All done with mirrors: Microscope tracks nanoparticles in 3-D

A clever new microscope design allows nanotechnology researchers at the National Institute of Standards and Technology (NIST) to track the motions of nanoparticles in solution as they dart around in three dimensions. The researchers hope the technology, which NIST plans to patent, will lead to a better understanding of the dynamics of nanoparticles in fluids and, ultimately, process control techniques to optimize the assembly of nanotech devices.

While some nanoscale fabrication techniques borrow from the lithography and solid state methods of the microelectronics industry, an equally promising approach relies on “directed self-assembly.” This capitalizes on physical properties and chemical affinities of nanoparticles in solutions to induce them to gather and arrange themselves in desired structures at desired locations.

Potential products include extraordinarily sensitive chemical and biological sensor arrays, and new medical and diagnostic materials based on “quantum dots” and other nanoscale materials. But when your product is too small to be seen, monitoring the assembly process is difficult.

Microscopes can help, but a microscope sees a three-dimensional fluid volume as a 2-D plane. There’s no real sense of the “up and down” movement of particles in its field of view except that they get more or less fuzzy as they move across the plane where the instrument is in focus. To date, attempts to provide a 3-D view of the movements of nanoparticles in solution largely have relied on that fuzziness. Optics theory and mathematics can estimate how far a particle is above or below the focal plane based on diffraction patterns in the fuzziness. The math, however, is extremely difficult and time consuming and the algorithms are imprecise in practice.

One alternative, NIST researchers reported at the annual meeting of the American Physical Society,* is to use geometry instead of algebra. Specifically, angled side walls of the microscopic sample well act as mirrors to reflect side views of the volume up to the microscope at the same time as the top view. (The typical sample well is 20 microns square and 15 microns deep.) The microscope sees each particle twice, one image in the horizontal plane and one in the vertical. Because the two planes have one dimension in common, it’s a simple calculation to correlate the two and figure out each particle’s 3-D path. “Basically, we reduce the problem of tracking in 3-D to the problem of tracking in 2-D twice,” explains lead author Matthew McMahon.

The 2-D problem is simpler to solve—several software techniques can calculate and track 2-D position to better than 10 nanometers. Measuring the nanoparticle motion at that fine scale—speeds, diffusion and the like—will allow researchers to calculate the forces acting on the particles and better understand the basic rules of interaction between the various components. That in turn will allow better design and control of nanoparticle assembly processes.

Ref: M. McMahon, A. Berglund, P. Carmichael, J. McClelland and J.A. Liddle. Orthogonal tracking microscopy for nanofabrication research. Paper presented on Monday, March 10, 2008, at the 2008 March Meeting of the American Physical Society, New Orleans, La., March 10-14, 2008.

Source: National Institute of Standards and Technology

Related stories:

Debut of TEAM 0.5, the World's Best Microscope
TEAM 0.5, the world's most powerful transmission electron microscope — capable of producing images with half‑angstrom resolution (half a ten-billionth of a meter), less than the diameter of a single hydrogen atom — has been installed at the Department of Energy's National Center for Electron Microscopy (NCEM) at Lawrence Berkeley National Laboratory.
Laser surgery probe targets individual cancer cells
Mechanical engineering Assistant Professor Adela Ben-Yakar at The University of Texas at Austin has developed a laser "microscalpel" that destroys a single cell while leaving nearby cells intact, which could improve the precision of surgeries for cancer, epilepsy and other diseases.
New ORNL process brings nanoparticles into focus
Scientists can study the biological impacts of engineered nanomaterials on cells within the body with greater resolution than ever because of a procedure developed by researchers at the Department of Energy's Oak Ridge National Laboratory.

Northwestern chemist investigates lost reds in Homer painting
More than 30 years ago, when Northwestern University chemist Richard Van Duyne developed a powerful new sensing technique, he never thought he would be using it to learn more about treasures in the Art Institute of Chicago's collection -- including a watercolor recently featured in the museum's exhibition "Watercolors by Winslow Homer: The Color of Light."
Argonne research unveiling the secrets of nanoparticle haloing
A glass of milk, a gallon of paint, and a bottle of salad dressing all look to the naked eye like liquids. But when viewed under a microscope these everyday liquids, called "colloids," actually contain small globules or particles that stay suspended in solution.
Are nanobots on their way?
[The first real steps towards building a microscopic device that can construct nano machines have been taken by US researchers. Writing in the peer-reviewed publication, International Journal of Nanomanufacturing from Inderscience Publishers, researchers describe an early prototype for a nanoassembler.
Nanobacteria – Are They Alive?
Tiny particles called nanobacteria have intrigued researchers in many ways since their discovery 20 years ago, but perhaps the most controversial question they pose is whether or not they are alive.
Nanoparticles Provide Detailed View Inside Living Animals
Using nanoparticles designed specifically to produce a bright Raman spectroscopic signal, a team of investigators at the Center for Cancer Nanotechnology Excellence Focused on Therapy Response (Stanford CCNE) has shown that it can produce whole-body images in small animals that can reveal the location of tumors and track how these nanoparticles traffic through the body.

News discussion:

Nanotechnology news