Point-of-care detection of extracellular vesicles: Sensitivity optimization and multiple-target detection

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

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

The role and application of small extracellular vesicles in glioma

Small extracellular vesicles (sEVs) are cell-derived, nanometer-sized particles enclosed by a lipid bilayer. All kinds of biological molecules, including proteins, DNA fragments, RNA, lipids, and metabolites, can be selectively loaded into sEVs and transmitted to recipient cells that are near and distant. Growing shreds of evidence show the significant biological function and the clinical significance of sEVs in cancers. Numerous recent studies have validated that sEVs play an important role in tumor progression and can be utilized to diagnose, stage, grading, and monitor early tumors. In addition, sEVs have also served as drug delivery nanocarriers and cancer vaccines. Although it is still infancy, the field of basic and translational research based on sEVs has grown rapidly. In this review, we summarize the latest research on sEVs in gliomas, including their role in the malignant biological function of gliomas, and the potential of sEVs in non-invasive diagnostic and therapeutic approaches, i.e., as nanocarriers for drug or gene delivery and cancer vaccines.

Nanoplasmonic sensors for extracellular vesicles and bacterial membrane vesicles

Extracellular vesicles (EVs) are promising tools for the early diagnosis of diseases, and bacterial membrane vesicles (MVs) are especially important in health and environment monitoring. However, detecting EVs or bacterial MVs presents significant challenges for the clinical translation of EV-based diagnostics. In this Review, we provide a comprehensive discussion on the basics of nanoplasmonic sensing and emphasize recent developments in nanoplasmonics-based optical sensors to effectively identify EVs or bacterial MVs. We explore various nanoplasmonic sensors tailored for EV or bacterial MV detection, emphasizing the application of localized surface plasmon resonance through gold nanoparticles and their multimers. Additionally, we highlight advanced EV detection techniques based on surface plasmon polaritons using plasmonic thin film and nanopatterned structures. Furthermore, we evaluate the improved detection capability of surface-enhanced Raman spectroscopy in identifying and classifying these vesicles, aided by plasmonic nanostructures. Nanoplasmonic sensing techniques have remarkable precision and sensitivity, making them a potential tool for accurate EV detection in clinical applications, facilitating point-of-care molecular diagnostics. Finally, we summarize the challenges associated with nanoplasmonic EV or bacterial MV sensors and offer insights into potential future directions for this evolving field.

Environmental pollutants exposure-derived extracellular vesicles: crucial players in respiratory disorders

BACKGROUND

Individual exposure to environmental pollutants, as one of the most influential drivers of respiratory disorders, has received considerable attention due to its preventability and controllability. Considering that the extracellular vesicle (EV) was an emerging intercellular communication medium, recent studies have highlighted the crucial role of environmental pollutants derived EVs (EPE-EVs) in respiratory disorders.

METHODS

PubMed and Web of Science were searched from January 2018 to December 2023 for publications with key words of environmental pollutants, respiratory disorders and EVs.

RESULTS

Environmental pollutants could disrupt airway intercellular communication by indirectly stimulating airway barrier cells to secrete endogenous EVs, or directly transmitting exogenous EVs, mainly by biological pollutants. Mechanistically, EPE-EVs transferred specific contents to modulate biological functions of recipient cells, to induce respiratory inflammation and impair tissue and immune function, which consequently contributed to the development of respiratory diseases, such as asthma, chronic obstructive pulmonary disease, pulmonary fibrosis, pulmonary hypertension, lung cancer and infectious lung diseases. Clinically, EVs could emerged as promising biomarkers and biological agents for respiratory diseases attributed by their specificity, convenience, sensibility and stability.

CONCLUSIONS

Further studies of EPE-EVs are helpful to understand the aetiology and pathology of respiratory diseases, and facilitate the precision respiratory medicine in risk screening, early diagnosis, clinical management and biotherapy.

Increasing the sensitivity and accuracy of detecting exosomes as biomarkers for cancer monitoring using optical nanobiosensors

The advancement of nanoscience and material design in recent times has facilitated the creation of point-of-care devices for cancer diagnosis and biomolecule sensing. Exosomes (EXOs) facilitate the transfer of bioactive molecules between cancer cells and diverse cells in the local and distant microenvironments, thereby contributing to cancer progression and metastasis. Specifically, EXOs derived from cancer are likely to function as biomarkers for early cancer detection due to the genetic or signaling alterations they transport as payload within the cancer cells of origin. It has been verified that EXOs circulate steadily in bodily secretions and contain a variety of information that indicates the progression of the tumor. However, acquiring molecular information and interactions regarding EXOs has presented significant technical challenges due to their nanoscale nature and high heterogeneity. Colorimetry, surface plasmon resonance (SPR), fluorescence, and Raman scattering are examples of optical techniques utilized to quantify cancer exosomal biomarkers, including lipids, proteins, RNA, and DNA. Many optically active nanoparticles (NPs), predominantly carbon-based, inorganic, organic, and composite-based nanomaterials, have been employed in biosensing technology. The exceptional physical properties exhibited by nanomaterials, including carbon NPs, noble metal NPs, and magnetic NPs, have facilitated significant progress in the development of optical nanobiosensors intended for the detection of EXOs originating from tumors. Following a summary of the biogenesis, biological functions, and biomarker value of known EXOs, this article provides an update on the detection methodologies currently under investigation. In conclusion, we propose some potential enhancements to optical biosensors utilized in detecting EXO, utilizing various NP materials such as silicon NPs, graphene oxide (GO), metal NPs, and quantum dots (QDs).

All-in-one detection of breast cancer-derived exosomal miRNA on a pen-based paper chip

Exosomal microRNAs (miRNAs) play a pivotal role in intercellular communication, regulating gene expression in target cells, and hold significant promise as cancer biomarkers for early detection and screening. However, achieving precise and viable detection of exosomal miRNAs remains a challenge. This paper proposes an all-in-one detection strategy for breast cancer-derived exosomal miRNA-21 on a pen-based paper chip (PPC). The PPC is constructed using a modified automatic pen and lateral flow assay (LFA), which results in a cost-effective fabrication process. The user only needs to add the sample and trigger the top of the self-contained PPC after a period of time to complete the entire detection process. To enhance the sensitivity of exosomal miRNA testing, an enzyme-free catalyzed hairpin assembly (CHA) is further introduced, enabling highly sensitive detection of miRNA-21 with a limit of detection (LOD) of 25 fmol. Additionally, the detection of miRNAs in differentially-expressed cells and clinical samples has also been successfully achieved with high specificity. Overall, the proposed PPC provides an effective tool for detecting early cancer, monitoring diseases, and establishing point of care testing (POCT).

