Detection of breast cancer-derived exosomes using the horseradish peroxidase-mimicking DNAzyme as an aptasensor

Role of aptamer technology in extracellular vesicle biology and therapeutic applications

Extracellular vesicles (EVs) are cell-derived nanosized membrane-bound vesicles that are important intercellular signalling regulators in local cell-to-cell and distant cell-to-tissue communication. Their inherent capacity to transverse cell membranes and transfer complex bioactive cargo reflective of their cell source, as well as their ability to be modified through various engineering and modification strategies, have attracted significant therapeutic interest. Molecular bioengineering strategies are providing a new frontier for EV-based therapy, including novel mRNA vaccines, antigen cross-presentation and immunotherapy, organ delivery and repair, and cancer immune surveillance and targeted therapeutics. The revolution of EVs, their diversity as biocarriers and their potential to contribute to intercellular communication, is well understood and appreciated but is ultimately dependent on the development of methods and techniques for their isolation, characterization and enhanced targeting. As single-stranded oligonucleotides, aptamers, also known as chemical antibodies, offer significant biological, chemical, economic, and therapeutic advantages in terms of their size, selectivity, versatility, and multifunctional programming. Their integration into the field of EVs has been contributing to the development of isolation, detection, and analysis pipelines associated with bioengineering strategies for nano-meets-molecular biology, thus translating their use for therapeutic and diagnostic utility.

Quercetin conjugated PSC-derived exosomes to inhibit intimal hyperplasia via modulating the ERK, Akt, and NF-κB signaling pathways in the rat carotid artery post balloon injury

The primary challenge in percutaneous coronary interventions for vascular restenosis is the occurrence of restenosis, which is defined by the excessive proliferation of neointimal tissue. Herein, our research team suggests that exosomes obtained from PSC, when paired with quercetin (Q@PSC-E), successfully reduce neointimal hyperplasia in a Sprague-Dawley rat model. Furthermore, the physical properties of the synthesized Q@PSC-E were examined using UV-vis, DLS, and FT-IR characterization techniques. The rats were subjected to balloon injury (BI) utilizing a 2-Fr Fogarty arterial embolectomy balloon catheter. Intimal hyperplasia and the degree of VSMC proliferation were evaluated using histological analysis in the rat groups that received a dosage of Q@PSC-E at 30 mg/kg/d. Significantly, Q@PSC-E inhibited cell proliferation through a pathway that does not include lipoxygenase, as demonstrated by [3H] thymidine incorporation, MTT, and flow cytometry studies. Additionally, the data indicate that Q@PSC-E hinders cell proliferation by targeting particular events that promote cell growth, including the activation of Akt and NF-κB, disruption of cell-cycle progression and also obstructs the ERK signaling pathway.

Nanoarchitectonics-based electrochemical aptasensors for highly efficient exosome detection

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

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.

Aptasensors Based on Non-Enzymatic Peroxidase Mimics: Current Progress and Challenges

Immunoassays based on antibodies as recognizing elements and enzymes as signal-generating modules are extensively used now in clinical lab diagnostics, food, and environmental analyses. However, the application of natural enzymes and antibodies has some drawbacks, such as relatively high manufacturing costs, thermal instability, and lot-to-lot variations that lower the reproducibility of results. Oligonucleotide aptamers are able to specifically bind their targets with high affinity and selectivity, so they represent a prospective alternative to protein antibodies for analyte recognition. Their main advantages include thermal stability and long shelf life, cost-efficient chemical synthesis, and negligible batch-to-batch variations. At the same time, a wide variety of non-protein peroxidase mimics are now available that show strong potential to replace protein enzymes. Here, we review and analyze non-protein biosensors that represent a nexus of these two concepts: aptamer-based sensors (aptasensors) with optical detection (colorimetric, luminescent, or fluorescent) based on different peroxidase mimics, such as DNAzymes, nanoparticles, or metal-organic frameworks.

Circulating tumor biomarkers in early-stage breast cancer: characteristics, detection, and clinical developments

Breast cancer is the most common form of cancer in women, contributing to high rates of morbidity and mortality owing to the ability of these tumors to metastasize via the vascular system even in the early stages of progression. While ultrasonography and mammography have enabled the more reliable detection of early-stage breast cancer, these approaches entail high rates of false positive and false negative results Mammograms also expose patients to radiation, raising clinical concerns. As such, there is substantial interest in the development of more accurate and efficacious approaches to diagnosing breast cancer in its early stages when patients are more likely to benefit from curative treatment efforts. Blood-based biomarkers derived from the tumor microenvironment (TME) have frequently been studied as candidate targets that can enable tumor detection when used for patient screening. Through these efforts, many promising biomarkers including tumor antigens, circulating tumor cell clusters, microRNAs, extracellular vesicles, circulating tumor DNA, metabolites, and lipids have emerged as targets that may enable the detection of breast tumors at various stages of progression. This review provides a systematic overview of the TME characteristics of early breast cancer, together with details on current approaches to detecting blood-based biomarkers in affected patients. The limitations, challenges, and prospects associated with different experimental and clinical platforms employed in this context are also discussed at length.

