Avoiding Pre-Isolation Step in Exosome Analysis: Direct Isolation and Sensitive Detection of Exosomes Using Gold-Loaded Nanoporous Ferric Oxide Nanozymes

Extracellular vesicles as critical mediators of maternal-fetal communication during pregnancy and their potential role in maternal metabolism

Extracellular vesicles (EVs) have been implicated in the pathophysiology of metabolic disorders by transferring biologically active molecules such as miRNAs and proteins to recipient cells, and influencing their metabolic pathways. Pregnancy is one of the greatest metabolic challenges faced by both the mother and the growing fetus, and this is fine-tuned by several factors, including hormones, soluble molecules, and molecules encapsulated in EVs released from the placenta. A wide range of EVs originating from the placenta are present in maternal circulation, and changes in their circulating levels and bioactivity (i.e., capacity to induce changes in the target cells) have been associated with several complications of pregnancies, including gestational diabetes mellitus (GDM), preeclampsia, preterm birth, and fetal growth restriction. Complications of pregnancies are associated with maternal metabolic dysfunction with short- and long-term consequences for both mother and child. However, the potential roles of circulating EVs originating from the placenta and other tissues (e.g. adipose tissue), on changes in maternal metabolism during normal and pregnancy complications have not been fully described. The aim of this brief review, thus, is to discuss the diversity of EVs, and their potential roles in the metabolic alterations during pregnancy, with a special focus on GDM.

Cancer biomarker profiling using nanozyme containing iron oxide loaded with gold particles

Nanozymes are nanomaterials with intrinsic magnetism and superparamagnetic properties. In the presence of an external magnet, nanozyme particles aggregate and redisperse without a foreign attraction. We evaluated the performances of nanozyme by changing the biosensing platforms and substituting other biological variants for a complete cancer assay detection. We investigated the expression of morphological variants in the transmission of signals using an electrochemical method. The signal responses, including signal enhancement with the nanozyme (Au-Fe₂O₃), showed a wide capturing range (greater than 80%, from 10² to 10⁵ cells ml^-1 in phosphate-buffered saline buffer, pH 7.4). The platform showed a fast response time within a dynamic range of 10-10⁵ cells ml^-1 for the investigated T47D cancer cell line. We also obtained higher responses for anti-HER2 (human epidermal receptor 2)/streptavidin interface as the biosensing electrode in the presence of T47D cancer cells. The positive assay produced a sixfold increase in current output compared to the negative target or negative biological variant. We calculated the limit of detection at 0.4 U ml^-1, and of quantitation at 4 U ml^-1 (units per millilitre). However, blood volume amounts in clinical settings may constrain diagnosis and increase detection limit value significantly.

Cancer-ID: Toward Identification of Cancer by Tumor-Derived Extracellular Vesicles in Blood

Extracellular vesicles (EVs) have great potential as biomarkers since their composition and concentration in biofluids are disease state dependent and their cargo can contain disease-related information. Large tumor-derived EVs (tdEVs, >1 μm) in blood from cancer patients are associated with poor outcome, and changes in their number can be used to monitor therapy effectiveness. Whereas, small tumor-derived EVs (<1 μm) are likely to outnumber their larger counterparts, thereby offering better statistical significance, identification and quantification of small tdEVs are more challenging. In the blood of cancer patients, a subpopulation of EVs originate from tumor cells, but these EVs are outnumbered by non-EV particles and EVs from other origin. In the Dutch NWO Perspectief Cancer-ID program, we developed and evaluated detection and characterization techniques to distinguish EVs from non-EV particles and other EVs. Despite low signal amplitudes, we identified characteristics of these small tdEVs that may enable the enumeration of small tdEVs and extract relevant information. The insights obtained from Cancer-ID can help to explore the full potential of tdEVs in the clinic.