Miniaturized Laser Probe for Exosome-Based Cancer Liquid Biopsy

Exosomes have been established as a valuable tool for clinical applications for the purpose of liquid biopsy and therapy. However, the clinical practice of exosomes as cancer biopsy markers is still to a very low extent. Active mode optical microcavity with microlaser emission has aroused as a versatile approach for chemical and biological sensing due to its benefits of larger photon population, increased effective Q-factor, decreased line width, and improved sensitivity. Herein, we report a label-free and precise quantification of exosome vesicles and surface protein profiling of breast cancer exosomes using functionalized active whispering gallery mode (WGM) microlaser probes. A detection limit of 40 exosomes per microresonator was achieved. The proposed system enabled a pilot assay of quantitative exosome analysis in cancer patients' blood with only a few microliters of sample consumption, holding good potential for large-scale cancer liquid biopsy. Multiplexed functionalization of the optical microresonator allowed us to profile cancer exosomal surface markers and distinct subclasses of breast cancer-associated exosomes and monitor drug treatment outcomes. Our findings speak volumes about the advantages of the WGM microlaser sensor, including very small sample consumption, low detection limit, high specificity, and ease of operation, offering a promising means for precious clinical sample analysis.

Polydiacetylene-based aptasensors for rapid and specific colorimetric detection of malignant exosomes

Exosomes (50-150 nm) play significant biological functions in intercellular communication and transportation of diverse biomolecules, including proteins and nucleic acids. In particular, malignant exosomes have received a great deal of attention as possible indicators for cancer detection and treatment. To swiftly and precisely identify malignant exosomes from normal exosomes in diverse bodily fluids, we developed polydiacetylene (PDA)-based aptasensors with distinct optical features exhibiting color shift in response to biological recognition. To identify epithelial cell adhesion molecules (EpCAM) overexpressed on the surface of malignant exosomes, anti-EpCAM aptamer-conjugated diacetylene monomer (TCDA-Apt) was synthesized and used to create anti-EpCAM aptamer-conjugated PDA (anti-EpCAM Apt-PDA) vesicles. In just 15 min following the reaction with malignant exosomes, the anti-EpCAM Apt-PDA vesicles underwent a visible color change from blue to purple. They showed high specificity to EpCAM-positive malignant exosomes over non-malignant exosomes, bovine serum albumin (BSA), and fibrinogen. Moreover, its effectiveness in the point-of-care (POC) detection of malignant exosomes was evaluated using human sera. Therefore, our PDA-based aptasensors have tremendous potential for on-site cancer diagnosis.

A state-of-the-art review of the recent advances in exosome isolation and detection methods in viral infection

Proteins, RNA, DNA, lipids, and carbohydrates are only some of the molecular components found in exosomes released by tumor cells. They play an essential role in healthy and diseased cells as messengers of short- and long-distance intercellular communication. However, since exosomes are released by every kind of cell and may be found in blood and other bodily fluids, they may one day serve as biomarkers for a wide range of disorders. In many pathological conditions, including cancer, inflammation, and infection, they play a role. It has been shown that the biogenesis of exosomes is analogous to that of viruses and that the exosomal cargo plays an essential role in the propagation, dissemination, and infection of several viruses. Bidirectional modulation of the immune response is achieved by the ability of exosomes associated with viruses to facilitate immunological escape and stimulate the body's antiviral immune response. Recently, exosomes have received a lot of interest due to their potential therapeutic use as biomarkers for viral infections such as human immunodeficiency virus (HIV), Hepatitis B virus (HBV), Hepatitis C virus (HCV), Epstein-Barr virus (EBV), and SARS-CoV-2. This article discusses the purification procedures and detection techniques for exosomes and examines the research on exosomes as a biomarker of viral infection.

Advances in colorimetric biosensors of exosomes: novel approaches based on natural enzymes and nanozymes

Exosomes are 30-150 nm vesicles derived from diverse cell types, serving as one of the most important biomarkers for early diagnosis and prognosis of diseases. However, the conventional detection method for exosomes faces significant challenges, such as unsatisfactory sensitivity, complicated operation, and the requirement of complicated devices. In recent years, colorimetric exosome biosensors with a visual readout underwent rapid development due to the advances in natural enzyme-based assays and the integration of various types of nanozymes. These synthetic nanomaterials show unique physiochemical properties and catalytic abilities, enabling the construction of exosome colorimetric biosensors with novel principles. This review will illustrate the reaction mechanisms and properties of natural enzymes and nanozymes, followed by a detailed introduction of the recent advances in both types of enzyme-based colorimetric biosensors. A comparison between natural enzymes and nanozymes is made to provide insights into the research that improves the sensitivity and convenience of assays. Finally, the advantages, challenges, and future directions of enzymes as well as exosome colorimetric biosensors are highlighted, aiming at improving the overall performance from different approaches.

Molybdenum Disulfide-Integrated Iron Organic Framework Hybrid Nanozyme-Based Aptasensor for Colorimetric Detection of Exosomes

Tumor-derived exosomes are considered as a potential marker in liquid biopsy for malignant tumor screening. The development of a sensitive, specific, rapid, and cost-effective detection strategy for tumor-derived exosomes is still a challenge. Herein, a visualized and easy detection method for exosomes was established based on a molybdenum disulfide nanoflower decorated iron organic framework (MoS2-MIL-101(Fe)) hybrid nanozyme-based CD63 aptamer sensor. The CD63 aptamer, which can specifically recognize and capture tumor-derived exosomes, enhanced the peroxidase activity of the hybrid nanozyme and helped to catalyze the 3,3',5,5'-tetramethylbenzidine (TMB)-H2O2 system to generate a stronger colorimetric signal, with its surface modification on the hybrid nanozyme. With the existence of exosomes, CD63 aptamer recognized and adsorbed them on the surface of the nanozyme, which rescued the enhanced peroxidase activity of the aptamer-modified nanozyme, resulting in a deep-to-moderate color change in the TMB-H2O2 system where the change is visible and can be monitored with ultraviolet-visible spectroscopy. In the context of optimal circumstances, the linear range of this exosome detection method is measured to be 1.6 × 104 to 1.6 × 106 particles/μL with a limit of detection as 3.37 × 103 particles/μL. Generally, a simple and accessible approach to exosome detection is constructed, and a nanozyme-based colorimetric aptamer sensor is proposed, which sheds light on novel oncological biomarker measurements in the field of biosensors.

