Covalent chemistry on nanostructured substrates enables noninvasive quantification of gene rearrangements in circulating tumor cells

Interfacial engineering for biomolecule immobilisation in microfluidic devices

Microfluidic devices are used for various applications in biology and medicine. From on-chip modelling of human organs for drug screening and fast and straightforward point-of-care (POC) detection of diseases to sensitive biochemical analysis, these devices can be custom-engineered using low-cost techniques. The microchannel interface is essential for these applications, as it is the interface of immobilised biomolecules that promote cell capture, attachment and proliferation, sense analytes and metabolites or provide enzymatic reaction readouts. However, common microfluidic materials do not facilitate the stable immobilisation of biomolecules required for relevant applications, making interfacial engineering necessary to attach biomolecules to the microfluidic surfaces. Interfacial engineering is performed through various immobilisation mechanisms and surface treatment techniques, which suitably modify the surface properties like chemistry and energy to obtain robust biomolecule immobilisation and long-term storage stability suitable for the final application. In this review, we provide an overview of the status of interfacial engineering in microfluidic devices, covering applications, the role of biomolecules, their immobilisation pathways and the influence of microfluidic materials. We then propose treatment techniques to optimise performance for various biological and medical applications and highlight future areas of development.

High-Viability Circulating Tumor Cells Sorting From Whole Blood at Single Cell Level Using Laser-Induced Forward Transfer-Assisted Microfiltration

The efficient isolation and molecular analysis of circulating tumor cells (CTCs) from whole blood at single-cell level are crucial for understanding tumor metastasis and developing personalized treatments. The viability of isolated cells is the key prerequisite for the downstream molecular analysis, especially for RNA sequencing. This study develops a laser-induced forward transfer -assisted microfiltration system (LIFT-AMFS) for high-viability CTC enrichment and retrieval from whole blood. The LIFT-compatible double-stepped microfilter (DSMF), central to this system, comprises two micropore layers: the lower layer's smaller micropores facilitate size-based cell separation, and the upper layer's larger micropores enable liquid encapsulating captured cells. By optimizing the design of the DSMFs, the system has a capture efficiency of 88% at the processing throughput of up to 15.0 mL min-1 during the microfilter-based size screening stage, with a single-cell yield of over 95% during the retrieval stage. The retrieved single cells, with high viability, are qualified for ex vivo culture and direct RNA sequencing. The cDNA yield from isolated CTCs surpassed 4.5 ng, sufficient for library construction. All single-cell sequencing data exhibited Q30 scores above 95.92%. The LIFT-AMFS shows promise in cellular and biomedical research.

Digital Quantitative Detection for Heterogeneous Protein and mRNA Expression Patterns in Circulating Tumor Cells

Hepatocellular carcinoma (HCC) circulating tumor cells (CTCs) exhibit significant phenotypic heterogeneity and diverse gene expression profiles due to epithelial-mesenchymal transition (EMT). However, current detection methods lack the capacity for simultaneous quantification of multidimensional biomarkers, impeding a comprehensive understanding of tumor biology and dynamic changes. Here, the CTC Digital Simultaneous Cross-dimensional Output and Unified Tracking (d-SCOUT) technology is introduced, which enables simultaneous quantification and detailed interpretation of HCC transcriptional and phenotypic biomarkers. Based on self-developed multi-real-time digital PCR (MRT-dPCR) and algorithms, d-SCOUT allows for the unified quantification of Asialoglycoprotein Receptor (ASGPR), Glypican-3 (GPC-3), and Epithelial Cell Adhesion Molecule (EpCAM) proteins, as well as Programmed Death Ligand 1 (PD-L1), GPC-3, and EpCAM mRNA in HCC CTCs, with good sensitivity (LOD of 3.2 CTCs per mL of blood) and reproducibility (mean %CV = 1.80-6.05%). In a study of 99 clinical samples, molecular signatures derived from HCC CTCs demonstrated strong diagnostic potential (AUC = 0.950, sensitivity = 90.6%, specificity = 87.5%). Importantly, by integrating machine learning, d-SCOUT allows clustering of CTC characteristics at the mRNA and protein levels, mapping normalized heterogeneous 2D molecular profiles to assess HCC metastatic risk. Dynamic digital tracking of eight HCC patients undergoing different treatments visually illustrated the therapeutic effects, validating this technology's capability to quantify the treatment efficacy. CTC d-SCOUT enhances understanding of tumor biology and HCC management.

