A colorimetric and photothermal dual-mode biosensing platform based on nanozyme-functionalized flower-like DNA structures for tumor-derived exosome detection

Bimetallic Single-Atom Nanozyme-Based Electrochemical-Photothermal Dual-Function Portable Immunoassay with Smartphone Imaging

Rapid and accurate detection of human epidermal growth factor receptor 2 (HER2) is crucial for the early diagnosis and prognosis of breast cancer. In this study, we reported an iron-manganese ion N-doped carbon single-atom catalyst (FeMn-NCetch/SAC) bimetallic peroxidase mimetic enzyme with abundant active sites etched by H2O2 and further demonstrated unique advantages of single-atom bimetallic nanozymes in generating hydroxyl radicals by density functional theory (DFT) calculations. As a proof of concept, a portable device-dependent electrochemical-photothermal bifunctional immunoassay detection platform was designed to achieve reliable detection of HER2. In the enzyme-linked reaction, H2O2 was generated by substrate catalysis via secondary antibody-labeled glucose oxidase (GOx), while FeMn-NCetch/SAC nanozymes catalyzed the decomposition of H2O2 to form OH*, which catalyzed the conversion of 3,3',5,5'-tetramethylbenzidine (TMB) to ox-TMB. The ox-TMB generation was converted from the colorimetric signals to electrical and photothermal signals by applied potential and laser irradiation, which could be employed for the quantitative detection of HER2. With the help of this bifunctional detection technology, HER2 was accurately detected in two ways: photothermally, with a linear scope of 0.01 to 2.0 ng mL-1 and a limit of detection (LOD) of 7.5 pg mL-1, and electrochemically, with a linear scope of 0.01 to 10 ng mL-1 at an LOD of 3.9 pg mL-1. By successfully avoiding environmental impacts, the bifunctional-based immunosensing strategy offers strong support for accurate clinical detection.

Nanozyme-Enabled Biomedical Diagnosis: Advances, Trends, and Challenges

As nanoscale materials with the function of catalyzing substrates through enzymatic kinetics, nanozymes are regarded as potential alternatives to natural enzymes. Compared to protein-based enzymes, nanozymes exhibit attractive characteristics of low preparation cost, robust activity, flexible performance adjustment, and versatile functionalization. These advantages endow them with wide use from biochemical sensing and environmental remediation to medical theranostics. Especially in biomedical diagnosis, the feature of catalytic signal amplification provided by nanozymes makes them function as emerging labels for the detection of biomarkers and diseases, with rapid developments observed in recent years. To provide a comprehensive overview of recent progress made in this dynamic field, here an overview of biomedical diagnosis enabled by nanozymes is provided. This review first summarizes the synthesis of nanozyme materials and then discusses the main strategies applied to enhance their catalytic activity and specificity. Subsequently, representative utilization of nanozymes combined with biological elements in disease diagnosis is reviewed, including the detection of biomarkers related to metabolic, cardiovascular, nervous, and digestive diseases as well as cancers. Finally, some development trends in nanozyme-enabled biomedical diagnosis are highlighted, and corresponding challenges are also pointed out, aiming to inspire future efforts to further advance this promising field.

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

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

A label-free colorimetric biosensor utilizing natural material for highly sensitive exosome detection

Exosomes, extracellular vesicles secreted by cells, play a crucial role in intercellular communication by transferring information from source cells to recipient cells. These vesicles carry important biomarkers, including nucleic acids and proteins, which provide valuable insights into the parent cells' status. As a result, exosomes have emerged as noninvasive indicators for the early diagnosis of cancer. Colorimetric biosensors have garnered significant attention due to their cost-effectiveness, simplicity, rapid response, and reproducibility. In this study, we employ sporopollenin microcapsules (SP), a natural biopolymer material derived from pollen, as a substrate for gold nanoparticles (AuNPs). By modifying the SP-Au complex with CD63 aptamers, we develop a label-free colorimetric biosensor for exosome detection. In the absence of exosomes, the SP-Au complex catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), resulting in a color change from colorless to blue. However, the addition of exosomes inhibits the catalytic activity of the SP-Au complex due to coverage of exosomes on AuNPs. This colorimetric biosensor exhibits high sensitivity and selectivity for exosome detection, with a detection limit of 10 particles/μL and a wide linear range of 10 - 108 particles/μL. Additionally, the SP-Au biosensor demonstrates remarkable resistance to serum protein adsorption and excellent catalytic stability even in harsh environments, making it highly suitable for clinical diagnostics.

