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.

Circular DNA is used as a template for the amplified detection of M13 phage ssDNA by a rolling circle amplification (RCA) process that synthesizes DNAzyme chains, thus enabling the colorimetric or chemiluminescent detection of the analyte.

Biomolecule–nanoparticle (NP) [or quantum‐dot (QD)] hybrid systems combine the recognition and biocatalytic properties of biomolecules with the unique electronic, optical, and catalytic features of NPs and yield composite materials with new functionalities. The biomolecule–NP hybrid systems allow the development of new biosensors, the synthesis of metallic nanowires, and the fabrication of nanostructured patterns of metallic or magnetic NPs on surfaces. These advances in nanobiotechnology are exemplified by the development of amperometric glucose sensors by the electrical contacting of redox enzymes by means of AuNPs, and the design of an optical glucose sensor by the biocatalytic growth of AuNPs. The biocatalytic growth of metallic NPs is used to fabricate Au and Ag nanowires on surfaces. The fluorescence properties of semiconductor QDs are used to develop competitive maltose biosensors and to probe the biocatalytic functions of proteases. Similarly, semiconductor NPs, associated with electrodes, are used to photoactivate bioelectrocatalytic cascades while generating photocurrents.

Dip-pen nanolithography (DPN) is a powerful method to pattern nanostructures on surfaces by the controlled delivery of an "ink" coating the tip of an atomic force microscope upon scanning and contacting with surfaces. The growing interest in the use of nanoparticles as structural and functional elements for the fabrication of nanodevices suggests that the DPN-stimulated patterning of nanoparticles on surfaces might be a useful technique to assemble hierarchical architectures of nanoparticles that could pave methodologies for functional nanocircuits or nanodevices. This Review presents different methodologies for the nanolithographic patterning of metallic, semiconductor, and metal oxide nanostructures on surfaces. The mechanisms involved in the formation of the nanostructures are discussed and the effects that control the dimensions of the resulting patterns are reviewed. The possible applications of the nanostructures are also addressed.

Gold‐nanoparticle‐functionalized enzymes act as “biocatalytic inks” for the generation of metallic nanowires via dip‐pen nanolithography. Deposition of nanoparticle‐modified oxidases or a phosphatase followed by development with their respective substrates and metal salts results in nanowires (see figure). This concept may be extended to the generation of other nanostructures via enzyme‐catalyzed particle growth.

Composite materials consisting of polyaniline/poly(4-styrene-sulfonate) (PAn/PSS) or polyaniline/Au nanoparticles capped with 2-mercaptoethane sulfonic acid (PAn/Au-NPs) are prepared in the form of thin films (thickness ca. 90 nm) on Au electrodes or in the form of microrods linked to a Au surface. The composite materials in the microrod structures are electrochemically prepared in porous alumina membranes coated with a Au film, followed by the dissolution of the membrane. Chronoamperometric experiments reveal that the charge transport in the PAn/Au-NPs system is ca. 25-fold enhanced as compared to the analogous PAn/PSS system. The different polyaniline composite assemblies were used as catalysts for the electrochemical oxidation of ascorbic acid and as electron-transfer mediators for the bioelectrocatalytic activation of glucose oxidase (GOx) toward the oxidation of glucose. The PAn/Au-NPs system in the microrod structure reveals superior function as the catalyst for the electrochemical oxidation of ascorbic acid and in the bioelectrocatalytic activation of GOx because of the high surface area of the assembly and the enhanced charge-transport properties of the composite material.

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.

Submonolayers of octadecylsiloxane (ODS) were prepared by adsorption from dilute solutions of octadecyltrichlorosilane (OTS) onto a series of different substrates: mica, native silicon (Si/SiO2), and mica coated with a defined number nSiO of SiO2 monolayers (nSiO ) 1, 2, 4, 6). Atomic force microscopy (AFM) was used to investigate the adsorption rate and the submonolayer island morphology as a function of the substrate composition. Two types of substrate effects were observedsfirst, an abrupt change of the shape, size, and height distribution of the submonolayer islands between mica and SiO2-coated mica or silicon substrates, and second, an exponential decrease of the adsorption rate with nSiO up to a thickness of about 6 SiO2 monolayers. The first effect is independent of the SiO2 film thickness and the nature of the underlying substrate (mica or Si) and is therefore believed to arise from the different surface concentrations of OH groups on mica and SiO2 surfaces. The adsorption rate decrease with nSiO, in contrast, appears to be a long-range, bulk effect of mica and might reflect an electrostatic interaction between the negatively charged mica surface and the polar head groups of the film molecules, which accelerates the adsorption in comparison to that of an uncharged substrate such as silicon.Self-assembled monolayers (SAMs) formed on solid substrates by spontaneous assembly of amphiphilic molecules from dilute solutions are often considered as solidstate analogs to Langmuir-Blodgett (LB) films prepared on a liquid subphase and transferred to a solid support. 1 Despite the striking similarities between these two classes of highly organized, supramolecular systems, regarding the type of film molecules and their uniform, densely packed assembly on the substrate surface, SAM films are generally strongly chemisorbed and often show pronounced, substrate-dependent properties unknown for LB films but rather typical for epitaxial overlayers. Organothiol molecules, for example, adsorb on coinage metal surfaces (Au, Ag, Cu) via specific sulfur-metal bonds onto a predefined coordination site lattice (e.g. 3-fold hollow sites on a Au(111) surface), whereby the lattice spacing and the lattice geometry of the particular metal determine the packing density and the surface orientation of the film molecules. 2 Other classes of SAM films, on the other hand, such as alkylsiloxane monolayers formed from alkylsilanol precursors on a variety of OH-terminated surfaces 3-5 (Si/SiO 2 , Al 2 O 3 , glass, mica, etc.), appear to lack any substrate influences 3,6,7 and are considered as the closest relatives to LB films known to date. 8 One major difference still existssthe covalent linkage between the silanol film molecules and the surface hydroxyl groups under Si-O-Si bond formationswhose role in the film growth process is still under debate. Whereas in some reports a substrate-decoupled growth mechanism was proposed, 7,8 in which the monolayer forms on a thin layer of adsorbed water and is sparsely anchored to the substrate via Si-O-...