Highly sensitive and stable self-powered biosensing for exosomes based on dual metal-organic frameworks nanocarriers

Two-dimensional nanozyme nanoarchitectonics customized electrochemical bio diagnostics and lab-on-chip devices for biomarker detection

Recent developments in nanomaterials and nanotechnology have advanced biosensing research. Two-dimensional (2D) nanomaterials or nanozymes, such as metal oxides, graphene and its derivatives, transition metal dichalcogenides, metal-organic frameworks, carbon-organic frameworks and MXenes, have garnered substantial attention in recent years owing to their unique properties, including high surface area, excellent electrical conductivity, and mechanical flexibility. Moreover, 2D nanozymes exhibit intrinsic enzyme-mimicking properties, including those of peroxidase, oxidase, catalase, and superoxide dismutase, making them well-suited for detecting biomarkers of interest and developing bio diagnostics at the point-of-care. Since 2D nanosystems offer ultra-high sensitivity, label-free detection, and real-time analysis, point-of-care testing and multiplexed biomarker detection, the demand is growing. Additionally, their biocompatibility and scalable fabrication make them cost-effective for widespread adoption. This review discusses the advantages of 2D nanozymes and their recent advancements in biosensing applications. This review summarizes the latest developments in 2D nanozymes, focusing on their synthesis, biocatalytic capabilities, and advancements in developing bio diagnostics and lab-on-chip devices for detecting cancer and non-cancer biomarkers. In addition, existing challenges and prospects in 2D nanozyme-based biosensors are identified, highlighting their biosensing potential and advocating for their expanded application in bio diagnostics and lab-on-chip devices.

Wash-Free Isolation and Quantification of Tumor-Derived Exosomes via In Situ-Formed Hydrogel

The isolation and detection of exosomes as tumor markers are of vital importance for the early diagnosis, therapeutic monitoring, and mechanistic studies of tumors. Here, exosomes derived from breast cancer cells were chosen as model targets, and a wash-free, enzyme-free, handheld mini centrifugation method based on hydrogels was developed to effectively isolate and detect breast cancer exosomes. Dual aptamers (CD63-T1 and EpCAM-T2) were employed to specifically recognize and capture breast cancer exosomes. This specific recognition triggered the formation of hybridization chain reaction (HCR) nanostructures on the captured exosomes through the interaction of hairpin 1 and the alginate complex (H1-Alg) and hairpin 2 (H2-Cy3). The interaction of Ca2+ and alginate enabled the in situ formation of a hydrogel on the exosome surface. Subsequent low-speed centrifugation using a handheld mini centrifuge facilitated the efficient isolation of the exosomes, thereby eliminating the need for tedious washing steps. Utilizing the classical chelation reaction of ethylene diamine tetraacetic acid (EDTA) with Ca2+, the hydrogel can be rapidly cleaved for enzyme-free release of exosomes. The method demonstrated excellent capture and release efficiencies of approximately 85% and 98%, respectively, for specific cancerous exosomes. Notably, the exosomes isolated by the hydrogel system retained excellent biological activity, making them suitable for further analysis and potential applications. Meanwhile, the highly sensitive detection of breast cancer exosomes based on this strategy could also be achieved with a lower limit of detection as low as 3.2 × 103 particles/mL. This work provides a novel and cost-effective strategy for the effective isolation and detection of tumor-derived exosomes, which can help to promote the subsequent application of exosomes in research.

3D DNA walkers integrated with self-reporting MOFs: Pioneering ratiometric electrochemical sensing for Staphylococcus aureus

The persistent global challenge of high incidence rates of foodborne bacterial pathogens continues to pose significant threats to both human health and public health security. Accurate determination of foodborne bacteria assumes paramount importance in effectively preventing and controlling related diseases. However, conventional bacterial detection methods often suffer limitations of cumbersome operation procedures, long time consumption, susceptibility to contamination or low sensitivity. The utilization of novel materials with direct self-reporting properties for developing ratiometric electrochemical biosensors offers a promising solution. Here, we present a ratiometric electrochemical aptasensor utilizing a magnetic 3D DNA walking machine and self-assembly of MOF for the sensitive detection of foodborne bacteria, with Staphylococcus aureus as the target model. A self-reporting MOF was employed as a signal probe, while [Fe(CN)6]3-/4- served as an inner reference probe. The introduction of target triggers the release of walker DNA from the walker/aptamer complexes, thereby initiating the DNA walking machine to produce numerous sticky sequences for further self-assembly of the linker probe-modified MOF on the magnetic beads surface. Quantification is accomplished by analyzing the ratio of the current signals. Attributed to the efficient magnetic separation, the self-reporting functionality of MOF, the cascade signal amplification strategy, and incorporation of a ratiometric signal output mode with self-calibration capability, this approach exhibits exceptional analytical performance and feasibility for testing complex samples. This study presents the first ratiometric aptasensor that integrates a DNA walking machine with a self-reporting MOF for the sensitive detection of bacteria. It offers a rapid, robust, and selective method for whole-cell detection without requiring complex sample preparation, demonstrating considerable potential in food safety monitoring and diagnosis of bacterial infections.

A dual-mode nanoplatform based on Cu2O@Au-Pt nanoenzyme and CHA-HCR DNA framework circuit for sensitive detection of CD122 and CD17

A Cu2O@Au-Pt nanoenzyme is prepared and integrated with a DNA nanocircuit to construct an electrochemical/colorimetric dual-mode sensing platform for the sensitive detection of CD122 and CD17, which are biomarkers for immune-related diseases.When CD122 is present, it triggers a catalyzed hairpin assembly (CHA) reaction, forming a double-stranded structure recognized by the DNA framework's "arms" (C-DNA), with methylene blue (MB) adsorbing onto it as an electron receptor. Methylene blue (MB) is adsorbed onto the double-stranded structure and introduced as a cathodic electron receptor. In the presence of the target CD17, it acts as a bridging molecule to engage in a hybridization chain reaction (HCR), producing HCR products that are specifically recognized by the other set of "arms" within the C-DNA, which captures abundant MB and generates a heightened response signal. MB can be electrochemically reduced to its reduced state to cause a change in solution color and an increase in RGB Blue values. This method offers a detection range of 0.0001-10,000 pM, with detection limits for CD122 and CD17 of 23.9 and 36.0 aM (S/N = 3) using the electrochemical method, and 26.2 and 26.6 aM (S/N = 3) in the colorimetric mode, respectively. This study presents a novel, reliable multi-target detection strategy for disease biomarkers.

Apical Anchoring and Cofactor Customizing To Achieve Ultrahigh Active Nanoenzymes for Removing O2 Interference in Glucose Electro-oxidation

Noble metal nanozymes (NMs) are promising alternatives to the fragile glucose oxidase (GOD), however, in all previously reported NMs, O2 consumes electrons from glucose by competing with electrodes, which remarkably limits the Faraday efficiency. The low NM utilization rate and sluggish mass transfer severely limit the electrocatalytic activity. Herein, we report the first Au nanozyme that can catalyze glucose electro-oxidation (GEO) via a distinctive O2 immune pathway with record-breaking mass activity based on apical anchoring and cofactor customization. Strategically, we design a cofactor of lipoic acid (ALA) that can accept electrons from glucose in preference to O2 for Au nanoparticles, and anchor AuNPs/ALA on top of sheared hydrophilic carbon nanotubes (T-SCNT/AuNPs/ALA). Mechanistically, ALA has highly reversible redox activity, and its reduction state is insensitive to O2, thus, it can mediate direct electron transfer between the electrode and AuNPs. In addition, compared to CNT/AuNPs, T-SCNT/AuNPs/ALA has a larger electrochemical surface area, lower charge transfer resistance, and superior hydrophilicity, which are favorable for improving the reaction rate and efficiency. Notably, this strategy can be used to design bilirubin oxidase mimics (T-SCNT/AuNPs/rutin), whose oxygen reduction activity significantly surpasses that of bilirubin oxidase. Consequently, compared to CNT/AuNPs, T-SCNT/AuNPs/ALA boosts the Faraday efficiency of GEO from 50% to 98%, shows a 755-fold increase in mass activity, and enables glucose biofuel cells to offer a 118-fold increase in power density. To the best of our knowledge, this is the first study to achieve a non-O2-interference GEO nanozyme by synergistically regulating the cofactor and catalytic interface and will guide the engineering of demand-specific electrocatalysts.

