A radial flow microfluidic device for ultra-high-throughput affinity-based isolation of circulating tumor cells

Novel Isolating Approaches to Circulating Tumor Cell Enrichment Based on Microfluidics: A Review

Circulating tumor cells (CTCs), derived from the primary tumor and carrying genetic information, contribute significantly to the process of tumor metastasis. The analysis and detection of CTCs can be used to assess the prognosis and treatment response in patients with tumors, as well as to help study the metastatic mechanisms of tumors and the development of new drugs. Since CTCs are very rare in the blood, it is a challenging problem to enrich CTCs efficiently. In this paper, we provide a comprehensive overview of microfluidics-based enrichment devices for CTCs in recent years. We explore in detail the methods of enrichment based on the physical or biological properties of CTCs; among them, physical properties cover factors such as size, density, and dielectric properties, while biological properties are mainly related to tumor-specific markers on the surface of CTCs. In addition, we provide an in-depth description of the methods for enrichment of single CTCs and illustrate the importance of single CTCs for performing tumor analyses. Future research will focus on aspects such as improving the separation efficiency, reducing costs, and increasing the detection sensitivity and accuracy.

Microfluidic-SERS Technologies for CTC: A Perspective on Clinical Translation

Enumeration and phenotypic profiling of circulating tumor cells (CTCs) provide critical information for clinical diagnosis and treatment monitoring in cancer. To achieve this goal, an integrated system is needed to efficiently isolate CTCs from patient samples and sensitively evaluate their phenotypes. Such integration would comprise a high-throughput single-cell processing unit for the isolation and manipulation of CTCs and a sensitive and multiplexed quantitation unit to detect clinically relevant signals from these cells. Surface-enhanced Raman scattering (SERS) has been used as an analytical method for molecular profiling and in vitro cancer diagnosis. More recently, its multiplexing capability and power to create distinct molecular signatures against their targets have garnered attention. Here, we share our insights into the combined power of microfluidics and SERS in realizing CTC isolation, enumeration, and detection from a clinical translation perspective. We highlight the key operational factors in CTC microfluidic processing and SERS detection from patient samples. We further discuss microfluidic-SERS integration and its clinical utility as a paradigm shift in clinical CTC-based cancer diagnosis and prognostication. Finally, we summarize the challenges and attempt to look forward to what lies ahead of us in potentially translating the technique into real clinical applications.

The integrated on-chip isolation and detection of circulating tumour cells

Circulating tumour cells (CTCs) are cancer cells shed from a primary tumour which intravasate into the blood stream and have the potential to extravasate into distant tissues, seeding metastatic lesions. As such, they can offer important insight into cancer progression with their presence generally associated with a poor prognosis. The detection and enumeration of CTCs is, therefore, critical to guiding clinical decisions during treatment and providing information on disease state. CTC isolation has been investigated using a plethora of methodologies, of which immunomagnetic capture and microfluidic size-based filtration are the most impactful to date. However, the isolation and detection of CTCs from whole blood comes with many technical barriers, such as those presented by the phenotypic heterogeneity of cell surface markers, with morphological similarity to healthy blood cells, and their low relative abundance (∼1 CTC/1 billion blood cells). At present, the majority of reported methods dissociate CTC isolation from detection, a workflow which undoubtedly contributes to loss from an already sparse population. This review focuses on developments wherein isolation and detection have been integrated into a single-step, microfluidic configuration, reducing CTC loss, increasing throughput, and enabling an on-chip CTC analysis with minimal operator intervention. Particular attention is given to immune-affinity, microfluidic CTC isolation, coupled to optical, physical, and electrochemical CTC detection (quantitative or otherwise).

Liquid-based biomarkers in breast cancer: looking beyond the blood

In recent decades, using circulating tumor cell (CTC), circulating tumor DNA (ctDNA), circulating tumor RNA (ctRNA), exosomes and etc. as liquid biomarkers has received enormous attention in various tumors, including breast cancer (BC). To date, efforts in the area of liquid biopsy predominantly focus on the analysis of blood-based markers. It is worth noting that the identifications of markers from non-blood sources provide unique advantages beyond the blood and these alternative sources may be of great significance in offering supplementary information in certain settings. Here, we outline the latest advances in the analysis of non-blood biomarkers, predominantly including urine, saliva, cerebrospinal fluid, pleural fluid, stool and etc. The unique advantages of such testings, their current limitations and the appropriate use of non-blood assays and blood assays in different settings are further discussed. Finally, we propose to highlight the challenges of these alternative assays from basic to clinical implementation and explore the areas where more investigations are warranted to elucidate its potential utility.

Sensitive Detection of Tumor Cells Using Protein Nanoparticles with Multiple Displays of DNA Aptamers and Bioluminescent Reporters

Simple and effective detection methods for circulating tumor cells are essential for early detection and progression monitoring of tumors. The use of DNA aptamer and bioluminescence is expected to be a key tool for the simple, effective, and sensitive detection of tumor cells. Herein, we designed multifunctional protein nanoparticles for the detection of tumor cells using DNA aptamer and bioluminescence. Fusion proteins (ELP-poly(d)-POIs), composed of elastin-like polypeptide (ELP) fused with protein of interests (POIs) via poly(aspartic acid) (poly(d)), formed the protein nanoparticles based on the temperature responsivity of ELP sequences, leading to multiply displayed POIs on the protein nanoparticles. In the present study, we focused on porcine circovirus type 2 replication initiation protein (Rep), which covalently conjugated with DNA aptamers, and NanoLuc luciferase (Nluc), which emitted a strong bioluminescence, as POIs. ELP-poly(d)-Rep and ELP-poly(d)-Nluc were constructed and formed the protein nanoparticles with multiply displayed Nluc and Rep (DNA aptamer) that amplified the bioluminescence signal and tumor recognition ability. Mucin-1 (MUC1)-overexpressing human breast tumor MCF7 cells and MUC1-recognizing aptamer (MUC1 aptamer) were selected as models. The MUC1 aptamer-conjugated protein nanoparticles exhibited a 13.7-fold higher bioluminescence signal to MCF-7 cells than to human embryonic kidney 293 (HEK293) cells, which express low levels of MUC1. Furthermore, the protein nanoparticles could detect up to 70.7 cells/mL of MCF-7 cells from a cell suspension containing HEK-293. The protein nanoparticles with multiple Rep and Nluc show a great potential as a material for detecting CTCs.

