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Nanosized PTFE-based core-shell particles can be prepared by emulsifier-free seed emulsion polymerization technique starting from spherical or rod-like PTFE seeds of different size. The shell can be constituted by the relatively high Tg polystyrene and polymethylmethacrylate as well as by low Tg polyacrylic copolymers. Peculiar thermal behavior of the PTFE component is observed due to the high degree of PTFE compartmentalization. A very precise control over the particle size can be exerted by properly adjusting the ratio between the monomers and the PTFE seed. Samples with uniformity ratios suited to build 2D and 3D colloidal crystals are easily prepared. 2D colloidal crystal of spheres leads to very small 2D nanostructuration, useful for the preparation of masks with a combination of nanosphere lithography and reactive ion etching. 3D colloidal crystals were also obtained featuring excellent opal quality.

Several authors demonstrated that an oligonucleotide based pH-sensitive construct can act as a switch between an open and a closed state by changing the pH. To validate this process, specially designed fluorescence dye-quencher substituted oligonucleotide constructs were developed to probe the switching between these two states. This paper reports on bulk and single molecule fluorescence investigations of a duplex-triplex pH sensitive oligonucleotide switch. On the bulk level, only a partial quenching of the fluorescence is observed, similarly to what is observed for other published switches and is supposed to be due to intermolecular interactions between oligonucleotide strands. On the single molecule level, each DNA-based nanometric construct shows a complete switching. These observations suggest the tendency of the DNA construct to associate at high concentration.

A multitude of DNA-based nanostructures of different size and dimensionality have appeared in the literature in the last few years. The programmed self-assembly of oligodeoxynucleotides can be employed to build DNA nanostructures by design in a very successful approach towards bottom-up nanofabrication. This review paper will focus on the developments in this area of research and on some of the properties of DNA that elicited the birth of this new area of research.

Nowadays, the development of experimental procedures for the determination of the secondary structure of RNA molecules is taking advantage of the novel single-molecule probing and imaging techniques. We report a method for the mapping of the secondary structure of RNA molecules spread on a flat surface by means of the atomic force microscope. Globular domains comprising groups of RNA secondary and tertiary structure elements separated by unstructured domains can be discerned in the micrographs and their position along the molecule contour can be measured directly on unstained specimens. We have analyzed the morphology of a population of single molecules of 3' fragments of the Turnip Yellow Mosaic Virus RNA shorter than 1 kb in different temperature and electrolytic conditions. We found a satisfying agreement of the shape of the imaged structures with previously available evidence. The method we have developed can be used to map also different types of RNA molecules and has the advantage of showing the distribution of the single molecule conformations within the population.

We here report that the formation and breakdown of an intramolecular cytosine-thymine (CT) motif DNA triple-helix can be performed repeatedly, quickly and independently of its local concentration without performance reduction over successive cycles; as a consequence, we propose that this set of characteristics makes the DNA duplex-triplex transition an ideal candidate to power simple nanometer-scale devices capable of maintaining effective performance regardless of their local concentration.

DNA is the molecule that encodes the hereditary information in living organisms. In the last years, the specific recognition abilities and the possibility to encode information that are intrinsic in the DNA molecule have been used to assemble nanoscale structures by design. As suggested by Ned Seeman, the recognized pioneer of this field,[1] the Holliday junction is the fundamental structural element around which a great variety of structures can be designed and implemented: this is a branching point where 4 chains of double-stranded DNA meet. By organizing a number of junctions in a proper fashion, it is possible to create rigid structures that overtake the intrinsic flexibility and stochasticity of polymers to create DNA nanoscale objects with the desired size and shape. Using this type of approach a number of monomeric or polymeric nano-objects can be assembled, with the added possibility of introducing tunable elements, that can change their geometry on an external signal, opening the way towards the construction of nanostructures with controllable dynamics. Using synthetic oligodeoxynucleotides (ODN), in our laboratory we have assembled parallelogram shaped nanostructures made of 4 blocked Holliday junctions that have “sticky ends” on their side. Programmed assembly of these ends brings to the construction of polymers that can be either flexible or rigid (100 nm of persistence length or more). Proper mixing and assembly of different monomer structures can yield different topologies: we can obtain linear, branched or circular nanostructures up to several hundred nanometers in size. The biochemical and structural characterization of these has been performed using gel eletrophoresis and atomic force microscopy. By proper functionalization of the ODNs used for the assembly, it is possible to include non-DNA objects on the structures: this seems a clever strategy to assemble (a desired number of) objects at a controlled distance on a nanostructure, with the possibility of also modulating their dynamics. As an example of this paradigm, we have assembled interacting fluorophores on a rigid parallelogram made of DNA, and we have measured a significant FRET. This does not take place if the fluorophores are, instead, free in solution, or even if they are assembled on incomplete (more flexible) parallelogram structures. Furthermore, by assemblying oligonucleotides in a pH-controlled triple helix, we have recently introduced a novel structural motif to the toolbox for DNA-based molecules constructions.[2] This tool is expected to expand further the possibilities of assemblying and controlling nanostructures made of DNA. [1] N. C. Seeman, Nature 2003, 421, 427. [2] M. Brucale, G. Zuccheri, B. Samorì, Org Biomol Chem 2005, 3, 575.

The nanometer scale is a special place where all sciences meet and develop a particularly strong interdisciplinarity. While biology is a source of inspiration for nanoscientists, chemistry has a central role in turning inspirations and methods from biological systems to nanotechnological use. DNA is the biological molecule by which nanoscience and nanotechnology is mostly fascinated. Nature uses DNA not only as a repository of the genetic information, but also as a controller of the expression of the genes it contains. Thus, there are codes embedded in the DNA sequence that serve to control recognition processes on the atomic scale, such as the base pairing, and others that control processes taking place on the nanoscale. From the chemical point of view, DNA is the supramolecular building block with the highest informational content. Nanoscience has therefore the opportunity of using DNA molecules to increase the level of complexity and efficiency in self-assembling and self-directing processes.