Carbon-coated magnetic nanoparticles as a removable protection layer extending the operation lifetime of bilirubin oxidase-based bioelectrode.

One of the factors hindering the development of enzymatic biosensors and biofuel cells in real-life applications is the time-dependant degradation of the biocatalysts on electrode surfaces. In this work, we present a new practical approach for extending the operation lifetimes of bioelectrocatalytic assemblies based on bilirubin oxidase (BOD). As evident by both spectroscopic and electrochemical measurements, an adsorption of carbon-coated magnetic nanoparticles (ccMNPs) onto a BOD/carbon nanotubes-deposited surface yields a stable bioelectrocathode system for mediatorless oxygen reduction.

Power Generation by Selective Self-Assembly of Biocatalysts.

Through a careful chemical and bioelectronic design we have created a system that uses self-assembly of enzyme-nanoparticle hybrids to yield bioelectrocatalytic functionality and to enable the harnessing of electrical power from biomass. Here we show that mixed populations of hybrids acting as catalyst carriers for clean energy production can be efficiently stored, self-assembled on functionalized stationary surfaces, and magnetically re-collected to make the binding sites on the surfaces available again. The methodology is based on selective interactions occurring between chemically modified surfaces and ligand-functionalized hybrids.

Magnetically induced enzymatic cascades - advancing towards multi-fuel direct/mediated bioelectrocatalysis.

A generic method to magnetically assemble enzymatic cascades on electrode surfaces is introduced. The versatile method enables the simultaneous activation of both direct and mediated electron transfer bioelectrocatalysis to harness different substrates, which can serve as multiple fuels and oxidizers in biofuel cells generating clean energy.

Enzymatic self-wiring in nanopores and its application in direct electron transfer biofuel cells.

A synthetic enzymatic activity in nanopores leading to the direct fabrication of modified electrodes applicable as biosensors and/or biofuel cell elements is reported. We demonstrate the heterogeneous enzymatic implanting of platinum nanoclusters, PtNCs, in glucose oxidase, GOx, immobilized on mesoporous carbon nanoparticles, MPCNP-modified surface. As the pores confine the growth of the clusters, the PtNC@GOx/MPCNP assembly becomes electrically wired to the matrix, demonstrating direct electron transfer, DET, bioelectrocatalytic properties that correlate with the applied duration of synthesis and cluster size.

Switchable aerobic/anaerobic multi-substrate biofuel cell operating on anodic and cathodic enzymatic cascade assemblies.

Enzymatic fuel cells may become more accessible for applications powering portable electronic devices by broadening the range of potentially usable fuels and oxidizers. In this work we demonstrate the operation of an integrated, yet versatile multi-substrate biofuel cell utilizing either glucose, fructose, sucrose or combinations of thereof as biofuels, and molecular oxygen originating from solution phase and/or an internal chemical source, as the oxidizer. In order to achieve this goal we designed an enzymatic cascade-functionalized anode consisting of invertase (INV), mutarotase (MUT), glucose oxidase (GOX), and fructose dehydrogenase (FDH), deposited on top of a mesoporous carbon nanoparticle matrix, in which electron relay molecules had been entrapped.

Controlled Vectorial Electron Transfer and Photoelectrochemical Applications of Layered Relay/Photosensitizer-Imprinted Au Nanoparticle Architectures on Electrodes.

Two configurations of molecularly imprinted bis-aniline-bridged Au nanoparticles (NPs) for the specific binding of the electron acceptor N,N'-dimethyl-4,4'-bipyridinium (MV(2+) ) and for the photosensitizer Zn(II)-protoporphyrin IX (Zn(II)-PP-IX) are assembled on electrodes, and the photoelectrochemical features of the two configurations are discussed. Configuration I includes the MV(2+) -imprinted Au NPs matrix as a base layer, on which the Zn(II)-PP-IX-imprinted Au NPs layer is deposited, while configuration II consists of a bilayer corresponding to the reversed imprinting order. Irradiation of the two electrodes in the presence of a benzoquinone/benzohydroquinone redox probe yields photocurrents of unique features: (i) Whereas configuration I yields an anodic photocurrent, the photocurrent generated by configuration II is cathodic.