Bioorthogonal Microbubbles with Antifouling Nanofilm for Instant and Suspended Enrichment of Circulating Tumor Cells

Integrating clinical rare cell enrichment, culture, and single-cell phenotypic profiling is currently hampered by the lack of competent technologies, which typically suffer from weak cell-interface collision affinity, strong nonspecific adsorption, and the potential uptake. Here, we report cells-on-a-bubble, a bioinspired, self-powered bioorthogonal microbubble (click bubble) that leverages a clickable antifouling nanointerface and a DNA-assembled sucker-like polyvalent cell surface, to enable instant and suspended isolation of circulating tumor cells (CTCs) within minutes. Using this biomimetic engineering strategy, click bubbles achieve a capture efficiency of up to 98%, improved by 20% at 15 times faster over their monovalent counterparts. Further, the buoyancy-activated bubble facilitates self-separation, 3D suspension culture, and in situ phenotyping of the captured single cancer cells. By using a multiantibody design, this fast, affordable micromotor-like click bubble enables suspended enrichment of CTCs in a cohort (n = 42) across three cancer types and treatment response evaluation, signifying its great potential to enable single-cell analysis and 3D organoid culture.

Hierarchical integration of DNA nanostructures and NanoGold onto a microchip facilitates covalent chemistry-mediated purification of circulating tumor cells in head and neck squamous cell carcinoma

It is well-established that the combined use of nanostructured substrates and immunoaffinity agents can enhance the cell-capture performance of the substrates, thus offering a practical solution to effectively capture circulating tumor cells (CTCs) in peripheral blood. Developing along this strategy, this study first demonstrated a top-down approach for the fabrication of tetrahedral DNA nanostructure (TDN)-NanoGold substrates through the hierarchical integration of three functional constituents at various length-scales: a macroscale glass slide, sub-microscale self-organized NanoGold, and nanoscale self-assembled TDN. The TDN-NanoGold substrates were then assembled with microfluidic chaotic mixers to give TDN-NanoGold Click Chips. In conjunction with the use of copper (Cu)-catalyzed azide-alkyne cycloaddition (CuAAC)-mediated CTC capture and restriction enzyme-triggered CTC release, TDN-NanoGold Click Chips allow for effective enumeration and purification of CTCs with intact cell morphologies and preserved molecular integrity. To evaluate the clinical utility of TDN-NanoGold Click Chips, we used these devices to isolate and purify CTCs from patients with human papillomavirus (HPV)-positive (+) head and neck squamous cell carcinoma (HNSCC). The purified HPV(+) HNSCC CTCs were then subjected to RT-ddPCR testing, allowing for detection of E6/E7 oncogenes, the characteristic molecular signatures of HPV(+) HNSCC. We found that the resulting HPV(+) HNSCC CTC counts and E6/E7 transcript copy numbers are correlated with the treatment responses in the patients, suggesting the potential clinical utility of TDN-NanoGold Click Chips for non-invasive diagnostic applications of HPV(+) HNSCC.

Recent advances in micro-/nanostructure array integrated microfluidic devices for efficient separation of circulating tumor cells

Circulating tumor cells (CTCs) released from the primary tumor to peripheral blood are promising targets for liquid biopsies. Their biological information is vital for early cancer detection, efficacy assessment, and prognostic monitoring. Despite the tremendous clinical applications of CTCs, development of effective separation techniques are still demanding. Traditional separation methods usually use batch processing for enrichment, which inevitably destroy cell integrity and affect the complete information acquisition. Considering the rarity and heterogeneity of CTCs, it is urgent to develop effective separation methods. Microfluidic chips with precise fluid control at the micron level are promising devices for CTC separation. Their further combination with micro-/nanostructure arrays adds more biomolecule binding sites and exhibit unique fluid barrier effect, which significantly improve the CTC capture efficiency, purity, and sensitivity. This review summarized the recent advances in micro-/nanostructure array integrated microfluidic devices for CTC separation, including microrods, nanowires, and 3D micro-/nanostructures. The mechanisms by which these structures contribute to improved capture efficiency are discussed. Two major categories of separation methods, based on the physical and biological properties of CTCs, are discussed separately. Physical separation includes the design and preparation of micro-/nanostructure arrays, while chemical separation additionally involves the selection and modification of specific capture probes. These emerging technologies are expected to become powerful tools for disease diagnosis in the future.