Recent developments in biosensing methods for extracellular vesicle protein characterization

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

Recent Advances in Detection for Breast-Cancer-Derived Exosomes

Breast cancer is the most common malignant tumor in women, its incidence is secret, and more than half of the patients are diagnosed in the middle and advanced stages, so it is necessary to develop simple and efficient detection methods for breast cancer diagnosis to improve the survival rate and quality of life of breast cancer patients. Exosomes are extracellular vesicles secreted by all kinds of living cells, and play an important role in the occurrence and development of breast cancer and the formation of the tumor microenvironment. Exosomes, as biomarkers, are an important part of breast cancer fluid biopsy and have become ideal targets for the early diagnosis, curative effect evaluation, and clinical treatment of breast cancer. In this paper, several traditional exosome detection methods, including differential centrifugation and immunoaffinity capture, were summarized, focusing on the latest research progress in breast cancer exosome detection. It was summarized from the aspects of optics, electrochemistry, electrochemiluminescence and other aspects. This review is expected to provide valuable guidance for exosome detection of clinical breast cancer and the establishment of more reliable, efficient, simple and innovative methods for exosome detection of breast cancer in the future.

Rapid immunomagnetic co-capture assay for quantification of lung Cancer associated exosomes

Exosomes derived from biological fluids have the potential to serve as a biomarker for the early detection of various cancers. However, the lack of reliable enrichment and detection methods posed a challenge for its clinical utility. In this work, we designed a rapid co-capture-based approach for targeted enrichment and detection of lung cancer-derived exosomes from human plasma. This method relies on the formation of a sandwich complex around the exosomes that involves magnetic nanoparticles coupled to CD151 to assist in the immunomagnetic selection of lung-derived exosomes and a secondary detection antibody (CD81) coupled to horseradish peroxidase for signal amplification. The performance of the co-capture method to detect exosomes has been optimized with known exosome concentrations in human plasma and exhibited good linearity (10⁸-10⁵ exosomes mL^-1) with a detection limit of 60.4 exosomes μL^-1. This study further investigated the potential of the developed assay to differentiate healthy and lung cancer patients using 18 clinical samples by quantifying the CD151+/ CD81+ lung-derived exosomes. In conclusion, this study demonstrated a rapid co-capture-based approach that offers simultaneous isolation and detection of exosomes compatible with low sample volume for detecting lung cancer patients.

Aptamer-Based Biosensors for the Colorimetric Detection of Blood Biomarkers: Paving the Way to Clinical Laboratory Testing

Clinical diagnostics for human diseases rely largely on enzyme immunoassays for the detection of blood biomarkers. Nevertheless, antibody-based test systems have a number of shortcomings that have stimulated a search for alternative diagnostic assays. Oligonucleotide aptamers are now considered as promising molecular recognizing elements for biosensors (aptasensors) due to their high affinity and specificity of target binding. At the moment, a huge variety of aptasensors have been engineered for the detection of various analytes, especially disease biomarkers. However, despite their great potential and excellent characteristics in model systems, only a few of these aptamer-based assays have been translated into practice as diagnostic kits. Here, we will review the current progress in the engineering of aptamer-based colorimetric assays as the most suitable format for clinical lab diagnostics. In particular, we will focus on aptasensors for the detection of blood biomarkers of cardiovascular, malignant, and neurodegenerative diseases along with common inflammation biomarkers. We will also analyze the main obstacles that have to be overcome before aptamer test systems can become tantamount to ELISA for clinical diagnosis purposes.

Colorimetric Aptasensor Based on Fe₃O₄-Cu2+ Nanozyme with Intrinsic Peroxidase-Like Activity in the Detection of Breast Cancer Exosomes

Because breast cancer cells such as MCF-7, exhibit vital and developmental signs by exosome secretion, diagnosing them in the blood can provide a good index of the presence of breast cancer. However, accurate and inexpensive detection of exosomes in clinical practice faces challenges. Therefore, in the presents study, an aptasensor based on CD63 aptameriron oxide-copper ion nanozymes (Fe₃O₄-Cu²⁺-NZs) was designed with the ability of the CD63 aptamer to interact with the exosome and the release of the Fe₃O₄-Cu²⁺-NZs for peroxidase-like activity on the tetramethylbenzidine (TMB). After fabrication of CD63 aptamer-Fe₃O₄-Cu²⁺-NZs based on hydrothermal method, their physicochemical properties were investigated with the SEM, TEM, DLS, Zeta, XRD and magnetization. To investigate the interaction of CD63 aptamer-Fe₃O₄-Cu²⁺-NZs with exosomes, the required exosomes were extracted from cultured MCF-7 cells. The performance of CD63 aptamer-Fe₃O₄-Cu²⁺-NZs on TMB degradation in the presence and absence of exosomes was investigated through UV-vis adsorption and ocular observations based on colour changes on laboratory and real samples. The results show that the absence of exosomes significantly inhibited the peroxidase-like activity of CD63 aptamer-Fe₃O₄-Cu²⁺-NZs due to the aptamer coating. Under optimal conditions, the designed CD63 aptamer-Fe₃O₄-Cu²⁺-NZs is capable of detecting exosomes in the range of 1.4 × 10⁴-5.6 × 10⁵ particles/μL with a detection limit of 5.91 × 10³ particles/μL. Also, this method showed a satisfactory outcome in detection of cancer cells in real samples. Overall, this colorimetric aptasensor can be used to diagnose breast cancer cells based on a simple and inexpensive approach.

Recent advances in the selection of cancer-specific aptamers for the development of biosensors

An early diagnosis has the potential to greatly decrease cancer mortality. For that purpose, specific cancer biomarkers have been molecularly targeted by aptamer sequences to enable an accurate and rapid detection. Aptamer-based biosensors for cancer diagnostics are a promising alternative to those using antibodies, due to their high affinity and specificity to the target molecules and advantageous production. Synthetic nucleic acid aptamers are generated by in vitro Systematic Evolution of Ligands by Exponential enrichment (SELEX) methodologies that have been improved over the years to enhance the efficacy and to shorten the selection process. Aptamers have been successfully applied in electrochemical, optical, photoelectrochemical and piezoelectrical-based detection strategies. These aptasensors comprise a sensitive, accurate and inexpensive option for cancer detection being used as point-of-care devices. This review highlights the recent advances in cancer biomarkers, achievements and optimizations made in aptamer selection, as well as the different aptasensors developed for the detection of several cancer biomarkers.

