Integrated microfluidic system for isolating exosome and analyzing protein marker PD-L1

Small extracellular vesicles detection using dielectrophoresis-based microfluidic chip for diagnosis of breast cancer

Small extracellular vesicles (sEVs) reflect the genotype and phenotype of original cells and are biomarkers for early diagnosis and treatment monitoring of tumors. Yet, their small size and low density make them difficult to isolate and detect in body fluid samples. This study proposes a novel acDEP-Exo chip filled with transparent micro-beads, which formed a non-uniform electrical field, and finally achieved rapid, sensitive, and tunable sEVs capture and detection. The method requires only 20-50 μL of sample, achieved a limit of detection (LOD) of 161 particles/μL, and can detect biomarkers within 13 min. We applied the chip to analyze the two markers of sEV's EpCAM and MUC1 in clinical plasma samples from breast cancer (BC) patients and healthy volunteers and found that the combined evaluation of sEV's biomarkers has extremely high sensitivity, specificity and accuracy. The present study introduces an alternative approach to sEVs isolation and detection, has a great potential in real-time sEVs-based liquid biopsy.

Recent progress in engineered extracellular vesicles and their biomedical applications

AIMS

To present the recent update on the isolation, engineering techniques for extracellular vesicles, limitations associated with different isolation techniques, different biomedical applications, and challenges of engineered extracellular vesicles for the benefit of researchers from academic, industry, etc. MATERIALS AND METHODS: Peer-reviewed articles from most recognized journals were collected, and presented information was analyzed to discuss collection, chemical, electroporation, cellular, and membrane surface engineering to design extracellular vesicles for various therapeutic applications. In addition, we present the applications and limitations of techniques for the collection of extracellular vesicles.

KEY FINDINGS

There is a need for isolation techniques with the gold standard. However, advanced extracellular vesicle isolation techniques showed improved recovery, and purity of extracellular vesicles. Tumor therapy is a major part of the therapy section that illustrates the role of engineered extracellular vesicles in synergetic therapy such as phototherapy, theragnostic, and delivery of genetic materials. In addition, extracellular vesicles have shown their potential in the treatment of retinal disorders, neurodegenerative disease, tuberculosis, osteoporosis, inflammatory bowel disease, vaccine production, and wound healing.

SIGNIFICANCE

Engineered extracellular vesicles can deliver cargo to the specific cells, elicit an immune response and could be used for the development of the vaccines in the future. However, the progress is at the initial stage. Overall, this review will provide a comprehensive understanding and could serve as a reference for researchers in the clinical translation of engineered extracellular vesicles in different biomedical fields.

Liquid biopsy for human cancer: cancer screening, monitoring, and treatment

Currently, tumor treatment modalities such as immunotherapy and targeted therapy have more stringent requirements for obtaining tumor growth information and require more accurate and easy-to-operate tumor information detection methods. Compared with traditional tissue biopsy, liquid biopsy is a novel, minimally invasive, real-time detection tool for detecting information directly or indirectly released by tumors in human body fluids, which is more suitable for the requirements of new tumor treatment modalities. Liquid biopsy has not been widely used in clinical practice, and there are fewer reviews of related clinical applications. This review summarizes the clinical applications of liquid biopsy components (e.g., circulating tumor cells, circulating tumor DNA, extracellular vesicles, etc.) in tumorigenesis and progression. This includes the development process and detection techniques of liquid biopsies, early screening of tumors, tumor growth detection, and guiding therapeutic strategies (liquid biopsy-based personalized medicine and prediction of treatment response). Finally, the current challenges and future directions for clinical applications of liquid biopsy are proposed. In sum, this review will inspire more researchers to use liquid biopsy technology to promote the realization of individualized therapy, improve the efficacy of tumor therapy, and provide better therapeutic options for tumor patients.

