Dual-Mode and Label-Free Detection of Exosomes from Plasma Using an Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring

An easy-operation aptasensor for simultaneous detection of multiple tumor-associated exosomal proteins based on multicolor fluorescent DNA nanoassemblies

As a promising liquid biopsy biomarker, exosomes have demonstrated great potential and advantages in the noninvasive tumor diagnosis. However, an accurate and sensitive method for tumors-associated exosomes detection is scarce. Herein, we presented an easy-operation aptasensor which simultaneously detect multiple exosomal proteins by using multicolor fluorescent DNA nanoassemblies (FDNs) and CD63 aptamer-modified magnetic beads (MNPs-AptCD63). In this system, the FDNs were firstly constructed by encapsulating different quantum dots (QDs) into rolling circle amplification (RCA) products that contained different aptamer sequences. Thus, the FDNs could selectively recognize the different exosomal proteins captured by the MNPs-AptCD63, and achieve the multiplex and sensitive detection according to the fluorescence of QDs. Benefiting from the signal amplification capacity and high selectivity of FDNs, this aptasensor not only could detect exosomes as low as 650 particles/μL, but also showed accurate analysis in clinical samples. In addition, we can also achieve point-of-care testing (POCT) due to the simple analysis steps and naked-eye observable fluorescence of QDs under the ultraviolet irradiation. We believe that our aptasensor could provide a promising platform for exosomes-based personalized diagnosis and precise monitoring of human health.

Label-Free Impedance Imaging of Single Extracellular Vesicles Using Interferometric Electrochemical Microscopy

Extracellular vesicles (EVs) are pivotal in various biological processes and diseases, yet their small size and heterogeneity pose challenges for single EV quantification. We introduce interferometric electrochemical microscopy (iECM), a sensitive label-free technique that combines interferometric scattering and electrochemical impedance imaging. This method enables the quantification of the impedance of single EVs, providing unique insights into their electrochemical properties, and allows for the simultaneous measurement of size and real-time monitoring of antibody binding. Notably, we discovered that the impedance spectra of EVs can serve as specific fingerprints to differentiate EVs from cancerous and healthy cells, establishing iECM as a unique platform for EV characterization and classification.

Design of a Multiparametric Biosensing Platform and Its Validation in a Study on Spontaneous Cell Detachment from Temperature Gradients

This article reports on a bioanalytical sensor device that hosts three different transducer principles: impedance spectroscopy, quartz-crystal microbalance with dissipation monitoring, and the thermal-current-based heat-transfer method. These principles utilize a single chip, allowing one to perform either microbalance and heat transfer measurements in parallel or heat transfer and impedance measurements. When taking specific precautions, the three measurement modalities can even be used truly simultaneously. The probed parameters are distinctly different, so that one may speak about multiparametric or "orthogonal" sensing without crosstalk between the sensing circuits. Hence, this sensor allows one to identify which of these label-free sensing principles performs best for a given bioanalytical application in terms of a high signal amplitude and signal-to-noise ratio. As a proof-of-concept, the three-parameter sensor was validated by studying the spontaneous, collective detachment of eukaryotic cells in the presence of a temperature gradient between the QCM chip and the supernatant liquid. In addition to heat transfer, detachment can also be monitored by the impedance- and QCM-related signals. These features allow for the distinguishing between different yeast strains that differ in their flocculation genes, and the sensor device enables proliferation monitoring of yeast colonies over time.

Exosome, a Rising Biomarkers in Liquid Biopsy: Advances of Label-Free and Label Strategy for Diagnosis of Cancer

Cancer is commonly considered as one of the most severe diseases, posing a significant threat to human health and society due to various serious challenges. These challenges include difficulties in accurate diagnosis and a high propensity to form metastasis. Tissue biopsy remains the gold standard for diagnosing and subtyping cancer. However, concerns arise from its invasive nature and the potential risk of metastasis during these complex diagnostic procedures. Meanwhile, liquid biopsy has recently witnessed the rapid advancements with the emergence of three prominent detection biomarkers: circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), and exosomes. Whereas, the very low abundance of CTCs combined with the instability of ctDNA intensify the challenges and decrease the accuracy of these two biomarkers for cancer diagnosis. While exosomes have gained widespread recognition as a promising biomarker in liquid biopsy due to their relatively low-invasive detection method, excellent biostability, rich resources, high abundance, and ability to provide valuable information about cancer. Therefore, it is crucial to systematically summarize recent advancements mainly in exosome-based detection methods for early cancer diagnosis. Specifically, this review will primarily focus on label-based and label-free strategies for detecting cancer using exosomes. We anticipate that this comprehensive analysis will enhance readers' understanding of the significance and value of exosomes in the fields of cancer diagnosis and therapy.

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.