A Micropillar Array Based Microfluidic Device for Rare Cell Detection and Single-Cell Proteomics

Advancements in single-cell-related technologies have opened new possibilities for analyzing rare cells, such as circulating tumor cells (CTCs) and rare immune cells. Among these techniques, single-cell proteomics, particularly single-cell mass spectrometric analysis (scMS), has gained significant attention due to its ability to directly measure transcripts without the need for specific reagents. However, the success of single-cell proteomics relies heavily on efficient sample preparation, as protein loss in low-concentration samples can profoundly impact the analysis. To address this challenge, an effective handling system for rare cells is essential for single-cell proteomic analysis. Herein, we propose a microfluidics-based method that offers highly efficient isolation, detection, and collection of rare cells (e.g., CTCs). The detailed fabrication process of the micropillar array-based microfluidic device is presented, along with its application for CTC isolation, identification, and collection for subsequent proteomic analysis.

Precise Filtration of Chronic Myeloid Leukemia Cells by an Ultrathin Microporous Membrane with Backflushing to Minimize Fouling

A cell filtration platform that affords accurate size separation and minimizes fouling was developed. The platform features an ultra-thin porous membrane (UTM) filter, a pumping head filtration with backflush (PHF), and cell size measurement (CSM) software. The UTM chip is an ultrathin free-standing membrane with a large window area of 0.68 mm2, a pore diameter of 5 to 9 μm, and a thickness of less than 0.9 μm. The PHF prevents filter fouling. The CSM software analyzes the size distributions of the supernatants and subnatants of isolated cells and presents the data visually. The D99 particle size of cells of the chronic myeloid leukemia (CML) line K562 decreased from 22.2 to 17.5 μm after passage through a 5-μm filter. K562 cells could be separated by careful selection of the pore size; the recovery rate attained 91.3%. The method was compared to conventional blocking models by evaluating the mean square errors (MSEs) between the measured and calculated filtering volumes. The filtering rate was fitted by a linear regression model with a significance that exceeded 0.99 based on the R2 value. The platform can be used to separate various soft biomaterials and afford excellent stability during filtration.

Recent Developments in Inertial and Centrifugal Microfluidic Systems along with the Involved Forces for Cancer Cell Separation: A Review

The treatment of cancers is a significant challenge in the healthcare context today. Spreading circulating tumor cells (CTCs) throughout the body will eventually lead to cancer metastasis and produce new tumors near the healthy tissues. Therefore, separating these invading cells and extracting cues from them is extremely important for determining the rate of cancer progression inside the body and for the development of individualized treatments, especially at the beginning of the metastasis process. The continuous and fast separation of CTCs has recently been achieved using numerous separation techniques, some of which involve multiple high-level operational protocols. Although a simple blood test can detect the presence of CTCs in the blood circulation system, the detection is still restricted due to the scarcity and heterogeneity of CTCs. The development of more reliable and effective techniques is thus highly desired. The technology of microfluidic devices is promising among many other bio-chemical and bio-physical technologies. This paper reviews recent developments in the two types of microfluidic devices, which are based on the size and/or density of cells, for separating cancer cells. The goal of this review is to identify knowledge or technology gaps and to suggest future works.

Toward Personalized Nanomedicine: The Critical Evaluation of Micro and Nanodevices for Cancer Biomarker Analysis in Liquid Biopsy

Liquid biopsy for the analysis of circulating cancer biomarkers (CBs) is a major advancement toward the early detection of cancer. In comparison to tissue biopsy techniques, liquid biopsy is relatively painless, offering multiple sampling opportunities across easily accessible bodily fluids such as blood, urine, and saliva. Liquid biopsy is also relatively inexpensive and simple, avoiding the requirement for specialized laboratory equipment or trained medical staff. Major advances in the field of liquid biopsy are attributed largely to developments in nanotechnology and microfabrication that enables the creation of highly precise chip-based platforms. These devices can overcome detection limitations of an individual biomarker by detecting multiple markers simultaneously on the same chip, or by featuring integrated and combined target separation techniques. In this review, the major advances in the field of portable and semi-portable micro, nano, and multiplexed platforms for CB detection for the early diagnosis of cancer are highlighted. A comparative discussion is also provided, noting merits and drawbacks of the platforms, especially in terms of portability. Finally, key challenges toward device portability and possible solutions, as well as discussing the future direction of the field are highlighted.

Detection of rare CTCs by electrochemical biosensor built on quaternary PdPtCuRu nanospheres with mesoporous architectures

Circulating tumor cells (CTCs) are promising liquid biopsy biomarkers for early cancer detection and anti-cancer therapy evaluation. The ultra-low abundance of CTCs in blood samples requires highly sensitive and accurate detection ways. In this study, we propose the design of a dual-recognition electrochemical biosensor to improve both the specificity and signal response. PdPtCuRu mesoporous nanospheres (PdPtCuRu MNSs) with excellent three dimensions (3D) nanopore structures were synthesized by one-pot method and connected to mucin 1 (MUC1) aptamer to serve as signal amplification probe. Besides, superconductive carbon black, Ketjen Black (KB), and gold nanoparticles (AuNPs) modified organometallic frame (CeMOF-Au) were combined to work as signal transducer. The characteristic branching structure of KB provides abundant contact points to load CeMOF-Au to heighten the interface electron transfer rate. In addition, AuNPs were reduced on the surface of CeMOF, which could effectively bind the capture antibody and further enhance the conductivity. Under the optimized condition, the limit of detection (LOD) of the as-constructed biosensor was less than 10 cells mL^-1 for model A549 cells, and showed good specificity and accuracy in spiked serum samples. We envision the as-proposed electrochemical biosensor would alternate as a useful tool for the clinical detection of CTCs for cancer diagnosis.

Comparative application of microfluidic systems in circulating tumor cells and extracellular vesicles isolation; a review

Cancer is a prevalent cause of mortality globally, where early diagnosis leads to a reduced death rate. Many researchers' common strategies are based on personalized diagnostic methods with rapid response and high accuracy. This technology was developed by applying liquid biopsy instead of tissue biopsies in the case of tumor cell analysis that facilitates point-of-care testing for cancer diagnosis and treatment. In recent years, significant progress in microfluidic technology led to the successful isolation, analysis, and monitoring of cancer biomarkers in body liquid biopsy with merits like high sensitivity and flexibility, low sample usage, cost effective, and the ability of automation. The most critical and informative markers in body liquid refer to circulating tumor cells (CTCs) and extracellular vesicles derived from tumors (EVs) that carry various biomarkers in their structure (DNAs, proteins, and RNAs) as compared to ctDNA. The released ctDNA has a low half-life and decreased sensitivity due to large amounts of nucleic acid in serum. This review intends to highlight different cancer screening tests with a particular focus on the details regarding the only FDA-approved and awaiting technologies for FDA clearance to isolate CTCs and EVs based on microfluidics systems.

