Appendix C
Paper published in Lab on a Chip,
May 2014
Focusing of sub-micrometer particles and bacteria enabled by
two-dimensional acoustophoresis
M. Antfolk, P. B. Muller, P. Augustsson, H. Bruus and T. Laurell
Abstract: Handling of sub-micrometer bioparticles such as bacteria are becoming increasingly
important in the biomedical eld and in environmental and food analysis. As
a result, there is an increased need for less labor-intensive and time-consuming handling
methods. Here, an acoustophoresis-based microuidic chip that uses ultrasound
to focus sub-micrometer particles and bacteria, is presented. The ability to focus submicrometer
bioparticles in a standing one-dimensional acoustic wave is generally limited
by the acoustic-streaming-induced drag force, which becomes increasingly signicant the
smaller the parti- cles are. By using two-dimensional acoustic focusing, i.e. focusing of
the sub-micrometer particles both horizontally and vertically in the cross section of a microchannel,
the acoustic streaming velocity eld can be altered to allow focusing. Here,
the focusability of E. coli and polystyrene particles as small as 0.5 m in diameter in microchannels
of square or rectangular cross sections, is demonstrated. Numerical analysis
was used to determine generic transverse particle trajectories in the channels, which revealed
spiral-shaped trajectories of the sub-micrometer particles towards the center of the
microchannel; this was also conrmed by experimental observations. The ability to focus
and enrich bacteria and other sub-micrometer bioparticles using acoustophoresis opens the
research eld to new microbiological applications.
http://dx.doi.org/10.1039/c4lc00202d
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