Mesenchymal‐Mode Migration Assay and Antimetastatic Drug Screening with High‐Throughput Microfluidic Channel Networks

Increasing evidence shows that activated mesenchymal migration is a key process of the metastatic cascade. Cancer cells usually gain such migratory capability through an epithelial‐to‐mesenchymal transition. Herein we present a high‐throughput microfluidic device with 3120 microchambers to specifically monitor mesenchymal migration. Through imaging of the whole chip and statistical analysis, we can evaluate the two key factors of velocity and percentage related to cell migratory capacity at different cell densities in culture. We also used the device to screen antimetastatic drugs for their inhibition of mesenchymal migration and prevention of metastatic malignancy. This device will provide an excellent platform for biologists to gain a better understanding of cancer metastasis.     

In Situ Single‐Cell Western Blot on Adherent Cell Culture

Integrating 2D culture of adherent mammalian cells with single‐cell western blotting (in situ scWB) uses microfluidic design to eliminate the requirement for trypsin release of cells to suspension, prior to single‐cell isolation and protein analysis. To assay HeLa cells from an attached starting state, we culture adherent cells in fibronectin‐functionalized microwells formed in a thin layer of polyacrylamide gel. To integrate the culture, lysis, and assay workflow, we introduce a one‐step copolymerization process that creates protein‐decorated microwells. After single‐cell culture, we lyse each cell in the microwell and perform western blotting on each resultant lysate. We observe cell spreading after overnight microwell‐based culture. scWB reports increased phosphorylation of MAP kinases (ERK1/2, p38) under hypertonic conditions. We validate the in situ scWB with slab‐gel western blot, while revealing cell‐to‐cell heterogeneity in stress responses.     

An Enzyme-Loaded Metal–Organic Framework-Assisted Microfluidic Platform Enables Single-Cell Metabolite Analysis

Colonization of cancer cells at secondary sites, a decisive step in tumor metastasis, is strongly dependent on the formation of metastatic microenvironments regulated by intrinsic single-cell metabolism traits. Herein, we report a single-cell microfluidic platform for high-throughput dynamic monitoring of tumor cell metabolites to evaluate tumor malignancy. This microfluidic device empowers efficient isolation of single cells (>99 %) in a squashed state similar to tumor extravasation, and employs enzyme-packaged metal–organic frameworks to catalyze tumor cell metabolites for visualization. The microfluidic evaluation was confirmed by in vivo assays, suggesting that the platform allowed predicting the tumorigenicity of captured tumor cells and screening metabolic inhibitors as anti-metastatic drugs. Furthermore, the platform efficiently detected various aggressive cancer cells in unprocessed whole blood samples with high sensitivity, showing potential for clinical application.     

Microfluidic Cell Deformability Assay for Rapid and Efficient Kinase Screening with the CRISPR‐Cas9 System

Herein we report a CRISPR‐Cas9‐mediated loss‐of‐function kinase screen for cancer cell deformability and invasive potential in a high‐throughput microfluidic chip. In this microfluidic cell separation platform, flexible cells with high deformability and metastatic propensity flowed out, while stiff cells remained trapped. Through deep sequencing, we found that loss of certain kinases resulted in cells becoming more deformable and invasive. High‐ranking candidates identified included well‐reported tumor suppressor kinases, such as chk2, IKK‐α, p38 MAPKs, and DAPK2. A high‐ranking candidate STK4 was chosen for functional validation and identified to play an important role in the regulation of cell deformability and tumor suppression. Collectively, we have demonstrated that CRISPR‐based on‐chip mechanical screening is a potentially powerful strategy to facilitate systematic genetic analyses.     

Dual‐micropillar‐based microfluidic platform for single embryonic stem cell‐derived neuronal differentiation

We developed the dual‐micropillar‐based microfluidic platform to direct embryonic stem (ES) cell fate. 4 × 4 dual‐micropillar‐based microfluidic platform consisted of 16 circular‐shaped outer micropillars and 8 saddle‐shaped inner micropillars in which single ES cells were cultured. We hypothesized that dual‐micropillar arrays would play an important role in controlling the shear stress and cell docking. Circular‐shaped outer micropillars minimized the shear stress, whereas saddle‐shaped inner micropillars allowed for docking of individual ES cells. We observed the effect of saddle‐shaped inner micropillars on cell docking in response to hydrodynamic resistance. We also demonstrated that ES cells cultured for 6 days within the dual‐micropillar‐based microfluidic platform differentiated into neural‐like cells. Therefore, this dual‐micropillar‐based microfluidic platform could be a potentially powerful method for screening of lineage commitments of single ES cells.     