Double spiral chip-embedded micro-trapezoid filters (SMT filters) for the sensitive isolation of CTCs of prostate cancer by spectral detection

Circulating tumor cells (CTCs) are cancer cells that are released from the original tumor and circulate in the blood vessels, carrying greatly similar constituents as the original tumor. Therefore, CTCs have a significant value in cancer prognosis, early diagnosis, and anti-cancer therapy. However, their rarity and heterogeneity make the isolation of CTCs an arduous task. In the present research, we propose a double spiral chip-embedded micro-trapezoid filter (SMT filter) for the sensitive isolation of the CTCs of prostate cancer by spectral detection. SMT filters were elongated to effectively capture CTCs and this distinctive design was conducive to their isolation and enrichment. The SMT filters were verified with tumor cells and artificial patient blood with a capture efficiency as high as 94% at a flow rate of 1.5 mL h^-1. As a further validation, the SMT filters were validated in isolating CTCs from 10 prostate cancers and other cancers in 4 mL blood samples. Also, the CTCs tested positive for each patient blood sample, ranging from 83-114 CTCs. Significantly, we advanced hyperspectral imaging to detect the characteristic spectrum of CTCs both captured in situ on SMT filters and enriched after isolation. The CTCs could be positively identified by hyperspectral imaging with complete integrity of the cell morphology and an improved characteristic spectrum. This represents a breakthrough in the conventional surface-enhanced Raman scattering (SERS) spectroscopy of nanoparticles. Also, the characteristic spectrum of the CTCs would be highly beneficial for distinguishing the cancer type and accurate for enumerating tumor cells with varied intensities. Furthermore, a novel integrated flower-shaped microfilter was presented with all these aforementioned merits. The success of both the SMT filters and characteristic spectral detection indicated their feasibility for further clinical analysis, the evaluation of cancer therapy, and for potential application.

Isolation of circulating tumor cells to diagnose melanoma and evaluate the efficacy of surgical resection using melanoma-specific microsystem

Melanoma is one of the most aggressive skin cancers due to its potential to metastasize widely in the body. The risk of metastasis is increased with later detection and increased thickness of the primary lesion, thus early identification and surgical removal is critical for higher survival rates for patients. However, even with appropriate treatment, some patients will develop recurrence which may be difficult to identify until advanced or causing symptoms. Recent advances in liquid biopsy have proposed less-invasive alternatives for cancer diagnosis and monitoring using minimal/zero invasion at sample collection, and circulating tumor cells(CTCs) have been considered a promising blood-based surrogate marker of primary tumors. However, previous CTC technologies relying on epithelial-cell adhesion molecules have limited to epithelial cells, thus hampering use of CTCs for non-epithelial cancers such as melanoma. Here, we used the Melanoma-specific OncoBean platform(MelanoBean) conjugated with melanoma specific antibodies(MCAM and MCSP). The device was used in comprehensive studies for diagnosing melanoma and evaluating surgery efficacy based on change in the number and characteristics of CTCs and CTC-clusters pre- and post-surgical treatment. Our study demonstrated that melanoma patients(n=45) at all stages(I-IV) have a noticeable number of MCTCs as well as MCTC-clusters compared to healthy donors(n=9)(P=0.0011), and surgical treatment leads to a significant decrease in the number of CTCs(P<0.0001). The CTCs recovered from the device underwent molecular profiling for melanoma-associated genes expression using multiplexed qRT-PCR, demonstrating the ability to monitor molecular signature through treatment. The presented MelanoBean and the comprehensive approach will empower prognostic value of CTCs in melanoma in much larger cohort studies.

Molecular biomarkers and liquid biopsies in lung cancer

Liquid biopsy refers to the identification of tumor-derived materials in body fluids including in blood circulation. In the age of immunotherapy and targeted therapies used for the treatment of advanced malignancies, molecular analysis of the tumor is considered a crucial step to guide management. In lung cancer, the concept of liquid biopsies is particularly relevant given the invasiveness of tumor biopsies in certain locations, and the potential risks of biopsy in a patient population with significant co-morbidities. Liquid biopsies have many advantages including non-invasiveness, lower cost, potential for genomic testing, ability to monitor tumor evolution through treatment, and the ability to overcome spatial and temporal intertumoral heterogeneity. The potential clinical applications of liquid biopsy are vast and include screening, detection of minimal residual disease and/or early relapse after curative intent treatment, monitoring response to immunotherapy, and identifying mutations that might be targetable or can confer resistance. Herein, we review the potential role of circulating tumor DNA and circulating tumor cells as forms of liquid biopsies and blood biomarkers in non-small cell lung cancer. We discuss the methodologies/platforms available for each, clinical applications, and limitations/challenges in incorporation into clinical practice. We additionally review emerging forms of liquid biopsies including tumor educated platelets, circular RNA, and exosomes.

Application of Microfluidics in Detection of Circulating Tumor Cells

Tumor metastasis is one of the main causes of cancer incidence and death worldwide. In the process of tumor metastasis, the isolation and analysis of circulating tumor cells (CTCs) plays a crucial role in the early diagnosis and prognosis of cancer patients. Due to the rarity and inherent heterogeneity of CTCs, there is an urgent need for reliable CTCs separation and detection methods in order to obtain valuable information on tumor metastasis and progression from CTCs. Microfluidic technology is increasingly used in various studies of CTCs separation, identification and characterization because of its unique advantages, such as low cost, simple operation, less reagent consumption, miniaturization of the system, rapid detection and accurate control. This paper reviews the research progress of microfluidic technology in CTCs separation and detection in recent years, as well as the potential clinical application of CTCs, looks forward to the application prospect of microfluidic technology in the treatment of tumor metastasis, and briefly discusses the development prospect of microfluidic biosensor.

