Nano Lett. http://dx.doi.org/10.1021/nl2022042 (2011)

Resolving the minutiae of the fibres driving cell migration is no easy task — particularly when it involves keeping the cells alive. Even the best attempts at nanoscale resolution of the three-dimensional structure of intracellular filaments have fallen short of the task of in vivo measurement in real time. Laura Estrada and Enrico Gratton have met this challenge by demonstrating that their technique, dubbed gold enhancement nanoimaging, enables highly reproducible imaging of filaments inside a living Chinese-hamster ovary cell.

The method involves decorating each filament with gold nanoparticles that adsorb to the surface of the fibre. Irradiation of the particles with near-infrared femtosecond pulses induces a photoacoustic effect, which incites a rapid expansion of the surrounding medium, producing a pressure wave, which propels the nanoparticles along the fibre. By simultaneously tracking the nanoparticles, Estrada and Gratton obtained a clear map of filaments inside the cells. The beauty of the approach lies with the simple fact that as the nanoparticles are electrostatically attached to the fibre, propulsion can only occur along the fibre — guaranteeing that the trajectory faithfully maps the surface of the filament.