Rapid Lipid-Based Approach for Normalization of Quantum-Dot-Detected Biomarker Expression on Extracellular Vesicles in Complex Biological Samples

Fluorescent, phosphorescent, magnetic resonance contrast and radioactive tracer labelling of extracellular vesicles

This review focusses on the significance of fluorescent, phosphorescent labelling and tracking of extracellular vesicles (EVs) for unravelling their biology, pathophysiology, and potential diagnostic and therapeutic uses. Various labeling strategies, such as lipid membrane, surface protein, luminal, nucleic acid, radionuclide, quantum dot labels, and metal complex-based stains, are evaluated for visualizing and characterizing EVs. Direct labelling with fluorescent lipophilic dyes is simple but generally lacks specificity, while surface protein labelling offers selectivity but may affect EV-cell interactions. Luminal and nucleic acid labelling strategies have their own advantages and challenges. Each labelling approach has strengths and weaknesses, which require a suitable probe and technique based on research goals, but new tetranuclear polypyridylruthenium(II) complexes as phosphorescent probes have strong phosphorescence, selective staining, and stability. Future research should prioritize the design of novel fluorescent probes and labelling platforms that can significantly enhance the efficiency, accuracy, and specificity of EV labeling, while preserving their composition and functionality. It is crucial to reduce false positive signals and explore the potential of multimodal imaging techniques to gain comprehensive insights into EVs.

Accurate Cancer Screening and Prediction of PD-L1-Guided Immunotherapy Efficacy Using Quantum Dot Nanosphere Self-Assembly and Machine Learning

Accurate quantification of exosomal PD-L1 protein in tumors is closely linked to the response to immunotherapy, but robust methods to achieve high-precision quantitative detection of PD-L1 expression on the surface of circulating exosomes are still lacking. In this work, we developed a signal amplification approach based on aptamer recognition and DNA scaffold hybridization-triggered assembly of quantum dot nanospheres, which enables bicolor phenotyping of exosomes to accurately screen for cancers and predict PD-L1-guided immunotherapeutic effects through machine learning. Through DNA-mediated assembly, we utilized two aptamers for simultaneous ultrasensitive detection of exosomal antigens, which have synergistic roles in tumor diagnosis and treatment prediction, and thus, we achieved better sample classification and prediction through machine-learning algorithms. With a drop of blood, we can distinguish between different cancer patients and healthy individuals and predict the outcome of immunotherapy. This approach provides valuable insights into the development of personalized diagnostics and precision medicine.

Multiplex Quantification of Exosomes via Multiple Types of Nanobeads Labeling Combined with Laser Scanning Detection

In recent years, exosomes have attracted attention in many aspects from basic research to clinical application, including therapeutic reagents or biomarkers for liquid biopsy. The increasing understanding of exosome's heterogeneous properties is expected to lead to more advanced exosome research, and there is therefore a need for a multiplex system that can easily classify and analyze exosomes in complex biological samples according to their properties. In this study, we developed a simple and sensitive multiplexed exosome quantification system based on ExoCounter, an exosome quantification system utilizing optical disk technology, by introducing nanobeads made of different materials as exosome labeling substances. The refractive indices suitable for nanobead materials were analyzed by computer simulation of optical diffraction generated by nanobeads. The results showed that polymer (FG), Au, and Ag nanobeads exhibited superior discrimination capability in terms of the amplitude and polarity of detection pulses generated by each nanobead. The specificity and detection sensitivity of three types of nanobeads were confirmed by detecting HER2-positive exosomes with anti-HER2 antibody-conjugated nanobeads. Furthermore, CD147-positive, HER2-positive, and CD81-positive exosomes in 12.5 μL of serum were simultaneously quantified with high discrimination performance using the anti-CD147 antibody, anti-HER2 antibody, or anti-CD81 antibody conjugated for FG beads, Au nanobeads, or Ag nanobeads, respectively. A limit of detection was also evaluated as low as 210 exosomes/μL. This system is a promising tool for advanced exosome research because it enables multiplexed detection of heterogeneous exosomes in serum with high specificity, accuracy, and sensitivity without purification.