Block Copolymer Patterns as Templates for the Electrocatalyzed Deposition of Nanostructures on Electrodes and for the Generation of Surfaces of Controlled Wettability.

ITO electrodes modified with a nanopatterned film of polystyrene-block-poly(2-vinylpyridine), PS-b-P2VP, where the P2VP domains are quaternized with iodomethane, are used for selective deposition of redox-active materials. Electrochemical studies (cyclic voltammetry, Faradaic impedance measurements) indicate that the PS domains insulate the conductive surface toward redox labels in solution. In turn, the quaternized P2VP domains electrostatically attract negatively charged redox labels solubilized in the electrolyte solution, resulting in an effective electron transfer between the electrode and the redox label.

Layered Metal Nanoparticle Structures on Electrodes for Sensing, Switchable Controlled Uptake/Release, and Photo-electrochemical Applications.

Layered metal nanoparticle (NP) assemblies provide highly porous and conductive composites of unique electrical and optical (plasmonic) properties. Two methods to construct layered metal NP matrices are described, and these include the layer-by-layer deposition of NPs, or the electropolymerization of monolayer-functionalized NPs, specifically thioaniline-modified metal NPs. The layered NP composites are used as sensing matrices through the use of electrochemistry or surface plasmon resonance (SPR) as transduction signals.

Enzyme-capped relay-functionalized mesoporous carbon nanoparticles: effective bioelectrocatalytic matrices for sensing and biofuel cell applications.

The porous high surface area and conducting properties of mesoporous carbon nanoparticles, CNPs (<500 nm diameter of NPs, pore dimensions ∼6.3 nm), are implemented to design electrically contacted enzyme electrodes for biosensing and biofuel cell applications. The relay units ferrocene methanol, Fc-MeOH, methylene blue, MB(+), and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid), ABTS(2-), are loaded in the pores of the mesoporous CNPs, and the pores are capped with glucose oxidase, GOx, horseradish peroxidase, HRP, or bilirubin oxidase, BOD, respectively.

Light-induced and redox-triggered uptake and release of substrates to and from mesoporous SiO nanoparticles.

The photonic- and redox-triggered cyclic uptake and release of organic substrates in functionalized mesoporous SiO nanoparticles (NPs) is demonstrated. The mesoporous SiO NPs are functionalized with nitrospiropyran photoisomerizable units. Rhodamine B is encapsulated in the channels of the SiO NPs and trapped by the hydrophobic nitrospiropyran capping units.

Photosystem I (PSI)/Photosystem II (PSII)-based photo-bioelectrochemical cells revealing directional generation of photocurrents.

Layered assemblies of photosystem I, PSI, and/or photosystem II, PSII, on ITO electrodes are constructed using a layer-by-layer deposition process, where poly N,N'-dibenzyl-4,4'-bipyridinium (poly-benzyl viologen, PBV(2+) ) is used as an inter-protein "glue". While the layered assembly of PSI generates an anodic photocurrent only in the presence of a sacrificial electron donor system, such as dichlorophenol indophenol (DCPIP)/ascorbate, the PSII-modified electrode leads, upon irradiation, to the formation of an anodic photocurrent (while evolving oxygen), in the absence of any sacrificial component. The photocurrent is generated by transferring the electrons from the PSII units to the PBV(2+) redox polymer.

Photosynthetic reaction center-functionalized electrodes for photo-bioelectrochemical cells.