Three-Dimensional DNA Hydrogel Mediated Dual-Mode Sensing Method for Quantification of Epithelial Cell Adhesion Molecule in Biological Fluid Samples

Monitoring changes in the expression of marker proteins in biological fluids is essential for biomarker-based disease diagnosis. Epithelial cell adhesion molecule (EpCAM) has been identified as a broad-spectrum biomarker for various chronic diseases and as a therapeutic target. However, the development of simple and reliable methods for quantifying EpCAM changes in biological fluids faces challenges due to the variability of its expression across different diseases, the presence of soluble forms, and matrix effects. In this paper, a surface-enhanced Raman scattering (SERS)-fluorescence (FL) dual-mode sensing method was established for quantification of trace EpCAM in biological fluids based on bimetallic Au@Ag nanoparticles and nitrogen-doped quantum dots encapsulated DNA hydrogel hybrid with graphene oxide (Au@Ag-NQDs/GO). The DNA hydrogel was constructed based on three-dimensional (3D) structure DNA-mediated strategy using an aptamer DNA (AptDNA) linker. The interaction of the AptDNA with EpCAM triggered the disassembly of the DNA hydrogel. Consequently, the release of Au@Ag nanoparticles induced an "on-off" switch in the SERS signal while the weakened FL quenching effect in Au@Ag-NQDs/GO system achieved "off-on" switch of FL signal, enabling the simultaneous SERS-FL quantification of EpCAM. The established dual-mode method exhibited outstanding sensitivity and stability in quantifying EpCAM in the range of 0.5-60.0 pg/mL, with the limits of detection (LODs) of SERS and FL as 0.17 and 0.35 pg/mL, respectively. When applied for real sample analysis, the method showed satisfactory specificity and recoveries in cancer cells lysate, serum, and urine samples with RSDs of 2.8-6.3%, 4.0-6.3%, and 2.8-5.7%, respectively. The developed SERS-FL sensing method offered a sensitive, reliable, and practical quantification strategy for trace EpCAM in diverse biological fluid samples, which would benefit the early diagnosis of disease and further health management.

Colorimetric aptasensor based on temporally controllable light-stimulated oxidase-mimicking fluorescein for the sensitive detection of exosomes in mild conditions

Analysis of exosomes provides important information for rapid and non-invasive screening of tumors. However, sensitive and convenient detection of exosomes remains technically challenging to date. Herein, a colorimetric aptasensor based on the light-stimulated oxidase-mimicking activity of FITC was constructed for detecting ovarian cancer (OC) exosomes. The aptasensor contained an EpCAM aptamer to capture OC exosomes. Cholesterol and fluorescein (FITC) were used to modify either end of the DNA (DNA anchor). The DNA anchor could combine with exosomes through a hydrophobic reaction between cholesterol and the lipid membrane. FITC oxidized 3,3',5,5'-tetramethylbenzidine (TMB) under a 365 nm LED light source in a temporally controllable manner under mild conditions, causing the solution to change from colorless to blue, and the corresponding UV-vis absorbance increased. Based on this principle, the exosomes were qualitatively analyzed by observing the color change with the naked eye. In parallel, the exosome concentration was also detected using UV-vis spectrophotometry. The linear range was from 2 × 105 to 100 × 105 particles per mL with a limit of detection of 1.77 × 105 particles per mL. The developed aptasensor also exhibited favorable selectivity and could discriminate the exosomes from OC cells and normal cells. Besides, the receiver operating characteristic (ROC) curve demonstrates that it is possible to distinguish between patients with OC and healthy donors (HDs) using exosomes as the biomarker. Our technology may expand the applications of DNA-based detection method-enabled OC diagnostic tools.

