Monika Fischler

Controlled Nucleation of DNA Metallization

The outstanding self-recognition properties of DNA have been exploited in the use of this biomolecule as a template for the construction of nanoscale assemblies and hybrid structures. 3] To further expand the utility of DNA for other applications, research is currently aimed at increasing its intrinsically low electric conductivity. The selective coating of DNA with a thin layer of a conductive element, such as Ag, Pd, Pt, Cu, or Co, has emerged as a promising avenue. Most coating procedures involve the reduction of electrostatically bound metal ions on the DNA by an exogeneous reductant to give small metal clusters attached to the DNA. In a second, development step, known from black-andwhite photography, these metal clusters function as nucleation sites for the reductive deposition of metal atoms until a continuous conductive coating is formed. Novel procedures aimed at increasing the selectivity of the metallization process are the decoration of DNA with functional groups to control the spatial distribution of the nucleation sites, the photochemical deposition of silver on DNA strands, and the formation of DNA–Pt adducts as precursors for metal deposition on DNA. The most critical step in the whole metallization process is the initial nucleation step. The uniformity and the distribution of the metal clusters define the homogeneity of the development

Ordered arrays of silicon pillars with controlled height and aspect ratio

We report the fabrication of ordered arrays of silicon pillars via a combination of nanosphere lithography (NSL) and reactive ion etching (RIE). For NSL we used monolayers of silica particles self-assembled onto silicon substrates as masks for the deposition of hexagonal arrays of chromium nanoislands. By changing the amount of the deposited metal we fabricated arrays of nanoislands with different size and spacing. By using these arrays as masks for RIE, silicon pillars with different height (up to 1100 nm) and aspect ratio (up to 12:1) could be obtained.

Metal nanoparticle–DNA hybrids – from assembly towards functional conjugates

The connection between metal nanoparticles and biomolecular systems has been intensively studied in recent decades as this field promises a vast variety of new applications. In this context DNA has been widely used in combination with nanoparticles for the generation of complex nanoarchitectures. Herein we would like to highlight some recent advances in gold nanoparticle–DNA research that demonstrate distinct functionality and open the prospect of a broad range of innovative applications in nanoelectronics, medicine, sensors, and various other areas related to material science.

DNA-Mediated Assembly of Metal Nanoparticles: Fabrication, Structural Features, and Electrical Properties

Many different synthetic routes have been developed in order to obtain metal nanoparticles of different sizes and shapes. The evolution of high-resolution physical measurements together with the elaboration of theoretical methods applicable to mesoscopic systems inspired many scientists to create fascinating ideas about how these nanoparticles can provide new technological breakthroughs; for example, in nanoelectronic, diagnostic, or sensing devices (de Jongh 1994; Schon and Simon 1995; Simon 1998; Feldheim and Foss 2002; Schmid 2004; Willner and Katz 2004; Rosi and Mirkin 2005). Nanoparticles with a diameter between one and several tens of nanometres possess an electronic structure that is an intermediate of the discrete electronic levels of an atom or molecule and the band structure of a bulk material. The resulting size-dependent change of physical properties is called the quantum size effect (QSE) or size quantization effect (Halperin 1986). 1

DNA-Based Assembly of Metal Nanoparticles: Structure and Functionality

In Chap. 12, Fischler and Simon provide an overview of the current state of the art of DNA-based assembly of metal nanoparticles in one, two and three dimensions. They have summarized different methods of liquid-phase synthesis of metal nanoparticles as well as their functionalization with DNA. The examples selected in this chapter show that the interdisciplinary research at the frontier between biomolecular chemistry, inorganic chemistry, and materials science leads to new materials with unique properties. Based on these properties one may anticipate a broad scope of applications for designing nucleic acid scaffolds to be used for both the assembly of surface-bound nanoparticle architectures as well as three-dimensional aggregates for bioanalytical and advanced materials research. When DNA is used as a template for the assembly of nanoparticles, the examples given in this chapter show that nanowires with metallic conductivity can be obtained. These results have already prompted exciting research on the set-up of functional devices of higher complexity. However, it is still a great challenge to develop these processes further in order to develop devices or even device architectures that are robust enough to be applied in nanoelectronic circuitry.