Ultrasensitive microfluidic analysis of circulating exosomes using a nanostructured graphene oxide/polydopamine coating

Electrochemical aptasensor for exosomal proteins profiling based on DNA nanotetrahedron coupled with enzymatic signal amplification

Exosomes are extracellular nanovesicles for transferring and delivering membrane and cytosolic molecules between cells. Detection and profiling of exosomal proteins can provide direct information on disease progression, which is important to the early diagnosis and monitoring of diseases. Herein, a well-designed electrochemical aptasensor was fabricated for the profiling of cancerous exosomal proteins based on DNA nanotetrahedron (NTH) coupled with Au nanoparticles (NPs) and enzymatic signal amplification. In this assay, the aptamer modified DNA NTHs were used as the recognition and capture unit, Au NPs-DNA conjugates coupled with horseradish peroxidase were used to realize signal amplification. This aptasensor achieves a detection limit down to 1.66 × 10⁴ particles/mL for HepG2 liver cancer exosomes. In addition, the analysis of plasma-derived exosomes in HepG2 liver cancer bearing mice at different cancer stages was also achieved. More importantly, the aptasensor can be used to profile four kinds of exosomal proteins by using the corresponding aptamer. The proposed electrochemical aptasensor may be served as a potential platform for exosome detection and exosomal proteins profiling.

Extracellular vesicle-based liquid biopsy holds great promise for the management of ovarian cancer

Ovarian cancer is a highly lethal gynecological disease because most patients are diagnosed in advanced stages due to a lack of appropriate markers or methods for early detection. Extracellular vesicles (EVs) are small biological vesicles released by all types of cells and are widely distributed in biofluids. These vesicles and their bioactive contents are involved in various aspects of tumorigenesis and development, and some of them could be detected in biofluids from liquid biopsy and used as markers for cancer management. Liquid biopsy is a recently developed method for disease diagnosis and real-time monitoring by detecting biomolecules in biofluids such as plasma. The operation is minimally invasive and relatively convenient, especially for patients with cancer. In this review, we describe the use of EV-based liquid biopsy in ovarian cancer and summarize recent advances in technologies for EV isolation and detection, as well as biomarkers identified from ovarian cancer-derived EVs, with a focus on their potential roles in diagnosis and progression monitoring. Although the advantages of liquid biopsy make this approach promising, some technological challenges remain, and qualified biomarkers for clinical use are still being explored.

Molecular and functional extracellular vesicle analysis using nanopatterned microchips monitors tumor progression and metastasis

Longitudinal cancer monitoring is crucial to clinical implementation of precision medicine. There is growing evidence indicating important functions of extracellular vesicles (EVs) in tumor progression and metastasis, including matrix remodeling via transporting matrix metalloproteases (MMPs). However, the clinical relevance of EVs remains largely undetermined, partially owing to challenges in EV analysis. Distinct from existing technologies mostly focused on characterizing molecular constituents of EVs, here we report a nanoengineered lab-on-a-chip system that enables integrative functional and molecular phenotyping of tumor-associated EVs. A generalized, high-resolution colloidal inkjet printing method was developed to allow robust and scalable manufacturing of three-dimensional (3D) nanopatterned devices. With this nanochip platform, we demonstrated integrative analysis of the expression and proteolytic activity of MMP14 on EVs to detect in vitro cell invasiveness and monitor in vivo tumor metastasis, using cancer cell lines and mouse models. Analysis of clinical plasma specimen showed that our technology could be used for cancer detection including accurate classification of age-matched controls and patients with ductal carcinoma in situ, invasive ductal carcinoma, or locally metastatic breast cancer in a training cohort (n = 30, 96.7% accuracy) and an independent validation cohort (n = 70, 92.9% accuracy). With clinical validation, our technology could provide a useful liquid biopsy tool to improve cancer diagnostics and real-time surveillance of tumor evolution in patients to inform personalized therapy.

Extracellular Vesicles: Current Analytical Techniques for Detection and Quantification

Since their first observation, understanding the biology of extracellular vesicles (EV) has been an important and challenging field of study. They play a key role in the intercellular communication and are involved in important physiological and pathological functions. Therefore, EV are considered as potential biomarkers for diagnosis, prognosis, and monitoring the response to treatment in some diseases. In addition, due to their properties, EV may be used for therapeutic purposes. In the study of EV, three major points have to be addressed: 1. How to isolate EV from cell culture supernatant/biological fluids, 2. how to detect them, and 3. how to characterize and quantify. In this review, we focus on the last two questions and provide the main analytical techniques up-to-date for detection and profiling of EV. We critically analyze the advantages and disadvantages of each one, aimed to be of relevance for all researchers working on EV biology and their potential applications.

Graphene-Based Strategies in Liquid Biopsy and in Viral Diseases Diagnosis

Graphene-based materials are intriguing nanomaterials with applications ranging from nanotechnology-related devices to drug delivery systems and biosensing. Multifunctional graphene platforms were proposed for the detection of several typical biomarkers (i.e., circulating tumor cells, exosomes, circulating nucleic acids, etc.) in liquid biopsy, and numerous methods, including optical, electrochemical, surface-enhanced Raman scattering (SERS), etc., have been developed for their detection. Due to the massive advancements in biology, material chemistry, and analytical technology, it is necessary to review the progress in this field from both medical and chemical sides. Liquid biopsy is considered a revolutionary technique that is opening unexpected perspectives in the early diagnosis and, in therapy monitoring, severe diseases, including cancer, metabolic syndrome, autoimmune, and neurodegenerative disorders. Although nanotechnology based on graphene has been poorly applied for the rapid diagnosis of viral diseases, the extraordinary properties of graphene (i.e., high electronic conductivity, large specific area, and surface functionalization) can be also exploited for the diagnosis of emerging viral diseases, such as the coronavirus disease 2019 (COVID-19). This review aimed to provide a comprehensive and in-depth summarization of the contribution of graphene-based nanomaterials in liquid biopsy, discussing the remaining challenges and the future trend; moreover, the paper gave the first look at the potentiality of graphene in COVID-19 diagnosis.

