Versatile label free biochip for the detection of circulating tumor cells from peripheral blood in cancer patients

Deep learning assisted holography microscopy for in-flow enumeration of tumor cells in blood

Currently, detection of circulating tumor cells (CTCs) in cancer patient blood samples relies on immunostaining, which does not provide access to live CTCs, limiting the breadth of CTC-based applications. Here, we take the first steps to address this limitation, by demonstrating staining-free enumeration of tumor cells spiked into lysed blood samples using digital holographic microscopy (DHM), microfluidics and machine learning (ML). A 3D-printed module for laser assembly was developed to simplify the optical set up for holographic imaging of cells flowing through a sheath-based microfluidic device. Computational reconstruction of the holograms was performed to localize the cells in 3D and obtain the plane of best focus images to train deep learning models. We developed a custom-designed light-weight shallow Network dubbed s-Net and compared its performance against off-the-shelf CNN models including ResNet-50. The accuracy, sensitivity and specificity of the s-Net model was found to be higher than the off-the-shelf ML models. By applying an optimized decision threshold to mixed samples prepared in silico, the false positive rate was reduced from 1 × 10^-2 to 2.77 × 10^-4. Finally, the developed DHM-ML framework was successfully applied to enumerate spiked MCF-7 breast cancer cells and SkOV3 ovarian cancer cells from lysed blood samples containing white blood cells (WBCs) at concentrations typical of label-free enrichment techniques. We conclude by discussing the advances that need to be made to translate the DHM-ML approach to staining-free enumeration of actual CTCs in cancer patient blood samples.

CTC-5: A novel digital pathology approach to characterise circulating tumour cell biodiversity

Metastatic progression and tumor evolution complicates the clinical management of cancer patients. Circulating tumor cell (CTC) characterization is a growing discipline that aims to elucidate tumor metastasis and evolution processes. CTCs offer the clinical potential to monitor cancer patients for therapy response, disease relapse, and screen 'at risk' groups for the onset of malignancy. However, such clinical utility is currently limited to breast, prostate, and colorectal cancer patients. Further understanding of the basic CTC biology of other malignancies is required to progress them towards clinical utility. Unfortunately, such basic clinical research is often limited by restrictive characterization methods and high-cost barrier to entry for CTC isolation and imaging infrastructure. As experimental clinical results on applications of CTC are accumulating, it is becoming clear that a two-tier system of CTC isolation and characterization is required. The first tier is to facilitate basic research into CTC characterization. This basic research then informs a second tier specialised in clinical prognostic and diagnostic testing. This study presented in this manuscript describes the development and application of a low-cost, CTC isolation and characterization pipeline; CTC-5. This approach uses an established 'isolation by size' approach (ScreenCell Cyto) and combines histochemical morphology stains and multiparametric immunofluorescence on the same isolated CTCs. This enables capture and characterization of CTCs independent of biomarker-based pre-selection and accommodates both single CTCs and clusters of CTCs. Additionally, the developed open-source software is provided to facilitate the synchronization of microscopy data from multiple sources (https://github.com/CTC5/). This enables high parameter histochemical and immunofluorescent analysis of CTCs with existing microscopy infrastructure without investment in CTC specific imaging hardware. Our approach confirmed by the number of successful tests represents a potential major advance towards highly accessible low-cost technology aiming at the basic research tier of CTC isolation and characterization. The biomarker independent approach facilitates closing the gap between malignancies with poorly, and well-defined CTC phenotypes. As is currently the case for some of the most commonly occurring breast, prostate and colorectal cancers, such advances will ultimately benefit the patient, as early detection of relapse or onset of malignancy strongly correlates with their prognosis.

A micropillar array-based microfluidic chip for label-free separation of circulating tumor cells: The best micropillar geometry?

INTRODUCTION

The information derived from the number and characteristics of circulating tumor cells (CTCs), is crucial to ensure appropriate cancer treatment monitoring. Currently, diverse microfluidic platforms have been developed for isolating CTCs from blood, but it remains a challenge to develop a low-cost, practical, and efficient strategy.

OBJECTIVES

This study aimed to isolate CTCs from the blood of cancer patients via introducing a new and efficient micropillar array-based microfluidic chip (MPA-Chip), as well as providing prognostic information and monitoring the treatment efficacy in cancer patients.

METHODS

We fabricated a microfluidic chip (MPA-Chip) containing arrays of micropillars with different geometries (lozenge, rectangle, circle, and triangle). We conducted numerical simulations to compare velocity and pressure profiles inside the micropillar arrays. Also, we experimentally evaluated the capture efficiency and purity of the geometries using breast and prostate cancer cell lines as well as a blood sample. Moreover, the device's performance was validated on 12 patients with breast cancer (BC) in different states.

RESULTS

The lozenge geometry was selected as the most effective and optimized micropillar design for CTCs isolation, providing high capture efficiency (>85 %), purity (>90 %), and viability (97 %). Furthermore, the lozenge MPA-chip was successfully validated by the detection of CTCs from 12 breast cancer (BC) patients, with non-metastatic (median number of 6 CTCs) and metastatic (median number of 25 CTCs) diseases, showing different prognoses. Also, increasing the chemotherapy period resulted in a decrease in the number of captured CTCs from 23 to 7 for the metastatic patient. The MPA-Chip size was only 0.25 cm² and the throughput of a single chip was 0.5 ml/h, which can be increased by multiple MPA-Chips in parallel.

CONCLUSION

The lozenge MPA-Chip presented a novel micropillar geometry for on-chip CTC isolation, detection, and staining, and in the future, the possibilities can be extended to the culture of the CTCs.

