A new technique simultaneously illuminates the location, orientation and rotation in 3D of individual gold nanorods. Gold nanorods have been used as orientation probes in optical imaging because of their shape-induced anisotropic optical properties and now we can do this even better. Gold nanorods have the benefits of being biocompatible and having optical properties that depend on their orientation. This new development provides full 360° rotational information about these nanorods without sacrificing spatial and time resolution. Previous techniques for tracking nanoprobes in the focal plane could only distinguish from 0 to 90°, so clockwise and counterclockwise movements looked the same. Researchers combined a technique known as differential interference contrast microscopy with image pattern recognition to achieve this breakthrough. Assessing the baseline patterns for each rotational angle involved using static, titled nanorods and a 360° rotating stage. As a first demonstration of the power of the technique, researchers followed functionalized gold nanorods on live cell membranes. Resolving the location, orientation and rotational movements of nanoparticles is important for gaining fundamental information about chemical interactions with nanostructured materials.
Determining Full Three-Dimensional Orientation of Single Anisotropic Nanoparticles by Differential Interference Contrast Microscopy