Extracellular vesicles derived from bone marrow mesenchymal stem cells loaded on magnetic nanoparticles delay the progression of diabetic osteoporosis via delivery of miR-150-5p

Extracellular vesicles derived from bone marrow mesenchymal stem cells (BMSC-EVs) are emerged as carriers of therapeutic targets against bone disorders, yet its isolation and purification are limited with recent techniques. Magnetic nanoparticles (MNPs) can load EVs with a unique targeted drug delivery system. We constructed gold-coated magnetic nanoparticles (GMNPs) by decorating the surface of the Fe3O4@SiO2 core and a silica shell with poly(ethylene glycol) (PEG)-aldehyde (CHO) and examined the role of BMSC-EVs loaded on GMNPs in diabetic osteoporosis (DO). The osteoporosis-related differentially expressed miR-150-5p was singled out by microarray analysis. DO models were then established in Sprague-Dawley rats by streptozotocin injection, where poor expression of miR-150-5p was validated in the bone tissues. Next, GMNPE was prepared by combining GMNPs with anti-CD63, after which osteoblasts were co-cultured with the GMNPE-BMSC-EVs. The re-expression of miR-150-5p facilitated osteogenesis in osteoblasts. GMNPE could promote the enrichment of EVs in the bone tissues of DO rats. BMSC-EVs delivered miR-150-5p to osteoblasts, where miR-150-5p targeted MMP14 and consequently activated Wnt/β-catenin pathway. This effect contributed to the enhancement of osteoblast proliferation and maturation. Furthermore, GMNPE enhanced the EV-based delivery of miR-150-5p to regulate the MMP14/Wnt/β-catenin axis, resulting in promotion of osteogenesis. Overall, our findings suggest the potential of GMNP-BMSC-EVs to strengthen osteoblast proliferation and maturation in DO, showing promise as an appealing drug delivery strategy against DO. 1. GMNPs-BMSCs-EVs-miR-150-5p promotes the osteogenesis of DO rats. 2. miR-150-5p induces osteoblast proliferation and maturation by targeting MMP14. 3. Inhibition of MMP14 activates Wnt/β-catenin and increases osteogenesis. 4. miR-150-5p activates the Wnt/β-catenin pathway by downregulating MMP14.

Emerging nano-scale delivery systems for the treatment of osteoporosis

Osteoporosis is a pathological condition characterized by an accelerated bone resorption rate, resulting in decreased bone density and increased susceptibility to fractures, particularly among the elderly population. While conventional treatments for osteoporosis have shown efficacy, they are associated with certain limitations, including limited drug bioavailability, non-specific administration, and the occurrence of adverse effects. In recent years, nanoparticle-based drug delivery systems have emerged as a promising approach for managing osteoporosis. Nanoparticles possess unique physicochemical properties, such as a small size, large surface area-to-volume ratio, and tunable surface characteristics, which enable them to overcome the limitations of conventional therapies. These nanoparticles offer several advantages, including enhanced drug stability, controlled release kinetics, targeted bone tissue delivery, and improved drug bioavailability. This comprehensive review aims to provide insights into the recent advancements in nanoparticle-based therapy for osteoporosis. It elucidates the various types of nanoparticles employed in this context, including silica, polymeric, solid lipid, and metallic nanoparticles, along with their specific processing techniques and inherent properties that render them suitable as potential drug carriers for osteoporosis treatment. Furthermore, this review discusses the challenges and future suggestions associated with the development and translation of nanoparticle drug delivery systems for clinical use. These challenges encompass issues such as scalability, safety assessment, and regulatory considerations. However, despite these challenges, the utilization of nanoparticle-based drug delivery systems holds immense promise in revolutionizing the field of osteoporosis management by enabling more effective and targeted therapies, ultimately leading to improved patient outcomes.

Paper-based biosensors as point-of-care diagnostic devices for the detection of cancers: a review of innovative techniques and clinical applications

The development and rapid progression of cancer are major social problems. Medical diagnostic techniques and smooth clinical care of cancer are new necessities that must be supported by innovative diagnostic methods and technologies. Current molecular diagnostic tools based on the detection of blood protein markers are the most common tools for cancer diagnosis. Biosensors have already proven to be a cost-effective and accessible diagnostic tool that can be used where conventional laboratory methods are not readily available. Paper-based biosensors offer a new look at the world of analytical techniques by overcoming limitations through the creation of a simple device with significant advantages such as adaptability, biocompatibility, biodegradability, ease of use, large surface-to-volume ratio, and cost-effectiveness. In this review, we covered the characteristics of exosomes and their role in tumor growth and clinical diagnosis, followed by a discussion of various paper-based biosensors for exosome detection, such as dipsticks, lateral flow assays (LFA), and microfluidic paper-based devices (µPADs). We also discussed the various clinical studies on paper-based biosensors for exosome detection.

Single-Droplet Microsensor for Ultra-Short Circulating EFGR Mutation Detection in Lung Cancer Based on Multiplex EFIRM Liquid Biopsy

Liquid biopsy is a rapidly emerging field that involves the minimal/non-invasive assessment of signature somatic mutations through the analysis of circulating tumor DNA (ctDNA) shed by tumor cells in bodily fluids. Broadly speaking, the unmet need in liquid biopsy lung cancer detection is the lack of a multiplex platform that can detect a mutation panel of lung cancer genes using a minimum amount of sample, especially for ultra-short ctDNA (usctDNA). Here, we developed a non-PCR and non-NGS-based single-droplet-based multiplexing microsensor technology, "Electric-Field-Induced Released and Measurement (EFIRM) Liquid Biopsy" (m-eLB), for lung cancer-associated usctDNA. The m-eLB provides a multiplexable assessment of usctDNA within a single droplet of biofluid in only one well of micro-electrodes, as each electrode is coated with different probes for the ctDNA. This m-eLB prototype demonstrates accuracy for three tyrosine-kinase-inhibitor-related EGFR target sequences in synthetic nucleotides. The accuracy of the multiplexing assay has an area under the curve (AUC) of 0.98 for L858R, 0.94 for Ex19 deletion, and 0.93 for T790M. In combination, the 3 EGFR assay has an AUC of 0.97 for the multiplexing assay.

