Complementary strands and redox intercalators can be self‐assembled into nanoscale structures capable of charge transfer at the electrode surface from DNA oligomers synthesized directly at covalently modified semiconductor silicon surfaces (see schematic representation).

Nanocrystals are under active investigation because of their interesting size-dependent properties and potential applications. Silicon nanocrystals have been studied for possible uses in optoelectronics, and may be relevant to the understanding of natural processes such as lightning strikes. Gas-phase methods can be used to prepare nanocrystals, and mass spectrometric techniques have been used to analyse Au and CdSe clusters. However, it is difficult to study nanocrystals by such methods unless they are synthesized in the gas phase. In particular, pre-prepared nanocrystals are generally difficult to sublime without decomposition. Here we report the observation that films of alkyl-capped silicon nanocrystals evaporate upon heating in ultrahigh vacuum at 200 degrees C, and the vapour of intact nanocrystals can be collected on a variety of solid substrates. This effect may be useful for the controlled preparation of new quantum-confined silicon structures and could facilitate their mass spectroscopic study and size-selection.

Polyoxometalates (POMs) are discrete, molecular metal oxides with dimensions ranging from about one to tens of ngstroms, a wide variety of topologies and compositions, and an extensive range of chemical and electronic properties which, together with their thermal and oxidative stabilities, are leading to applications in catalysis, electrooptics, magnetics, medicine, and biology. [1][2][3] Consequently, POMs are attractive as functional components of active materials. In recent years, systematic methods for POM synthesis and derivatization have been developed, providing an expanding range of robust "designer" components for "bottom-up" materials synthesis, and a major challenge now facing those engaged in POM research is to devise generic methods for constructing functional nanoscale architectures from these versatile building blocks.The self-assembly of organic monolayers on surfaces has developed over the last two decades into a powerful strategy for the construction of hierarchical structures from molecular components and, although self-assembled inorganic monolayers have received much less attention, several groups have investigated the incorporation of POMs into surface-confined structures. Ordered monolayers of POMs have been obtained on silver and gold by adsorption from solution, [4,5] and evaporative solution deposition has been used to produce catalytically active POM layers on highly oriented pyrolytic graphite (HOPG). [6][7][8] Hybrid organic-POM multilayered magnetic structures have been produced by LangmuirBlodgett techniques, [9][10][11] while electrostatic layer-by-layer assembly with cationic polyelectrolytes has produced more robust hybrid structures.[12] These approaches rely upon either electrostatic interactions or ill-defined chemisorption for the assembly of POM monolayers or multilayers and, to our knowledge, the only example of well defined covalent attachment to a surface is that of a thiol-derivatized POM on gold nanoparticles.[13] Our previous work has shown that monofunctional alkoxide POM derivatives [(RO)MW 5 O 18 ] nÀ (M = Ti, Zr, Nb) are accessible through hydrolytic aggregation reactions involving metal alkoxides.

The various surface types involved in the synthesis of DNA upon alcohol-terminated monolayers at Si(111) surfaces were probed using scanning tunneling microscopy (STM). Images of the initial hydrogenterminated layer showed the typical step and terrace features which are retained after alkylation with 4,4′-dimethoxytrityl-1-undecenol. The method of deprotection for oligonucleotides synthesized at these monolayer films was shown to have a dramatic effect on the surface. After treatment with methylamine, rinsing with water caused considerable etching of the surface; however, this was avoided by the use of a dry ethyl acetate and ether wash. There is little indication of DNA for surfaces covered with single stranded material as judged by STM imaging or tunneling spectroscopy experiments. However, after hybridization with the complementary strand, DNA-Si(111) substrates gave stable images that do not typically show the step and terrace features of the underlying alkyl monolayer. Instead wormlike features are seen that are interpreted as containing aligned DNA molecules lying nearly parallel to the surface. IntroductionDNA-modified surfaces are increasingly considered for applications beyond the relatively well-established microarrays for genomics 1,2 toward materials and nanotechnological applications. 3-5 Materials to which DNA has been attached include insulators, commonly glass 2,6 or the native oxide of silicon, 2,7-9 metal surfaces, particularly gold, 10-28 and also molecular-based compounds such as synthetic polymers. [29][30][31] More recently, DNA-semiconductor surfaces have been prepared for CdSe/ZnS quantum dots 32 and bulk