Ultrasensitive Analysis of Exosomes Using a 3D Self-Assembled Nanostructured SiO2 Microfluidic Chip

Enhancing Analysis of Extracellular Vesicles by Microfluidics

Extracellular vesicles (EVs) play crucial roles in intercellular communication and hold great promise as biomarkers for noninvasive disease diagnosis. Intensive research efforts have been devoted to discovering the EV subpopulations responsible for specific functions or with enhanced effectiveness as disease markers, through extensive EV purification and content analysis. However, their high heterogeneity in size and cargo composition poses significant challenges for reaching such goals. Isolation methods like ultracentrifugation and size-exclusion chromatography, as well as content analysis approaches like polymerase chain reaction and enzyme-linked immunosorbent assay, have made significant contributions to improving our understanding of EV biology. Nonetheless, these methods face limitations in isolation efficiency, EV purity, and detection sensitivity and specificity due to issues like large sample consumption, unsatisfactory purity, and insufficient resolution in EV subtyping. Microfluidic technology presents promising solutions to these challenges, leveraging their intrinsic capabilities in precise flow and external energy field manipulation, sample compartmentalization, and signal enhancement at the micro- and nanoscale. Hence, this review summarizes the recent developments in microfluidics-enabled EV analysis, paying special attention to the unique microfluidic features exploited. Strategies such as viscoelastic and inertial flow, fluid mixing, and external-field-assisted approaches in improving EV purification, as well as compartmentalization and micro/nanostructures for enhancing EV detection, are examined. Furthermore, the current limitations and potential future directions are discussed to inspire advancements in this rapidly developing field.

Small extracellular vesicles: crucial mediators for prostate cancer

Small extracellular vesicles (sEVs) play a critical role in the progression, diagnosis, and treatment of prostate cancer (PCa), particularly within the tumor microenvironment (TME). Acting as novel biomarkers and agents for targeted biological therapy, sEVs contribute significantly to improving patient survival. These vesicles transport a variety of biomolecules, including proteins, nucleic acids, and lipids, which are instrumental in remodeling the TME, facilitating intercellular communication, and influencing key processes such as tumor growth, metastasis, and therapy resistance. A thorough understanding of sEV heterogeneity, including their biogenesis, characteristics, and potential applications, is essential. Recent advances have illuminated the origins, formation processes, and molecular cargo of PCa-derived sEVs (PCa-sEVs), enhancing our understanding of their role in disease progression. Furthermore, sEVs show promise as diagnostic markers, with potential applications in early detection and prognostic assessment in PCa. Therapeutically, natural and engineered sEVs offer versatile applications, including drug delivery, gene therapy, and immunomodulation, underscoring their potential in PCa management. This review delves into the substantial potential of sEVs in clinical practices for PCa.

Methods for Extracellular Vesicle Isolation: Relevance for Encapsulated miRNAs in Disease Diagnosis and Treatment

Extracellular vesicles (EVs) are nanovesicles that facilitate intercellular communication by carrying essential biomolecules under physiological and pathological conditions including microRNAs (miRNAs). They are found in various body fluids, such as blood, urine, and saliva, and their levels fluctuate with disease progression, making them valuable diagnostic tools. However, isolating EVs is challenging due to their small size and biological complexity. Here, we summarize the principles behind the most common EV isolation methods including ultracentrifugation, precipitation, immunoaffinity, sorting, ultrafiltration, size exclusion chromatography, and microfluidics while highlighting protocol strengths and weaknesses. We also review the main strategies to identify and quantify circulating miRNAs with a particular focus on EV-encapsulated miRNAs. Since these miRNAs hold special clinical interest derived from their superior stability and therapeutic potential, the information provided here should provide valuable guidance for future research initiatives in the promising field of disease diagnostic and treatment based on EV-encapsulated miRNAs.

Demystifying EV heterogeneity: emerging microfluidic technologies for isolation and multiplexed profiling of extracellular vesicles

Extracellular vesicles (EVs) are heterogeneous lipid containers carrying complex molecular cargoes, including proteins, nucleic acids, glycans, etc. These vesicles are closely associated with specific physiological characteristics, which makes them invaluable in the detection and monitoring of various diseases. However, traditional isolation methods are often labour-intensive, inefficient, and time-consuming. In addition, single biomarker analyses are no longer accurate enough to meet diagnostic needs. Routine isolation and molecular analysis of high-purity EVs in clinical applications is even more challenging. In this review, we discuss a promising solution, microfluidic-based techniques, that combine efficient isolation and multiplex detection of EVs, to further demystify EV heterogeneity. These microfluidic-based EV multiplexing platforms will hopefully facilitate development of liquid biopsies and offer promising opportunities for personalised therapy.