Peptide-graphene logic sensing system for dual-mode detection of exosomes, molecular information processing and protection

Peptides with highly sequence-dependent recognition, assembly, and encoding abilities can perform functions similar to DNA or even better, such as biosensing, molecular information processing, coding, or storage. However, the combination of versatile peptides and 2D materials are rarely used for multipurpose integrated applications, including biosensing, information processing and security. Herein, peptide-graphene sensing system was comprehensively used for dual-signal sensing of tumor-derived exosomes (TDEs), logic computing, and information protection. The system used fluorescent-labeled CD63-binding peptide CP05 and graphene oxide (GO) to selectively detect CD63 and TDEs by fluorescence and resonance light scattering. From three levels such as matter, energy, and information analysis, the matter and energy changes in GO-CP05 peptide sensing system were transformed into valuable information, which achieve the dual-mode quantitative detection of TDEs and its marker CD63, and the actual serum analysis. This matter-energy interaction network was also informationized, and utilized for parallel and batch logic computing, two kinds of molecular crypto-steganography (based on peptide sequence and Boolean logic relationships), which facilitates development of intelligent sensing and advanced information technology. This work not only provides a new method for sensitive detection of important disease markers, but also provides ideas for integrating molecular sensing and informatization to open molecular digitization.

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.

Nano-Brush Structure for Rapid Label-Free Differentiation of Alzheimer's Disease Stages and Direct Capture of Neuron-Derived Exosomes from Human Blood Plasma

The measurement of the neurofilament light chain (NFL) in human blood plasma/serum is a promising liquid biopsy for Alzheimer's disease (AD) diagnosis, offering advantages over conventional neuroimaging techniques recommended in clinical guidelines. Here, a controllable nano-brush structure comprising upstanding silicon nanowires coated with indium tin oxide was employed as the sensing substrate. This nano-brush structure was modified with an NFL antibody (NFLAb) via silane coupling and then further connected as the extended gate in a field-effect transistor (EGFET). Notable signal differences emerged within a 2 min timeframe, enabling the label-free differentiation in human blood plasmas among four distinct cohorts: healthy controls, subjective cognitive decline, mild cognitive impairment, and dementia due to AD. Our study indicates that achieving a surface roughness exceeding 400 nm on the modified nano-brush structure enables the effective electrical sensing in our EGFETs. These distinct electrical responses measured via the NFLAb-modified nano-brush EGFETs can be attributed to the combined effects of the captured NFLs and NFL-specific neuron-derived exosomes (NDEs) found in dementia patients, as confirmed by electron spectroscopy for chemical analysis, atomic force microscopy, and scanning electron microscopy. Finally, the potential of quantitatively detecting NDEs on the NFLAb-modified nano-brush structure was demonstrated using spiked solutions containing NFL-specific NDEs from IMR-32 neuroblast cells, wherein concentration-dependent changes were observed in the EGFETs output signal. Our findings show that the NFLAb-modified nano-brush EGFET enables rapid, label-free differentiation between healthy individuals and patients at varying stages of AD.

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.

Tuning the plasmonic and catalytic signals of Au@Pt nanoparticles for dual-mode biosensing

Dual-mode biosensors have gained great attention due to their excellent detection accuracy provided by the mutual verification of output signals. However, current strategies for dual-mode sensing mainly rely on a signal probe exhibiting dual properties that may encounter unreliability. Herein, we report a dual-mode biosensing strategy by modulating the plasmonic and catalytic activities of nanoparticles through a surface growing approach. Ascorbic acid enables the growing of Au shell on Au@Pt NPs to tune both their peroxidase-like activity and plasmonic signal. Enzyme-catalyzed reactions can generate ascorbic acid to modulate the plasmonic and catalytic activities of nanoparticles. Combined with enzyme-linked immunosorbent assay, it enables dual-mode immunoassays of carbofuran with both a colorimetric readout by a spectrometer down to 0.1 ppb and a naked-eye readout of 5 ppb. This dual-mode biosensing technique advantages in tunable sensitivity and robustness, holding promise as an analytical platform for biomedical diagnosis and food safety.

Parallel SPR and QCM-D Quantitative Analysis of CD9, CD63, and CD81 Tetraspanins: A Simple and Sensitive Way to Determine the Concentration of Extracellular Vesicles Isolated from Human Lung Cancer Cells

Tetraspanins, including CD9, CD63, and CD81, are transmembrane biomarkers that play a crucial role in regulating cancer cell proliferation, invasion, and metastasis, as well as plasma membrane dynamics and protein trafficking. In this study, we developed simple, fast, and sensitive immunosensors to determine the concentration of extracellular vesicles (EVs) isolated from human lung cancer cells using tetraspanins as biomarkers. We employed surface plasmon resonance (SPR) and quartz crystal microbalance with dissipation (QCM-D) as detectors. The monoclonal antibodies targeting CD9, CD63, and CD81 were oriented vertically in the receptor layer using either a protein A sensor chip (SPR) or a cysteamine layer that modified the gold crystal (QCM-D) without the use of amplifiers. The SPR studies demonstrated that the interaction of EVs with antibodies could be described by the two-state reaction model. Furthermore, the EVs' affinity to monoclonal antibodies against tetraspanins decreased in the following order: CD9, CD63, and CD81, as confirmed by the QCM-D studies. The results indicated that the developed immunosensors were characterized by high stability, a wide analytical range from 6.1 × 10⁴ particles·mL^-1 to 6.1 × 10⁷ particles·mL^-1, and a low detection limit (0.6-1.8) × 10⁴ particles·mL^-1. A very good agreement between the results obtained using the SPR and QCM-D detectors and nanoparticle tracking analysis demonstrated that the developed immunosensors could be successfully applied to clinical samples.