An electroactive microwell array device to realize simultaneous trapping of single cancer cells and clusters

The importance of circulating tumor cells (CTCs) as biomarkers has been greatly increased for early diagnosis and detection of cancer metastases. Along with a single form of CTCs, CTC clusters have recently attracted much attention due to their characteristics, such as suppression of apoptosis and survival from immune responses with high metastatic potential. Thus, it is highly necessary to investigate not only single cells but clustered cells at the same time to perform precise analysis of the current cancer state and develop suitable treatment. However, no cancer marker-free microfluidic devices have been realized to trap single cells and clusters at the same time in a single device yet. In this paper, we introduced a novel microfluidic device utilizing a microwell-on-electrode (MOE) array to realize simultaneous trapping of a single cell and clustered cells at a single cell/cluster level. Cell-sized microwells fabricated on interdigitated electrodes efficiently arrayed single cells with high trapping efficiency and single-cell occupancy (more than 90%) using dielectrophoresis (DEP). This high single cell trapping performance of MOE allows arraying of single clusters by trapping one of the cells that constitute a cluster. The feasibility of the MOE device for simultaneous arraying of single cancer cells and clusters was demonstrated by trapping a mixture of single cancer cells and clusters and measuring the size distribution of trapped clusters, which was almost identical with that of introduced cell population. Our work demonstrated that the developed MOE device can be one of the promising methods for trapping single cancer cells as well as clusters on a single device for cancer diagnosis and performing further analyses at a single cell/cluster level.

Detection of live breast cancer cells in bright-field microscopy images containing white blood cells by image analysis and deep learning

SIGNIFICANCE

Circulating tumor cells (CTCs) are important biomarkers for cancer management. Isolated CTCs from blood are stained to detect and enumerate CTCs. However, the staining process is laborious and moreover makes CTCs unsuitable for drug testing and molecular characterization.

AIM

The goal is to develop and test deep learning (DL) approaches to detect unstained breast cancer cells in bright-field microscopy images that contain white blood cells (WBCs).

APPROACH

We tested two convolutional neural network (CNN) approaches. The first approach allows investigation of the prominent features extracted by CNN to discriminate in vitro cancer cells from WBCs. The second approach is based on faster region-based convolutional neural network (Faster R-CNN).

RESULTS

Both approaches detected cancer cells with higher than 95% sensitivity and 99% specificity with the Faster R-CNN being more efficient and suitable for deployment presenting an improvement of 4% in sensitivity. The distinctive feature that CNN uses for discrimination is cell size, however, in the absence of size difference, the CNN was found to be capable of learning other features. The Faster R-CNN was found to be robust with respect to intensity and contrast image transformations.

CONCLUSIONS

CNN-based DL approaches could be potentially applied to detect patient-derived CTCs from images of blood samples.

A review of enrichment methods for circulating tumor cells: from single modality to hybrid modality

Circulating tumor cell (CTC) analysis as a liquid biopsy can be used for early diagnosis of cancer, evaluating cancer progression, and assessing treatment efficacy. The enrichment of CTCs from patient blood is important for CTC analysis due to the extreme rarity of CTCs. This paper updates recent advances in CTC enrichment methods. We first review single-modality methods, including biophysical and biochemical methods. Hybrid-modality methods, combining at least two single-modality methods, are gaining increasing popularity for their improved performance. Then this paper reviews hybrid-modality methods, which are categorized into integrated and sequenced hybrid-modality methods. The state of the art indicates that the CTC capture efficiencies of integrated hybrid-modality methods can reach 85% or higher by taking advantage of the superimposed and enhanced capture effects from multiple single-modality methods. Moreover, a hybrid method integrating biophysical with biochemical methods is characterized by both high processing rate and high specificity.

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.

Circulating Tumor Cells: Technologies and Their Clinical Potential in Cancer Metastasis

Circulating tumor cells (CTCs) are single cells or clusters of cells within the circulatory system of a cancer patient. While most CTCs will perish, a small proportion will proceed to colonize the metastatic niche. The clinical importance of CTCs was reaffirmed by the 2008 FDA approval of CellSearch^®, a platform that could extract EpCAM-positive, CD45-negative cells from whole blood samples. Many further studies have demonstrated the presence of CTCs to stratify patients based on overall and progression-free survival, among other clinical indices. Given their unique role in metastasis, CTCs could also offer a glimpse into the genetic drivers of metastasis. Investigation of CTCs has already led to groundbreaking discoveries such as receptor switching between primary tumors and metastatic nodules in breast cancer, which could greatly affect disease management, as well as CTC-immune cell interactions that enhance colonization. In this review, we will highlight the growing variety of isolation techniques for investigating CTCs. Next, we will provide clinically relevant context for CTCs, discussing key clinical trials involving CTCs. Finally, we will provide insight into the future of CTC studies and some questions that CTCs are primed to answer.

Anticlogging Hemofiltration Device for Mass Collection of Circulating Tumor Cells by Ligand-Free Size Selection

A new hemofiltration system was developed to continuously capture circulating tumor cells (CTCs) from a large volume of whole blood using a column that was packed with antifouling zwitterionized silica microspheres. The silica microspheres were modified with sulfobetaine silane (SBSi) to inhibit fouling, resist clogging, and give a high surface wettability and prolonged operation time. Packed microspheres with different diameters formed size-controllable interstitial pores that effectively captured CTCs by ligand-free size selection. For optimized performance of the hemofiltration system, operational factors, including the size of microspheres, flow rate, and cross-sectional area of the column, were considered with respect to the removal rate for colorectal cancer cells and the retention rate for white blood cells and red blood cells. The captured CTCs were collected from the column by density sedimentation. A large quantity of colorectal cancer cells was spiked into sheep blood, and the sample was circulated for 5 h with a total operational volume of 2 L followed by collection and culture in vitro. The results showed that the proposed hemofiltration device selectively removed abundant CTCs from in vitro circulatory blood. The viable cells were harvested for amplification and potential applications for precision medicine.

Microtechnology-enabled filtration-based liquid biopsy: challenges and practical considerations

Liquid biopsy, an important enabling technology for early diagnosis and dynamic monitoring of cancer, has drawn extensive attention in the past decade. With the rapid developments of microtechnology, it has been possible to manipulate cells at the single-cell level, which dramatically improves the liquid biopsy capability. As the microtechnology-enabled liquid biopsy matures from proof-of-concept demonstrations towards practical applications, a main challenge it is facing now is to process clinical samples which are usually of a large volume while containing very rare targeted cells in complex backgrounds. Therefore, a high-throughput liquid biopsy which is capable of processing liquid samples with a large volume in a reasonable time along with a high recovery rate of rare targeted cells from complex clinical liquids is in high demand. Moreover, the purity, viability and release feasibility of recovered targeted cells are the other three key impact factors requiring careful considerations. To date, among the developed techniques, micropore-type filtration has been acknowledged as the most promising solution to address the aforementioned challenges in practical applications. However, the presently reported studies about micropore-type filtration are mostly based on trial and error for device designs aiming at different cancer types, which requires lots of efforts. Therefore, there is an urgent need to investigate and elaborate the fundamental theories of micropore-type filtration and key features that influence the working performances in the liquid biopsy of real clinical samples to promote the application efficacy in practical applications. In this review, the state of the art of microtechnology-enabled filtration is systematically and comprehensively summarized. Four key features of the filtration, including throughput, purity, viability and release feasibility of the captured targeted cells, are elaborated to provide the guidelines for filter designs. The recent progress in the filtration mode modulation and sample standardization to improve the filtration performance of real clinical samples is also discussed. Finally, this review concludes with prospective views for future developments of filtration-based liquid biopsy to promote its application efficacy in clinical practice.