A comprehensive review on recent advances in exosome isolation and characterization: Toward clinical applications

Exosomes are small, round vesicles in the 30 and 120 nm diameter range released by all living cell types. Exosomes play many essential functions in intercellular communication and tissue crosstalk in the human body. They can potentially be used as strong biomarkers and therapeutic agents for early diagnosis, therapy response, and prognosis of different diseases. The main requirements for exosomal large-scale clinical practice application are rapid, easy, high-yield, high purity, characterization, safety, low cost, and therapeutic efficacy. Depending on the sample types, environmental insults, and exosome quantity, exosomes can be isolated from various sources, including body fluids, solid tissues, and cell culture medium using different procedures. This study comprehensively analyzed the current research progress in exosome isolation and characterization strategies along with their advantages and disadvantages. The provided information will make it easier to select exosome separation methods based on the types of biological samples available, and it will facilitate the use of exosomes in translational and clinical research, particularly in cancer. Lay abstract Exosomes have recently received much attention due to their potential to function as biomarkers and novel therapeutic agents for early diagnosis, therapeutic response, and prognosis in various diseases. This review summarizes many approaches for isolating and characterizing exosomes, focusing on developing technologies, and provides an in-depth comparison and analysis of each method, including its principles, advantages, and limitations.

Magnetic 3D macroporous MOF oriented urinary exosome metabolomics for early diagnosis of bladder cancer

Bladder cancer (BCa) exhibits the escalating incidence and mortality due to the untimely and inaccurate early diagnosis. Urinary exosome metabolites, carrying critical tumor cell information and directly related to bladder, emerge as promising non-invasive diagnostic biomarkers of BCa. Herein, the magnetic 3D ordered macroporous zeolitic imidazolate framework-8 (magMZIF-8) is synthesized and used for efficient urinary exosome isolation. Notably, beyond retaining the single crystals and micropores of conventional ZIF-8, MZIF-8 is further enhanced with highly oriented and ordered macropores (150 nm) and the large specific surface area (973 m2·g-1), which could enable the high purity and yield separation of exosomes via leveraging the combination of size exclusion, affinity, and electrostatic interactions between magMZIF-8 and the surfaces of exosome. Furthermore, the magnetic and hydrophilic properties of magMZIF-8 will further simplify the process and enhance the efficiency of separation. After conditional optimization, a 50 mL of urine is sufficient for exosome metabolomics analysis, and the time for isolating exosomes from 42 urine samples was 2 hours only. Incorporating machine learning algorithms with LC-MS/MS analysis of the metabolic patterns obtained from isolated exosomes, early-stage BCa patients were differentiated from healthy controls, with area under the curve (AUC) value of 0.844-0.9970 in the training set and 0.875-1.00 in the test set, signifying its potential as a reliable diagnostic tool. This study offers a promising approach for the non-invasive and efficient diagnosis of BCa on a large scale via exosome metabolomics.

Enhancing the performance of porous silicon biosensors: the interplay of nanostructure design and microfluidic integration

This work presents the development and design of aptasensor employing porous silicon (PSi) Fabry‒Pérot thin films that are suitable for use as optical transducers for the detection of lactoferrin (LF), which is a protein biomarker secreted at elevated levels during gastrointestinal (GI) inflammatory disorders such as inflammatory bowel disease and chronic pancreatitis. To overcome the primary limitation associated with PSi biosensors-namely, their relatively poor sensitivity due to issues related to complex mass transfer phenomena and reaction kinetics-we employed two strategic approaches: First, we sought to optimize the porous nanostructure with respect to factors including layer thickness, pore diameter, and capture probe density. Second, we leveraged convection properties by integrating the resulting biosensor into a 3D-printed microfluidic system that also had one of two different micromixer architectures (i.e., staggered herringbone micromixers or microimpellers) embedded. We demonstrated that tailoring the PSi aptasensor significantly improved its performance, achieving a limit of detection (LOD) of 50 nM-which is >1 order of magnitude lower than that achieved using previously-developed biosensors of this type. Moreover, integration into microfluidic systems that incorporated passive and active micromixers further enhanced the aptasensor's sensitivity, achieving an additional reduction in the LOD by yet another order of magnitude. These advancements demonstrate the potential of combining PSi-based optical transducers with microfluidic technology to create sensitive label-free biosensing platforms for the detection of GI inflammatory biomarkers.