Machine Learning-Aided Intelligent Monitoring of Multivariate miRNA Biomarkers Using Bipolar Self-powered Sensors

Breast cancer has become the most prevalent form of cancer among women on a global scale. The early and timely diagnosis of breast cancer is of the utmost importance for improving the survival rate of patients with this disease. The occurrence of breast cancer is typically accompanied by the dysregulation of multiple microRNA (miRNA) expression profiles. Consequently, simultaneous detection of multiple miRNAs is vital for the early and accurate diagnosis of breast cancer. In this study, a bipolar self-powered sensor was developed for the simultaneous detection of miRNA-451 and miRNA-145 breast cancer biomarkers based on the specific catalytic properties of enzymes. Selenides with a microporous hollow cubic structure were designed and prepared, which can markedly enhance the enzyme load and activity, as well as detection sensitivity, due to their extensive surface area and three-dimensional porous channel. The designed bipolar self-powered sensor platform is integrated into the commercial chip, and the signal is presented in the smartphone interface, thereby enabling real-time and continuous monitoring. Furthermore, machine learning was utilized to predict miRNA detection, which encompasses numerous stages, including data collection, feature extraction, model training, and validation. In comparison to the limited sensing efficiency of self-powered biosensors driven by enzyme biofuel cells, our bipolar self-powered sensor achieved simultaneous quantitative analysis of multiple miRNA targets, thereby providing a robust tool for a more comprehensive understanding of miRNA function and its association with cancers.

Understanding the Electrochemical MOF Sensors in Detecting Cancer with Special Emphasis on Breast Carcinoma Biomarkers

Cancer is a disease that claims millions of lives each year, often because early symptoms go unnoticed, a situation which severely impacts society. Point-of-care biosensors using metal-organic frameworks (MOFs) have the power to transform cancer biomarker detection due to their exceptional structural and conductive properties. This review discusses the electrochemical sensor's design and development of electroactive MOF materials with mechanistic insights. It highlights recent advancements in utilizing MOF composites to effectively detect cancer biomarkers in real samples. The emphasis on the critical application of MOFs in breast cancer biomarker detection presents its importance for women's health. The review thoroughly examines the adjustable structures, porosity, and fabrication capabilities of MOFs in identifying cancer biomarkers. It provides a detailed analysis of methods to enhance the sensitivity and applicability of MOF composites for cancer detection. Furthermore, the review explores strategies to boost sensor performance, tackles existing challenges head-on, and outlines promising prospects. It emphasizes the urgent need for advanced cancer detection tools and aims to motivate researchers to develop innovative solutions.

High-power "nesting-doll" biofuel cell enabled by free-standing electrodes with inherent enzymatic function

Biofuel cell (BFC) is a type of green energy device based on the biocatalyst-mediated redox reaction. However, their relatively low performance has limited their wider application. Here, we proposed a novel all-in-one strategy to design the free-standing electrodes with the inherent enzyme-like activity and high conductivity, in which, the dynamic limitations of the enzyme-electrode interface were eliminated. This approach facilitated rapid electron transfer by removing the need to coat enzymes on the electrode. Furthermore, the enzyme-mimic characteristic enhanced the stability of BFC. Notably, the step-by-step "ionic corrosion-electrografting coordination" of Cu foam yielded the free-standing cathode, which exhibited excellent laccase-like activity. Concurrently, the in-situ loading of gold particles on the Ni foam can serve as an exemplary mimic of the glucose oxidase. Furthermore, a "nesting doll" nanozyme BFC device was developed, in which, the anode was placed inside the cathode to create a multi-shell coaxial configuration. The four-tier devices demonstrated an elevated open-circuit voltage of 1.7 V, and the output power density was 3639.0 μW cm⁻2 measured by resistance method, which was superior to that of the reported literatures. This study presents a pioneering approach to improving output performance and stability, thereby broadening the potential scope of BFC application.

Emerging biosensing platforms based on metal-organic frameworks (MOFs) for detection of exosomes as diagnostic cancer biomarkers: case study for the role of the MOFs

Exosomes, which are considered nanoscale extracellular vesicles (EVs), are secreted by various cell types and widely distributed in different biological fluids. They consist of multifarious bioactive molecules and use systematic circulation for their transfer to adjoining cells. This phenomenon enables exosomes to take part in intercellular and intracellular communications. They serve as novel and important cancer biomarkers due to their ability to be obtained from various biological fluids and the presence of nucleic acids, proteins, glycoconjugates, and lipids in their structure. The advancement of sensitive and selective exosome detection approaches continues to be a critical challenge that must be addressed. Metal-organic frameworks (MOFs) are a class of 2D and 3D synthetic organic and crystalline nanomaterials, forming through the self-assembly of organic linking molecules and metal ions. The exploration of MOF-based molecules in the recognition of exosomes is an essential aspect in the development of cutting-edge sensing platforms due to their tunable pore structures, excellent adsorption capabilities, and high surface area. Their advantages allow for the inclusion of a large number of electroactive molecules and biological elements, thereby enhancing their electrical conductivity and selectivity, respectively. The synergetic effect of nanomaterials and bioreceptors allows for efficient detection probes. In this review, the different roles of MOFs in the biosensing of exosomes are highlighted, providing a comprehensive understanding of biosensing approaches in this area. In addition, probes based on MOFs and different bioreceptors are investigated for detecting these important cancer biomarkers. The current gaps in this field and future perspectives are discussed.

A split organic photophotochemical transistor/vision sensing platform based on MNZ composite and ZIF-67/CuCoO nanospheres for ultra-sensitive detection of CEA

In this study, a novel organic photophotochemical transistor (OPECT) biosensing platform was proposed for dual-mode detection of CEA. The dual-mode detecting system is achieved benefit from the exceptional photoelectric performance of MIL-53(Fe) -NH2@ZnIn2S4 (MNZ) and the peroxidase enzyme (POD) activity of ZIF-67/Cu0.76Co2.24O4 (ZIF-67/CuCoO). Ab2- ZIF-67/CuCoO probe was immobilized on a 96-well plate by enzyme-linked immunosorbent assay, which accelerated the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) by hydrogen peroxide and thus successfully realized visual detection of CEA. Additionally, in OPECT biosensing mode, the oxidized form of TMB (oxTMB·) serves as a consumptive agents of the electron donor AA, which cause the photocurrent change of MNZ heterojunction, leading to a decrease in the channel current of poly (ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) organic transistor. The integration of nanobiocatalysts and the OPECT system demonstrates excellent detection performance for CEA, with a detection limit as low as 3.24 fg mL-1 and expanded their prospective applications for clinical detection of nucleic acids, proteins, and other tumor markers.

Portable Self-Powered/Colorimetric Dual-Mode Sensing Platform Based on Multifunctional Bioconjugates for Precise On-Site Detection of Acetamiprid

Neonicotinoid insecticides have been widely applied in modern agriculture to improve crop productivity, but their residues have adverse impacts on the environment and human health. Hence, to address these issues, a portable self-powered/colorimetric dual-mode sensing platform was developed for the simple, rapid, precise, and sensitive on-site detection of acetamiprid (ATM) residues in vegetables. In this case, a multifunctional bioconjugate with specific recognition capability, excellent enzyme-like activity, and loading capacity is the key to the sensing design. Using an Eppendorf (EP) tube as a miniaturized laboratory, the bioconjugates and the colorimetric test strip were integrated into the EP tube, and combined with a nanozyme-based self-powered sensing platform (with an area of 1.5 × 1.5 cm2), accurate on-site detection of ATM was achieved, with detection limits as low as 2.9 fg·mL-1 (self-powered method) and 31.5 fg·mL-1 (colorimetry), respectively. Notably, we simulated the actual insecticidal situation based on the field application concentration and quantified the pesticide residues in vegetables. The relative errors of our method and the standard high-performance liquid chromatography method were 0.15% (the self-powered method) and 1.8% (colorimetry), respectively. The portable dual-mode sensing platform with high sensitivity and accuracy opened up a new avenue for the development of on-site pesticide residue analysis in the next generation of agricultural products.