Salivary exosomal microRNA profile as biomonitoring tool for diagnosis and prognosis of patients with head and neck squamous cell carcinoma: a systematic review

OBJECTIVE

Exosomes are extracellular vesicles found in saliva and other body fluids. These vesicles range in size from 30 to 150 nm and play a crucial role in intercellular communication, transporting different biomolecules, actively targeting cells. These vesicles regulate both physiological and pathological processes within recipient cells. MicroRNAs (miRs) are transported within exosomes and are delivered to target cells where they influence signaling pathways, taking on a crucial regulatory role in oncogenesis; for example, they are implicated in progression and infiltration of various cancers, such as head and neck squamous cell carcinoma (HNSCC).

MATERIAL AND METHODS

A systematic literature search based on specific keywords, according to the PRISMA guidelines, was carried out on PubMed, Web of Science, Scopus, and Google Scholar. Only original articles were selected during this review. The risk of bias was assessed by QUADAS-2.

RESULTS

At the end of the selection process 9 articles were included. In these studies, 41 miRs showed differential expression between healthy subjects and patient with HNSCC. The techniques varied among studies for the extraction and analysis of exosomal miRs. We presented also salivary exosomal miRs pathways, to give insights about pathogenetic mechanisms.

CONCLUSIONS

Exosomal microRNA are promising biomarkers for HNSCC detection. MiR-10b-5p, miR-486-5p, miR-24-3p, miR-412-3p, and miR-512-3p are the most promising markers applicable to diagnostics, while miR-1307-5p and miR-519c-3p resulted overexpressed and correlated to worse survival outcomes.

Recent Advances in Microfluidic-Based Extracellular Vesicle Analysis

Extracellular vesicles (EVs) serve as vital messengers, facilitating communication between cells, and exhibit tremendous potential in the diagnosis and treatment of diseases. However, conventional EV isolation methods are labor-intensive, and they harvest EVs with low purity and compromised recovery. In addition, the drawbacks, such as the limited sensitivity and specificity of traditional EV analysis methods, hinder the application of EVs in clinical use. Therefore, it is urgent to develop effective and standardized methods for isolating and detecting EVs. Microfluidics technology is a powerful and rapidly developing technology that has been introduced as a potential solution for the above bottlenecks. It holds the advantages of high integration, short analysis time, and low consumption of samples and reagents. In this review, we summarize the traditional techniques alongside microfluidic-based methodologies for the isolation and detection of EVs. We emphasize the distinct advantages of microfluidic technology in enhancing the capture efficiency and precise targeting of extracellular vesicles (EVs). We also explore its analytical role in targeted detection. Furthermore, this review highlights the transformative impact of microfluidic technology on EV analysis, with the potential to achieve automated and high-throughput EV detection in clinical samples.

Rapid automated extracellular vesicle isolation and miRNA preparation on a cost-effective digital microfluidic platform

As a prerequisite for extracellular vesicle (EV) -based studies and diagnosis, effective isolation, enrichment and retrieval of EV biomarkers are crucial to subsequent analyses, such as miRNA-based liquid biopsy for non-small-cell lung cancer (NSCLC). However, most conventional approaches for EV isolation suffer from lengthy procedure, high cost, and intense labor. Herein, we introduce the digital microfluidic (DMF) technology to EV pretreatment protocols and demonstrate a rapid and fully automated sample preparation platform for clinical tumor liquid biopsy. Combining a reusable DMF chip technique with a low-cost EV isolation and miRNA preparation protocol, the platform completes automated sample processing in 20-30 min, supporting immediate RT-qPCR analyses on EV-derived miRNAs (EV-miRNAs). The utility and reliability of the platform was validated via clinical sample processing for EV-miRNA detection. With 23 tumor and 20 non-tumor clinical plasma samples, we concluded that EV-miR-486-5p and miR-21-5p are effective biomarkers for NSCLC with a small sample volumn (20-40 μL). The result was consistent to that of a commercial exosome miRNA extraction kit. These results demonstrate the effectiveness of DMF in EV pretreatment for miRNA detection, providing a facile solution to EV isolation for liquid biopsy.