Nanoarchitectonics-based electrochemical aptasensors for highly efficient exosome detection

Exosomes, a type of extracellular vesicles, have attracted considerable attention due to their ability to provide valuable insights into the pathophysiological microenvironment of the cells from which they originate. This characteristic implicates their potential use as diagnostic disease biomarkers clinically, including cancer, infectious diseases, neurodegenerative disorders, and cardiovascular diseases. Aptasensors, which are electrochemical aptamers based biosensing devices, have emerged as a new class of powerful detection technology to conventional methods like ELISA and Western analysis, primarily because of their capability for high-performance bioanalysis. This review covers the current research landscape on the detection of exosomes utilizing nanoarchitectonics strategy for the development of electrochemical aptasensors. Strategies involving signal amplification and biofouling prevention are discussed, with an emphasis on nanoarchitectonics-based bio-interfaces, showcasing their potential to enhance sensitivity and selectivity through optimal conduction and mass transport properties. The ongoing challenges to broaden the clinical applications of these biosensors are also highlighted.

Biporous silica nanostructure-induced nanovortex in microfluidics for nucleic acid enrichment, isolation, and PCR-free detection

Efficient pathogen enrichment and nucleic acid isolation are critical for accurate and sensitive diagnosis of infectious diseases, especially those with low pathogen levels. Our study introduces a biporous silica nanofilms-embedded sample preparation chip for pathogen and nucleic acid enrichment/isolation. This chip features unique biporous nanostructures comprising large and small pore layers. Computational simulations confirm that these nanostructures enhance the surface area and promote the formation of nanovortex, resulting in improved capture efficiency. Notably, the chip demonstrates a 100-fold lower limit of detection compared to conventional methods used for nucleic acid detection. Clinical validations using patient samples corroborate the superior sensitivity of the chip when combined with the luminescence resonance energy transfer assay. The enhanced sample preparation efficiency of the chip, along with the facile and straightforward synthesis of the biporous nanostructures, offers a promising solution for polymer chain reaction-free detection of nucleic acids.

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.

Prostate cancer-derived small extracellular vesicle proteins: the hope in diagnosis, prognosis, and therapeutics

Current diagnostic tools for prostate cancer (PCa) diagnosis and risk stratification are insufficient. The hidden onset and poor efficacy of traditional therapies against metastatic PCa make this disease a heavy burden in global men's health. Prostate cancer-derived extracellular vesicles (PCDEVs) have garnered attention in recent years due to their important role in communications in tumor microenvironment. Recent advancements have demonstrated PCDEVs proteins play an important role in PCa invasion, progression, metastasis, therapeutic resistance, and immune escape. In this review, we briefly discuss the applications of sEV proteins in PCa diagnosis and prognosis in liquid biopsy, focus on the roles of the PCa-derived small EVs (sEVs) proteins in tumor microenvironment associated with cancer progression, and explore the therapeutic potential of sEV proteins applied for future metastatic PCa therapy.

High Throughput and Noninvasive Exosomal PD-L1 Detection for Accurate Immunotherapy Response Prediction via Tim4-Functionalized Magnetic Core-Shell Metal-Organic Frameworks

