'Artificial noses' come closer to reality
By using nanotechnology- or more specifically "nano-electromechanical systems", or NEMS-scientists have taken a major step towards creating 'artificial noses'.india Updated: Apr 24, 2009 19:12 IST
By using nanotechnology- or more specifically "nano-electromechanical systems", or NEMS-scientists have taken a major step towards creating ''artificial noses''.
In a bid to track down single molecules, nano researchers have developed NEMS, which are actually minute strings that resonate in characteristic fashion.
If a molecule docks onto one of the strings, then it becomes heavier, and its oscillations become measurably slower. But until recently, such methods have not been utilised in many practical applications.
However, physicists at LMU Munich have now made a breakthrough in this field-they have constructed a system of nanostrings made of non-conducting material, where each string can be electrically excited separately.
In this way, thousands of these strings can be produced on a small chip.
"By measuring the period of oscillation, we could therefore detect chemical substances with molecular precision. Ideally, you would have several thousand strings sitting on a chip the size of a fingernail, each one for highly specifically recognizing a single molecule - so you could build an extremely sensitive ''artificial nose'', for example," explained Quirin Unterreithmeier, first author of the study.
And one of the devices that could be created with this system is a highly sensitive "artificial nose" that detects various molecules - pollutants for example - individually.
However, until recently, getting such systems to work has proven technically difficult-one problem being to produce and measure the oscillations.
While the nanostrings can be made to oscillate by magnetomechanical, piezoelectric or electrothermal excitement, this only works if the nanostrings are made of metal, or are at least metal-coated, which in turn greatly dampens the oscillations, preventing sensitive measurement.
Not only does it allow the detection of a single molecule, it also makes it harder to distinguish the different signals from differently oscillating strings.
The newly developed method now avoids these difficulties.
The researchers have constructed an NEMS in which the nanostrings are excited individually by dielectric interaction - the same phenomenon that makes hair stand on end in winter.
Using this physical principle, the nanostrings, which are made of electrically non-conducting silicon nitride, are excited to resonate when exposed to an oscillating inhomogeneous electric field, and their vibration then measured.
The alternating electric field required for this stimulation was produced between two gold electrodes right up close to the string and two other electrodes measured the oscillations.
"We created this setup using etching techniques. But this was easily done - even repeated ten thousand times on a chip. The only thing to do now is to make sure the strings can be individually addressed by a suitable circuit," said a co-author of the study.
Overall, the methods could turn out to be a technically easy exercise - but one that will allow a breakthrough in chemical analysis.