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.

Translating cancer exosomes detection into the color change of phenol red based on target-responsive DNA microcapsules

Emerging evidence indicates that exosomes can be used as a potential biomarker for monitoring diseases, including cancer. However, enhancing the sensing performance in terms of convenience and sensitivity remains an urgent demand for exosomes detection. In this study, a pH-sensitive colorimetric biosensing strategy was developed for exosomes detection by integrating stimuli-responsive DNA microcapsules and acetylcholinesterase to produce acetic acid. The constructed DNA microcapsules consisted of DNA shells crosslinked by anti-CD63 aptamers and loaded with acetylcholinesterase. With exosomes addition, an energetically stabilized aptamer-CD63 compound was produced and microcapsules dissociated due to the reaction of surface protein CD63 of exosomes and aptamer of CD63, resulting in the release of encapsulated AChE. Through a simple centrifugation separation, unreacted DNA microcapsules were removed and the supernatant containing released acetylcholinesterase collected, which was then used for colorimetric exosomes detection through the ability of acetylcholinesterase to hydrolyze acetylcholine to release acetic acid. The resulting decreased solution pH was detected with phenol red indicator, with the sharp color transition conveniently by naked eye. Exosomes quantification was also achieved using the solution's absorption intensity ratio of 558 vs. 432 nm. The linear range was from 2.0 × 10³ to 5.0 × 10⁵ particles/μL, and the limit of detection and limit of quantification were 1.2 × 10³ particles/μL and 2.2 × 10³ particles/μL, respectively. In addition, this proposed strategy for exosomes detection showed a relative standard deviation of 3.1% and high recovery efficiency (>94%), exhibiting a bright application future in exsomes analysis.

A dual-modal aptasensor based on a multifunctional acridone derivate for exosomes detection

Exosomes are promising biomarkers for cancer screening, but the development of a robust approach that can sensitively and accurately detect exosomes remains challenging. In the present study, an aptasensor based on the multifunctional signal probe 10-benzyl-2-amino-acridone (BAA) was developed for the colorimetric and photoelectrochemical detection and quantitation of exosomes. Exosomes are captured by cholesterol DNA anchor-modified magnetic beads (MBs) through hydrophobic interactions. This capture process can be monitored under a confocal fluorescence microscope using BAA as the fluorescent signal probe. The aptamer modified copper oxide nanoparticles (CuO NPs) then bind to mucin 1 (MUC1) on the surface of the exosomes to form a sandwich structure (MBs-Exo-CuO NPs). Finally, the MBs-Exo-CuO NPs are dissolved in nitric acid to generate Cu²⁺, which inhibits the visible-light-induced oxidase mimic activity and photoelectrochemical activity of BAA simultaneously. The changes in absorbance and photocurrent intensities are directly proportional to the concentration of exosomes. In this dual-modal aptasensor, the colorimetric assay can achieve rapid screening and identification, which is especially useful for point-of-care testing. The UV-vis absorbance and photocurrent assays then provide quantitative information, with a limit of detection of 1.09 × 10³ particles μL^-1 and 1.38 × 10³ particles μL^-1, respectively. The proposed aptasensor thus performs dual-modal detection and quantitation of exosomes. This aptasensor provides a much-needed toolset for exploring the biological roles of exosomes in specific diseases, particularly in the clinical setting.

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.

AuNP Aptasensor for Hodgkin Lymphoma Monitoring

A liquid biopsy based on circulating small extracellular vesicles (SEVs) has not yet been used in routine clinical practice due to the lack of reliable analytic technologies. Recent studies have demonstrated the great diagnostic potential of nanozyme-based systems for the detection of SEV markers. Here, we hypothesize that CD30-positive Hodgkin and Reed-Sternberg (HRS) cells secrete CD30 + SEVs; therefore, the relative amount of circulating CD30 + SEVs might reflect classical forms of Hodgkin lymphoma (cHL) activity and can be measured by using a nanozyme-based technique. A AuNP aptasensor analytics system was created using aurum nanoparticles (AuNPs) with peroxidase activity. Sensing was mediated by competing properties of DNA aptamers to attach onto surface of AuNPs inhibiting their enzymatic activity and to bind specific markers on SEVs surface. An enzymatic activity of AuNPs was evaluated through the color reaction. The study included characterization of the components of the analytic system and its functionality using transmission and scanning electron microscopy, nanoparticle tracking analysis (NTA), dynamic light scattering (DLS), and spectrophotometry. AuNP aptasensor analytics were optimized to quantify plasma CD30 + SEVs. The developed method allowed us to differentiate healthy donors and cHL patients. The results of the CD30 + SEV quantification in the plasma of cHL patients were compared with the results of disease activity assessment by positron emission tomography/computed tomography (PET-CT) scanning, revealing a strong positive correlation. Moreover, two cycles of chemotherapy resulted in a statistically significant decrease in CD30 + SEVs in the plasma of cHL patients. The proposed AuNP aptasensor system presents a promising new approach for monitoring cHL patients and can be modified for the diagnostic testing of other diseases.

A colorimetric aptasensor based on a hemin/EpCAM aptamer DNAzyme for sensitive exosome detection

Exosomes are considered as potential biomarkers that can reflect information from their parent cell-associated cancer microenvironment.