Recent progress in quantitative technologies for the analysis of cancer-related exosome proteins

Exosomes are a kind of extracellular vesicles, which play a significant role in intercellular communication and molecular exchange. Cancer-derived exosomes are potential and ideal biomarkers for the early diagnosis and treatment monitoring of cancers because of their abundant biological information and contribution to the interaction between cancer cells and the tumor microenvironment. However, there are a number of drawbacks, such as low sensitivity and tedious steps, in conventional detection techniques. Furthermore, exosome quantification is not enough to accurately distinguish cancer patients from healthy individuals. Therefore, developing efficient, accurate, and inexpensive exosome surface protein analysis techniques is necessary and critical. In recent years, a considerable number of researchers have presented novel detection strategies in this field. This review summarizes the recent progress in quantitative technologies for the analysis of cancer-related exosome proteins, mainly including the detection methods based on aptamers, nanomaterials, and antibodies, discusses a roadmap for future developments, and aims to offer an innovative perspective of exosome research.

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.

A Review of Labeling Approaches Used in Small Extracellular Vesicles Tracing and Imaging

Small extracellular vesicles (sEVs), a subset of extracellular vesicles (EVs) originating from the endosomal compartment, are a kind of lipid bilayer vesicles released by almost all types of cells, serving as natural carriers of nucleic acids, proteins, and lipids for intercellular communication and transfer of bioactive molecules. The current findings suggest their vital role in physiological and pathological processes. Various sEVs labeling techniques have been developed for the more advanced study of the function, mode of action, bio-distribution, and related information of sEVs. In this review, we summarize the existing and emerging sEVs labeling techniques, including fluorescent labeling, radioisotope labeling, nanoparticle labeling, chemical contrast agents labeling, and label-free technique. These approaches will pave the way for an in-depth study of sEVs. We present a systematic and comprehensive review of the principles, advantages, disadvantages, and applications of these techniques, to help promote applications of these labeling approaches in future research on sEVs.

Combination of specific proteins as markers for accurate detection of extracellular vesicles using proximity ligation-mediated bHCR amplification

As the molecular characteristics of extracellular vesicles (EVs) are closely related to the occurrence and progression of cancer, the detection of tumor-derived EVs provides a promising non-invasive tool for the early diagnosis and treatment of cancer. However, it would be difficult for most of the existing methods to avoid false positives because the obtained result declares the amounts of proteins, but cannot accurately reflect the protein sources, including EV proteins and interfering proteins, in the actual samples. In this manuscript, a robust, accurate, and sensitive fluorescent strategy for profiling EV proteins is developed by using the combination of specific proteins as markers (Co-marker). Our strategy relies on the Co-marker recognition-activated cascade bHCR amplification, which forms numerous G-quadruplex structures that are integrated with fluorescent dyes for signal transduction. Notably, the detection accuracy can be improved owing to the effective avoidance of false positives from interfering proteins or single protein markers. Moreover, by using the double-positive protein recognition mode, unpurified detection can be achieved that avoids time-consuming EVs purification procedures. With its capacities of accuracy, portability, sensitivity, high throughput, and non-purification, the developed strategy might provide a practical tool for EV identification and the related early diagnosis and treatment of cancer.

Isolation of Bovine Milk Exosome Using Electrophoretic Oscillation Assisted Tangential Flow Filtration with Antifouling of Micro-ultrafiltration Membrane Filters

Tangent flow-driven ultrafiltration (TF-UF) is an efficient isolation process of milk exosomes without morphological deformation. However, the TF-UF approach with micro-ultrafiltration SiN_x membrane filters suffers from the clogging and fouling of micro-ultrafiltration membrane filter pores with large bioparticles. Thus, it is limited in the long term, continuous isolation of large quantities of exosomes. In this work, we introduced electrophoretic oscillation (EPO) in the TF-UF approach to remove pore clogging and fouling of with micro-ultrafiltration SiN_x membrane filters by large bioparticles. As a result, the combined EPO-assisted TF (EPOTF) filtration can isolate large quantities of bovine milk exosomes without deformation. Furthermore, several morphological and biological analyses confirmed that the EPOTF filtration approach could isolate the milk exosomes in high concentrations with high purity and intact morphology. In addition, the uptake test of fluorescent-labeled exosomes by the keratinocyte cells visualized the biological function of purified exosomes. Hence, compared to the TF-UF process, the EPOTF filtration produced a higher yield of bovine milk exosomes without stopping the filtering process for over 200 h. Therefore, this isolation process enables scalable and continuous production of morphologically intact exosomes from bovine milk, suggesting that high-quality exosome purification is possible for future applications such as drug nanocarriers, diagnosis, and treatments.

