Programmed Nanoparticles Organize Themselves Into Highly Complex Structures
Animal and plant cells are prominent examples of how nature constructs larger units in a targeted, pre-programmed manner using smaller elements as building blocks. Nanotechnology researchers take their cue from this 'bottom-up' approach by exploiting the ability of suitably structured nano materials to 'self-assemble' into higher-order architectures. A research group headed by Professor Dr. Axel Müller of the University of Bayreuth (now at Mainz University) and including Dr. Andreas Walther from DWI Interactive Materials Research at RWTH Aachen as well as researchers from the universities of Jena and Helsinki now published a paper in the prestigious scientific journal “Nature” describing a new principle for the self-assembly of patterned nanoparticles. Their findings facilitate the production of novel functional nanostructures and open up new vistas for further research in nano-engineering.
The self-assembly process commences with chain-like macromolecules 10 to 20 nanometers in size, so-called “triblock terpolymers.” They are composed of three connected linear sections, the “blocks.” With the help of solvents, the research team was able to cause the triblock macromolecules to combine into nanoparticles with a diameter of about 50 nanometers. The scientists applied this technique to two types of triblock terpolymers, which differed in the chemical composition of the middle blocks, A-B-C and A-D-C, respectively.
The first type results in nanoparticles with a single bonding site tending to form spherical clusters, while the latter creates nanoparticles with two bonding sites tending to form linear superstructures. Importantly, in both cases the structure of the nanoparticles is pre-programmed by the chemical structure of the source macromolecule in a similar way as the structure of a protein is determined by its amino acid sequence.
Now the differently structured nanoparticles were combined to form, in a process of co-aggregation, into a completely new superstructure, in which nanoparticles generated from “A – B – C” molecules alternated with molecules originating from “A – D – C“ molecules in a precisely defined pattern. Viewed under a transmission electron microscope, the new superstructure bears a strong resemblance to a colorful caterpillar.
New Vistas in Nano-Engineering
The novel approach opens up significant opportunities in nano-engineering. Particularly promising is the large number of macromolecules readily available to function as building blocks. They can be used to incorporate specific properties in the resultant superstructures, such as sensitivity to environmental stimuli like temperature, light, electric and magnetic fields, etc. Possible applications include nanolithography and controlled drug release applications.
"Our work demonstrates that our understanding of soft nanotechnology is already very far advanced, as we are able to generate highly complex structures through molecular programming,” explained RWTH researcher Dr. Andreas Walther. “Nature organizes matter not only spatially, but also in time. We have come very far in the programming of spatial organization, but what we still lack is the ability to realize efficient control processes in time. This is one of the tasks we set ourselves at DWI.”