Advances in Exosome Analysis Methods with an Emphasis on Electrochemistry

Review of advances in glycan analysis on exosomes, cancer cells, and circulating cancer-derived glycoproteins with an emphasis on electrochemistry

Glycosylation, the intricate process of adding carbohydrate motifs to proteins, lipids, and exosomes on the cell surface, is crucial for both physiological and pathological mechanisms. Alterations in glycans significantly affect cancer cell metastasis by mediating cell-cell and cell-matrix interactions. The subtle changes in glycosylation during malignant transformations highlight the importance of analyzing cell and exosome surface glycosylation for prognostic and early treatment strategies in cancer. This review focuses on recent advancements in sensors for detecting surface glycans on cancer cells, exosomes, and circulating cancer-derived glycoproteins. Among various methods, electrochemical biosensors stand out as a promising tool, offering rapid and cost-effective glycan detection. These devices detect glycan interactions by measuring changes in electrical signals resulting from specific binding events. Techniques such as differential pulse voltammetry, impedance spectroscopy, and chrono amperometry are commonly employed for glycan detection using electrochemical biosensors. Researchers are exploring novel electrode materials and surface functionalization strategies to enhance sensor performance. Notably, selective binding probes such as lectins, aptamers, antibodies, and boronic acids are discussed, with lectins being the most prevalent for specific glycan analysis. By highlighting the significance of electrochemical techniques, emphasizing the role of selective binding probes, integrating microfluidics and miniaturized devices could lead to point-of-care applications for cancer diagnosis and monitoring. This review aims to provide valuable insights for researchers and clinicians working in the field of cancer glycomics.

Elements of liquid biopsies: isolation, analysis, and clinical application in cancer diagnosis to prognosis

INTRODUCTION

The liquid biopsy is a breakthrough in the field of medical diagnostics. It serves as a sentinel that can quietly detect even the subtlest aberrations that indicate the presence of disease. They make it possible to uncover relevant genetic factors of tumors with minimal to no risk to cancer patients. Liquid biopsies allow detailed diagnosis, dynamic treatment monitoring, and accurate prognosis. They are also invaluable in diagnosing other diseases such as infectious diseases and aberrant gene mutations.

AREAS COVERED

The present review undertakes an in-depth analysis of the existing status of liquid biopsy diagnostic tools, focusing on their principal components. Furthermore, the review highlights pertinent and recent research in this field to provide a comprehensive understanding of the current state of this technology and its prospects.

EXPERT OPINION

Despite new and upcoming research in liquid biopsies, multiple areas need to be further explored before the viable transition into the clinical arena. With the advancements in tools such as artificial intelligence and machine learning and the integration of these technologies with liquid biopsies, these challenges are being addressed and will eventually lead to the development of a highly evolved liquid biopsy diagnostic tools.

A catalytic assembly triggered DNAzyme motor on spherical nucleic acids for sensitive small extracellular vesicle detection

The expression levels of small extracellular vesicles (sEVs) are closely associated with several significant biological processes, which can be used as a crucial biomarker for cancer diagnosis, such as colorectal cancer. More efforts are still necessary to amplify sEV detection sensitivity, as their expression is minimal during the early stages of colorectal cancer. Through the integration of a catalytic assembly-triggered DNAzyme motor and gold nanoparticle (AuNP) aggregation, we have developed a triple signal amplified biosensor for the detection of sEVs. In this method, the catalytic assembly triggered DNAzyme motor continuously cleaved on the hairpin probe which is fixed on the surface of AuNPs, leaving a single-stranded sequence on the surface of AuNPs to induce the aggregation. This approach employs a triple signal amplification process to enhance the efficiency of the reaction and circumvent the issue of expensive and readily degradable proteases. The signal output system is based on dynamic light scattering technology, which enables ultra-sensitive detection of sEVs with a detection limit of 3.08 particles per μL. The present strategy exhibits significant potential for the analysis of a variety of additional analytes in clinical research disciplines due to its appealing analytical capabilities.

CRISPR/Cas13a Trans-Cleavage and Catalytic Hairpin Assembly Cascaded Signal Amplification Powered SERS Aptasensor for Ultrasensitive Detection of Gastric Cancer-Derived Exosomes

Cancer-derived exosomes carry a large number of specific molecular profiles from cancer cells and have emerged as ideal biomarkers for early cancer diagnosis. Accurate detection of ultralow-abundance exosomes in complex biological samples remains a great challenge. Herein, a novel SERS aptasensor powered by cascaded signal amplification of CRISPR/Cas13a trans-cleavage and catalytic hairpin assembly (CHA) was proposed for ultrasensitive detection of gastric cancer-derived exosomes, which included hairpin-structured recognition aptamers (MUC1-apt), cascaded signal amplification (i.e., CRISPR/Cas13a trans-cleavage and CHA), SERS tags, and silver nanorods (AgNRs) sensing chip. In the presence of SGC-7901 cell-derived exosomes, MUC1-apt specifically bound to MUC1 proteins highly expressed on exosomes via its contained MUC1 aptamer with its exposed RNA fragments activating the CRISPR/Cas13a trans-cleavage to cleave the uracil-modified hairpin reporter, and the cleavage products further triggered the downstream CHA reaction to form numerous duplexes, which can, in turn, capture a large number of SERS tags onto the AgNRs sensing chip to generate a significantly enhanced Raman signal. The proposed SERS aptasensor exhibits good performance on analysis of exosomes, i.e., rapid response within 60 min, single-particle sensitive detection from a 2 μL biological sample, good specificity in distinguishing SGC-7901 cell-derived exosomes against other exosomes, good uniformity, excellent repeatability, and satisfactory recoveries in human serum, and good universality to expand the detection of multiplex exosomes, which indicates that the SERS aptasensor provides a valuable reference for clinical diagnosis of early cancer.

