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Posted: Jan 15, 2014
Microscopic fountain pen adds new functionality to AFM microscopy
(Nanowerk News) An AFM’s cantilever has a fine tip that can be used to map surfaces at the nanoscale.
The movements of the tip are monitored using laser light reflected from the
cantilever. If you could manufacture a hollow cantilever and pass a liquid
through it, as happens in a fountain pen, then you could kill two birds with
one stone. In addition to mapping surfaces, you could also use it to make
highly localized measurements of the concentration of specific chemicals. This
concept was the brainchild of Dr Peter Schön, a researcher
who leads the “Enabling Technologies” Strategic Research Orientation at MESA+
The hollow cantilever of an AFM (tip is not shown now) is filled with mercury. The drop at the end is a chemical sensor.
The liquid selected was mercury, as it has the ideal properties for this purpose, such as
an extremely clean surface. The researchers have created a cantilever with a
microscopic tube running through it. The tube’s lining has special mechanical
properties, to contain the mercury as it is pumped through under high pressure
(6 bar). Using this system, it has proved possible to create a perfect droplet
at the tip. The droplet itself is the sensor, moreover it can easily be
replaced in situ by a new sensor - the next droplet. It is also
important that electrical current is only conducted through the mercury in the
microscopic tube and not via parts of the cantilever, so as not to affect the
measurement result. This goal, too, was successfully achieved.
A sensor of such exquisite sensitivity can be used to measure concentrations of specific
chemicals on biomolecules and biomembranes, for example. It can also be used in
combination with AFM, to make highly localized measurements of corrosion while
at the same time gathering other information about the surface in question.
This makes for a particularly powerful combination of measurement methods.
Details of the “fountain pen’s” mechanism of action were recently published in “Analytical
Chemistry”. The researchers are now focusing on ways of combining this
technique with an AFM tip. They are also developing a technique for efficiently
releasing the used mercury droplet to make way for a “clean” sensor.
In the course of this study Dr Schön cooperated with micromechanics experts from the
Transducers Science and Technology group (which is also part of MESA+) and with
a spinoff company, SmartTip (www.smarttip.nl)
Source: University of Twente
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