Nanoscale Magnetic Stir Bars For Tiny Liquid Droplets
Researchers in Singapore have developed nanometer-sized magnetic stir bars for stirring tiny volumes of liquids.
Asian Scientist (Jul. 11, 2013) – Anyone who has ever worked in a laboratory has seen them: magnetic stirrers that rotate magnetic stir bars in liquids to mix them.
Effective stirring is essential in chemical and biological experiments. This is usually achieved with magnetic stirrers and stir bars. However, this does not work in the tiny channels and droplets used in lab-on-a-chip applications and for microliter-scale experiments in the biosciences.
Previously developed micrometer-sized stir bars are too big to remain suspended because they are pulled to the bottom of the vessel by both gravity and magnetic attraction. At the same time, they are too small to completely stir the solution when they are on the bottom. Therefore, a large part of the liquid remains unmixed.
Hence, inexpensive stir bars that are small enough but still able to absorb external magnetic energy and efficiently translate it to stir tiny volumes are thus high on the wish list.
Now, a team at the Nanyang Technological University in Singapore has found a solution to this problem: tiny silicon dioxide coated rods made of lined-up iron oxide nanoparticles.
In their paper published in Angewandte Chemie, the researchers described chains made of 40 nanometer-long iron oxide particles that act as the world’s smallest magnetic stir bars.
These easy-to-make bars are so small that they remain suspended in solution, and addition of a large number of stir bars ensures that all of the liquid is stirred. In the magnetic field of a conventional magnetic stir plate, the individual stir bars move independently, making it possible to thoroughly mix droplets of just a few picoliters.
The team demonstrated the effectiveness of these nano-sized stir bars by stirring picoliter-sized drops of emulsion on a commercial magnetic stirrer.
The article can be found at: Chen et al. (2013) Stirring In Suspension: Nanometer-Sized Magnetic Stir Bars.
Source: Angewandte Chemie.
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