Sequential Ensemble-Decision Aliquot Ranking Isolation and Fluorescence In Situ Hybridization Identification of Rare Cells from Blood by Using Concentrated Peripheral Blood Mononuclear Cells

Isolation and analysis of circulating rare cells is a promising approach for early detection of cancer and other diseases and for prenatal diagnosis. Isolation of rare cells is usually difficult due to their heterogeneity as well as their low abundance in peripheral blood. We previously reported a two-stage ensemble-decision aliquot ranking platform (S-eDAR) for isolating circulating tumor cells from whole blood with high throughput, high recovery rate (>90%), and good purity (>70%), allowing detection of low surface antigen-expressing cancer cells linked to metastasis. However, due to the scarcity of these cells, large sample volumes and large quantities of antibodies were required to isolate sufficient cells for downstream analysis. Here, we drastically increased the number of nucleated cells analyzed by first concentrating peripheral blood mononuclear cells (PBMCs) from whole blood by density gradient centrifugation. The S-eDAR platform was capable of isolating rare cells from concentrated PBMCs (10⁸/mL, equivalent to processing ∼20 mL of whole blood in the 1 mL sample volume used by our instrument) at a high recovery rate (>85%). We then applied the S-eDAR platform for isolating rare fetal nucleated red blood cells (fNRBCs) from concentrated PBMCs spiked with umbilical cord blood cells and confirmed fNRBC recovery by immunostaining and fluorescence in situ hybridization, demonstrating the potential of the S-eDAR system for isolating rare fetal cells from maternal PBMCs to improve noninvasive prenatal diagnosis.

A Review on Microdevices for Isolating Circulating Tumor Cells

Cancer metastasis is the primary cause of high mortality of cancer patients. Enumeration of circulating tumor cells (CTCs) in the bloodstream is a very important indicator to estimate the therapeutic outcome in various metastatic cancers. The aim of this article is to review recent developments on the CTC isolation technologies in microdevices. Based on the categories of biochemical and biophysical isolation approaches, a literature review and in-depth discussion will be included to provide an overview of this challenging topic. The current excellent developments suggest promising CTC isolation methods in order to establish a precise indicator of the therapeutic outcome of cancer patients.

Characterization of a novel automated microfiltration device for the efficient isolation and analysis of circulating tumor cells from clinical blood samples

The detection and analysis of circulating tumor cells (CTCs) may enable a broad range of cancer-related applications, including the identification of acquired drug resistance during treatments. However, the non-scalable fabrication, prolonged sample processing times, and the lack of automation, associated with most of the technologies developed to isolate these rare cells, have impeded their transition into the clinical practice. This work describes a novel membrane-based microfiltration device comprised of a fully automated sample processing unit and a machine-vision-enabled imaging system that allows the efficient isolation and rapid analysis of CTCs from blood. The device performance was characterized using four prostate cancer cell lines, including PC-3, VCaP, DU-145, and LNCaP, obtaining high assay reproducibility and capture efficiencies greater than 93% after processing 7.5 mL blood samples spiked with 100 cancer cells. Cancer cells remained viable after filtration due to the minimal shear stress exerted over cells during the procedure, while the identification of cancer cells by immunostaining was not affected by the number of non-specific events captured on the membrane. We were also able to identify the androgen receptor (AR) point mutation T878A from 7.5 mL blood samples spiked with 50 LNCaP cells using RT-PCR and Sanger sequencing. Finally, CTCs were detected in 8 out of 8 samples from patients diagnosed with metastatic prostate cancer (mean ± SEM = 21 ± 2.957 CTCs/mL, median = 21 CTCs/mL), demonstrating the potential clinical utility of this device.

Differential Sorting of Microparticles Using Spiral Microchannels with Elliptic Configurations

Label-free, size-dependent cell-sorting applications based on inertial focusing phenomena have attracted much interest during the last decade. The separation capability heavily depends on the precision of microparticle focusing. In this study, five-loop spiral microchannels with a height of 90 µm and a width of 500 µm are introduced. Unlike their original spiral counterparts, these channels have elliptic configurations of varying initial aspect ratios, namely major axis to minor axis ratios of 3:2, 11:9, 9:11, and 2:3. Accordingly, the curvature of these configurations increases in a curvilinear manner through the channel. The effects of the alternating curvature and channel Reynolds number on the focusing of fluorescent microparticles with sizes of 10 and 20 µm in the prepared suspensions were investigated. At volumetric flow rates between 0.5 and 3.5 mL/min (allowing separation), each channel was tested to collect samples at the designated outlets. Then, these samples were analyzed by counting the particles. These curved channels were capable of separating 20 and 10 µm particles with total yields up to approximately 95% and 90%, respectively. The results exhibited that the level of enrichment and the focusing behavior of the proposed configurations are promising compared to the existing microfluidic channel configurations.

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.

Microfluidics for label-free sorting of rare circulating tumor cells

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

Prognostic and therapeutic significance of circulating tumor cells in patients with lung cancer

BACKGROUND

Lung cancer is the second most common cancer and the main cause of cancer-related mortality worldwide. In spite of various efforts that have been made to facilitate the early diagnosis of lung cancer, most patients are diagnosed when the disease is already in stage IV, which is generally associated with the occurrence of distant metastases and a poor survival. Moreover, a large proportion of these patients will relapse after treatment, heralding the need for the stratification of lung cancer patients in addition to identifying those who are at a higher risk of relapse and, thus, require alternative and/or additional therapies. Recently, circulating tumor cells (CTCs) have been considered as valuable markers for the early diagnosis, prognosis and risk stratification of cancer patients, and they have been found to be able to predict the survival of patients with various types of cancer, including lung cancer. Additionally, the characterization of CTCs has recently provided fascinating insights into the heterogeneity of tumors, which may be instrumental for the development of novel targeted therapies.