Advanced technologies for molecular diagnosis of cancer: State of pre-clinical tumor-derived exosome liquid biopsies

Exosomes are membrane-defined extracellular vesicles (EVs) approximately 40-160 ​nm in diameter that are found in all body fluids including blood, urine, and saliva. They act as important vehicles for intercellular communication between both local and distant cells and can serve as circulating biomarkers for disease diagnosis and prognosis. Exosomes play a key role in tumor metastasis, are abundant in biofluids, and stabilize biomarkers they carry, and thus can improve cancer detection, treatment monitoring, and cancer staging/prognosis. Despite their clinical potential, lack of sensitive/specific biomarkers and sensitive isolation/enrichment and analytical technologies has posed a barrier to clinical translation of exosomes. This review presents a critical overview of technologies now being used to detect tumor-derived exosome (TDE) biomarkers in clinical specimens that have potential for clinical translation.

Nanostructured-Based Optical Readouts Interfaced with Machine Learning for Identification of Extracellular Vesicles

Extracellular vesicles (EVs) are shed from cancer cells into body fluids, enclosing molecular information about the underlying disease with the potential for being the target cancer biomarker in emerging diagnosis approaches such as liquid biopsy. Still, the study of EVs presents major challenges due to their heterogeneity, complexity, and scarcity. Recently, liquid biopsy platforms have allowed the study of tumor-derived materials, holding great promise for early-stage diagnosis and monitoring of cancer when interfaced with novel adaptations of optical readouts and advanced machine learning analysis. Here, recent advances in labeled and label-free optical techniques such as fluorescence, plasmonic, and chromogenic-based systems interfaced with nanostructured sensors like nanoparticles, nanoholes, and nanowires, and diverse machine learning analyses are reviewed. The adaptability of the different optical methods discussed is compared and insights are provided into prospective avenues for the translation of the technological approaches for cancer diagnosis. It is discussed that the inherent augmented properties of nanostructures enhance the sensitivity of the detection of EVs. It is concluded by reviewing recent integrations of nanostructured-based optical readouts with diverse machine learning models as novel analysis ventures that can potentially increase the capability of the methods to the point of translation into diagnostic applications.

Nanostructures and Nanotechnologies for the Detection of Extracellular Vesicle

Liquid biopsy has been taken as a minimally invasive examination and a promising surrogate to the clinically applied tissue-based test for the diagnosis and molecular analysis of cancer. Extracellular vesicles (EVs) carry complex molecular information from the tumor, allowing for the multicomponent analysis of cancer and would be beneficial to personalized medicine. In this review, the advanced nanomaterials and nanotechniques for the detection and molecular profiling of EVs, highlight the advantages of nanotechnology in the high-purity isolation and the high-sensitive and high-specific identification of EVs, are summarized. An outlook on the clinical application of nanotechnology-based liquid biopsy in the diagnosis, prognostication, and surveillance of cancer is also provided. It provides information for developing liquid biopsy based on EVs by discussing the advantages and challenges of functionalized nanomaterials and various nanotechnologies.

Nucleic acid and nanomaterial-assisted signal-amplified strategies in fluorescent analysis of circulating tumor cells and small extracellular vesicles

As two main types of liquid biopsy markers, both circulating tumor cells (CTCs) and small extracellular vesicles (sEVs) play important roles in the diagnosis and prognosis of cancers. CTCs are malignant cells that detach from the original tumor tissue and enter the circulation of body fluids. sEVs are nanoscale vesicles secreted by normal cells or pathological cells. However, CTCs and sEVs in body fluids are scarce, leading to great difficulties in the accurate analysis of related diseases. For the sensitive detection of CTCs and sEVs in body fluids, various types of nucleic acid and nanomaterial-assisted signal amplification strategies have been developed. In this review, we summarize the recent advances in fluorescent detection of CTCs and sEVs in liquid biopsy based on nucleic acid and nanomaterial-assisted signal amplification strategies. We also discuss their advantages, challenges, and future prospects.