Extracellular Vesicles: Current Analytical Techniques for Detection and Quantification

Since their first observation, understanding the biology of extracellular vesicles (EV) has been an important and challenging field of study. They play a key role in the intercellular communication and are involved in important physiological and pathological functions. Therefore, EV are considered as potential biomarkers for diagnosis, prognosis, and monitoring the response to treatment in some diseases. In addition, due to their properties, EV may be used for therapeutic purposes. In the study of EV, three major points have to be addressed: 1. How to isolate EV from cell culture supernatant/biological fluids, 2. how to detect them, and 3. how to characterize and quantify. In this review, we focus on the last two questions and provide the main analytical techniques up-to-date for detection and profiling of EV. We critically analyze the advantages and disadvantages of each one, aimed to be of relevance for all researchers working on EV biology and their potential applications.

Nanozyme-based electrochemical biosensors for disease biomarker detection

In recent years, a new group of nanomaterials named nanozymes that exhibit enzyme-mimicking catalytic activity has emerged as a promising alternative to natural enzymes. Nanozymes can address some of the intrinsic limitations of natural enzymes such as high cost, low stability, difficulty in storage, and specific working conditions (i.e., narrow substrate, temperature and pH ranges). Thus, synthesis and applications of hybrid and stimuli-responsive advanced nanozymes could revolutionize the current practice in life sciences and biosensor applications. On the other hand, electrochemical biosensors have long been used as an efficient way for quantitative detection of analytes (biomarkers) of interest. As such, the use of nanozymes in electrochemical biosensors is particularly important to achieve low cost and stable biosensors for prognostics, diagnostics, and therapeutic monitoring of diseases. Herein, we summarize the recent advances in the synthesis and classification of common nanozymes and their application in electrochemical biosensor development. After briefly overviewing the applications of nanozymes in non-electrochemical-based biomolecular sensing systems, we thoroughly discuss the state-of-the-art advances in nanozyme-based electrochemical biosensors, including genosensors, immunosensors, cytosensors and aptasensors. The applications of nanozymes in microfluidic-based assays are also discussed separately. We also highlight the challenges of nanozyme-based electrochemical biosensors and provide some possible strategies to address these limitations. Finally, future perspectives on the development of nanozyme-based electrochemical biosensors for disease biomarker detection are presented. We envisage that standardization of nanozymes and their fabrication process may bring a paradigm shift in biomolecular sensing by fabricating highly specific, multi-enzyme mimicking nanozymes for highly sensitive, selective, and low-biofouling electrochemical biosensors.

Microfluidic device for high-throughput affinity-based isolation of extracellular vesicles

Immunoaffinity based EV isolation technologies use antibodies targeting surface markers on EVs to provide higher isolation specificity and purity compared to existing approaches. One standing challenge for researchers is how to release captured EVs from the substrate to increase downstream and biological studies. The strong binding between the antibody and antigen or the antibody and substrate is commonly unbreakable without operating at conditions outside of the critical physiological range, making the release of EVs problematic. Additionally, immuno-affinity approaches are usually low-throughput due to their low flow velocity to ensure adequate time for antibody-antigen binding. To overcome these limitations, we modified the OncoBean chip, a previously reported circulating tumor cell isolation microfluidic device. The OncoBean chip is a radial flow microfluidic device with bean-shape microposts functionalized with biotin-conjugated EPCAM antibody through biotin-avidin link chemistry. It was demonstrated that the high surface area and varying shear rate provided by the bean-shaped posts and the radial flow design in the chip, enabled efficient capture of CTCs at high flow rate. We replace the anti-EPCAM with antibodies that recognize common EV surface markers to achieve high-throughput EV isolation. Moreover, by incorporating desthiobiotin-conjugated antibodies, EVs can be released from the device after capture, which offers a significant improvement over the existing isolation. The released EVs were found to be functional by confirming their uptake by cells using flow cytometry and fluorescent microscopy. We believe the proposed technology can facilitate both the study of EVs as cell-to-cell communicators and the further identification of EV markers.