Extracellular Vesicle Preparation and Analysis: A State-of-the-Art Review

In recent decades, research on Extracellular Vesicles (EVs) has gained prominence in the life sciences due to their critical roles in both health and disease states, offering promising applications in disease diagnosis, drug delivery, and therapy. However, their inherent heterogeneity and complex origins pose significant challenges to their preparation, analysis, and subsequent clinical application. This review is structured to provide an overview of the biogenesis, composition, and various sources of EVs, thereby laying the groundwork for a detailed discussion of contemporary techniques for their preparation and analysis. Particular focus is given to state-of-the-art technologies that employ both microfluidic and non-microfluidic platforms for EV processing. Furthermore, this discourse extends into innovative approaches that incorporate artificial intelligence and cutting-edge electrochemical sensors, with a particular emphasis on single EV analysis. This review proposes current challenges and outlines prospective avenues for future research. The objective is to motivate researchers to innovate and expand methods for the preparation and analysis of EVs, fully unlocking their biomedical potential.

Empowering Exosomes with Aptamers for Precision Theranostics

As information messengers for cell-to-cell communication, exosomes, typically small membrane vesicles (30-150 nm), play an imperative role in the physiological and pathological processes of living systems. Accumulating studies have demonstrated that exosomes are potential biological candidates for theranostics, including liquid biopsy-based diagnosis and drug delivery. However, their clinical applications are hindered by several issues, especially their unspecific detection and insufficient targeting ability. How to upgrade the accuracy of exosome-based theranostics is being widely explored. Aptamers, benefitting from their admirable characteristics, are used as excellent molecular recognition elements to empower exosomes for precision theranostics. With high affinity against targets and easy site-specific modification, aptamers can be incorporated with platforms for the specific detection of exosomes, thus providing opportunities for advancing disease diagnostics. Furthermore, aptamers can be tailored and functionalized on exosomes to enable targeted therapeutics. Herein, this review emphasizes the empowering of exosomes by aptamers for precision theranostics. A brief introduction of exosomes and aptamers is provided, followed by a discussion of recent progress in aptamer-based exosome detection for disease diagnosis, and the emerging applications of aptamer-functionalized exosomes for targeted therapeutics. Finally, current challenges and opportunities in this research field are presented.

Monitoring the electroactive cargo of extracellular vesicles can differentiate various cancer cell lines

Extracellular vesicles (EVs) are pivotal in cell-to-cell communication due to the array of cargo contained within these vesicles. EVs are considered important biomarkers for identification of disease, however most measurement approaches have focused on monitoring specific surface macromolecular targets. Our study focuses on exploring the electroactive component present within cargo from EVs obtained from various cancer and non-cancer cell lines using a disk carbon fiber microelectrode. Variations in the presence of oxidizable components were observed when the total cargo from EVs were measured, with the highest current detected in EVs from MCF7 cells. There were differences observed in the types of oxidizable species present within EVs from MCF7 and A549 cells. Single entity measurements showed clear spikes due to the detection of oxidizable cargo within EVs from MCF7 and A549 cells. These studies highlight the promise of monitoring EVs through the presence of varying electroactive components within the cargo and can drive a wave of new strategies towards specific detection of EVs for diagnosis and prognosis of various diseases.

Proximity hybridization based "turn-on" DNA tweezers for accurate and enzyme-free small extracellular vesicle analysis

Small extracellular vesicles (sEVs) are a type of extracellular vesicle that carries many types of molecular information. The identification of sEVs is essential for the non-invasive detection and treatment of illnesses. Hence, there is a significant need for the development of simple, sensitive, and precise methods for sEV detection. Herein, a DNA tweezers-based assay utilizing a "turn-on" mechanism and proximity ligation was suggested for the efficient and rapid detection of sEVs through amplified fluorescence. The target facilitates the proximity combination of the C1 probe and C2 probe, resulting in the formation of a complete extended sequence. The elongated sequence can cyclically initiate the hairpin probe (HP), leading to the activation of DNA tweezers. An excellent linear correlation was achieved, with a limit of detection of 57 particles per μL. Furthermore, it has been effectively employed to analyze sEVs under intricate experimental conditions, demonstrating a promising and pragmatic prospect for future applications. Given that the identification of sEVs was successfully accomplished using a single-step method that exhibited exceptional sensitivity and strong resistance to interference, the proposed technique has the potential to provide a beneficial platform for accurate recognition of sEVs and early detection of diseases.

Electrochemical detection of extracellular vesicles for early diagnosis: a focus on disease biomarker analysis

This review article presents a detailed examination of the integral role that electrochemical detection of extracellular vesicles (EVs) plays, particularly focusing on the potential application for early disease diagnostics through EVs biomarker analysis. Through an exploration of the benefits and challenges presented by electrochemical detection vetted for protein, lipid, and nucleic acid biomarker analysis, we underscore the significance of these techniques. Evidence from recent studies renders this detection modality imperative in identifying diverse biomarkers from EVs, leading to early diagnosis of diseases such as cancer and neurodegenerative disorders. Recent advancements that have led to enhanced sensitivity, specificity and point-of-care testing (POCT) potential are elucidated, along with equipment deployed for electrochemical detection. The review concludes with a contemplation of future perspectives, recognizing the potential shifts in disease diagnostics and prognosis, necessary advances for broad adoption, and potential areas of ongoing research. The objective is to propel further investigation into this rapidly burgeoning field, thereby facilitating a potential paradigm shift in disease detection, monitoring, and treatment toward human health management.

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.

Label-Free, Sensitive, and Versatile Colorimetric Method for Molecule Detection via the G-Quadruplex-Based Signal Quenching Strategy

Signal amplification strategies have emerged as a prominent tool in the field of improving the detection sensitivity of small extracellular vesicles (sEVs). It is important to highlight that the utilization of signal quenching strategies is not commonly implemented. A detection technique for sEVs was established based on the unwinding of G-quadruplex using Klenow fragment polymerase (KF), which served as an inspiration for this study. This system is characterized by its simplicity and lack of labeling, making it an efficient approach for signal quenching. In the presence of sEVs, the CD63 aptamer in the capture@sMBs complex binds with the CD63 protein on the surface of sEVs to release trigger sequences, which were employed as a primer to mediate the DNA polymerase/endonuclease-assisted signal recycling. The signal recycling process produces numerous single-stranded DNA sequences that can bind to the toehold section of the G-quadruplex. This leads to the rupture of the G-quadruplex structure and the subsequent deactivation of a DNAzyme generated by the G-quadruplex structure and hemin, thereby inhibiting its biological catalytic function. Consequently, the G-quadruplex structure would undergo a transformation to a duplex structure, leading to the emergence of a discernible differential signal that can be noticed in a majority of instances, even without the aid of magnification devices. The decrease in the prominent signal allows for the efficient analysis of target sEVs, which exhibit a notably low detection limit. In addition to the detection of sEVs, the approach has also been utilized for the investigation of miRNA-21. The approach demonstrates a high level of selectivity and robustness in its capacity to differentiate between target miRNA and base-mismatched miRNA as well as other miRNA families. This statement suggests that the assay holds significant promise for use in biochemical research and clinical diagnosis.

