When a component is so small it precludes the design of the necessary tools for its manufacture, one route long anticipated has been to “teach” individual parts to self-assemble into the desired product.

Now a team of INT researchers headed by Mario Ruben have adopted a trick from nature: synthetic adhesives being applied to magnetic molecules in such a way that the latter docked on to the proper positions on a nanotube without any intervention to fabricate an electronic nano-device

In nature, leaves grow through a similar self-organising process without any impetus from subordinate mechanisms. The adoption of such principles to the manufacture of electronic components is a paradigm shift with the nano-switch developed by a team of scientists from Centre National de la Recherche Scientifique (CNRS) in Grenoble, Institut de Physique et Chimie des Matériaux at the University of Strasbourg, and KIT’s INT.

It is one of the invention’s particular features that, unlike the conventional electronic components, the new component does not consist of metals, alloys or oxides but entirely of soft materials such as carbon nanotubes and molecules.

Terbium, the only magnetic metal  that is used in the device, is embedded in organic material. It reacts very sensitively to external magnetic fields. Information as to how this atom aligns along such  fields is efficiently passed on to the current flowing through the nanotube.

The Grenoble CNRS research group headed by Dr Wolfgang Wernsdorfer succeeded in electrically reading out magnetism in the nano-component environment. The demonstrated possibility of addressing electrically single magnetic molecules, opens a new world to spintronics, where memory, logic and possibly quantum logic may be integrated. 

The function of the spintronic nano-device is described in July Nature Materials with low temperatures of some one degree Kelvin, or -272 degrees Celsius. Efforts are now being taken by the team to increase the component’s working temperature in the near future.

Three dimensional plasmon ruler

The world’s first t3D plasmon rulers, able to measure nanometer scale spatial changes in molecular systems, have been developed by researchers with the US Department of Energy (DOE)’s Lawrence Berkeley National Lab  together with Stuttgart University  Germany.

These 3D plasmon rulers could provide scientists with unprecedented details of such critical dynamic events in biology as the interaction of DNA with enzymes, the folding of proteins, the motion of peptides or the vibrations of cell membranes. It might even help with the magnetic nanomaterial self organisation..

“We’ve demonstrated a 3D plasmon ruler, based on coupled plasmonic oligomers in combination with high-resolution plasmon spectroscopy, that enables us to retrieve the complete spatial configuration of complex macromolecular and biological processes, and to track the dynamic evolution of these processes,” says (left above) Paul Alivisatos, director of Berkeley Lab and leader of this research.

Alivisatos, the Larry and Diane Bock Professor of Nanotechnology at the University of California (UC), Berkeley, is senior author of the  paper “Three-Dimensional Plasmon Rulers” co-authored by Laura Na Liu, Mario Hentschel, with Thomas Weiss and Harald Giessen from Stuttgart, in the journal Science. 

Nanometer scales are where biology and material sciences converge. As human machines and devices shrink to the size of biomolecules, scientists need tools by which to precisely measure minute structural changes and distances.

Researchers have developed specific linear rulers  based on the electronic surface waves known as “plasmons,” which are generated when light travels through the confined dimensions of noble metal nanoparticles or structures, such as gold or silver.

“Two noble metallic nanoparticles in close proximity will couple with each other through their plasmon resonances to generate a light-scattering spectrum that depends strongly on the distance between the two nanoparticles,” Alivisatos says. “This light-scattering effect has been used to create linear plasmon rulers that have been used to measure nanoscale distances in biological cells.”

"Compared to other molecular rulers based on chemical dyes and fluorescence resonance energy transfer (FRET), plasmon rulers neither blink nor photobleach but offer exceptional photostability and brightness.

But, until now plasmon rulers could only be used to measure distances along one dimension, a limitation that hampers comprehensive understanding of all biological and other soft-matter processes that take place in 3D.

“Plasmonic coupling in multiple nanoparticles placed in proximity to each other leads to light scattering spectra that are sensitive to a complete set of 3D motions,” says Laura Na Liu, the corresponding author of the paper.

“The key to our success is that we were able to create sharp spectral features in the otherwise broad resonance profile of plasmon-coupled nanostructures by using interactions between quadrupolar and dipolar modes.”

Liu, who at the time the work was done was a member of Alivisatos’ research group, is now visiting Professor with Rice University, explains that typical dipolar plasmon resonances are broad because of radiative damping.

As a result, the simple coupling between multiple particles produces indistinct spectra that are not readily converted into distances. The co-authors overcame this with a 3D ruler constructed from five gold nanorods of individually controlled length and orientation, in which one nanorod is placed perpendicular between two pairs of parallel rod  nanorods to form a structure that resembles the letter H.

“The strong coupling between the single nanorod and the two parallel nanorod pairs suppresses radiative damping and allows for the excitation of two sharp quadrupolar resonances that enable high-resolution plasmon spectroscopy,” Liu says.  “Any conformational change in this 3D plasmonic structure will produce readily observable changes in the optical spectra.”

Not only did conformational changes in their 3D plasmon rulers alter light scattering wavelengths, but the spatial freedom afforded by the single perpendicular nanorod allows the Berkeley researchers to distinguish directional as well as magnitude of structural changes.

“As a proof of concept, we fabricated a series of samples with high-precision EBL and layer-by-layer stacking nano techniques, then embedded them with our 3D plasmon rulers in a dielectric medium on a glass substrate,” says Liu says. “Results were in excellent agreement with the calculated spectra.”

Alivisatos, Liu and their co-authors envision a future in which a multiple assortment of 3D plasmon rulers would, through biochemical linkers, be attached to a sample macromolecule, for example, to various points along a strand of DNA or RNA, or at different positions on a protein or peptide.

The sample macromolecule would then be exposed to light and the optical responses of the 3D plasmon rulers would be measured via dark field microspectroscopy.

“The realization of 3D plasmon rulers using nanoparticles and biochemical linkers is challenging, but 3D nano particle assemblies with desired symmetries and configurations have been already been demonstrated,” Liu says.

“We believe these exciting experimental achievements along with the introduction of our new concept will pave the road toward the realisation of 3D plasmon rulers in biological and other soft-matter systems.”