A simple method for evaluating the trapping performance of acoustic tweezers.
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ABSTRACT:
SUBMITTER: Li Y
PROVIDER: S-EPMC3598766 | biostudies-other | 2013 Feb
REPOSITORIES: biostudies-other
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Project description:Confinement of living microorganisms and self-propelled particles by an external trap provides a means of analysing the motion and behaviour of active systems. Developing a tweezer with a trapping radius large compared with the swimmers' size and run length has been an experimental challenge, as standard optical traps are too weak. Here we report the novel use of an acoustic tweezer to confine self-propelled particles in two dimensions over distances large compared with the swimmers' run length. We develop a near-harmonic trap to demonstrate the crossover from weak confinement, where the probability density is Boltzmann-like, to strong confinement, where the density is peaked along the perimeter. At high concentrations the swimmers crystallize into a close-packed structure, which subsequently 'explodes' as a travelling wave when the tweezer is turned off. The swimmers' confined motion provides a measurement of the swim pressure, a unique mechanical pressure exerted by self-propelled bodies.
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Project description:Here we report the use of optoelectronic tweezers and dynamic virtual electrodes to address multiwalled carbon nanotubes (MWCNTs) with trap stiffness values of approximately 50 fNmum. Both high-speed translation (>200 mums) of individual-MWCNTs and two-dimensional trapping of MWCNT ensembles are achieved using 100,000 times less optical power density than single beam laser tweezers. Modulating the virtual electrode's intensity enables tuning of the MWCNT ensemble's number density by an order of magnitude on the time scale of seconds promising a broad range of applications in MWCNT science and technology.
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