During the last few years, intensive research efforts have been directed toward the application of several highly efficient light-harvesting photosynthetic proteins, including reaction centers (RCs), photosystem I (PSI), and photosystem II (PSII), as key components in the light-triggered generation of fuels or electrical power. This review highlights recent advances for the nano-engineering of photo-bioelectrochemical cells through the assembly of the photosynthetic proteins on electrode surfaces. Various strategies to immobilize the photosynthetic complexes on conductive surfaces and different methodologies to electrically wire them with the electrode supports are presented.

Electrochemical switching of photoelectrochemical processes at CdS QDs and photosystem I-modified electrodes.

Photoactive inorganic CdS quantum dots (QDs) or the native photosystem I (PSI) is immobilized onto a pyrroloquinoline quinone (PQQ) monolayer linked to Au electrodes to yield hybrid relay/QDs (or photosystem) assemblies. By the electrochemical biasing of the electrode potential, the relay units are retained in their oxidized PQQ or reduced PQQH(2) states. The oxidized or reduced states of the relay units dictate the direction of the photocurrent (anodic or cathodic).

Amplified surface plasmon resonance and electrochemical detection of Pb2+ ions using the Pb2+-dependent DNAzyme and hemin/G-quadruplex as a label.

The hemin/G-quadruplex nanostructure and the Pb(2+)-dependent DNAzyme are implemented to develop sensitive surface plasmon resonance (SPR) and electrochemical sensing platforms for Pb(2+) ions. A complex consisting of the Pb(2+)-dependent DNAzyme sequence and a ribonuclease-containing nucleic acid sequence (corresponding to the substrate of the DNAzyme) linked to a G-rich domain, which is "caged" in the complex structure, is assembled on Au-coated glass surfaces or Au electrodes. In the presence of Pb(2+) ions, the Pb(2+)-dependent DNAzyme cleaves the substrate, leading to the separation of the complex and to the self-assembly of the hemin/G-quadruplex on the Au support.

Integrated photosystem II-based photo-bioelectrochemical cells.

Photosynthesis is a sustainable process that converts light energy into chemical energy. Substantial research efforts are directed towards the application of the photosynthetic reaction centres, photosystems I and II, as active components for the light-induced generation of electrical power or fuel products. Nonetheless, no integrated photo-bioelectrochemical device that produces electrical power, upon irradiation of an aqueous solution that includes two inter-connected electrodes is known.

Biomolecule/nanomaterial hybrid systems for nanobiotechnology.

The integration of biomolecules with metallic or semiconductor nanoparticles or carbon nanotubes yields new hybrid nanostructures of unique features that combine the properties of the biomolecules and of the nano-elements. These unique features of the hybrid biomolecule/nanoparticle systems provide the basis for the rapid development of the area of nanobiotechnology. Recent advances in the implementation of hybrid materials consisting of biomolecules and metallic nanoparticles or semiconductor quantum dots will be discussed.

Photochemical switching of the phase-transition temperatures of p-NIPAM-Pt nanoparticles thermosensitive polymer composites associated with electrodes: functional electrodes for switchable electrocatalysis.

The thermosensitive poly(N-isopropylacrylamide) (p-NIPAM) is electropolymerized onto Au surfaces. The incorporation of the photoisomerizable N-carboxyethyl nitrospiropyran compound into p-NIPAM allows the reversible photochemical control of the gel-to-solid phase-transition temperatures of the polymer. Whereas the gel-to-solid phase-transition temperature of the nitrospiropyran-modified p-NIPAM is 33±2 °C, the phase-transition temperature of the nitromerocyanine-functionalized p-NIPAM matrix corresponds to 38±1 °C.

Amplified surface plasmon resonance based DNA biosensors, aptasensors, and Hg2+ sensors using hemin/G-quadruplexes and Au nanoparticles.