Exosomal PD-L1 has been increasingly considered a noninvasive and accurate predictive marker for immunotherapy treatment response. However, the clinical monitoring of exosomal PD-L1 expression is still limited by its complex biological environment as well as the lack of a robust isolation strategy. Here, a Tim4-functionalized magnetic core-shell metal-organic framework (denoted as Fe3O4@SiO2-ILI-01@Tim4) was facilely constructed via layer-by-layer assembly. Owing to the strongly hydrophilic organic ligand of 1,3-bis(4-carboxybutyl)imidazolium bromide (ILI), magnetic Fe3O4@SiO2-ILI-01@Tim4 was endowed with the merits of low nonspecific adsorption and quick, easy, and convenient isolation of exosomes. The capture efficiency of Fe3O4@SiO2-ILI-01@Tim4 reached as high as 90.3 ± 0.5% and the recovery rate for exosomes was up to 93.0 ± 6.1%. The purity of the isolated exosomes was 7.5 times higher than that via the ultracentrifugation (UC) method. By further combination with immunofluorescence assay, high throughput and noninvasive exosomal PD-L1 detection for accurate immunotherapy response prediction was achieved. The prognosis accuracy of the developed Fe3O4@SiO2-ILI-01@Tim4-based strategy reached 85.7%, whereas the prognosis accuracy of the clinical gold standard, the PD-L1 combined positive score (CPS) test, was only 57.1%. Most interestingly, the developed method is especially suitable for those patients receiving false negative results in the CPS test. The proposed Fe3O4@SiO2-ILI-01@Tim4 is a highly efficient and robust technique showing great potential in high throughput and noninvasive exosomal PD-L1 detection for accurately predicting immunotherapy efficacy.

Extracellular vesicles: a rising star for therapeutics and drug delivery

Extracellular vesicles (EVs) are nano-sized, natural, cell-derived vesicles that contain the same nucleic acids, proteins, and lipids as their source cells. Thus, they can serve as natural carriers for therapeutic agents and drugs, and have many advantages over conventional nanocarriers, including their low immunogenicity, good biocompatibility, natural blood-brain barrier penetration, and capacity for gene delivery. This review first introduces the classification of EVs and then discusses several currently popular methods for isolating and purifying EVs, EVs-mediated drug delivery, and the functionalization of EVs as carriers. Thereby, it provides new avenues for the development of EVs-based therapeutic strategies in different fields of medicine. Finally, it highlights some challenges and future perspectives with regard to the clinical application of EVs.

Emerging integrated SERS-microfluidic devices for analysis of cancer-derived small extracellular vesicles

Cancer-derived small extracellular vesicles (sEVs) are specific subgroups of lipid bilayer vesicles secreted from cancer cells to the extracellular environment. They carry distinct biomolecules (e.g., proteins, lipids and nucleic acids) from their parent cancer cells. Therefore, the analysis of cancer-derived sEVs can provide valuable information for cancer diagnosis. However, the use of cancer-derived sEVs in clinics is still limited due to their small size, low amounts in circulating fluids, and heterogeneous molecular features, making their isolation and analysis challenging. Recently, microfluidic technology has gained great attention for its ability to isolate sEVs in minimal volume. In addition, microfluidics allows the isolation and detection of sEVs to be integrated into a single device, offering new opportunities for clinical application. Among various detection techniques, surface-enhanced Raman scattering (SERS) has emerged as a promising candidate for integrating with microfluidic devices due to its ultra-sensitivity, stability, rapid readout, and multiplexing capability. In this tutorial review, we start with the design of microfluidics devices for isolation of sEVs and introduce the key factors to be considered for the design, and then discuss the integration of SERS and microfluidic devices by providing descriptive examples of the currently developed platforms. Lastly, we discuss the current limitations and provide our insights for utilising integrated SERS-microfluidics to isolate and analyse cancer-derived sEVs in clinical settings.

Substantial dimerized G-quadruplex signal units engineered by cutting-mediated exponential rolling circle amplification for ultrasensitive and label-free detection of exosomes

Sensitive and accurate determination of tumor-derived exosomes from complicated biofluids is an important prerequisite for early tumor diagnosis through exosome-based liquid biopsy. Herein, a label-free fluorescence immunoassay protocol for ultrasensitive detection of exosomes was developed by engineering substantial dimerized guanine-quadruplex (Dimer-G4) signal units via in situ cutting-mediated exponential rolling circle amplification (CM-ERCA). First, exosomes were captured and enriched via immunomagnetic separation. Then, molecular recognition was built by the formation of antibody-aptamer sandwich immunocomplex through the specific binding of the designed aptamer-primers with the targeted exosomes. The accuracy of exosome detection was significantly improved by the specific recognition of two typical exosomal protein markers simultaneously. Eventually, in situ CM-ERCA was triggered by a perfect match between the multifunctional circular DNA template and the aptamer-primer on exosomal surface. Amplicons of CM-ERCA loaded with Dimer-G4 were exponentially accumulated during continuous cyclic amplification, dramatically lighting up the thioflavin T (ThT) and generating substantial Dimer-G4 signal units. As a result, ultrasensitive detection of exosomes with the detection limit down to 2.4 × 10² particles/mL was achieved due to the fluorescence enhancement of substantial Dimer-G4 signal units, which is ahead of most of available fluorescence-based methods reported currently. In addition, the intense fluorescence emission and favorable anti-interference of the proposed immunoassay supports identification of exosomes direct in human serums, overcoming the limitations of conventional G4/ThT in serum analysis and revealing its potential for exosome-based liquid biopsy.