Fast quantification of extracellular vesicles levels in early breast cancer patients by Single Molecule Detection Array (SiMoA)

PURPOSE

Preliminary reports suggest that extracellular vesicles (EVs) might be a promising biomarker for breast cancer (BC). However, the quantification of plasmatic levels of EVs is a complex task. To overcome these limitations, we developed a new, fast, and easy to use assay for the quantification of EVs directly in plasma based on the use of Single-Molecule Array (SiMoA).

METHODS

By using SiMoA to identify CD9+/CD63+ EVs, we analyzed plasma samples of 181 subjects (95 BC and 86 healthy controls, HC). A calibration curve, made of a serial dilution of lyophilized standards from human plasma, was used in each run to ensure the obtainment of quantitative results from the assay. In a subgroup of patients, EVs concentrations were estimated in plasma before and after 30 days from cancer surgery. Additional information on the size of EVs were also acquired using a Nanosight system to obtain a clearer understanding of the mechanism underlying the releases of EVs associated with the presence of cancer.

RESULTS

The measured levels of EVs resulted significantly higher in BC patients (median values 1179.1 ng/µl vs 613.0 ng/µl, p < 0.0001). ROC curve was used to define the optimal cut-off level of the test at 1034.5 ng/µl with an AUC of 0.75 [95% CI 0.68-0.82]. EVs plasmatic concentrations significantly decreased after cancer surgery compared to baseline values (p = 0.014). No correlation was found between EVs concentration and clinical features of BC.

CONCLUSION

SiMoA assay allows plasmatic EVs levels detection directly without any prior processing. EVs levels are significantly higher in BC patients and significantly decreases after cancer surgery.

Exosomes as Powerful Engines in Cancer: Isolation, Characterization and Detection Techniques

Exosomes, powerful extracellular nanovesicles released from almost all types of living cells, are considered the communication engines (messengers) that control and reprogram physiological pathways inside target cells within a community or between different communities. The cell-like structure of these extracellular vesicles provides a protective environment for their proteins and DNA/RNA cargos, which serve as biomarkers for many malicious diseases, including infectious diseases and cancers. Cancer-derived exosomes control cancer metastasis, prognosis, and development. In addition to the unique structure of exosomes, their nanometer size and tendency of interacting with cells makes them a viable novel drug delivery solution. In recent years, numerous research efforts have been made to quantify and characterize disease-derived exosomes for diagnosis, monitoring, and therapeutic purposes. This review aims to (1) relate exosome biomarkers to their origins, (2) focus on current isolation and detection methods, (3) discuss and evaluate the proposed technologies deriving from exosome research for cancer treatment, and (4) form a conclusion about the prospects of the current exosome research.

Rapid enrichment and sensitive detection of extracellular vesicles through measuring the phospholipids and transmembrane protein in a microfluidic chip

Extracellular vesicles (EVs) have attracted tremendous attention in recent years and quantification of EVs is a key issue in the evaluation of vesicle-based diagnostics and therapeutic development, but it's quite challenging to determine whether higher protein expression signals are due to larger vesicle amount or higher protein content within each vesicle. To solve this problem, herein, we proposed a strategy based on staining phospholipid bilayers of EVs with lipophilic dyes to evaluate their lipid amount, which was subsequently normalized as an internal standard for studying the expression of transmembrane protein (i.e., CD63) on EVs in different samples. In addition, a microfluidic platform based on electrophoresis technology was invented to effectively enrich and detect EVs. Small fluorescent labeling molecules (i.e., uncombined aptamers) were on-chip removed from EVs without pre-separation via ultracentrifugation or ultrafiltration which were indispensable in nanoparticle tracking analysis (NTA) and flow cytometry techniques and the performance of this assay is comparable to NTA. Finally, it was found obvious difference in the expression of CD63 on EVs before and after normalization based on lipid amount in plasma samples. This method is expected to provide more accurate information when comparing the expression levels of EVs biomarkers in different samples.

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.

Aptamer-based biosensors and application in tumor theranostics

An aptamer is a short oligonucleotide chain that can specifically recognize targeting analytes. Due to its high specificity, low cost, and good biocompatibility, aptamers as the targeting elements of biosensors have been applied widely in non-invasive tumor imaging and treatment in situ to replace traditional methods. In this review, we will summarize recent advances in using aptamer-based biosensors in tumor diagnosis. After a brief introduction of the advantage of aptamers compared with enzyme sensors and immune sensors, the different sensing designs and mechanisms based on 3 signal transduction modes will be reviewed to cover different kinds of analytical methods, including: electrochemistry analysis, colorimetry analysis, and fluorescence analysis. Finally, the prospective advantages of aptamer-based biosensors in tumor theranostics and post-treatment monitoring are also evaluated in this review.

Protein biomarkers in breast cancer-derived extracellular vesicles for use in liquid biopsies

Breast cancer is the most common malignant disease in women worldwide. Early diagnosis and treatment can greatly improve the management of breast cancer. Liquid biopsies are becoming convenient detection methods for diagnosing and monitoring breast cancer due to their noninvasiveness and ability to provide real-time feedback. A range of liquid biopsy markers, including circulating tumor proteins, circulating tumor cells, and circulating tumor nucleic acids, have been implemented for breast cancer diagnosis and prognosis, with each having its own advantages and limitations. Circulating extracellular vesicles are messengers of intercellular communication that are packed with information from mother cells and are found in a wide variety of bodily fluids; thus, they are emerging as ideal candidates for liquid biopsy biomarkers. In this review, we summarize extracellular vesicle protein markers that can be potentially used for the early diagnosis and prognosis of breast cancer or determining its specific subtypes.