Light-activated tetrazines enable precision live-cell bioorthogonal chemistry

Bioorthogonal cycloaddition reactions between tetrazines and strained dienophiles are widely used for protein, lipid and glycan labelling because of their extremely rapid kinetics. However, controlling this chemistry in the presence of living mammalian cells with a high degree of spatial and temporal precision remains a challenge. Here we demonstrate a versatile approach to light-activated formation of tetrazines from photocaged dihydrotetrazines. Photouncaging, followed by spontaneous transformation to reactive tetrazine, enables live-cell spatiotemporal control of rapid bioorthogonal cycloaddition with dienophiles such as trans-cyclooctenes. Photocaged dihydrotetrazines are stable in conditions that normally degrade tetrazines, enabling efficient early-stage incorporation of bioorthogonal handles into biomolecules such as peptides. Photocaged dihydrotetrazines allow the use of non-toxic light to trigger tetrazine ligations on living mammalian cells. By tagging reactive phospholipids with fluorophores, we demonstrate modification of HeLa cell membranes with single-cell spatial resolution. Finally, we show that photo-triggered therapy is possible by coupling tetrazine photoactivation with strategies that release prodrugs in response to tetrazine ligation.

Circulating tumor cells: A step toward precision medicine in hepatocellular carcinoma

Serum alpha-fetoprotein and radiologic imaging are the most commonly used tests for early diagnosis and dynamic monitoring of treatment response in hepatocellular carcinoma (HCC). However, the accuracy of these tests is limited, and they may not reflect the underlying biology of the tumor. Thus, developing highly accurate novel HCC biomarkers reflecting tumor biology is a clinically unmet need. Circulating tumor cells (CTCs) have long been proposed as a noninvasive biomarker in clinical oncology. Most CTC assays utilize immunoaffinity-based, size-based, and/or enrichment-free mechanisms followed by immunocytochemical staining to characterize CTCs. The prognostic value of HCC CTC enumeration has been extensively validated. Subsets of CTCs expressing mesenchymal markers are also reported to have clinical significance. In addition, researchers have been devoting their efforts to molecular characterizations of CTCs (e.g. genetics and transcriptomics) as molecular profiling can offer a more accurate readout and provide biological insights. As new molecular profiling techniques, such as digital polymerase chain reaction, are developed to detect minimal amounts of DNA/RNA, several research groups have established HCC CTC digital scoring systems to quantify clinically relevant gene panels. Given the versatility of CTCs to provide intact molecular and functional data that reflects the underlying tumor, CTCs have great potential as a noninvasive biomarker in HCC. Large-scale, prospective studies for HCC CTCs with a standardized protocol are necessary for successful clinical translation.

Designer tetrahedral DNA framework-based microfluidic technology for multivalent capture and release of circulating tumor cells

Circulating tumor cells (CTCs) have been recognized as a general biomarker for the early detection, diagnosis and therapy monitoring of cancer. Due to their extreme rarity in peripheral blood, the isolation and analysis of CTCs with high efficiency, high purity and high viability remains a tremendous technological challenge. Herein, we combined tetrahedral DNA framework (TDFs), herringbone channel (HB) chip, together with aptamer-triggered hybridization chain reaction (apt-HCR) to develop an efficient microfluidic system (T-μFS) for capture and release of simulated CTCs. The capture efficiency of MCF-7 ​cells was from 83.3% to 94.2% when the cell numbers ranged from 10 to 10³ using our T-μFS in the whole blood. The release efficiency of the MCF-7 ​cells was 96.2% and the MCF-7 ​cell viability after release was 94.6% using our T-μFS in PBS buffer. Reculture and RT-qPCR studies showed that there was almost no damage by the capture and release treatment for the MCF-7 ​cells viability. These results revealed that our T-μFS could be developed as an integrated and automatic technical platform with great performance for multivalent capture and release of CTCs and have a wide application prospect for tumor liquid biopsy.

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Three-dimensional amine modified tetrahedral DNA frameworks (TDFs) as rigid scaffolds were anchored on the aldehyde modified substrate of HB-chip, which provided the better spatial orientation compared with single-stranded DNA.

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Aptamer partially hybridized to an initiator was employed to trigger HCR reaction, and HCR produced modified long products with multi-branched arms for multivalent binding on TDFs to improve the capture efficiency of CTCs.

