Passive Dielectrophoretic Focusing of Particles and Cells in Ratchet Microchannels

Abstract

Focusing particles into a tight stream is critical for many microfluidic particle-handling devices such as flow cytometers and particle sorters. This work presents a fundamental study of the passive focusing of polystyrene particles in ratchet microchannels via direct current dielectrophoresis (DC DEP). We demonstrate using both experiments and simulation that particles achieve better focusing in a symmetric ratchet microchannel than in an asymmetric one, regardless of the particle movement direction in the latter. The particle focusing ratio, which is defined as the microchannel width over the particle stream width, is found to increase with an increase in particle size or electric field in the symmetric ratchet microchannel. Moreover, it exhibits an almost linear correlation with the number of ratchets, which can be explained by a theoretical formula that is obtained from a scaling analysis. In addition, we have demonstrated a DC dielectrophoretic focusing of yeast cells in the symmetric ratchet microchannel with minimal impact on the cell viability.

Analysis of microorganisms with nonlinear electrokinetic microsystems

“…Mentioned previously, yeast cells provide a great basis for the testing of novel EK techniques, specifically when the extended use may apply to other types of prokaryotic or eukaryotic cells. Recent DEP studies for lab‐on‐a‐chip technology and integrated system designs have the common theme of using yeast as a model organism with great interest in cell response to thermal shock and viability as well as differentiation in ratchet microchannels [32–34]. Many bioanalytical applications require rapid sorting of cells, which can be achieved by focusing the particles of interest into a stream within a microchannel; this is especially useful for developing integrated systems that seek to perform multiple functions within a single device.…”

“…provides more insight into particle focusing specifically in ratchet microchannels. This group utilizes yeast as a test particle to prove that the viability of particles will remain high despite Joule heating‐induced temperature elevation [32]. They tested three ratcheting strategies: symmetric, asymmetric forward, and asymmetric backward as depicted in Fig.…”

“…The top channel, a symmetric ratchet with a forward (to the right) velocity of cells, proves to be the most effective, while the bottom channel, an asymmetric ratchet with a backward (to the left) velocity of cells proves to be the most ineffective. Adapted from [32], open access article under Creative International Public License 4.0 (2020). (C) Scanning electron microscope images of viable and a non‐viable heat‐exposed yeast cells and Illustration of the two‐electrode system employed for the quick assessment of cell viability by Fernando‐Juan et al.…”

Determination of the Empirical Electrokinetic Equilibrium Condition of Microorganisms in Microfluidic Devices

“…Numerous groups have utilized iEK microfluidic techniques for the study and manipulation of DNA [ 23 , 24 , 25 ], proteins [ 26 , 27 , 28 ], viruses [ 9 , 10 , 11 ], bacteria [ 13 , 15 , 19 ], yeast [ 29 , 30 , 31 ], mammalian cells [ 32 , 33 , 34 , 35 ], and even parasites [ 20 ]. All of these studies illustrate the growing interest in the development of iEK microfluidic systems for microorganism analysis.…”

An IB-LBM design of a microfluidics-based cell capture system

“…Compared to passive techniques, active techniques commonly involve higher costs as they require additional devices to produce external fields, and some additional work may be needed in active techniques such as the magnetic labeling of non-magnetic particles. 10 On the contrary, passive techniques are simpler and easy to implement. So they have attracted more attention in the past years, such as the inertial focusing of microparticles, 11 the separation of blood cells via the pinched flow, 12 or the crossflow.…”