Nanoscale, Lego by Lego
JOHNS HOPKINS (US)—Forget the giant robots and blocky spaceships. A team of engineers is snapping together Legos to visualize life at the nanoscale.
The team at Johns Hopkins University is hoping to explain the behavior of particles, cells, and molecules in environments far too small to see with the naked eye, essentially recreating microscopic activity at a scale that they can more easily observe.
The aim is to better characterize what goes on inside tiny lab-on-a-chip devices, known as microfluidic arrays, which are commonly used to sort tiny things by size, shape, or composition. The engineers’ eventual goal is to improve the design and fabrication of lab-on-a-chip technology.
The minuscule forces at work at such a small magnitude—such as the nanoscale level—are difficult to measure. To solve their small problem, the Johns Hopkins engineers decided to think big.
Led by Joelle Frechette and German Drazer, assistant professors of chemical and biomolecular engineering, the team worked not with expensive high-tech equipment, but rather with beads a few millimeters in diameter, an aquarium filled with goopy glycerol and Lego pegs arranged on a Lego board.
The idea comes from the concept of “dimensional analysis,” in which a process is studied at a different size and time scale while keeping the governing principles the same.
“Microfluidic arrays are like miniature chemical plants,” Frechette says. “One of the key components of these devices is the ability to separate one type of constituent from another. We investigated a microfluidic separation method that we suspected would remain the same when you scale it up from micrometers or nanometers to something as large as the size of billiard balls.”
Frechette and Drazer constructed an array using cylindrical Lego pegs stacked two high and arranged in rows and columns on a Lego board to create a lattice of obstacles. The board was attached to a Plexiglas sheet to improve its stiffness and pressed up against one wall of a Plexiglas aquarium tank filled with glycerol. Stainless steel beads of three different sizes, as well as plastic ones, were manually released from the top of the array; their paths to the bottom were tracked and timed with a camera.
The entire setup, Drazer says, cost a few hundred dollars and could easily be replicated as a science fair experiment.
Team members performed multiple trials using each type of bead. They progressively rotated the board, increasing the relative angle between gravity and the columns of the array (that is, altering the forcing angle).
“There are forces present between a particle and an obstacle when they get really close to each other which are present whether the system is at the micro- or nanoscale or as large as the Lego board,” Frechette says. “In this separation method, the periodic arrangement of the obstacles allows the small effect of these forces to accumulate, and amplify, which we suspect is the mechanism for particle separation.”
This principle could be applied to the design of micro- or nanofluidic arrays, she adds, so that they could be fabricated to “sort particles that had a different roughness, different charge or different size. They should follow a different path in an array and could be collected separately.”
The research was funded by grants from the National Science Foundation and the American Chemical Society Petroleum Research Fund. Their study on this technique was published in the Aug. 14 issue of Physical Review Letters.
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