Liquid biopsy techniques and lung cancer: diagnosis, monitoring and evaluation

Lung cancer stands as the most prevalent form of cancer globally, posing a significant threat to human well-being. Due to the lack of effective and accurate early diagnostic methods, many patients are diagnosed with advanced lung cancer. Although surgical resection is still a potential means of eradicating lung cancer, patients with advanced lung cancer usually miss the best chance for surgical treatment, and even after surgical resection patients may still experience tumor recurrence. Additionally, chemotherapy, the mainstay of treatment for patients with advanced lung cancer, has the potential to be chemo-resistant, resulting in poor clinical outcomes. The emergence of liquid biopsies has garnered considerable attention owing to their noninvasive nature and the ability for continuous sampling. Technological advancements have propelled circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), extracellular vesicles (EVs), tumor metabolites, tumor-educated platelets (TEPs), and tumor-associated antigens (TAA) to the forefront as key liquid biopsy biomarkers, demonstrating intriguing and encouraging results for early diagnosis and prognostic evaluation of lung cancer. This review provides an overview of molecular biomarkers and assays utilized in liquid biopsies for lung cancer, encompassing CTCs, ctDNA, non-coding RNA (ncRNA), EVs, tumor metabolites, TAAs and TEPs. Furthermore, we expound on the practical applications of liquid biopsies, including early diagnosis, treatment response monitoring, prognostic evaluation, and recurrence monitoring in the context of lung cancer.

Monitoring of Medical Wastewater by Sensitive, Convenient, and Low-Cost Determination of Small Extracellular Vesicles Using a Glycosyl-Imprinted Sensor

The monitoring of small extracellular vesicles (sEVs) in medical waste is of great significance for the prevention of the spread of infectious diseases and the treatment of environmental pollutants in medical waste. Highly sensitive and selective detection methods are urgently needed due to the low content of sEVs in waste samples and the complex sample composition. Herein, a glycosyl-imprinted electrochemical sensor was constructed and a novel strategy for rapid, sensitive, and selective sEVs detection was proposed. The characteristic trisaccharide at the end of the glycosyl chain of the glycoprotein carried on the surface of the sEVs was used as the template molecule. The glycosyl-imprinted polymer films was then prepared by electropolymerization with o-phenylenediamine (o-PD) and 3-aminophenylboronic acid (m-APBA) as functional monomers. sEVs were captured by the imprinted cavities through the recognition and adsorption of glycosyl chains of glycoproteins on sEVs. The m-APBA molecule also acted as a signal probe and was then attached on the immobilized glycoprotein on the surface of sEVs by boric acid affinity. The electrochemical signal of m-APBA was amplificated due to the abundant glycoproteins on the surface of sEVs. The detection range of the sensor was 2.1 × 104 to 8.7 × 107 particles/mL, and the limit of detection was 1.7 × 104 particles/mL. The sensor was then applied to the determination of sEVs in medical wastewater and urine, which showed good selectivity, low detection cost, and good sensitivity.

High-sensitivity detection of low-concentration heavy metal ions in solution by multiple reflection enhanced absorption (MREA) spectroscopy

Heavy metal ions (Cr6+, Co2+, Ni2+, and Cu2+) in the electroplating and electrolysis industries are significantly related to process parameters and product quality, even at lower concentrations. Absorption spectroscopy is widely used for substance qualitative and quantitative analysis, which is an analytical method with the potential for real-time monitoring of heavy metal ions concentration in industrial processes. In this paper, a low-concentration heavy metal ion analysis method based on multiple reflection enhanced absorption (MREA) is proposed. Compared with traditional absorption, MREA has the advantages of low concentration detection limit and high-sensitivity. First, a reflective film (Al-SiO2) was prepared and a multiple reflection optical structure was designed to realize multiple parallel reflections of light in the solution medium. Then absorption spectra of low-concentration Cr6+, Co2+, Ni2+ and Cu2+ solutions were measured by MREA and traditional absorption methods. Finally, spectral bandwidth and incident light spots were optimized to obtain a superior absorption enhancement effect. The results showed that MREA could effectively increase the substance absorbance compared with traditional absorption. At the same time, with the optimal spectral bandwidth (0.4 nm) and incident light spot (1 mm), the detection limit of Cr6+, Co2+, Ni2+ and Cu2+ was reduced by 81.48%, 82.52%, 80.92% and 82.93%, respectively. The sensitivity was improved by 5-6 times, which was more obvious for low-concentration detection. In addition, the MREA method can achieve ion concentration analysis when Cr6+, Co2+, Ni2+, and Cu2+ coexist, and the linear correlative coefficients of the C-A curves were all greater than 0.999. Moreover, by adjusting reflectivity of the reflective film and the number of reflections in the optical structure, the results of the MREA method can be further optimized for the low-concentration heavy metal ion analysis. The MREA method has the advantages of simplicity, rapidity and versatility, which can provide the technical foundation for real-time monitoring method development of low-concentration heavy metal ions in industrial processes.