Extracellular vesicle biomarkers for pancreatic cancer diagnosis: a systematic review and meta-analysis

BACKGROUND

Extracellular vesicle (EV) biomarkers have promising diagnosis and screening capacity for several cancers, but the diagnostic value for pancreatic cancer (PC) is controversial. The aim of our study was to review the diagnostic performance of EV biomarkers for PC.

METHODS

We performed a systematic review of PubMed, Medline, and Web Of Science databases from inception to 18 Feb 2022. We identified studies reporting the diagnostic performance of EV biomarkers for PC and summarized the information of sensitivity, specificity, area under the curve (AUC), or receiver operator characteristic (ROC) curve) in according to a pre-designed data collection form. Pooled sensitivity and specificity was calculated using a random-effect model.

RESULTS

We identified 39 studies, including 2037 PC patients and 1632 noncancerous, seven of which were conducted independent validation tests. Seventeen studies emphasized on EV RNAs, sixteen on EV proteins, and sixteen on biomarker panels. MiR-10b, miR-21, and GPC1 were the most frequently reported RNA and protein for PC diagnosis. For individual RNAs and proteins, the pooled sensitivity and specificity were 79% (95% CI: 77-81%) and 87% (95% CI: 85-89%), 72% (95% CI: 69-74%) and 77% (95% CI: 74-80%), respectively. the pooled sensitivity and specificity of EV RNA combined with protein panels were 84% (95% CI: 81-86%) and 89% (95% CI: 86-91%), respectively. Surprisingly, for early stage (stage I and II) PC EV biomarkers showed excellent diagnostic performance with the sensitivity of 90% (95% CI: 87-93%) and the specificity of 94% (95% CI: 92-95%). Both in sensitivity and subgroup analyses, we did not observe notable difference in pooled sensitivity and specificity. Studies might be limited by the isolation and detection techniques of EVs to a certain extent.

CONCLUSIONS

EV biomarkers showed appealing diagnostic preference for PC, especially for early stage PC. Solving the deficiency of technologies of isolation and detection EVs has important implications for application these novel noninvasive biomarkers in clinical practice.

DNA Nanowire Guided-Catalyzed Hairpin Assembly Nanoprobe for In Situ Profiling of Circulating Extracellular Vesicle-Associated MicroRNAs

Extracellular vesicle-associated miRNAs (EV-miRNAs) are emerging as a new type of noninvasive biomarker for disease diagnosis. Their relatively low abundance, however, makes accurate detection challenging. Here, we designed a DNA nanowire guided-catalyzed hairpin assembly (NgCHA) nanoprobe for profiling EV-miRNAs. NgCHA showed high penetrability to EVs, which allowed rapid delivery of the probes into EVs. In the presence of targeted miRNAs within EVs, a fluorescent signal could be generated and amplified by confining the catalytic hairpin assembly system within the nanowires, thus greatly enhancing the analytical sensitivity. We showed that EV-miRNAs from various cell lines could be accurately quantified by NgCHA in situ. By using a four-EV-miRNA panel, this platform can identify patients with breast cancer at an early stage with 95.2% sensitivity and 86.7% specificity. Its applications for risk assessment as well as cancer type prediction were also successfully demonstrated. This platform is sensitive, low-cost, and simple compared with current methods. It may thus serve as a promising tool for the noninvasive diagnosis and monitoring of cancers and other diseases through EV-miRNA profiling.

Multiplexed Profiling of Extracellular Vesicles for Biomarker Development

Extracellular vesicles (EVs) are cell-derived membranous particles that play a crucial role in molecular trafficking, intercellular transport and the egress of unwanted proteins. They have been implicated in many diseases including cancer and neurodegeneration. EVs are detected in all bodily fluids, and their protein and nucleic acid content offers a means of assessing the status of the cells from which they originated. As such, they provide opportunities in biomarker discovery for diagnosis, prognosis or the stratification of diseases as well as an objective monitoring of therapies. The simultaneous assaying of multiple EV-derived markers will be required for an impactful practical application, and multiplexing platforms have evolved with the potential to achieve this. Herein, we provide a comprehensive overview of the currently available multiplexing platforms for EV analysis, with a primary focus on miniaturized and integrated devices that offer potential step changes in analytical power, throughput and consistency.

