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A 'glass-blower' working at the nano scale

25 March 2013

Researchers are using the electrical properties of a scanning electron microscope to reduce the diameter of glass capillary tubes down to nano-scale levels.

Lorenz Steinbock uses an electron microsocope at EPFL's Centre for MicroNanotechnology to control the shrinking of a glass capillary (photo: Alain Herzog/EPFL)

If you have ever thrown an empty crisp packet into the fire, you will be aware of a striking outcome: the plastic shrivels and bends into itself, until it turns into a small crumpled and blackened ball.

This phenomenon is explained by the tendency of materials to pick up their original features in the presence of the right stimulus. Hence, this usually happens when heating materials that were originally shaped at high temperatures and cooled afterwards.

Researchers at the Ecole Polytechnique Fédérale de Lausanne (EPFL) realised that this phenomenon occurred with ultrathin quartz tubes (capillary tubes) under the beam of a scanning electron microscope.

"This is not the original microscope's purpose," explains Lorentz Steinbock, a researcher at the Laboratory of Nanoscale Biology and co-author of a paper on this subject published in the journal, Nano-letters. "The temperature increase is explained by an accumulation of electrons in the glass. Electrons accumulate because glass is a non-conductive material." .

As the glass shrinks, it can be seen live on the microscope screen. "It's like a glass-blower. Thanks to the possibilities provided by the new microscope at EPFL's Centre of Micronanotechnology (MIC), the operator can adjust the microscope's voltage and electric field strength while observing the tube's reaction.

"Thus, the person operating the microscope can very precisely control the shape he wants to give to the glass", says Aleksandra Radenovic, an assistant professor in charge of the laboratory.

At the end of this process, the capillary tube's ends are perfectly controllable in diameter, ranging from 200 nanometers to fully closed. The scientists tested their slimmed down tubes in an experiment aiming to detect DNA segments in a sample.

The test sample was moved from one container to another on a microfluidic chip. Whenever a molecule crossed the 'channel' connecting the containers, the variation of the ion current was measured. As expected, the EPFL team obtained more accurate results with a tube reduced to the size of 11nm than with standard market models.

"By using a capillary tube costing only a few cents, in five minutes we are able to make a device that can replace "nano-channels" sold for hundreds of dollars!" explains Aleksandra Radenovic.

These nano-fillers have a potential beyond laboratory usage. "We can imagine industrial applications in ultra-high precision printers, as well as opportunities in surgery, where micro-pipettes of this type could be used at a cell's scale", says the researcher.
 
For the time being, the method for manufacturing nano-capillary tubes is manual, the transition to an industrial scale will take some time. However, the researchers have been able to demonstrate the concept behind their discovery and have registered a patent.


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