A valve‐based microfluidic device for on‐chip single cell treatments

Assays toward single‐cell analysis have attracted the attention in biological and biomedical researches to reveal cellular mechanisms as well as heterogeneity. Yet nowadays microfluidic devices for single‐cell analysis have several drawbacks: some would cause cell damage due to the hydraulic forces directly acting on cells, while others could not implement biological assays since they could not immobilize cells while manipulating the reagents at the same time. In this work, we presented a two‐layer pneumatic valve‐based platform to implement cell immobilization and treatment on‐chip simultaneously, and cells after treatment could be collected non‐destructively for further analysis. Target cells could be encapsulated in sodium alginate droplets which solidified into hydrogel when reacted with Ca²⁺. The size of hydrogel beads could be precisely controlled by modulating flow rates of continuous/disperse phases. While regulating fluid resistance between the main channel and passages by the integrated pneumatic valves, on‐chip capture and release of hydrogel beads was implemented. As a proof of concept for on‐chip single‐cell treatments, we showed cellular live/dead staining based on our devices. This method would have potential in single cell manipulation for biochemical cellular assays.     

In Situ Scatheless Cell Detachment Reveals Correlation between Adhesion Strength and Viability at Single‐Cell Resolution

Single‐cell biology provides insights into some of the most fundamental processes in biology and promotes the understanding of life's mysteries. As the technologies to study single‐cells expand, they will require sophisticated analytical tools to make sense of various behaviors and components of single‐cells as well as their relations in the adherent tissue culture. In this paper, we revealed cell heterogeneity and uncovered the connections between cell adhesion strength and cell viability at single‐cell resolution by extracting single adherent cells of interest from a standard tissue culture by using a microfluidic chip‐based live single‐cell extractor (LSCE). We believe that this method will provide a valuable new tool for single‐cell biology.     

Magnetically and Near‐Infrared Light‐Powered Supramolecular Nanotransporters for the Remote Control of Enzymatic Reactions

Cancer is one of the primary causes of death worldwide. A high‐precision analysis of biomolecular behaviors in cancer cells at the single‐cell level and more effective cancer therapies are urgently required. Here, we describe the development of a magnetically‐ and near infrared light‐triggered optical control method, based on nanorobotics, for the analyses of cellular functions. A new type of nanotransporters, composed of magnetic iron nanoparticles, carbon nanohorns, and liposomes, was synthesized for the spatiotemporal control of cellular functions in cells and mice. Our technology will help to create a new state‐of‐the‐art tool for the comprehensive analysis of “real” biological molecular information at the single‐cell level, and it may also help in the development of innovative cancer therapies.     

In Situ Spatial Complementation of Aptamer‐Mediated Recognition Enables Live‐Cell Imaging of Native RNA Transcripts in Real Time

Direct cellular imaging of the localization and dynamics of biomolecules helps to understand their function and reveals novel mechanisms at the single‐cell resolution. In contrast to routine fluorescent‐protein‐based protein imaging, technology for RNA imaging remains less well explored because of the lack of enabling technology. Herein, we report the development of an aptamer‐initiated fluorescence complementation (AiFC) method for RNA imaging by engineering a green fluorescence protein (GFP)‐mimicking turn‐on RNA aptamer, Broccoli, into two split fragments that could tandemly bind to target mRNA. When genetically encoded in cells, endogenous mRNA molecules recruited Split‐Broccoli and brought the two fragments into spatial proximity, which formed a fluorophore‐binding site in situ and turned on fluorescence. Significantly, we demonstrated the use of AiFC for high‐contrast and real‐time imaging of endogenous RNA molecules in living mammalian cells. We envision wide application and practical utility of this enabling technology to in vivo single‐cell visualization and mechanistic analysis of macromolecular interactions.     