Isolation and usage of exosomes in central nervous system diseases

BACKGROUND

Exosomes are vesicles secreted by all types of mammalian cells. They are characterized by a double-layered lipid membrane structure. They serve as carriers for a plethora of signal molecules, including DNA, RNA, proteins, and lipids. Their unique capability of effortlessly crossing the blood-brain barrier underscores their critical role in the progression of various neurological disorders. This includes, but is not limited to, diseases such as Alzheimer's, Parkinson's, and ischemic stroke. Establishing stable and mature methods for isolating exosomes is a prerequisite for the study of exosomes and their biomedical significance. The extraction technologies of exosomes include differential centrifugation, density gradient centrifugation, size exclusion chromatography, ultrafiltration, polymer coprecipitation, immunoaffinity capture, microfluidic, and so forth. Each extraction technology has its own advantages and disadvantages, and the extraction standards of exosomes have not been unified internationally.

AIMS

This review aimed to showcase the recent advancements in exosome isolation techniques and thoroughly compare the advantages and disadvantages of different methods. Furthermore, the significant research progress made in using exosomes for diagnosing and treating central nervous system (CNS) diseases has been emphasized.

CONCLUSION

The varying isolation methods result in differences in the concentration, purity, and size of exosomes. The efficient separation of exosomes facilitates their widespread application, particularly in the diagnosis and treatment of CNS diseases.

Engineered Extracellular Vesicles in Wound Healing: Design, Paradigms, and Clinical Application

The severe quality of life and economic burden imposed by non-healing skin wounds, infection risks, and treatment costs are affecting millions of patients worldwide. To mitigate these challenges, scientists are relentlessly seeking effective treatment measures. In recent years, extracellular vesicles (EVs) have emerged as a promising cell-free therapy strategy, attracting extensive attention from researchers. EVs mediate intercellular communication, possessing excellent biocompatibility and stability. These features make EVs a potential tool for treating a plethora of diseases, including those related to wound repair. However, there is a growing focus on the engineering of EVs to overcome inherent limitations such as low production, relatively fixed content, and targeting capabilities of natural EVs. This engineering could improve both the effectiveness and specificity of EVs in wound repair treatments. In light of this, the present review will introduce the latest progress in the design methods and experimental paradigms of engineered EVs applied in wound repair. Furthermore, it will comprehensively analyze the current clinical research status and prospects of engineered EVs within this field.

Exosomal miRNAs from neutrophils act as accurate biomarkers for gastric cancer diagnosis

BACKGROUND

Gastric cancer (GC) is the third leading cause of cancer-related death worldwide. Sensitive and accurate biomarkers can greatly aid in early diagnosis and favorable prognosis. Neutrophils are the most abundant immune cells in human circulation and play a critical role in tumor progression. Neutrophil-derived exosomes (Neu-Exo) contain abundant bioactive molecules and are critically involved in disease progression.

METHODS

We proposed a Dynabeads-based (CD66b antibody-coupled) separation and detection system for Neu-Exo analysis. Dual antibody-assisted fluorescent Dynabeads was established to detect Neu-Exo abundance. MiRNA signature of Neu-Exo was identified by RNA sequencing. QRT-PCR and droplet digital PCR (ddPCR) were used for candidate miRNA detection and the potential of Neu-Exo miRNAs in the diagnosis of gastric cancer was evaluated.

RESULTS

Dual antibody-assisted fluorescent Dynabeads obtained a detection limit of 7.8 × 105 particles/mL of Neu-Exo and a recovery rate of 81 % under optimized conditions. ROC curve indicated that the abundance of CD66b+ Neu-Exo could well distinguish GC patients from healthy controls (HC) (AUC > 0.8). Additionally, miR-223-3p was found among the top differentially expressed miRNAs in Neu-Exo and presented superior diagnostic value in gastric cancer. Droplet digital PCR (ddPCR) significantly improved the diagnostic efficiency to differentiate GC patients from HC and benign gastric diseases (BGD) patients (AUC > 0.9).

CONCLUSION

The Dynabeads-based separation and detection system, assisted with ddPCR analysis, provides a promising platform to enrich Neu-Exo and analyze miRNA profile for gastric cancer liquid biopsy.

