Researchers at DESY’s Center for Free-Electron Laser Science, along with colleagues from around the world, recently showed that laser-induced alignment can be accomplished to significantly improve molecular imaging methods, according to a study published in the Journal of the American Chemical Society.
An optical laser can be used to align complex biomolecules for single-molecule imaging. Image Credit: DESY-CFEL–CMI, Muhamed Amin
Researchers can reconstruct the structure of nanoparticles and biomolecules using single-particle diffractive imaging (SPI) with X-ray free-electron lasers. However, the technique frequently calls for imaging up to several billion nanoparticles to produce the image, and its sharpness and clarity are limited.
The geometric confinement of the molecules in the X-ray imaging experiment will substantially aid in recovering the molecular orientation and, hence, structure retrieval. This thereby solves a significant problem in single-particle diffractive imaging. This unique development paves the path for SPI-based solutions to three-dimensional protein and macromolecule structures.
Laser-induced alignment uses the interplay between a laser pulse’s electric field and the molecule's anisotropic polarizability. The molecule follows the laser pulse's electric field after the pulse causes a brief electric dipole moment in it.
The molecules spin into an orientation where the polarizability interaction is optimum to align the molecule’s most polarizable axis with the laser polarization. This fixes the molecules in space by causing them to align geometrically.
In the current study, the researchers computationally demonstrated that nanoparticles and proteins can be strongly aligned utilizing conventional laser technology. After analyzing 150,000 proteins from the worldwide protein databank (PDB), they discovered that most proteins could be aligned under realistic experimental settings. This improves their visibility during single-particle diffraction tests.
The findings address a long-standing issue in single-particle imaging: molecules are often caught in random orientations, making 3D reconstruction difficult. The researchers also predict that cooling the molecules to cryogenic temperatures, which the group is currently implementing, improves the degree of alignment and reduces potential radiation damage, further refining the technique.
This innovation has far-reaching implications for structural biology and nanotechnology, allowing scientists to view molecular structures in unprecedented detail. It could also change drug development, biomolecular research, and materials science. Future investigations will combine these laser techniques with XFEL imaging to attain sub-nanometer resolution, bringing researchers closer to real-time viewing of molecular dynamics.
Journal Reference:
Amin, M. et al. (2025) Laser-Induced Alignment of Nanoparticles and Macromolecules for Coherent-Diffractive-Imaging Applications. Journal of the American Chemical Society. doi.org/10.1021/jacs.4c15679