CONCLUSIONS

Here we review our current understanding of the significance of CTCs in lung cancer metastasis. We also discuss prominent studies reporting the utility of enumeration and characterization of CTCs in lung cancer patients as prognostic and pharmacodynamic biomarkers for those who are at a higher risk of metastasis and drug resistance.

Liquid biopsy: one cell at a time

As an alternative target to surgically resected tissue specimens, liquid biopsy has gained much attention over the past decade. Of the various circulating biomarkers, circulating tumor cells (CTCs) have particularly opened new windows into the metastatic cascade, with their functional, biochemical, and biophysical properties. Given the extreme rarity of intact CTCs and the associated technical challenges, however, analyses have been limited to bulk-cell strategies, missing out on clinically significant sources of information from cellular heterogeneity. With recent technological developments, it is now possible to probe genetic material of CTCs at the single-cell resolution to study spatial and temporal dynamics in circulation. Here, we discuss recent transcriptomic profiling efforts that enabled single-cell characterization of patient-derived CTCs spanning diverse cancer types. We further highlight how expression data of these putative biomarkers have advanced our understanding of metastatic spectrum and provided a basis for the development of CTC-based liquid biopsies to track, monitor, and predict the efficacy of therapy and any emergent resistance.

CTC analysis: an update on technological progress

There is a growing need for a more accurate, real-time assessment of tumor status and the probability of metastasis, relapse, or response to treatment. Conventional means of assessment include imaging and tissue biopsies that can be highly invasive, may not provide complete information of the disease's heterogeneity, and not ideal for repeat analysis. Therefore, a less-invasive means of acquiring similar information at greater time points is necessary. Liquid biopsies are samples of a patients' peripheral blood and hold potential of addressing these criteria. Ongoing research has revealed that a tumor can release circulating cells, genetic materials (DNA or RNA), and exosomes into circulation. These potential biomarkers can be captured in a liquid biopsy and analyzed to determine disease status. To achieve these goals, numerous technologies have been developed. In this review, we discuss both prominent and newly developed technologies for circulating tumor cell capture and analysis and their clinical impact.

High-Throughput Automated Microscopy of Circulating Tumor Cells

Circulating tumor cells (CTCs) have the potential of becoming the gold standard marker for cancer diagnosis, prognosis and monitoring. However, current methods for its isolation and characterization suffer from equipment variability and human operator error that hinder its widespread use. Here we report the design and construction of a fully automated high-throughput fluorescence microscope that enables the imaging and classification of cancer cells that were labeled by immunostaining procedures. An excellent agreement between our machine vision-based approach and a state-of-the-art microscopy equipment was achieved. Our integral approach provides a path for operator-free and robust analysis of cancer cells as a standard clinical practice.

The current status of the clinical utility of liquid biopsies in cancer

Introduction: Liquid biopsies have attracted considerable attention as potential diagnostic, prognostic, predictive, and screening assays in oncology. The term liquid biopsies include circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) in the blood. While many liquid biopsy technologies are under active investigation, relatively few liquid biopsy assays have been proven to serve as a diagnostic surrogate for biopsies of metastatic disease as predictive biomarkers to guide the selection of therapy in the clinic. Areas covered: The objective of this review is to highlight the status of liquid biopsies in solid tumors in the oncology literature with attention to proven utility as diagnostic surrogates for macrometastases. Expert opinion: Carefully designed clinical-translational studies are needed to establish the diagnostic accuracy and clinical utility of liquid biopsy biomarkers in oncology. Investigators must fully consider relevant pre-analytical variables, assay sensitivity, bioinformatics considerations as well as the clinical utility of rare event profiling in the context of the normal blood background. Future liquid biopsy research should address the concern that not all DNA mutations are expressed and should provide the means to discover potential therapeutic targets in metastatic patients via a minimally invasive blood draw.

Bioelectricity, Its Fundamentals, Characterization Methodology, and Applications in Nano-Bioprobing and Cancer Diagnosis

Bioelectricity is an essential characteristic of a biological system that has played an important role in medical diagnosis particularly in cancer liquid biopsy. However, its biophysical origin and measurements have presented great challenges in experimental methodologies. For instance, in dynamic cell processes, bioelectricity cannot be accurately determined as a static electrical potential via electrophoresis. Cancer cells fundamentally differ from normal cells by having a much higher rate of glycolysis resulting in net negative charges on cell surfaces. The most recent investigations on cancer cell surface charge that is the direct bio-electrical manifestation of the "Warburg Effect," which can be directly monitored by specially designed nanoprobes, has been provided. The most up-to-date research results from charge-mediated cell targeting are reviewed. Correlations between the cell surface charge and cancer cell metabolism are established based on cell/probe electrostatic interactions. Bioelectricity is utilized not only as an analyte for investigation of the metabolic state of the cancer cells, but also applied in electrostatically and magnetically capturing of the circulating tumor cells from whole blood. Also reviewed is on the isolation of Candida albicans via bioelectricity-driven nanoparticle binding on fungus with surface charges.