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This is the first time that only employed DNA nanostructures in a microfluidic device system to capture CTCs, and all DNA nanostructures could be efficiently removed by enzymes without harming cells.

Nanomaterial-Based Immunocapture Platforms for the Recognition, Isolation, and Detection of Circulating Tumor Cells

Circulating tumor cells (CTCs) are a type of cancer cells that circulate in the peripheral blood after breaking away from solid tumors and are essential for the establishment of distant metastasis. Up to 90% of cancer-related deaths are caused by metastatic cancer. As a new type of liquid biopsy, detecting and analyzing CTCs will provide insightful information for cancer diagnosis, especially the in-time disease status, which would avoid some flaws and limitations of invasive tissue biopsy. However, due to the extremely low levels of CTCs among a large number of hematologic cells, choosing immunocapture platforms for CTC detection and isolation will achieve good performance with high purity, selectivity, and viability. These properties are directly associated with precise downstream analysis of CTC profiling. Recently, inspired by the nanoscale interactions of cells in the tissue microenvironment, platforms based on nanomaterials have been widely explored to efficiently enrich and sensitively detect CTCs. In this review, various immunocapture platforms based on different nanomaterials for efficient isolation and sensitive detection of CTCs are outlined and discussed. First, the design principles of immunoaffinity nanomaterials are introduced in detail. Second, the immunocapture and release of platforms based on nanomaterials ranging from nanoparticles, nanostructured substrates, and immunoaffinity microfluidic chips are summarized. Third, recent advances in single-cell release and analysis of CTCs are introduced. Finally, some perspectives and challenges are provided in future trends of CTC studies.

Accurate Isolation of Circulating Tumor Cells via a Heterovalent DNA Framework Recognition Element-Functionalized Microfluidic Chip

Detection of circulating tumor cells (CTCs) has provided a noninvasive and efficient approach for early diagnosis, treatment, and prognosis of cancer. However, efficient capture of CTCs in the clinical environment is very challenging because of the extremely rare and heterogeneous expression of CTCs. Herein, we fabricated a multimarker microfluidic chip for the enrichment of heterogeneous CTCs from peripheral blood samples of breast cancer patients. The multimarker aptamer cocktail DNA nanostructures (TP-multimarker) were modified on a deterministic lateral displacement (DLD)-patterned microfluidic chip to enhance the capture efficiency through the size selection effect of DLD arrays and the synergistic effect of multivalent aptamers. As compared to a monovalent aptamer-modified chip, the multimarker chip exhibits enhanced capture efficiency toward both high and low epithelial cell adhesion molecule expression cell lines, and the DNA nanostructure-functionalized chip enables the accurate capture of different phenotypes of CTCs. In addition, the DNA nanoscaffold makes nucleases more accessible to the aptamers to release cells with molecular integrity and outstanding cell viability.

Circulating tumor cells in colorectal cancer in the era of precision medicine

Colorectal cancer (CRC) is one of the main causes of cancer-related morbidity and mortality across the globe. Although serum biomarkers such as carcinoembryonic antigen (CEA) and carbohydrate antigen 19–9 (CA-199) have been prevalently used as biomarkers in various cancers, they are neither very sensitive nor highly specific. Repeated tissue biopsies at different times of the disease can be uncomfortable for cancer patients. Additionally, the existence of tumor heterogeneity and the results of local biopsy provide limited information about the overall tumor biology. Against this backdrop, it is necessary to look for reliable and noninvasive biomarkers of CRC. Circulating tumor cells (CTCs), which depart from a primary tumor, enter the bloodstream, and imitate metastasis, have a great potential for precision medicine in patients with CRC. Various efficient CTC isolation platforms have been developed to capture and identify CTCs. The count of CTCs, as well as their biological characteristics and genomic heterogeneity, can be used for the early diagnosis, prognosis, and prediction of treatment response in CRC. This study reviewed the existing CTC isolation techniques and their applications in the clinical diagnosis and treatment of CRC. The study also presented their limitations and provided future research directions.

