Control of Particles in Microelectrode Devices

The impact of the convective fluid motion induced by the electric fields on the dielectrophoretic manipulation of particles is investigated theoretically and experimentally. By means of a simplified model a channel with a periodic array of microelectrodes we show that electroconvective flows induce the formation of traps for particles, providing a dynamical mechanism to control microparticles in such devices. We demonstrate experimentally the theoretically predicted dynamical phenomena.

Figure 1

(a) The arrangement of an interdigitated electrode array. (b) SEM image of the titanium DEP chip with 24 parallel electrodes. (c) Electric field strength, $|E{|}^2$, in a plane $10\mu \mathrm{m}$ above the electrodes.

Figure 2

(a) Plot of the real part of the Clausius-Mossotti function for ${ϵ}_m=80{ϵ}_0$, ${\sigma }_m=0.001\mathrm{S}{\mathrm{m}}^{-1}$, ${ϵ}_p=2.5{ϵ}_0$, and ${\sigma }_p=0.009\mathrm{S}{\mathrm{m}}^{-1}$. (b) Streamlines of the cellular flow used in the model.

Figure 3

(a) Particle trajectories with $n$-DEP for point II in Fig. 4, corresponding to $\omega =5\mathrm{MHz}$, ${\rho }_m/{\rho }_p=0.95$, $\beta =0.15d$, and $a=1.5\mu \mathrm{m}$, with a flow moving from the gap to the electrodes. (b) For point I in Fig. 4, $a=0.75\mu \mathrm{m}$, with the same flow as before. For the same parameters with $p$-DEP in (c) and (d), respectively.

Figure 4

(a)–(e) Image sequence showing the DEP-electro-thermoal-convective trapping of $1\mu \mathrm{m}$ diameter latex beads and the effect of a low frequency disturbance. The potential is $10V_{pk\mathrm{\text{−}}pk}$, the main frequency is 10 KHz, and perturbing frequency is 100 Hz. The focus is at 6 microns above the electrodes. (f) Phase portrait of our model, in arbitrary scales, showing the stable (white circles) and unstable (black circles) fixed points. (g) The bifurcation diagram in the parameter space $(a,{\mathit{u}}_0)$, region I is where trapping occurs. (h) The ratio of particles initially within the trapping zone, escaped after 10 cycles, as a function of the frequency of perturbation, with $ϵ=0.1$.