Recent Advances in Microfluidic Platform for Physical and Immunological Detection and Capture of Circulating Tumor Cells

CTCs (circulating tumor cells) are well-known for their use in clinical trials for tumor diagnosis. Capturing and isolating these CTCs from whole blood samples has enormous benefits in cancer diagnosis and treatment. In general, various approaches are being used to separate malignant cells, including immunomagnets, macroscale filters, centrifuges, dielectrophoresis, and immunological approaches. These procedures, on the other hand, are time-consuming and necessitate multiple high-level operational protocols. In addition, considering their low efficiency and throughput, the processes of capturing and isolating CTCs face tremendous challenges. Meanwhile, recent advances in microfluidic devices promise unprecedented advantages for capturing and isolating CTCs with greater efficiency, sensitivity, selectivity and accuracy. In this regard, this review article focuses primarily on the various fabrication methodologies involved in microfluidic devices and techniques specifically used to capture and isolate CTCs using various physical and biological methods as well as their conceptual ideas, advantages and disadvantages.

Liquid biopsy: a step closer to transform diagnosis, prognosis and future of cancer treatments

Over the past decade, invasive techniques for diagnosing and monitoring cancers are slowly being replaced by non-invasive methods such as liquid biopsy. Liquid biopsies have drastically revolutionized the field of clinical oncology, offering ease in tumor sampling, continuous monitoring by repeated sampling, devising personalized therapeutic regimens, and screening for therapeutic resistance. Liquid biopsies consist of isolating tumor-derived entities like circulating tumor cells, circulating tumor DNA, tumor extracellular vesicles, etc., present in the body fluids of patients with cancer, followed by an analysis of genomic and proteomic data contained within them. Methods for isolation and analysis of liquid biopsies have rapidly evolved over the past few years as described in the review, thus providing greater details about tumor characteristics such as tumor progression, tumor staging, heterogeneity, gene mutations, and clonal evolution, etc. Liquid biopsies from cancer patients have opened up newer avenues in detection and continuous monitoring, treatment based on precision medicine, and screening of markers for therapeutic resistance. Though the technology of liquid biopsies is still evolving, its non-invasive nature promises to open new eras in clinical oncology. The purpose of this review is to provide an overview of the current methodologies involved in liquid biopsies and their application in isolating tumor markers for detection, prognosis, and monitoring cancer treatment outcomes.

Relevance of Circulating Tumor Cells as Predictive Markers for Cancer Incidence and Relapse

Shedding of cancer cells from the primary site or undetectable bone marrow region into the circulatory system, resulting in clinically overt metastasis or dissemination, is the hallmark of unfavorable invasive cancers. The shed cells remain in circulation until they extravasate to form a secondary metastatic lesion or undergo anoikis. The circulating tumor cells (CTCs) found as single cells or clusters carry a plethora of information, are acknowledged as potential biomarkers for predicting cancer prognosis and cancer progression, and are supposed to play key roles in determining tailored therapies for advanced diseases. With the advent of novel technologies that allow the precise isolation of CTCs, more and more clinical trials are focusing on the prognostic and predictive potential of CTCs. In this review, we summarize the role of CTCs as a predictive marker for cancer incidence, relapse, and response to therapy.

Negative-Selection Enrichment of Circulating Tumor Cells from Peripheral Blood Using the Microfluidic CTC-iChip

The ability to isolate and analyze rare circulating tumor cells (CTCs) holds the potential to increase our understanding of cancer evolution and allows monitoring of disease and therapeutic responses through a relatively non-invasive blood-based biopsy. While many methods have been described to isolate CTCs from the blood, the vast majority rely on size-based sorting or positive selection of CTCs based on surface markers, which introduces bias into the downstream product by making assumptions about these heterogenous cells. Here we describe a negative-selection protocol for enrichment of CTCs through removal of blood components including red blood cells, platelets, and white blood cells. This procedure results in a product that is amenable to downstream single-cell analytics including RNA-Seq, ATAC-Seq and DNA methylation, droplet digital PCR (ddPCR) for tumor specific transcripts, staining and extensive image analysis, and ex vivo culture of patient-derived CTCs.

State-of-the-arts techniques and current evolving approaches in the separation and detection of circulating tumor cell

Circulating tumor cells (CTCs) are cancer cells that shed from the primary tumor and then enter the circulatory system, a small part of which may evolve into metastatic cancer under appropriate microenvironment conditions. The detection of CTCs is a truly noninvasive, dynamic monitor for disease changes, which has considerable clinical implications in the selection of targeted drugs. However, their inherent rarity and heterogeneity pose significant challenges to their isolation and detection. Even the "gold standard", CellSearch™, suffers from high expenses, low capture efficiency, and the consumption of time. With the advancement of CTCs analysis technologies in recent years, the yield and efficiency of CTCs enrichment have gradually been improved, as well as detection sensitivity. In this review, the isolation and detection strategies of CTCs have been completely described and the potential directions for future research and development have also been highlighted through analyzing the challenges faced by current strategies.

Small extracellular vesicles in cancer

Extracellular vesicles (EV) are lipid-bilayer enclosed vesicles in submicron size that are released from cells. A variety of molecules, including proteins, DNA fragments, RNAs, lipids, and metabolites can be selectively encapsulated into EVs and delivered to nearby and distant recipient cells. In tumors, through such intercellular communication, EVs can regulate initiation, growth, metastasis and invasion of tumors. Recent studies have found that EVs exhibit specific expression patterns which mimic the parental cell, providing a fingerprint for early cancer diagnosis and prognosis as well as monitoring responses to treatment. Accordingly, various EV isolation and detection technologies have been developed for research and diagnostic purposes. Moreover, natural and engineered EVs have also been used as drug delivery nanocarriers, cancer vaccines, cell surface modulators, therapeutic agents and therapeutic targets. Overall, EVs are under intense investigation as they hold promise for pathophysiological and translational discoveries. This comprehensive review examines the latest EV research trends over the last five years, encompassing their roles in cancer pathophysiology, diagnostics and therapeutics. This review aims to examine the full spectrum of tumor-EV studies and provide a comprehensive foundation to enhance the field. The topics which are discussed and scrutinized in this review encompass isolation techniques and how these issues need to be overcome for EV-based diagnostics, EVs and their roles in cancer biology, biomarkers for diagnosis and monitoring, EVs as vaccines, therapeutic targets, and EVs as drug delivery systems. We will also examine the challenges involved in EV research and promote a framework for catalyzing scientific discovery and innovation for tumor-EV-focused research.