DNAzyme-Based Biosensors: Immobilization Strategies, Applications, and Future Prospective

Since their discovery almost three decades ago, DNAzymes have been used extensively in biosensing. Depending on the type of DNAzyme being used, these functional oligonucleotides can act as molecular recognition elements within biosensors, offering high specificity to their target analyte, or as reporters capable of transducing a detectable signal. Several parameters need to be considered when designing a DNAzyme-based biosensor. In particular, given that many of these biosensors immobilize DNAzymes onto a sensing surface, selecting an appropriate immobilization strategy is vital. Suboptimal immobilization can result in both DNAzyme detachment and poor accessibility toward the target, leading to low sensing accuracy and sensitivity. Various approaches have been employed for DNAzyme immobilization within biosensors, ranging from amine and thiol-based covalent attachment to non-covalent strategies involving biotin-streptavidin interactions, DNA hybridization, electrostatic interactions, and physical entrapment. While the properties of each strategy inform its applicability within a proposed sensor, the selection of an appropriate strategy is largely dependent on the desired application. This is especially true given the diverse use of DNAzyme-based biosensors for the detection of pathogens, metal ions, and clinical biomarkers. In an effort to make the development of such sensors easier to navigate, this paper provides a comprehensive review of existing immobilization strategies, with a focus on their respective advantages, drawbacks, and optimal conditions for use. Next, common applications of existing DNAzyme-based biosensors are discussed. Last, emerging and future trends in the development of DNAzyme-based biosensors are discussed, and gaps in existing research worthy of exploration are identified.

Biosensor-based assay of exosome biomarker for early diagnosis of cancer

Cancer imposes a severe threat to people's health and lives, thus pressing a huge medical and economic burden on individuals and communities. Therefore, early diagnosis of cancer is indispensable in the timely prevention and effective treatment for patients. Exosome has recently become an attractive cancer biomarker in noninvasive early diagnosis because of the unique physiology and pathology functions, which reflects remarkable information regarding the cancer microenvironment, and plays an important role in the occurrence and evolution of cancer. Meanwhile, biosensors have gained great attention for the detection of exosomes due to their superior properties, such as convenient operation, real-time readout, high sensitivity, and remarkable specificity, suggesting promising biomedical applications in the early diagnosis of cancer. In this review, the latest advances of biosensors regarding the assay of exosomes were summarized, and the superiorities of exosomes as markers for the early diagnosis of cancer were evaluated. Moreover, the recent challenges and further opportunities of developing effective biosensors for the early diagnosis of cancer were discussed.

Multicommutated Flow Analysis System for Determination of Horseradish Peroxidase and Its Inhibitors

A fully mechanized multicommutated flow analysis (MCFA) system dedicated to determining horseradish peroxidase (HRP) activity was developed. Detection was conducted using a flow-through optoelectronic detector-constructed of paired LEDs operating according to the paired emitter-detector diode (PEDD) principle. The PEDD-MCFA system is dedicated to monitoring the enzyme-catalyzed oxidation of p-phenylenediamine (pPD) by a hydrogen peroxide. Under optimized conditions, the presented bioanalytical system was characterized by a linear response range (33.47-200 U/L) with a detection limit at 10.54 U/L HRP activity and 1.66 mV·L/U sensitivity, relatively high throughput (12 signals recordings per hour), and acceptable precision (RSD below 6%). Additionally, the utility of the developed PEDD-MCFA system for the determination of HRP inhibitors allowing the detection of selected thiols at micromolar levels, is demonstrated. The practical utility of the flow system was illustrated by the analysis of some dietary supplements containing L-cysteine, N-acetylcysteine, and L-glutathione.

An artificial enzyme cascade amplification strategy for highly sensitive and specific detection of breast cancer-derived exosomes

Tumor-related exosomes, which are heterogeneous membrane-enclosed nanovesicles shed from cancer cells, have been widely recognized as potential noninvasive biomarkers for early cancer diagnosis. Herein, an artificial enzyme cascade amplification strategy based on a switchable DNA tetrahedral (SDT) scaffold was proposed for quantification of breast cancer-derived exosomes. The SDT scaffold is composed of G-quadruplex mimicking DNAzyme sequences on its two single-stranded edges and glucose oxidase (GOx) on the four termini of the complementary strands. In the initial state, the SDT scaffold is blocked by the switch strand which consists of partial complementary domains with the DNA tetrahedron and a MUC1 aptamer. MCF-7 exosomes could release the quadruplex-forming sequences through the recognition of the MUC1 aptamer. The newly formed DNAzyme brings GOx into spatial proximity and induces high-efficiency enzyme cascade catalytic reactions on the SDT. Consequently, high sensitivity toward MCF-7 exosome analysis was obtained with a wide linear range of 3.8 × 10⁶ to 1.2 × 10⁸ particles per mL and a limit of detection of 1.51 × 10⁵ particles per mL. In addition, such a DNAzyme reconfiguration strategy was able to distinguish MCF-7 exosomes from other breast cancer cell derived exosomes, indicating its excellent method specificity. The proposed enzyme cascade strategy not only provides a novel signal transformation and amplification nanoplatform for quantifying the specific populations of exosomes, but also can be further expanded to the analysis of multiple cancer biomarkers.