Nb2CTx-supported bimetallic NPs@ZIF-8 nanohybrid as ECL signal amplifier and peroxidase mimics for chromogranin a immunosensing in human serum and saliva

Niobium carbide (Nb2CTx), a key component of the MXene family renowned for its utilization in lithium-ion batteries and supercapacitors, remains largely underutilized in biosensing applications. This study introduces a notably sensitive and label-free dual-mode electrochemiluminescence (ECL) and colorimetric immunosensor to specifically detect chromogranin A (CgA) in biological fluids. Initially, AuAg bimetallic nanoparticles (BiMNPs) were synthesized using Nb2CTx as a reducing and supporting material. Furthermore, a promising approach has been put forward to increase the efficacy of the ECL of [Ru (bpy)3]2+ system by integrating the combined use of the zeolitic imidazolate framework-8 (ZIF-8) and the Nb2CTx coated bimetallic NPs. Incorporation produces a significant ~165-fold increase in electrochemical signals and a 4-fold improvement in ECL signals. In particular, BiMNPs@ZIF-8 nanohybrid exhibited significantly enhanced peroxidase-like activity compared to bare BiMNPs, demonstrating synergistic peroxidase enzyme mimicry. This improved activity makes it a potent catalyst for the H₂O₂-mediated oxidation of 3,3,5,5, tetramethylbenzidine (TMB), generating the characteristic blue color. Furthermore, the ECL method achieved a detection range of 0.001 to 1000 pg/mL with LOD of 0.11 fg/mL, while the colorimetric method achieved a LOD of 100 pg/mL and a linear range of 0.1 to 4000 ng/mL. The practical applicability of the sensor was validated by analyzing CgA levels in human serum and saliva samples.

Promoted electrochemical performance by MOF on MOF composite catalyst of microbial fuel cell: CuCo-MOF@ZIF-8 and the comparison between two-step hydrothermal method and dual-solution method

The microbial fuel cell (MFC) is a device that simultaneously achieves electricity generation and sewage degradation. In this study, a novel cathode catalyst metal-organic frameworks (MOFs) have been fabricated by two-step hydrothermal and dual-solution method (CuCo-MOF@ZIF-8). The synthesized trimetal MOFs exhibited a 3D badminton-like structure morphology and porosity. The results of the characterizations showed that CuCo-MOF@ZIF-8 possesses greater surface area porosity and novel functional groups. The Trimetal MOF-on-MOF mode not only demonstrated the stability of the structure but also enhanced its mechanism. Molecular mechanism analysis revealed changes in the organic ligand and metal binding site due to the transformation of Cu2+ to Cu+, Co2+ to Co3+, and Zn-N to Zn-O organic connection. Furthermore, differences between the two fabrication methods were compared. The solid-state single preparation (CuCo-MOF@ZIF-8-1), was synthesized using the two-step hydrothermal method; the liquid mixed preparation material (CuCo-MOF@ZIF-8-2), was synthesized using the dual-solution method; they exhibited completely different chemical structures and morphologies during material testing and characterization. The maximum output power density of CuCo-MOF@ZIF-8-2-MFC was 246.38 mW/m2, about 2.49 times of ZIF-8 (98.72 mW/m2). The output voltage of CuCo-MOF@ZIF-8-1-MFC was measured at 357 mV over 10 d, while that of CuCo-MOF@ZIF-8-2-MFC reached 365 mV over 12 d.

Entropy-driven self-assembled enzyme-DNA nanomatrix cascade DNAzyme-CRISPR/cas system for multiplexed enhancement of self-powered sensing platform for protein detection

Clustered Regularly Interspaced Short Palindromic Repeats and CRISPR-associated Proteins (CRISPR/Cas) system can accurately identify and cleave target DNA sequences, while the effective combination of DNA nanomatrix and entropy-driven self-assembled enzymes can significantly enhance the sensitivity, stability, and diversified functionality of sensors through highly ordered molecular arrangement and spontaneous efficient assembly processes. Herein, a carbon-encapsulated MoS2 hollow nanorod (C-MoS2) with excellent conductivity and multiple active sites is used to construct bioanode of biofuel cell by integrating it with an entropy-driven self-assembled enzyme-DNA nanomatrix cascade DNAzyme-CRISPR/Cas system. When thrombin binds aptamer, it exposes the trigger strand on the anode, initiating chain displacement. This activates DNAzyme, triggering a cascade reaction that cleaves and releases the probe strand. The probe then binds CrRNA, forming a multimeric complex with Cas protein.When non-specific cleavage of the single strand occurs, it leads to the release of glucose oxidase (GOD) from the DNA matrix and causes a significant decrease in the value of the system's open-circuit voltage (EOCV). The EOCV values show a good negative correlation with the concentration of thrombin (TB) in the range of 0.00001-100 nM, achieving a limit of detection of 3.55 fM (S/N = 3).

Ultrasensitive self-powered biosensor with facile chemical signal amplification strategy using hydrogen peroxide-triggered silver oxidation reaction

The amplification strategies used for self-powered biosensor based on biofuel cell (BFC-SPB) need to be further developed. Because the currently developed strategies utilized the complicated hybridization of DNA or poorly readable current signal of capacitors for amplification, which limits the practical application in public health emergencies. Here, we present a facile chemical amplification strategy for BFC-SPB. The 5-min amplification was triggered by simply adding H2O2 solution dropwise to the sensing cathode after the formation of the immune sandwich. The Ag NP of immunoprobe were oxidized to Ag(I), which can be served as the electron acceptor of the cathode. The amount of immunoprobe was positively correlated with that of the antigen, resulting in corresponding and high concentration of Ag(I) after the amplification, which enhanced the ability of the cathode as the electron acceptor. Meanwhile the glucose oxidation reaction (GOR) was performed on the bioanode modified with glucose oxidase (GOx). After assembling the bioanode and sensing cathode, the open circuit voltage of the BFC-SPB, measured by digital multimeter, distinctly rised with the elevated concentration of the antigen. To demonstrate the proof of concept, immunoglobulin G (IgG), selecting as a model analyte, was sensitively detected using this method. Result indicated that the limit of detection was 4.4 fg mL-1 (0.03 amol mL-1) in the linear range of 1 pg mL-1-10 μg mL-1. This work initiates a brand-new way of chemical amplification strategy for BFC-SPB, and offers a promising platform for practical applications.

Dual-electrode signal amplification self-powered biosensing platform based on nanozyme boosting target-induced DNA nanospace array for ultrasensitive detection of sugarcane Pokkah Boeng disease pathogenic bacteria

Sugarcane is a crop with significant economic importance worldwide. However, pokkah boeng disease poses a serious threat to its production and the sustainable development. There is a pressing necessity for precise and portable detection methods. We develop a dual-electrode signal amplification biosensing platform, for highly sensitive detection of sugarcane pokkah boeng disease pathogenic bacteria. This innovative platform integrates highly catalytic AuNPs/Mn3O4 nanozymes with N-GDY, along with a target-induced development of DNA nanostructure arrays. AuNPs/N-GDY serves as dual electrode substrates, and AuNPs/Mn3O4 nanozymes are surface-loaded as the bioanode. The biocathode is constructed by introducing DNA nanospace arrays onto the electrode through target-induced methods. [Ru(NH3)6]3+ is embedded into the nucleic acid double-helix scaffold via electrostatic adsorption, generating an EOCV signal that is strongly correlated with the target concentration. To further enhance sensitivity, the detection platform is combined with a capacitor to amplify the detection signal, utilizing its high power density, which results in a 22.5-fold increase in sensitivity. The method offers a linear detection range of 0.0001 to 10,000 pM and an detection limit of 32.5 aM (S/N = 3). This method supplies a novel approach for real-time monitoring and competent oversight of pokkah boeng disease pathogenic bacteria.

Simple strategy for dual-responsive ratio electrochemical-colorimetric detection of nitrite in food and environment

A dual-responsive ratio electrochemical-colorimetric method for nitrite (NO2-) is established based on the combination of nanoenzyme (Mn3O4) catalysis with diazotization reactions. The Mn3O4 can oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue TMBox. The NO2- induces the diazotization reaction of TMBox, leading to a decrease of  the signal at 652 nm and the generation of a new signal from diazotized TMBox at 445 nm. Furthermore, the presence of NO2- reduces the electrochemical oxidation signal of TMB and simultaneously provides its electrochemical signal. Compared with traditional single-mode detection, dual-mode detection offers higher sensitivity, lower detection limits, and better interference resistance. The inherent advantages of this method make it feasible to detect NO2- in real samples, offering broad prospects for applications in food safety and environmental monitoring.