Multistage Digital-to-Analogue Chip Based on a Weighted Flow Resistance Network for Soft Actuators

A control chip with a multistage flow-rate regulation function based on the correlation between the flow resistance and flow rate has been developed in this article. Compared with the traditional proportional solenoid valve, this kind of flow valve based on microfluidic technology has the characteristics of being light-weight and having no electric drive. It solves such technical problems as how the current digital microfluidic chip can only adjust the flow switch, and the adjustment of the flow rate is difficult. To linearize the output signal, we propose a design method of weighted resistance. The output flow is controlled by a 4-bit binary pressure signal. According to the binary value of the 4-bit pressure signal at the input, the output can achieve 16-stage flow adjustment. Furthermore, we integrate the three-dimensional flow resistance network, multilayer structure microvalve, and parallel fluid network into a single chip by using 3D printing to obtain a modular flow control unit. This structure enables the microflow control signal to be converted from a digital signal to an analogue signal (DA conversion), and is suitable for microflow driving components, such as in microfluidic chip sampling systems and proportional mixing systems. In the future, we expect this device to even be used in the automatic control system of a miniature pneumatic soft actuator.

A label-free microfluidic chip for the highly selective isolation of single and cluster CTCs from breast cancer patients

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Our results showed that this new chip had an important clinical value of patients with metastatic breast cancer.

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CTCs count showed good prospects in monitoring cancer prognosis and guiding future individualized treatment.

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We have manufactured a new microfluidic chip to isolate and identify CTCs and CTCs clusters with high throughput.

Background

Circulating tumor cells (CTCs) existing in peripheral blood can be used to predict the prognosis and survival of cancer patients. The study was designed to detect circulating tumor cells and circulating tumor single cell genes by applying microfluidic chip technology. It was used to explore the clinical application value in breast cancer.

Methods

We have developed a size-based CTCs sorting microfluidic chip, which contains a hexagonal array and a micro-pipe channel array to isolate and confirm both single CTCs and CTCs clusters. The sorting performance of the as-fabricated chip was tested by analyzing the clinical samples collected from 129 breast cancer patients and 50 healthy persons.

Results

In this study, the chip can detect different immunophenotypes of CTCs in breast cancer patients. It was found that the new microfluidic device had high sensitivity (73.6%) and specificity (82.0%) in detecting CTCs. By detecting the blood samples of 129 breast cancer patients and 50 healthy blood donors, it was found that the number of CTCs was not associated with clinical factors such as age, gender, pathological type, and tumor size of breast cancer patients (P > 0.05), but was associated with TNM staging of breast cancer, with or without metastasis (P < 0.005). There was a statistically significant difference in the number of CTCs between luminal A (ER+/PR+/HER2-) and HER-2+ (ER-/PR-/HER2+) (P < 0.05). The best cut-off level distinguished by CTC between the breast cancer patients and the healthy persons was 3.5 cells/mL, with 0.845 for AUC-ROC, 0.790–0.901 for 95% CI, 73.6% for sensitivity, and 82% for specificity (P = 0.000). The combination of CTC, CEA, CA125 and CA153 can provide more effective breast cancer screening.

Conclusions

The CTCs analysis method presented here doesn't rely on the specific antibody, such as anti-EpCAM, which would avoid the missed inspection caused by antibody-relied methods and offer more comprehensive biological information for clinical breast cancer diagnosis and treatment.

Recent Advances in Microfluidics-Based Chromatography—A Mini Review

Microfluidics-based liquid chromatography is based on the miniaturization of the different types of liquid chromatography (LC) systems (e.g., affinity, adsorption, size exclusion, ion exchange) on a microchip to perform on-chip separation of different types of analytes. On-chip chromatography finds applications in genomics, proteomics, biomarker discovery, and environmental analysis. Microfluidics-based chromatography has good reproducibility and small sample consumption. However, the on-chip chromatography fabrication techniques are often more challenging to perform than conventional LC column preparation. Different research groups have attempted to develop different techniques to fabricate microfluidics-based LC systems. In this review, we will summarize the recent advances in microfluidics-based chromatography.

Effect of Varying Expression of EpCAM on the Efficiency of CTCs Detection by SERS-Based Immunomagnetic Optofluidic Device

Simple Summary

In this work we present a magnetically supported SERS-based immunoassay based on solid SERS-active support for the detection of circulating tumor cells. The SERS response in our optofluidic device was correlated with the level of EpCAM expression. The level of EpCAM cell expression in four cell lines with relatively high (human metastatic prostate adenocarcinoma cells (LNCaP)), medium (human metastatic prostate adenocarcinoma cells (LNCaP)), weak (human metastatic prostate adenocarcinoma cells (LNCaP)), and no EpCAM expressions (cervical cancer cells (HeLa) has been estimated using Western Blot method supported by immunochemistry and correlated with responses of immunomagnetic SERS-based analysis. The capture efficiency of developed assay was investigated in metastatic lung cancer patients. The assay demonstrates the capability to detect circulating tumor cells from blood samples over a broad linear range (from 1 to 100 cells/mL) reflecting clinically relevant amount of CTCs depending on the stage of metastasis, age, applied therapy.

Abstract

The circulating tumor cells (CTCs) isolation and characterization has a great potential for non-invasive biopsy. In the present research, the surface–enhanced Raman spectroscopy (SERS)-based assay utilizing magnetic nanoparticles and solid SERS-active support integrated in the external field assisted microfluidic device was designed for efficient isolation of CTCs from blood samples. Magnetic nanospheres (Fe₂O₃) were coated with SERS-active metal and then modified with p-mercaptobenzoic acid (p-MBA) which works simultaneously as a Raman reporter and linker to an antiepithelial-cell-adhesion-molecule (anti-EpCAM) antibodies. The newly developed laser-induced SERS-active silicon substrate with a very strong enhancement factor (up to 10⁸) and high stability and reproducibility provide the additional extra-enhancement in the sandwich plasmonic configuration of immune assay which finally leads to increase the efficiency of detection. The sensitive immune recognition of cancer cells is assisted by the introducing of the controllable external magnetic field into the microfluidic chip. Moreover, the integration of the SERS-active platform and p-MBA-labeled immuno-Ag@Fe₂O₃ nanostructures with microfluidic device offers less sample and analytes demand, precise operation, increase reproducibly of spectral responses, and enables miniaturization and portability of the presented approach. In this work, we have also investigated the effect of varying expression of the EpCAM established by the Western Blot method supported by immunochemistry on the efficiency of CTCs’ detection with the developed SERS method. We used four target cancer cell lines with relatively high (human metastatic prostate adenocarcinoma cells (LNCaP)), medium (human metastatic prostate adenocarcinoma cells (LNCaP)), weak (human metastatic prostate adenocarcinoma cells (LNCaP)), and no EpCAM expressions (cervical cancer cells (HeLa)) to estimate the limits of detection based on constructed calibration curves. Finally, blood samples from lung cancer patients were used to validate the efficiency of the developed method in clinical trials.

