Silica seed particles improve the efficiency and throughput of nanoparticle acoustic trapping

Silica has rarely been used as a seed particle material in acoustic trapping of nanoparticles. Here we use fluorescent nanoparticles, which are frequently used as a model system, to demonstrate that throughput and nanoparticle trapping efficiency can be improved by using silica seed particles as opposed to traditionally used polystyrene seed particles. The 10 times larger dipole scattering coefficient of silica seed particles compared with polystyrene seed particles in water leads to a higher retention force against fluid flow and thus enables higher throughput. Seed particles retained at an actuation voltage of approximately 10 V p.p. can withstand flow rates up to 2100 ± 200 μl/min for silica and 200 ± 50 μl/min for polystyrene. Furthermore, silica is found to be 40%-2000% more efficient (number of trapped nanoparticles as measured by fluorescent intensity) than polystyrene seed particles in trapping 270-nm polystyrene nanoparticles from suspensions of 1010-1011 particles/ml. Moreover, after enriching nanoparticles into a silica seed particle cluster, the washing flow rate can be increased from 30 μl/min to 200 μl/min (the flow rate at which polystyrene clusters are unstable), halving the total sample processing time without losing the silica seed particle cluster or compromising the nanoparticle trapping efficiency. Thus, material properties (particularly density) of the seed particles are critical to both nanoparticle trapping efficiency and throughput.