Tango of dual nanoparticles: Interplays between exosomes and nanomedicine

Exosomes are lipid bilayer vesicles released from cells as a mechanism of intracellular communication. Containing information molecules of their parental cells and inclining to fuse with targeted cells, exosomes are valuable in disease diagnosis and drug delivery. The realization of their clinic applications still faces difficulties, such as lacking technologies for fast purification and functional reading. The advancement of nanotechnology in recent decades makes it promising to overcome these difficulties. In this article, we summarized recent progress in utilizing the physiochemical properties of nanoparticles (NPs) to enhance exosome purification and detection sensitivity or to derive novel technologies. We also discussed the valuable applications of exosomes in NPs‐based drug delivery. Till now most studies in these fields are still at the laboratory research stage. Translation of these bench works into clinic applications still has a long way to go.

Magnetic-Nanowaxberry-Based Simultaneous Detection of Exosome and Exosomal Proteins for the Intelligent Diagnosis of Cancer

Exosome concentration and exosomal proteins are regarded as promising cancer biomarkers. Herein, a waxberry-like magnetic bead (magnetic-nanowaxberry) which has huge surface area and strong affinity was synthesized to couple with aptamer for exosome capture and recovery. Subsequently, we developed a fluorescent assay for the sensitive, accurate, and simultaneous quantification of exosome and cancer-related exosomal proteins [epidermal growth factor receptor (EGFR) and epithelial cell adhesion molecule (EpCAM)] by using triple-colored probes to recognize EGFR and EpCAM or spontaneously anchor to the lipid bilayer. In this design, the interference of soluble proteins can be avoided due to the dual recognition strategy. Moreover, the lipid-based quantification of exosome concentration can improve the accuracy. Besides, the simultaneous detection mode can save samples and simplify the operation steps. Consequently, the assay shows high sensitivity (the limits of detection are down to 0.96 pg/mL for EGFR, 0.19 pg/mL for EpCAM, and 2.4 × 10⁴ particles/μL for exosome), high specificity, and satisfactory accuracy. More importantly, this technique is successfully used to analyze exosomes in plasma to distinguish cancer patients from healthy individuals. To improve the diagnostic efficacy, the deep learning was used to exploit the potential pattern hidden in data obtained by the proposed method. Also, the accuracy for the intelligent diagnosis of cancer can achieve 96.0%. This study provides a new avenue for developing new biosensors for exosome analysis and intelligent disease diagnosis.

Calibration-free analysis of surface proteins on single extracellular vesicles enabled by DNA nanostructure

Extracellular vesicles (EVs) are essential intercellular communicators that are of increasing interest as diagnostic biomarkers. Exploring their biological functions and clinical values, however, remains challenging due to their small sizes and high heterogeneity. Herein, we report an ultrasensitive method that employs target-initiated construction of DNA nanostructure to detect single EVs with an input as low as 100 vesicles/μL. Taking advantage of both DNA nanostructure labeling and EV membrane staining, the method can also permit calibration-free analysis of the protein profiles among different EV samples, leading to clear EV differentiation by their cell of origin. Moreover, this method allows co-localization of dual protein markers on the same EV, and the increased number of EVs carrying dual tumor proteins present in human serum could differentiate cancer patients at the early developmental stage from healthy controls. Our results demonstrate the great potential of this single-EV visualization method in non-invasive detection of the EV-based protein biomarkers for cancer diagnosis and treatment monitoring.

Advanced Nanotechnologies for Extracellular Vesicle-Based Liquid Biopsy

Extracellular vesicles (EVs) are emerging as a new source of biomarkers in liquid biopsy because of their wide presence in most body fluids and their ability to load cargoes from disease-related cells. Owing to the crucial role of EVs in disease diagnosis and treatment, significant efforts have been made to isolate, detect, and analyze EVs with high efficiency. A recent overview of advanced EV detection nanotechnologies is discussed here. First, several key challenges in EV-based liquid biopsies are introduced. Then, the related pivotal advances in nanotechnologies for EV isolation based on physical features, chemical affinity, and the combination of nanostructures and chemical affinity are summarized. Next, a summary of high-sensitivity sensors for EV detection and advanced approaches for single EV detection are provided. Later, EV analysis is introduced in practical clinical scenarios, and the application of machine learning in this field is highlighted. Finally, future opportunities for the development of next-generation nanotechnologies for EV detection are presented.