A photothermal aptasensor based on rolling circle amplification-enriched DNAzyme for portable detection of ochratoxin A in grape juice

Aptasensors for detection of ochratoxin A (OTA) have been extensively studied, but the majority of them require costly and large-scale equipment as signal readers. Herein, a photothermal aptasensor capable of portable detection of OTA through a thermometer was developed on basis of aptamer structural switching and rolling circle amplification (RCA)-enriched DNAzyme. Oligonucleotides and alkaline phosphatase (ALP) modified magnetic beads were prepared. The binding of aptamers to OTA led to the release of ALP labeled complementary DNA. After magnetic separation, ALP catalyzed the padlock dephosphorylation, inhibiting the subsequent RCA reaction. This process converted the OTA concentration into the amount of the photothermal reagent oxTMB produced from the catalytic reaction induced by RCA-enriched DNAzyme. Under the optimal conditions, the detection limit (LOD) of this aptasensor was 2.28 nM in a clean buffer, while the LOD reached 2.43 nM in 2 % grape juice. The good performance of the photothermal aptasensor makes it possible to measure OTA pollution in low resource environments.

Pt/Zn-TCPP Nanozyme-Based Flexible Immunoassay for Dual-Mode Pressure-Temperature Monitoring of Low-Abundance Proteins

Pressure and temperature, as common physical parameters, are important for monitoring human health. In contrast, single-mode monitoring is prone to causing experimental errors. Herein, we innovatively designed a dual-mode flexible sensing platform based on a platinum/zinc-meso-tetrakis(4-carboxyphenyl)porphyrin (Pt/Zn-TCPP) nanozyme for the quantitative monitoring of carcinoembryonic antigen (CEA) in biological fluids with pressure and temperature readouts. The Pt/Zn-TCPP nanozyme with catalytic and photothermal efficiencies was synthesized by means of integrating photosensitizers into porous materials. The flexible sensing system after the antigen-antibody reaction recognized the pressure using a flexible skin-like pressure sensor with a digital multimeter readout, whereas the temperature was acquired via the photoheat conversion system of the Pt/Zn-TCPP nanozyme under 808 nm near-infrared (NIR) irradiation using a portable NIR imaging camera on a smartphone. Meanwhile, the dual-mode flexible sensing system was carried out on a homemade three-dimensional (3D)-printed device. Results revealed that the developed dual-mode immunosensing platform could exhibit good pressure and temperature responses within the dynamic range of 0.5-100 ng mL-1 CEA with the detection limits of 0.24 and 0.13 ng mL-1, respectively. In addition, the pressure and temperature were sensed simultaneously without crosstalk interference. Importantly, the dual-mode flexible immunosensing system can effectively avoid false alarms during the measurement, thus providing great potential for simple and low-cost development for point-of-care testing.

One-step and label-free ratiometric fluorescence assay for the detection of plasma exosome towards cancer diagnosis

Exosomes are closely associated with tumor development and are regarded as viable biomarkers for cancer. Here, a ratiometric fluorescence method was proposed for the one-step and label-free detection of plasma exosomes. A bicolor streptavidin magnetic beads were specifically created with an immobilized Cy5-labeled hairpin aptamer for CD63 (Cy5-Apt) on its surface to identify exosome, and a green color SYBR Green I (SGI) embedded in the stem of Cy5-Apt to respond to exosomes. After exosome capture, the Cy5-Apt could undergo a conformational shift and release the encapsulated SGI, allowing exosome measurement based on the fluorescence ratio of Cy5 and SGI. The enrichment, separation and detection of exosomes in proposed method could be completed in one step (30 min), which is a significant improvement over previous method. Furthermore, the use of ratiometric fluorescence and magnetic separation allows for exosome enrichment and interference elimination from complex matrices, improving accuracy and sensitivity. Particularly, the assay could detect exosomes in plasma and has potential to distinguish lung cancer patients from healthy volunteers with an area under the receiver operator characteristic curve of 0.85. Besides, the study provided an efficient method for analyzing the various divisions of exosomes by merely modifying the aptamer, which holds great promise for point-of-care applications.