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

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

Optical, electrochemical and electrical (nano)biosensors for detection of exosomes: A comprehensive overview

Exosomes are small extracellular vesicles involved in many physiological activities of cells in the human body. Exosomes from cancer cells have great potential to be applied in clinical diagnosis, early cancer detection and target identification for molecular therapy. While this field is gaining increasing interests from both academia and industry, barriers such as supersensitive detection techniques and highly-efficient isolation methods remain. In the clinical settings, there is an urgent need for rapid analysis, reliable detection and point-of-care testing (POCT). With these challenges to be addressed, this article aims to review recent developments and technical breakthroughs including optical, electrochemical and electrical biosensors for exosomes detection in the field of cancer and other diseases and demonstrate how nanobiosensors could enhance the performance of conventional sensors. Working strategies, limit of detections, advantages and shortcomings of the studies are summarized. New trends, challenges and future perspectives of exosome-driven POCT in liquid biopsy have been discussed.

Therapeutic Potential of Extracellular Vesicles in Degenerative Diseases of the Intervertebral Disc

Extracellular vesicles (EVs) are lipid membrane particles carrying proteins, lipids, DNA, and various types of RNA that are involved in intercellular communication. EVs derived from mesenchymal stem cells (MSCs) have been investigated extensively in many different fields due to their crucial role as regeneration drivers, but research for their use in degenerative diseases of the intervertebral disc (IVD) has only started recently. MSC-derived EVs not only promote extracellular matrix synthesis and proliferation in IVD cells, but also reduce apoptosis and inflammation, hence having multifunctional beneficial effects that seem to be mediated by specific miRNAs (such as miR-233 and miR-21) within the EVs. Aside from MSC-derived EVs, IVD-derived EVs (e.g., stemming from notochordal cells) also have important functions in IVD health and disease. This article will summarize the current knowledge on MSC-derived and IVD-derived EVs and will highlight areas of future research, including the isolation and analysis of EV subpopulations or exposure of MSCs to cues that may enhance the therapeutic potential of released EVs.

Progress in Microfluidics-Based Exosome Separation and Detection Technologies for Diagnostic Applications

Exosomes are secreted by most cell types and circulate in body fluids. Recent studies have revealed that exosomes play a significant role in intercellular communication and are closely associated with the pathogenesis of disease. Therefore, exosomes are considered promising biomarkers for disease diagnosis. However, exosomes are always mixed with other components of body fluids. Consequently, separation methods for exosomes that allow high-purity and high-throughput separation with a high recovery rate and detection techniques for exosomes that are rapid, highly sensitive, highly specific, and have a low detection limit are indispensable for diagnostic applications. For decades, many exosome separation and detection techniques have been developed to achieve the aforementioned goals. However, in most cases, these two techniques are performed separately, which increases operation complexity, time consumption, and cost. The emergence of microfluidics offers a promising way to integrate exosome separation and detection functions into a single chip. Herein, an overview of conventional and microfluidics-based techniques for exosome separation and detection is presented. Moreover, the advantages and drawbacks of these techniques are compared.

AuNP-Amplified Surface Acoustic Wave Sensor for the Quantification of Exosomes

In this study, we report a gold nanoparticle (AuNP)-amplified surface acoustic wave (SAW) sensor for exosome detection with high sensitivity. The SAW chip was self-assembled with mercapto acetic acid to generate carboxylic groups via the Au-S bond. Anti-CD63 was then anchored onto the chip by pretreatment with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide,1-hydroxypyrrolidine-2,5-dione (NHS). Due to the existence of a membrane protein, CD63, on the exosome surface, exosomes could be bound onto the antibody-immobilized SAW chip. To amplify the detection signal, both the biotin-conjugated epithelial cell adhesion molecule (EpCAM) antibody as a secondary antibody and AuNP-labeled streptavidin were applied onto the exosome-bound SAW chip, resulting in AuNP assembly on the chip through biotin-avidin recognition. The sensor was capable of detecting 1.1 × 10³ particles/mL exosomes, which was about 2 orders of magnitude higher than those detected by the strategy without using signal amplification. The sensor also achieved a satisfactory specificity and could detect the low-abundance exosomes directly in blood samples from cancer patients with minimal disturbance. This makes the SAW sensor useful for early diagnosis of cancer.

Cancer Liquid Biopsy Using Integrated Microfluidic Exosome Analysis Platforms

Liquid biopsies serve as both powerful noninvasive diagnostic tools for early cancer screening and prognostic tools for monitoring cancer progression and treatment efficacy. Exosomes are promising biomarkers for liquid biopsies, since these nano-sized extracellular vesicles (EVs) enrich proteins, lipids, mRNAs, and miRNAs from cells of origin, including cancer cells. Although exosomes are abundantly present in various bodily fluids, conventional exosome isolation and detection methods that rely on benchtop equipment are time-consuming, expensive, and involve complicated non-portable procedures. As an alternative, recently developed microfluidic platforms can perform effective exosome separation and detection for liquid biopsies using a single device. Such methods offer advantages of integrity, speed, cost-efficiency, and portability over conventional benchtop and early microfluidic-based single-functional methods which can only separate or detect exosomes separately. These advances have made exosome-based point-of-care (POC) applications possible. This review outlines recent integrated microfluidic-based exosomal detection strategies to guide future development of such devices for use in liquid biopsies for early cancer screening, prognostic monitoring, and other potential POC applications.