[Preparation of dual-functional composite magnetic nanomaterials modified with different metals/aptamers and their performance in exosome enrichment]

外泌体作为一种细胞外囊泡,其内容物可以反映亲代细胞的重要信息,而自身也具有独特的结构,能够执行特征的生物学功能。基于外泌体的表面化学和生物学特征,制备了不同类型的金属/适配体(Apt)双功能复合磁性纳米材料,并将其应用于外泌体的富集纯化。将适配体和外泌体表面目标膜蛋白的特异性结合性能与以钛、锆为代表的金属氧化物和外泌体磷脂双层膜的特异性亲和作用结合,可极大地提高分离材料对外泌体的分离选择性和富集容量。分别以Fe₃O₄@Zr-MOFs、Fe₃O₄@Zr-Ti-MOFs和Fe₃O₄@TiO₂等金属有机框架(MOFs)/金属氧化物磁性纳米材料为基底,制备对应的双功能MOFs/金属氧化物-适配体复合磁性纳米材料Fe₃O₄@Zr-MOFs-Apt、Fe₃O₄@Zr-Ti-MOFs-Apt和Fe₃O₄@TiO₂-Apt,并进一步对不同材料的外泌体富集性能加以评价。以超速离心法提取的模型外泌体以及尿液为样品,对修饰相同质量适配体和不同含量金属氧化物的双功能材料的富集性能加以对比。将3种双功能磁性纳米材料应用于尿液外泌体的富集,得到的外泌体裂解后经质谱鉴定,分别得到233、343和832个外泌体蛋白。这一结果也表明双功能磁性纳米材料可以充分结合核酸适配体亲和的高选择性和金属氧化物的高富集容量优势,对于复杂生物样品中外泌体的快速、高效分离纯化具有潜在的应用价值,而针对材料制备和分离纯化方法的设计也为新型外泌体富集材料的设计提供了一条可行的新思路。

Primary breast cancer biomarkers based on glycosylation and extracellular vesicles detected from human serum

Background

Breast cancer is a very common cancer that can be severe if not discovered early. The current tools to detect breast cancer need improvement. Cancer has a universal tendency to affect glycosylation. The glycosylation of circulating extracellular vesicle‐associated glycoproteins, and mucins may offer targets for detection methods and have been only explored in a limited capacity.

Aim

Our aim was to develop an approach to detect the aberrant glycosylation of mucins and extracellular vesicle‐associated glycoproteins from human sera using fluorescent nanoparticles, and preliminarily evaluate this approach for the differential diagnosis of breast cancer.

Methods and results

The assay involved immobilizing glycosylated antigens using monoclonal antibodies and then probing their glycosylation by using lectins and glycan‐specific antibodies coated on Eu⁺³‐doped nanoparticles. Detection of mucin 1 and mucin 16 glycosylation with wheat germ agglutinin, and detection of the extracellular vesicle‐associated CD63 were found to have better diagnostic ability for localized breast cancer than the conventional assays for mucin 1 and mucin 16 based tumor markers when the receiver operating characteristics were compared.

Conclusions

These results indicate that successful differential diagnosis of primary breast cancer may be aided by detecting cancer‐associated glycosylation of mucin 1 and mucin 16, and total concentration of CD63, in human serum.

Application of selected biosensor techniques in clinical diagnostics

INTRODUCTION

Examination of disease biomarkers mostly performed on crude materials, such as serum, meets some obstacles, resulting from sample complexity and the wide range of concentrations and sizes of the components. Techniques currently used in clinical diagnostics are usually time-consuming and expensive. The more sensitive and portable devices are needed for early diagnostics. Chemical sensors are devices that convert chemical information into parameters suitable for fast and precise processing and measurement.

AREA COVERED

We review the use of biosensors and their possible application in early diagnostics of some diseases like cancer or viral infections. We focus on different types of biorecognition and some technical modifications, lowering the limit of detection potentially attractive to medical practitioners.

EXPERT OPINION

Among the new diagnostic strategies, the use of biosensors is of increasing interest. In these techniques, the capture ligand interacts with the analyte of interest. Measuring interactions between partners in real time by surface plasmon resonance yields valuable information about kinetics and affinity in a short time and without labels. Importantly, the tendency in such techniques is to make biosensor devices smaller and the test results apparent with the naked eye, so they can be used in point-of-care medicine.

CD151 enrichment in exosomes of luminal androgen receptor breast cancer cell line contributes to cell invasion

Breast cancer is the most common and highly heterogeneous disease in women worldwide. Given the challenges in the treatment of advanced metastatic breast cancer, it is necessary to understand the molecular mechanisms related to disease progression. Exosomes play various roles in the progression of tumors, including promoting the invasion and advancing the distant metastasis. To study the molecular mechanisms related to the progression of luminal androgen receptor (LAR) breast cancer, we first isolated exosomes of MDA-MB-453 cells, a representative cell line of LAR. Through quantitative proteomic analysis, we identified 180 proteins specifically enriched in exosomes after comparing with those in cells, microvesicles, and the 150K supernatant. Among these, CD151, a protein involved in the regulation of cell motility was the most enriched one. CD151-knockdown exosomes reduced the invasion ability of the recipient breast cancer cell and lowered the phosphorylation level of tyrosine-protein kinase Lck, indicating that the invasion of LAR breast cancer may be due to CD151-enriched exosomes. Our work reports for the first time that CD151 was highly abundant in the exosomes of MDA-MB-453 cells and expands the understanding of the development process of LAR subtype, suggesting CD151 may be a potential candidate for the treatment of LAR breast cancer.

Emerging Diagnostic Potential of Tumor-derived Exosomes

Exosomes carry genetic information originating from their parental cells, raising their possibility as novel noninvasive biomarkers for cancer. Tumor-derived exosomes (TEXs) have a variety of endogenous cargos that reflect the pathophysiology status and information of tumor cells. TEXs are increasingly being recognized as potential biomarkers for cancer diagnosis prognosis, and monitoring. It is important to develop a variety of sensitive methods, including probes and biomaterials to isolate exosomes. A variety of approaches for detecting exosomes have been established. By combining exosome DNA and RNA sequencing tools, exosome proteomics analysis and immunoassay technology, it is expected that exosomes will gain widespread use in the diagnosis and treatment of cancer.

