Recent investigations into the stability of nanoparticle traps formed in parallel electrode arrays by joint DEP and ACEO have shown that there is trapping both at positive and negative DEP which changes form as the particle size changes [1, 2]. This is an important phenomenon with many applications, such as in sensor devices where one needs to selectively trap and manipulate nanoparticles for detection purposes. What is also important is that the method can operate at very small scales and can be used for mass processing of a sample, in contrast to mechanical methods.
The trapping and manipulation of nanoparticles by joint ACEO and DEP using a convection-diffusion equation model to simulate ensembles of nanoparticles is investigated in this paper. The nanoparticles are suspended in a solution over an array of parallel electrodes and two signals are applied, which might be of different frequency, one to cause the DEP force on the particles and the other to induce the ACEO fluid motion.
The results obtained demonstrate, as also observed in [1] and [2], that there is a critical particle radius for the ACEO "whirls" or circular traps to form, which may be different for positive and negative DEP. It has also been found that the only stable trapping zone at positive DEP is at the electrode edges and that trapping at the centre of the circular ACEO patterns in positive DEP is unstable. Moreover, it has been demonstrated that it is possible to trap particles over the electrodes inside the whirls formed by ACEO during negative DEP [1, 2].
Finally, the concept of nanoparticle trapping by joint DEP and ACEO is extended in this work by demonstrating that it is possible to either selectively trap or place particles of different properties, such as size or dielectric properties, or to fine-tune the position of the particles, by changing the DEP excitation voltage.
[1] I. Tuval, I. Mezic, F. Bottausci, Y. Zhang, N. MacDonald, and O. Piro. Control of particles in microelectrode devices. Phys. Rev. Lett., 95:236002, 2005.
[2] T. Skytte, P. Skafte-Pedersen, and M. Pedersen. Particle manipulation in microfluidics by ac electroosmosis and dielectrophoresis. DTU, January 2006.
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