Terminal deoxynucleotidyl transferase based signal amplification for enzyme-linked aptamer-sorbent assay of colorectal cancer exosomes

Exosomes have received increasingly significant attention and have shown great clinical value as biomarkers for a number of diseases. However, there is still a lack of a highly sensitive and visualized method for the detection of exosomes in numerous samples simultaneously. Here, we developed a high-throughput, colorimetric and simple method to detect colorectal cancer (CRC) exosomes based on terminal deoxynucleotidyl transferase (TdT)-aided ultraviolet signal amplification. Anti-A33, a CRC exosomal protein marker, was selected as a capture probe, and a facility-prepared EpCAM (CRC exosomal protein) aptamer-Au-primer complex was used as a signal probe. After the CRC exosomes were captured onto the surface of 96-well plates, the primer was extended to the poly(biotin-adenine) chains with the help of TdT, resulting in an increase in the binding amount of avidin-modified horseradish peroxidase (Av-HRP) for H₂O₂-mediated oxidation of 3,3',5,5'-tetramethyl benzidine (TMB) in enzyme-linked aptamer-sorbent assay (ELASA). The results showed that the incorporation of ploy(biotin-A) enabled approximately 10.4-fold signal amplification. This approach achieved a linear range of 9.75 × 10³-1.95 × 10⁶ particles/μL for CRC cell-derived exosomes. The feasibility of the developed assay was evaluated using clinical serum samples. CRC patients (n = 16) could be clearly and successfully distinguished from healthy individuals (n = 9). Furthermore, this proposed platform holds considerable potential for the detection of different targets, simply by changing the aptamer and antibody.

Surface plasmon resonance assay for exosomes based on aptamer recognition and polydopamine-functionalized gold nanoparticles for signal amplification

A novel surface plasmon resonance (SPR) strategy is introduced for the specific determination of exosomes based on aptamer recognition and polydopamine-functionalized gold nanoparticle (Au@PDA NP)-assisted signal amplification. Exosomes derived from hepatic carcinoma SMMC-7721 were selected as the model target. SMMC-7721 exosomes can be specifically captured by the aptamer ZY-sls that was complementary to the DNA tetrahedron probes (DTPs), and then the CD63 aptamer-linked Au@PDA NPs recognized SMMC-7721 exosomes for signal amplification. The DTPs were modified on a Au film for preventing Au deposition on the surface during the introduction of HAuCl₄, and PDA coated on the AuNPs was used to reduce HAuCl₄ in situ without any reductant assistance. It results in a further enhanced SPR signal. The assay can clearly distinguish SMMC-7721 exosomes from others (HepG2 exosomes, Bel-7404 exosomes, L02 exosomes, MCF-7 exosomes, and SW480 exosomes, respectively). SMMC-7721 exosomes are specifically determined as low as 5.6 × 10⁵ particles mL^-1. The method has successfully achieved specific determination of SMMC-7721 exosomes even in 50% of human serum without any pretreatment. Graphical abstract A novel surface plasmon resonance (SPR) strategy was introduced for the specific determination of exosomes based on aptamer recognition and polydopamine functionalized gold nanoparticles (Au@PDA NPs). The SPR signal was improved using the Au@PDA NPs assisted amplification.

A nature-inspired colorimetric and fluorescent dual-modal biosensor for exosomes detection

As non-invasive biomarkers, exosomes are of great significance to diseases diagnosis. However, sensitive and accurate detection of exosomes still remains technical challenges. Herein, inspired by nature's "one-to-many" concept, we design a biosensor mimicking the cactus with numerous thorns to detect exosomes. The biosensor is composed of CD63 antibodies, resembling the roots of cactus, to capture exosomes, and the exosomes resemble the stems. Cholesterol-labeled DNA (DNA anchor) binding to streptavidin modified horseradish peroxidase (HRP) can insert into exosomes membrane, which seems the thorns. The readout signal is produced through HRP-catalyzed hydrogen peroxide (H₂O₂) mediated oxidation of 1,4-phenylenediamine (PPD) to form 2,5-diamino-NN'-bis-(p-aminophenyl)-1,4-benzoquinone di-imine (PPDox). The PPDox can quench fluorescence of fluorescein through inner filter effect (IFE), which provides fluorescent signal for exosomes detection. Based on this principle, the obtained exosomes solution is qualitatively and quantitatively analyzed by our biosensor, with the comparison to current standard methods by nanoparticle tracking analysis (NTA) and commercial enzyme-linked immunosorbent assay (ELISA) kit. The linear range is from 1.0 × 10⁴ to 5.0 × 10⁵ particles μL^-1 with the limit of detection 3.40 × 10³ particles μL^-1 and 3.12 × 10³ particles μL^-1 for colorimetric and fluorescent assays, respectively. Meanwhile, our biosensor exhibits good selectivity, and can eliminate the interference from proteins. This dual-modal biosensor shows favorable performance towards analytical application in clinic samples, pushing one step further towards practical clinical use.

