PNAS: Photothermal imaging can detect gold nanoparticles
Researchers have used gold nanoparticles as orientation sensors by combining their plasmonic properties with polarization imaging techniques and tracking them using photothermal imaging, according to an article published online Feb. 1 in Proceedings of the National Academy of Sciences.

Nanoparticles are actively exploited as biological imaging probes and tracking single nanoparticles over long periods would give researchers new information about materials, including living systems that incorporate them, according to Stephan Link, PhD, assistant professor of chemistry at Rice University in Houston.

Link and colleagues demonstrated that the orientation of single gold nanoparticles can be determined from both the transverse and longitudinal surface plasmon resonance by using polarization-sensitive photothermal imaging.

A scanning tunneling microscope can capture images of nanoparticles tagged with fluorescent molecules, but fluorophores can deteriorate in as little as 30 seconds while gold nanorods can be "lit up" at will, said Link.

Photothermal imaging can detect nanoparticles as small as five nanometers, which makes them useful for biological applications. "These gold nanorods are biocompatible. They are not toxic to cells," said first author Wei-Shun Chang, PhD, postdoctoral fellow at Rice.

"Our work is more geared to the fundamentals," Link added. "Maybe we can optimize the conditions, and then a physician or somebody who's engineering a probe can take it from there.”