Amplified EQCM-D detection of extracellular vesicles using 2D gold nanostructured arrays fabricated by block copolymer self-assembly

Extracellular vesicles (EVs) are routinely released from nearly all cell types as transport vehicles and for cell communication. Crucially, they contain biomolecular content for the identification of health and disease states that can be detected from readily accessible physiological fluids, including urine, plasma, or saliva. Despite their clinical utility within noninvasive diagnostic platforms such as liquid biopsies, the currently available portfolio of analytical approaches are challenged by EV heterogeneity in size and composition, as well as the complexity of native biofluids. Quartz crystal microbalance with dissipation monitoring (QCM-D) has recently emerged as a powerful alternative for the phenotypic detection of EVs, offering multiple modes of analyte discrimination by frequency and dissipation. While providing rich data for sensor development, further progress is required to reduce detection limits and fully exploit the technique's potential within biosensing. Herein, we investigate the impact of nanostructuring the sensor electrode surface for enhancing its detection capabilities. We employ self-assembly of the block copolymer polystyrene-block-poly(4-vinylpyridine) to create well defined 2D gold islands via selective impregnation of the pyridine domain with gold precursors and subsequent removal of the template. When matched to the EV length scale, we find a 4-fold improvement in sensitivity despite a 4-fold reduction in area for analyte and ligand anchoring in comparison to a flat sensor surface. Creation of tailored and confined sensing regions interspersed by non-binding silica provides optimal spatial orientation for EV capture with reduced steric effects and negative cooperativity of grafted antibodies, offering a promising route for facilitated binding and enhanced performance of sensor platforms.

Clinical Application of Small Extracellular Vesicles in Gynecologic Malignancy Treatments

Small extracellular vesicles (sEVs) are the key mediators of intercellular communication. They have the potential for clinical use as diagnostic or therapeutic biomarkers and have been explored as vectors for drug delivery. Identification of reliable and noninvasive biomarkers, such as sEVs, is important for early diagnosis and precise treatment of gynecologic diseases to improve patient prognosis. Previous reviews have summarized routine sEVs isolation and identification methods; however, novel and unconventional methods have not been comprehensively described. This review summarizes a convenient method of isolating sEVs from body fluids and liquid biopsy-related sEV markers for early, minimally invasive diagnosis of gynecologic diseases. In addition, the characteristics of sEVs as drug carriers and in precision treatment and drug resistance are introduced, providing a strong foundation for identifying novel and potential therapeutic targets for sEV therapy. We propose potential directions for further research on the applications of sEVs in the diagnosis and treatment of gynecologic diseases.

Recent developments in biosensing methods for extracellular vesicle protein characterization

Research into extracellular vesicles (EVs) has grown significantly over the last few decades with EVs being widely regarded as a source of biomarkers for human health and disease with massive clinical potential. Secreted by every cell type in the body, EVs report on the internal cellular conditions across all tissue types. Their presence in readily accessible biofluids makes the potential of EV biosensing highly attractive as a noninvasive diagnostic platform via liquid biopsies. However, their small size (50-250 nm), inherent heterogeneity, and the complexity of the native biofluids introduce challenges for effective characterization, thus, limiting their clinical utility. This has led to a surge in the development of various novel EV biosensing techniques, with capabilities beyond those of conventional methods that have been directly transferred from cell biology. In this review, key detection principles used for EV biosensing are summarized, with a focus on some of the most recent and fundamental developments in the field over the last 5 years. This article is categorized under: Diagnostic Tools > Biosensing Diagnostic Tools > In Vitro Nanoparticle-Based Sensing.

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.

Quantification of Desiccated Extracellular Vesicles by Quartz Crystal Microbalance

Extracellular vesicle (EV) quantification is a procedure through which the biomedical potential of EVs can be used and their biological function can be understood. The number of EVs isolated from cell culture media depends on the cell status and is especially important in studies on cell-to-cell signaling, disease modeling, drug development, etc. Currently, the methods that can be used to quantify isolated EVs are sparse, and each have limitations. In this report, we introduce the application of a quartz crystal microbalance (QCM) as a biosensor for quantifying EVs in a small drop of volatile solvent after it evaporates and leaves desiccated EVs on the surface of the quartz crystal. The shifts in the crystal’s resonant frequency were found to obey Sauerbrey’s relation for EV quantities up to 6 × 10⁷, and it was determined that the biosensors could resolve samples that differ by at least 2.7 × 10⁵ EVs. A ring-shaped pattern enriched in EVs after the samples had dried on the quartz crystal is also reported and discussed. QCM technology is highly sensitive and only requires small sample volumes and is significantly less costly compared with the approaches that are currently used for EV quantification.