Extracellular Vesicles and Their Zeta Potential as Future Markers Associated with Nutrition and Molecular Biomarkers in Breast Cancer

A nutritional intervention promotes the loss of body and visceral fat while maintaining muscle mass in breast cancer patients. Extracellular vesicles (EVs) and their characteristics can be potential biomarkers of disease. Here, we explore the changes in the Zeta potential of EVs; the content of miRNA-30, miRNA-145, and miRNA-155; and their association with body composition and biomarkers of metabolic risk in breast cancer patients, before and 6 months after a nutritional intervention. Clinicopathological data (HER2neu, estrogen receptor, and Ki67), anthropometric and body composition data, and plasma samples were available from a previous study. Plasma EVs were isolated and characterized in 16 patients. The expression of miRNA-30, miRNA-145, and miRNA-155 was analyzed. The Zeta potential was associated with HER2neu (β = 2.1; p = 0.00), Ki67 (β = -1.39; p = 0.007), estrogen positive (β = 1.57; p = 0.01), weight (β = -0.09; p = 0.00), and visceral fat (β = 0.004; p = 0.00). miRNA-30 was associated with LDL (β = -0.012; p = 0.01) and HDL (β = -0.02; p = 0.05). miRNA-155 was associated with visceral fat (β = -0.0007; p = 0.05) and Ki67 (β = -0.47; p = 0.04). Our results reveal significant associations between the expression of miRNA-30 and miRNA-155 and the Zeta potential of the EVs with biomarkers of metabolic risk and disease prognosis in women with breast cancer; particularly, the Zeta potential of EVs can be a new biomarker sensitive to changes in the nutritional status and breast cancer progression.

Nanomaterials for Molecular Detection and Analysis of Extracellular Vesicles

Extracellular vesicles (EVs) have emerged as a novel resource of biomarkers for cancer and certain other diseases. Probing EVs in body fluids has become of major interest in the past decade in the development of a new-generation liquid biopsy for cancer diagnosis and monitoring. However, sensitive and specific molecular detection and analysis are challenging, due to the small size of EVs, low amount of antigens on individual EVs, and the complex biofluid matrix. Nanomaterials have been widely used in the technological development of protein and nucleic acid-based EV detection and analysis, owing to the unique structure and functional properties of materials at the nanometer scale. In this review, we summarize various nanomaterial-based analytical technologies for molecular EV detection and analysis. We discuss these technologies based on the major types of nanomaterials, including plasmonic, fluorescent, magnetic, organic, carbon-based, and certain other nanostructures. For each type of nanomaterial, functional properties are briefly described, followed by the applications of the nanomaterials for EV biomarker detection, profiling, and analysis in terms of detection mechanisms.

Evaluation of Exosomal Coding and Non-Coding RNA Signature in Obese Adolescents

Exosomes may contribute to the pathogenesis of obesity through their action as communication mediators. As we have previously demonstrated, in obese adolescents, some circulating miRNAs modified the C-type natriuretic peptide (CNP) expression and were associated with changes in metabolic functions. At present no data are available on miRNA transport by exosomes in this condition. To verify and compare the presence and the expression of CNP/NPR-B/NPR-C, and some miRNAs (miR-33a-3p/miR-223-5p/miR-142-5p/miRNA-4454/miRNA-181a-5p/miRNA-199-5p), in circulating exosomes obtained from the same cohort of obese (O, n = 22) and normal-weight adolescents (N, n = 22). For the first time, we observed that exosomes carried CNP and its specific receptors only randomly both in O and N, suggesting that exosomes are not important carriers for the CNP system. On the contrary, exosomal miRNAs resulted ubiquitously and differentially expressed in O and N. O showed a significant decrease (p < 0.01) in the expression of all miRNAs except for miR-4454 and miR-142-5p. We have found significant correlations among miRNAs themselves and with some inflammatory/metabolic factors of obesity. These relationships may help in finding new biomarkers, allowing us to recognize, at an early stage, obese children and adolescents at high risk to develop the disease complications in adult life.

A highly sensitive lateral flow immunoassay for the rapid and on-site detection of enrofloxacin in milk

Enrofloxacin (ENR) is a veterinary antibiotic used to treat bacterial infections in livestock. It chiefly persists in foods and dairy products, which in turn pose severe risks to human health. Hence it is very important to detect the ENR in foods and dairy products to safeguard human health. Herein, we attempted to develop a single-step detection lateral flow immunochromatographic assay (LFIA) using gold nanoparticles (AuNPs) for the rapid and on-site detection of ENR in milk samples. An anti-enrofloxacin monoclonal antibody (ENR-Ab) was conjugated with AuNPs for the specific detection of ENR in milk samples. For sensitivity improvement, many optimization steps were conducted on LFIA test strips. The visual limit of detection (vLOD) was found to be 20 ng/ml with a cut-off value of 50 ng/ml in the milk samples. The obtained LOD and cut-off value were within the safety limit guidelines of the Ministry of food and drug safety, South Korea. The test strip showed negligible cross-reactivity with ENR analogs, and other components of antibiotics, this indicates the high specificity of the LFIA test strip towards ENR. The designed test strip showed good reliability. The visual test results can be seen within 10 min without the need for special equipment. Therefore, the test strip can be employed as a potential detection strategy for the qualitative on-site detection of enrofloxacin in milk samples.

Unveiling the underpinnings of various non-conventional ELISA variants: a review article

INTRODUCTION

Enzyme-linked immunosorbent assay (ELISA) is a key bio-analytical technique used for the detection of a large array of antigenic substances of scientific, clinical, food safety, and environmental importance. The assay primarily involves capturing and detecting target analytes using specific antigen-antibody interactions. The wide usage of ELISA shoulders on its high specificity and reproducibility. Notwithstanding, the conventional microwell plate-based format of ELISA has some major drawbacks, such as long assay time (4 - 18 h), large sample volumes requirement (100 - 200 μL), lack of multiplicity, and burdensome procedures that limit its utility in rapid and affordable diagnostics.

AREAS COVERED

Here, we reviewed microfluidic-ELISA, paper-ELISA, aptamer-ELISA, and those based on novel incubation such as heat-ELISA, pressure-ELISA, microwave-ELISA, and sound-ELISA. Further, the current trends and future prospects of these ELISA protocols in clinical diagnostics are discussed.

EXPERT OPINION

The reviewed non-conventional ELISA formats are relatively rapid, require low reagent volumes, are multiplexable, and could be performed in a low-cost setup. In our opinion, these non-conventional variants of ELISA are on a par with the conventional format for clinical diagnostics and fundamental biological research and hold added clinical translational potential for quick, inexpensive, and convenient measurements.