An Electrochemical Biosensor Designed by Using Zr-Based Metal-Organic Frameworks for the Detection of Glioblastoma-Derived Exosomes with Practical Application

Glioblastoma (GBM) is one of the most fatal tumors in the brain, and its early diagnosis remains technically challenging due to the complex repertoires of oncogenic alterations and blood-brain barrier (BBB). GBM-derived specific exosomes can cross the BBB and circulate in body fluids, so they can be noninvasive biomarkers for the early diagnosis of GBM. Herein, we propose a sensitive and label-free electrochemical biosensor designed by using Zr-based metal-organic frameworks (Zr-MOFs) for the detection of GBM-derived exosomes with practical application. In the design, a peptide ligand can specifically bind with human epidermal growth factor receptor (EGFR) and EGFR variant (v) III mutation (EGFRvIII), which are overexpressed on the GBM-derived exosomes. Meanwhile, Zr-MOFs encapsulated with methylene blue can absorb on the surface of the exosomes due to the interaction between Zr⁴⁺ and the intrinsic phosphate groups outside of exosomes. Consequently, the concentration of exosomes can be directly quantified by monitoring the electroactive molecules inside MOFs, ranging from 9.5 × 10³ to 1.9 × 10⁷ particles/μL with the detection of limit of 7.83 × 10³ particles/μL. Furthermore, this proposed biosensor can distinguish GBM patients from healthy groups, demonstrating the great prospect for early clinical diagnosis.

Electrochemical Detection of Tumor-Derived Extracellular Vesicles on Nanointerdigitated Electrodes

Tumor-derived extracellular vesicles (tdEVs) are attracting much attention due to their essential function in intercellular communication and their potential as cancer biomarkers. Although tdEVs are significantly more abundant in blood than other cancer biomarkers, their concentration compared to other blood components remains relatively low. Moreover, the presence of particles in blood with a similar size as that of tdEVs makes their selective and sensitive detection further challenging. Therefore, highly sensitive and specific biosensors are required for unambiguous tdEV detection in complex biological environments, especially for decentralized point-of-care analysis. Here, we report an electrochemical sensing scheme for tdEV detection, with two-level selectivity provided by a sandwich immunoassay and two-level amplification through the combination of an enzymatic assay and redox cycling on nanointerdigitated electrodes to respectively enhance the specificity and sensitivity of the assay. Analysis of prostate cancer cell line tdEV samples at various concentrations revealed an estimated limit of detection for our assay as low as 5 tdEVs/μL, as well as an excellent linear sensor response spreading over 6 orders of magnitude (10-106 tdEVs/μL), which importantly covers the clinically relevant range for tdEV detection in blood. This novel nanosensor and associated sensing scheme opens new opportunities to detect tdEVs at clinically relevant concentrations from a single blood finger prick.