Dual-function nanostructured platform for isolation of nasopharyngeal carcinoma circulating tumor cells and EBV DNA detection

Circulating tumor cells (CTCs) and plasma levels of Epstein-Barr virus (EBV) DNA are sensitive prognostic tools for monitoring disease status in nasopharyngeal carcinoma (NPC) patients. Herein, we introduce a novel and low-cost platform for capturing CTCs, the Si nanowires/microscale pyramids (NWs/MPs) hierarchical substrate, which could capture NPC cells in vitro and also detect EBV DNA at very low concentrations. In this study, Si NWs/MPs hierarchical substrates with varying wire length were fabricated using a metal-assisted chemical etching method. Anti-EpCAM antibodies were further conjugated on the substrate for capturing NPC CTCs in vitro. Capture efficiency was evaluated using immunofluorescence and scanning electronic microscopy (SEM) was utilized to understand cell morphology. The Si NWs/MPs substrate was also transformed into a Surface enhanced Raman scattering (SERS) substrate by coating with Ag nanoparticles (AgNPs) for detection of EBV DNA by Raman spectroscopy. The results demonstrated that Si NWs/MPs with 20 min of etch time had the best capturing performance. Additionally, SEM observations revealed good contact of CTCs with Si NWs/MPs substrates. Moreover, the AgNPs-coated NWs/MPs substrate was shown to be a sensitive EBV DNA detector, by which the DNA detection limit can reach up to 10^-13M. In conclusion, the Si NWs/MPs platform not only exhibits superior cell capturing ability, but also can sensitively detect EBV DNA at very low concentrations. This platform has great potential to become a promising diagnostic tool for monitoring disease status and prognostication of NPC patients.

Sheathless High-Throughput Circulating Tumor Cell Separation Using Viscoelastic non-Newtonian Fluid

Circulating tumor cells (CTCs) have attracted increasing attention as important biomarkers for clinical and biological applications. Several microfluidic approaches have been demonstrated to separate CTCs using immunoaffinity or size difference from other blood cells. This study demonstrates a sheathless, high-throughput separation of CTCs from white blood cells (WBCs) using a viscoelastic fluid. To determine the fluid viscoelasticity and the flow rate for CTC separation, and to validate the device performance, flow characteristics of 6, 13, and 27 μm particles in viscoelastic fluids with various concentrations were estimated at different flow rates. Using 0.2% hyaluronic acid (HA) solution, MCF-7 (Michigan Cancer Foundation-7) cells mimicking CTCs in this study were successfully separated from WBCs at 500 μL/min with a separation efficiency of 94.8%. Small amounts of MCF-7 cells (~5.2%) were found at the center outlet due to the size overlap with WBCs.

Recent advances in microfluidic methods in cancer liquid biopsy

Early cancer detection, its monitoring, and therapeutical prediction are highly valuable, though extremely challenging targets in oncology. Significant progress has been made recently, resulting in a group of devices and techniques that are now capable of successfully detecting, interpreting, and monitoring cancer biomarkers in body fluids. Precise information about malignancies can be obtained from liquid biopsies by isolating and analyzing circulating tumor cells (CTCs) or nucleic acids, tumor-derived vesicles or proteins, and metabolites. The current work provides a general overview of the latest on-chip technological developments for cancer liquid biopsy. Current challenges for their translation and their application in various clinical settings are discussed. Microfluidic solutions for each set of biomarkers are compared, and a global overview of the major trends and ongoing research challenges is given. A detailed analysis of the microfluidic isolation of CTCs with recent efforts that aimed at increasing purity and capture efficiency is provided as well. Although CTCs have been the focus of a vast microfluidic research effort as the key element for obtaining relevant information, important clinical insights can also be achieved from alternative biomarkers, such as classical protein biomarkers, exosomes, or circulating-free nucleic acids. Finally, while most work has been devoted to the analysis of blood-based biomarkers, we highlight the less explored potential of urine as an ideal source of molecular cancer biomarkers for point-of-care lab-on-chip devices.

Insights on CTC Biology and Clinical Impact Emerging from Advances in Capture Technology

Circulating tumor cells (CTCs) and circulating tumor microemboli (CTM) have been shown to correlate negatively with patient survival. Actual CTC counts before and after treatment can be used to aid in the prognosis of patient outcomes. The presence of circulating tumor materials (CTMat) can advertise the presence of metastasis before clinical presentation, enabling the early detection of relapse. Importantly, emerging evidence is indicating that cancer treatments can actually increase the incidence of CTCs and metastasis in pre-clinical models. Subsequently, the study of CTCs, their biology and function are of vital importance. Emerging technologies for the capture of CTC/CTMs and CTMat are elucidating vitally important biological and functional information that can lead to important alterations in how therapies are administered. This paves the way for the development of a "liquid biopsy" where treatment decisions can be informed by information gleaned from tumor cells and tumor cell debris in the blood.

Technologies for circulating tumor cell separation from whole blood

The importance of early cancer diagnosis and improved cancer therapy has been clear for years and has initiated worldwide research towards new possibilities in the care strategy of patients with cancer using technological innovations. One of the key research fields involves the separation and detection of circulating tumor cells (CTC) because of their suggested important role in early cancer diagnosis and prognosis, namely, providing easy access by a liquid biopsy from blood to identify metastatic cells before clinically detectable metastasis occurs and to study the molecular and genetic profile of these metastatic cells. Provided the opportunity to further progress the development of technology for treating cancer, several CTC technologies have been proposed in recent years by various research groups and companies. Despite their potential role in cancer healthcare, CTC methods are currently mainly used for research purposes, and only a few methods have been accepted for clinical application because of the difficulties caused by CTC heterogeneity, CTC separation from the blood, and a lack of thorough clinical validation. Therefore, the standardization and clinical application of various developed CTC technologies remain important subsequent necessary steps. Because of their suggested future clinical benefits, we focus on describing technologies using whole blood samples without any pretreatment and discuss their advantages, use, and significance. Technologies using whole blood samples utilize size-based, immunoaffinity-based, and density-based methods or combinations of these methods as well as positive and negative enrichment during separation. Although current CTC technologies have not been truly implemented yet, they possess high potential as future clinical diagnostic techniques for the individualized therapy of patients with cancer. Thus, a detailed discussion of the clinical suitability of these new advanced technologies could help prepare clinicians for the future and can be a foundation for technologies that would be used to eliminate CTCs in vivo.