Geldanaycin-encapsulated magnetic nanoparticle for isolation of myosin in proteomics

The grafting of a drug molecule, i.e., geldanamycin (GA) onto polyethyleneimine (PEI)-coated magnetic nanoparticle produces a novel composite, GA@Fe3O4-NH2. The composite is confirmed by characterizations with FT-IR, Raman, SEM, EDS, VSM and TEM. Due to the high binding-affinity of GA with myosin heavy chain (MYH), GA@Fe3O4-NH2 exhibits excellent adsorption performance towards myosin. Consequently, a solid-phase extraction procedure is established for highly efficient and selective separation of myosin from pig heart extract. At pH 6.0, an adsorption efficiency of 97.1 % is achieved for treating 100 μg mL-1 myosin (0.1 mL) with 0.1 mg GA@Fe3O4-NH2 as adsorbent. The adsorption behavior of myosin onto GA@Fe3O4-NH2 fits Langmuir model, corresponding to a theoretical adsorption capacity of 518.1 mg g-1. The adsorbed myosin can be readily recycled by the SDS solution (1 %, m/m) with an elution efficiency of 91.8 %. According to circular dichroism spectroscopy, the conformational changes of myosin during adsorption and elution are reversible. For practical application, myosin is successfully isolated from the pig left ventricular protein extract with GA@Fe3O4-NH2, and SDS-PAGE and LC-MS/MS showed that myosin had high purity and a total of 716 proteins could be identified. Significantly, Geldamycin-encapsulated magnetic nanoparticle for the separation of myosin well exploits the potential of the nanomaterials modified by drug molecules in the separation and purification of target proteins.

Polyvalent aptamer scaffold coordinating light-responsive oxidase-like nanozyme for sensitive detection of zearalenone

An efficient aptasensor was developed for the colorimetric determination of zearalenone (ZEN) based on polyvalent aptamer scaffold and light-responsive oxidase-like nanozyme. The sensitivity and efficiency of the development method were significantly improved owing to rich aptamers and signal labels (3, 4-dihydroxybenzoic acid, PCA) packed in the scaffold. The scaffold integrated functions of target recognition, surface immobilization and signal transduction. The photoresponsive nanoenzyme of TiO2-PCA was formed by PCA coordinated with Ti (IV) on the surface of TiO2. TiO2-PCA catalyzed dissolved oxygen rather than H2O2 to generate colorimetric signal by stimulating the chromogenic substrate, which made the assay greener and safer. The detection limit of colorimetric mode was 0.0087 ng/mL and the satisfactory recoveries 92.00 %-111.00 % were achieved in spiked food samples. This strategy opens new horizons for sensitive detection of small molecule hazards and promises to be a powerful tool for safeguarding food safety.

Pyroelectric-Effect-Assisted Near-Infrared-Driven Photoelectrochemical Biosensor Based on Exponential DNA Amplifier for MicroRNA Detection

Although near-infrared responsive photoelectrochemical (PEC) biosensors have less damage to biological components compared to UV-visible light, they still reveal an inferior response due to the rapid recombination of photogenerated electron-hole. In this study, a near-infrared-driven PEC biosensor is fabricated for microRNA (miRNA) detection via integrating photoelectricity and pyroelectricity. Upon the introduction of target miRNA-21, the exponential DNA amplifier is triggered based on enzyme-assisted strand displacement amplification (SDA), releasing multiple Ag2S reporter probes to hybridize with capture probes immobilized on a CdS-2-mercaptobenzimidazole (2MBI)-modified photoelectrode. As a result, under the stimulation of NIR, the photoelectric conversion of Ag2S NPs generates the photocurrents. In addition, due to the strong hole acceptor ability of MBI, the pyroelectric effect of CdS-2MBI nanocomposites is enhanced, which generates highly pyroelectro-induced charge separation efficiency and induces the pyroelectric current benefited from the spontaneous polarization of CdS-2MBI caused by the temperature variation under the function of Ag2S nanoheaters. Impressively, this PEC biosensor has achieved the sensitive and selective determination of miRNA-21 with a detection limit as low as 54 fM. Overall, this NIR-driven PEC biosensor based on pyroelectric and photoelectric effects opens up a new horizon for bioanalysis and early disease diagnosis.

