold chip and characterized by SPR signal amplitudes. Secondly, copper ion (Cu2+) adsorbed into the skeleton of poly-T sequences DNA, with the aid of ascorbic acid (VC) to achieve the Cu2+ reduction, copper nanostructures (CuNPs) was synchronously generated onto the single nucleotide chain anchoring in dsDNA derivatives and the formation was featured by transmission electron micrographs (TEM) and electrochemistry. Lastly, dsDNA-complexed CuNPs (CuNPs@dsDNA) triggered the final signal amplification via real-time conversion of the additive catechol violet (CV) into oligomer or chelation precipitation by CuNPs-tagged reporters. With the proposed setups, a precise and replicable DNA sensing platform for specific target oligo was obtained with a detection limit down to 3.21 femtomolar, demonstrating a beneficial overlapping exploitation of nanomaterials and biochemical reaction as unique SPR infrastructure. Such triple-amplification strategic setups, the possibility of various methods abutment and biocompatibility weight reactor was amassed and adapted to more biological detection field.

We report a simple, versatile, and rapid method for the fabrication of optically-transparent large-area carbon nanotube (CNT) films via flotation assembly. After solvent-induced assembly, floating films were transferred to a flat supporting substrate to form conductive and transparent CNT film electrodes. The resulting electrodes, with uniform 40 ± 20 nm multi-walled CNT (MWCNT) layers, were characterized by electrochemical and microscopy methods. The flotation method does not require specialized thin-film instrumentation and avoids the need for surfactants and pre-oxidized CNTs which can hamper electrochemical performance. A proof-of-concept nanostructured bioelectrode demonstrating high sensitivity for glucose was developed with an electropolymerized poly(pyrene-adamantane) layer for host–guest immobilization of active β-cyclodextrin tagged GOx enzymes. The polymer provides pyrene groups for cross-linking to CNTs and pendant adamantane groups for binding the β-cyclodextrin groups of the tagged enzyme. This demonstration offers a new approach for the preparation of stable and transparent CNT film electrodes with attractive electrochemical properties towards future photobio- and bio-electrochemical fuel cells, electrochemical sensors, and electroanalysis.

In this work, we synthesized the one-dimensional nanostructure of zinc 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (ZnTPyP) via a self-assembly technique. Using sodium dodecyl sulfate (SDS) as “soft template”, the self-assembled ZnTPyP (SA-ZnTPyP) had the morphology of hexagonal nanoprisms with a uniform size (diameter of 100 nm). The SA-ZnTPyP exhibited remarkably different spectral properties compared to those of the original ZnTPyP. The as-prepared SA-ZnTPyP was used to modify glassy carbon electrodes (GCE), and the electrochemiluminescence (ECL) behaviors of the SA-ZnTPyP/GCE were investigated. The hydrophilic carbon dots (C-dots) could efficiently prevent the dissolution of SA-ZnTPyP in DMF containing 0.1 mol L–1 TBAP and, simultaneously, could accelerate electron transfer. Therefore, the enhanced ECL was realized by C-dots/SA-ZnTPyP/GCE by using H2O2 as co-reactant. This amplification of ECL was further studied by ECL spectroscopies and cyclic voltammetry, and the corresponding mechanism was proposed.

Nanomaterials have become essential components for the development of biosensors since such nanosized compounds were shown to clearly increase the analytical performance. The improvements are mainly related to an increased surface area, thus providing an enhanced accessibility for the analyte, the compound to be detected, to the receptor unit, the sensing element. Nanomaterials can also add value to biosensor devices due to their intrinsic physical or chemical properties and can even act as transducers for the signal capture. Among the vast amount of examples where nanomaterials demonstrate their superiority to bulk materials, the combination of different nano-objects with different characteristics can create phenomena which contribute to new or improved signal capture setups. These phenomena and their utility in biosensor devices are summarized in a non-exhaustive way where the principles behind these synergetic effects are emphasized.

