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The monoclonal anti-dsRNA antibody J2 binds double-stranded RNAs (dsRNA) in an apparently sequence-nonspecific way. The mAb only recognizes antigens with double-stranded regions of at least 40 bp and its affinity to poly(A) poly(U) and to dsRNAs with mixed base pair composition is about tenfold higher than to poly(I) poly(C). Because no specific binding site could be determined, the number, the exact dimensions, and other distinct features of the binding sites on a given antigen are difficult to evaluate by biochemical methods. We therefore employed scanning force microscopy (SFM) as a method to analyze antibody-dsRNA interaction and protein-RNA binding in general. Several in vitro-synthesized dsRNA substrates, generated from the Dictyostelium PSV-A gene, were used. In addition to the expected sequence-nonspecific binding, imaging of the complexes indicated preferential binding of antibodies to the ends of dsRNA molecules as well as to certain internal sites. Analysis of 2,000 bound antibodies suggested that the consensus sequence of a preferential internal binding site is A 2 N 9 A 3 N 9 A 2 , thus presenting A residues on one face of the helix. The site was verified by site-directed mutagenesis, which abolished preferential binding to this region. The data demonstrate that SFM can be efficiently used to identify and characterize binding sites for proteins with no or incomplete sequence specificity. This is especially the case for many proteins involved in RNA metabolism.

The reproducible micromachining of hollow metal tips on Si cantilevers and their applicability to scanning probe microscopy techniques are described. Provided with apertures below 130 nm and hollow pyramidal tips proved to be highly suited probes for scanning near-field optical microscopy (SNOM). First results of combined SFM/SNOM measurements together with scanning electron microscopy (SEM) photographs of the new sensors are presented. The SNOM images show a resolution of about 100 nm demonstrating the usefulness of these probes.

The International Rosetta Mission is set for a rendezvous with Comet 67 P/Churyumov-Gerasimenko in 2014. On its 10 year journey to the comet, the spacecraft will also perform a fly-by of the two asteroids Stein and Lutetia in 2008 and 2010, respectively. The mission goal is to study the origin of comets, the relationship between cometary and interstellar material and its implications with regard to the origin of the Solar System. Measurements will be performed that shed light into the development of cometary activity and the processes in the surface layer of the nucleus and the inner coma. The Micro-Imaging Dust Analysis System (MIDAS) instrument is an essential element of Rosetta's scientific payload. It will provide 3D images and statistical parameters of pristine cometary particles in the nm-μm range from Comet 67P/Churyumov-Gerasimenko. According to cometary dust models and experience gained from the Giotto and Vega missions to 1P/Halley, there appears to be an abundance of particles in this size range, which also covers the building blocks of pristine interplanetary dust particles. The dust collector of MIDAS will point at the comet and collect particles drifting outwards from the nucleus surface. MIDAS is based on an Atomic Force Microscope (AFM), a type of scanning microprobe able to image small structures in 3D. AFM images provide morphological and statistical information on the dust population, including texture, shape, size and flux. Although the AFM uses proven laboratory technology, MIDAS is its first such application in space. This paper describes the scientific objectives and background, the technical implementation and the capabilities of MIDAS as they stand after the commissioning of the flight instrument, and the implications for cometary measurements

Scanning force microscopy (SFM), operated in the attractive imaging mode, enables the precise measurement of the force between tip and sample over a tip–sample distance ranging from contact to tens of nanometers. The basic long range interactions (>1 nm: i.e., hydrodynamic, electrostatic, van der Waals, and capillary forces) between tip and sample have been measured and will be discussed. Each force leads to a different mode of operation in profiling samples. The most critical part of the SFM is the force sensor. Exact knowledge of the sensor properties is required for the interpretation of SFM measurements. We have used micromachined silicon sensors consisting of a monolithic silicon cantilever with integrated silicon tip and have performed a detailed characterization of the tip geometry and resonance properties. Examples of surface images on different samples (conductors, insulators and biological materials) and structures, ranging from atomic steps up to several microns high features, have been investigated to demonstrate capabilities and problems in SFM imaging.