On-demand controlled bidirectional DNAzyme path for ultra-sensitive heavy metal ion detection

A bidirectional self-powered biosensor is constructed for the quasi-simultaneous detection of Pb2+ and Hg2+ based on MoS2@CuS heterostructures as an accelerator and hybridization chain reaction (HCR) as a signal amplification strategy. MoS2@CuS heterostructures significantly facilitate electron transfer between glucose and bioelectrodes, thereby greatly improving the detection signal of self-powered biosensors. This novel biosensor employs the unique sequences of DNAzymes to isolate Pb2+ and Hg2+ by the cleavage effect and thymine (T)-Hg2+-thymine (T) structures, respectively. In the process, Pb2+ cuts the sequence of DNAzyme at the bioanode to trigger glucose oxidation to monitor Pb2+. The as-formed T-Hg2+-T structures activate HCR to reduce [Ru(NH3)6]3+ to detect Hg2+ at the biocathode. It is noteworthy that this biosensor not only realizes Pb2+ or Hg2+ detection in a single-electrode, respectively, but also can quasi-simultaneously detect both Pb2+ and Hg2+ in the bioanode and the biocathode. The novel self-powered biosensor identifies Pb2+ in the range of 106 fM to 10 fM with a limit of detection (LOD) of 3.1 fM and Hg2+ in the range of 106 fM to 1 fM with an LOD of 0.33 fM.

Self-Powered FEN1 Biosensor Based on Accelerated CRISPR/Cas Trans-Cleavage around Porous Fe3O4 Nanoparticles

Flap endonuclease 1 (FEN1) is a structure-specific endonuclease that plays a critical role in the maintenance of genome integrity. In this work, we demonstrate a novel self-powered electrochemical FEN1 biosensor for potential applications in molecular diagnosis. Porous Fe3O4 nanoparticles are first prepared, and single-strand DNA probes are absorbed on the surface of the nanoparticles. Thus, electrochemical species of [Fe(CN)6]3- can be encapsulated inside the porous nanoparticles with the molecular gate of negatively charged DNA. On the other hand, a dumbbell structured DNA probe with 5' flap is designed. FEN1 is able to cleave the flap and activate the CRISPR/Cas system for the digestion of single-stranded DNA around Fe3O4 nanoparticles. As a result, the leakage of [Fe(CN)6]3- contributes to an enhanced electrochemical response, which can be used to reveal the level of FEN1. The high sensitivity of this biosensor is due to the application of porous nanomaterials and Mn2+ accelerated CRISPR/Cas cleavage. It succeeds in detection of biological samples and screening of FEN1 inhibitors. Therefore, this proposed method has potential applications in the early diagnosis of diseases and drug discovery.

Sensitive and reliable lab-on-paper biosensor for label-free detection of exosomes by electrochemical impedance spectroscopy

A new, sensitive, and cost-effective lab-on-paper-based immunosensor was designed based on electrochemical impedance spectroscopy (EIS) for the detection of exosomes. EIS was selected as the determination method since there was a surface blockage in electron transfer by binding the exosomes to the transducer. Briefly, the carbon working electrode (WE) on the paper electrode (PE) was modified with gold particles (AuPs@PE) and then conjugated with anti-CD9 (Anti-CD9/AuPs@PE) for the detection of exosomes. Variables involved in the biosensor design were optimized with the univariate mode. The developed method presents the limit of detection of  8.7 × 102 exosomes mL-1, which is lower than that of many other available methods under the best conditions. The biosensor was also tested with urine samples from cancer patients with high recoveries. Due to this  a unique, low-cost, biodegradable technology is presented that can directly measure exosomes without labeling them for early cancer or metastasis detection.

Recent advances in microbial fuel cell-based self-powered biosensors: a comprehensive exploration of sensing strategies in both anode and cathode modes

With the rapid development of society, it is of paramount importance to expeditiously assess environmental pollution and provide early warning of toxicity risks. Microbial fuel cell-based self-powered biosensors (MFC-SPBs) have emerged as a pivotal technology, obviating the necessity for external power sources and aligning with the prevailing trends toward miniaturization and simplification in biosensor development. In this case, vigorous advancements in MFC-SPBs have been acquired in past years, irrespective of whether the target identification event transpires at the anode or cathode. The present article undertakes a comprehensive review of developed MFC-SPBs, categorizing them into substrate effect and microbial activity effect based on the nature of the target identification event. Furthermore, various enhancement strategies to improve the analytical performance like accuracy and sensitivity are also outlined, along with a discussion of future research trends and application prospects of MFC-SPBs for their better developments.

Recent Advances on the Metal-Organic Frameworks-Based Biosensing Methods for Cancer Biomarkers Detection

Sensitive and selective detection of cancer biomarkers is crucial for early diagnosis and treatment of cancer, one of the most dangerous diseases in the world. Metal-organic frameworks (MOFs), a class of hybrid porous materials fabricated through the assembly of metal ions/clusters and organic ligands, have attracted increasing attention in the sensing of cancer biomarkers, due to the advantages of adjustable size, high porosity, large surface area and ease of modification. MOFs have been utilized to not only fabricate active sensing interfaces but also arouse a variety of measurable signals. Several representative analytical technologies have been applied in MOF-based biosensing strategies to ensure high detection sensitivity toward cancer biomarkers, such as fluorescence, electrochemistry, electrochemiluminescence, photochemistry and colorimetric methods. In this review, we summarized recent advances on MOFs-based biosensing strategies for the detection of cancer biomarkers in recent three years based on the categories of metal nodes, and aimed to provide valuable references for the development of innovative biosensing platform for the purpose of clinical diagnosis.

Host-Guest Interaction Mediated Perovskite@Metal-Organic Framework Z-Scheme Heterojunction Enabled Paper-Based Photoelectrochemical Sensing

Exploring the high-performance photoelectronic properties of perovskite quantum dots (QDs) is desirable for paper-based photoelectrochemical (PEC) sensing;however, challenges remain in improving their stability and fundamental performance. Herein, a novel Z-scheme heterostructure with host-guest interaction by the confinement of CH3NH3PbBr3 QDs within Cu3(BTC)2 metal-organic framework (MOF) crystal (MAPbBr3@Cu3(BTC)2) is successfully constructed on the paper-based PEC device for ultrasensitive detection of Ochratoxin A (OTA), with the assistance of the exciton-plasmon interaction (EPI) effect. The host-guest interaction is estabilished by encapsulating MAPbBr3 QDs as guests within Cu3(BTC)2 MOF as a host, which prevents MAPbBr3 QDs from being damaged in the polar system, offering access to long-term stability with high-performance PEC properties. Benefiting from the precise alignment of energy levels, the photogenerated charge carriers can migrate according to the Z-scheme charge-transfer pathway under the driving force of the internal electric field, achieving a high photoelectric conversion efficiency. Upon OTA recognition, the EPI effect is activated to modulate the exciton response in MAPbBr3 QDs by accelerating radiative decay, finally achieving sensitive OTA sensing with a detection limit of 0.017 pg mL-1. We believe this work renders new insight into designing host-guest Z-scheme heterojunctions in constructing the paper-based PEC sensing platforms for environmental monitoring.

Glucose-based biofuel cells and their applications in medical implants: A review

In glucose biofuel cells (G-BFCs), glucose oxidation at the anode and oxygen reduction at the cathode yield electrons, which generate electric energy that can power a wide range of electronic devices. Research associated with the development of G-BFCs has increased in popularity among researchers because of the eco-friendly nature of G-BFCs (as related to their construction) and their evolution from inexpensive bio-based materials. In addition, their excellent specificity towards glucose as an energy source, and other properties, such as small size and weight, make them attractive within various demanding applied environments. For example, G-BFCs have received much attention as implanted devices, especially for uses related to cardiac activities. Envisioned pacemakers and defibrillators powered by G-BFCs would not be required to have conventional lithium batteries exchanged every 5-10 years. However, future research is needed to develop G-BFCs demonstrating more stable power consistency and improved lifespan, as well as solving the challenges in converting laboratory-made implantable G-BFCs into implanted devices in the human body. The categorization of G-BFCs as a subcategory of different biofuel cells and their performance is reviewed in this article.

Pushing Forward the DNA Walkers in Connection with Tumor-Derived Extracellular Vesicles

Extracellular vesicles (EVs) are microparticles released from cells in both physiological and pathological conditions and could be used to monitor the progression of various pathological states, including neoplastic diseases. In various EVs, tumor-derived extracellular vesicles (TEVs) are secreted by different tumor cells and are abundant in many molecular components, such as proteins, nucleic acids, lipids, and carbohydrates. TEVs play a crucial role in forming and advancing various cancer processes. Therefore, TEVs are regarded as promising biomarkers for the early detection of cancer in liquid biopsy. However, the currently developed TEV detection methods still face several key scientific problems that need to be solved, such as low sensitivity, poor specificity, and poor accuracy. To overcome these limitations, DNA walkers have emerged as one of the most popular nanodevices that exhibit better signal amplification capability and enable highly sensitive and specific detection of the analytes. Due to their unique properties of high directionality, flexibility, and efficiency, DNA walkers hold great potential for detecting TEVs. This paper provides an introduction to EVs and DNA walker, additionally, it summarizes recent advances in DNA walker-based detection of TEVs (2018-2024). The review highlights the close relationship between TEVs and DNA walkers, aims to offer valuable insights into TEV detection and to inspire the development of reliable, efficient, simple, and innovative methods for detecting TEVs based on DNA walker in the future.