Homogeneous, Low-volume, Efficient, and Sensitive Quantitation of Circulating Exosomal PD-L1 for Cancer Diagnosis and Immunotherapy Response Prediction

Immunotherapy has revolutionized cancer treatment, but its efficacy is severely hindered by the lack of effective predictors. Herein, we developed a homogeneous, low-volume, efficient, and sensitive exosomal programmed death-ligand 1 (PD-L1, a type of transmembrane protein) quantitation method for cancer diagnosis and immunotherapy response prediction (HOLMES-Exo_PD-L1 ). The method combines a newly evolved aptamer that efficiently binds to PD-L1 with less hindrance by antigen glycosylation than antibody, and homogeneous thermophoresis with a rapid binding kinetic. As a result, HOLMES-Exo_PD-L1 is higher in sensitivity, more rapid in reaction time, and easier to operate than existing enzyme-linked immunosorbent assay (ELISA)-based methods. As a consequence of an outstanding improvement of sensitivity, the level of circulating exosomal PD-L1 detected by HOLMES-Exo_PD-L1 can effectively distinguish cancer patients from healthy volunteers, and for the first time was found to correlate positively with the metastasis of adenocarcinoma. Overall, HOLMES-Exo_PD-L1 brings a fresh approach to exosomal PD-L1 quantitation, offering unprecedented potential for early cancer diagnosis and immunotherapy response prediction.

Efficient Visual Chemosensor for Hexavalent Chromium via a Controlled Strategy for Signal Amplification in Water

Generally, 3,3',5,5'-tetramethylbenzidine (TMB) cannot react with hydrogen peroxide (H₂O₂) in neutral pH or in water at room temperature and pressure. Herein, we found that hexavalent chromium (Cr⁶⁺) can trigger TMB reacting with H₂O₂ (TMB-H₂O₂) in ultrapure water along with a weak signal output. Then, to implement signal amplification effectively, we designed a ternary nanohybrid material containing graphene oxide (GO) nanosheets, gold nanoparticles (Au NPs), and hyperbranched polyethylenimine (PEI) to form rGO/PEI/Au nanohybrids via chemical bonding. After addition of a trace amount of Cr⁶⁺, rGO/PEI/Au nanohybrids can effectively catalyze TMB-H₂O₂ in ultrapure water; thus, a visual chemosensor and electronic spectrum quantitative analysis method for Cr⁶⁺ based on chromium-stimulated peroxidase mimetic activity of rGO/PEI/Au nanohybrids were established. The visual chemosensor exhibits excellent selectivity and interference immunity against 34 other interfering substances with a detection limit as low as 2.14 nM. The visual chemosensor for Cr⁶⁺ with a low detection limit and high selectivity is expected to have a potential application in environmental analysis, monitoring, and human health maintenance.

Electrochemical biosensing to move forward in cancer epigenetics and metastasis: A review

Early detection and effective treatment are crucial to reduce the physical, emotional, and financial pressure exerted by growing cancer burden on individuals, families, communities, and health systems. Currently, it is clear that the accurate analysis of emerging cancer epigenetic and metastatic-related biomarkers at different molecular levels is envisaged as an exceptional solution for early and reliable diagnosis and the improvement of therapy efficiency through personalized treatments. Within this field, electrochemical biosensing has demonstrated to be competitive over other emerging and currently used methodologies for the determination of these biomarkers accomplishing the premises of user-friendly, multiplexing ability, simplicity, reduced costs and decentralized analysis, demanded by clinical oncology, thus priming electrochemical biosensors to spark a diagnostic revolution for cancer prediction and eradication. This review article critically discusses the main characteristics, opportunities and versatility exhibited by electrochemical biosensing, through highlighting representative examples published during the last two years, for the reliable determination of these emerging biomarkers, with great diagnostic, predictive and prognostic potential. Special attention is paid on electrochemical affinity biosensors developed for the single or multiplexed determination of methylation events, non-coding RNAs, ctDNA features and metastasis-related protein biomarkers both in liquid and solid biopsies of cancer patients. The main challenges to which further work must be addressed and the impact of these advances should have in the clinical acceptance of these emerging biomarkers are also discussed which decisively will contribute to understand the molecular basis involved in the epigenetics and metastasis of cancer and to apply more efficient personalized therapies.