Microfluidic Platforms for Real-Time In Situ Monitoring of Biomarkers for Cellular Processes

Cellular processes are mechanisms carried out at the cellular level that are aimed at guaranteeing the stability of the organism they comprise. The investigation of cellular processes is key to understanding cell fate, understanding pathogenic mechanisms, and developing new therapeutic technologies. Microfluidic platforms are thought to be the most powerful tools among all methodologies for investigating cellular processes because they can integrate almost all types of the existing intracellular and extracellular biomarker-sensing methods and observation approaches for cell behavior, combined with precisely controlled cell culture, manipulation, stimulation, and analysis. Most importantly, microfluidic platforms can realize real-time in situ detection of secreted proteins, exosomes, and other biomarkers produced during cell physiological processes, thereby providing the possibility to draw the whole picture for a cellular process. Owing to their advantages of high throughput, low sample consumption, and precise cell control, microfluidic platforms with real-time in situ monitoring characteristics are widely being used in cell analysis, disease diagnosis, pharmaceutical research, and biological production. This review focuses on the basic concepts, recent progress, and application prospects of microfluidic platforms for real-time in situ monitoring of biomarkers in cellular processes.

Engineered exosomes for tissue regeneration: from biouptake, functionalization and biosafety to applications

Exosomes are increasingly recognized as important effector molecules that regulate intercellular signaling pathways. Notably, certain types of exosomes can induce therapeutic responses, including cell proliferation, angiogenesis, and tissue repair. The use of exosomes in therapy is a hot spot in current research, especially in regenerative medicine. Despite the therapeutic potential, problems have hindered their success in clinical applications. These shortcomings include low concentration, poor targeting and limited loading capability. To fully realize their therapeutic potential, certain modifications are needed in native exosomes. In the present review, we summarize the exosome modification and functionalization strategies. In addition, we provide an overview of potential clinical applications and highlight the issues associated with the biosafety and biocompatibility of engineered exosomes in applications.

Extracellular Vesicles: Techniques and Biomedical Applications Related to Single Vesicle Analysis

Extracellular vesicles (EVs) are extensively dispersed lipid bilayer membrane vesicles involved in the delivery and transportation of molecular payloads to certain cell types to facilitate intercellular interactions. Their significant roles in physiological and pathological processes make EVs outstanding biomarkers for disease diagnosis and treatment monitoring as well as ideal candidates for drug delivery. Nevertheless, differences in the biogenesis processes among EV subpopulations have led to a diversity of biophysical characteristics and molecular cargos. Additionally, the prevalent heterogeneity of EVs has been found to substantially hamper the sensitivity and accuracy of disease diagnosis and therapeutic monitoring, thus impeding the advancement of clinical applications. In recent years, the evolution of single EV (SEV) analysis has enabled an in-depth comprehension of the physical properties, molecular composition, and biological roles of EVs at the individual vesicle level. This review examines the sample acquisition tactics prior to SEV analysis, i.e., EV isolation techniques, and outlines the current state-of-the-art label-free and label-based technologies for SEV identification. Furthermore, the challenges and prospects of biomedical applications based on SEV analysis are systematically discussed.

Review of the advances in lipid anchors-based biosensors for the isolation and detection of exosomes

Exosomes are nanoparticles with a bilayer lipid structure that carry cargo from their cells of origin. These vesicles are vital to disease diagnosis and therapeutics; however, conventional isolation and detection techniques are generally complicated, time-consuming, and costly, thus hampering the clinical applications of exosomes. Meanwhile, sandwich-structured immunoassays for exosome isolation and detection rely on the specific binding of membrane surface biomarkers, which may be limited by the type and amount of target protein present. Recently, lipid anchors inserted into the membranes of vesicles through hydrophobic interactions have been adopted as a new strategy for extracellular vesicle manipulation. By combining nonspecific and specific binding, the performance of biosensors can be improved variously. This review presents the reaction mechanisms and properties of lipid anchors/probes, as well as advances in the development of biosensors. The combination of signal amplification methods with lipid anchors is discussed in detail to provide insights into the design of convenient and sensitive detection techniques. Finally, the advantages, challenges, and future directions of lipid anchor-based exosome isolation and detection methods are highlighted from the perspectives of research, clinical use, and commercialization.