Exosomal Surface Protein Detection with Quantum Dots and Immunomagnetic Capture for Cancer Detection

Exosomes carry molecular contents reflective of parental cells and thereby hold great potential as a source of biomarkers for non-invasive cancer detection and monitoring. However, simple and rapid exosomal molecular detection remains challenging. Here, we report a facile method for exosome surface protein detection using quantum dot coupled with immunomagnetic capture and enrichment. In this method, exosomes were captured by magnetic beads based on CD81 protein expression. Surface protein markers of interest were recognized by primary antibody and then detected by secondary antibody-conjugated quantum dot with fluorescent spectroscopy. Validated by ELISA, our method can specifically detect different surface markers on exosomes from different cancer cell lines and differentiate cancer exosomes from normal exosomes. The clinical potential was demonstrated with pilot plasma samples using HER2-positive breast cancer as the disease model. The results show that exosomes from HER2-positive breast cancer patients exhibited a five times higher level of HER2 expression than healthy controls. Exosomal HER2 showed strong diagnostic power for HER2-positive patients, with the area under the curve of 0.969. This quantum dot-based exosome method is rapid (less than 5 h) and only requires microliters of diluted plasma without pre-purification, practical for routine use for basic vesicle research, and clinical applications.

Membrane Feature-Inspired Profiling of Extracellular Vesicles for Pancreatic Cancer Diagnosis

Extracellular vesicles (EVs) have recently emerged as a promising tumor biomarker, and EV phenotyping offers many benefits for cancer diagnosis. However, the practicality of EV assays remains a challenge due to macromolecule disturbances, biomarker heterogeneities, and EV abundance limitations. Here, we demonstrate a membrane-based biosensor for precise and sensitive EV identification. The sensor synergistically integrates EV capture and detection by virtue of EV membrane features (membrane protein and lipid bilayer), comprising antibody-conjugated magnetic beads (AbMBs) and duplex-specific nuclease (DSN)-mediated amplification cycles. Bivalent cholesterol (biChol)-modified RNA-DNA duplexes are designed to insert into the EV membrane, transforming EV signals into RNA signals and initiating the signal amplification. The membrane-based signal production pattern eliminates protein interference. By employing four antibodies specific to PCa-related membrane proteins, the AbMB-biChol platform enables the successful differentiation and monitoring of PCa-related EVs and distinguishes PCa patients from healthy donors with improved efficacy, exhibiting superior efficiency over the analyses based on clinically used biomarker CA19-9 and PCa-related proteins. As such, the developed system has great potential for clinical PCa diagnosis.

A Holistic Review of the State-of-the-Art Microfluidics for Exosome Separation: An Overview of the Current Status, Existing Obstacles, and Future Outlook

Exosomes, a class of small extracellular vesicles (30-150 nm), are secreted by almost all types of cells into virtually all body fluids. These small vesicles are attracting increasing research attention owing to their potential for disease diagnosis and therapy. However, their inherent heterogeneity and the complexity of bio-fluids pose significant challenges for their isolation. Even the "gold standard," differential centrifugation, suffers from poor yields and is time-consuming. In this context, recent developments in microfluidic technologies have provided an ideal system for exosome extraction and these devices exhibit some fascinating properties such as high speeds, good portability, and low sample volumes. In this review, the focus is on the state-of-the-art microfluidic technologies for exosome isolation and highlight potential directions for future research and development by analyzing the challenges faced by the current strategies.

Review: Multiplexed profiling of biomarkers in extracellular vesicles for cancer diagnosis and therapy monitoring

Extracellular vesicles (EVs) are nanoscale vesicles secreted by normal and pathological cells. The types and levels of surface proteins and internal nucleic acids in EVs are closely related to their original cells, tumor occurrence, and development. Thus, the sensitive and accurate detection of EV biomarkers is a reliable approach for noninvasive disease diagnosis and treatment response monitoring. However, the purification and molecular profiling of these EVs are technically challenging. Much effort has been dedicated to developing new methods for the detection of multiple EV biomarkers. In this review, we summarize the recent progress in EV protein and nucleic acid biomarker analysis. Additionally, we systematically discuss the advantages of multiplexed EV biomarker detection for accurate cancer diagnosis, therapy monitoring, and cancer screening. This article aims to present an overview of all kinds of analytical technologies for assessing EVs and their applications in clinical settings.

