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Electrostatic potential to trap nano-sized objects

EU-funded scientists are performing ground-breaking research for the self-assembly of nanometre-sized objects. The resulting elucidation of mechanisms to confine and control biological molecules is also gaining international recognition.
Electrostatic potential to trap nano-sized objects
Controlling the self-assembly of nano-structures such as nanoparticles (NPs) or nanorods (dimensions of the atomic or molecular scale) opens the door to fabrication of materials with unique electrical, magnetic and/or optical properties. Directing self-assembly by trapping nanometre-sized objects has become an active area of research in fields such as quantum optics, biophysics and clinical medicine, yet it remains technically challenging.

Scientists serendipitously discovered unexpected geometry-induced effects on the confinement of charged colloids and macromolecules through attractive (electrostatic) interactions with like-charged confining walls in weakly ionic solutions. They initiated the EU-funded project 'Self-assembly of confined colloidal objects for the study of nano-optic phenomena' (PHOTONANOFLUIDIX) to elucidate the nature of these effects.

In particular, scientists are investigating the origin of this unexpected attractive force between like-charged entities and its dependence on ionic solution strength, particle size and confinement dimensions. Such knowledge will enable them to optimise the self-assembly of charged metallic or dielectric nano-objects into crystal lattices for the study of light-scattering phenomena (plasmonic and photonic effects).

Exciting progress was made in the first reporting period. Scientists applied numerical calculations of the electrostatic potential to explain the experimentally observed trapping of single nano-objects. Further experiments with trapped gold NPs in solutions of varying ionic strengths and different channel geometries were performed, demonstrating excellent agreement between theory and experimental results.

Going well beyond the originally proposed work, scientists demonstrated the trapping of single lipid vesicles as well. They showed that the tailored spatially modulated electrostatic potential of the ionic silt can trap and levitate charged objects in solution. This enables contact-free, directed self-assembly of single proteins and macromolecules into high-density arrays. This ground-breaking work led to a publication in the prestigious peer-reviewed scientific journal Nature (Nature 467, 692-695 (6 October 2010)).

An enhanced theoretical understanding of the fundamental trapping mechanisms for single nano-objects has opened the door to several unforeseen lines of research. The trapping of soft biological objects promises exciting new applications in biology and biophysics in addition to, or perhaps even in combination with, the originally intended optical applications.

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