Exosome-specific tumor diagnosis via biomedical analysis of exosome-containing microRNA biomarkers

Exosome-containing microRNAs (exomiRs) can be employed as potential biomarkers for tumor diagnosis and have drawn much attention in the past few years. However, the separation of exosomes and the detection of exomiRs are still inconvenient or even difficult to implement. Thus, it is important to develop a simple, accurate, and reliable strategy for the separation of exosomes and the biomedical analysis of exomiRs. Herein, a novel exosome-specific tumor diagnosis strategy was constructed by integrating the rapid magnetic exosome-enrichment platform and the Ru(bpy)32+-polymer amplified electrochemiluminescence (ECL) strategy. This strategy realized the rapid and efficient capture of tumor-derived exosomes through a biological-affinity identification platform of the EpCAM antibody. The biomedical analysis of exomiRs achieved a preferable specificity and high sensitivity of 103 particles. Furthermore, we investigated the performance index for clinical blood samples from tumor patients; the results indicated that the exosome-specific tumor diagnosis strategy readily and consistently responded to exomiRs. These results indicated that the exosome-specific tumor diagnosis strategy provided new opportunities for the sensitive and efficient analysis of tumor-derived exomiRs. This strategy greatly simplified the biomedical analysis process and established the non-destructive detection mode of fluid biopsy for tumors.

Assembly of Black Phosphorus Nanosheets and MOF to Form Functional Hybrid Thin-Film for Precise Protein Capture, Dual-Signal and Intrinsic Self-Calibration Sensing of Specific Cancer-Derived Exosomes

As the emerging and noninvasive biomarkers, exosomes play an important role in cancer screening, cancer-related immune response, and the physiological process. The sensitive, specific, and efficient detection of cancer cell-derived exosomes is of significance for early cancer diagnosis of patients. This work developed a novel dual-signal and intrinsic self-calibration aptasensor of exosomes based on a functional hybrid thin-film platform. This platform was constructed via facile assembly of black phosphorus nanosheets (BPNSs) and ferrocene (Fc)-doped metal-organic frameworks (ZIF-67) on indium tin oxide (ITO) slice, followed by combining methylene blue (MB)-labeled single- strand DNA aptamer on ITO slice. The resultant aptamer-BPNSs/Fc/ZIF-67/ITO platform had dual redox-signal responses of MB (labeled on aptamer) and Fc (doped into ZIF-67). In the presence of specific cancer cell-derived exosomes, the redox current of MB regularly reduced and that of Fc (as reference) hardly changed. An intrinsic self-calibration aptasensor was achieved and enabled sensitive detection of exosomes, showing a limit of detection down to 100 particles mL^-1. The aptasensor with a capability of precise protein capture can efficiently determine specific cancer cell-derived exosomes in practical human serum and plasma samples from healthy individuals and breast cancer patients. In light of excellent performances, this aptasensor can be expanded to multiple biomarkers from cell line exosomes and is beneficial for exploring advanced techniques for high-performance detection of exosomes derived from different types of cancer cells. This work promotes the development of current techniques for early cancer screening and clinical diagnosis.

de la Fuente J, Moros M. Nanoparticle-based biosensors for detection of extracellular vesicles in liquid biopsies

Selecting the appropriate nanoparticle, functionalization chemistry and sensing methodology can speed up the translation of liquid biopsies into the clinic.

Nanoenzymes in disease diagnosis and therapy

This feature article highlights various nanoenzymes and their bio-applications in disease diagnosis and therapy. Current challenges and future trends of nanoenzymes are also discussed.

