The group overcame current limitations in EFM-based identification and characterization techniques by measuring the dielectric constant, or permittivity, of objects. This gives an indication of how the material an object is made of reacts to an applied electric field. By increasing the electrical resolution of the microscope by almost two orders of magnitude, in order to be able to detect ultra-weak forces, and using geometrically stable nano-tips alongside as a precise method of modeling their results that takes into account the physics of a system and all its geometrical artifacts, they were able quantify the nano-objects’ dielectric constants precisely and use these as a ‘fingerprint’. This allowed them to distinguish between objects of identical shape but different composition, which would otherwise be impossible to recognize without labeling.
“Previously, EFM images had been limited to the surface structure, and were only able to distinguish between metallic and non-metallic nano-objects in black-and-white experiments,” explains Laura, lead author on the study. “Now we have quantitatively recognized nano-objects made of very similar materials and with low dielectric constants, as is the case with many biological complexes.”
“Our method, an non-invasive way of determining the internal state of objects and correlate these with their functions without slicing or labeling, will be an invaluable tool for diverse areas of scientific research,” says Gabriel. “It is particularly important in nanomedicine for biomedical diagnostics, opening the door to quantitative label-free detection of biological macromolecules such as viruses based on their dielectric properties.”
The researchers have applied their technique to important biological complexes, such as viruses. By unraveling for the first time the dielectric properties of such nano-objects, they may be able to uncover important aspects of a virus’s functionality. With their technique, they discriminated between empty and DNA-containing viruses, for example, which are the ones that can insert their genetic material into a host cell’s DNA.
“These results are also a breakthrough in the fundamental study of nanoscale dielectrics, which are the building blocks that determine the performance of the new generation of nano-electronic devices around today,” adds Laura. “Our new technique promises to shed light on questions about the dielectric properties of newly developed nanocomposites and hybrid nanodevices, and can tell us at how small a scale a dielectric object can retain its properties – in other words, how small we can go.”
To read the paper visit the Nature Materials website here.
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Media coverage:
http://www.lswn.it/comunicati/stampa/2012/riconoscimento_nano_oggetti_e_virus_senza_marcatori
http://www.sciencedaily.com/releases/2012/07/120709093046.htm
http://phys.org/news/2012-07-scientists-fingerprint-nanoscale-viruses.html
http://www.teinteresa.es/salud/Investigadores-espanoles-descubren-celulas-empujones_0_733727017.html