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 trophoblast cell clusters for early detection of placenta accreta spectrum disorders

Placenta accreta spectrum (PAS) is a high-risk obstetrical condition associated with significant morbidity and mortality. Current clinical screening modalities for PAS are not always conclusive. Here, we report a nanostructure-embedded microchip that efficiently enriches both single and clustered circulating trophoblasts (cTBs) from maternal blood for detecting PAS. We discover a uniquely high prevalence of cTB-clusters in PAS and subsequently optimize the device to preserve the intactness of these clusters. Our feasibility study on the enumeration of cTBs and cTB-clusters from 168 pregnant women demonstrates excellent diagnostic performance for distinguishing PAS from non-PAS. A logistic regression model is constructed using a training cohort and then cross-validated and tested using an independent cohort. The combined cTB assay achieves an Area Under ROC Curve of 0.942 (throughout gestation) and 0.924 (early gestation) for distinguishing PAS from non-PAS. Our assay holds the potential to improve current diagnostic modalities for the early detection of PAS.

Well-Defined Nanostructured Biointerfaces: Strengthened Cellular Interaction for Circulating Tumor Cells Isolation

The topographic features at the cell-material biointerface are critical for cellular sensing of the extracellular environment (ECM) and have gradually been recognized as key factors that regulate cell adhesion behavior. Herein, a well-defined nanostructured biointerface is fabricated via a new generation of mussel-inspired polymer coating to mimic the native ECM structures. Upon the bioinert background presence and biospecific ligands conjugation, the affinity of cancer cells to the resulting biofunctional surfaces, which integrate topographic features and biochemical cues, is greatly strengthened. Both the conjugated bioligand density, filopodia formation, and focal adhesion expression are significantly enhanced by the surficial nano-features with an optimized size-scale. Thus, this nanostructured biointerface exhibits high capture efficiency for circulating tumor cells (CTCs) with high sensitivity, high biospecificity, and high purity. Benefiting from the unique bioligands conjugation chemistry herein, the captured cancer cells can be responsively detached from the biointerfaces without damage for downstream analysis. The present biofunctional nanostructured interfaces offer a good solution to address current challenges to efficiently isolate rare CTCs from blood samples for earlier cancer diagnosis.

Covalent Chemistry-Mediated Multimarker Purification of Circulating Tumor Cells Enables Noninvasive Detection of Molecular Signatures of Hepatocellular Carcinoma

Transcriptomic profiling of tumor tissues introduces a large database, which has led to improvements in the ability of cancer diagnosis, treatment, and prevention. However, performing tumor transcriptomic profiling in the clinical setting is very challenging since the procurement of tumor tissues is inherently limited by invasive sampling procedures. Here, we demonstrated the feasibility of purifying hepatocellular carcinoma (HCC) circulating tumor cells (CTCs) from clinical patient samples with improved molecular integrity using Click Chips in conjunction with a multimarker antibody cocktail. The purified CTCs were then subjected to mRNA profiling by NanoString nCounter platform, targeting 64 HCC-specific genes, which were generated from an integrated data analysis framework with 8 tissue-based prognostic gene signatures from 7 publicly available HCC transcriptomic studies. After bioinformatics analysis and comparison, the HCC CTC-derived gene signatures showed high concordance with HCC tissue-derived gene signatures from TCGA database, suggesting that HCC CTCs purified by Click Chips could enable the translation of HCC tissue molecular profiling into a noninvasive setting.

Aptamer-Based Detection of Circulating Targets for Precision Medicine

The past decade has witnessed ongoing progress in precision medicine to improve human health. As an emerging diagnostic technique, liquid biopsy can provide real-time, comprehensive, dynamic physiological and pathological information in a noninvasive manner, opening a new window for precision medicine. Liquid biopsy depends on the sensitive and reliable detection of circulating targets (e.g., cells, extracellular vesicles, proteins, microRNAs) from body fluids, the performance of which is largely governed by recognition ligands. Aptamers are single-stranded functional oligonucleotides, capable of folding into unique tertiary structures to bind to their targets with superior specificity and affinity. Their mature evolution procedure, facile modification, and affinity regulation, as well as versatile structural design and engineering, make aptamers ideal recognition ligands for liquid biopsy. In this review, we present a broad overview of aptamer-based liquid biopsy techniques for precision medicine. We begin with recent advances in aptamer selection, followed by a summary of state-of-the-art strategies for multivalent aptamer assembly and aptamer interface modification. We will further describe aptamer-based micro-/nanoisolation platforms, aptamer-enabled release methods, and aptamer-assisted signal amplification and detection strategies. Finally, we present our perspectives regarding the opportunities and challenges of aptamer-based liquid biopsy for precision medicine.