Integrated "lab-on-a-chip" microfluidic systems for isolation, enrichment, and analysis of cancer biomarkers

The liquid biopsy has garnered considerable attention as a complementary clinical tool for the early detection, molecular characterization and monitoring of cancer over the past decade. In contrast to traditional solid biopsy techniques, liquid biopsy offers a less invasive and safer alternative for routine cancer screening. Recent advances in microfluidic technologies have enabled handling of liquid biopsy-derived biomarkers with high sensitivity, throughput, and convenience. The integration of these multi-functional microfluidic technologies into a 'lab-on-a-chip' offers a powerful solution for processing and analyzing samples on a single platform, thereby reducing the complexity, bio-analyte loss and cross-contamination associated with multiple handling and transfer steps in more conventional benchtop workflows. This review critically addresses recent developments in integrated microfluidic technologies for cancer detection, highlighting isolation, enrichment, and analysis strategies for three important sub-types of cancer biomarkers: circulating tumor cells, circulating tumor DNA and exosomes. We first discuss the unique characteristics and advantages of the various lab-on-a-chip technologies developed to operate on each biomarker subtype. This is then followed by a discussion on the challenges and opportunities in the field of integrated systems for cancer detection. Ultimately, integrated microfluidic platforms form the core of a new class of point-of-care diagnostic tools by virtue of their ease-of-operation, portability and high sensitivity. Widespread availability of such tools could potentially result in more frequent and convenient screening for early signs of cancer at clinical labs or primary care offices.

Reliable Detection of Extracellular PD-L1 by DNA Computation-Mediated Microfluidics

Extracellular vesicle PD-L1 (programmed death-1 ligand 1) is of greater value in tumor diagnosis, prognosis, and efficacy monitoring of anti-PD-1/PD-L1 immunotherapy. However, soluble PD-L1 interferes with the accurate detection of extracellular vesicle (EV) PD-L1. Here, we developed a microfluidic differentiation method for the detection of extracellular PD-L1, without the interference of soluble, by DNA computation with lipid probes and PD-L1 aptamer as inputs (DECLA). For the developed DECLA method, a cholesterol-DNA probe was designed that efficiently embeds into the EV membrane, and an aptamer-based PD-L1 probe was used for PD-L1 recognition. Due to the stable secondary structure of the designed connector, only cobinding of cholesterol-DNA and PD-L1 affinity probe induced biotin-labeled connector activation, while soluble PD-L1 cannot hybridize. As a result, PD-L1 EVs can be efficiently captured by streptavidin-functioned herringbone chip and quantified by anti-CD63-induced fluorescence signal. The high specificity of dual-input DNA computation allied to the high sensitivity of microfluidic-based detection was suitable for distinguishing lung cancer patients from healthy donors, highlighting its potential translation to clinical diagnosis and therapy monitoring.

Rapid exosome isolation and in situ multiplexed detection of exosomal surface proteins and microRNAs on microfluidic platform

Exosomes are considered as promising biomarkers for early cancer diagnosis and prognosis. However, the majority of the research studies focused on a single type of exosomal biomarkers, which cannot comprehensively reflect the state of cancer for accurate diagnosis. To address this problem, we presented a ship-shaped microfluidic device containing a microcolumn array for simultaneous in situ detection of exosomal surface proteins and miRNAs. Exosomes were first captured in the microchannels modified with CD63 protein aptamer. Exosomal surface proteins and miRNAs were simultaneously detected in four parallel channels to avoid the interference of fluorescent signals using specific aptamers labeled by Cy5 and catalytic hairpin assembly (CHA) based signal amplification strategy. The limit of detection for multiplexed markers in exosomes was 83 exosomes per μL, which is comparable to previously reported methods. Through quantitative analysis of two disease-specific surface proteins and miRNAs derived from different cancer cells and clinical serum samples, different cancer subtypes as well as cancer patients and healthy people could be significantly distinguished. These results suggest that this simple, highly sensitive, and more accurate analytical strategy by simultaneous in situ profiling of different types of exosomal biomarkers has potential applications in cancer diagnosis and stage monitoring.