Rapid liquid biopsy for Mohs surgery: rare target cell separation from surgical margin lavage fluid with a high recovery rate and selectivity

In melanoma surgery, it is difficult to identify residual scattered tumor cells at the surgical margin because of invasive growth. Mohs surgery, widely applied to increase the cure rate and decrease the recurrence rate of melanoma, involves examination of the tissue for tumor cells after tissue removal. Here, we established a liquid biopsy platform for rapid (<5 h), sensitive examination of residual tumor cells at the margin after Mohs surgery using clinical samples from patients with pigment nevus for a demonstration. The design involved highly sensitive, selective rare target cell separation from surgical margin lavage fluid (SMLF) through micropore-arrayed filtration. High recovery rates (86.7% ± 16.3% and 72.7% ± 46.7%, respectively) for separation of spiked 5 A375s (cultured human melanoma cells) and 1 A375 from 1 mL PBS were achieved for this platform. Detection of SMLF samples from patients with pigment nevus was performed, and many (66-7420) Melan-A-positive target cells were successfully recovered and identified, demonstrating the application performance of this rapid liquid biopsy for Mohs surgery in clinical practice. Moreover, a high-selectivity separation of larger target A375 cells from smaller background Jurkat cells was achieved with a high enrichment factor (4.2 ± 1.1). In clinical practice, high selectivity contributes to effective depletion of red blood cells (RBCs), thus ensuring verification of target cells from samples with severe RBC contamination. Furthermore, target cells were obtained with high purity (2.7-35.2%). The capability of this method for rare-cell separation with a high recovery rate and good selectivity may facilitate improvement of performance of Mohs surgery for real clinical practice, including shortening examination time and increasing detection sensitivity.

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.

Continuous Separation of Circulating Tumor Cells from Whole Blood Using a Slanted Weir Microfluidic Device

The separation of circulating tumor cells (CTCs) from the peripheral blood is an important issue that has been highlighted because of their high clinical potential. However, techniques that depend solely on tumor-specific surface molecules or just the larger size of CTCs are limited by tumor heterogeneity. Here, we present a slanted weir microfluidic device that utilizes the size and deformability of CTCs to separate them from the unprocessed whole blood. By testing its ability using a highly invasive breast cancer cell line, our device achieved a 97% separation efficiency, while showing an 8-log depletion of erythrocytes and 5.6-log depletion of leukocytes. We also developed an image analysis tool that was able to characterize the various morphologies and differing deformability of the separating cells. From the results, we believe our system possesses a high potential for liquid biopsy, aiding future cancer research.

A high-throughput liquid biopsy for rapid rare cell separation from large-volume samples

Liquid biopsy techniques for rare tumor cell separation from body fluids have shown enormous promise in cancer detection and prognosis monitoring. This work established a high-throughput liquid biopsy platform with a high recovery rate and a high cell viability based on a previously reported 2.5D micropore-arrayed filtration membrane. Thanks to its high porosity (>40.2%, edge-to-edge space between the adjacent micropores <4 μm), the achieved filtration throughputs can reach >110 mL min-1 for aqueous samples and >17 mL min-1 for undiluted whole blood, only driven by gravity with no need for any extra pressure loading. The recoveries of rare lung tumor cells (A549s) spiked in PBS (10 mL), unprocessed BALF (10 mL) and whole blood (5 mL) show high recovery rates (88.0 ± 3.7%, 86.0 ± 5.3% and 83.2 ± 6.2%, respectively, n = 5 for every trial) and prove the high performance of this platform. Successful detection of circulating tumor cells (CTCs) from whole blood samples (5 mL) of lung cancer patients (n = 5) was demonstrated. In addition, it was both numerically and experimentally proved that a small edge-to-edge space was significant to improve the viability of the recovered cells and the purity of the target cell recovery, which was reported for the first time to the best of the authors' knowledge. This high-throughput technique will expand the detecting targets of liquid biopsy from the presently focused CTCs in whole blood to the exfoliated tumor cells (ETCs) in other large-volume clinical samples, such as BALF, urine and pleural fluid. Meanwhile, the technique is easy to operate and ready for integration with other separation and analysis tools to fulfill a powerful system for practical clinical applications of liquid biopsy.

Electrical-Charge-Mediated Cancer Cell Targeting via Protein Corona-Decorated Superparamagnetic Nanoparticles in a Simulated Physiological Environment

A critical issue in nanomedicine is on the understanding of nano-bio interface behaviors, particularly when the nanoparticles are inevitably decorated by protein coronas in the physiological fluids. In this study, the effects of particle surface corona on cancer cell targeting were investigated in simulated physiological fluids. Cell targeting was achieved by two strategies: (1) using conventional epithelial cell adhesion molecule antibody-functionalized Fe₃O₄ nanoparticles and (2) rendering the same but naked magnetic nanoparticles electrically positively charged, enabling them to electrostatically bind onto the negatively charged cancer cells. The cell-particle electrostatic binding was found to be much stronger with faster reaction kinetics than the immunological interactions even at 4 nC. Both types of nanoparticles were decorated with various protein coronas by administration in a simulated physiological system. Well-decorated by protein coronas, the electrically charged particles retained strong electrostatic interactions with cancer cells, even upon reversal of the particle zeta potential from positive to negative. This behavior was explained by a nonuniform corona modulation of the particle surface charge distributions, exposing locally positively charged regions, capable of strong electrostatic cell binding and magnetic capturing in a physiological environment. This fundamental discovery paves new way for sensitive detection of circulating tumor cells in whole blood in clinical settings.

Progress in Circulating Tumor Cell Research Using Microfluidic Devices

Circulating tumor cells (CTCs) are a popular topic in cancer research because they can be obtained by liquid biopsy, a minimally invasive procedure with more sample accessibility than tissue biopsy, to monitor a patient’s condition. Over the past decades, CTC research has covered a wide variety of topics such as enumeration, profiling, and correlation between CTC number and patient overall survival. It is important to isolate and enrich CTCs before performing CTC analysis because CTCs in the blood stream are very rare (0–10 CTCs/mL of blood). Among the various approaches to separating CTCs, here, we review the research trends in the isolation and analysis of CTCs using microfluidics. Microfluidics provides many attractive advantages for CTC studies such as continuous sample processing to reduce target cell loss and easy integration of various functions into a chip, making “do-everything-on-a-chip” possible. However, tumor cells obtained from different sites within a tumor exhibit heterogenetic features. Thus, heterogeneous CTC profiling should be conducted at a single-cell level after isolation to guide the optimal therapeutic path. We describe the studies on single-CTC analysis based on microfluidic devices. Additionally, as a critical concern in CTC studies, we explain the use of CTCs in cancer research, despite their rarity and heterogeneity, compared with other currently emerging circulating biomarkers, including exosomes and cell-free DNA (cfDNA). Finally, the commercialization of products for CTC separation and analysis is discussed.

