Enhancing optofluidic actuation of micro-objects by tagging with plasmonic nanoparticles

Julien Burgin, Satyabrata Si, Marie-Hélène Delville, and Jean-Pierre Delville

We report experimentally and theoretically on the significant exaltation of optical forces on microparticles when they are partially coated by metallic nanodots and shined with laser light within the surface plasmon resonance. Optical forces on both pure silica particles and silica-gold raspberries are characterized using an optical chromatography setup to measure the variations of the Stokes drag versus laser beam power. Results are compared to the Mie theory prediction for both pure dielectric particles and core-shell ones with a shell described as a continuous dielectric-metal composite of dielectric constant determined from the Maxwell-Garnett approach. The observed quantitative agreement demonstrates that radiation pressure forces are directly related to the metal concentration on the microparticle surface and that metallic nanodots increase the magnitude of optical forces compared to pure dielectric particles of the same overall size, even at very low metal concentration. Behaving as “micro-sized nanoparticles”, the benefit of microparticles coated with metallic nanodots is thus twofold: it significantly enhances optofluidic manipulation and motion at the microscale, and brings nanometric optical, chemical or biological capabilities to the microscale.

DOI