One of the best tools to "see" things at nano and atomic scales is the atomic force microscope (AFM). This device uses a tipped probe to scan surfaces and produce a 3D image of an object. The probe—sometimes comprised of one atom—is attached to a cantilever. As the cantilever moves to scan the surface, the tip of the probe is monitored by a laser that reflects each movement. The reflection of the laser light is recorded by a computer to produce a map of the surface of the object.
Researchers at the MESA+ Institute of Nanotechnology of the University of Twente in the Netherlands have added a new and interesting feature to the AFM; they created a hollow cantilever though which mercury is passed.
The mercury drops, forced from the cantilever by pressure, can be used as a type of sensor. With this style of cantilever, not only can the AFM be used to scan surfaces, but also for other applications, such as to accurately measure the concentration of certain chemicals on biomolecules or biomembanes.
The researchers, led by Dr. Peter Schön, who directs the "enabling technologies" research center at MESA, selected mercury as the pumping liquid. The cantilever has a microscopic tube running through it and, to create a perfect droplet, the researchers lined the interior of the tube with materials that have special mechanical properties to contain the mercury as it is pumped at a pressure of 6 bar. The droplet (as seen in the figure) is the sensor itself. As drops are being pumped, the next droplet constitutes another sensor that replaces in situ the previous sensor.
The results of this research on the microscopic "fountain pen" were published in Analytical Chemistry on Jan. 15.
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