Progress, opportunity, and perspective on exosome isolation - efforts for efficient exosome-based theranostics

Exosomes are small extracellular vesicles with diameters of 30-150 nm. In both physiological and pathological conditions, nearly all types of cells can release exosomes, which play important roles in cell communication and epigenetic regulation by transporting crucial protein and genetic materials such as miRNA, mRNA, and DNA. Consequently, exosome-based disease diagnosis and therapeutic methods have been intensively investigated. However, as in any natural science field, the in-depth investigation of exosomes relies heavily on technological advances. Historically, the two main technical hindrances that have restricted the basic and applied researches of exosomes include, first, how to simplify the extraction and improve the yield of exosomes and, second, how to effectively distinguish exosomes from other extracellular vesicles, especially functional microvesicles. Over the past few decades, although a standardized exosome isolation method has still not become available, a number of techniques have been established through exploration of the biochemical and physicochemical features of exosomes. In this work, by comprehensively analyzing the progresses in exosome separation strategies, we provide a panoramic view of current exosome isolation techniques, providing perspectives toward the development of novel approaches for high-efficient exosome isolation from various types of biological matrices. In addition, from the perspective of exosome-based diagnosis and therapeutics, we emphasize the issue of quantitative exosome and microvesicle separation.

Cell derived extracellular vesicles: from isolation to functionalization and biomedical applications

Extracellular vesicles (EVs) are shed from most mammalian cells by different processes. EVs possess several distinct advantages, including excellent biocompatibility, good bio-stability and low immunogenicity. Moreover, they play significant roles in physiological and pathological processes. Challenges in EV research mainly concern highly efficient isolation, specific membrane surface engineering and further development of EV applications in biomedical fields. In this review, we summarize the recent and representative research regarding isolation, engineering and biomedical applications of EVs, which represent important research focus areas. These three aspects have not ever been systematically classified and summarized in previous reviews. Finally, we give our insights into the key issues concerning EVs and their future development for biomedical applications.

Isolation and analysis of extracellular vesicles in a Morpho butterfly wing-integrated microvortex biochip

With the function of mediating intercellular communication between cells, extracellular vesicles (EVs) have been intently studied for their physiopathology and clinical application values. However, efficient EV isolation from biological fluids remains a significant challenge. To address this, this work constructs a new microvortex chip that can isolate EVs efficiently by integrating the lipid nanoprobe modified Morpho Menelaus (M. Menelaus) butterfly wing into microfluidic chip. M. Menelaus wing is well known for its orderly arranged periodic nanostructures and can generate microvortex when liquid passes through it, leading to increased interaction between EVs and M. Menelaus wing. In addition, the nanoprobe containing lipid tails can be inserted into EVs through their lipid bilayer membrane structure. Based on the described properties, high-throughput enrichment of EVs with over 70% isolation efficiency was realized. Moreover, it was demonstrated that the nanoprobe system based on M. Menelaus wing enabled downstream biological analysis of nucleic acids and proteins in EVs. Microvortex chips showed potential application value in efficient EV isolation for biomedical research and cancer diagnosis.

Exosome-specific tumor diagnosis via biomedical analysis of exosome-containing microRNA biomarkers

Exosome-containing microRNAs (exomiRs) can be employed as potential biomarkers for tumor diagnosis and have drawn much attention in the past few years. However, the separation of exosomes and the detection of exomiRs are still inconvenient or even difficult to implement. Thus, it is important to develop a simple, accurate, and reliable strategy for the separation of exosomes and the biomedical analysis of exomiRs. Herein, a novel exosome-specific tumor diagnosis strategy was constructed by integrating the rapid magnetic exosome-enrichment platform and the Ru(bpy)32+-polymer amplified electrochemiluminescence (ECL) strategy. This strategy realized the rapid and efficient capture of tumor-derived exosomes through a biological-affinity identification platform of the EpCAM antibody. The biomedical analysis of exomiRs achieved a preferable specificity and high sensitivity of 103 particles. Furthermore, we investigated the performance index for clinical blood samples from tumor patients; the results indicated that the exosome-specific tumor diagnosis strategy readily and consistently responded to exomiRs. These results indicated that the exosome-specific tumor diagnosis strategy provided new opportunities for the sensitive and efficient analysis of tumor-derived exomiRs. This strategy greatly simplified the biomedical analysis process and established the non-destructive detection mode of fluid biopsy for tumors.

Phenotypic analysis of extracellular vesicles: a review on the applications of fluorescence

Extracellular vesicles (EVs) have numerous potential applications in the field of healthcare and diagnostics, and research into their biological functions is rapidly increasing. Mainly because of their small size and heterogeneity, there are significant challenges associated with their analysis and despite overt evidence of the potential of EVs in clinical diagnostic practice, guidelines for analytical procedures have not yet been properly established. Here, we present an overview of the main methods for studying the properties of EVs based on the principles of fluorescence. Setting aside the isolation, purification and physicochemical characterization strategies which answer questions about the size, surface charge and stability of EVs (reviewed elsewhere), we focus on available optical tools that enable the direct analysis of phenotype and mechanisms of interaction with tissues. In brief, the topics on which we elaborate range from the most popular approaches such as nanoparticle tracking analysis and flow cytometry, to less commonly used techniques such as fluorescence depolarization and microarrays as well as emerging areas such as fast fluorescence lifetime imaging microscopy (FLIM). We highlight that understanding the strengths and limitations of each method is essential for choosing the most appropriate combination of analytical tools. Finally, future directions of this rapidly developing area of medical diagnostics are discussed.

