Electric light orchestra! Enhanced photocurrents are generated in an assembly that consists of CdS nanoparticles linked to a gold electrode by carbon nanotubes (see picture, TEOA=triethanolamine). The enhanced photocurrents are attributed to the effective transport of conduction‐band electrons through the carbon nanotube to the electrode, a process that competes with electron–hole recombination in the CdS semiconductor nanoparticles.

Dedicated to Professor Mordecai Rabinovitz on the occasion of his 70th birthdayThe electrical contacting of redox enzymes such as glucose oxidase, with electrodes is of fundamental importance for the development of amperometric biosensors [1] and biofuel cells.[2] The tethering of redox-active units to the enzyme [3] or the immobilization of the biocatalysts in redox-active polymers [4] have been reported as means of establishing electrical communication between the redox centers of enzymes and electrodes.Recently, our laboratory reported the surface reconstitution of apo-proteins (e.g. apo-glucose oxidase (apo-GOx)) on cofactor-functionalized monolayers associated with electrodes as a general method to establish electrical communication between redox sites in proteins and electrodes. The reconstitution of apo-GOx on a relay-functionalized flavin adenine dinucleotide (FAD) monolayer (e.g. pyrroloquinoline quinone (PQQ) linked to FAD), [5] or on FAD-functionalized Au nanoparticles, [6] or on FAD-functionalized carbon nanotubes [7] proved to be effective means of bringing the redox enzyme into electrical contact with the electrodes, and unprecedented high electron-transfer turnover rates were observed.One of the challenges is the electrochemical activation of the biocatalyzed oxidation or reduction of a substrate at the

Magnetic nanoparticles consisting of undecanoate-capped magnetite (average diameter approximately 4.5 nm; saturated magnetization, M(s), 38.5 emu g(-1)) are used to control and switch the hydrophobic or hydrophilic properties of the electrode surface. A two-phase system consisting of an aqueous buffer solution and a toluene phase that includes the suspended capped magnetic nanoparticles is used to control the interfacial properties of the electrode surface. The magnetic attraction of the functionalized particles to the electrode by means of an external magnet yields a hydrophobic interface that acts as an insulating layer, prohibiting interfacial electron transfer. The retraction of the magnetic particles from the electrode to the upper toluene phase by means of the external magnet generates a hydrophilic electrode that reveals effective interfacial electron transfer. The electron-transfer resistance and double-layer capacitance of the electrode surface upon the attraction and retraction of the functionalized magnetic particles to and from the electrode, respectively, by means of the external magnet were probed by Faradaic impedance spectroscopy (R(et) = 170 Omega and C(dl) = 40 microF sm(-2) in the hydrophilic state of the electrode and R(et) = 22 k Omega and C(dl) = 0.5 microF sm(-2) in the hydrophobic state of the interface). The magnetoswitchable control of the interface enables magnetic switching of the bioelectrocatalytic oxidation of glucose in the presence of glucose oxidase and ferrocene dicarboxylic acid to "ON" and "OFF" states.

Three different configurations of Au‐nanoparticle/CdS‐nanoparticle arrays are organized on Au/quartz electrodes for enhanced photocurrent generation. In one configuration, Au‐nanoparticles are covalently linked to the electrode and the CdS‐nanoparticles are covalently linked to the bare Au‐nanoparticle assembly. The resulting photocurrent, φ = 7.5 %, is ca. 9‐fold higher than the photocurrent originating from a CdS‐nanoparticle layer that lacks the Au‐nanoparticles, φ = 0.8 %. The enhanced photocurrent in the Au/CdS nanoparticle array is attributed to effective charge separation of the electron–hole pair by the injection of conduction‐band electrons from the CdS‐ to the Au‐nanoparticles. Two other configurations involving electrostatically stabilized bipyridinium‐crosslinked Au/CdS or CdS/Au nanoparticle arrays were assembled on the Au/quartz crystal. The photocurrent quantum yields in the two systems are φ = 10 % and φ = 5 %, respectively. The photocurrents in control systems that include electrostatically bridged Au/CdS or CdS/Au nanoparticles by oligocationic units that lack electron‐acceptor units are substantially lower than the values observed in the analogous bipyridinium‐bridged systems. The enhanced photocurrents in the bipyridinium‐crosslinked systems is attributed to the stepwise electron transfer of conduction‐band electrons to the Au‐nanoparticles by the bipyridinium relay bridge, a process that stabilizes the electron–hole pair against recombination and leads to effective charge separation.

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Enhanced photocurrents are detected in the presence of bipyridinium‐modified CdS nanoparticles associated with electrodes. The enhanced photocurrents originate from vectorial electron transfer that retards recombination processes. The Figure shows different architectures for CdS nanoparticles on Au electrodes.

Magnetic switching of redox reactions and bioelectrocatalytic transformations is accomplished in the presence of relay-functionalized magnetite particles (Fe 3 O 4 ). The electrochemistry of a naphthoquinone (1), pyrroloquinoline quinone (2; PQQ), microperoxidase-11 (3), a ferrocene derivative (4) and a bipyridinium derivative (5), functionalized magnetic particles, is switched ™ON∫ and ™OFF∫ by an external magnet upon the attraction of the magnetic particles to an electrode or their retraction from the electrode, respectively. The magneto-switchable activation and deactivation of the electrochemical oxidation of the ferrocene-functionalized magnetic particles and the electrochemical reduction of the bipyridinium-functionalized magnetic particles are used for the triggering of mediated bioelectrocatalytic oxidation of glucose, in the presence of glucose oxidase (GOx), and bioelectrocatalytic reduction of nitrate (NO 3 À ), in the presence of nitrate re-ductase (NR), respectively. Magnetic particles functionalized with a PQQ ± NAD dyad are used for the magnetic switching of the bioelectrocatalytic oxidation of lactate in the presence of lactate dehydrogenase (LDH). The coupling of these particles with a ferrocenemonolayer-functionalized electrode allows the dual and selective sensing of lactate and glucose in the presence of LDH and GOx, respectively, by using an external magnet to switch the detection mode.

Elektronentransport durch Nanoröhren: Dies wird als Erklärung für die höheren Photoströme in einem System aus CdS‐Nanopartikeln angeboten, die über Kohlenstoffnanoröhren mit einer Goldelektrode verknüpft sind (siehe Bild, TEOA=Triethanolamin). Der effektive Transport von Leitungsbandelektronen durch die Nanoröhre zur Elektrode konkurriert mit der Elektron‐Loch‐Rekombination in den CdS‐Halbleiter‐Nanopartikeln.