A team of New York University researchers has created a new way to visualize crystals by peering inside their structures, akin to having X-ray vision. Their new technique—which they aptly named “Crystal Clear”—combines the use of transparent particles and microscopes with lasers that allow scientists to see each unit that makes up the crystal and to create dynamic three-dimensional models.
“This is a powerful platform for studying crystals,” says Stefano Sacanna, professor of chemistry at NYU and the principal investigator for the study, published in the journal Nature Materials. “Previously, if you looked at a colloidal crystal through a microscope, you could only get a sense of its shape and structure of the surface. But we can now see inside and know the position of every unit in the structure.”
Atomic crystals are solid materials whose building blocks are positioned in a repeating, orderly fashion. Every now and then, an atom is missing or out of place, resulting in a defect. The arrangement of atoms and defects is what creates different crystalline materials—from table salt to diamonds—and gives them their properties.
To study crystals, many scientists, including Sacanna, look to crystals composed of miniscule spheres called colloidal particles rather than atoms. Colloidal particles are tiny—often around a micrometer in diameter, or dozens of times smaller than a human hair—but are much larger than atoms and therefore easier to see under a microscope.
A see-through structure
In their ongoing work to understand how colloidal crystals form, the researchers recognized the need to see inside these structures. Led by Shihao Zang, a PhD student in Sacanna’s lab and the study’s first author, the team set out to create a method to visualize the building blocks inside a crystal. They first developed colloidal particles that were transparent and added dye molecules to label them, making each particle possible to distinguish under a microscope using their fluorescence.
A microscope alone wouldn’t allow the researchers to see inside a crystal, so they turned to an imaging technique called confocal microscopy, which uses a laser beam that scans through material to produce targeted fluorescence from the dye molecules. This reveals each two-dimensional plane of a crystal, which can be stacked on top of each other to build a three-dimensional digital model and identify the location of each particle. The models can be rotated, sliced, and taken apart to look inside the crystals and see any defects.
