Nový mikroskop pro nanočástice se zobrazením v 3 D

One promising nanoscale fabrication technique relies on directed self-assembly -- the inducement of nanoparticles in solution to gather and arrange themselves in desired structures at desired locations. Potential products that could utilize this method include extraordinarily sensitive chemical and biological sensor arrays, and new medical and diagnostic materials based on quantum dots; however, when your product is too small to be seen, monitoring the assembly process is difficult.

While microscopes can help, they see a 3-D 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. 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.

Researchers at NIST recently developed a new microscope design to track the motions of nanoparticles in solution as they dart around in 3-D by using geometry instead of algebra. Specifically, angled sidewalls 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 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.

The 2-D problem proved simpler to solve -- several software techniques can calculate and track 2-D position to better than 10 nm. Measuring the nanoparticle motion at that fine scale 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.