Emerging methods in biomarker identification for extracellular vesicle-based liquid biopsy

Extracellular vesicles (EVs) are released by many cell types and distributed within various biofluids. EVs have a lipid membrane-confined structure that allows for carrying unique molecular information originating from their parent cells. The species and quantity of EV cargo molecules, including nucleic acids, proteins, lipids, and metabolites, may vary largely owing to their parent cell types and the pathophysiologic status. Such heterogeneity in EV populations provides immense challenges to researchers, yet allows for the possibility to prognosticate the pathogenesis of a particular tissue from unique molecular signatures of dispersing EVs within biofluids. However, the inherent nature of EV's small size requires advanced methods for EV purification and evaluation from the complex biofluid. Recently, the interdisciplinary significance of EV research has attracted growing interests, and the EV analytical platforms for their diagnostic prospect have markedly progressed. This review summarizes the recent advances in these EV detection techniques and methods with the intention of translating an EV-based liquid biopsy into clinical practice. This article aims to present an overview of current EV assessment techniques, with a focus on their progress and limitations, as well as an outlook on the clinical translation of an EV-based liquid biopsy that may augment current paradigms for the diagnosis, prognosis, and monitoring the response to therapy in a variety of disease settings.

Tailor-Made Nanomaterials for Diagnosis and Therapy of Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers worldwide due to its aggressiveness and the challenge to early diagnosis and treatment. In recent decades, nanomaterials have received increasing attention for diagnosis and therapy of PDAC. However, these designs are mainly focused on the macroscopic tumor therapeutic effect, while the crucial nano-bio interactions in the heterogeneous microenvironment of PDAC remain poorly understood. As a result, the majority of potent nanomedicines show limited performance in ameliorating PDAC in clinical translation. Therefore, exploiting the unique nature of the PDAC by detecting potential biomarkers together with a deep understanding of nano-bio interactions that occur in the tumor microenvironment is pivotal to the design of PDAC-tailored effective nanomedicine. This review will introduce tailor-made nanomaterials-enabled laboratory tests and advanced noninvasive imaging technologies for early and accurate diagnosis of PDAC. Moreover, the fabrication of a myriad of tailor-made nanomaterials for various PDAC therapeutic modalities will be reviewed. Furthermore, much preferred theranostic multifunctional nanomaterials for imaging-guided therapies of PDAC will be elaborated. Lastly, the prospects of these nanomaterials in terms of clinical translation and potential breakthroughs will be briefly discussed.

Accurate Cancer Diagnosis and Stage Monitoring Enabled by Comprehensive Profiling of Different Types of Exosomal Biomarkers: Surface Proteins and miRNAs

Exosomes are recognized as promising biomarkers for early cancer diagnosis and prognosis owing to a large amount of biological information they carried. But the key is that single type of exosomal biomarker analysis is not sufficient enough for accurate cancer diagnosis and stage monitoring due to the insufficient information and high false positive signal. To address the challenge, here simultaneous in situ detection of different types of exosomal biomarkers (surface proteins: CD81, ephrin type-A receptor 2, and carbohydrate antigen 19-9; miRNAs: miR-451a, miR-21, and miR-10b) is conducted with a 3D microfluidic chip, which works in conjunction with quantum dot (QD) labeling and vesicle fusion technology. After exosomes are efficiently captured by the microfluidic chip, the quantification of multiple exosomal proteins is achieved by using three kinds of QDs with the same excitation and different emission wavelengths, and virus-mimicking fusogenic vesicles encapsulating three exquisitely engineered molecular beacons are introduced for ultrasensitive detection of multiple exosomal miRNAs without requiring RNA extraction. Through comprehensive profiling different types of exosomal biomarkers, the false positive rate is substantially avoided and the accuracy of cancer diagnosis and stage monitoring is improved to ≈100%, which are critical to cancer effective treatment and favorable prognosis.