Exosome aggregation mediated stop-flow paper-based portable device for rapid exosome quantification

Exosome quantification is important for estimation of informative messengers (e.g., proteins, lipids, RNA, etc.) involving physiological and pathological effects. This work aimed to develop a simple and rapid distance-based paper portable device using exosome-capture vesicles (polydiacetylene conjugated with antiCD81) for exosome quantification in cell cultures. This novel concept relied on distinct aggregation of exosomes and exosome-capture vesicles leading to different solvent migration. Distances of the migration were used as signal readouts, which could be detected by naked eye. PDA-antiCD81 as exosome-capture vesicles were optimized (e.g., size, reaction ratio, and concentration) and the paper designs were investigated (e.g., diameter of sample reservoir and lamination layer) to enhance the solvent stop-flow effects. Finally, exosome screening on three cell culture samples (COLO1, MDA-MB-231, and HuR-KO1 subclone) was demonstrated. The method could linearly measure exosome concentrations in correlation with solvent migration distances in the range of 10⁶ -10¹⁰ particles/mL (R²  > 0.98) from the cell culture samples. The exosome concentration measurements by the developed device were independently assessed by nanoparticle tracking analysis. Results demonstrated no statistically significant difference (p > 0.05) by t-test. This low-cost and rapid device allows a portable platform for exosome quantification without the requirement of expensive equipment and expertise of operation. The developed device could potentially be useful for quantification of other biomarker-related extracellular vesicles.

Rapid Enrichment and Detection of Extracellular Vesicles Enabled by CuS-Enclosed Microgels

Extracellular vesicles (EVs) are cell-derived membranous vesicles that exist in nearly all biological fluids, including blood and urine; and carry a great number of cargo molecules such as protein, nucleic acids, and lipid. They may play important roles in cell-cell communication and modulation of pathological processes, which, however, are not yet well understood, calling for highly sensitive, specific, and rapid methods for EV detection and quantification in biological samples. Here, we report the CuS-enclosed microgels that not only help enrich EVs carrying specific protein markers from complex biomatrices, but also produce strong chemiluminescence (CL) to realize sensitive detection of the target EVs. A detection limit of 104 EV particles/mL was achieved with these microgels by targeting EV proteins like CD63 and HER2, with a dynamic range up to 108 particles/mL. Direct detection of EVs in human serum and cell culture medium without tedious sample preparation was demonstrated, consuming much less sample compared to ELISA and Western Blot. We envision that our method will be valuable for quick quantification of EVs in biological samples, benefiting disease monitoring and functional study.

A hybridization chain reaction based assay for fluorometric determination of exosomes using magnetic nanoparticles and both aptamers and antibody as recognition elements

Exosomes represent a new generation of biomarkers for the early diagnosis of hepatic carcinoma. A fluorometric assay is presented that is based on the hybridization chain reaction and magnetic nanoparticles for the highly sensitive determination of exosome (from HepG2 cells). Antibody as the recognition element was modified on the surface of magnetic nanoparticles. Antibody was used to capture the exosome. The Probe 1 was consisted of aptamer sequence and trigger sequence. Aptamer sequence will bind with the surface protein of exosome. The trigger sequence will hybridize with the probe2 (FAM-labeled) and the probe3 (FAM-labeled). So the product of the hybridization chain reaction will present a strong fluorescence signal. The fluorescence product of hybridization chain reaction will link with magnetic nanoparticles through the 'magnetic nanoparticles-antibody-exosome-aptamer' structure. The product can be separated from the matrix due to the present of the magnetic nanoparticles. The excitation was set at 490 nm. The fluorescence value of the emission spectra at 519 nm was set as the signal response. The linear range of this assay is from 1000 to 10⁷ particles·mL^-1. The detection limit is 100 particles·mL^-1. This assay was applied to the determination of exosome from the hepatic carcinoma cells. Graphical abstractIn the presence of exosmes, the hybridization chain reaction was triggered and strong green fluorescence will be produced. Moreover, the magnetic particles can separate the products from the matrix.