An original interfacial hybrid cross-linker molecule combined electrochemical and photochemical properties by substitution of two functional groups, pyrene, and diazirine. The first group enables anchoring by strong π-stacking interaction or by electropolymerization onto multi-walled carbon nanotubes (MWCNT). The other photoreactive group allows the covalent link with biomolecules under long-wavelength UV illumination. Diazirine was chosen due to its ability to photogenerate high reactive radicals under UV irradiation. The photoreactivity of these immobilized nanostructured conductive surfaces was tested towards the covalent attachment of tyrosinase which is well known to oxidize a large range of phenolic compounds and its yield and availability was evaluated by amperometric measurements of catechol by using molecular dioxygen. The architecture exhibiting the best analytical characteristics obtained for catechol was then chosen to detect dopamine.

A highly efficient surface plasmon resonance (SPR)-based DNA assay was developed, by employing noncovalently functionalized graphene nanosheets as a substrate, and enzymatic catalysis-induced polymerization as mass relay. The objective of this strategy was manifold: first of all, to sensitize the overall SPR output by in situ optimized electrogeneration of graphene thin-film, which was characterized by atomic force microscopic topography; secondly, to regulate the self-assembly and orientation of biotinylated capture probes on nickel-chelated nitrilotriacetic acid (NTA) scaffolds, that anchored onto graphene-supported pyrenyl derivatives; and lastly, to synergize the signal amplification via real-time conversion of the additive aniline into polyaniline precipitation by horseradish peroxidase-tagged reporters. With this setup, a precise and replicable DNA sensing platform for specific targets was achieved with a detection limit down to femtomolar, thus demonstrating a beneficial exploration and exploitation of two-dimensional nanomaterials as unique SPR infrastructure. The possibility of such ″bottom-up″ architecture mounted with ″top-down″ weight reactor would be most likely extensible and adaptable to protein determinations.

The simultaneous determination of ascorbic acid and uric acid has a major importance in biomedical and pharmaceutical science. A glassy carbon electrode modified with β-cyclodextrin entrapped in polyethyleneimine was developed for the determination of ascorbic and uric acids in binary mixtures using square wave voltammetry. In order to characterize the electrode modification, Raman spectra were obtained. The modified electrode was successfully applied for the determination of ascorbic and uric acid in urine with good recoveries. The limit of detection for ascorbic acid was 0.22 µM.

900- and 100-nm-diameter polystyrene beads were combined with electrogenerated photosensitive poly-[tris(4,4-bis(3-pyrrol-1-ylpropyloxy)bipyridinyl)ruthenium(II)], (poly-[RuII-pyrrole]), metallopolymer on glassy carbon electrodes. Nanosphere lithography (NSL) with 900-nm-diameter microbead mask affords the realization of a nanostructured polymer (after dissolution of the polystyrene templates) with a typical highly-organized honeycomb nanostructure. NSL with 100-nm-diameter-nanobead mask allowed the achievement of a highly macroporous metallopolymer. The nanostructured Ru(II)-based metallopolymer was characterized by 3D laser scanning confocal microscopy and scanning electron microscopy (SEM). Electrochemical and photoelectrochemical studies demonstrate the enhancement of redox probe diffusion in the polymer layer for nanopatterned poly-[RuII-pyrrole]. This is accompanied with photocurrent enhancement for nanostructured polymer, especially in the case of poly-[RuII-pyrrole] obtained by the 100 nm-nanobead NSL. Keywords: Nanosphere lithography, Ruthenium complexes, Electropolymerization, Metallopolymers, Photoelectrochemistry

We report the non-covalent functionalization of multiwalled carbon nanotubes with pyrene monomers bearing a boronic acid function. These functionalized electrodes were used to wire horseradish peroxidase via formation of a covalent boronic ester bond under mild conditions with the glycosylated enzyme. By attaching glucose oxidase at the same time, a bi-enzymatic system was elaborated and showed efficient bioelectrocatalytic oxygen reduction under physiological conditions.