A novel olfactory biosensor based on ZIF-8@SWCNT integrated with nanosome-AuNPs/Prussian blue for sensitive detection of hexanal

Hexanal is considered as an important volatile compound indicator for the assessment of freshness and maturity of foods. Therefore, sensitive and stable monitoring of hexanal is highly desired. Herein, an efficient receptor immobilization strategy based on ZIF-8@ Single-walled carbon nanotube (SWCNT) and nanosomes-AuNPs/Prussian blue (PB) was proposed for the development of olfactory biosensors. ZIF-8@SWCNT as dual support materials provided a high density of active sites for nanosomes loading. Moreover, the co-electrodeposition of nanosomes-AuNPs and PB on the sensor interface effectively amplified the electrochemical signal and maintained the activity of the receptor. The combination of ZIF-8@SWCNT with AuNPs/PB imparts excellent sensing performance of the biosensor with a wide detection range of 10-16-10-9 M, a low detection limit of 10-16 M for hexanal, and a long storage stability of 15 days. These results indicate that our biosensor can be a powerful tool for versatile applications in food and other related industries.

A sensitive and versatile electrochemical sensor based on hybridization chain reaction and CRISPR/Cas12a system for antibiotic detection

A sensitive electrochemical platform was constructed with NH2-Cu-MOF as electrochemical probe to detect antibiotics using CRISPR/Cas12a system triggered by hybridization chain reaction (HCR). The sensing system consists of two HCR systems. HCR1 occurred on the electrode surface independent of the target, generating long dsDNA to connect signal probes and producing a strong electrochemical signal. HCR2 was triggered by target, and the resulting dsDNA products activated the CRISPR/Cas12a, thereby resulting in effective and rapid cleavage of the trigger of HCR1, hindering the occurrence of HCR1, and reducing the number of NH2-Cu-MOF on the electrode surface. Eventually, significant signal change depended on the target was obtained. On this basis and with the help of the programmability of DNA, kanamycin and ampicillin were sensitively detected with detection limits of 60 fM and 10 fM (S/N = 3), respectively. Furthermore, the sensing platform showed good detection performance in milk and livestock wastewater samples, demonstrating its great application prospects in the detection of antibiotics in food and environmental water samples.

Four birds with one stone: Aggregation-induced emission-type zeolitic imidazolate framework-8 based bionic nanoreactor for portable detection of olaquindox in environmental water and swine urine by smartphone

The abuse of olaquindox (OLA) as both an antimicrobial agent and a growth promoter poses significant threats to the environment and human health. While nanoreactors have proven effective in hazard detection, their widespread adoption has been hindered by tedious chemical processes and limited functionality. In this study, we introduce a novel green self-assembly strategy utilizing invertase, horseradish peroxidase, antibodies, and gold nanoclusters to form an aggregation-induced emission-type zeolitic imidazolate framework-8 nanoreactor. The results demonstrate that the lateral flow immunoassay not only allows for qualitative naked eye detection but also enables optical analysis through the fluorescence generated by aggregated gold nanoclusters and enzyme-catalyzed enhancement of visible colorimetric signals. To accommodate more detection scenarios, the photothermal effects and redox reactions of the nanoreactor can fulfill the requirements of thermal sensing and electrochemical analysis for smartphone applications. Remarkably, the proposed approach achieves a detection limit 17 times lower than conventional methods. Besides, the maximum linear range spans from 0.25 to 5 μg/L with high specificity, and the recovery is 85.2-112.9% in environmental water and swine urine. The application of this high-performance nanoreactor opens up avenues for the construction of multifunctional biosensors with great potential in monitoring hazardous materials.

Weak Value Amplification-Based Biochip for Highly Sensitive Detection and Identification of Breast Cancer Exosomes

Exosomes constitute an emerging biomarker for cancer diagnosis because they carry multiple proteins that reflect the origins of the parent cell. The highly sensitive detection of exosomes is a crucial prerequisite for the diagnosis of cancer. In this study, we report an exosome detection system based on quantum weak value amplification (WVA). The WVA detection system consists of a reflection detection light path and a Zr-ionized biochip. Zr-ionized biochips effectively capture exosomes through the specific interaction between zirconium dioxide and the phosphate groups on the lipid bilayer of exosomes. Aptamer-modified gold nanoparticles (Au NPs) are then used to specifically recognize proteins on exosomes to enhance the detection signal. The sensitivity and resolution of the detection system are 2944.07 nm/RIU and 1.22 × 10-5 RIU, respectively. The concentration of exosomes can be directly quantified by the WVA system, ranging from 105-107 particles/mL with the detection limit of 3 × 104 particles/mL. The use of Au NPs-EpCAM for the specific enhancement of breast cancer MDA-MB-231 exosomes is demonstrated. The results indicate that the WVA detection system can be a promising candidate for the detection of exosomes as tumor markers.

Multiple signal amplification strategy induced by biomarkers of lung cancer: A self-powered biosensing platform adapted for smartphones

Lung cancer is a major malignant cancer with low survival rates, and early diagnosis is crucial for effective treatment. Herein, a biosensing platform that is self-powered derived from a capacitor-coupled EBFC has been developed for ultra-sensitive real-time identification of microRNA-21 (miRNA-21) with the assistance of a mobile phone. The flexible substrate of the platform is prepared on a carbon paper modified with graphdiyne and gold nanoparticles. The biosensor employs DNAzyme-mediated dual strand displacement amplification, which enhances the signal output intensity of the EBFC and improves selectivity. The coupling of the capacitor with the EBFC significantly amplifies the sensing signal, causing a 10.6-fold surge in current respond and further improving the sensitivity of the sensing platform. The established detection approach demonstrates a linear relationship varied from 0.0001 to 10,000 pM, with a sensitivity down to 32.3 aM as the minimum detectable limit, which has been effectively utilized for detecting miRNA-21 in practical samples. This sensing system provides strong support for the construction of portable detection devices, and the strategy of the platform construction provides an effective method for ultra-sensitive and accurate detection of miRNA, holding great potential in clinical diagnosis, prognosis evaluation, and drug screening for cancer.

Fabrication of NiCo Bimetallic MOF Films on 3D Foam with Assistance of Atomic Layer Deposition for Non-Invasive Lactic Acid Sensing

Lactic acid (LA) is an important downstream product of glycolysis in living cells and is abundant in our body fluids, which are strongly associated with diseases. The development of enzyme-free LA sensors with high sensitivity and low consumption remains a challenge. 2D metal-organic frameworks (MOFs) are considered to be promising electrochemical sensing materials and have attracted much attention in recent years. Compared to monometallic MOFs, the construction of bimetallic MOFs (BMOFs) can obtain a larger specific surface area, thereby increasing the exposed active site. 3D petal-like NixCoy MOF films on nickel foams (NixCoy BMOF@Ni foams) are successfully prepared by combining atomic layer deposition-assisted technology and hydrothermal strategy. The established NixCoy BMOF@Ni foams demonstrate noticeable LA sensing activity, and the study is carried out on behalf of the Ni1Co5 BMOF@Ni foam, which has a sensitivity of up to 9030 μA mM-1 cm-2 with a linear range of 0.01-2.2 mM and the detection limit is as low as 0.16 μM. Additionally, the composite has excellent stability and repeatability for the detection of LA under a natural air environment with high accuracy and reliability. Density functional theory calculation is applied to study the reaction process between composites and LA, and the result suggests that the active site in the NiCo BMOF film favors the adsorption of LA relative to the active site of monometallic MOF film, resulting in improved performance. The developed composite has a great potential for the application of noninvasive LA biosensors.