The synchronization of multiple signal amplifications for label-free and sensitive aptamer-based sensing of a protein biomarker

The abnormal variation of the mucin 1 (MUC1) protein level is associated with the development of multiple cancers, and the monitoring of trace MUC1 can be useful for early disease diagnosis. Here, on the basis of the synchronization of DNA-fueled sequence recycling and dual rolling circle amplification (RCA), the establishment of a non-label and highly sensitive fluorescent aptamer-based detection strategy for the MUC1 protein biomarker is described. The target MUC1 binds the aptamer hairpin probe and causes its structure switching to release an ssDNA tail to trigger the recycling of the complex via two toehold-mediated strand displacement reactions under assistance of a fuel DNA. Such a recycling amplification leads to the formation of a partial dsDNA duplex with two primers at both ends, which cooperatively bind the circular DNA ring template to start the dual RCA to produce many G-quadruplex sequences. The protoporphyrin IX dye further associates with the G-quadruplex structures to show a dramatically elevated fluorescent signal for sensitively detecting MUC1 with a low detection limit of 0.5 pM. The established aptamer-based detecting strategy is also highly selective and can realize assay of MUC1 in diluted human serums, highlighting its potential for the detection of different protein biomarkers at low contents.

Identification of a novel RNA aptamer that selectively targets breast cancer exosomes

Breast cancer is a leading cause of cancer mortality in women. Despite advances in its management, the identification of new options for early-stage diagnosis and therapy of this tumor still represents a crucial challenge. Increasing evidence indicates that extracellular vesicles called exosomes may have great potential as early diagnostic biomarkers and regulators of many cancers, including breast cancer. Therefore, exploiting molecules able to selectively recognize them is of great interest. Here, we developed a novel differential SELEX strategy, called Exo-SELEX, to isolate nucleic acid aptamers against intact exosomes derived from primary breast cancer cells. Among the obtained sequences, we optimized a high-affinity aptamer (ex-50.T) able to specifically recognize exosomes from breast cancer cells or patient serum samples. Furthermore, we demonstrated that the ex.50.T is a functional inhibitor of exosome cellular uptake and antagonizes cancer exosome-induced cell migration in vitro. This molecule provides an innovative tool for the specific exosome detection and the development of new therapeutic approaches for breast cancer.

New insight into G-quadruplexes; diagnosis application in cancer

Biochemical properties and flexibility of nitrogenous bases allow DNA to fold into higher-order structures. Among different DNA secondary structure, G-quadruplexes (tetrapelexes-G4) - which are formed in guanine rich sequences - have gained more attention because of their biological significance, therapeutic intervention, and application in molecular device and biosensor. G4-quadruplex studies categorize into three main fields, in vivo, in vitro, and in silico. The in vitro field includes G4 synthetic oligonucleotides. This review focuses on the G-quadruplex synthetic aptamers structure features and considers the applicability of G4-aptamers for cancer biomarkers detection. Various biosensing methods will be reviewed based on G-quadruplex aptamers for cancer detection.

Immunoassay-aptasensor for the determination of tumor-derived exosomes based on the combination of magnetic nanoparticles and hybridization chain reaction

The detection of tumor-related exosomes is of great significance. In this work, a fluorescence aptasensor was designed for the determination of tumor-related exosomes based on the capture of magnetic nanoparticles (MNPs) and specific recognition of an aptamer. MNPs were used as substrates to capture the exosomes by modifying the CD63 antibody on the MNP surface. Probe 1 consists of PDL-1 aptamer sequence and a section of other sequences. PDL-1 expression was observed on the surface of exosomes; the aptamer of PDL-1 could combine with PDL-1 with high affinity. Thus, the immunoassay-type compounds of "MNPs-exosomes-probe 1" were formed. The other section of probe 1 triggered the HCR with probe 2 and probe 3 and formed the super-long dsDNA. The addition of GelRed resulted in the generation of an amplified fluorescence signal. The proposed design demonstrated a good linearity with the exosome concentration ranging from 300 to 107 particles per mL and with a low detection limit of 100 particles per mL. This aptasensor also exhibited high specificity for tumor-related exosomes, and was successfully applied in biological samples.

Recent advances in visual detection for cancer biomarkers and infectious pathogens

It is an urgency to detect infectious pathogens or cancer biomarkers using rapid, simple, convenient and cost-effective methods in complex biological samples. Many existing approaches (traditional virus culture, ELISA or PCR) for the pathogen and biomarker assays face several challenges in the clinical applications that require lengthy time, sophisticated sample pre-treatment and expensive instruments. Due to the simple and rapid detection manner as well as no requirement of expensive equipment, many visual detection methods have been considered to resolve the aforementioned problems. Meanwhile, various new materials and colorimetric/fluorescent methods have been tried to construct new biosensors for infectious pathogens and biomarkers. However, the recent progress of these aspects is rarely reviewed, especially in terms of integration of new materials, microdevice and detection mechanism into the visual detection systems. Herein, we provide a broad field of view to discuss the recent progress in the visual detection of infectious pathogens and cancer biomarkers along with the detection mechanism, new materials, novel detection methods, special targets as well as multi-functional microdevices and systems. The novel visual approaches for the infectious pathogens and biomarkers, such as bioluminescence resonance energy transfer (BRET), metal-induced metallization and clustered regularly interspaced short palindromic repeats (CRISPR)-based biosensors, are discussed. Additionally, recent advancements in visual assays utilizing various new materials for proteins, nucleic acids, viruses, exosomes and small molecules are comprehensively reviewed. Future perspectives on the visual sensing systems for infectious pathogens and cancers are also proposed.