Programmable DNA Circuit-Facilitated Determination of Circulating Extracellular Vesicle PD-L1 for Lung Cancer Diagnosis and Immunotherapy Response Prediction

Circulating extracellular vesicle (EV) PD-L1 is correlated with the occurrence and progression of lung cancer and has great potential as a valuable diagnostic and immunotherapy predictive biomarker. In this work, we propose a fluorescent biosensing method for the sensitive and accurate determination of circulating EV PD-L1. Specifically, after the phosphatidylserine-targeting peptide-assisted magnetic enrichment, a programmable DNA circuit is designed to translate the presence of PD-L1 to the appearance of numerous duplex DNA probes on the circulating EV surface. Upon fructose treatment, these newly formed duplex DNA probes are released from the EV surface to activate the trans-cleavage activity of CRISPR/Cas12a system, which finally produces a significant fluorescence signal. Experimental results reveal that the method not only enables sensitive determination of EV PD-L1 with a detection limit of 67 particles/mL but also demonstrates the potential use in the diagnosis and immunotherapy response prediction of lung cancer in a principle-of-proof study. Therefore, the method may provide a useful tool for EV PD-L1 determination, which may provide valuable information for the precise diagnosis and personalized treatment of lung cancer patients.

Plant-derived extracellular vesicles (PDEVs) in nanomedicine for human disease and therapeutic modalities

BACKGROUND

The past few years have witnessed a significant increase in research related to plant-derived extracellular vesicles (PDEVs) in biological and medical applications. Using biochemical technologies, multiple independent groups have demonstrated the important roles of PDEVs as potential mediators involved in cell-cell communication and the exchange of bio-information between species. Recently, several contents have been well identified in PDEVs, including nucleic acids, proteins, lipids, and other active substances. These cargoes carried by PDEVs could be transferred into recipient cells and remarkably influence their biological behaviors associated with human diseases, such as cancers and inflammatory diseases. This review summarizes the latest updates regarding PDEVs and focuses on its important role in nanomedicine applications, as well as the potential of PDEVs as drug delivery strategies to develop diagnostic and therapeutic agents for the clinical management of diseases, especially like cancers.

CONCLUSION

Considering its unique advantages, especially high stability, intrinsic bioactivity and easy absorption, further elaboration on molecular mechanisms and biological factors driving the function of PDEVs will provide new horizons for the treatment of human disease.

Combining sensors and actuators with electrowetting-on-dielectric (EWOD): advanced digital microfluidic systems for biomedical applications

The concept of digital microfluidics (DMF) enables highly flexible and precise droplet manipulation at a picoliter scale, making DMF a promising approach to realize integrated, miniaturized "lab-on-a-chip" (LOC) systems for research and clinical purposes. Owing to its simplicity and effectiveness, electrowetting-on-dielectric (EWOD) is one of the most commonly studied and applied effects to implement DMF. However, complex biomedical assays usually require more sophisticated sample handling and detection capabilities than basic EWOD manipulation. Alternatively, combined systems integrating EWOD actuators and other fluidic handling techniques are essential for bringing DMF into practical use. In this paper, we briefly review the main approaches for the integration/combination of EWOD with other microfluidic manipulation methods or additional external fields for specified biomedical applications. The form of integration ranges from independently operating sub-systems to fully coupled hybrid actuators. The corresponding biomedical applications of these works are also summarized to illustrate the significance of these innovative combination attempts.