Integration of Lateral Filter Arrays with Immunoaffinity for Circulating‐Tumor‐Cell Isolation

Circulating tumor cells (CTCs) are an important biomarker for cancer prognosis and treatment monitoring. However, the heterogeneity of the physical and biological properties of CTCs limits the efficiency of various approaches used to isolate small numbers of CTCs from billions of normal blood cells. To address this challenge, we developed a lateral filter array microfluidic (LFAM) device to integrate size‐based separation with immunoaffinity‐based CTC isolation. The LFAM device consists of a serpentine main channel, through which most of a sample passes, and an array of lateral filters for CTC isolation. The unique device design produces a two‐dimensional flow, which reduces nonspecific, geometric capture of normal cells as typically observed in vertical filters. The LFAM device was further functionalized by immobilizing antibodies that are specific to the target cells. The resulting devices captured pancreatic cancer cells spiked in blood samples with (98.7±1.2) % efficiency and were used to isolate CTCs from patients with metastatic colorectal cancer.     

Current Advances in Highly Multiplexed Antibody‐Based Single‐Cell Proteomic Measurements

Single‐cell measurements have played a critical role in revealing the complex signaling dynamics and heterogeneity present in cells, but there is still much to learn. Measuring samples from bulk populations of cells often masks the information and dynamics present in subsets of cells. Common single‐cell protein studies rely on fluorescent microscopy and flow cytometry but are limited in multiplexing ability owing to spectral overlap. Recently, technology advancements in single‐cell proteomics have allowed highly multiplexed measurement of multiple parameters simultaneously by using barcoded microfluidic enzyme‐linked immunosorbent assays and mass cytometry techniques. In this review, we will describe recent work around multiparameter single‐cell protein measurements and critically analyze the techniques.     

Droplet Microfluidics—A Tool for Single‐Cell Analysis

Droplet microfluidics allows the isolation of single cells and reagents in monodisperse picoliter liquid capsules and manipulations at a throughput of thousands of droplets per second. These qualities allow many of the challenges in single‐cell analysis to be overcome. Monodispersity enables quantitative control of solute concentrations, while encapsulation in droplets provides an isolated compartment for the single cell and its immediate environment. The high throughput allows the processing and analysis of the tens of thousands to millions of cells that must be analyzed to accurately describe a heterogeneous cell population so as to find rare cell types or access sufficient biological space to find hits in a directed evolution experiment. The low volumes of the droplets make very large screens economically viable. This Review gives an overview of the current state of single‐cell analysis involving droplet microfluidics and offers examples where droplet microfluidics can further biological understanding.     

Spectrally Combined Encoding for Profiling Heterogeneous Circulating Tumor Cells Using a Multifunctional Nanosphere‐Mediated Microfluidic Platform

Comprehensive phenotypic profiling of heterogeneous circulating tumor cells (CTCs) at single‐cell resolution has great importance for cancer management. Herein, a novel spectrally combined encoding (SCE) strategy was proposed for multiplex biomarker profiling of single CTCs using a multifunctional nanosphere‐mediated microfluidic platform. Different cellular biomarkers uniquely labeled by multifunctional nanosphere barcodes, possessing identical magnetic tags and distinct optical signatures, enabled isolation of heterogeneous CTCs with over 91.6 % efficiency and in situ SCE of phenotypes. By further trapping individual CTCs in ordered microstructures on chip, composite single‐cell spectral signatures were conveniently and efficiently obtained, allowing reliable spectral‐readout for multiplex biomarker profiling. This SCE strategy exhibited great potential in multiplex profiling of heterogeneous CTC phenotypes, offering new avenues for cancer study and precise medicine.     

High‐throughput microfluidic device for single cell analysis using multiple integrated soft lithographic pumps

The ability to accurately control fluid transport in microfluidic devices is key for developing high‐throughput methods for single cell analysis. Making small, reproducible changes to flow rates, however, to optimize lysis and injection using pumps external to the microfluidic device are challenging and time‐consuming. To improve the throughput and increase the number of cells analyzed, we have integrated previously reported micropumps into a microfluidic device that can increase the cell analysis rate to ∼1000 cells/h and operate for over an hour continuously. In order to increase the flow rates sufficiently to handle cells at a higher throughput, three sets of pumps were multiplexed. These pumps are simple, low‐cost, durable, easy to fabricate, and biocompatible. They provide precise control of the flow rate up to 9.2 nL/s. These devices were used to automatically transport, lyse, and electrophoretically separate T‐Lymphocyte cells loaded with Oregon green and 6‐carboxyfluorescein. Peak overlap statistics predicted the number of fully resolved single‐cell electropherograms seen. In addition, there was no change in the average fluorescent dye peak areas indicating that the cells remained intact and the dyes did not leak out of the cells over the 1 h analysis time. The cell lysate peak area distribution followed that expected of an asynchronous steady‐state population of immortalized cells.     

