查看更多>>摘要：Abstract We describe an improved method for determining the electroosmotic mobility and zeta potential of surfaces based on a current‐monitoring method. This technique eliminates the requirement for measurements of channel dimensions and sample conductivities, leading to a simple high precision measurement. The zeta potential of PDMS is measured for native surfaces and surfaces treated with a nonionic surfactant in low‐conductivity?electrolytes.
查看更多>>摘要：Abstract The boundary effects on DC‐electrokinetic behavior of colloidal cylinder(s) in the vicinity of a conducting wall is investigated through a computational model. The contribution of the hydrodynamic drag, gravity, electrokinetic (i.e., electrophoretic and dielectrophoretic), and colloidal forces (i.e., forces due to the electrical double layer and van der Waals interactions) are incorporated in the model. The contribution of electrokinetic and colloidal forces are included by introducing the resulting forces as an external force acting on the particle(s). The colloidal forces are implemented with the prescribed expressions from the literature, and the electrokinetic force is obtained by integrating the corresponding Maxwell stress tensor over the particles' surfaces. The electrokinetic slip‐velocity together with the thin electrical double layer assumption is applied on the surfaces. The position and velocity of the particles and the resulting electric and flow fields are obtained and the physical insight for the behavior of the colloidal cylinders are discussed in conjunction with the experimental observations in the?literature.
查看更多>>摘要：Abstract Microfluidic cell enrichment by dielectrophoresis, based on biophysical and electrophysiology phenotypes, requires that cells be resuspended from their physiological media into a lower conductivity buffer for enhancing force fields and enabling the dielectric contrast needed for separation. To ensure that sensitive cells are not subject to centrifugation for resuspension and spend minimal time outside of their culture media, we present an on‐chip microfluidic strategy for swapping cells into media tailored for dielectrophoresis. This strategy transfers cells from physiological media into a 100‐fold lower conductivity media by using tangential flows of low media conductivity at 200‐fold higher flow rate versus sample flow to promote ion diffusion over the length of a straight channel architecture that maintains laminarity of the flow‐focused sample and minimizes cell dispersion across streamlines. Serpentine channels are used downstream from the flow‐focusing region to modulate hydrodynamic resistance of the central sample outlet versus flanking outlets that remove excess buffer, so that cell streamlines are collected in the exchanged buffer with minimal dilution in cell numbers and at flow rates that support dielectrophoresis. We envision integration of this on‐chip sample preparation platform prior to or post‐dielectrophoresis, in‐line with on‐chip monitoring of the outlet sample for metrics of media conductivity, cell velocity, cell viability, cell position, and collected cell numbers, so that the cell flow rate and streamlines can be tailored for enabling dielectrophoretic separations from heterogeneous samples.
查看更多>>摘要：Abstract Heterogeneity in organelle size has been associated with devastating human maladies such as neurodegenerative diseases or cancer. Therefore, assessing the size‐based subpopulation of organelles is imperative to understand the biomolecular foundations of these diseases. Here, we demonstrated a ratchet migration mechanism using insulator‐based dielectrophoresis in conjunction with a continuous flow component that allows the size‐based separation of submicrometer particles. The ratchet mechanism was realized in a microfluidic device exhibiting an array of insulating posts, tailoring electrokinetic and dielectrophoretic transport. A numerical model was developed to elucidate the particle migration and the size‐based separation in various conditions. Experimentally, the size‐based separation of a mixture of polystyrene beads (0.28 and 0.87 μ$\umu $m) was accomplished demonstrating good agreement with the numerical model. Furthermore, the size‐based separation of mitochondria was investigated using a mitochondria mixture isolated from HepG2 cells and HepG2 cells carrying the gene Mfn‐1 knocked out, indicating distinct size‐related migration behavior. With the presented continuous flow separation device, larger amounts of fractionated organelles can be collected in the future allowing access to the biomolecular signature of mitochondria subpopulations differing in size.