An Electrochemiluminescent Sensor Based on Glycosyl Imprinting and Aptamer for the Detection of Cancer-Related Extracellular Vesicles

Cancer-related extracellular vesicles (EVs) are considered important biomarkers for cancer diagnosis because they can convey a large amount of information about tumor cells. In order to detect cancer-related EVs efficiently, an electrochemiluminescence (ECL) sensor for the specific identification and highly sensitive detection of EVs in the plasma of cancer patients was constructed based on dual recognitions by glycosyl-imprinted polymer (GIP) and aptamer. The characteristic glycosyl Neu5Ac-α-(2,6)-Gal-β-(1-4)-GlcNAc trisaccharide on the surface of EVs was used as a template molecule and 3-aminophenylboronic acid as a functional monomer to form a glycosyl-imprinted polymer by electropolymerization. After glycosyl elution, the imprinted film specifically recognized and adsorbed the EVs in the sample, and then the CD63 aptamer-bipyridine ruthenium (Aptamer-Ru(bpy)) was added to combine with the CD63 glycoprotein on the extracellular vesicle's surface, thus providing secondary recognition of the EVs. Finally, the EVs were quantitatively detected according to the ECL signal produced by the labeled bipyridine ruthenium. When more EVs were captured by the imprinted film, more probes were obtained after incubation, and the ECL signal was stronger. Under the optimized conditions, the ECL signal showed a good linear relationship with the concentration of EVs in the range of 9.5 × 102 to 9.5 × 107 particles/mL, and the limit of detection was 641 particles/mL. The GIP sensor can discriminate between the EV contents of cancer patients and healthy controls with high accuracy. Because of its affordability, high sensitivity, and ease of use, it is anticipated to be employed for cancer early detection and diagnosis.

Immobilization-free dual-aptamer-based photoelectrochemical platform for ultrasensitive exosome assay

Exosomes, involved in cancer-specific biological processes, are promising noninvasive biomarkers for early diagnosis of cancer. Herein, an immobilization-free dual-aptamer-based photoelectrochemical (PEC) biosensor was proposed for the enrichment and quantification of cancer exosome based on photoactive bismuch oxyiodide/gold/cadmium sulfide (BiOI/Au/CdS) composites, nucleic acid-based recognition and signal amplification. In this biosensor, the recognition of exosome by two aptamers would trigger the deoxyribonucleotidyl transferase (TdT) enzyme-aided polymerization, leading to the enrichment of alkaline phosphatase (ALP) on Fe3O4 surface. After magnetic separation, ALP could catalyze the generation of ascorbic acid (AA) as electron donor and initiate the following redox cycle reaction for further signal amplification. Furthermore, all the above processes were performed in solution, the recognition and signal amplification efficiency would be superior than the heterogeneous strategy owing to the avoidance of steric hindrance effect. As a result, the proposed PEC biosensor was capable of enriching and detecting of cancer exosomes with high sensitivity and selectivity. The linear range of the biosensor was from 1.0 × 102 particles·μL-1 to 1.0 × 106 particles·μL-1 and the detection limit was estimated to be 21 particles·μL-1. Therefore, the proposed PEC biosensor holds great promise in quantifying tumor exosome for nondestructive early clinical cancer diagnosis and various other bioassay applications.

Integrating Reliable Pt-S Bond-Mediated 3D DNA Nanomachine with Magnetic Separation in a Homogeneous Electrochemical Strategy for Exosomal MicroRNA Detection with Low Background and High Sensitivity

Precise and sensitive analysis of exosomal microRNA (miRNA) is of great importance for noninvasive early disease diagnosis, but it remains a great challenge to detect exosomal miRNA in human blood samples because of their small size, high sequence homology, and low abundance. Herein, we integrated reliable Pt-S bond-mediated three-dimensional (3D) DNA nanomachine and magnetic separation in a homogeneous electrochemical strategy for the detection of exosomal miRNA with low background and high sensitivity. The 3D DNA nanomachine was easily prepared via a facile and rapid freezing method, and it was capable of resisting the influence of biothiols, thus endowing it with high stability. Notably, the as-developed magnetic 3D DNA nanomachine not only enabled the detection system to have a low background but also coupled with liposome nanocarriers to synergistically amplify the current signal. Consequently, by ingeniously combining the low background and multiple signal-amplification strategies in homogeneous electrochemical biosensing, highly sensitive detection of exosomal miRNA was successfully achieved. More significantly, with good anti-interference ability, the as-proposed method could effectively discriminate plasma samples from cancer patients and healthy subjects, thus showing a high potential for application in the nondestructive early clinical diagnosis of disease.

Exploring the Versatility of Exosomes: A Review on Isolation, Characterization, Detection Methods, and Diverse Applications

Extracellular vesicles (EVs) are crucial mediators of intercellular communication and can be classified based on their physical properties, biomolecular structure, and origin. Among EVs, exosomes have garnered significant attention due to their potential as therapeutic and diagnostic tools. Exosomes are released via fusion of multivesicular bodies on plasma membranes and can be isolated from various biofluids using methods such as differential ultracentrifugation, immune affinity capture, ultrafiltration, and size exclusion chromatography. Herein, an overview of different techniques for exosome characterization and isolation, as well as the diverse applications of exosome detection, including their potential use in drug delivery and disease diagnosis, is provided. Additionally, we discuss the emerging field of exosome detection by sensors, which offers an up-and-coming avenue for point-of-care diagnostic tools development. Overall, this review aims to provide a exhaustive and up-to-date summary of the current state of exosome research.

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.