Feasibility of novel approaches to detect viable Mycobacterium tuberculosis within the spectrum of the tuberculosis disease

Tuberculosis (TB) is a global disease caused by Mycobacterium tuberculosis (Mtb) and is manifested as a continuum spectrum of infectious states. Both, the most common and clinically asymptomatic latent tuberculosis infection (LTBI), and the symptomatic disease, active tuberculosis (TB), are at opposite ends of the spectrum. Such binary classification is insufficient to describe the existing clinical heterogeneity, which includes incipient and subclinical TB. The absence of clinically TB-related symptoms and the extremely low bacterial burden are features shared by LTBI, incipient and subclinical TB states. In addition, diagnosis relies on cytokine release after antigenic T cell stimulation, yet several studies have shown that a high proportion of individuals with immunoreactivity never developed disease, suggesting that they were no longer infected. LTBI is estimated to affect to approximately one fourth of the human population and, according to WHO data, reactivation of LTBI is the main responsible of TB cases in developed countries. Assuming the drawbacks associated to the current diagnostic tests at this part of the disease spectrum, properly assessing individuals at real risk of developing TB is a major need. Further, it would help to efficiently design preventive treatment. This quest would be achievable if information about bacterial viability during human silent Mtb infection could be determined. Here, we have evaluated the feasibility of new approaches to detect viable bacilli across the full spectrum of TB disease. We focused on methods that specifically can measure host-independent parameters relying on the viability of Mtb either by its direct or indirect detection.

Quantification of a COVID-19 Antibody Assay Using a Lateral Flow Test and a Cell Phone

Although several biomedical assays have been developed to screen for antibodies against SARS-CoV-2, very few can be completed without drawing blood. We developed a rapid lateral flow screening tool that used saliva samples and yielded rapid results that could be quantified using a cell phone. This assay provided the sensitive detection of IgG antibodies against SARS-CoV-2 within 10 min. We started by synthesising, modifying, and characterising gold nanoparticles. Using these particles as a coloured label, we developed a lateral flow strip made of nitrocellulose, glass fibre, and cellulose material. We quantified our visual results using pictures acquired with a cell phone and calculated a limit of detection of 4 ng/mL of antibodies against the SARS-CoV-2 spike protein.

Microfluidics-Based Point-of-Care Testing (POCT) Devices in Dealing with Waves of COVID-19 Pandemic: The Emerging Solution

Recent advances in microfluidics-based point-of-care testing (POCT) technology such as paper, array, and beads have shown promising results for diagnosing various infectious diseases. The fast and timely detection of viral infection has proven to be a critical step for deciding the therapeutic outcome in the current COVID-19 pandemic, which in turn not only enhances the patient survival rate but also reduces the disease-associated comorbidities. In the present scenario, rapid, noninvasive detection of the virus using low cost and high throughput microfluidics-based POCT devices embraces the advantages over existing diagnostic technologies, for which a centralized lab facility, expensive instruments, sample pretreatment, and skilled personnel are required. Microfluidic-based multiplexed POCT devices can be a boon for clinical diagnosis in developing countries that lacks a centralized health care system and resources. The microfluidic devices can be used for disease diagnosis and exploited for the development and testing of drug efficacy for disease treatment in model systems. The havoc created by the second wave of COVID-19 led several countries' governments to the back front. The lack of diagnostic kits, medical devices, and human resources created a huge demand for a technology that can be remotely operated with single touch and data that can be analyzed on a phone. Recent advancements in information technology and the use of smartphones led to a paradigm shift in the development of diagnostic devices, which can be explored to deal with the current pandemic situation. This review sheds light on various approaches for the development of cost-effective microfluidics POCT devices. The successfully used microfluidic devices for COVID-19 detection under clinical settings along with their pros and cons have been discussed here. Further, the integration of microfluidic devices with smartphones and wireless network systems using the Internet-of-things will enable readers for manufacturing advanced POCT devices for remote disease management in low resource settings.

Highly Sensitive Nanomagnetic Quantification of Extracellular Vesicles by Immunochromatographic Strips: A Tool for Liquid Biopsy

Extracellular vesicles (EVs) are promising agents for liquid biopsy—a non-invasive approach for the diagnosis of cancer and evaluation of therapy response. However, EV potential is limited by the lack of sufficiently sensitive, time-, and cost-efficient methods for their registration. This research aimed at developing a highly sensitive and easy-to-use immunochromatographic tool based on magnetic nanoparticles for EV quantification. The tool is demonstrated by detection of EVs isolated from cell culture supernatants and various body fluids using characteristic biomarkers, CD9 and CD81, and a tumor-associated marker—epithelial cell adhesion molecules. The detection limit of 3.7 × 10⁵ EV/µL is one to two orders better than the most sensitive traditional lateral flow system and commercial ELISA kits. The detection specificity is ensured by an isotype control line on the test strip. The tool’s advantages are due to the spatial quantification of EV-bound magnetic nanolabels within the strip volume by an original electronic technique. The inexpensive tool, promising for liquid biopsy in daily clinical routines, can be extended to other relevant biomarkers.

Harnessing the Therapeutic Potential of Extracellular Vesicles for Biomedical Applications Using Multifunctional Magnetic Nanomaterials

Extracellular vesicles (e.g., exosomes) carrying various biomolecules (e.g., proteins, lipids, and nucleic acids) have rapidly emerged as promising platforms for many biomedical applications. Despite their enormous potential, their heterogeneity in surfaces and sizes, the high complexity of cargo biomolecules, and the inefficient uptake by recipient cells remain critical barriers for their theranostic applications. To address these critical issues, multifunctional nanomaterials, such as magnetic nanomaterials, with their tunable physical, chemical, and biological properties, may play crucial roles in next-generation extracellular vesicles (EV)-based disease diagnosis, drug delivery, tissue engineering, and regenerative medicine. As such, one aims to provide cutting-edge knowledge pertaining to magnetic nanomaterials-facilitated isolation, detection, and delivery of extracellular vesicles and their associated biomolecules. By engaging the fields of extracellular vesicles and magnetic nanomaterials, it is envisioned that their properties can be effectively combined for optimal outcomes in biomedical applications.

Malnutrition and Biomarkers: A Journey through Extracellular Vesicles

Extracellular vesicles (EVs) have been identified as active components in cellular communication, which are easily altered both morphologically and chemically by the cellular environment and metabolic state of the body. Due to this sensitivity to the conditions of the cellular microenvironment, EVs have been found to be associated with disease conditions, including those associated with obesity and undernutrition. The sensitivity that EVs show to changes in the cellular microenvironment could be a reflection of early cellular alterations related to conditions of malnutrition, which could eventually be used in the routine monitoring and control of diseases or complications associated with it. However, little is known about the influence of malnutrition alone; that is, without the influence of additional diseases on the heterogeneity and specific content of EVs. To date, studies in “apparently healthy” obese patients show that there are changes in the size, quantity, and content of EVs, as well as correlations with some metabolic parameters (glucose, insulin, and serum lipids) in comparison with non-obese individuals. In light of these changes, a direct participation of EVs in the development of metabolic and cardiovascular complications in obese subjects is thought to exist. However, the mechanisms through which this process might occur are not yet fully understood. The evidence on EVs in conditions of undernutrition is limited, but it suggests that EVs play a role in the maintenance of homeostasis and muscle repair. A better understanding of how EVs participate in or promote cellular signaling in malnutrition conditions could help in the development of new strategies to treat them and their comorbidities.