Emerging Trends of Bilirubin Oxidases at the Bioelectrochemical Interface: Paving the Way for Self-Powered Electrochemical Devices and Biosensors

Bilirubin oxidases (BODs) [EC 1.3.3.5 - bilirubin: oxygen oxido-reductase] are enzymes that belong to the multicopper oxidase family and can oxidize bilirubin, diphenols, and aryl amines and reduce the oxygen by direct four-electron transfer from the electrode with almost no electrochemical overpotential. Therefore, BOD is a promising bioelectrocatalyst for (self-powered) biosensors and/or enzymatic fuel cells. The advantages of electrochemically active BOD enzymes include selective biosensing, biocatalysis for efficient energy conversion, and electrosynthesis. Owing to the rise in publications and patents, as well as the expanding interest in BODs for a range of physiological conditions, this Review analyzes scientific literature reports on BOD enzymes and current hypotheses on their bioelectrocatalysis. This Review evaluates the specific research outcomes of the BOD in enzyme (protein) engineering, immobilization strategies, and challenges along with their bioelectrochemical properties, limitations, and applications in the fields of (i) biosensors, (ii) self-powered biosensors, and (iii) biofuel cells for powering bioelectronics.

Dual-mode self-powered photoelectrochemical and colorimetric determination of procalcitonin accomplished by multienzyme-expressed Ni4Cu2 bimetallic hollow nanospheres and spherical nanoflower-MoS2/Cu2ZnSnS4/Bi2S3

Bacterial infections, viral infections and autoimmune diseases pose a considerable threat to human health. Procalcitonin (PCT) has emerged as a biomarker for the detection of these diseases. To ensure accurate and reliable results, we propose a dual-mode approach that incorporates self-validation and self-correction mechanisms. Herein, we develop a dual-mode self-powered photoelectrochemical (PEC) and colorimetric sensor to determine PCT. The self-powered PEC sensor was constructed with a photoanode of spherical nanoflower-MoS2/Cu2ZnSnS4/Bi2S3 material and a photocathode of CuInS2 material. Ni4Cu2 bimetallic hollow nanospheres (BHNs) possess superoxide dismutase and catalase performance, which facilitate superoxide anion radical (·O2-) and H2O2 circulating generation, promoting the separation of photogenerated electrons and holes to amplify photocurrent signal. Thus Ni4Cu2 BHNs is used as a marker material for PEC sensor. Meanwhile, in colorimetric mode, Ni4Cu2 BHNs converts blue oxTMB to a colourless TMB for colorimetric detection of PCT. Based on this principle, dual-mode determination of PCT with high sensitivity is achieved. The dual-mode method not only demonstrates outstanding properties and practicability, but also presents an effective, highly efficient and reliable method for detecting PCT.

Ratiometric Electrochemiluminescence of Zirconium Metal-Organic Framework as a Single Luminophore for Sensitive Detection of HPV-16 DNA

This study developed a new zirconium metal-organic framework (MOF) luminophore named Zr-DPA@TCPP with dual-emission electrochemiluminescence (ECL) characteristics at a resolved potential. First, Zr-DPA@TCPP with a core-shell structure was effectively synthesized through the self-assembly of 9,10-di(p-carboxyphenyl)anthracene (DPA) and 5,10,15,20-tetra(4-carboxyphenyl)porphyrin (TCPP) as the respective organic ligands and the Zr cluster as the metal node. The reasonable integration of the two organic ligands DPA and TCPP with ECL properties into a single monomer, Zr-DPA@TCPP, successfully exhibited synchronous anodic and cathodic ECL signals. Besides, due to the impressively unique property of ferrocene (Fc), which can quench the anodic ECL but cannot affect the cathodic ECL signal, the ratiometric ECL biosensor was cleverly designed by using the cathode signal as an internal reference. Thus, combined with DNA recycle amplification reactions, the ECL biosensor realized sensitive ratiometric detection of HPV-16 DNA with the linear range of 1 fM-100 pM and the limit of detection (LOD) of 596 aM. The distinctive dual-emission properties of Zr-DPA@TCPP provided a new idea for the development of ECL luminophores and opened up an innovative avenue of fabricating the ratiometric ECL platform.

Towards a REASSURED reality: A less-is-more electronic design strategy for self-powered glucose test

Sensing strategies adopting minimal electronic systems help in realizing REASSURED diagnostic tests. However, the challenge in developing such strategies escalates with demand in power and electronics during pursuit of reliable and accurate sensing. Herein, we present an electronic design strategy using a smart strip, operating with power generated from 3.5 μL of serum sample, to reveal glucose concentration through a response preserved in a capacitor. Further, by integrating an NFC tag alongside the strip, we devised a self-powered glucose measuring card, mobile-glucocard (or mGlucocard) for retrieving this stored digital response using smartphone, enabling 'connected mobile-health diagnostics'. The response from our device relates linearly to glucose concentration offering a sensitivity of 11.3 mV/mM and good correlation (R = 0.974) with colorimetric reference method. Interestingly, the design strategy uses only four components - two resistors, diode, and capacitor - of simple architecture likely transferable to printed technologies to deliver advanced self-powered sustainable devices.

Faraday cage-type self-powered immunosensor based on hybrid enzymatic biofuel cell

Self-powered immunosensors (SPIs) based on enzymatic biofuel cell (EBFC) have low sensitivity and poor stability due to the high impedance of the immune sandwich and the vulnerability of enzymes to environmental factors. Here, we applied the Faraday cage-type sensing mode on a hybrid biofuel cell (HBFC)-based SPI for the first time, which exhibited high sensitivity and stability. Cytokeratin 19 fragment (CYFRA 21-1) was used as a model analyte. Au nanoparticle-reduced graphene oxide (Au-rGO) composite was used as the supporting matrix for immunoprobe immobilized with detection antibody and glucose dehydrogenase (GDH), also the builder for Faraday cage structure on the bioanode in the presence of antigen. After the combination of immunoprobe, antigen, and the antibody on the bioanode, the Faraday cage was constructed in case the AuNP-rGO was applied as a conductive cage for electron transfer from GDH to the bioanode without passing through the poorly conductive protein. With the assistance of the Faraday cage structure, the impedance of the bioanode decreased significantly from 4000 to 300 Ω, representing a decline of over 90%. The sensitivity of the SPI, defined as the changes of open circuit voltage (OCV) per unit concentration of the CYFRA 21-1, was 68 mV [log (ng mL-1)]-1. In addition, Fe-N-C was used as an inorganic cathode material to replace enzyme for oxygen reduction reaction (ORR), which endowed the sensor with 4-week long-term stability. This work demonstrates a novel sensing platform with high sensitivity and stability, bringing the concept of hybrid biofuel cell-based self-powered sensor.

Recent advances in metal-organic frameworks: Synthesis, application and toxicity

Metal-organic frameworks (MOFs) are a new class of crystalline porous hybrid materials with high porosity, large specific surface area and adjustable channel structure and biocompatibility, which are being investigated with increasing interest for energy storage and conversion, gas adsorption/separation, catalysis, sensing and biomedicine. However, the practical applications of MOFs make them release into the environment inevitable, posing a threat to humans and organisms. In this article, we cover advances in the currently available MOFs synthesis methods and the emerging applications of MOFs, especially in the biomedical field (therapeutic agents and bioimaging). Additionally, after evaluating the current status of main exposure routes and affecting factors in the field of MOFs-toxicity, the molecular mechanism is also clarified and identified. Knowledge gaps are identified from such a summarization and frontier development are explored for MOFs. Afterwards, we also present the limitations, challenges, and future perspectives in the study of the entire life cycle of MOFs. This review emphasizes the need for a more targeted discussion of the latest, widely used and effective versatile material class in order to exploit the full potential of high-performance and non-toxicity MOFs in the future.

Rational Integration of SnMOF/SnO2 Hybrid on TiO2 Nanotube Arrays: An Effective Strategy for Accelerating Formaldehyde Sensing Performance at Room Temperature

Formaldehyde is ubiquitously found in the environment, meaning that real-time monitoring of formaldehyde, particularly indoors, can have a significant impact on human health. However, the performance of commercially available interdigital electrode-based sensors is a compromise between active material loading and steric hindrance. In this work, a spaced TiO2 nanotube array (NTA) was exploited as a scaffold and electron collector in a formaldehyde sensor for the first time. A Sn-based metal-organic framework was successfully decorated on the inside and outside of TiO2 nanotube walls by a facile solvothermal decoration strategy. This was followed by regulated calcination, which successfully integrated the preconcentration effect of a porous Sn-based metal-organic framework (SnMOF) structure and highly active SnO2 nanocrystals into the spaced TiO2 NTA to form a Schottky heterojunction-type gas sensor. This SnMOF/SnO2@TiO2 NTA sensor achieved a high room-temperature formaldehyde response (1.7 at 6 ppm) with a fast response (4.0 s) and recovery (2.5 s) times. This work provides a new platform for preparing alternatives to interdigital electrode-based sensors and offers an effective strategy for achieving target preconcentrations for gas sensing processes. The as-prepared SnMOF/SnO2@TiO2 NTA sensor demonstrated excellent sensitivity, stability, reproducibility, flexibility, and convenience, showing excellent potential as a miniaturized device for medical diagnosis, environmental monitoring, and other intelligent sensing systems.

