Orthogonal Microscope Tracks Nanoparticles in Solution in 3D

A new microscope allows scientists to track the motions of nanoparticles in solution as they move in three dimensions (3D). The technology 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.

Some nanoscale fabrication techniques use the lithography and solid state methods of the microelectronics industry. An alternative 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 new medical and diagnostic materials, extraordinarily sensitive chemical and biologic sensor arrays, and other nanoscale materials.

U.S. National Institute of Standards and Technology (NIST; Gaithersburg, MD, USA) scientists created an orthogonal microscope where angled side walls of the microscopic sample well act as mirrors and reflect side views of the volume up to the microscope at the same time as the top view. 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, a simple calculation correlates the two and figures out each particle's 3D path. "Basically, we reduce the problem of tracking in 3D to the problem of tracking in 2D twice, explained Matthew McMahon of the NIST.

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

The new microscope design and function was presented at the Meeting of the American Physical Society (New Orleans, LA. USA), March 10-14, 2008.


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National Institute of Standards and Technology