One-step multiplex analysis of breast cancer exosomes using an electrochemical strategy assisted by gold nanoparticles

Exosomes, as a non-invasive biomarker, perform an important role in breast cancer screening and prognosis monitoring. However, establishing a simple, sensitive, and reliable exosome analysis technique remains challenging. Herein, a one-step multiplex analysis electrochemical aptasensor based on a multi-probe recognition strategy was constructed to analyze breast cancer exosomes. HER2-positive breast cancer cell (SK-BR-3) exosomes were selected as the model targets and three aptamers including CD63, HER2 and EpCAM aptamers were used as the capture units. Methylene blue (MB) functionalized HER2 aptamer and ferrocene (Fc) functionalized EpCAM aptamer, which were modified on gold nanoparticles (Au NPs), i.e. MB-HER2-Au NPs and Fc-EpCAM-Au NPs, were used as signal units. When the mixture of target exosomes, MB-HER2-Au NPs and Fc-EpCAM-Au NPs were added on the CD63 aptamer modified gold electrode, two Au NPs modified by MB and Fc could be specifically captured on the electrode by the recognition of three aptamers with target exosomes. Then one-step multiplex analysis of exosomes was achieved by detecting two independent electrochemical signals. This strategy can not only distinguish breast cancer exosomes from other exosomes (including normal exosomes and other tumor exosomes) but also HER2-positive breast cancer exosomes and HER2-negative breast cancer exosomes. Besides, it had high sensitivity and can detect SK-BR-3 exosomes with a concentration as low as 3.4 × 10³ particles mL^-1. Crucially, this method can be applicable to the examination of exosomes in complicated samples, which is anticipated to afford assistance for the screening and prognosis of breast cancer.

Hydrogel Microneedles Extracting Exosomes for Early Detection of Colorectal Cancer

There are several methods for early diagnosis of tumors, such as detecting circulating tumor DNAs, detecting circulating tumor cells, or imaging with tumor-targeting contrast agents. However, these assays are time-consuming and may cause patient discomfort during the biopsy collecting process. Here, we develop a facile method for early diagnosis of tumors by extracting exosomes from interstitial fluid (ISF) using hydrogel microneedles (MNs). The hydrogel MNs expand in the skin to absorb the ISF, and the tumor exosomes contained in the ISF bind with the glypican-1 antibodies inside the hydrogel of MNs. After removing the hydrogel on the MNs, exosomes are separately purified from the ISF to analyze tumor-related biomarkers. Finally, colorectal cancer can be diagnosed by ELISA for the colorectal cancer-induced model mice. This noninvasive hydrogel MN system to obtain the exosome samples would play an important role in early cancer diagnosis.

Extracellular Vesicles, as Drug-Delivery Vehicles, Improve the Biological Activities of Astaxanthin

Astaxanthin (AST) exhibits potent antioxidant and anti-inflammatory activities but poor stability and biological efficacy, which limit its application in the food and medical industries. In the present study, a new strategy was proposed to enhance the biological activities of AST using fetal bovine serum-derived extracellular vesicles (EVs). Saponin-assisted incubation was used to load AST owing to its high encapsulation efficiency and loading capacity. AST-incorporated EVs (EV-ASTs) maintained their original EV morphology and showed high stability at 4 °C, 25 °C, and 37 °C over a 28-day period, which was attributed to the protective environment provided by the phospholipid bilayer membrane of the EVs. Additionally, the EV-ASTs exhibited excellent antioxidant and anti-inflammatory activities in HaCaT keratinocytes and RAW 264.7 macrophage cells, respectively; these were significantly higher than those of free AST. Furthermore, the mechanism associated with the enhanced biological activities of EV-ASTs was evaluated by analyzing the expression of genes involved in antioxidation and anti-inflammation, in parallel with cellular in vitro assays. These results provide insights into methods for improving the performance of hydrophobic drugs using nature-derived EVs and will contribute to the development of novel drug-delivery systems.

Practical tips and new trends in electrochemical biosensing of cancer-related extracellular vesicles

To tackle cancer and provide prompt diagnoses and prognoses, the constantly evolving biosensing field is continuously on the lookout for novel markers that can be non-invasively analysed. Extracellular vesicles (EVs) may represent a promising biomarker that also works as a source of biomarkers. The augmented cellular activity of cancerous cells leads to the production of higher numbers of EVs, which can give direct information on the disease due to the presence of general and cancer-specific surface-tethered molecules. Moreover, the intravesicular space is enriched with other molecules that can considerably help in the early detection of neoplasia. Even though EV-targeted research has indubitably received broad attention lately, there still is a wide lack of practical and effective quantitative procedures due to difficulties in pre-analytical and analytical phases. This review aims at providing an exhaustive outline of the recent progress in EV detection using electrochemical and photoelectrochemical biosensors, with a focus on handling approaches and trends in the selection of bioreceptors and molecular targets related to EVs that might guide researchers that are approaching such an unstandardised field.

Biomimetic 3D Recognition with 2D Flexible Nanoarchitectures for Ultrasensitive and Visual Extracellular Vesicle Detection

Despite increasing recognition of extracellular vesicles being important circulating biomarkers in disease diagnosis and prognosis, current strategies for extracellular vesicle detection remain limited due to the compromised sample purification and extensive labeling procedures in complex body fluids. Here, we developed a 2D magnetic platform that greatly improves capture efficiency and readily realizes visible signal conversion for extracellular vesicle detection. The technology, termed high-affinity recognition and visual extracellular vesicle testing (HARVEST), leverages 2D flexible Fe₃O₄-MoS₂ nanostructures to recognize extracellular vesicles through multidentate affinity binding and feasible magnetic separation, thus enhancing the extracellular vesicle capture performance with both yield and separation time, affording high sensitivity with the detection limit of 20 extracellular vesicle particles/μL. Through integration with lipid labeling chemistry and the fluorescence visualization system, the platform enables rapid and visible detection. The number of extracellular vesicles can be feasibly determined by smart mobile phones, readily adapted for point-of-care diagnosis. When clinically evaluated, the strategy accurately differentiates melanoma samples from the normal cohort with an AUC of 0.98, demonstrating the efficient extracellular vesicle detection strategy with 2D flexible platforms for cancer diagnosis.

Redox-labelled electrochemical aptasensors with nanosupported cancer cells

The transfer of redox-labelled bioelectrochemical sensors from proteins to cells is not straightforward because of the cell downward force issue on the surface of the sensors. In this paper, 20-nm-thick nanopillars are introduced to overcome this issue, in a well-controlled manner. We show on both molecular dynamics simulations and experiments that suspending cells a few nanometers above an electrode surface enables redox-labelled tethered DNA aptamer probes to move freely, while remaining at an interaction distance from a target membrane protein, i. e. epithelial cell adhesion molecule (EpCAM), which is typically overexpressed in cancer cells. By this nanopillar configuration, the interaction of aptamer with cancer cells is clearly observable, with 13 cells as the lower limit of detection. Nanoconfinement induced by the gap between the electrode surface and the cell membrane appears to improve the limit of detection and to lower the melting temperature of DNA aptamer hairpins, offering an additional degree of freedom to optimize molecular recognition mechanisms. This novel nanosupported electrochemical DNA cell sensor scheme including Brownian-fluctuating redox species opens new opportunities for the design of all-electrical sensors using redox-labelled probes.