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.

Cancer Exosomes: An Overview and the Applications of Flow

Cancer is one of the most prevalent and disruptive diseases affecting the population, and as such, is the subject of major research efforts. Recently, these efforts have been put towards understanding the role that exosomes can play in the progression of cancer. Exosomes are small extracellular vesicles ranging from 40–150 nm in size that carry bioactive molecules like proteins, DNA, RNA, miRNA, and surface receptors. One of the most important features of exosomes is their ability to easily travel throughout the body, extending the reach of parent cell’s signaling capabilities. Cancer derived exosomes (CDEs) carry dangerous cargo that can aid in the metastasis, and disease progression through angiogenesis, promoting epithelial to mesenchymal transition, and immune suppression. Exosomes can transport these molecules to cells in the tumor environment as well as distant premetastatic locations making them an extremely versatile tool in the toolbelt of cancer. This review aims to compile the present knowledge and understanding of the involvement of exosomes in the progression of cancer as well as current production, isolation, and purification methods, with particular interest on flow perfusion bioreactor and microfluidics systems, which allow for accurate modeling and production of exosomes.

Electrochemical nano-sensing interface for exosomes analysis and cancer diagnosis

Exosomes are a class of the nanosized extracellular vesicles, which have emerged as representative liquid biopsy biomarkers. To date, the electrochemical nanosensors are of great significance in the exosome detection with the advantages of easy operation, high accuracy and reliable repeatability. Especially, the growing field of nano interface has provided the electrochemical sensing platforms for the accurate exosomes analysis. The incorporation of multiple nanomaterials can take advantages and synergistic properties of functional units. So, based on the integration of with nanomaterial-based signal transduction and specific biorecognition, the nano-sensing interface provides excellent electrochemical features owing to rapid mass transport and excellent conductivity. The nano-sensing interface with a wide variety of morphologies and structure also provides the large active surface area for the immobilization of bio-capturing agents. Furthermore, through the design of nanostructured electrode array, the efficiency of transducer can be greatly improved. It should be noticed that the elaboration of a proper sensor requires the profound knowledge of the nano-sensing interface. Therefore, this article presents a review of the recent advance in exosomes detection based on the electrochemical nano-sensing interface, including electrochemical analysis principles, exosome sensing mechanisms, nano-interface construction strategies, as well as the typical diagnosis application. In particular, the article is focused on the exploration of the various electrochemical sensing performance of nano-interface in the exosome detection. We have also prospected the future trend and challenge of the electrochemical nano-sensing interface for exosomes analysis in clinical cancer diagnosis.

Si nanowire Bio-FET for electrical and label-free detection of cancer cell-derived exosomes

Exosomes are highly important in clinical diagnosis due to their high homology with their parental cells. However, conventional exosome detection methods still face the challenges of expensive equipment, low sensitivity, and complex procedures. Field effect transistors (FETs) are not only the most essential electronic component in the modern microelectronics industry but also show great potential for biomolecule detection owing to the advantages of rapid response, high sensitivity, and label-free detection. In this study, we proposed a Si nanowire field-effect transistor (Si-NW Bio-FET) device chemically modified with specific antibodies for the electrical and label-free detection of exosomes. The Si-NW FETs were fabricated by standard microelectronic processes with 45 nm width nanowires and packaged in a polydimethylsiloxane (PDMS) microfluidic channel. The nanowires were further modified with the specific CD63 antibody to form a Si-NW Bio-FET. The use of the developed Si-NW Bio-FET for the electrical and label-free detection of exosomes was successfully demonstrated with a limit of detection (LOD) of 2159 particles/mL. In contrast to other technologies, in this study, Si-NW Bio-FET provides a unique strategy for directly quantifying and real-time detecting exosomes without labeling, indicating its potential as a tool for the early diagnosis of cancer.