On-Chip Biogenesis of Circulating NK Cell-Derived Exosomes in Non-Small Cell Lung Cancer Exhibits Antitumoral Activity

As the recognition between natural killer (NK) cells and cancer cells does not require antigen presentation, NK cells are being actively studied for use in adoptive cell therapies in the rapidly evolving armamentarium of cancer immunotherapy. In addition to utilizing NK cells, recent studies have shown that exosomes derived from NK cells also exhibit antitumor properties. Furthermore, these NK cell-derived exosomes exhibit higher stability, greater modification potentials and less immunogenicity compared to NK cells. Therefore, technologies that allow highly sensitive and specific isolation of NK cells and NK cell-derived exosomes can enable personalized NK-mediated cancer therapeutics in the future. Here, a novel microfluidic system to collect patient-specific NK cells and on-chip biogenesis of NK-exosomes is proposed. In a small cohort of non-small cell lung cancer (NSCLC) patients, both NK cells and circulating tumor cells (CTCs) were isolated, and it is found NSCLC patients have high numbers of NK and NK-exosomes compared with healthy donors, and these concentrations show a trend of positive and negative correlations with bloodborne CTC numbers, respectively. It is further demonstrated that the NK-exosomes harvested from NK-graphene oxide chip exhibit cytotoxic effect on CTCs. This versatile system is expected to be used for patient-specific NK-based immunotherapies along with CTCs for potential prognostic/diagnostic applications.

Chemo-specific designs for the enumeration of circulating tumor cells: advances in liquid biopsy

Advanced materials and chemo-specific designs at the nano/micrometer-scale have ensured revolutionary progress in next-generation clinically relevant technologies. For example, isolating a rare population of cells, like circulating tumor cells (CTCs) from the blood amongst billions of other blood cells, is one of the most complex scientific challenges in cancer diagnostics. The chemical tunability for achieving this degree of exceptional specificity for extra-cellular biomarker interactions demands the utility of advanced entities and multistep reactions both in solution and in the insoluble state. Thus, this review delineates the chemo-specific substrates, chemical methods, and structure-activity relationships (SARs) of chemical platforms used for isolation and enumeration of CTCs in advancing the relevance of liquid biopsy in cancer diagnostics and disease management. We highlight the synthesis of cell-specific, tumor biomarker-based, chemo-specific substrates utilizing functionalized linkers through chemistry-based conjugation strategies. The capacity of these nano/micro substrates to enhance the cell interaction specificity and efficiency with the targeted tumor cells is detailed. Furthermore, this review accounts for the importance of CTC capture and other downstream processes involving genotypic and phenotypic CTC analysis in real-time for the detection of the early onset of metastases progression and chemotherapy treatment response, and for monitoring progression free-survival (PFS), disease-free survival (DFS), and eventually overall survival (OS) in cancer patients.

Coupling Nanostructured Microchips with Covalent Chemistry Enables Purification of Sarcoma-Derived Extracellular Vesicles for Downstream Functional Studies

Tumor-derived extracellular vesicles (EVs) play essential roles in intercellular communication during tumor growth and metastatic evolution. Currently, little is known about the possible roles of tumor-derived EVs in sarcoma because the lack of specific surface markers makes it technically challenging to purify sarcoma-derived EVs. In this study, a specific purification system is developed for Ewing sarcoma (ES)-derived EVs by coupling covalent chemistry-mediated EV capture/ release within a nanostructure-embedded microchip. The purification platform-ES-EV Click Chip-takes advantage of specific anti-LINGO-1 recognition and sensitive click chemistry-mediated EV capture, followed by disulfide cleavage-driven EV release. Since the device is capable of specific and efficient purification of intact ES EVs with high purity, ES-EV Click Chip is ideal for conducting downstream functional studies of ES EVs. Absolute quantification of the molecular hallmark of ES (i.e., EWS rearrangements) using reverse transcription Droplet Digital PCR enables specific quantification of ES EVs. The purified ES EVs can be internalized by recipient cells and transfer their mRNA cargoes, exhibiting their biological intactness and potential role as biological shuttles in intercellular communication.

