Mittuniversitetet

We briefly present a method for the parameterization of assembly systems derived from their ability to form unique structures. The concept of bond uniqueness is introduced and we show how it influences the number of unique structures that a programmable, or algorithmic, self-assembly system can create. Further, we argue that programmable self-assembly systems create embedded, additional computation that is reflected in the complexity of the generated structures and show how this complexity is related to the bond uniqueness of the building blocks. A brief introduction to sticky graphs, a mathematical tool for modeling self-assembly systems, is given. From the theoretical discussions it becomes clear that building blocks for programmable self-assembly need to have at least four distinct, geometrically separated bonds. A scheme for the production of building blocks with well-directed bonds for programmable self-assembly using DNA-nanoparticles is presented. The introduced procedure is a completely bottom–up approach and can be used to produce quite advanced PSA building blocks like nanoparticle eight-mers with eight bonds. Initial experiments are presented.

Self-assembly of complex, non-periodic nanostructures can only be achieved by using anisotropic building-blocks. The building blocks need to have at least four bonds pointing in separate directions [J. Comput. Theor. Nanosci. 3, 391 (2006)]. We have previously presented a method for the synthesis of such building-blocks using DNA-functionalized gold nanoparticles. Here, we report on the progress in the experimental realization of this scheme. The first goal, in a process to make programmable self-assembly building-blocks using nanoparticles, is the production of dimers with different DNA-functions on the two component particles. We report on the fabrication of anisotropically functionalized dimers of nanoparticles of two different sizes. As a result of their anisotropy, these demonstrator building blocks can be made to assemble into spherical structures.

DNA self-assembly is a powerful route to the production of very small, complex structures. When used in combination with nanoparticles it is likely to become a key technology in the production of nanoelectronics in the future. Previously, demonstrated nanoparticle assemblies have mainly been periodic and highly symmetric arrays, unsuited as building blocks for any complex circuits. With the invention of DNA-scaffolded origami reported earlier this year (Rothemund P W K 2006 Nature 440 (7082) 297–302), a new route to complex nanostructures using DNA has been opened. Here, we give a short review of the field and present the current status of our experiments were DNA origami is used in conjunction with nanoparticles. Gold nanoparticles are functionalized with thiolated single stranded DNA. Strands that are complementary to the gold particle strands can be positioned on the self-assembled DNA-structure in arbitrary patterns. This property should allow an accurate positioning of the particles by letting them hybridize on the lattice. We report on our recent experiments on this system and discuss open problems and future applications.

An important problem in nanotechnology is to develop a method for assembling complex, aperiodic, structures. While simple self-assembly will not be able to address this problem, programmable-, or algorithmic-, self-assembly is powerful enough to be a potential solution. Here, we address the question of how the basic properties of the constituent building blocks are related to the periodicity of the resulting assembly. By introducing the parameters unique structures, which gives a measure of the complexity of an assembly, and bond uniqueness, which gives a measure of how the building blocks fit together, we show how to quantify the structural quality of a general assembly system and present relations between the parameters. The introduced methods will be helpful when designing assembly systems to be used for direct fabrication of nanosystems or for nano-scaffolds and addressable arrays.

Nanoparticles coated with single stranded DNA have been shown to efficiently hybridize to targets of complementary DNA. This property might be used to implement programmable (or algorithmic) self-assembly to build nanoparticle structures. However, we argue that a DNA coated nanoparticle by itself cannot be used as a programmable self-assembly building block since it does not have directed bonds. A general scheme for assembling and purifying nanoparticle eight-mers with eight geometrically well-directed bonds is presented together with some preliminary experimental work.