Urinary MicroRNAs as Emerging Class of Noninvasive Biomarkers

MicroRNAs (miRNAs) are endogenous noncoding RNAs, which regulate gene expression on the post-transcriptional level. Since miRNAs are involved in the regulation of apoptosis, cellular proliferation, differentiation, and other important cellular processes, their deregulation is important for the development of a wide range of diseases including cancer. Apart from tissue, specific disease-related miRNA signatures can be found in body fluids as well. Especially for urologic diseases or injuries, urine miRNAs represent a promising group of biomarkers. Despite a large number of studies describing the importance of urinary miRNAs, there is a lack of recommendations for urine management and subsequent miRNA analysis. Thus, in this chapter, we aim to describe the origin and functions of urinary miRNAs and discuss the technical aspects of their detection including the pre-analytical phase principles and new directions in quantification, which could forward urine miRNA into clinical practice.

Exosome aggregation mediated stop-flow paper-based portable device for rapid exosome quantification

Exosome quantification is important for estimation of informative messengers (e.g., proteins, lipids, RNA, etc.) involving physiological and pathological effects. This work aimed to develop a simple and rapid distance-based paper portable device using exosome-capture vesicles (polydiacetylene conjugated with antiCD81) for exosome quantification in cell cultures. This novel concept relied on distinct aggregation of exosomes and exosome-capture vesicles leading to different solvent migration. Distances of the migration were used as signal readouts, which could be detected by naked eye. PDA-antiCD81 as exosome-capture vesicles were optimized (e.g., size, reaction ratio, and concentration) and the paper designs were investigated (e.g., diameter of sample reservoir and lamination layer) to enhance the solvent stop-flow effects. Finally, exosome screening on three cell culture samples (COLO1, MDA-MB-231, and HuR-KO1 subclone) was demonstrated. The method could linearly measure exosome concentrations in correlation with solvent migration distances in the range of 10⁶ -10¹⁰ particles/mL (R²  > 0.98) from the cell culture samples. The exosome concentration measurements by the developed device were independently assessed by nanoparticle tracking analysis. Results demonstrated no statistically significant difference (p > 0.05) by t-test. This low-cost and rapid device allows a portable platform for exosome quantification without the requirement of expensive equipment and expertise of operation. The developed device could potentially be useful for quantification of other biomarker-related extracellular vesicles.

Rapid Enrichment and Detection of Extracellular Vesicles Enabled by CuS-Enclosed Microgels

Extracellular vesicles (EVs) are cell-derived membranous vesicles that exist in nearly all biological fluids, including blood and urine; and carry a great number of cargo molecules such as protein, nucleic acids, and lipid. They may play important roles in cell-cell communication and modulation of pathological processes, which, however, are not yet well understood, calling for highly sensitive, specific, and rapid methods for EV detection and quantification in biological samples. Here, we report the CuS-enclosed microgels that not only help enrich EVs carrying specific protein markers from complex biomatrices, but also produce strong chemiluminescence (CL) to realize sensitive detection of the target EVs. A detection limit of 104 EV particles/mL was achieved with these microgels by targeting EV proteins like CD63 and HER2, with a dynamic range up to 108 particles/mL. Direct detection of EVs in human serum and cell culture medium without tedious sample preparation was demonstrated, consuming much less sample compared to ELISA and Western Blot. We envision that our method will be valuable for quick quantification of EVs in biological samples, benefiting disease monitoring and functional study.

Single-molecule biosensors: Recent advances and applications

Single-molecule biosensors serve the unmet need for real time detection of individual biological molecules in the molecular crowd with high specificity and accuracy, uncovering unique properties of individual molecules which are hidden when measured using ensemble averaging methods. Measuring a signal generated by an individual molecule or its interaction with biological partners is not only crucial for early diagnosis of various diseases such as cancer and to follow medical treatments but also offers a great potential for future point-of-care devices and personalized medicine. This review summarizes and discusses recent advances in nanosensors for both in vitro and in vivo detection of biological molecules offering single-molecule sensitivity. In the first part, we focus on label-free platforms, including electrochemical, plasmonic, SERS-based and spectroelectrochemical biosensors. We review fluorescent single-molecule biosensors in the second part, highlighting nanoparticle-amplified assays, digital platforms and the utilization of CRISPR technology. We finally discuss recent advances in the emerging nanosensor technology of important biological species as well as future perspectives of these sensors.

Graphene Oxide-Based Biosensors for Liquid Biopsies in Cancer Diagnosis

Liquid biopsies use blood or urine as test samples, which are able to be continuously collected in a non-invasive manner. The analysis of cancer-related biomarkers such as circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), microRNA, and exosomes provides important information in early cancer diagnosis, tumor metastasis detection, and postoperative recurrence monitoring assist with clinical diagnosis. However, low concentrations of some tumor markers, such as CTCs, ctDNA, and microRNA, in the blood limit its applications in clinical detection and analysis. Nanomaterials based on graphene oxide have good physicochemical properties and are now widely used in biomedical detection technologies. These materials have properties including good hydrophilicity, mechanical flexibility, electrical conductivity, biocompatibility, and optical performance. Moreover, utilizing graphene oxide as a biosensor interface has effectively improved the sensitivity and specificity of biosensors for cancer detection. In this review, we discuss various cancer detection technologies regarding graphene oxide and discuss the prospects and challenges of this technology.