Determining the Efficiency of Single Molecule Quantum Dot Labeling of HER2 in Breast Cancer Cells

Quantum dots exhibit unique properties compared to other fluorophores, such as bright fluorescence and lack of photobleaching, resulting in their widespread utilization as fluorescent protein labels in the life sciences. However, their application is restricted to relative quantifications due to lacking knowledge about the labeling efficiency. We here present a strategy for determining the labeling efficiency of quantum dot labeling of HER2 in overexpressing breast cancer cells. Correlative light- and liquid-phase electron microscopy of whole cells was used to convert fluorescence intensities into the underlying molecular densities of the quantum dots. The labeling procedure with small affinity proteins was optimized yielding a maximal labeling efficiency of 83%, which was applicable to the high amount of ∼1.5 × 10⁶ HER2 per cell. With the labeling efficiency known, it is now possible to derive the absolute protein expression levels in the plasma membrane and its variation within a cell and between cells.

Extracellular Vesicles in Cancer Detection: Hopes and Hypes

Early cancer diagnosis is critical for improving patient survival and mortality rates, but most diagnostics on solid tumors rely on imaging tests with limited sensitivity and specificity to identify potential cases, which are then confirmed by tissue biopsies. However, this process is usually not suitable for cancer screening or evaluation of tumor responses to treatment. Liquid biopsies have the potential to bridge this gap, but few such assays have been approved for cancer applications. Extracellular vesicles hold particular promise for liquid biopsy diagnostics but are currently limited by the lack of robust methods for isolation and analysis. New isolation and analysis techniques, however, show promise to improve the clinical utility of extracellular vesicle-based cancer diagnosis.

Comprehensive Characterization of Nanosized Extracellular Vesicles from Central and Peripheral Organs : Implications for Preclinical and Clinical Applications

Extracellular vesicles (EV) are nano-sized vesicles that have been garnering a lot of attention for their valuable role as potential diagnostic markers and therapeutic vehicles for a plethora of pathologies. Whilst EV markers from biofluids such as plasma, serum, urine, cerebrospinal fluid and in vitro cell culture based platforms have been extensively studied, a significant knowledge gap that remains is the characterization of specific organ derived EVs (ODE). Here, we present a standardized protocol for isolation and characterization of purified EV isolated from brain, heart, lung, kidney and liver from rat and postmortem human tissue. Next, using quantitative mass spectrometry based proteomics, we characterized the respective tissue EV proteomes that identified synaptophysin (SYP), caveolin-3 (CAV3), solute carrier family 22 member 2 (SLC22A2), surfactant protein B (SP-B), and fatty acid-binding protein 1 (FABP1) as potential markers for the brain, heart, kidney, lung, and liver-EV, respectively. These respective tissue specific markers were further validated using both immunoblotting and a nanoplasmonic platform- single EV imaging analysis in the two species. To summarize, our study for the first time using traditional biochemical and high precision technology platforms provide a valuable proof of concept approach in defining specific ODE markers which further could be developed as potential therapeutic candidates for respective end-organ associated pathologies.

Quantum Dot Labeling and Visualization of Extracellular Vesicles

Extracellular vesicles (EVs) are important mediators of intercellular communication. Their role in disease processes, uncovered mostly over the last two decades, makes them potential biomarkers, leading to a need to fundamentally understand EV biology. Direct visualization of EVs can provide insights into EV behavior, but current labeling techniques are often restricted by false-positive signals and rapid photobleaching. Hence, we developed a method of labeling EVs through conjugation with quantum dots (QDs)-high photoluminescent nanosized semi-conductors-using click chemistry. We showed that QD-EV conjugation could be tailored by altering QD to EV ratio or by using a catalyst. This conjugation chemistry was stable in a biological environment and upon storage for up to a week. Using size-exclusion chromatography, QD-EV conjugates could be separated from unconjugated QDs, enabling EV-specific signal detection. We demonstrate that these QD-EV conjugates can be live- and fixed-imaged in high resolution on cells and in tissue sheets, and the conjugates have better photostability compared with the commonly used EV dye DiI. We labeled two distinct EV populations: human semen EVs (sEVs) from fresh semen samples donated by healthy volunteers and brain EVs (bEVs) from excised rat brain tissues. We visualized QD-sEVs in epithelial sheets isolated from human vaginal mucosa and time-lapse imaged QD-bEV interactions with microglial BV-2 cells. The development of the QD-EV conjugate will benefit the study of EV localization, movement, and function and accelerate their potential use as biomarkers, therapeutic agents, or drug-delivery vehicles.