Aptamer-Assisted Traceless Isolation of PD-L1-Positive Small Extracellular Vesicles for Dissecting Their Subpopulation Signature and Function

Small extracellular vesicles (sEVs) are heterogeneous membrane-bound vesicles that carry numerous bioactive molecules. Studies have reported that sEVs carrying PD-L1 on the surface could contribute to immunosuppression; however, the precise mechanisms are unclear. To fully dissect their mode of action, it requires qualified methods to specifically isolate natural PD-L1-positive sEVs from heterogeneous sEVs. This study reported an aptamer-assisted capture-and-release strategy for traceless isolation of PD-L1-positive sEVs. The PD-L1 aptamer-anchored magnetic microspheres enable the specific capture of PD-L1-positive sEVs. The traceless release of captured PD-L1-positive sEVs was triggered by competition of complementary oligonucleotides, endowing the obtained label-free PD-L1-positive sEVs with natural properties. Benefited from this traceless isolation strategy, the distinct molecule profiles in adhesion and immuno-regulation between PD-L1-positive and PD-L1-negative sEVs were revealed. Compared to PD-L1-negative sEVs, PD-L1-positive sEVs were much more concentrated in cadherin binding, accompanied by increased adhesion to lymphatic endothelial cells and T cells but decreased adhesion to the extracellular matrix. Moreover, PD-L1-positive sEVs could transfer their enriched immunosuppressive "synapse"-related proteins to antigen-presenting cells, thereby inducing a tolerogenic-like phenotype. In summary, the present work dissects the subpopulation signature and action mode of PD-L1-positive sEVs for the first time and provides a general approach to the traceless isolation of sEV subpopulations.

Recent developments in isolating methods for exosomes

Exosomes are the smallest extracellular vesicles that can be released by practically all cell types, and range in size from 30 nm to 150 nm. As the major marker of liquid biopsies, exosomes have great potential for disease diagnosis, therapy, and prognosis. However, their inherent heterogeneity, the complexity of biological fluids, and the presence of nanoscale contaminants make the isolation of exosomes a great challenge. Traditional isolation methods of exosomes are cumbersome and challenging with complex and time-consuming operations. In recent years, the emergence of microfluidic chips, nanolithography, electro-deposition, and other technologies has promoted the combination and innovation of the isolation methods. The application of these methods has brought very considerable benefits to the isolation of exosomes such as ultra-fast, portable integration, and low loss. There are significant functional improvements in isolation yield, isolation purity, and clinical applications. In this review, a series of methods for the isolation of exosomes are summarized, with emphasis on the emerging methods, and in-depth comparison and analysis of each method are provided, including their principles, merits, and demerits.

Microfluidic Strategies for Extracellular Vesicle Isolation: Towards Clinical Applications

Extracellular vesicles (EVs) are double-layered lipid membrane vesicles released by cells. Currently, EVs are attracting a lot of attention in the biological and medical fields due to their role as natural carriers of proteins, lipids, and nucleic acids. Thus, they can transport useful genomic information from their parental cell through body fluids, promoting cell-to-cell communication even between different organs. Due to their functionality as cargo carriers and their protein expression, they can play an important role as possible diagnostic and prognostic biomarkers in various types of diseases, e.g., cancers, neurodegenerative, and autoimmune diseases. Today, given the invaluable importance of EVs, there are some pivotal challenges to overcome in terms of their isolation. Conventional methods have some limitations: they are influenced by the starting sample, might present low throughput and low purity, and sometimes a lack of reproducibility, being operator dependent. During the past few years, several microfluidic approaches have been proposed to address these issues. In this review, we summarize the most important microfluidic-based devices for EV isolation, highlighting their advantages and disadvantages compared to existing technology, as well as the current state of the art from the perspective of the use of these devices in clinical applications.

Microfluidic Technology for the Isolation and Analysis of Exosomes

Exosomes are lipid-bilayer enclosed vesicles with diameters of 30-150 nm, which play a pivotal role in cell communication by transporting their cargoes such as proteins, lipids, and genetic materials. In recent years, exosomes have been under intense investigation, as they show great promise in numerous areas, especially as bio-markers in liquid biopsies. However, due to the high heterogeneity and the nano size of exosomes, the separation of exosomes is not easy. This review will deliver an outline of the conventional methods and the microfluidic-based technologies for exosome separation. Particular attention is devoted to microfluidic devices, highlighting the efficiency of exosome isolation by these methods. Additionally, this review will introduce advances made in the integrated microfluidics technologies that enable the separation and analysis of exosomes.