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

The biomolecular contents of extracellular vesicles, such as exosomes, have been shown to be crucial in intercellular communication and disease propagation. As a result, there has been a recent surge in the exploration of novel biosensing platforms that can sensitively and specifically detect exosomal content such as proteins and nucleic acids, with a view toward application in diagnostic assays. Here, we demonstrate dual-mode and label-free detection of plasma exosomes using an electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D). The platform adopts a direct immunosensing approach to effectively capture exosomes via their surface protein expression of CD63. By combining QCM-D with a tandem in situ electrochemical impedance spectroscopy measurement, we are able to demonstrate relationships between mass, viscoelasticity and impedance inducing properties of each functional layer and analyte. In addition to lowering the limit of detection (by a factor of 2-4) to 6.71 × 10⁷ exosome-sized particles (ESP) per mL in 25% v/v serum, the synergy between dissipation and impedance response introduces improved sensing specificity by offering further distinction between soft and rigid analytes, thereby promoting EQCM-D as an important technique for exosome analysis.

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

The biomolecular contents of extracellular vesicles, such as exosomes, have been shown to be crucial in intercellular communication and disease propagation. As a result, there has been a recent surge in the exploration of novel biosensing platforms that can sensitively and specifically detect exosomal content such as proteins and nucleic acids, with a view toward application in diagnostic assays. Here, we demonstrate dual-mode and label-free detection of plasma exosomes using an electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D). The platform adopts a direct immunosensing approach to effectively capture exosomes via their surface protein expression of CD63. By combining QCM-D with a tandem in situ electrochemical impedance spectroscopy measurement, we are able to demonstrate relationships between mass, viscoelasticity and impedance inducing properties of each functional layer and analyte. In addition to lowering the limit of detection (by a factor of 2–4) to 6.71 × 10⁷ exosome-sized particles (ESP) per mL in 25% v/v serum, the synergy between dissipation and impedance response introduces improved sensing specificity by offering further distinction between soft and rigid analytes, thereby promoting EQCM-D as an important technique for exosome analysis.

Multiplexed Profiling of Extracellular Vesicles for Biomarker Development

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

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

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

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.

Small extracellular vesicles in cancer

Extracellular vesicles (EV) are lipid-bilayer enclosed vesicles in submicron size that are released from cells. A variety of molecules, including proteins, DNA fragments, RNAs, lipids, and metabolites can be selectively encapsulated into EVs and delivered to nearby and distant recipient cells. In tumors, through such intercellular communication, EVs can regulate initiation, growth, metastasis and invasion of tumors. Recent studies have found that EVs exhibit specific expression patterns which mimic the parental cell, providing a fingerprint for early cancer diagnosis and prognosis as well as monitoring responses to treatment. Accordingly, various EV isolation and detection technologies have been developed for research and diagnostic purposes. Moreover, natural and engineered EVs have also been used as drug delivery nanocarriers, cancer vaccines, cell surface modulators, therapeutic agents and therapeutic targets. Overall, EVs are under intense investigation as they hold promise for pathophysiological and translational discoveries. This comprehensive review examines the latest EV research trends over the last five years, encompassing their roles in cancer pathophysiology, diagnostics and therapeutics. This review aims to examine the full spectrum of tumor-EV studies and provide a comprehensive foundation to enhance the field. The topics which are discussed and scrutinized in this review encompass isolation techniques and how these issues need to be overcome for EV-based diagnostics, EVs and their roles in cancer biology, biomarkers for diagnosis and monitoring, EVs as vaccines, therapeutic targets, and EVs as drug delivery systems. We will also examine the challenges involved in EV research and promote a framework for catalyzing scientific discovery and innovation for tumor-EV-focused research.

Nanoplasmonic Sensor Approaches for Sensitive Detection of Disease-Associated Exosomes

Exosomes are abundantly secreted by most cells that carry membrane and cytosolic factors that can reflect the physiologic state of their source cells and thus have strong potential to serve as biomarkers for early diagnosis, disease staging, and treatment monitoring. However, traditional diagnostic or prognostic applications that might use exosomes are hindered by the lack of rapid and sensitive assays that can exploit their biological information. An array of assay approaches have been developed to address this deficit, including those that integrate immunoassays with nanoplasmonic sensors to measure changes in optical refractive indexes in response to the binding of low concentrations of their targeted molecules. These sensors take advantage of enhanced and tunable interactions between the electron clouds of nanoplasmonic particles and structures and incident electromagnetic radiation to enable isolation-free and ultrasensitive quantification of disease-associated exosome biomarkers present in complex biological samples. These unique advantages make nanoplasmonic sensing one of the most competitive approaches available for clinical applications and point-of-care tests that evaluate exosome-based biomarkers. This review will briefly summarize the origin and clinical utility of exosomes and the limitations of current isolation and analysis approaches before reviewing the specific advantages and limitations of nanoplasmonic sensing devices and indicating what additional developments are necessary to allow the translation of these approaches into clinical applications.

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.

Magnetic Lateral Flow Immunoassay for Small Extracellular Vesicles Quantification: Application to Colorectal Cancer Biomarker Detection

Colorectal cancer (CRC) is the third leading cause of cancer death and the fourth most common cancer in the world. Colonoscopy is the most sensitive test used for detection of CRC; however, their procedure is invasive and expensive for population mass screening. Currently, the fecal occult blood test has been widely used as a screening tool for CRC but displays low specificity. The lack of rapid and simple methods for mass screening makes the early diagnosis and therapy monitoring difficult. Extracellular vesicles (EVs) have emerged as a novel source of biomarkers due to their contents in proteins and miRNAs. Their detection would not require invasive techniques and could be considered as a liquid biopsy. Specifically, it has been demonstrated that the amount of CD147 expressed in circulating EVs is significant higher for CRC cell lines than for normal colon fibroblast cell lines. Moreover, CD147-containing EVs have been used as a biomarker to monitor response to therapy in patients with CRC. Therefore, this antigen could be used as a non-invasive biomarker for the detection and monitoring of CRC in combination with a Point-of-Care platform as, for example, Lateral Flow Immunoassays (LFIAs). Here, we propose the development of a quantitative lateral flow immunoassay test based on the use of magnetic nanoparticles as labels coupled to inductive sensor for the non-invasive detection of CRC by CD147-positive EVs. The results obtained for quantification of CD147 antigen embedded in EVs isolated from plasma sample have demonstrated that this device could be used as a Point-of-Care tool for CRC screening or therapy monitoring thanks to its rapid response and easy operation.