Recent advances in microfluidic technologies for circulating tumor cells: enrichment, single-cell analysis, and liquid biopsy for clinical applications

Circulating tumor cells (CTCs) detach from primary or metastatic lesions and circulate in the peripheral blood, which is considered to be the cause of distant metastases. CTC analysis in the form of liquid biopsy, enumeration and molecular analysis provide significant clinical information for cancer diagnosis, prognosis and therapeutic strategies. Despite the great clinical value, CTC analysis has not yet entered routine clinical practice due to lack of efficient technologies to perform CTC isolation and single-cell analysis. Taking the rarity and inherent heterogeneity of CTCs into account, reliable methods for CTC isolation and detection are in urgent demand for obtaining valuable information on cancer metastasis and progression from CTCs. Microfluidic technology, featuring microfabricated structures, can precisely control fluids and cells at the micrometer scale, thus making itself a particularly suitable method for rare CTC manipulation. Besides the enrichment function, microfluidic chips can also realize the analysis function by integrating multiple detection technologies. In this review, we have summarized the recent progress in CTC isolation and detection using microfluidic technologies, with special attention to emerging direct enrichment and enumeration in vivo. Further, few insights into single CTC molecular analysis are also demonstrated. We have provided a review of potential clinical applications of CTCs, ranging from early screening and diagnosis, tumor progression and prognosis, treatment and resistance monitoring, to therapeutic evaluation. Through this review, we conclude that the clinical utility of CTCs will be expanded as the isolation and analysis techniques are constantly improving.

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.

Tumor-cell detection, labeling and phenotyping with an electron-doped bifunctional signal-amplifier

Cancer cell enumeration and phenotyping can predict the prognosis and the therapy efficacy in patients, yet it remains challenging to detect the rare tumor cells. Herein, we report an octopus-inspired, bifunctional aptamer signal amplifier-based cytosensor (OApt-cytosensor) for sensitive cell analysis. By assembling high-affinity antibodies on an electrode surface, the target cells could be specifically captured and thus been sandwiched by the cell surface marker-specific DNA aptamers. These on-cell aptamers function as electrochemical signal amplifiers by base-selective electronic doping with methylene blue. Such a sandwich configuration enables highly sensitive cell detection down to 10 cells/mL (equal to ~1-2 cells at a sampling volume of 150 μL), even in a large excess of nontarget blood cells. This approach also reveals the cell-surface markers and tracks the cellular epithelial-to-mesenchymal transition induced by signaling regulators. Furthermore, the electron-doped aptamer shows remarkable cell fluorescent labeling that guides the release of the captured cells from electrode surface via electrochemistry. These features make OApt-cytosensor a promising tool in revealing the heterogeneous cancer cells and anticancer drug screening at the single-cell level.

Purification of HCC-specific extracellular vesicles on nanosubstrates for early HCC detection by digital scoring

We report a covalent chemistry-based hepatocellular carcinoma (HCC)-specific extracellular vesicle (EV) purification system for early detection of HCC by performing digital scoring on the purified EVs. Earlier detection of HCC creates more opportunities for curative therapeutic interventions. EVs are present in circulation at relatively early stages of disease, providing potential opportunities for HCC early detection. We develop an HCC EV purification system (i.e., EV Click Chips) by synergistically integrating covalent chemistry-mediated EV capture/release, multimarker antibody cocktails, nanostructured substrates, and microfluidic chaotic mixers. We then explore the translational potential of EV Click Chips using 158 plasma samples of HCC patients and control cohorts. The purified HCC EVs are subjected to reverse-transcription droplet digital PCR for quantification of 10 HCC-specific mRNA markers and computation of digital scoring. The HCC EV-derived molecular signatures exhibit great potential for noninvasive early detection of HCC from at-risk cirrhotic patients with an area under receiver operator characteristic curve of 0.93 (95% CI, 0.86 to 1.00; sensitivity = 94.4%, specificity = 88.5%).

Nanotechnology-Assisted Isolation and Analysis of Circulating Tumor Cells on Microfluidic Devices

Circulating tumor cells (CTCs), a type of cancer cell that spreads from primary tumors into human peripheral blood and are considered as a new biomarker of cancer liquid biopsy. It provides the direction for understanding the biology of cancer metastasis and progression. Isolation and analysis of CTCs offer the possibility for early cancer detection and dynamic prognosis monitoring. The extremely low quantity and high heterogeneity of CTCs are the major challenges for the application of CTCs in liquid biopsy. There have been significant research endeavors to develop efficient and reliable approaches to CTC isolation and analysis in the past few decades. With the advancement of microfabrication and nanomaterials, a variety of approaches have now emerged for CTC isolation and analysis on microfluidic platforms combined with nanotechnology. These new approaches show advantages in terms of cell capture efficiency, purity, detection sensitivity and specificity. This review focuses on recent progress in the field of nanotechnology-assisted microfluidics for CTC isolation and detection. Firstly, CTC isolation approaches using nanomaterial-based microfluidic devices are summarized and discussed. The different strategies for CTC release from the devices are specifically outlined. In addition, existing nanotechnology-assisted methods for CTC downstream analysis are summarized. Some perspectives are discussed on the challenges of current methods for CTC studies and promising research directions.

