Optically induced electrokinetic concentration and sorting of colloids

Abstract

We demonstrate an optically induced ac electrokinetic technique that rapidly and continuously accumulates colloids on a parallel-plate electrode surface resulting in a crystalline-like aggregation. Electrothermal hydrodynamics produce a microfluidic vortex that carries suspended particles toward its center where they are trapped by local ac electrokinetic hydrodynamic forces. We characterize the rate of particle aggregation as a function of the applied ac voltage, ac frequency and illumination intensity. Hundreds of polystyrene particles (1.0 μm) suspended in a low conductivity solution (2.4 mS m −1 ) were captured at a range of voltages (5-20 V pp ) and frequencies (20-150 kHz) with an optical power of approximately 20 mW. This technique was not restricted to near infrared (1064 nm) illumination and was also demonstrated at 532 nm. The sorting capability of this technique was demonstrated with a solution containing 0.5 μm, 1.0 μm and 2.0 μm polystyrene particles. This dynamic optically induced technique rapidly concentrates, sorts and translates colloidal aggregates with a simple parallel-plate electrode configuration and can be used for a variety of lab-on-a-chip applications.

Microfluidic Technology for Cell Manipulation

“…Through coupling of the effects, REP can manipulate a large quantity of micro-and nano-sized particles at once at an arbitrary location in a microfluidic chip. The capability has been demonstrated by various experiments (Figure 6) [25,58,[61][62][63]109]. In this section, we introduce the various aspects of REP, including the underlying principle, operating environment, and current challenges.…”

“…Rapid electrokinetic patterning (REP) is a hybrid technique that utilizes simultaneous application of a uniform AC electric field and an optical laser beam for manipulation of a diverse set of particles [26,58,[60][61][62][63]. While the two driving sources provide the electrokinetic effect and the optical effect, the combination of the two produces an additional electrothermal effect.…”

“…Generally, REP is realized in a simple microfluidic chip structure consisting of two parallel plate electrodes, a microchannel, and inlet and outlet reservoirs (Figure 7) [25,58,[61][62][63][64]. In the REP chip, a transparent indium tin oxide (ITO)-coated glass substrate is used to create a pair of electrodes for particle flow visualization, imaging, and laser irradiation.…”

“…Based on this combination, particles are manipulated by separate mechanisms for each of the two driving sources and a new mechanism derived from the interaction of the two driving forces. Rapid electrokinetic patterning (REP) is an example of the hybrid manipulation technique [26,58,[60][61][62][63]. REP is a non-invasive manipulation technique that utilizes the simultaneous application of a uniform alternating current (AC) electric field and an optical laser beam.…”

“…This capability has been demonstrated in various experiments. Williams et al carried out particle manipulation in a variety of forms using REP [61][62][63]. Micro-sized colloids were rapidly trapped and configured into various shapes on an electrode surface by the optical landscapes produced by an Nd:YVO 4 laser under the application of a uniform electric field.…”