Capsulation of EBTAC into ZIF-8 for the development of a signal-on fluorescent biosensor to detect alkaline phosphatase

Diseases such as liver cancer, extrahepatic biliary obstruction and osteocarcinoma are closely associated with the abnormal level of alkaline phosphatase (ALP). Hence, it is essential to develop a convenient assay to detect ALP activity. Herein, a novel signal-on fluorescent biosensor on account of the fluorescence signal of the aggregation-induced emission (AIE) fluorochrome 2,2',2'',2'''-((ethene-1,1,2,2-tetrayltetrakis(benzene-4,1-diyl))tetrakis(oxy))tetraacetic acid (EBTAC) encapsulated zeolitic imidazolate framework-8 (ZIF-8@EBTAC) was designed to monitor ALP. Due to the aggregation-induced emission of EBTAC, the synthetic ZIF-8@EBTAC shows robust fluorescence. Once pyrophosphate (ppi) was added, its complexation with Zn2+ in ZIF-8 triggered the collapse of the ZIF-8 framework, releasing encapsulated EBTAC molecules and restoring to free state, leading to the dramatical decrease in fluorescence. ALP could catalyze the hydrolysis of ppi to phosphate (pi), which is difficult to bind to Zn2+ and has little effect on the fluorescence of ZIF-8@EBTAC. Therefore, with the assistance of the substrate ppi, the ultimate fluorescence of ZIF-8@EBTAC was positively related with ALP activity. The constructed biosensor was able to monitor the ALP activity well from 0.01 to 100 U L-1, and a detection limit of 0.01 U L-1 was achieved. Based on the ability of EBTAC serving as a fluorescent probe with aggregation-induced luminescence properties, this proposed design can be applied to diverse targets and provide new ideas for the establishment of fluorescent biosensors.

Flexible Self-Powered Sensing System Based on Novel DNA Circuit Strategy and Graphdiyne for Thalassemia Gene by Rapid Naked-Eye Tracking and Open-Circuit Voltage

Based on the controllable instantaneous self-assembly ability of long-chain branched DNA nanostructures and the synergistic effect between nucleic acid amplification without enzymes, a highly sensitive and highly specific self-powered biosensing platform is developed. Two-dimensional graphdiyne is prepared, modified on flexible carbon cloth, and then functionalized with gold nanoparticles. When DNA mi-tubes are applied on it, target thalassemia gene CD122 triggers a dual-catalytic hairpin assembly reaction. The generated nanoscale DNA is precisely captured by the DNA mi-tube, exposing binding sites and activating the hybridization chain reaction to form long-chain branched DNA. Double-stranded DNA, along with dendritic DNA carrying a large number of guanine bases, precisely captures the signal molecule methylene blue (MB), generating a significant electrochemical signal. The redox reaction of MB also causes a proportional change in the system's color, achieving a colorimetric detection functionality. An efficient dual-mode self-powered sensing platform, therefore, is established for detecting the thalassemia gene CD122. The linear response range of target concentration to open-circuit voltage and RGB Blue value is 0.0001-10,000 pM. The detection limit under electrochemical mode is 36.3 aM (S/N = 3), and under colorimetric mode, it is as low as 12.1 aM (S/N = 3). The new method exhibits high sensitivity, excellent selectivity, and high accuracy, providing a universal strategy for designing novel biosensing platforms that can be extended to the detection of other biomolecules.

Zirconium-based metal-organic framework loaded agarose hydrogels for fluorescence turn-on detection of nerve agent simulant vapor

Developing reliable sensors that accurately detect deadly chemical gases is critical to global security. Nerve agents are one of the most dangerous chemicals in the world and are often found in gaseous forms in the environment, which remain a challenge to detect because of their low levels. In this paper, a fluorescent probe based on a Zr-based metal-organic framework UiO-66-NH2 was proposed. The specific binding between the Zr-O site of UiO-66-NH2 and diethyl chlorophosphate (DCP) blocked the ligand-to-metal charge transfer (LMCT) process in UiO-66-NH2, thereby enabling the fluorescence turn-on detection of DCP. More importantly, a simple and portable hydrogel soft-solid platform (UiO-66-NH2@Aga) was constructed by incorporating UiO-66-NH2 into the formation process of agarose (Aga) hydrogel for fast and sensitive detection of gaseous DCP. When the hydrogel was exposed to a low concentration of DCP vapor, its fluorescence changed from colorless to bright blue, allowing visualization of the DCP gas for analysis. The UiO-66-NH2@Aga integrated solid-state platform showed an excellent response to DCP vapor in the detection range of 1.98 to 9.90 ppm and with a detection limit of 1.16 ppm. This work opened up a unique way to design a convenient, low cost and practical gas physical examination platform.

Nanozyme-Based Biofuel Cell Ingeniously Coupled with Luminol Chemiluminescence System through In Situ Co-Reactant Generation for Dual-Signal Biosensing

Classical luminol-based chemiluminescence (CL) is the process of emitting light enhanced by the addition of coreactant hydrogen peroxide (H2O2). To address the instability issue of H2O2 decomposition, herein, we proposed a nanozyme-based biofuel cell (BFC) ingeniously coupled with a luminol CL system via in situ generation of H2O2. Specifically, the gold nanoparticle (AuNP) nanozyme with glucose oxidase-like activity can act as the anodic enzyme of BFC to catalyze the oxidation of glucose to produce H2O2 and electrons. In this case, H2O2 as a coreactant enhanced the CL intensity and the cathode of the BFC obtained electrons to generate the open circuit voltage (EOCV) signals. As a result, a dual-signal biosensing platform was successfully constructed. Interestingly, the AuNPs-catalyzed system operates in an alkaline medium, which precisely meets the pH requirement for luminol luminescence. Such a BFC-CL system not only greatly lessens the effect of unstable exogenous H2O2 on the signal stability but also enhances the CL of luminol. Furthermore, both CL and EOCV signals present a positive correlation with the glucose concentration. Therefore, this novel BFC-CL system shows good performance for dual-signal biosensing, which would serve as a valuable guideline for the design and application of BFC-based self-powered or CL biosensors.

Target-Controlled Redox Reaction and Ru(II) Release of a Smart Metal-Organic Framework Nanomaterial for Highly Sensitive Ratiometric Homogeneous Electroanalysis of Cadmium(II)

In this work, a highly sensitive ratiometric homogeneous electroanalysis (HEA) strategy of cadmium(II) (Cd2+) was proposed via a Cd2+-controlled redox reaction and Ru(bpy)32+ (Ru(II)) release from a smart metal-organic framework (MOF) nanomaterial. For achieving this purpose, Ru(II) was entrapped ingeniously into the pores of an MOF material (UiO-66-NH2) and subsequently gated by the double-strand hybrids of a Cd2+-aptamer (Apt) and its complementary sequences (CP) to form a novel smart nanomaterial (denoted as Ru@UiO-66-NH2); meanwhile, Fe(III) was selected as an additional probe present in electrolyte to facilitate the Ru(II) redox reaction: Fe(III) + Ru(II) → Fe(II) + Ru(III). Owing to the strong binding effect of the Cd2+ target to the specific Apt, the Apt-CP hybridization at Ru@UiO-66-NH2 would be destroyed in the presence of Cd2+, and the related Apt was further induced away from the smart nanomaterial, leading to the opening of the gate and release of Ru(II). Meanwhile, the released Ru(II) was quickly oxidized chemically by Fe(III) to Ru(III). On the basis of the generated Ru(III) and consumed Fe(III), the ratio of the reduction currents between Ru(III) and Fe(III) exhibits an enhancement and it is dependent on the level of Cd2+; thus, a novel HEA strategy of Cd2+ was then designed. Under the optimal conditions, the HEA sensor shows a wide linearity ranging from 10.0 pM to 500.0 nM, and the achieved detection limit of Cd2+ is 3.3 pM. The as-designed ratiometric HEA strategy not only offers a unique idea to realize a simple and sensitive assay for Cd2+ but also possesses significant potential as an effective tool to be introduced for other target analysis just via altering the specific Apt.