DNA Nanomachines for Identifying Cancer Biomarkers in Body Fluids and Cells

Identifying molecular biomarkers promises to significantly improve the accuracy in cancer diagnosis at its early stage. DNA nanomachines, which are designable and switchable nanostructures made of DNA, show broad potential to detect tumor biomarkers with noninvasive, inexpensive, highly sensitive, and highly specific advantages. This Feature summarizes the recent DNA nanomachine-based platforms for the early detection of cancer biomarkers, both from body fluids and in cells.

Interaction of indole-3-acetic acid with horseradish peroxidase as a potential anticancer agent: from docking to molecular dynamics simulation

The oxidation process, catalyzed by the peroxidase enzymes, occurs in all domains of life to detoxify the hydrogen peroxide toxicity. The most well-known, applicable and vastly studied member of the peroxidases family is horseradish peroxidase (HRP), especially the isoenzyme C (HRP C). HRP (primarily HRP C) is commercially available and applicable in biotechnology and diagnosis. Recently, a novel application of HRP has been introduced in cancer therapy as the combination of HRP with indole-3-acetic acid (IAA). The anticancer activity of HRP/IAA complex is through oxidation of IAA by HRP in hypoxic tumor condition, which leads to apoptosis and cancerous cell death. However, the molecular interaction of HRP/IAA has not been elucidated. Identifying the interaction of IAA with HRP would provide a better insight into its function and applications. In this study, molecular docking and molecular dynamics (MD) simulation were applied to determine the molecular interaction of the IAA/HRP complex. The docking study represented that IAA bound at the 'exposed' heme edge of the HRP enzyme, and the IAA entrance to the enzyme was situated at the carboxymethyl side-chain of the selected structure. Our computational results showed the HRP/IAA complex structure stability. While hydrogen bond formation with ARG38 and HIS42 stabilized the substrate, hydrophobic interactions with Phe68, Gly69, Leu138, Pro139, Pro141 and Phe179 contributed to IAA/HRP complex stability. The results can help to better understand peroxidase enzyme activity and would pave the way for future development of new therapeutics with improved anticancer efficacy.Communicated by Ramaswamy H. Sarma.

A review on methods for diagnosis of breast cancer cells and tissues

Breast cancer has seriously been threatening physical and mental health of women in the world, and its morbidity and mortality also show clearly upward trend in China over time. Through inquiry, we find that survival rate of patients with early‐stage breast cancer is significantly higher than those with middle‐ and late‐stage breast cancer, hence, it is essential to conduct research to quickly diagnose breast cancer. Until now, many methods for diagnosing breast cancer have been developed, mainly based on imaging and molecular biotechnology examination. These methods have great contributions in screening and confirmation of breast cancer. In this review article, we introduce and elaborate the advances of these methods, and then conclude some gold standard diagnostic methods for certain breast cancer patients. We lastly discuss how to choose the most suitable diagnostic methods for breast cancer patients. In general, this article not only summarizes application and development of these diagnostic methods, but also provides the guidance for researchers who work on diagnosis of breast cancer.

Recent advances of aptasensors for exosomes detection

Exosomes are nanoscale phospholipid bilayer membrane-enclosed vesicles released from cells with diameters of 30-150 nm. Their contents reflect significant information regarding the cancer microenvironment from their parent cells, which attracts increasing attention as potential biomarkers for noninvasive early diagnosis. Among their detection methods, aptasensor has been becoming an attractive star with its properties of affordability, easy to use, fast response, high sensitivity, remarkable specificity, and multiplexing capability. This review mainly summarizes the recent advances of single-stranded DNA (ssDNA) aptamer-based sensors for cancer and tumor-derived exosomes detection. Firstly, we present a brief overview of aptamers and exosomes. Then, we introduce the exosomal proteins used as potential biomarkers of various cancers, and their specific ssDNA aptamers used in aptasensors. We emphasize eight major types of aptasensors: fluorescent, electrochemical, colorimetric, luminescence, lateral flow strips, surface-enhanced Raman scattering, surface plasmon resonance, and giant magnetoresistance sensors, based on fabrication methods, bio-recognition mechanism, as well as detection evaluation. The future directions and challenges are finally proposed for aptamers and their more applications in exosomes research.

Aptamer-Cholesterol-Mediated Proximity Ligation Assay for Accurate Identification of Exosomes

Accurate identification of exosomes plays an essential role in facilitating disease diagnosis and therapies. Herein, we proposed an Aptamer-cholesterol-mediated Proximity Ligation Assay (AcmPLA) for accurate identification of exosomes in a dual-probe strategy, one aptamer probe for recognition of exosomal innate surface protein CD63 and another cholesterol probe for biolipid layer targeting. By integrating a proximity ligation of probes bound with exosomal biomarkers for specific recognition and a rolling circle amplification (RCA) strategy for signal amplification, we have successfully developed an exosomes-surface approach that can perform "AND" logic analysis of dual biomarkers, which not only could be used for exosomes quantification, but also for exosomes tracing. Besides RCA-initiated signal amplification, CD9 antibody-labeled magnetic beads were used to capture exosomes for isolation and secondary signal enrichment. Our approach can achieve specific exosomes isolation and accurate identification and thus could be exploited for broad applications in biological science, biomedical engineering, and personalized medicine.

Recent developments of nanoenzyme-based colorimetric sensors for heavy metal detection and the interaction mechanism

This work highlights the application and interaction mechanism of metal nanoparticles, metal oxides, metal sulfides, graphene-based nanomaterials and G-quadruplex, etc. in nanoenzyme-based colorimetric sensors.