Advances in liquid biopsy on-chip for cancer management: Technologies, biomarkers, and clinical analysis

Liquid biopsy, as a minimally invasive method of gleaning insight into the dynamics of diseases through a patient fluid sample, has been growing in popularity for cancer diagnosis, prognosis, and monitoring. While many technologies have been developed and validated in research laboratories, there has also been a push to expand these technologies into other clinical settings and as point of care devices. In this article, we discuss and evaluate microchip-based technologies for circulating tumor cell (CTC), exosome, and circulating tumor nucleic acid (ctNA) capture, detection, and analysis. Such integrated systems streamline otherwise multiple-step, manual operations to get a sample-to-answer quantitation. In addition, analysis of disease biomarkers is suited to point of care settings because of ease of use, low consumption of sample and reagents, and high throughput. We also cover the basics of biomarkers and their detection in biological fluid samples suitable for liquid biopsy on-chip. We focus on emerging technologies that process a small patient sample with high spatial-temporal resolution and derive clinically meaningful results through on-chip biomarker sensing and downstream molecular analysis in a simple workflow. This critical review is meant as a resource for those interested in developing technologies for capture, detection, and analysis platforms for liquid biopsy in a variety of settings.

A Label Free Disposable Device for Rapid Isolation of Rare Tumor Cells from Blood by Ultrasounds

The use of blood samples as liquid biopsy is a label-free method for cancer diagnosis that offers benefits over traditional invasive biopsy techniques. Cell sorting by acoustic waves offers a means to separate rare cells from blood samples based on their physical properties in a label-free, contactless and biocompatible manner. Herein, we describe a flow-through separation approach that provides an efficient separation of tumor cells (TCs) from white blood cells (WBCs) in a microfluidic device, “THINUS-Chip” (Thin-Ultrasonic-Separator-Chip), actuated by ultrasounds. We introduce for the first time the concept of plate acoustic waves (PAW) applied to acoustophoresis as a new strategy. It lies in the geometrical chip design: different to other microseparators based on either bulk acoustic waves (BAW) or surface waves (SAW, SSAW and tSAW), it allows the use of polymeric materials without restrictions in the frequency of work. We demonstrate its ability to perform high-throughput isolation of TCs from WBCs, allowing a recovery rate of 84% ± 8% of TCs with a purity higher than 80% and combined viability of 85% at a flow rate of 80 μL/min (4.8 mL/h). The THINUS-Chip performs cell fractionation with low-cost manufacturing processes, opening the door to possible easy printing fabrication.

MICROFLUIDIC CHIP FOR CANCER CELL DETECTION AND DIAGNOSIS

Since cancer becomes the most deadly disease to our health, research on early detection on cancer cells is necessary for clinical treatment. The combination of microfluidic device with cell biology has shown a unique method for cancer cell research. In the present review, recent development on microfluidic chip for cancer cell detection and diagnosis will be addressed. Some typical microfluidic chips focussed on cancer cells and their advantages for different kinds of cancer cell detection and diagnosis will be listed, and the cell capture methods within the microfluidics will be simultaneously mentioned. Then the potential direction of microfluidic chip on cancer cell detection and diagnosis in the future is also discussed.

Size-based separation methods of circulating tumor cells

Circulating tumor cells (CTCs) originate from the primary tumor mass and enter into the peripheral bloodstream. Compared to other "liquid biopsy" portfolios such as exosome, circulating tumor DNA/RNA (ctDNA/RNA), CTCs have incomparable advantages in analyses of transcriptomics, proteomics, and signal colocalization. Hence, CTCs hold the key to understanding the biology of metastasis and play a vital role in cancer diagnosis, treatment monitoring, and prognosis. Size-based enrichment features are prominent in CTC isolation. It is a label-free, simple and fast method. Enriched CTCs remain unmodified and viable for a wide range of subsequent analyses. In this review, we comprehensively summarize the differences of size and deformability between CTCs and blood cells, which would facilitate the development of technologies of size-based CTC isolation. Then we review representative size-/deformability-based technologies available for CTC isolation and highlight the recent achievements in molecular analysis of isolated CTCs. To wrap up, we discuss the substantial challenges facing the field, and elaborate on prospects.

NanoVelcro rare-cell assays for detection and characterization of circulating tumor cells

Circulating tumor cells (CTCs) are cancer cells shredded from either a primary tumor or a metastatic site and circulate in the blood as the potential cellular origin of metastasis. By detecting and analyzing CTCs, we will be able to noninvasively monitor disease progression in individual cancer patients and obtain insightful information for assessing disease status, thus realizing the concept of "tumor liquid biopsy". However, it is technically challenging to identify CTCs in patient blood samples because of the extremely low abundance of CTCs among a large number of hematologic cells. In order to address this challenge, our research team at UCLA pioneered a unique concept of "NanoVelcro" cell-affinity substrates, in which CTC capture agent-coated nanostructured substrates were utilized to immobilize CTCs with remarkable efficiency. Four generations of NanoVelcro CTC assays have been developed over the past decade for a variety of clinical utilities. The 1st-gen NanoVelcro Chips, composed of a silicon nanowire substrate (SiNS) and an overlaid microfluidic chaotic mixer, were created for CTC enumeration. The 2nd-gen NanoVelcro Chips (i.e., NanoVelcro-LMD), based on polymer nanosubstrates, were developed for single-CTC isolation in conjunction with the use of the laser microdissection (LMD) technique. By grafting thermoresponsive polymer brushes onto SiNS, the 3rd-gen Thermoresponsive NanoVelcro Chips have demonstrated the capture and release of CTCs at 37 and 4 °C respectively, thereby allowing for rapid CTC purification while maintaining cell viability and molecular integrity. Fabricated with boronic acid-grafted conducting polymer-based nanomaterial on chip surface, the 4th-gen NanoVelcro Chips (Sweet chip) were able to purify CTCs with well-preserved RNA transcripts, which could be used for downstream analysis of several cancer specific RNA biomarkers. In this review article, we will summarize the development of the four generations of NanoVelcro CTC assays, and the clinical applications of each generation of devices.