Tri-Channel Electrochemical Immunobiosensor for Combined Detections of Multiple Exosome Biomarkers of Lung Cancer

Current methods for the early diagnosis of cancer can be invasive and costly. In recent years, exosomes have been recognized as potential biomarkers for cancer diagnostics. The common methods for quantitative detection of exosomes, such as nanoparticle tracking analysis (NTA) and flow cytometry, rely on large-scale instruments and complex operation, with results not specific for cancer. Herein, we present a tri-channel electrochemical immunobiosensor for enzyme-free and label-free detecting carcino-embryonic antigen (CEA), neuron-specific enolase (NSE), and cytokeratin 19 fragments (Cyfra21-1) from exosomes for specific early diagnosis of lung cancer. The electrochemical immunobiosensor showed good selectivity and stability. Under optimum experimental conditions, the linear ranges were from 10^-3 to 10 ng/mL for CEA, 10^-4 to 10² ng/mL for NSE, and 10^-3 to 10² ng/mL for Cyfra21-1, and a detection limit down to 10^-4 ng/mL was achieved. Furthermore, we performed exosome analysis in three kinds of lung cancer. The results showed a distinct expression level of exosomal markers in different types. These works provide insight into a promising alternative for the quantification of exosomal markers in specific diseases in the following clinical bioassays.

Therapeutic Strategy of Mesenchymal-Stem-Cell-Derived Extracellular Vesicles as Regenerative Medicine

Extracellular vesicles (EVs) are lipid bilayer membrane particles that play critical roles in intracellular communication through EV-encapsulated informative content, including proteins, lipids, and nucleic acids. Mesenchymal stem cells (MSCs) are pluripotent stem cells with self-renewal ability derived from bone marrow, fat, umbilical cord, menstruation blood, pulp, etc., which they use to induce tissue regeneration by their direct recruitment into injured tissues, including the heart, liver, lung, kidney, etc., or secreting factors, such as vascular endothelial growth factor or insulin-like growth factor. Recently, MSC-derived EVs have been shown to have regenerative effects against various diseases, partially due to the post-transcriptional regulation of target genes by miRNAs. Furthermore, EVs have garnered attention as novel drug delivery systems, because they can specially encapsulate various target molecules. In this review, we summarize the regenerative effects and molecular mechanisms of MSC-derived EVs.

Development of electrochemical aptasensors detecting phosphate ions on TMB substrate with epoxy-based mesoporous silica nanoparticles

This study, it is aimed to develop an electrochemical aptasensor that can detect phosphate ions using 3.3'5.5' tetramethylbenzidine (TMB). It is based on the principle of converting the binding affinity of the target molecule phosphate ion (PO₄^3-) into an electrochemical signal with specific aptamer sequences for the aptasensor to be developed. The aptamer structure served as a gate for the TMB to be released and was used to trap the TMB molecule in mesoporous silica nanoparticles (MSNPs). The samples for this study were characterized by transmission electron spectroscopy (TEM), Brunner-Emmet-Teller, dynamic light scattering&electrophoretic light scattering, and induction coupled plasma atomic emission spectroscopy. According to TEM analysis, MSNPs have a morphologically hexagonal structure and an average size of 208 nm. In this study, palladium-carbon nanoparticles (Pd/C NPs) with catalytic reaction were used as an alternative to the biologically used horseradish peroxidase (HRP) enzyme for the release of TMB in the presence of phosphate ions. The limit of detection (LOD) was calculated as 0.983 μM, the limit of determination (LOQ) was calculated as 3.276 μM, and the dynamic linear phosphate range was found to be 50-1000 μM. The most important advantage of this bio-based aptasensor assembly is that it does not contain molecules such as a protein that cannot be stored for a long time at room temperature, so its shelf life is very long compared to similar systems developed with antibodies. The proposed sensor shows good recovery in phosphate ion detection and is considered to have great potential among electrochemical sensors.

Aptamers as Recognition Elements for Electrochemical Detection of Exosomes

Exosome analysis is emerging as an attractive noninvasive approach for disease diagnosis and treatment monitoring in the field of liquid biopsy. Aptamer is considered as a promising molecular probe for exosomes detection because of the high binding affinity, remarkable specificity, and low cost. Recently, many approaches have been developed to further improve the performance of electrochemical aptamer based(E-AB) sensors with a lower limit of detection. In this review, we focus on the development of using aptamer as a specific recognition element for exosomes detection in electrochemical sensors. We first introduce recent advances in evolving aptamers against exosomes. Then, we review methods of immobilization aptamers on electrode surfaces, followed by a summary of the main strategies of signal amplification. Finally, we present the insights of the challenges and future directions of E-AB sensors for exosomes analysis.

Dumbbell structure probe-triggered rolling circle amplification (RCA)-based detection scaffold for sensitive and specific neonatal infection-related small extracellular vesicle (sEV) detection

Small extracellular vesicles (sEVs) have been reported to play important roles in cell-to-cell communication and are promising biomarkers for the early diagnosis of infections. Therefore, it is in high demand to develop a method that can integrate easy-to-operate sEV isolation and sensitive quantification. We herein propose a novel detection scaffold for sEV isolation via low-speed centrifugation and the quantification of sEVs through DNAzyme-based signal amplification. The detection scaffold is established through dumbbell probe-based RCA (rolling circle amplification), containing repeated CD63 aptamer sections and DNAzyme sections. The original state of the DNAzyme section is locked in a hairpin structure in the detection scaffold. In the presence of sEVs, the CD63 aptamer recognizes and binds with sEVs, leading to the aggregation of sEVs, which can be isolated by low-speed centrifugation and the exposure of the DNAzyme section. After the catalytic fluorescence signal generation from the DNAzyme-based molecular beacon (MB) cleavage, the method exhibited a detection range of 10² to 10⁶ particles per μL. Considering the high sensitivity and wash-free and easy-to-operate features, the strategy reported herein paves a new avenue for the effective determination of sEVs and other membrane biomolecules in fundamental and applied research.

