For the first time, researchers can keep multiple nanoparticles in focus while tracking their 3D orientations on a surface with unprecedented angular resolution. The new technique can accurately track anisotropic gold particles that are tilted out of the horizontal plane and has the advantage of not relying on particle interactions with the surface to keep track of them. This technique takes advantage of the optical properties of gold; at certain frequencies of light electrons in the gold are stimulated to collectively oscillate, known as surface plasmon resonance. For gold nanorods the frequency of light needed to induce surface plasmon resonance differs for the long axis of the rod compared to the short axis. This technique takes advantage of this difference. The power of the technique was demonstrated by studying modified gold nanoparticles landing on lipid membrane bilayers. While a significant fraction is "frozen" on the surface, many particles are not. The capability to follow the 3D movements of nanoparticles will greatly enhance our understanding of the way nanoparticles interact with surfaces.
Three-Dimensional High-Resolution Rotational Tracking with Superlocalization Reveals Conformations of Surface-Bound Anisotropic Nanoparticles