Advanced Self-Powered Biofuel Cells with Capacitor and Nanogenerator for Biomarker Sensing

Self-powered biofuel cells (BFCs) have evolved for highly sensitive detection of biomarkers such as noncodon micro ribonucleic acids (miRNAs) in the presence of interfering substrates. Self-charging supercapacitive BFCs for in vivo and in vitro cellular microenvironments represent the most prevalent sensing mechanism for diagnosis. Therefore, self-powered biosensing (SPB) with a capacitor and contact separation with a triboelectric nanogenerator (TENG) offers electrochemical and colorimetric dual-mode detection via improved electrical signal intensity. In this review, we discuss three major components: stretchable self-powered BFC design, miRNA sensing, and impedance spectroscopy. A specific focus is given to 1) assembling of sensors for biomarkers, 2) electrical output signal intensification, and 3) role of supercapacitors and nanogenerators in SPBs. We outline the key features of stretchable SPBs and the sequence of miRNA sensing by SPBs. We have emphasized the need of a supercapacitor and nanogenerator for SPBs in the context of advanced assembly of the sensing unit. Finally, we outline the role of impedance spectroscopy in the detection and estimation of biomarkers. We highlight key challenges in SPBs for biomarker sensing, which needs improved sensing accuracy, integration strategies of electrochemical biosensing for in vitro and in vivo microenvironments, and the impact of miRNA sensing on cancer diagnostics. This article attempts a specific focus on the accuracy and limitations of sensing unit for miRNA biomarkers and associated tool for boosting electrical signal intensity for a potential big step further.

Asymmetrically split DNAzyme-based colorimetric and electrochemical dual-modal biosensor for detection of breast cancer exosomal surface proteins

Exosomal surface proteins are potentially useful for breast cancer diagnosis and awareness of risk. However, some detection techniques involving complex operations and expensive instrumentation are limited to advance to clinical applications. To solve this problem, we develop a dual-modal sensor combining naked-eye detection and electrochemical assay of exosomal surface proteins from breast cancer. Most of existing sensors rely on aptamers recognizing exosomes and generating amplified signals at the same time, which require well-designed aptamer probes to avoid difficulties in identifying exosomes. In our work, aptamers not bound by the exosomes can serve as complete templates to induce formation of G quadruplexes. The peroxidase activity of the G-quadruplex/hemin DNAzyme catalyze substrates can generate both color and electrochemical signals. The developed dual-modal sensor offers a remarkable capability to differentiate nonmetastatic, metastatic breast cancer patients, and healthy individuals through the analysis of exosomal surface proteins. The sensor's distinctive features, including its universality, simplicity, and cost-effectiveness, position it as a promising diagnostic tool in breast cancer research and clinical practice.

Electrochemical detection of glycoproteins using boronic acid-modified metal-organic frameworks as dual-functional signal reporters

The sensitive analysis of glycoproteins is of great importance for early diagnosis and prognosis of diseases. In this work, a sandwich-type electrochemical aptasensor was developed for the detection of glycoproteins using 4-formylphenylboric acid (FPBA)-modified Cu-based metal-organic frameworks (FPBA-Cu-MOFs) as dual-functional signal probes. The target captured by the aptamer-modified electrode allowed the attachment of FPBA-Cu-MOFs based on the interaction between boronic acid and glycan on glycoproteins. Large numbers of Cu2+ ions in FPBA-Cu-MOFs produced an amplified signal for the direct voltammetric detection of glycoproteins. The electrochemical aptasensor showed a detection limit as low as 6.5 pg mL-1 for prostate specific antigen detection. The method obviates the use of antibody and enzymes for molecular recognition and signal output. The dual-functional MOFs can be extended to the design of other biosensors for the determination of diol-containing biomolecules in clinical diagnosis.

Enhancing biosensing with fourfold amplification and self-powering capabilities: MoS2@C hollow nanorods-mediated DNA hexahedral framework architecture for amol-level liver cancer tumor marker detection

Two-dimensional carbon-coated molybdenum disulfide (MoS₂@C) hollow nanorods are combined with nucleic acid signal amplification strategies and DNA hexahedral nanoframework to construct a novel self-powered biosensing platform for ultra-sensitive dual-mode detection of tumor suppressor microRNA-199a. The nanomaterial is applied on carbon cloth and then modified with glucose oxidase or using as bioanode. A large number of double helix DNA chains are produced on bicathode by nucleic acid technologies including 3D DNA walker, hybrid chain reaction and DNA hexahedral nanoframework to adsorb methylene blue, producing high E^OCV signal. Methylene blue also is reduced and an increased RGB Blue value is observed. For microRNA-199a detection, the assay shows a extensive linear range of 0.0001-100 pM with a low detection limit of 4.94 amol/L (S/N = 3). The method has been applied to the detection of actual serum samples, providing a novel method for the accurate and sensitive detection of tumor markers.

Flexible carbon fiber cloth supports decorated with cerium metal- organic frameworks and multi-walled carbon nanotubes for simultaneous on-site detection of Cd2+ and Pb2+ in food and water samples

The widespread heavy metal pollution endangers human health; hence, accurate on-site detection and quantification of heavy metal content in the surroundings is a vital step in reversing the harmful effect. Herein, an electrochemical sensor based on flexible cerium metal-organic framework@multi-walled carbon nanotubes/carbon cloth (CeMOF@MWCNTs/CC) was constructed for simultaneous on-site detection of Cd²⁺ and Pb²⁺ in food and water samples. The rich carboxyl groups of MWCNTs provided abundant sites for the adsorption of Cd²⁺ and Pb²⁺, and the mutual conversion of Ce³⁺ and Ce⁴⁺ in CeMOF facilitated the reduction and reoxidation of metal ions. The prepared electrode showed excellent performance in the simultaneous measurement of Cd²⁺ and Pb²⁺, with detection limits of 2.2 ppb and 0.64 ppb, respectively. More importantly, the sensing platform has been successfully used to detect simultaneously Cd²⁺ and Pb²⁺ in grain and water samples, and the detection results were consistent with the standard methods, showing great potential in environmental monitoring and food safety.

Constructed a self-powered sensing platform based on nitrogen-doped hollow carbon nanospheres for ultra-sensitive detection and real-time tracking of double markers

Acute myocardial infarction (AMI) is acute necrosis of a portion of the myocardium caused by myocardial ischemia, which seriously threatens people's health and life safety. Its early diagnosis is a difficult problem in clinical medicine. Research has found that the abnormal expression of microRNA-199a (miR-199a) and microRNA-499 (miR-499) was closely related to AMI disease. In this work, we took advantage of the structural advantages of nitrogen-doped hollow carbon nanospheres (N-HCNSs) to design an ultra-sensitive, portable real-time monitoring visual self-powered biosensor system, which based on dual-target miRNAs triggered catalytic hairpin assembly (CHA) for sensitive detection of miR-199a and miR-499. In addition, the capacitor and the smartphone are introduced into the system to realize the secondary improvement of system sensitivity and portable real-time visual monitoring. Under optimized conditions, in the linear range of 0.1-100000 aM, the detection limits of miR-199a and miR-499 are 0.031 and 0.027 aM, respectively. At the same time, the ultra-sensitive detection of miRNAs is realized in the serum sample, and the recovery rate of miR-199a and miR-499 are 98.0-106.0% (RSD: 0.6-8.1%) and 94.0-109.7% (RSD: 1.8-7.7%), respectively. The method is simple, sensitive and can be used for real-time tracking and portable monitoring of related diseases.

Diagnostic approaches for dengue infection

INTRODUCTION

Every year, a significant rise in dengue incidence observed is responsible for 10% of fever episodes in children and adolescents in endemic countries. Considering that the symptoms of dengue are similar to those of many other viruses, early diagnosis of the disease has long been difficult, and lack of sensitive diagnostic tools may be another factor contributing to a rise in dengue incidence.

AREAS COVERED

This review will highlight dengue diagnostics strategies and discuss other possible targets for dengue diagnosis. Understanding the dynamics of the immune response and how it affects viral infection has enabled informed diagnosis. As more technologies emerge, precise assays that include some clinical markers need to be included.

EXPERT OPINION

Future diagnostic strategies will require the use both viral and clinical markers in a serial manner with the use of artificial intelligence technology to determine from the first point of illness to better determine severity status and management. A definitive endpoint is not in the horizon as the disease as well as the virus is constantly evolving and hence many developed assays need to be constantly changing some of their reagents periodically as newer genotypes and probably too serotypes emerge.