Multi-layer assembly of cellulose nanofibrils in a microfluidic device for the selective capture and release of viable tumor cells from whole blood

According to reports by the World Health Organization (WHO), cancer-related deaths reached almost 10 million in 2018. Nearly 65% of these deaths occurred in low- to middle-income countries, a trend that is bound to increase since cancer diagnostics are not currently considered a priority in resource-limited settings (RLS). Thus, cost-effective and specific cancer screening and diagnostics tools are in high demand, particularly in RLS. The selective isolation and up-concentration of rare cells while maintaining cell viability and preventing phenotypic changes is a powerful tool to allow accurate and sensitive downstream analysis. Here, multi-layer cellulose nanofibril-based coatings functionalized with anti-EpCAM antibodies on the surface of disposable microfluidic devices were optimized for specific capture of target cells, followed by efficient release without significant adverse effects. HCT 116 colon cancer cells were captured in a single step with >97% efficiency at 41.25 μL min-1 and, when spiked in whole blood, an average enrichment factor of ∼200-fold relative to white blood cells was achieved. The release of cells was performed by enzymatic digestion of the cellulose nanofibrils which had a negligible impact on cell viability. In particular, >80% of the cells were recovered with at least 97% viability in less than 30 min. Such performance paves the way to expand and improve clinical diagnostic applications by simplifying the isolation of circulating tumor cells (CTCs) and other rare cells directly from whole blood.

Dual-Isolation and Profiling of Circulating Tumor Cells and Cancer Exosomes from Blood Samples with Melanoma Using Immunoaffinity-Based Microfluidic Interfaces

Melanoma is among the most aggressive cancers, and its rate of incidence continues to grow. Early detection of melanoma has been hampered due to the lack of promising markers for testing. Recent advances in liquid biopsy have proposed noninvasive alternatives for cancer diagnosis and monitoring. Circulating tumor cells (CTCs) and cancer-exosomes are gaining influence as promising biomarkers because of their cancer-associated molecular markers and signatures. However, technologies that offer the dual-isolation of CTCs and exosomes using a single sample have not been thoroughly developed. The dual-utilization OncoBean (DUO) device is conjugated with melanoma specific antibodies, MCAM and MCSP, enabling simultaneous CTC and exosome isolations. Using blood samples from patients, CTCs and exosomes are specifically isolated from a single sample and then undergo molecular profiling for comprehensive study. Melanoma patients have 0-17CTCs mL-1 and 299 µg exosomal protein mL-1 while healthy donors display fewer than 2CTCs and 75.6 µg of exosomes mL-1, respectively. It is also demonstrated that both markers express melanoma-associated genes using multiplex qRT-PCR to test for expression pattern of a 96 gene panel. The dual isolation and molecular characterization will allow for further research into melanoma to identify viable markers for disease progression and treatment efficacy.

Incorporation of lateral microfiltration with immunoaffinity for enhancing the capture efficiency of rare cells

The methods for isolating rare cells such as circulating tumor cells (CTCs) can be generally classified into two categories: those based on physical properties (e.g., size) and methods based on biological properties (e.g., immunoaffinity). CellSearch, the only FDA-approved method for the CTC-based cancer prognosis, relies on immunoaffinity interactions between CTCs and antibodies immobilized on magnetic particles. Immunoaffinity-based CTC isolation has also been employed in microfluidic devices, which show higher capture efficiency than CellSearch. We report here our investigation of combining size-based microfiltration into a microfluidic device with immunoaffinity for enhanced capture efficiency of CTCs. The device consists of four serpentine main channels, and each channel contains an array of lateral filters that create a two-dimensional flow. The main flow is through the serpentine channel, allowing the majority of the sample to pass by while the secondary flow goes through the lateral filters. The device design is optimized to make all fluid particles interact with filters. The filter sizes range from 24 to 12 µm, being slightly larger than or having similar dimension of CTCs. These filters are immobilized with antibodies specific to CTCs and thus they function as gates, allowing normal blood cells to pass by while forcing the interactions between CTCs and antibodies on the filter surfaces. The hydrodynamic force experienced by a CTC was also studied for optimal experimental conditions to ensure immunoaffinity-enabled cell capture. The device was evaluated by capturing two types of tumor cells spiked in healthy blood or a buffer, and we found that their capture efficiency was between 87.2 and 93.5%. The platform was further validated by isolating CTCs from blood samples of patients with metastatic pancreatic cancer.

Immunomagnetic separation of circulating tumor cells with microfluidic chips and their clinical applications

Circulating tumor cells (CTCs) are tumor cells detached from the original lesion and getting into the blood and lymphatic circulation systems. They potentially establish new tumors in remote areas, namely, metastasis. Isolation of CTCs and following biological molecular analysis facilitate investigating cancer and coming out treatment. Since CTCs carry important information on the primary tumor, they are vital in exploring the mechanism of cancer, metastasis, and diagnosis. However, CTCs are very difficult to separate due to their extreme heterogeneity and rarity in blood. Recently, advanced technologies, such as nanosurfaces, quantum dots, and Raman spectroscopy, have been integrated with microfluidic chips. These achievements enable the next generation isolation technologies and subsequent biological analysis of CTCs. In this review, we summarize CTCs' separation with microfluidic chips based on the principle of immunomagnetic isolation of CTCs. Fundamental insights, clinical applications, and potential future directions are discussed.

Possible role of circulating tumor cells in early detection of lung cancer

The prognosis of lung cancer varies highly depending on the disease stage at diagnosis, from a 5-year survival rate close to 90% in stage I, to 10% or less in stage IV disease. The enhancement of early diagnosis of this malignancy is mandatory to improve prognosis, because lung cancer patients stay long asymptomatic or few symptomatic after disease onset. Nowadays, liquid biopsy has emerged as a minimally-invasive tool to address the urgent need for real time monitoring, stratification, and personalized treatment of malignancies, including lung cancer. Liquid biopsy refers to a class of biomarkers, including circulating tumor cells (CTCs), cell-free circulating tumor DNA (ctDNA) and tumor-derived extracellular vesicles (tdEV). Since CTCs represent a crucial step in disease progression and metastasis, we reviewed here the scientific literature about the use of CTCs in early diagnosis of lung cancer; different techniques, and different strategies (e.g., source of analysis sample or high-risk groups of patients) were discussed showing the potential of implementing liquid biopsy in the clinical routine of non-metastatic lung cancer.