Advanced liquid biopsy technologies for circulating biomarker detection

Liquid biopsy is a new diagnostic concept that provides important information for monitoring and identifying tumor genomes in body fluid samples. Detection of tumor origin biomolecules like circulating tumor cells (CTCs), circulating tumor specific nucleic acids (circulating tumor DNA (ctDNA), circulating tumor RNA (ctRNA), microRNAs (miRNAs), long non-coding RNAs (lnRNAs)), exosomes, autoantibodies in blood, saliva, stool, urine, etc. enables cancer screening, early stage diagnosis and evaluation of therapy response through minimally invasive means. From reliance on painful and hazardous tissue biopsies or imaging depending on sophisticated equipment, cancer management schemes are witnessing a rapid evolution towards minimally invasive yet highly sensitive liquid biopsy-based tools. Clinical application of liquid biopsy is already paving the way for precision theranostics and personalized medicine. This is achieved especially by enabling repeated sampling, which in turn provides a more comprehensive molecular profile of tumors. On the other hand, integration with novel miniaturized platforms, engineered nanomaterials, as well as electrochemical detection has led to the development of low-cost and simple platforms suited for point-of-care applications. Herein, we provide a comprehensive overview of the biogenesis, significance and potential role of four widely known biomarkers (CTCs, ctDNA, miRNA and exosomes) in cancer diagnostics and therapeutics. Furthermore, we provide a detailed discussion of the inherent biological and technical challenges associated with currently available methods and the possible pathways to overcome these challenges. The recent advances in the application of a wide range of nanomaterials in detecting these biomarkers are also highlighted.

An electrochemiluminescent aptasensor for amplified detection of exosomes from breast tumor cells (MCF-7 cells) based on G-quadruplex/hemin DNAzymes

Exosomes are non-invasive biomarkers for cancer diagnosis. Herein, we describe an electrochemiluminescent (ECL) aptasensor for the detection of exosomes from breast tumor cells. Mercaptopropionic acid (MPA)-modified Eu³⁺-doped CdS nanocrystals (MPA-CdS:Eu NCs) and H₂O₂ were used as ECL emitters and coreactant, respectively. The exosomes are recognized and captured by the CD63 aptamer, and then form a G-quadruplex/hemin DNAzyme, which efficiently catalyzes the decomposition of H₂O₂, resulting in the decreased ECL signal of MPA-CdS:Eu NCs. The exosomes from breast tumor cells (MCF-7 cells) can be detected in the range of 3.4 × 10⁵ to 1.7 × 10⁸ particles per mL. The limit of detection (LOD) was estimated to be 7.41 × 10⁴ particles per mL at a signal-to-noise ratio of 3. The aptasensor has been successfully used to detect exosomes in the serum.

Enhancing the colorimetric detection of H2O2 and ascorbic acid on polypyrrole coated fluconazole-functionalized POMOFs

A new fluconazole-functionalized polyoxometalate-based metal-organic framework (POMOF) [Ag₃(FKZ)₂(H₂O)₂][H₃SiW₁₂O₄₀] (AgFKZSiW₁₂) was successfully constructed, and its polypyrrole (PPy) coated composite AgFKZSiW₁₂@PPy was also obtained via a facile 'in situ' oxidation polymerization process. The peroxidase-like activity evaluation indicates that the maximized synergistic effect from the integration of PPy, SiW₁₂ clusters, HFKZ drug molecules, and Ag ions deeply enhanced the overall performance. More importantly, AgFKZSiW₁₂@PPy exhibits the fastest response time (30 s) among all the reported peroxidase mimics to date, including the pristine AgFKZSiW₁₂ (2 min). Moreover, the AgFKZSiW₁₂@PPy-based colorimetric biosensing platform towards H₂O₂ and ascorbic acid (AA) exhibits limits of detection (LOD) as low as 0.12 μM and 2.7 μM, respectively. This work reveals a promising prospect in medical diagnosis and biotechnology for colorimetric biosensor fabrication with high performance through the introduction of PPy.

Nanoarchitectured peroxidase-mimetic nanozymes: mesoporous nanocrystalline α- or γ-iron oxide?

Next-generation nanozyme based biosensing: mesoporous nanocrystalline α- or γ-iron oxide?

Superparamagnetic nanoarchitectures for disease-specific biomarker detection

Synthesis, bio-functionalization, and multifunctional activities of superparamagnetic-nanostructures have been extensively reviewed with a particular emphasis on their uses in a range of disease-specific biomarker detection and associated challenges.