Structure-switching aptamer triggering hybridization displacement reaction for label-free detection of exosomes

Exosomes play important roles in intercellular communications, tumor migration and invasion. However, the specific detection of cancer exosomes remains as a big challenge due to its low concentration in biofluids. Therefore, the sensitive and selective detection of cancer cells-derived exosomes has attracted growing attention owing to their potential in diagnostic and prognostic applications. Activatable strategies have received great attention for the detection of low abundant analytes due to their high sensitivity. Herein, based on molecular recognition between DNA aptamer and exosome surface biomarker (protein tyrosine kinase-7), a novel activatable and label-free strategy was designed for highly sensitive and specific sensing of exosomes. In this work, the target exosomes trigger strand replacement reaction to form G-quadruplex, which result in an obvious fluorescence enhancement of N-methylmesoporphyrin IX due to the bonding between G-quadruplex and N-methylmesoporphyrin IX. Under the optimum experimental conditions, the linear range for exosomes was measured to be 5.0 × 10⁵-5.0 × 10⁷ particles/μL and the detection limit (LOD) was calculated to be 3.4 × 10⁵ particles/μL (3σ). This assay possesses high specificity to distinguish exosomes derived from different cell lines, and has successfully been validated in patient and healthy plasma samples. Furthermore, the probe can effectively detect the exosomes in 30% fetal bovine serum, indicating that the biological matrix has a negligible effect on this method. This developed label-free, convenient and highly sensitive biosensor will offer a great opportunity for exosomes quantification in biological study and clinical application.

Lipid Nanovesicles by Microfluidics: Manipulation, Synthesis, and Drug Delivery

Lipid nanovesicles, including endogenous exosomes and synthetic lipid nanoparticles, have shown great potential in disease diagnostics, drug delivery, and cancer biology. Naturally secreted nanovesicles are promising biomarkers for early detection of cancers in vitro. Synthetic nanovesicles serve as robust drug delivery systems with enhanced tumor targeting in vivo. Microfluidic platforms with features of excellent flow control and rapid mixing are exploited as versatile tools for studying lipid nanovesicles of small sizes and delicate structures. Here, an overview of microfluidics for precise manipulation and synthesis of lipid nanovesicles is provided. The mechanisms of isolation and detection of exosomes in microfluidics, as well as the clinical utility of exosomes for cancer diagnosis, are discussed. Several microfluidic designs for controlled assembly of a variety of lipid nanovesicles are highlighted. Opportunities and outstanding challenges of microfluidics-based investigation of lipid nanovesicles are discussed.

Emerging Nanotechnologies for Liquid Biopsy: The Detection of Circulating Tumor Cells and Extracellular Vesicles

Liquid biopsy enables noninvasive and dynamic analysis of molecular or cellular biomarkers, and therefore holds great potential for the diagnosis, prognosis, monitoring of disease progress and treatment efficacy, understanding of disease mechanisms, and identification of therapeutic targets for drug development. In this review, the recent progress in nanomaterials, nanostructures, nanodevices, and nanosensors for liquid biopsy is summarized, with a focus on the detection and molecular characterization of circulating tumor cells (CTCs) and extracellular vesicles (EVs). The developments and advances of nanomaterials and nanostructures in enhancing the sensitivity, specificity, and purity for the detection of CTCs and EVs are discussed. Sensing techniques for signal transduction and amplification as well as visualization strategies are also discussed. New technologies for the reversible release of the isolated CTCs and EVs and for single-CTC/EV analysis are summarized. Emerging microfluidic platforms for the integral on-chip isolation, detection, and molecular analysis are also included. The opportunities, challenges, and prospects of these innovative materials and technologies, especially with regard to their feasibility in clinical applications, are discussed. The applications of nanotechnology-based liquid biopsy will bring new insight into the clinical practice in monitoring and treatment of tumor and other significant diseases.

Efficient isolation and sensitive quantification of extracellular vesicles based on an integrated ExoID-Chip using photonic crystals

Extracellular vesicles (EVs), involved in many diseases and pathophysiological processes, have emerged as potential biomarkers for cancer diagnosis. However, efficient isolation and detection of EVs still remain challenging. Here, we report an integrated chip for isolation of EVs with a double-filtration unit and ultrasensitive detection using photonic crystal (PC) nanostructure. Nanofiltration membranes were integrated into the device to isolate and enrich the EVs of 20-200 nm in size based on size-exclusion. Then, CD63 aptamers were used to combine the EVs on the nanofiltration membrane with a pore size of 20 nm, and excess aptamers passed through the membrane to bind with CD63 immobilized on the PC nanostructure. Benefitting from the fluorescence enhancement effect of the PC nanostructure in competition assays, the EVs could be quantified sensitively by analyzing the concentration of excess aptamers. Due to the high sensitivity, the limit of detection was as low as 8.9 × 10³ EVs per mL with a low sample consumption of only 20 μL. Furthermore, serum samples from breast cancer patients and healthy donors could be successfully distinguished. Thus, this microfluidic chip provides an effective method for pre-screening of cancer in clinical samples.

