Colloidal quantum dots, proteins, viruses, DNA and all other nanoparticles have acoustic vibrations that can act as ‘fingerprints’ to identify their shape, size and mechanical properties, yet high-resolution Raman spectroscopy in this low-energy range has been lacking. Here, we introduce extraordinary acoustic Raman (EAR) spectroscopy, a new technique to measure the Raman-active vibrations of single isolated nanoparticles in the 0.1–10 wavenumber range with ∼0.05 wavenumber resolution. Key to the high resolution is the ability to isolate individual nanoparticles from an ensemble to remove inhomogeneous broadening effects. Also, this approach does not require resonant nanoparticles like other analogous approaches (e.g., those using the pump-probe optical Kerr effect for single nanoparticle studies). This single molecule/nanoparticle sensitivity is achieved by a nanoaperture laser tweezer setup. We show how it can be used to distinguish proteins and measure material anisotropy in nanoparticles. I will also discuss more generally nanoaperture optical tweezers and their applications to sensing and studying protein interactions.
rgordon@uvic.ca