An Immune-Magnetophoretic Device for the Selective and Precise Enrichment of Circulating Tumor Cells from Whole Blood

Here, we validated the clinical utility of our previously developed microfluidic device, GenoCTC, which is based on bottom magnetophoresis, for the isolation of circulating tumor cells (CTCs) from patient whole blood. GenoCTC allowed 90% purity, 77% separation rate, and 80% recovery of circulating tumor cells at a 90 μL/min flow rate when tested on blood spiked with epithelial cell adhesion molecule (EpCAM)-positive Michigan Cancer Foundation-7 (MCF7) cells. Clinical studies were performed using blood samples from non-small cell lung cancer (NSCLC) patients. Varying numbers (2 to 114) of CTCs were found in each NSCLC patient, and serial assessment of CTCs showed that the CTC count correlated with the clinical progression of the disease. The applicability of GenoCTC to different cell surface biomarkers was also validated in a cholangiocarcinoma patient using anti-EPCAM, anti-vimentin, or anti-tyrosine protein kinase MET (c-MET) antibodies. After EPCAM-, vimentin-, or c-MET-positive cells were isolated, CTCs were identified and enumerated by immunocytochemistry using anti-cytokeratin 18 (CK18) and anti-CD45 antibodies. Furthermore, we checked the protein expression of PDL1 and c-MET in CTCs. A study in a cholangiocarcinoma patient showed that the number of CTCs varied depending on the biomarker used, indicating the importance of using multiple biomarkers for CTC isolation and enumeration.

Microfluidic device for high-throughput affinity-based isolation of extracellular vesicles

Immunoaffinity based EV isolation technologies use antibodies targeting surface markers on EVs to provide higher isolation specificity and purity compared to existing approaches. One standing challenge for researchers is how to release captured EVs from the substrate to increase downstream and biological studies. The strong binding between the antibody and antigen or the antibody and substrate is commonly unbreakable without operating at conditions outside of the critical physiological range, making the release of EVs problematic. Additionally, immuno-affinity approaches are usually low-throughput due to their low flow velocity to ensure adequate time for antibody-antigen binding. To overcome these limitations, we modified the OncoBean chip, a previously reported circulating tumor cell isolation microfluidic device. The OncoBean chip is a radial flow microfluidic device with bean-shape microposts functionalized with biotin-conjugated EPCAM antibody through biotin-avidin link chemistry. It was demonstrated that the high surface area and varying shear rate provided by the bean-shaped posts and the radial flow design in the chip, enabled efficient capture of CTCs at high flow rate. We replace the anti-EPCAM with antibodies that recognize common EV surface markers to achieve high-throughput EV isolation. Moreover, by incorporating desthiobiotin-conjugated antibodies, EVs can be released from the device after capture, which offers a significant improvement over the existing isolation. The released EVs were found to be functional by confirming their uptake by cells using flow cytometry and fluorescent microscopy. We believe the proposed technology can facilitate both the study of EVs as cell-to-cell communicators and the further identification of EV markers.

OPENchip: an on-chip in situ molecular profiling platform for gene expression analysis and oncogenic mutation detection in single circulating tumour cells

Liquid biopsy holds promise towards practical implementation of personalized theranostics of cancer. In particular, circulating tumour cells (CTCs) can provide clinically actionable information that can be directly linked to prognosis or therapy decisions. In this study, gene expression patterns and genetic mutations in single CTCs are simultaneously analysed by strategically combining microfluidic technology and in situ molecular profiling technique. Towards this, the development and demonstration of the OPENchip (On-chip Post-processing ENabling chip) platform for single CTC analysis by epithelial CTC enrichment and subsequent in situ molecular profiling is reported. For in situ molecular profiling, padlock probes that identify specific desired targets to examine biomarkers of clinical relevance in cancer diagnostics were designed and used to create libraries of rolling circle amplification products. We characterize the OPENchip in terms of its capture efficiency and capture purity, and validate the probe design using different cell lines. By integrating the obtained results, molecular analyses of CTCs from metastatic breast cancer (HER2 (ERBB2) gene expression and PIK3CA mutations) and metastatic pancreatic cancer (KRAS gene mutations) patients were demonstrated without any off-chip processes. The results substantiate the potential implementation of early molecular detection of cancer through sequencing-free liquid biopsy.

Recent Advances in Microfluidic Platforms Applied in Cancer Metastasis: Circulating Tumor Cells' (CTCs) Isolation and Tumor-On-A-Chip

Cancer remains the leading cause of death worldwide despite the enormous efforts that are made in the development of cancer biology and anticancer therapeutic treatment. Furthermore, recent studies in oncology have focused on the complex cancer metastatic process as metastatic disease contributes to more than 90% of tumor-related death. In the metastatic process, isolation and analysis of circulating tumor cells (CTCs) play a vital role in diagnosis and prognosis of cancer patients at an early stage. To obtain relevant information on cancer metastasis and progression from CTCs, reliable approaches are required for CTC detection and isolation. Additionally, experimental platforms mimicking the tumor microenvironment in vitro give a better understanding of the metastatic microenvironment and antimetastatic drugs' screening. With the advancement of microfabrication and rapid prototyping, microfluidic techniques are now increasingly being exploited to study cancer metastasis as they allow precise control of fluids in small volume and rapid sample processing at relatively low cost and with high sensitivity. Recent advancements in microfluidic platforms utilized in various methods for CTCs' isolation and tumor models recapitulating the metastatic microenvironment (tumor-on-a-chip) are comprehensively reviewed. Future perspectives on microfluidics for cancer metastasis are proposed.

