With the help of a tightly focused laser, researchers at the University of Rochester have figured out a way to assess the axial alignment of individual molecules. Their findings, published in this week's Physical Review Letters, could lead to more efficient solar energy devices and even a better understanding of how proteins in the body fold.
All molecules have an axis along which energy is absorbed and emitted. Because of this, two molecules that are well aligned will exchange energy more easily and react more readily than two that aren't. In order to ascertain whether or not molecules are aligned, however, researchers had to image them with a special kind of laser. Normal light vibrates within a single plane¿two-dimensionally, so to speak. To scan molecules, the team converted normal laser light into radial-polarized light, which radiates vibrations outward in several planes. This beam enabled the researchers to create a tiny, three-dimensional electric field and scan a molecule from all conceivable angles. When the beam aligned with the molecule's axis, the molecule absorbed the beam's energy and emitted a telltale burst of fluorescence.
The discovery could have numerous applications. If in the future scientists can figure out how to manipulate the orientations of molecules, they could, for example, optimize solar panels to absorb the solar energy most efficiently. The technique should also help researchers to better understand certain biochemical processes. "By imaging the dipole movement of certain molecules we can see exactly how certain chemical reactions happen," says Lukas Novotny of the University of Rochester. Indeed, his team's work already indicates that molecular axis alignments can serve as markers to track molecular movements such the folding of proteins. "Cells in the body communicate through proteins located in their membranes," Novotny explains. "During an exchange of information, the shape of the proteins changes. By attaching molecular markers to the protein and monitoring their orientation and position, we should be able to better understand communication between cells."