Target Cell Detection via Microfluidic Magnetic Beads Assay

We present a novel cell detection device based on a magnetic bead cell assay and microfluidic Coulter counting technology. The device can detect specific target cells ratios, as well as cells size distribution and concentrations. The device consists of two identical micro Coulter counters separated by a fluid chamber where an external magnetic field is applied. Target cells conjugated with magnetic beads are retarded by the magnetic field; transit time of a target cell passing through the second counter is longer than that through the first counter. In comparison, a non-target cell transit through two counters with nearly the same time. We demonstrated the transit time delay increased approximately linearly with the increasing target cell concentration. The limit of detection (LOD) of the assay was estimated to be 5.6% in terms of target cell ratio.

Numerical Investigation of the Coulter Principle in a Microfluidic Device

Coulter counters are analytical microfluidic instrument used to measure the size and concentration of biological cells or colloid particles suspended in electrolyte. The underlying working mechanism of Coulter counters is the Coulter principle which relies on the fact that when low-conductive cells pass through an electric field these cells cause disturbances in the measurement (current or voltage). Useful information about these cells can be obtained by analyzing these disturbances if an accurate correlation between the measured disturbances and cell characteristics. In this paper we use computational fluid dynamics method to investigate this correlation. The flow field is described by solving the Navier-Stokes equations, the electric field is represented by a Laplace’s equation in which the conductivity is calculated from the Navier-Stokes equations, and the cell motion is calculated by solving the equations of motion. The accuracy of the code is validated by comparing with analytical solutions. The study is based on a coplanar Coulter counter with three inlets that consist of two sheath flow inlet and one conductive flow inlet. The effects of diffusivity, cell size, sheath flow rate, and cell geometry are discussed in details. The impacts of electrode size, gap between electrodes and electrode location on the measured distribution are also studied.

Synthetic Nanoscale Architectures for Lipoprotein Separation

Current low density lipoprotein (LDL) apheresis procedures are expensive and time consuming. We report here a novel technique to detect and separate nanoparticles using solid state nanopores. Our technique relies on the resistive pulse phenomenon used in coulter counters. We used a 150nm diameter nanopore to detect nanoparticles that closely resembled HDL and LDL in terms of their size and surface charge. Statistical analysis of the translocation data revealed that our setup preferentially allowed the particles resembling HDL to pass thorough while restricting the translocation of the particles that resembled LDL.

Measurement of Budding Yeast Growth Rate With MOSFET-Based Microfluidic Coulter Counters

Many bioassays are performed on an ensemble of cells and assay results depend crucially on the state of cells relative to one another. If the cells in the ensemble are disordered with respect to one variable, then the measurements that depend on that variable are confounded by averaging. One solution to this is to maintain the cell cycle synchrony for the cells in the ensemble. To do this, it is extremely important to accurately measure the cell growth rate. For example, the volume growth rate of budding yeast is closely linked to many aspects of the cell cycle. Therefore, investigation of the volume growth rate of budding yeast has become an appealing research topic because of its important implications in achieving cell cycle synchrony. In this paper, we report on applications of novel microfluidic sensing technique to measure the volume growth rate of individual budding yeast. We apply our recently developed MOSFET-based microfluidic Coulter counters to detect the volume of budding yeast when it is translocated through the sensing aperture forth and back, controlled by adjusting the direction of electroosmotic flow inside the microfluidic device. Our results indicate that because of the enhanced sensitivity of the MOSFET-based microfluidic Coulter counter, it is possible to measure the volume growth rate of individual budding yeast over its whole cell cycle. The measurement results clearly showed the volume growth of the individual budding yeast.

A novel method for measuring dynamic changes in cell volume

Many cell types regulate their volume in response to extracellular tonicity changes through a complex series of adaptive mechanisms. Several methods that are presently used to measure cell volume changes include Coulter counters, fluorescent techniques, electronic impedance, and video microscopy. Although these methods are widely used and accepted, there are limitations associated with each technique. This paper describes a new method to measure changes in cell volume based on the principle that fluid flow within a rigid system is well determined. For this study, cos-7 cells were plated to line the inner lumen of a glass capillary and stimulated to swell or shrink by altering the osmolarity of the perfusing solution. The cell capillary was connected in series with a blank reference capillary, and differential pressure changes across each tube were monitored. The advantages of this method include 1) ability to continuously monitor changes in volume during rapid solution changes, 2) independence from cell morphology, 3) presence of physiological conditions with cell surface contacts and cell-cell interactions, 4) no phototoxic effects such as those associated with fluorescent methods, and 5) ability to report from large populations of cells. With this method, we could detect the previously demonstrated enhanced volume regulation of cells overexpressing the membrane phosphoprotein phospholemman, which has been implicated in osmolyte transport.