Comparative Study of Gold and Carbon Nanoparticles in Nucleic Acid Lateral Flow Assay

A lateral flow assay (LFA) is a paper-based, point-of-need test designed to detect a specific analyte in complex samples in low-resource settings. Although LFA has been successfully used in different applications, its use is still limited when high sensitivity is required, especially in the diagnosis of an early-stage condition. The limit of detection (LOD) is clearly related to the signal-generating system used to achieve the visual readout, in many cases involving nanoparticles coupled to a biomolecule, which, when combined, provides sensitivity and specificity, respectively. While colloidal gold is currently the most-used label, other detection systems are being developed. Carbon nanoparticles (CNPs) demonstrate outstanding features to improve the sensitivity of this technology by producing an increased contrast in the paper background. Based on the necessity of sensitivity improvement, the aim of this work is a comparative study, in terms of analytical performance, between commercial streptavidin gold nanoparticles (streptAv-AuNPs) and avidin carbon nanoparticles (Av-CNPs) in a nucleic acid lateral flow assay. The visual LOD of the method was calculated by serial dilution of the DNA template, ranging from 0.0 to 7 pg μL-1/1.5 × 104 CFU mL-1). The LFA achieved visual detection of as low as 2.2 × 10-2 pg μL-1 using Av-CNPs and 8.4 × 10-2 pg μL-1 using streptAv-AuNPs. These LODs could be obtained without the assistance of any instrumentation. The results demonstrate that CNPs showed an increased sensitivity, achieving the nanomolar range even by visual inspection. Furthermore, CNPs are the cheapest labels, and the suspensions are very stable and easy to modify.

Recent advances in sensitivity enhancement for lateral flow assay

Conventional lateral flow assay (LFA) is typically performed by observing the color changes in the test lines by naked eyes, which achieves considerable commercial success and has a significant impact on the fields of food safety, environment monitoring, disease diagnosis, and other applications. However, this qualitative detection method is not very suitable for low levels of disease biomarkers' detection. Although many nanomaterials are used as new labels for LFA, additional readers limit their application to some extent. Fortunately, a lot of work has been done for improving the sensitivity of LFA. In this review, currently reported LFA sensitivity enhancement methods with an objective evaluation are summarized, such as sample pretreatment, the change of flow rate, and label evolution, and future development direction and challenges of LFAs are discussed.

Recent advances in nanomaterial-based biosensors for the detection of exosomes

Exosomes are a type of extracellular vesicle actively secreted by almost all eukaryotic cells. They are ideal candidates for reliable next-generation biomarkers in the early diagnosis and therapeutic response evaluation of cancer. Thus, the quantification of exosomes is crucial in facilitating clinical research and application. Compared with traditional materials, nanomaterials have better optical, magnetic, electrical, and catalytic properties due to their small size, high specific surface area, and variable structure. The incorporation of nanomaterials into sensing systems is an attractive approach towards improving sensitivity and can provide improved sensor selectivity and stability. In this paper, we summarize the progress in nanomaterial-based exosome detection methods, including electrochemical biosensors, photoelectrochemical biosensors, colorimetric biosensors, fluorescence biosensors, chemiluminescence biosensors, electrochemiluminescence biosensors, surface plasmon resonance biosensors, and surface-enhanced Raman spectroscopy biosensors. Moreover, future research directions and challenges in exosome detection methods are discussed. We hope that this article will offer an overview of nanomaterial-based exosome detection techniques and open new avenues in disease research.Graphical abstract.

Tutorial: design and fabrication of nanoparticle-based lateral-flow immunoassays

Lateral-flow assays (LFAs) are quick, simple and cheap assays to analyze various samples at the point of care or in the field, making them one of the most widespread biosensors currently available. They have been successfully employed for the detection of a myriad of different targets (ranging from atoms up to whole cells) in all type of samples (including water, blood, foodstuff and environmental samples). Their operation relies on the capillary flow of the sample throughout a series of sequential pads, each with different functionalities aiming to generate a signal to indicate the absence/presence (and, in some cases, the concentration) of the analyte of interest. To have a user-friendly operation, their development requires the optimization of multiple, interconnected parameters that may overwhelm new developers. In this tutorial, we provide the readers with: (i) the basic knowledge to understand the principles governing an LFA and to take informed decisions during lateral flow strip design and fabrication, (ii) a roadmap for optimal LFA development independent of the specific application, (iii) a step-by-step example procedure for the assembly and operation of an LF strip for the detection of human IgG and (iv) an extensive troubleshooting section addressing the most frequent issues in designing, assembling and using LFAs. By changing only the receptors, the provided example procedure can easily be adapted for cost-efficient detection of a broad variety of targets.

Facile fluorescent aptasensor using aggregation-induced emission luminogens for exosomal proteins profiling towards liquid biopsy

Surface protein patterns of tumor-derived exosomes could be promising noninvasive diagnostic biomarkers for liquid biopsy. However, a convenient and cost-effective platform for exosomal protein profiling is still lacking. Herein, a facile fluorescent aptasensor is developed to assess exosomal tumor-associated proteins, combining aptamers, aggregation-induced emission luminogens (AIEgens), and graphene oxide (GO) as recognition elements, fluorescent dye, and the quencher, respectively. Specifically, numberous TPE-TAs could bind one aptamer and form aggregates rapidly, resulting in an amplified fluorescence signal. In the absence of tumor-derived exosomes, GO absorbs the TPE-TAs/aptamer complex, allowing fluorescence quenching. When the target exosomes are introduced, the aptamer preferentially binds with its target. Thus the TPE-TAs/aptamer complexes detach from GO surface, followed by the appearance of a "turn-on" fluorescent signal. Under the optimized conditions, the linear range of target exosomes is estimated to be 4.07 × 10⁵ to 1.83 × 10⁷ particles/μL (0.68-30.4 pM) with a detection limit of 3.43 × 10⁵ particles/μL (0.57 pM). This strategy demonstrated great performance in differentiating prostate cancer from healthy individuals (AUC: 0.9790). Furthermore, by profiling three tumor-associated protein markers including epidermal growth factor receptor (EGFR), epithelial cell adhesion molecule (EpCAM), and human epidermal growth factor receptor 2 (HER2) on exosomes in a breast tumor cohort, this sensing platform diagnoses breast tumors with high efficiency (AUC: 0.9845) and exhibits a high sensitivity of 97.37% for distinguishing malignant breast cancers, where the stage I cases were detected with 92.31% sensitivity. Therefore, this aptasensor provides a promising strategy to profile tumor-derived exosomal proteins for early diagnosis in liquid biopsy.

