Hybrid electrokinetics for separation, mixing, and concentration of colloidal particles

Abstract

The advent of nanotechnology has facilitated the preparation of colloidal particles with adjustable sizes and the control of their size-dependent properties. Physical manipulation, such as separation, mixing, and concentration, of these colloidal particles represents an essential step for fully utilizing their potential in a wide spectrum of nanotechnology applications. In this study, we investigate hybrid electrokinetics, the combination of dielectrophoresis and electrohydrodynamics, for active manipulation of colloidal particles ranging from nanometers to micrometers in size. A concentric electrode configuration, which is optimized for generating electrohydrodynamic flow, has been designed to elucidate the effectiveness of hybrid electrokinetics and define the operating regimes for different microfluidic operations. The results indicate that the relative importance of electrohydrodynamics increases with decreasing particle size as predicted by a scaling analysis and that electrohydrodynamics is pivotal for manipulating nanoscale particles. Using the concentric electrodes, we demonstrate separation, mixing, and concentration of colloidal particles by adjusting the relative strengths of different electrokinetic phenomena. The effectiveness of hybrid electrokinetics indicates its potential to serve as a generic technique for active manipulation of colloidal particles in various nanotechnology applications.

System Integration - A Major Step toward Lab on a Chip

“…This is beneficial for developing point-of-care diagnostic systems taking advantage of the recent advancement of portable electronics. Furthermore, multiple electrokinetic phenomena can be combined to perform various microfluidic operations such as mixing, concentration and separation on a single device with low applied AC potential (< 10 V pp ) [146]. These characteristics make electrokinetics a potential technology for developing fully integrated lab-on-a-chip systems.…”

“…Fundamental microfluidic operations such as mixing [146,164,165] (Figure 7a), pumping [166-168], concentration [169,170] (Figure 7b and 7c) and separation [171-174] (Figure 7d and 7e) based on AC electrokinetics can be performed with low AC voltage, which presents an advantage of AC electrokinetics over DC electrokinetics. Another interesting characteristic of electrokinetics is the fact that the magnitude and direction of various electrokinetic forces depend on a number of inter-related parameters including frequency, magnitude and phase of the electric field, and the physical properties of the fluid and particles.…”

“…For example, a hybrid electrokinetic bioprocessor has been developed. In this device, the long-range AC electroosmosis can transport embedded particles in the solution to the regions near the electrode surface and the short-range electrophoretic and dielectrophoretic forces effectively trap the target particles on the electrode surface [146,175]. Furthermore, drug delivery [176], cell separation [177] and temporal and signal enhancement for immunoassays have been facilitated with AC electrokinetics.…”

“…(A) Fluorescence images of electrokinetic-induced mixing (top) and diffusion-based mixing (bottom) at the beginning (left) and after 10 sec (right) [146]. (B) Schematic for particle concentration with hybrid electrokinetics.…”

“…(B) Schematic for particle concentration with hybrid electrokinetics. Long range fluid motion drives particles to regions near the electrode where other local electrokinetic forces trap the particles [146]. (C) Concentration nanoparticles on top of the electrode with hybrid electrokinetics [146].…”