We report the first example of a glucose/H2O2 biofuel cell operating at 5 mM glucose under air at 37 °C in 0.14 M NaCl. At a bienzymatic cathode, the direct wiring of horseradish peroxidase (HRP) achieves the electrocatalytic reduction of H2O2 concomitantly produced during the oxidation of glucose by glucose oxidase (GOx) in the presence of O2. At the bienzymatic anode, the indirect wiring of glucose oxidase achieves electrocatalytic glucose oxidation while catalase removes trace of H2O2 and, in combination with GOx, traces of O2. The bienzymatic catalysis involved GOx at both electrodes. The biofuel cell exhibits OCV of 450 mV and maximum power output of 30 μW cm−2 at 0.3 V in 5 mM glucose and 0.14 M NaCl at 37 °C. This represents a novel alternative to the use of copper oxidases in conventional glucose/O2 biofuel cells for implantable applications. Keywords: Carbon nanotubes, Peroxidase, Glucose oxidase, Biofuel cells, Hydrogen peroxide

Patterned nanoscale molecular films will be a key componentof advanced devices such as novel chemical and biologicalsensors and nanoelectronic systems. For long-establishedsurface modification strategies such as the use of self-assembledmonolayers ofalkanethiolsat noblemetal surfacesandreactionsofsilanesatoxidesurfaces,patterningstrategieshave reached a high level of sophistication.

The enhanced electrochemiluminescence (ECL) of peroxydisulfate was observed on Au nanoparticles (Au NPs) electrodeposited on ITO electrode. Glucose oxidase (GOD) and horseradish peroxidase (HRP) were self-assembled upon Au NPs. Thus, a “signal-off” ECL biosensor to detect glucose by integrating biocatalytic precipitation (BCP) has been achieved. The morphologies of Au NPs and GOD-HRP/Au NPs modified ITO were characterized by scanning electron microscopy (SEM). The electrochemical behaviors of the Au NPs/ITO, GOD-HRP/Au NPs/ITO and BCP/GOD-HRP/Au NPs/ITO were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The resulted biosensor combined the ECL amplification by Au NPs with the self-assembled bi-enzymes integrated BCP system presents a wide linear range from 8.0 × 10−7 to 2.0 × 10−2 M, and with a high sensitivity of 1.0 × 10−7 M and good stability for glucose detection.

The medical diagnostic, the industry, and the biotechnology require rapid, sensitive, and easy to use methods for trypsin activity determination. A simple approach, which meets all these requirements, based on Quartz Crystal Microbalance (QCM) was developed, analytically characterized and described in the present work. QCM application allows rapid trypsin activity evaluation by real time monitoring of the enzymatic degradation of the substrate. The new approach suggested in this work takes advantage of nanoparticles loaded gelatin employment as a trypsin substrate, deposited on the QCM crystal. The heavy nanoparticles leave the substrate layer together with the products of its enzymatic degradation provoking thus a greater decrease of the total QCM crystal mass compared with the non charged substrate. As a result, a higher sensor frequency response occurs. A 10 fold improvement of the LOD was achieved for trypsin activity evaluation applying the proposed method with Ag nanoparticles loaded gelatin (7.5×10 −4 U mL −1 vs. 7.5×10 −3 U mL −1 obtained by the “classic” QCM method). The approach subject of this work can be applied with any substrate degrading enzyme.

A new stable solid-state electrochemiluminescence (ECL) sensor was fabricated by electropolymerizing tris ((4-(2-pyrrol-1-ylethyl)-4′-methyl-2,2′-bipyridine) ruthenium(II) complex (denoted as Ru(L)3) upon glassy carbon electrode (GCE). Meanwhile, 3.5-fold enhanced ECL intensity of polyRu(L)3/GCE was obtained in H2O/CH3CN solvent instead of H2O. Interestingly, an obvious ECL quenching was observed by introducing gold nanoparticles onto the polymer film. Atomic force microscope (AFM) was used to characterize the obtained polyRu(L)3 film and nanogold seeds/polyRu(L)3 film morphologies. The electrochemical and ECL behaviors were investigated by cyclic voltammetry. Based on the efficient quenching, a new glucose ECL biosensor as a model was accomplished by in situ growing-up gold seeds in AuCl 4 - solution induced by biologically generated H2O2. The linear range to detect glucose is from 5.0 × 10−5 M to 2.0 × 10−3 M with the limit of detection of 2.5 × 10−5 M.