A highly sensitive electrochemical aptasensor for cocaine detection based on CRISPR-Cas12a and terminal deoxynucleotidyl transferase as signal amplifiers

Cocaine is one of the mainly used illegal drugs in the world. Using the signal amplification elements of terminal deoxynucleotidyl transferase (TdT) and CRISPR-Cas12a, a highly sensitive and simple electrochemical aptasensor was introduced for cocaine quantification. When, no cocaine existed in the sample, the 3'-end of complementary strand of aptamer (CS) was extended by TdT, leading to the activation of CRISPR-Cas12a and remaining of very short oligonucleotides on the working electrode. So, the current signal was remarkably promoted. With the presence of cocaine, CS left the electrode surface. Thus, nothing changed following the incubation of TdT and CRISPR-Cas12a and the Aptamer/Cocaine complex presented on the electrode. Consequently, the [Fe(CN)₆]^3-/4- could not freely reach the electrode surface and the signal response was weak. Under optimal situations, the biosensor revealed a wide linear relation from 40 pM to 150 nM with detection limit of 15 pM for cocaine. The sensitivity of the analytical system was comparable and even better than other reported methods for cocaine detection. The designed method displayed excellent cocaine selectivity. The aptasensor could work well for cocaine assay in serum samples. So, the aptasensor is expected to be an efficient analytical method with broad applications in the determination of diverse analytes.

Aptasensors for Cancerous Exosome Detection

Cancerous exosomes that carry multiple biomarkers are attractive targets for the early diagnosis and therapy of cancer. As one of the powerful molecular recognition tools, aptamers with excellent binding affinity and specificity toward biomarkers have been exploited to construct various aptamer-based biosensors (aptasensors) for exosome detection. Here, we review recent advances in aptasensors for the detection of cancerous exosomes. We first discuss the importance and potential of cancerous exosomes in cancer diagnosis and then summarize some conventional aptasensors from the perspective of biomarker recognition and signal collection strategies. Finally, we comment on the outlook for aptasensor research and new directions for cancerous exosome detection.

Surface plasmon resonance biosensor for exosome detection based on reformative tyramine signal amplification activated by molecular aptamer beacon

Human epidermal growth factor receptor 2 (HER2)-positive exosomes play an extremely important role in the diagnosis and treatment options of breast cancers. Herein, based on the reformative tyramine signal amplification (TSA) enabled by molecular aptamer beacon (MAB) conversion, a label-free surface plasmon resonance (SPR) biosensor was proposed for highly sensitive and specific detection of HER2-positive exosomes. The exosomes were captured by the HER2 aptamer region of MAB immobilized on the chip surface, which enabled the exposure of the G-quadruplex DNA (G4 DNA) that could form peroxidase-like G4-hemin. In turn, the formed G4-hemin catalyzed the deposition of plentiful tyramine-coated gold nanoparticles (AuNPs-Ty) on the exosome membrane with the help of H₂O₂, generating a significantly enhanced SPR signal. In the reformative TSA system, the horseradish peroxidase (HRP) as a major component was replaced with nonenzymic G4-hemin, bypassing the defects of natural enzymes. Moreover, the dual-recognition of the surface proteins and lipid membrane of the desired exosomes endowed the sensing strategy with high specificity without the interruption of free proteins. As a result, this developed SPR biosensor exhibited a wide linear range from 1.0 × 10⁴ to 1.0 × 10⁷ particles/mL. Importantly, this strategy was able to accurately distinguish HER2-positive breast cancer patients from healthy individuals, exhibiting great potential clinical application.

Engineered red blood cell membrane for sensitive and precise electrochemical detection of salivary exosomes

As a kind of promising non-invasive biomarker, exosomes naturally occurring in saliva have recently attracted considerable attention in view of their potential use in the diagnosis of oral diseases. Herein, we propose a new electrochemical method for the sensitive and precise detection of salivary exosomes. A red blood cell membrane (RBCM) engineered with CD63 aptamer is the core element of the method and is used to camouflage a gold electrode, thus giving the electrode superior antifouling and targeting ability. Target exosomes presented in saliva are recognized and captured by the highly specific interaction between the exosomal CD63 and the aptamers engineered in RBCM. Then, silver nanoparticles modified with CD63 aptamers are recruited onto the electrode surface to generate significant electrochemical signals, which enables the sensitive detection of target exosomes. By using human oral squamous cell carcinoma CAL27 cell-derived exosomes as a model, the method allows target salivary exosome detection in a wide linear range from 5 × 10² to 1 × 10⁶ particles per mL and a low detection limit of 2.07 × 10² particles per mL. Moreover, the method displays good reproducibility and is feasible for detecting target exosomes with high precision in saliva samples. Overall, the method may provide a useful tool for salivary exosome detection and may have great potential for practical use in the clinical diagnosis of oral diseases.

DNase I-assisted 2'-O-methyl molecular beacon for amplified detection of tumor exosomal microRNA-21

An end-modified 2'-O-methyl molecular beacon (eMB) with unique nuclease resistance was designed and prepared. The eMB can resist the enzymatic digestion by DNase I, which would otherwise occur upon the hybridization of the eMB with a complementary sequence. As a result, the coupling use of eMBs and DNase I allows highly sensitive detection of miRNA with a limit of detection (LOD) of 2.5 pM. The analytical strategy was further used for detection of tumor exosomal microRNA-21, and down to 0.86 μg mL^-1 A375 exosomes were detected. Overall, the present method can effectively quantify tumor-derived exosomes for cancer diagnosis.

