The riblike structures seen here depict atomic planes in two nonidentical platinum particles (2 nm in diameter), which were imaged while they drifted and rotated freely in solution.
Fidgety kids and skittish birds don’t sit still long enough to have their pictures taken. Neither do nanoparticles floating and rotating around in solution. But that hasn’t stopped a team of researchers from producing three-dimensional images of angstrom-sized metal particles in solution at near-atomic resolution (Science 2015, DOI: 10.1126/science.aab1343).
The imaging technique used by the researchers, based on transmission electron microscopy (TEM), may enable scientists to monitor dynamics of individual particles within a colloid in their native state. Structural details gleaned from the imaging method may also lead to new uses for nanoparticles in catalysis, biological imaging, and other areas.
TEM generates 2-D projections of 3-D objects. One way microscopists produce 3-D TEM images is by painstakingly piecing together multiple 2-D images of a rigidly supported sample as it is tilted at various angles. Another way is to record images of many identical particles trapped in various orientations in ice. But those methods aren’t suitable for high-resolution imaging of nanoparticles that are freely rotating in solution.
Drawing on a liquid-sampling technique the researchers reported in 2012 , they packaged a few droplets of colloidal platinum nanoparticles in a nanosized graphene bubble. Then they used a microscope equipped with a highly sensitive detector to zoom in on individual particles and record many short-exposure images.
Because the particles were constantly moving, the images were inherently low quality. But by applying a computational technique the researchers developed for this purpose, they were able to produce high-resolution 3-D reconstructions of randomly moving nonidentical particles.
This work is likely to make an impact in biological imaging, catalysis, and other fields, says Joerg R. Jinschek, a TEM specialist for microscope maker FEI who is based in the Netherlands. Jinschek explains that attaching a colloidal particle to a rigid surface—as has been done for imaging purposes in the past—can alter its structure. Because structure and other properties often depend on a particle’s state or environment, researchers want detailed information about nanoparticles in their natural states, Jinschek says. He adds that being able to image freely moving nanoparticles in liquids, as was done in the new study, will help scientists determine relationships between a nanoparticle’s structure and its function.