Sensor-Integrated Microfluidic Approaches for Liquid Biopsies Applications in Early Detection of Cancer

Cancer represents one of the conditions with the most causes of death worldwide. Common methods for its diagnosis are based on tissue biopsies-the extraction of tissue from the primary tumor, which is used for its histological analysis. However, this technique represents a risk for the patient, along with being expensive and time-consuming and so it cannot be frequently used to follow the progress of the disease. Liquid biopsy is a new cancer diagnostic alternative, which allows the analysis of the molecular information of the solid tumors via a body fluid draw. This fluid-based diagnostic method displays relevant advantages, including its minimal invasiveness, lower risk, use as often as required, it can be analyzed with the use of microfluidic-based platforms with low consumption of reagent, and it does not require specialized personnel and expensive equipment for the diagnosis. In recent years, the integration of sensors in microfluidics lab-on-a-chip devices was performed for liquid biopsies applications, granting significant advantages in the separation and detection of circulating tumor nucleic acids (ctNAs), circulating tumor cells (CTCs) and exosomes. The improvements in isolation and detection technologies offer increasingly sensitive and selective equipment's, and the integration in microfluidic devices provides a better characterization and analysis of these biomarkers. These fully integrated systems will facilitate the generation of fully automatized platforms at low-cost for compact cancer diagnosis systems at an early stage and for the prediction and prognosis of cancer treatment through the biomarkers for personalized tumor analysis.

Epithelial-Mesenchymal Plasticity in Circulating Tumor Cells, the Precursors of Metastasis

Circulating tumor cells offer an unprecedented window into the metastatic cascade, and to some extent can be considered as intermediates in the process of metastasis. They exhibit dynamic oscillations in epithelial to mesenchymal plasticity and provide important opportunities for prognosis, therapy response monitoring, and targeting of metastatic disease. In this manuscript, we review the involvement of epithelial-mesenchymal plasticity in the early steps of metastasis and what we have learned about its contribution to genomic instability and genetic diversity, tumor progression and therapeutic responses using cell culture, mouse models and circulating tumor cells enriched from patients.

Microfluidics for label-free sorting of rare circulating tumor cells

A review discussing the working principles and performances of label-free CTC sorting methods.

Acoustofluidic methods in cell analysis

Cellular analysis is a central concept for both biology and medicine. Over the past two decades, acoustofluidic technologies, which marry acoustic waves with microfluidics, have significantly contributed to the development of innovative approaches for cellular analysis. Acoustofluidic technologies enable precise manipulations of cells and the fluids that confine them, and these capabilities have been utilized in many cell analysis applications. In this review article, we examine various applications where acoustofluidic methods have been implemented, including cell imaging, cell mechanotyping, circulating tumor cell phenotyping, sample preparation in clinics, and investigation of cell-cell interactions and cell-environment responses. We also provide our perspectives on the technological advantages, limitations, and potential future directions for this innovative field of methods.

Microfluidic technologies for circulating tumor cell isolation

Metastasis is the main cause of tumor-related death, and the dispersal of tumor cells through the circulatory system is a critical step in the metastatic process. Early detection and analysis of circulating tumor cells (CTCs) is therefore important for early diagnosis, prognosis, and effective treatment of cancer, enabling favorable clinical outcomes in cancer patients. Accurate and reliable methods for isolating and detecting CTCs are necessary to obtain this clinical information. Over the past two decades, microfluidic technologies have demonstrated great potential for isolating and detecting CTCs from blood. The present paper reviews current advanced microfluidic technologies for isolating CTCs based on various biological and physical principles, and discusses their fundamental advantages and drawbacks for subsequent cellular and molecular assays. Owing to significant genetic heterogeneity among CTCs, microfluidic technologies for isolating individual CTCs have recently been developed. We discuss these single-cell isolation methods, as well as approaches to overcoming the limitations of current microfluidic CTC isolation technologies. Finally, we provide an overview of future innovative microfluidic platforms.

Immunofunctional photodegradable poly(ethylene glycol) hydrogel surfaces for the capture and release of rare cells

Circulating tumor cells (CTCs) play a central role in cancer metastasis and represent a rich source of data for cancer prognostics and therapeutic guidance. Reliable CTC recovery from whole blood therefore promises a less invasive and more sensitive approach to cancer diagnosis and progression tracking. CTCs, however, are exceedingly rare in whole blood, making their quantitative recovery challenging. Several techniques capable of isolating these rare cells have been introduced and validated, yet most suffer from low CTC purity or viability, both of which are essential to develop a clinically viable CTC isolation platform. To address these limitations, we introduce a patterned, immunofunctional, photodegradable poly(ethylene glycol) (PEG) hydrogel capture surface for the isolation and selective release of rare cell populations. Flat and herringbone capture surfaces were successfully patterned via PDMS micromolding and photopolymerization of photolabile PEG hydrogels. Patterned herringbone surfaces, designed to convectively transport cells to the capture surface, exhibited improved capture density relative to flat surfaces for target cell capture from buffer, buffy coat, and whole blood. Uniquely, captured cells were released for collection by degrading the hydrogel capture surface with either bulk or targeted irradiation with cytocompatible doses of long wavelength UV light. Recovered cells remained viable following capture and release and exhibited similar growth rates as untreated control cells. The implementation of molded photodegradable PEG hydrogels as a CTC capture surface provides a micropatternable, cytocompatible platform that imparts the unique ability to recover pure, viable CTC samples by selectively releasing target cells.

Highlighting the uniqueness in dielectrophoretic enrichment of circulating tumor cells

Circulating tumor cells (CTCs) play an essential role in the metastasis of tumors, and thus can serve as a valuable prognostic factor for malignant diseases. As a result, the ability to isolate and characterize CTCs is essential. This review underlines the potential of dielectrophoresis for CTCs enrichment. It begins by summarizing the key performance parameters and challenges of CTCs isolation using microfluidics. The two main categories of CTCs enrichment-affinity-based and label-free methods-are analysed, emphasising the advantages and disadvantages of each as well as their clinical potential. While the main argument in favour of affinity-based methods is the strong specificity of CTCs isolation, the major advantage of the label-free technologies is in preserving the integrity of the cellular membrane, an essential requirement for downstream characterization. Moving forward, we try to answer the main question: "What makes dielectrophoresis a method of choice in CTCs isolation?" The uniqueness of dielectrophoretic CTCs enrichment resides in coupling the specificity of the isolation process with the conservation of the membrane surface. The specificity of the dielectrophoretic method stems from the differences in the dielectric properties between CTCs and other cells in the blood: the capacitances of the malignantly transformed cellular membranes of CTCs differ from those of other cells. Examples of dielectrophoretic devices are described and their performance evaluated. Critical requirements for using dielectrophoresis to isolate CTCs are highlighted. Finally, we consider that DEP has the potential of becoming a cytometric method for large-scale sorting and characterization of cells.