Coupled Electrorotation: Two Proximate Microspheres Spin in Registry with an AC Electric Field

Abstract

We report a novel approach to micro‐ and nanoparticle rotation, uniting the fine translational control afforded by optical trapping with the flexibility and simplicity of dipole–field‐induced coupled electrorotation (CER). Fluorescence imaging using a microparticle photopatterning technique was combined with optical trapping to quantify both the senses and speeds of rotation for individual pairs of particles. Laser tweezers allowed controlled positioning of a pair of particles within a dipole field while simultaneously providing an axis about which the particles rotated. The particle–particle interactions inherent in CER offer several distinct advantages compared with electrorotation in multipole fields. Results from several investigations highlight the utility of this approach, including quantification of rotation in spheres as small as 750 nm in diameter, observation of rotation rates as high as 1800 rpm, fabrication of coupled electrorotational ”antigears”, trapping and rotation of sphere dimers, and exploitation of the registry of sphere rotation to probe the dielectric properties of immobile objects.

Review Article—Dielectrophoresis: Status of the theory, technology, and applications

“…Giner et al 56 employed the dipole approximation for heterogeneous ͑shelled͒ particles to model the formation of longitudinal and transverse pearl chains observed in DEP experiments of mixtures of yeast cells and latex particles. The effect of mutual interactions in governing the coupled electrorotation of two dielectric microspheres has been investigated both theoretically and experimentally by Simpson et al 57 The effect that pearl chaining of cells has on the DEP cross-over frequency, and how dipole-dipole interactions influence electrorotation ͑in-cluding the observation of a new precession effect͒, has been studied both theoretically and experimentally. 58 The effect of the perturbing influence of boundaries has not received as much attention as that given to particle-particle interactions.…”

Inducing self-rotation of cells with natural and artificial melanin in a linearly polarized alternating current electric field

“…Electrorotation (ROT), which is another non-invasive ACEK technique for cell manipulation, has been utilized to induce rotations in either a single cell 26,27 or in coupled microspheres. 28,29 This approach typically uses multiple electrodes 26,27,30,31 and requires a phase difference between a) For cell preparation and viability, correspondence should be addressed to: ken-liu@cuhk.edu.hk b)…”

Interaction between cells in dielectrophoresis and electrorotation experiments

“…The effect of mutual interactions on cell electrorotation in rotating fields has not been generally considered. However, the rotation produced by the interaction between two cells in a linearly polarized field was described by Mahaworasilpa et al 17 An interesting technique based on this coupled electrorotation of two dielectric microspheres was investigated both theoretically and experimentally by Simpson et al 18,19 Numerical computations, based on finite element methods ͑FEMs͒ or boundary element methods ͑BEMs͒, enable the modeling of realistic structures and shapes of bioparticles, as well as the interaction effects between them, in all orders of multipole expansion. However, the different size scales involved in the problem ͑nanometers for the membrane thickness and micrometers for the cell diameter͒ lead to inaccurate solutions unless very dense grids and sophisticated adaptive meshing techniques are used.…”