Thiolated nucleic acid hairpin nanostructures that include in their stem region a "caged" G-quadruplex sequence, and in their single-stranded loop region oligonucleotide recognition sequences for DNA, adenosine monophosphate (AMP), or Hg(2+) ions were linked to bare Au surfaces or to Au nanoparticles (NPs) linked to Au surfaces. The opening of the hairpin nanostructures associated with the bare Au surface by the complementary target DNA, AMP substrate, or Hg(2+) ions, in the presence of hemin, led to the self-assembly of hemin/G-quadruplexes on the surface. The resulting dielectric changes on the surface exhibited shifts in the surface plasmon resonance (SPR) spectra, thus providing a readout signal for the recognition events.

Electrochemically triggered Au nanoparticles "sponges" for the controlled uptake and release of a photoisomerizable dithienylethene guest substrate.

1,2-Di(2-methyl-5-(N-methylpyridinium)-thien-3-yl)-cyclopentene undergoes a reversible photoisomerization between open and closed states. The closed isomer state exhibits electron acceptor properties, whereas its irradiation using visible light (λ > 530 nm) yields the open state that lacks electron acceptor features. The electropolymerization of thioaniline-functionalized Au nanoparticles (NPs) in the presence of the closed photoisomer state yields a molecularly imprinted Au NPs matrix, cross-linked by redox-active bis-aniline π-donor bridges.

Photochemically and electrochemically triggered Au nanoparticles "sponges".

Stimuli-triggered wettability of surfaces and controlled uptake and release of substrates by "smart" materials are essential for drug delivery and microfluidic control. A composite "sponge" consisting of bis-aniline-bridged Au nanoparticles (NPs), functionalized with photoisomerizable nitrospiropyran/nitromerocyanine that includes selective imprinted molecular recognition sites for N,N'-bis(3-sulfonatopropyl)-4,4'-bipyridinium (PVS) was electropolymerized on a Au electrode. The system is triggered by photonic and/or electrical signals to yield four different states exhibiting variable binding/release capacities for PVS and controlled wettability of the surface.

Molecularly imprinted Au nanoparticles composites on Au surfaces for the surface plasmon resonance detection of pentaerythritol tetranitrate, nitroglycerin, and ethylene glycol dinitrate.

Molecularly imprinted Au nanoparticles (NPs) composites are generated on Au-coated glass surfaces. The imprinting process involves the electropolymerization of thioaniline-functionalized Au NPs (3.5 nm) on a thioaniline monolayer-modified Au surface in the presence of a carboxylic acid, acting as a template analogue for the respective explosive.

Nano-engineered flavin-dependent glucose dehydrogenase/gold nanoparticle-modified electrodes for glucose sensing and biofuel cell applications.

A three-dimensional composite consisting of the oxygen-insensitive flavin-dependent glucose dehydrogenase, GDH, and Au nanoparticles (NPs) is assembled on a Au surface using an electropolymerization process. The bis-aniline-cross-linked GDH/Au NPs composite reveals effective electrical contact with the electrode (ket=1100 s(-1)), and the effective bioelectrocatalyzed oxidation is driven by the enzyme/NPs matrix. The GDH/Au NPs-functionalized electrode is implemented as an amperometric glucose sensor, and it reveals superior functions when compared to an analogous glucose oxidase/Au NPs system.

Electrified Au nanoparticle sponges with controlled hydrophilic/hydrophobic properties.

Molecularly imprinted Au nanoparticle (NP) composites for the selective binding of the electron acceptors N,N'-dimethyl-4,4'-bipyridinium, MV(2+) (1), or bis-N-methylpyridinium-4,4'-ethylene, BPE(2+) (2), are prepared by the electropolymerization of thioaniline-functionalized Au NPs in the presence of the electron acceptor molecules and the subsequent rinsing off of the imprint substrates. The electrochemical oxidation of the π-donor bisaniline units bridging the Au NPs yields the quinoid electron acceptor bridges, which are re-reduced to the bisaniline state. By the cyclic oxidation and reduction of the bridging units, they are reversibly switched between the π-acceptor and the π-donor states, thus allowing the electrochemically triggered uptake and release of the electron acceptors (1 or 2) to and from the imprinted sites.