Differential identification of GSH for acute coronary syndrome using a colorimetric sensor based on nanoflower-like artificial nanozymes

The ability to detect glutathione (GSH) concentrations in human blood offered a simple and non-invasive method to monitor changes associated with cardiovascular diseases, cancers and diabetes. We showed the potential of employing catalytically active protein-directed nanoflower-like artificial nanozymes (apo-TF-MnOx NFs) by bio-mineralization method to produce simple and visible colorimetric sensor for GSH. The experiments proved that apo-TF-MnOx NFs exhibited peroxidase, catalase- and superoxide dismutase-like activities, but the most notable feature was the excellent peroxidase-like activity, which could efficiently catalyze the oxidation reaction of 3,3',5,5'- tetramethylbenzidine (TMB) in the existence of hydrogen peroxide (H2O2) to generate a blue product. Some outcomes also indicated that the apo-TF-MnOx NFs had stronger peroxidase-like activity, which was proved by the Michaelis-Menten constant (Km) and maximum initial velocity (Vmax). Hence, we used the peroxidase-like activity to develop a GSH colorimetric biosensor. Fortunately, the colorimetric platform exhibited a sensitive response to H2O2 and GSH in the range of 5 μМ to 300 μМ and 0.5 μМ to 35 μМ with a limit of detection of 3.29 μM and 0.15 μM (S/N = 3) under optimal conditions. The feasibility of the simple method was confirmed by qualitative detection of H2O2 and GSH in blood samples from acute coronary syndrome patients. A key outcome of our study was the ability to realized differential identification of GSH for acute coronary syndrome and healthy human without invasive treatment which was an advantage over other methods. This work not only proposed a new type of nanozymes, but also showed the multiple advantages of the apo-TF-MnOx NFs for the construction of biosensors. Thus, we believe that apo-TF-MnOx NFs with strong peroxidase-like activity can be employed as nanozymes and be widely applied in the fields of medicine and biological sensors.

Plant-Derived Vesicle-Like Nanoparticles: Clinical Application Exploration and Challenges

The utilization of plant-derived vesicle-like nanoparticles (PDVLNs) has shown effectiveness in the prevention/treatment of inflammatory-mediated diseases, malignancies, and immune-related diseases, such as acute liver injury, allergic asthma, gastric cancer and so on. This highlights the promising potential of PDVLNs as biotherapeutics. Furthermore, it should be noted that PDVLNs possess the ability to function as both natural and engineered drug carriers, making them an appealing option. This review aims to present the appropriate extraction methods of PDVLNs, summarize the applications of PDVLNs in different diseases, and provide an outlook on the prospects of PDVLNs. At the same time, the authors also express their discussion on the current limitations of PDVLNs.

Post-Assay Chemical Enhancement for Highly Sensitive Lateral Flow Immunoassays: A Critical Review

Lateral flow immunoassay (LFIA) has found a broad application for testing in point-of-care (POC) settings. LFIA is performed using test strips-fully integrated multimembrane assemblies containing all reagents for assay performance. Migration of liquid sample along the test strip initiates the formation of labeled immunocomplexes, which are detected visually or instrumentally. The tradeoff of LFIA's rapidity and user-friendliness is its relatively low sensitivity (high limit of detection), which restricts its applicability for detecting low-abundant targets. An increase in LFIA's sensitivity has attracted many efforts and is often considered one of the primary directions in developing immunochemical POC assays. Post-assay enhancements based on chemical reactions facilitate high sensitivity. In this critical review, we explain the performance of post-assay chemical enhancements, discuss their advantages, limitations, compared limit of detection (LOD) improvements, and required time for the enhancement procedures. We raise concerns about the performance of enhanced LFIA and discuss the bottlenecks in the existing experiments. Finally, we suggest the experimental workflow for step-by-step development and validation of enhanced LFIA. This review summarizes the state-of-art of LFIA with chemical enhancement, offers ways to overcome existing limitations, and discusses future outlooks for highly sensitive testing in POC conditions.