Microfluidic device for on-chip isolation and detection of circulating exosomes in blood of breast cancer patients

Tumor-derived circulating exosomes have been recognized as a promising biomarker source for cancer diagnosis via a less invasive procedure. The integration of isolation and detection of exosomes in routine clinical settings is still challenging. In this study, we developed a new microfluidic device for immunomagnetic separation and detection of blood exosomes in situ. The microfluidic device may empower the integration of target exosome analysis via high surface to volume ratios of immunomagnetic beads and highly precise fluid control with the aid of microvalves. The obtained microfluidic device was capable of on-chip isolation and detection of circulating exosomes within 1.5 h. The captured exosomes could be directly visualized with an inverted fluorescence microscope in situ by tetramethylbenzidine-based colorimetric sensing. It was revealed that a statistically significant increase (p < 0.01) in EpCAM-positive exosomes was captured for cancer patients (n = 10) on the device when compared to healthy individuals (n = 10). The device also demonstrated high predicting accuracy for tumor exosomal markers with a sensitivity of 90% and a specificity of >95% using receiver operating characteristic curves. The microfluidic device might provide a new platform to assist cancer diagnosis and molecular classification in an automated and simple fashion.

Conductance-Based Biophysical Distinction and Microfluidic Enrichment of Nanovesicles Derived from Pancreatic Tumor Cells of Varying Invasiveness

Diagnostics based on exosomes and other extracellular vesicles (EVs) are emerging as strategies for informing cancer progression and therapies, since the lipid content and macromolecular cargo of EVs can provide key phenotypic and genotypic information on the parent tumor cell and its microenvironment. We show that EVs derived from more invasive pancreatic tumor cells that express high levels of tumor-specific surface proteins and are composed of highly unsaturated lipids that increase membrane fluidity, exhibit significantly higher conductance versus those derived from less invasive tumor cells, based on dielectrophoresis measurements. Furthermore, through specific binding of the EVs to gold nanoparticle-conjugated antibodies, we show that these conductance differences can be modulated in proportion to the type as well as level of expressed tumor-specific antigens, thereby presenting methods for selective microfluidic enrichment and cytometry-based quantification of EVs based on invasiveness of their parent cell.

Label-Free Exosome Detection Based on a Low-Cost Plasmonic Biosensor Array Integrated with Microfluidics

Localized surface plasmon resonance-based plasmonic biosensors are interesting candidates for the design of portable optical biosensor platforms owing to their integration, miniaturization, multiparameter, real-time, and label-free detection characteristics. Plasmonic biosensor arrays that have been combined with microfluidics have been developed herein to detect exosomes label-free. Gold nano-ellipsoid arrays were fabricated with low-cost anodic aluminum oxide thin films that act as shadow masks for evaporation of Au. The nano-ellipsoid arrays were integrated with a microfluidic chip to achieve multiparameter detection. The anti-CD63 antibody that is specific to the exosome transmembrane protein CD63 is modified on the surface of the nano-ellipsoids. Exosome samples were injected into the biosensor platform at different concentrations and detected successfully. The detection limit was 1 ng/mL. The proposed plasmonic biosensor array can be universally applicable for the detection of other biomarkers by simply changing the antibody on the surface of the Au nano-ellipsoids. Moreover, this biosensor platform is envisaged to be potentially useful in the development of low-cost plasmonic-based biosensors for biomarker detection and for the investigation of exosomes for noninvasive disease diagnoses.

Immuno-capture of extracellular vesicles for individual multi-modal characterization using AFM, SEM and Raman spectroscopy

Tumor-derived extracellular vesicles (tdEVs) are promising blood biomarkers for cancer disease management. However, blood is a highly complex fluid that contains multiple objects in the same size range as tdEVs (30 nm-1 μm), which obscures an unimpeded analysis of tdEVs. Here, we report a multi-modal analysis platform for the specific capture of tdEVs on antibody-functionalized stainless steel substrates, followed by their analysis using SEM, Raman spectroscopy and AFM, at the single EV level in terms of size and size distribution, and chemical fingerprint. After covalent attachment of anti-EpCAM (epithelial cell adhesion molecule) antibodies on stainless steel substrates, EV samples derived from a prostate cancer cell line (LnCAP) were flushed into a microfluidic device assembled with this stainless steel substrate for capture. To track the captured objects between the different analytical instruments and subsequent correlative analysis, navigation markers were fabricated onto the substrate from a cyanoacrylate glue. Specific capture of tdEVs on the antibody-functionalized surface was demonstrated using SEM, AFM and Raman imaging, with excellent correlation between the data acquired by the individual techniques. The particle distribution was visualized with SEM. Furthermore, a characteristic lipid-protein band at 2850-2950 cm-1 was observed with Raman spectroscopy, and with AFM the size distribution and surface density of the captured EVs was assessed. Finally, correlation of SEM and Raman images enabled discrimination of tdEVs from cyanoacrylate glue particles, highlighting the capability of this multi-modal analysis platform for distinguishing tdEVs from contamination. The trans-instrumental compatibility of the stainless steel substrate and the possibility to spatially correlate the images of the different modalities with the help of the navigation markers open new avenues to a wide spectrum of combinations of different analytical and imaging techniques for the study of more complex EV samples.

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.