查看更多>>摘要：Abstract The ability to transport and store a large human blood inventory for transfusions is an essential requirement for medical institutions. Thus, there is an important need for rapid and low‐cost characterization tools for analyzing the properties of human red blood cells (RBCs) while in storage. In this study, we investigate the ability to use dielectrophoresis (DEP) for measuring the storage‐induced changes in RBC electrical properties. Fresh human blood was collected, suspended in K2‐EDTA anticoagulant, and stored in a blood bank refrigerator for a period of 20 days. Cells were removed from storage at 5‐day intervals and subjected to a glutaraldehyde crosslinking reaction to “freeze” cells at their ionic equilibrium at that point in time and prevent ion leakage during DEP analysis. The DEP behavior of RBCs was analyzed in a high permittivity DEP buffer using a three‐dimensional DEP chip (3DEP) and also compared to measurements taken with a 2D quadrupole electrode array. The DEP analysis confirms that RBC electrical property changes occur during storage and are only discernable with the use of the cell crosslinking reaction above a glutaraldehyde fixation concentration of 1.0?w/v%. In particular, cytoplasm conductivity was observed to decrease by more than 75% while the RBC membrane conductance was observed to increase by more than 1000% over a period of 20 days. These results show that the presented combination of chemical crosslinking and DEP can be used as rapid characterization tool for monitoring electrical properties changes of human RBCs while subjected to refrigeration in blood bank storage.
Sandra StankeChristian WengerFrank F. BierRalph H?lzel...
13页
查看更多>>摘要：Abstract The use of alternating current (AC) electrokinetic forces, like dielectrophoresis and AC electroosmosis, as a simple and fast method to immobilize sub‐micrometer objects onto nanoelectrode arrays is presented. Due to its medical relevance, the influenza virus is chosen as a model organism. One of the outstanding features is that the immobilization of viral material to the electrodes can be achieved permanently, allowing subsequent handling independently from the electrical setup. Thus, by using merely electric fields, we demonstrate that the need of prior chemical surface modification could become obsolete. The accumulation of viral material over time is observed by fluorescence microscopy. The influences of side effects like electrothermal fluid flow, causing a fluid motion above the electrodes and causing an intensity gradient within the electrode array, are discussed. Due to the improved resolution by combining fluorescence microscopy with deconvolution, it is shown that the viral material is mainly drawn to the electrode edge and to a lesser extent to the electrode surface. Finally, areas of application for this functionalization technique are presented.
Sanaz HabibiHwi Yong LeeHector Moncada‐HernandezAdrienne R. Minerick...
15页
查看更多>>摘要：Abstract The ability to strategically induce or suppress cell lysis is critical for many cellular‐level diagnostic and therapeutic applications conducted within electrokinetic microfluidic platforms. The chemical and structural integrity of sub‐cellular components is important when inducing cell lysis. However, metal electrodes and electrolytes participate in undesirable electrochemical reactions that alter solution composition and potentially damage protein, RNA, and DNA integrity within device microenvironments. For many biomedical applications, cell viability must be maintained even when device‐imposed cell‐stressing stimuli (e.g., electrochemical reaction byproducts) are present. In this work, we explored a novel and tunable method to accurately induce or suppress device‐imposed artifacts on human red blood cell (RBC) lysis in non‐uniform AC electric fields. For precise tunability, a dielectric hafnium oxide (HfO2) layer was used to prevent electron transfer between the electrodes and the electric double layer and thus reduce harmful electrochemical reactions. Additionally, a low concentration of Triton X‐100 surfactant was explored as a tool to stabilize cell membrane integrity. The extent of hemolysis was studied as a function of time, electrode configuration (T‐shaped and star‐shaped), cell position, applied non‐uniform AC electric field, with uncoated and HfO2 coated electrodes (50?nm), and absence and presence of Triton X‐100 (70?μM). Tangible outcomes include a parametric analysis relying upon literature and this work to design, tune, and operate electrokinetic microdevices to intentionally induce or suppress cellular lysis without altering intracellular components. Implications are that devices can be engineered to leverage or minimize device‐imposed biological artefacts extending the versatility and utility of electrokinetic diagnostics.
NSTL
Wiley