Isolation of cell nuclei in microchannels by short-term chemical treatment via two-step carrier medium exchange

Laborless, Automated Microfluidic Tandem Cell Processor for Visualizing Intracellular Molecules of Mammalian Cells

Visualization and quantification of intracellular molecules of mammalian cells are crucial steps in clinical diagnosis, drug development, and basic biological research. However, conventional methods rely mostly on labor-intensive, centrifugation-based manual operations for exchanging the cell carrier medium and have limited reproducibility and recovery efficiency. Here we present a microfluidic cell processor that can perform four-step exchange of carrier medium, simply by introducing a cell suspension and fluid reagents into the device. The reaction time period for each reaction step, including fixation, membrane permeabilization, and staining, was tunable in the range of 2 to 15 min by adjusting the volume of the reaction tube connecting the neighboring exchanger modules. We double-stained the cell nucleus and cytoskeleton (F-actin) using the presented device with an overall reaction period of ∼30 min, achieving a high recovery ratio and high staining efficiency. Additionally, intracellular cytokine (IL-2) was visualized for T cells to demonstrate the feasibility of the device as a pretreatment system for downstream flow-cytometric analysis. The presented approach would facilitate the development of laborless, automated microfluidic systems that integrate cell processing and analysis operations and would pave a new path to high-throughput biological experiments.

Single-Cell Point Constrictions for Reagent-Free High-Throughput Mechanical Lysis and Intact Nuclei Isolation

Highly localized (point) constrictions featuring a round geometry with ultra-sharp edges in silicon have been demonstrated for the reagent-free continuous-flow rapid mechanical lysis of mammalian cells on a single-cell basis. Silicon point constrictions, robust structures formed by a single-step dry etching process, are arranged in a cascade along microfluidic channels and can effectively rupture cells delivered in a pressure-driven flow. The influence of the constriction size and count on the lysis performance is presented for fibroblasts in reference to total protein, DNA, and intact nuclei levels in the lysates evaluated by biochemical and fluoremetric assays and flow-cytometric analyses. Protein and DNA levels obtained from an eight-constriction treatment match or surpass those from a chemical method. More importantly, many intact nuclei are found in the lysates with a relatively high nuclei-isolation efficiency from a four-constriction treatment. Point constrictions and their role in rapid reagent-free disruption of the plasma membrane could have implications for integrated sample preparation in future lab-on-a-chip systems.

Mechanical property characterization of hundreds of single nuclei based on microfluidic constriction channel

As label-free biomarkers, the mechanical properties of nuclei are widely treated as promising biomechanical markers for cell type classification and cellular status evaluation. However, previously reported mechanical parameters were derived from only around 10 nuclei, lacking statistical significances due to low sample numbers. To address this issue, nuclei were first isolated from SW620 and A549 cells, respectively, using a chemical treatment method. This was followed by aspirating them through two types of microfluidic constriction channels for mechanical property characterization. In this study, hundreds of nuclei were characterized, producing passage times of 0.5 ± 1.2 s for SW620 nuclei in type I constriction channel (n = 153), 0.045 ± 0.047 s for SW620 nuclei in type II constriction channel (n = 215) and 0.50 ± 0.86 s for A549 nuclei in type II constriction channel. In addition, neural network based pattern recognition was used to classify the nuclei isolated from SW620 and A549 cells, producing successful classification rates of 87.2% for diameters of nuclei, 85.5% for passage times of nuclei and 89.3% for both passage times and diameters of nuclei. These results indicate that the characterization of the mechanical properties of nuclei may contribute to the classification of different tumor cells.

Slanted, asymmetric microfluidic lattices as size-selective sieves for continuous particle/cell sorting

Hydrodynamic microfluidic platforms have been proven to be useful and versatile for precisely sorting particles/cells based on their physicochemical properties. In this study, we demonstrate that a simple lattice-shaped microfluidic pattern can work as a virtual sieve for size-dependent continuous particle sorting. The lattice is composed of two types of microchannels ("main channels" and "separation channels"). These channels cross each other in a perpendicular fashion, and are slanted against the macroscopic flow direction. The difference in the densities of these channels generates an asymmetric flow distribution at each intersection. Smaller particles flow along the streamline, whereas larger particles are filtered and gradually separated from the stream, resulting in continuous particle sorting. We successfully sorted microparticles based on size with high accuracy, and clearly showed that geometric parameters, including the channel density and the slant angle, critically affect the sorting behaviors of particles. Leukocyte sorting and monocyte purification directly from diluted blood samples have been demonstrated as biomedical applications. The presented system for particle/cell sorting would become a simple but versatile unit operation in microfluidic apparatus for chemical/biological experiments and manipulations.

On-Chip Magnetic Particle-Based Immunoassays Using Multilaminar Flow for Clinical Diagnostics

Magnetic particles have become popular in recent years for immunoassays due to their high surface-to-volume ratio and the ease of their manipulation. However, such assays also require multiple reaction and washing steps that are both time-consuming and manually laborious. Here, we describe a setup and methodology for performing rapid immunoassays on magnetic particles in continuous flow via their deflection through multiple laminar flow streams of reagents and washing solutions. In particular, we focus on the use of the microfluidic platform for a C-reactive protein (CRP) sandwich immunoassay in less than 60 s.

Acoustofluidic Transfer of Inflammatory Cells from Human Sputum Samples

For sputum analysis, the transfer of inflammatory cells from liquefied sputum samples to a culture medium or buffer solution is a critical step because it removes the inflammatory cells from the presence of residual dithiothreitol (DTT), a reagent that reduces cell viability and interferes with further sputum analyses. In this work, we report an acoustofluidic platform for transferring inflammatory cells using standing surface acoustic waves (SSAW). In particular, we exploit the acoustic radiation force generated from a SSAW field to actively transfer inflammatory cells from a solution containing residual DTT to a buffer solution. The viability and integrity of the inflammatory cells are maintained during the acoustofluidic-based cell transfer process. Our acoustofluidic technique removes residual DTT generated in sputum liquefaction and facilitates immunophenotyping of major inflammatory cells from sputum samples. It enables cell transfer in a continuous flow, which aids the development of an automated, integrated system for on-chip sputum processing and analysis.

Standing surface acoustic wave (SSAW)-based cell washing

Cell/bead washing is an indispensable sample preparation procedure used in various cell studies and analytical processes. In this article, we report a standing surface acoustic wave (SSAW)-based microfluidic device for cell and bead washing in a continuous flow. In our approach, the acoustic radiation force generated in a SSAW field is utilized to actively extract cells or beads from their original medium. A unique configuration of tilted-angle standing surface acoustic wave (taSSAW) is employed in our device, enabling us to wash beads with >98% recovery rate and >97% washing efficiency. We also demonstrate the functionality of our device by preparing high-purity (>97%) white blood cells from lysed blood samples through cell washing. Our SSAW-based cell/bead washing device has the advantages of label-free manipulation, simplicity, high biocompatibility, high recovery rate, and high washing efficiency. It can be useful for many lab-on-a-chip applications.

Ultrafast cell switching for recording cell surface transitions: new insights into epidermal growth factor receptor signalling

A pinched-flow deflection technology was developed for rapid single cell switching between biochemical microenvironments. Millisecond switching was used to stimulate and preserve epidermal growth factor receptor (EGFR) autophosphorylation transitions. Intramolecular phosphorylation initiates signal transduction, is silenced by phosphatase activity until EGFR dimerization enables intermolecular phosphorylation to initiate downstream signalling.