A gas-pressure-assisted ratiometric atomic flame assay for the point-of-care testing of tumor-cell-derived exosomes

The multicolor-based point-of-care testing (POCT) of tumor cell-derived exosomes is of vital importance for understanding tumor growth and metastasis. Multicolor-based ratiometric signals most often rely on molecular optics, such as fluorescence resonance energy transfer (FRET)-dependent molecular fluorescence and localized surface plasmon resonance (LSPR)-related molecular colorimetry. However, finding acceptable FRET donor-acceptor fluorophore pairs and the kinetically slow color responses during size-related molecular colorimetry have greatly impeded POCT applications. Herein, an atomic flame was used to develop a visual sensing platform for the POCT of tumor-cell-derived exosomes. In comparison with common molecular optics, the atomic flame possessed the advantages of providing both a variety of ratiometric flame signals and fast response sensitivity. The integration of a gas-pressure-assisted flame reaction and dual-aptamer recognition guaranteed the sensitive and selective analysis of exosomes with a low limit of detection (LOD) of 7.6 × 10² particles per mL. Such a novel optical signal will inspire the development of more user-friendly POCT approaches.

Progress in Nanomaterials-Based Optical and Electrochemical Methods for the Assays of Exosomes

Exosomes with diameters of 30-150 nm are small membrane-bound vesicles secreted by a variety of cells. They play an important role in many biological processes, such as tumor-related immune response and intercellular signal transduction. Exosomes have been considered as emerging and noninvasive biomarkers for cancer diagnosis. Recently, a large number of optical and electrochemical biosensors have been proposed for sensitive detection of exosomes. To meet the increasing demands for ultrasensitive detection, nanomaterials have been integrated with various techniques as powerful components. Because of their intrinsic merits of biological compatibility, excellent physicochemical features and unique catalytic ability, nanomaterials have significantly improved the analytical performances of exosome biosensors. In this review, we summarized the recent progress in nanomaterials-based biosensors for the detection of cancer-derived exosomes, including fluorescence, colorimetry, surface plasmon resonance spectroscopy, surface enhanced Raman scattering spectroscopy, electrochemistry, electrochemiluminescence and so on.

Research of exosome in bone metastasis through dual aptamer recognition based entropy-driven amplification

Sensitive and accurate detection of exosome will greatly facilitate the early diagnosis of diverse diseases, such as cancers. Herein, a novel dual aptamer recognition based entropy-driven amplification was established for accurate analysis of exosomes. There are two main procedures in the proposed biosensor, including dual aptamer based recognition of exosome and entropy-driven catalytic system based signal recycling. In the recognition process, designed SMBs-S1 probe and S2-S4 probe complex, containing a CD63 aptamer and an EpCAM aptamer, respectively, are utilized for cooperated identification of exosomes. S4 probe was then released from S2-S4 probe complex through chain replacement of S5. The released S4 probe triggers entropy-driven catalytic system based signal recycling and endow the method a superior sensitivity. Impressively, owing to the cooperated identification of CD63 and EpCAM protein, the method exhibited a superior specificity and stayed stable under the interference of free CD63 and/or EpCAM protein. We believe that the sensitive, accurate strategy will provide a powerful tool for multiple biomarkers analysis and related clinical applications.

Ultrasensitive quantification of extracellular vesicles through dual signal amplification for the early diagnosis and prognosis of chronic obstructive pulmonary disease (COPD)

Accurate quantification of low-abundant EVs plays an essential role in the diagnosis and treatment of chronic obstructive pulmonary disease (COPD). Aptamers, which can specifically recognize and bind with protein molecules through transformation, make it possible to integrate DNA polymerase-based amplification strategies for protein detection. Thus, we have designed an allosteric probe and demonstrated its feasibility to convert the detection signals of EVs (extracellular vesicles) to nucleic acids through the specific recognition of target EVs. In addition, we have integrated the Nt.BstNBI and DNA polymerase based ssDNA generation process with the Exo III recycle process and greatly improved the detection sensitivity. The presence of target EVs initiates the Nt.BstNBI triggered multiple cycle amplification, enabling the achievement of high sensitivity and excellent selectivity, holding great potential in disease diagnosis and biomedical research.

Metal-Organic Framework-Functionalized Paper-Based Electrochemical Biosensor for Ultrasensitive Exosome Assay

The exosome has emerged as a promising noninvasive biomarker for the early diagnosis of cancer. Therefore, it is highly desirable to develop simple, inexpensive, and user-friendly biosensors for convenient, sensitive, and quantitative exosome assay. Herein, we developed a simple and cost-efficient electrochemical biosensor by combining a metal-organic framework (MOF)-functionalized paper and a screen-printed electrode (SPE) for portable, ultrasensitive, and quantitative determination of cancer-derived exosomes. In principle, the biosensor relied on recognition of the exosome by Zr-MOFs and aptamer to initiate the hybridization chain reaction (HCR) and the formation of DNAzyme for signal amplification. Benefiting from the high signal amplification ability of HCR, the label-free paper-based biosensor is capable of ultrasensitive exosome assay with a detection limit down to 5 × 10³ particles/mL, which is superior to that of most reported methods. Moreover, the proposed paper-based biosensor possessed the advantages of low cost, simple operation, and high sensitivity, making it affordable and deliverable for point-of-care (POC) diagnosis in resource-limited settings.

Dual-Aptamer-Assisted AND Logic Gate for Cyclic Enzymatic Signal Amplification Electrochemical Detection of Tumor-Derived Small Extracellular Vesicles

Small extracellular vesicles (sEVs), often referred to as exosomes, are potential biomarkers for noninvasive cancer diagnosis. However, because of their phenotype heterogeneity, precise detection of tumor-derived sEVs is a great challenge. Herein, a dual-aptamer-assisted AND logic gate was fabricated for sensitive electrochemical detection of tumor-derived sEVs based on a cyclic enzymatic signal amplification strategy. Four different tumor-derived sEVs were used to verify the feasibility of the AND logic gate, and CCRF-CEM sEVs were successfully detected by this assay. The electrochemical assay shows a good linear response from 4 × 10³ to 8 × 10⁷ particles/μL, with a detection limit of 920 particles/μL, for CCRF-CEM sEVs, indicating potential application in accurate cancer diagnostics.