A circulating tumor cell-based digital assay for the detection of EGFR T790M mutation in advanced non-small cell lung cancer

Determining the status of epidermal growth factor receptor (EGFR) T790M mutation is crucial for guiding further treatment intervention in advanced non-small cell lung cancer (NSCLC) patients who develop acquired resistance to initial EGFR tyrosine kinase inhibitor (TKI) treatment. Circulating tumor cells (CTCs) which contain plentiful copies of well-preserved RNA offer an ideal source for noninvasive detection of T790M mutation in NSCLC. We developed a CTC-based digital assay which synergistically integrates NanoVelcro Chips for enriching NSCLC CTCs and reverse-transcription droplet digital PCR (RT-ddPCR) for quantifying T790M transcripts in the enriched CTCs. We collected 46 peripheral arterial and venous blood samples from 27 advanced NSCLC patients for testing this CTC-based digital assay. The results showed that the T790M mutational status observed by the CTC-based digital assay matched with those observed by tissue-based diagnostic methods. Furthermore, higher copy numbers of T790M transcripts were observed in peripheral arterial blood than those detected in the matched peripheral venous blood. In short, our results demonstrated the potential of the NanoVelcro CTC-digital assay for noninvasive detection of the T790M mutation in NSCLC, and suggested that peripheral arterial blood sampling may offer a more abundant CTC source than peripheral venous blood in advanced NSCLC patients.

Fluidic Multivalent Membrane Nanointerface Enables Synergetic Enrichment of Circulating Tumor Cells with High Efficiency and Viability

The ubiquitous biomembrane interface, with its dynamic lateral fluidity, allows membrane-bound components to rearrange and localize for high-affinity multivalent ligand-receptor interactions in diverse life activities. Inspired by this, we herein engineered a fluidic multivalent nanointerface by decorating a microfluidic chip with aptamer-functionalized leukocyte membrane nanovesicles for high-performance isolation of circulating tumor cells (CTCs). This fluidic biomimetic nanointerface with active recruitment-binding afforded significant affinity enhancement by 4 orders of magnitude, exhibiting 7-fold higher capture efficiency compared to a monovalent aptamer functionalized-chip in blood. Meanwhile, this soft nanointerface inherited the biological benefits of a natural biomembrane, minimizing background blood cell adsorption and maintaining excellent CTC viability (97.6%). Using the chip, CTCs were successfully detected in all cancer patient samples tested (17/17), suggesting the high potential of this fluidity-enhanced multivalent binding strategy in clinical applications. We expect this bioengineered interface strategy will lead to the design of innovative biomimetic platforms in the biomedical field by leveraging natural cell-cell interaction with a natural biomaterial.

Nanostructured Substrates for Detection and Characterization of Circulating Rare Cells: From Materials Research to Clinical Applications

Circulating rare cells in the blood are of great significance for both materials research and clinical applications. For example, circulating tumor cells (CTCs) have been demonstrated as useful biomarkers for "liquid biopsy" of the tumor. Circulating fetal nucleated cells (CFNCs) have shown potential in noninvasive prenatal diagnostics. However, it is technically challenging to detect and isolate circulating rare cells due to their extremely low abundance compared to hematologic cells. Nanostructured substrates offer a unique solution to address these challenges by providing local topographic interactions to strengthen cell adhesion and large surface areas for grafting capture agents, resulting in improved cell capture efficiency, purity, sensitivity, and reproducibility. In addition, rare-cell retrieval strategies, including stimulus-responsiveness and additive reagent-triggered release on different nanostructured substrates, allow for on-demand retrieval of the captured CTCs/CFNCs with high cell viability and molecular integrity. Several nanostructured substrate-enabled CTC/CFNC assays are observed maturing from enumeration and subclassification to molecular analyses. These can one day become powerful tools in disease diagnosis, prognostic prediction, and dynamic monitoring of therapeutic response-paving the way for personalized medical care.