Revealing elasticity of largely deformed cells flowing along confining microchannels

Deformability is a hallmark of malignant tumor cells. Characterizing cancer cell deformation can reveal how cancer cell metastasizes through tiny gaps in tissues. However, many previous reports only focus on the cancer cell behaviors under small deformation regimes, which may not be representative for the behaviors under large deformations as in the in vivo metastatic processes. Here, we investigate a wide range of cell elasticity using our recently developed confining microchannel arrays. We develop a relation between the elastic modulus and cell shape under different deformation levels based on a modified contact theory and the hyperelastic Tatara theory. We demonstrate good agreements between the model prediction and experimental results. Strikingly, we discover a clear ‘modulus jump’ of largely deformed cells compared to that of small deformed cells, offering further biomechanical properties of the cells. Likely, such a modulus jump can be considered as a label-free marker reflecting the elasticity of intracellular components including the nucleus during cell translocation in capillaries and tissue constrictions. In essence, we perform cell classification based on the distinct micromechanical properties of four cell lines, i.e. one normal cell line (MCF-10A) and three cancer cell lines (MCF-7, MDA-MB-231 and PC3) and achieved reasonable efficiencies (efficiency >65%). Finally, we study the correlation between large-deformational elasticity and translocation rates of the floating cells in the microchannels. Together, our results demonstrate the quantitative analysis of the biomechanical properties of single floating cells, which provide an additional label-free physical biomarker toward more effective cancer diagnosis.

Deformability is a hallmark of malignant tumor cells.

The Continuous Concentration of Particles and Cancer Cell Line Using Cell Margination in a Groove-Based Channel

In the capillary venules, blood cells auto-separate with red blood cells aggregating near the centre of vessel and the nucleated cells marginating toward the wall of vessel. In this experiment, we used cell margination to help enrich the Jurkat cells via a groove-based channel which provides a vertical expansion-contraction structure, wherein the red blood cells invade the grooves and push the Jurkat cells to the bottom of the channel. The secondary flows induced by the anisotropic grooves bring the Jurkat cells to the right sidewall. Rigid, 13-µm diameter polystyrene particles were spiked into the whole blood to verify the operating principle under various working conditions, and then tests were carried out using Jurkat cells (~15 µm). The performance of this device was quantified by analysing the cell distribution in a transverse direction at the outlet, and then measuring the cell concentration from the corresponding outlets. The results indicate that Jurkat cells were enriched by 22.3-fold with a recovery rate of 83.4%, thus proving that this microfluidic platform provides a gentle and passive way to isolate intact and viable Jurkat cells.

Materials and microfluidics: enabling the efficient isolation and analysis of circulating tumour cells

We present a critical review of microfluidic technologies and material effects on the analyses of circulating tumour cells (CTCs) selected from the peripheral blood of cancer patients. CTCs are a minimally invasive source of clinical information that can be used to prognose patient outcome, monitor minimal residual disease, assess tumour resistance to therapeutic agents, and potentially screen individuals for the early diagnosis of cancer. The performance of CTC isolation technologies depends on microfluidic architectures, the underlying principles of isolation, and the choice of materials. We present a critical review of the fundamental principles used in these technologies and discuss their performance. We also give context to how CTC isolation technologies enable downstream analysis of selected CTCs in terms of detecting genetic mutations and gene expression that could be used to gain information that may affect patient outcome.

Current approaches for avoiding the limitations of circulating tumor cells detection methods-implications for diagnosis and treatment of patients with solid tumors

Eight million people die of cancer each year and 90% of deaths are caused by systemic disease. Circulating tumor cells (CTCs) contribute to the formation of metastases and thus are the subject of extensive research and an abiding interest to biotechnology and pharmaceutical companies. Recent technological advances have resulted in greatly improved CTC detection, enumeration, expansion, and culture methods. However, despite the fact that nearly 150 years have passed since the first detection and description of CTCs in human blood and enormous technological progress that has taken place in this field, especially within the last decade, few CTC detection methods have been approved for routine clinical use. This reflects the substantial methodological problems related to the nature of these cells, their heterogeneity, and diverse metastatic potential. Here, we provide an overview of CTC phenotypes, including the plasticity of CTCs and the relevance of inflammation and cell fusion phenomena for CTC biology. We also review the literature on CTC detection methodology-its recent improvements, clinical significance, and efforts of its clinical application in cancer patients management. At present, CTC detection remains a challenging diagnostic approach as a result of numerous current methodological limitations. This is especially problematic during the early stages of the disease due to the small numbers of CTCs released into the blood of cancer patients. Nonetheless, the rapid development of novel techniques of CTC detection and enumeration in peripheral blood is expected to expedite their implementation in the clinical setting. It is of utmost importance to understand the biology of CTCs and their distinct populations as a prerequisite for achieving this ultimate goal.

High-Throughput Selective Capture of Single Circulating Tumor Cells by Dielectrophoresis at a Wireless Electrode Array

We demonstrate continuous high-throughput selective capture of circulating tumor cells by dielectrophoresis at arrays of wireless electrodes (bipolar electrodes, BPEs). The use of BPEs removes the requirement of ohmic contact to individual array elements, thus enabling otherwise unattainable device formats. Capacitive charging of the electrical double layer at opposing ends of each BPE allows an AC electric field to be transmitted across the entire device. Here, two such designs are described and evaluated. In the first design, BPEs interconnect parallel microchannels. Pockets extruding from either side of the microchannels volumetrically control the number of cells captured at each BPE tip and enhance trapping. High-fidelity single-cell capture was achieved when the pocket dimensions were matched to those of the cells. A second, open design allows many non-targeted cells to pass through. These devices enable high-throughput capture of rare cells and single-cell analysis.

Circulating tumor markers: harmonizing the yin and yang of CTCs and ctDNA for precision medicine

Current trajectory of clinical care is heading in the direction of personalized medicine. In an ideal scenario, clinicians can obtain extensive diagnostic and prognostic information via minimally-invasive assays. Information available in the peripheral blood has the potential to bring us closer to this goal. In this review we highlight the contributions of circulating tumor cells and circulating tumor DNA and RNA (ctDNA/ctRNA) towards cancer therapeutic field. We discuss clinical relevance, summarize available and upcoming technologies, and hypothesize how future care could be impacted by a combined study.