Microfluidic Technology for Clinical Applications of Exosomes

Exosomes, a type of nanovesicle, are distinct cellular entities specifically capable of carrying various cargos between cells. It has been hypothesized that exosomes, as an enriched source of biomolecules, may serve as biomarkers for various diseases. This review introduces general aspects of exosomes, presents the challenges in exosome research, discusses the potential of exosomes as biomarkers, and describes the contribution of microfluidic technology to enable their isolation and analysis for diagnostic and disease monitoring. Additionally, clinical applications of exosomes for diagnostic purposes are also summarized.

Application of Microfluidic Chips in Separation and Analysis of Extracellular Vesicles in Liquid Biopsy for Cancer

Extracellular vesicles (EVs) are becoming a promising biomarker in liquid biopsy of cancer. Separation EV from cell culture medium or biofluids with high purity and quality remains a technique challenge. EV manipulation techniques based on microfluidics have been developed in the last decade. Microfluidic-based EV separation techniques developed so far can be classified into two categories: surface biomarker-dependent and size-dependent approaches. Microfluidic techniques allow the integration of EV separation and analysis on a single chip. Integrated EV separation and on-chip analysis have shown great potential in cancer diagnosis and monitoring treatment of responses. In this review, we discuss the development of microfluidic chips for EV separation and analysis. We also detail the clinical application of these microfluidic chips in the liquid biopsy of various cancers.

Multiplexed immunophenotyping of circulating exosomes on nano-engineered ExoProfile chip towards early diagnosis of cancer

Circulating exosomes have been studied as a promising biomarker for non-invasive cancer diagnosis, as they are implicated in tumor initiation, progression, and metastasis. However, the clinical significance of circulating exosomes has not been revealed thoroughly, due to the technical limitation in sensitive and multiplexed detection of cargoes on exosomes, such as proteins and nucleic acids. Herein we developed an integrated exosome profiling platform (ExoProfile chip) to afford superior sensitivity and multiplexed capability for quantitative detection of a panel of surface protein markers on exosomes. To achieve this goal, we innovatively constructed 3D porous serpentine nanostructures via patterned colloidal self-assembly to provide enormous reaction sites and improve biosensing efficiency of exosomes. Meanwhile, the switchable microfluidic design enabled the simultaneous detection of eight markers on single addition of exosome samples. The ExoProfile chip was validated with purified exosomes from SKOV3 cells, which yielded a limit of detection of 21 exosomes per μL. We applied the ExoProfile chip to clinical analysis of circulating exosomes using only 10 μL ovarian cancer plasma and completing the analysis within 3 h. The diagnostic power of seven markers (EGFR, HER2, CA125, FRα, CD24, EpCAM, and CD9 plus CD63) were evaluated with receiver operator characteristic curve and heatmap clustering. Compared to single biomarker, the combined assessment of a biomarker panel was demonstrated to display improved accuracy in distinguishing early and late stage cancer. The results suggested the ExoProfile chip as a promising platform for molecular fingerprinting of circulating exosomes towards early cancer diagnosis.

Liquid Biopsies for Ovarian Carcinoma: How Blood Tests May Improve the Clinical Management of a Deadly Disease

Ovarian cancers (OvC) are frequent, with more than 22,000 new cases each year for 14,000 deaths in the United States. Except for patients with BRCA1 or BRCA2 mutations, diagnostic methods, prognostic tools, and therapeutic strategies have not much improved in the last two decades. High throughput tumor molecular analyses have identified important alterations involved in ovarian carcinoma growth and spreading. However, these data have not modified the clinical management of most of patients. Moreover, tumor sample collection requires invasive procedures not adapted to objectives, such as the screening, prediction, or assessment of treatment efficacy, monitoring of residual disease, and early diagnosis of relapse. In recent years, circulating tumor biomarkers (also known as "liquid biopsies") such as circulating tumor cells, circulating nucleotides (DNA or miRNA), or extracellular vesicles, have been massively explored through various indications, platforms, and goals, but their use has not yet been validated in routine practice. This review describes the methods of analysis and results related to liquid biopsies for ovarian epithelial cancer. The different settings that a patient can go through during her journey with OvC are explored: screening and early diagnosis, prognosis, prediction of response to systemic therapies for advanced stages, and monitoring of residual subclinical disease.

Liquid Biopsies for Ovarian Carcinoma: How Blood Tests May Improve the Clinical Management of a Deadly Disease

Ovarian cancers (OvC) are frequent, with more than 22,000 new cases each year for 14,000 deaths in the United States. Except for patients with BRCA1 or BRCA2 mutations, diagnostic methods, prognostic tools, and therapeutic strategies have not much improved in the last two decades. High throughput tumor molecular analyses have identified important alterations involved in ovarian carcinoma growth and spreading. However, these data have not modified the clinical management of most of patients. Moreover, tumor sample collection requires invasive procedures not adapted to objectives, such as the screening, prediction, or assessment of treatment efficacy, monitoring of residual disease, and early diagnosis of relapse. In recent years, circulating tumor biomarkers (also known as "liquid biopsies") such as circulating tumor cells, circulating nucleotides (DNA or miRNA), or extracellular vesicles, have been massively explored through various indications, platforms, and goals, but their use has not yet been validated in routine practice. This review describes the methods of analysis and results related to liquid biopsies for ovarian epithelial cancer. The different settings that a patient can go through during her journey with OvC are explored: screening and early diagnosis, prognosis, prediction of response to systemic therapies for advanced stages, and monitoring of residual subclinical disease.

