Fine-Tuning Electrokinetic Injections Considering Nonlinear Electrokinetic Effects in Insulator-Based Devices

Abstract

The manner of sample injection is critical in microscale electrokinetic (EK) separations, as the resolution of a separation greatly depends on sample quality and how the sample is introduced into the system. There is a significant wealth of knowledge on the development of EK injection methodologies that range from simple and straightforward approaches to sophisticated schemes. The present study focused on the development of optimized EK sample injection schemes for direct current insulator-based EK (DC-iEK) systems. These are microchannels that contain arrays of insulating structures; the presence of these structures creates a nonuniform electric field distribution when a potential is applied, resulting in enhanced nonlinear EK effects. Recently, it was reported that the nonlinear EK effect of electrophoresis of the second kind plays a major role in particle migration in DC-iEK systems. This study presents a methodology for designing EK sample injection schemes that consider the nonlinear EK effects exerted on the particles being injected. Mathematical modeling with COMSOL Multiphysics was employed to identify proper voltages to be used during the EK injection process. Then, a T-microchannel with insulating posts was employed to experimentally perform EK injection and separate a sample containing two types of similar polystyrene particles. The quality of the EK injections was assessed by comparing the resolution (Rs) and number of plates (N) of the experimental particle separations. The findings of this study establish the importance of considering nonlinear EK effects when planning for successful EK injection schemes.

High-Resolution Charge-Based Electrokinetic Separation of Almost Identical Microparticles

“…After 10 μL of the microparticle suspensions was introduced into reservoir A (Figure a), platinum wire electrodes were placed into the four reservoirs. For EK sample injection, three distinct sets of voltages were applied (Table ) to follow the steps: loading, gating, and injection. , With an EK injection process, there is uneven particle distribution at the intersection of the T-device, which allows the red particles, which have the higher μ EK , to migrate further . The run time refers to the duration of each voltage step; the duration of the injection step was determined by the time required for the particles to elute from the post array.…”

“…However, similar reliable techniques are not available for separating micron-sized particles, including intact microorganisms . Microfluidic devices are robust platforms for the rapid analysis of a wide range of particles, from macromolecules to parasites. − An important microfluidics subfield is electrokinetics (EK), which refers to the manipulation of particles and fluid with electric fields. Electrokinetics allows combining several EK phenomena within the same system, providing ample options when designing separation processes for bioparticles, such as cells, cell organelles, and exosomes .…”

Separation of Cells and Microparticles in Insulator-Based Electrokinetic Systems

“…The same method was used to discriminate between the strains of pathogenic Streptococcus mitis and Pseudomonas aeruginosa . The Lapizco-Encinas research group has published several studies on the EK separations of microparticles and cells in an array of iEK systems. ,− A recent study illustrated that carefully selected operating conditions and accurate mathematical modeling allow for the successful separation of almost identical microparticles with a slight difference in electrical charge of only 3.6 mV . Several studies by this group have targeted the separation and trapping of mixtures of cells.…”

Concepts and recent advances in microchip electrophoresis coupled to mass spectrometry: Technologies and applications

“…To form the sample plug, the applied voltage at the buffer inlet is turned off for a short time interval (typically between 1 and 5 s), allowing the diffusion of the sample into the separation channel (Figure 2C). In this methodology, the sample volume is defined by the diffusion time and the magnitude of the applied electric field [33].…”