The polyoxometalate [PMo11O39]7− was synthesized and used as catalyst for the reduction of nitrite ions. This mono-lacunary keggin anion, cited as PMo11, was confined within a matrix of either oxidized single-walled carbon nanotubes (ox-SWCNTs) or reduced graphene oxide (rGO) on glassy carbon (GC) electrodes to improve the electron transfers. Five different configurations were characterized using cyclic voltammetry and evaluated in an amperometric sensor setup for nitrite detection where the amount of the different components were optimized. The configuration using only ox-SWCNTs and PMo11 on GCE showed best sensitivities of up to 44.41 mA Lmol−1 and a satisfying reproducibility (RSD: ∼2.64% for four identic electrodes). Furthermore, a linear range between 3.0 × 10−5 mol L−1 and 1.6 × 10−2 mol L−1 with a detection limit of 3.0 × 10−5 mol L−1 was obtained. The final sensor setup also showed good selectivity towards interfering ions.

The controlled self-assembly of precise and well-defined photochemically and electrochemically active carbohydrate-coated nanoparticles offers the exciting prospect of biocompatible catalysts for energy storage/conversion and biolabeling applications. Here an aqueous nanoparticle system has been developed with a versatile outer layer for host-guest molecule encapsulation via β-cyclodextrin inclusion complexes. A β-cyclodextrin-modified polystyrene polymer was first obtained by copper nanopowder click chemistry. The glycopolymer enables self-assembly and controlled encapsulation of tetrazine-naphthalimide, as a model redox-active agent, into nanoparticles via nanoprecipitation. Cyclodextrin host-guest interactions permit encapsulation and internanoparticle cross-linking for the formation of fluorescent compound and clustered self-assemblies with chemically reversible electroactivity in aqueous solution. Light scattering experiments revealed stable particles with hydrodynamic diameters of 138 and 654 nm for nanoparticles prepared with tetrazine, of which 95% of the nanoparticles represent the smaller objects by number. Dynamic light scattering revealed differences as a function of preparation method in terms of size, 3-month stability, polydispersity, radius of gyration, and shape factor. Individual self-assemblies were visualized by atomic force microscopy and fluorescence microscopy and monitored in real-time by nanoparticle tracking analysis. UV-vis and fluorescence spectra provided insight into the optical properties and critical evidence for host-guest encapsulation as evidenced by solvachromatism and enhanced tetrazine uptake. Cyclic voltammetry was used to investigate the electrochemical properties and provided further support for encapsulation and an estimate of the tetrazine loading capacity in tandem with light scattering data.

Tetrazines were immobilized onto electrogenerated films of polypyrrole functionalized with β -cyclodextrin. Their immobilization was ascribed to the formation of the inclusion complexes between the tetrazines derivatives and the β -cyclodextrin cavity. We proved that the resulting supramolecular material kept the electrochemical and fluorescent properties of tetrazines. This original architecture was used with success as a “bridge” to immobilize the β -cyclodextrin-tagged glucose oxidase, chosen as an enzyme model, to prove the efficiency of the method to build new supra-biomolecular architectures.

A photoelectrode was designed by electrodeposition of a pyrrole monomer modified with a polypyridyl Ru(II) complex bearing benzo[i]dipyrido-[3,2-a:2′.3′-c]phenazine (dppn) ligand. Owing to the intercalating properties of these immobilized complexes towards DNA double helix, cocaine aptamer was immobilized on the modified electrodes thanks to its stem-loop configuration in order to design a photoelectrochemical cocaine aptasensor. Especially using a double-fragment aptamer strategy, the binding of cocaine and the formation of the aptamer/cocaine complex was successfully observed and modeled by a Langmuir-Freundlich isotherm, giving access to an apparent dissociation constant K d of 3.8 mmol L −1 . The photoelectrochemical aptasensor exhibits a LOD of 10 nmol L −1 and linear range of 1 10 −8 –5 10 −4 mol L −1 .