Liquid Biopsies for Ovarian Carcinoma: How Blood Tests May Improve the Clinical Management of a Deadly Disease

Ovarian cancers (OvC) are frequent, with more than 22,000 new cases each year for 14,000 deaths in the United States. Except for patients with BRCA1 or BRCA2 mutations, diagnostic methods, prognostic tools, and therapeutic strategies have not much improved in the last two decades. High throughput tumor molecular analyses have identified important alterations involved in ovarian carcinoma growth and spreading. However, these data have not modified the clinical management of most of patients. Moreover, tumor sample collection requires invasive procedures not adapted to objectives, such as the screening, prediction, or assessment of treatment efficacy, monitoring of residual disease, and early diagnosis of relapse. In recent years, circulating tumor biomarkers (also known as "liquid biopsies") such as circulating tumor cells, circulating nucleotides (DNA or miRNA), or extracellular vesicles, have been massively explored through various indications, platforms, and goals, but their use has not yet been validated in routine practice. This review describes the methods of analysis and results related to liquid biopsies for ovarian epithelial cancer. The different settings that a patient can go through during her journey with OvC are explored: screening and early diagnosis, prognosis, prediction of response to systemic therapies for advanced stages, and monitoring of residual subclinical disease.

Liquid biopsy in ovarian cancer: recent advances in circulating extracellular vesicle detection for early diagnosis and monitoring progression

The current biomarkers available in the clinic are not enough for early diagnosis or for monitoring disease progression of ovarian cancer. Liquid biopsy is a minimally invasive test and has the advantage of early diagnosis and real-time monitoring of treatment response. Although significant progress has been made in the usage of circulating tumor cells and cell-free DNA for ovarian cancer diagnosis, their potential for early detection or monitoring progression remains elusive. Extracellular vesicles (EVs) are a heterogeneous group of lipid membranous particles released from almost all cell types. EVs contain proteins, mRNA, DNA fragments, non-coding RNAs, and lipids and play a critical role in intercellular communication. Emerging evidence suggests that EVs have crucial roles in cancer development and metastasis, thus holding promise for liquid biopsy-based biomarker discovery for ovarian cancer diagnosis. In this review, we discuss the advantages of EV-based liquid biopsy, summarize the protein biomarkers identified from EVs in ovarian cancer, and highlight the utility of new technologies recently developed for EV detection with an emphasis on their use for diagnosing ovarian cancer, monitoring cancer progression, and developing personalized medicine.

Ultrasensitive and Reversible Nanoplatform of Urinary Exosomes for Prostate Cancer Diagnosis

Prostate cancer cell-derived exosomes in urine have been extensively studied recently and regarded as novel biomarkers for cancer diagnosis and prognosis, which presents wide prospects in clinical applications. Sensitive detection and specific capture methods are essential for exosomes analysis. Herein, a dual functional platform composed of superparamagnetic conjunctions and molecular beacons (SMC-MB) is reported. The SMC-MB platform is designed based on aptamer immunoaffinity with ultrasensitive detection efficiency and reversible isolation capacity, which, respectively, profit from nonenzymatic amplification methods and magnetic separation along with restriction cleavage. It is noteworthy that exosomes quantification was exactly amplified and transformed into single strand DNA detection. Correlated measurements evidence that the limit of detection of SMC-MB is as low as ∼100 particles/μL in urine, and a linear relationship meets between the logarithmic concentration of exosomes and fluorescence intensity of the molecular beacon. Furthermore, employing prostate specific membrane antigen (PSMA) aptamer, the platform adapted to detect and capture PMSA-positive exosomes from urine samples provides excellent diagnostic efficiency for prostate cancer (PCa). The expression of typical biomarkers of PCa, i.e., PSA and PCA3 mRNA, is significantly higher in PSMA-positive exosomes. Altogether, the platform and strategy described in this paper are promising in urinary exosomes analysis and prostate cancer detection.

Microfluidic on-demand engineering of exosomes towards cancer immunotherapy

Extracellular vesicles (EVs), particularly exosomes (30-150 nm), are an emerging delivery system in mediating cellular communications, which have been observed for priming immune responses by presenting parent cell signaling proteins or tumor antigens to immune cells. Therefore, preparation of antigenic exosomes that can play therapeutic roles, particularly in cancer immunotherapy, is emerging. However, standard benchtop methods (e.g., ultracentrifugation and filtration) lack the ability to purify antigenic exosomes specifically among other microvesicle subtypes, due to the non-selective and time-consuming (>10 h) isolation protocols. Exosome engineering approaches, such as the transfection of parent cells, also suffer from poor yields, low purity, and time-consuming operations. In this paper, we introduce a streamlined microfluidic cell culture platform for integration of harvesting, antigenic modification, and photo-release of surface engineered exosomes in one workflow, which enables the production of intact, MHC peptide surface engineered exosomes for cytolysis activation. A PDMS microfluidic cell culture chip is simply cast from a 3D-printed mold. This proof-of-concept study demonstrated the enhanced ability of harvested exosomes in antigen presentation and T cell activation, by decorating melanoma tumor peptides on the exosome surface (e.g., gp-100, MART-1, and MAGE-A3). Such surface engineered antigenic exosomes were harvested in real-time from the on-chip culture of leukocytes isolated from human blood, leading to much faster cellular uptake. The activation of gp100-specific CD8 T cells which were purified from the spleen of 2 Pmel1 transgenic mice was evaluated using surface engineered exosomes prepared from murine antigen presenting cells. Antigen-specific CD8 T cell proliferation was significantly induced by the engineered exosomes compared to that by native, non-engineered exosomes. This microfluidic platform serves as an automated and highly integrated cell culture device for rapid and real-time production of therapeutic exosomes that could advance cancer immunotherapy.