Ultrasensitive detection of exosomes by microchip electrophoresis combining with triple amplification strategies

The analysis of exosomes is significant as they can be used for various pathophysiological processes, especially cancer related intercellular communication. Therefore, a convenient, reliable, and sensitive detection method is urgently needed. Strand displacement amplification (SDA) and catalytic hairpin assembly (CHA) are two kinds of effective isothermal nucleic acid amplification methods. In this article, an efficient quantitative MCE method for detecting human breast cancer cell (MCF-7) exosomes assisted by triple amplification strategies combining cholesterol probe (Chol-probe) with SDA-CHA was first developed. CD63 aptamer was immobilized on the avidin magnetic beads to specifically capture exosomes and then Chol-probe with high affinity was spontaneously inserted into the exosome membrane, which was the first step of amplification strategy to improve detection sensitivity. After magnetic separation, Chol-probe could complement ssDNA and trigger SDA, producing a large number of DNA sequences (Ta) to trigger CHA, achieving SDA-CHA amplification. Under optimal conditions, the detection limit (LOD) for MCF-7 exosomes was as low as 26 particle/μL (S/N = 3). This method provides an effective approach for sensitive and accurate quantification of tumor exosomes, and can be expected to detect exosomes in clinical samples.

Recent Advances in the DNA-Mediated Multi-Mode Analytical Methods for Biological Samples

DNA-mediated nanotechnology has become a research hot spot in recent decades and is widely used in the field of biosensing analysis due to its distinctive properties of precise programmability, easy synthesis and high stability. Multi-mode analytical methods can provide sensitive, accurate and complementary analytical information by merging two or more detection techniques with higher analytical throughput and efficiency. Currently, the development of DNA-mediated multi-mode analytical methods by integrating DNA-mediated nanotechnology with multi-mode analytical methods has been proved to be an effective assay for greatly enhancing the selectivity, sensitivity and accuracy, as well as detection throughput, for complex biological analysis. In this paper, the recent progress in the preparation of typical DNA-mediated multi-mode probes is reviewed from the aspect of deoxyribozyme, aptamer, templated-DNA and G-quadruplex-mediated strategies. Then, the advances in DNA-mediated multi-mode analytical methods for biological samples are summarized in detail. Moreover, the corresponding current applications for biomarker analysis, bioimaging analysis and biological monitoring are introduced. Finally, a proper summary is given and future prospective trends are discussed, hopefully providing useful information to the readers in this research field.

A Label-Free and Antibody-Free Molecularly Imprinted Polymer-Based Impedimetric Sensor for NSCLC-Cells-Derived Exosomes Detection

In this study, a label-free and antibody-free impedimetric biosensor based on molecularly imprinting technology for exosomes derived from non-small-cell lung cancer (NSCLC) cells was established. Involved preparation parameters were systematically investigated. In this design, with template exosomes anchored on a glassy carbon electrode (GCE) by decorated cholesterol molecules, the subsequent electro-polymerization of APBA and elution procedure afforded a selective adsorption membrane for template A549 exosomes. The adsorption of exosomes caused a rise in the impedance of the sensor, so the concentration of template exosomes can be quantified by monitoring the impedance of GCEs. Each procedure in the establishment of the sensor was monitored with a corresponding method. Methodological verification showed great sensitivity and selectivity of this method with an LOD = 2.03 × 10³ and an LOQ = 4.10 × 10⁴ particles/mL. By introducing normal cells and other cancer cells derived exosomes as interference, high selectivity was proved. Accuracy and precision were measured, with an obtained average recovery ratio of 100.76% and a resulting RSD of 1.86%. Additionally, the sensors' performance was retained at 4 °C for a week or after undergoing elution and re-adsorption cycles seven times. In summary, the sensor is competitive for clinical translational application and improving the prognosis and survival for NSCLC patients.