Homogenous Magneto-Fluorescent Nanosensor for Tumor-Derived Exosome Isolation and Analysis

Tumor-derived exosomes carrying unique surface proteins have shown great promise as novel biomarkers for liquid biopsies. However, point-of-care analysis for tumor-derived exosomes in the blood with low-cost and easy processing is still challenging. Herein, we develop an integrated approach, homogenous magneto-fluorescent exosome (hMFEX) nanosensor, for rapid and on-site tumor-derived exosomes analysis. Tumor-derived exosomes are captured immunomagnetically, which further initiates the aptamer-triggered assembly of DNA three-way junctions in homogenous solution containing aggregation-induced emission luminogens and graphene oxide, resulting in an amplified fluorescence signal. By integrating magnetic isolation and enhanced fluorescence measurement, the hMFEX nanosensor detects tumor-derived exosomes in the dynamic range spanning 5 orders of magnitude with high specificity, and the limit of detection is 6.56 × 10⁴ particles/μL. Analyzing tumor-derived exosomes in limited volume plasma from breast cancer patients demonstrates the excellent clinical diagnostic efficacy of the hMFEX nanosensor. This study provides new insights into the point-of-care testing of tumor-derived exosomes for cancer diagnostics.

Carbon-Coated Superparamagnetic Nanoflowers for Biosensors Based on Lateral Flow Immunoassays

Superparamagnetic iron oxide nanoflowers coated by a black carbon layer (Fe3O4@C) were studied as labels in lateral flow immunoassays. They were synthesized by a one-pot solvothermal route, and they were characterized (size, morphology, chemical composition, and magnetic properties). They consist of several superparamagnetic cores embedded in a carbon coating holding carboxylic groups adequate for bioconjugation. Their multi-core structure is especially efficient for magnetic separation while keeping suitable magnetic properties and appropriate size for immunoassay reporters. Their functionality was tested with a model system based on the biotin-neutravidin interaction. For this, the nanoparticles were conjugated to neutravidin using the carbodiimide chemistry, and the lateral flow immunoassay was carried out with a biotin test line. Quantification was achieved with both an inductive magnetic sensor and a reflectance reader. In order to further investigate the quantifying capacity of the Fe3O4@C nanoflowers, the magnetic lateral flow immunoassay was tested as a detection system for extracellular vesicles (EVs), a novel source of biomarkers with interest for liquid biopsy. A clear correlation between the extracellular vesicle concentration and the signal proved the potential of the nanoflowers as quantifying labels. The limit of detection in a rapid test for EVs was lower than the values reported before for other magnetic nanoparticle labels in the working range 0-3 × 107 EVs/μL. The method showed a reproducibility (RSD) of 3% (n = 3). The lateral flow immunoassay (LFIA) rapid test developed in this work yielded to satisfactory results for EVs quantification by using a precipitation kit and also directly in plasma samples. Besides, these Fe3O4@C nanoparticles are easy to concentrate by means of a magnet, and this feature makes them promising candidates to further reduce the limit of detection.

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.

Magnetic Lateral Flow Immunoassays

A new generation of magnetic lateral flow immunoassays is emerging as powerful tool for diagnostics. They rely on the use of magnetic nanoparticles (MNP) as detecting label, replacing conventional gold or latex beads. MNPs can be sensed and quantified by means of external devices, allowing the development of immunochromatographic tests with a quantitative capability. Moreover, they have an added advantage because they can be used for immunomagnetic separation (IMS), with improvements in selectivity and sensitivity. In this paper, we have reviewed the current knowledge on magnetic-lateral flow immunoassay (LFIA), coupled with both research and commercially available instruments. The work in the literature has been classified in two categories: optical and magnetic sensing. We have analysed the type of magnetic nanoparticles used in each case, their size, coating, crystal structure and the functional groups for their conjugation with biomolecules. We have also taken into account the analytical characteristics and the type of transduction. Magnetic LFIA have been used for the determination of biomarkers, pathogens, toxins, allergens and drugs. Nanocomposites have been developed as alternative to MNP with the purpose of sensitivity enhancement. Moreover, IMS in combination with other detection principles could also improve sensitivity and limit of detection. The critical analysis in this review could have an impact for the future development of magnetic LFIA in fields requiring both rapid separation and quantification.

Optical, electrochemical and electrical (nano)biosensors for detection of exosomes: A comprehensive overview

Exosomes are small extracellular vesicles involved in many physiological activities of cells in the human body. Exosomes from cancer cells have great potential to be applied in clinical diagnosis, early cancer detection and target identification for molecular therapy. While this field is gaining increasing interests from both academia and industry, barriers such as supersensitive detection techniques and highly-efficient isolation methods remain. In the clinical settings, there is an urgent need for rapid analysis, reliable detection and point-of-care testing (POCT). With these challenges to be addressed, this article aims to review recent developments and technical breakthroughs including optical, electrochemical and electrical biosensors for exosomes detection in the field of cancer and other diseases and demonstrate how nanobiosensors could enhance the performance of conventional sensors. Working strategies, limit of detections, advantages and shortcomings of the studies are summarized. New trends, challenges and future perspectives of exosome-driven POCT in liquid biopsy have been discussed.

Recent advances in high-sensitivity detection methods for paper-based lateral-flow assay

Paper-based lateral-flow assays (LFAs) have achieved considerable commercial success and continue to have a significant impact on medical diagnostics and environmental monitoring. Conventional LFAs are typically performed by examining the color changes in the test bands by naked eye. However, for critical biochemical markers that are present in extremely small amounts in the clinical specimens, this readout method is not quantitative, and does not provide sufficient sensitivity or suitable detection limit for a reliable assay. Diverse technologies for high-sensitivity LFA detection have been developed and commercialization efforts are underway. In this review, we aim to provide a critical and objective overview of the recent progress in high-sensitivity LFA detection technologies, which involve the exploitation of the physical and chemical responses of transducing particles. The features and biomedical applications of the technologies, along with future prospects and challenges, are also discussed.

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.