Probing Low‐Copy‐Number Proteins in a Single Living Cell

Single‐cell analysis techniques are essential for understanding the microheterogeneity and functions of cells. Low‐copy‐number proteins play important roles in cell functioning, but their measurement in single cells remains challenging. Herein, we report an approach, called plasmonic immunosandwich assay (PISA), for probing low‐copy‐number proteins in single cells. This approach combined in vivo immunoaffinity extraction and plasmon‐enhanced Raman scattering (PERS). Target proteins were specifically extracted from the cells by microprobes modified with monoclonal antibody or molecularly‐imprinted polymer (MIP), followed by labeling with Raman‐active nanotags. The PERS detection, with Raman intensity enhanced by 9 orders of magnitude, provided ultrasensitive detection at the single‐molecule level. Using this approach, we found that alkaline phosphatase and survivin were expressed in distinct levels in cancer and normal cells, and that extended culture passage resulted in reduced expression of survivin. We further developed acupuncture needle‐based PISA for probing low‐copy‐number proteins in living bodies.     

Three‐dimensional microfluidic chip with twin‐layer herringbone structure for high efficient tumor cell capture and release via antibody‐conjugated magnetic microbeads

Harvesting rare circulating tumor cells (CTCs) from human blood is distinctly substantial to monitor tumor stage and evaluate therapeutic efficacy. As a proof‐of‐concept study, a microfluidic chip with twin‐layer herringbone grooves was developed to isolate and recover tumor cells with high efficiency based on the immunoreaction between cells and antibody‐conjugated microbeads (MBs) under local magnetic field. Functional MBs were initially localized onto the internal channel wall through the magnetic guidance. Then, infused tumor cells were deviated into the herringbone groove via passive microvortex and were further trapped through an irreversible interaction with MBs. Upon the removal of magnet, the captured cells and residual MBs were released from the channel and collected for further analysis in cell adhesion and proliferation in vitro. Capture efficiency of tumor cells reached up to ∼90% and limit of detection was down to 50 cells per mL based on this approach. Furthermore, recovery rate of tumor cells was as high as ∼94%, and potencies of cell attachment and proliferation was well maintained in retrieved cells. Hence, the present technique has a great potential for the isolation, quantitation and recovery of CTCs for cancer theranostic guidance and biomolecular analysis.     

A modular single-cell pipette microfluidic chip coupling to ETAAS and ICP-MS for single cell analysis

Accurate single-cell capture is a crucial step for single cell biological and chemical analysis. Conventional single-cell capturing often confront operational complexity, limited efficiency, cell damage, large scale but low accuracy, incompetence in the acquirement of nano-upgraded single-cell liquid. Flow cytometry has been widely used in large-scale single-cell detection, while precise single-cell isolation relies on both a precision operating platform and a microscope, which is not only extre...     

Hydrogel microfluidic co‐culture device for photothermal therapy and cancer migration

We developed the photo‐crosslinkable hydrogel microfluidic co‐culture device to study photothermal therapy and cancer cell migration. To culture MCF7 human breast carcinoma cells and metastatic U87MG human glioblastoma in the microfluidic device, we used 10 w/v% gelatin methacrylate (GelMA) hydrogels as a semi‐permeable physical barrier. We demonstrated the effect of gold nanorod on photothermal therapy of cancer cells in the microfluidic co‐culture device. Interestingly, we observed that metastatic U87MG human glioblastoma largely migrated toward vascular endothelial growth factor (VEGF)‐treated GelMA hydrogel‐embedding microchannels. The main advantage of this hydrogel microfluidic co‐culture device is to simultaneously analyze the physiological migration behaviors of two cancer cells with different physiochemical motilities and study gold nanorod‐mediated photothermal therapy effect. Therefore, this hydrogel microfluidic co‐culture device could be a potentially powerful tool for photothermal therapy and cancer cell migration applications.     

Morphometric Cell Classification for Single‐Cell MALDI‐Mass Spectrometry Imaging

The large‐scale and label‐free molecular characterization of single cells in their natural tissue habitat remains a major challenge in molecular biology. We present a method that integrates morphometric image analysis to delineate and classify individual cells with their single‐cell‐specific molecular profiles. This approach provides a new means to study spatial biological processes such as cancer field effects and the relationship between morphometric and molecular features.