Dual nanozyme based on ultrathin 2D conductive MOF nanosheets intergraded with gold nanoparticles for electrochemical biosensing of H2O2 in cancer cells

A trifunctional surface ligand-directed general synthesis of 2D MOF hybrid nanozymes for customizable applications

Two-dimensional metal-organic frameworks (2DMOFs)-based hybrid nanozymes integrate the excellent catalytic activity of 2DMOFs with intriguing properties of other functional nanomaterials, offering great opportunities in biosensing and catalysis applications. However, the versatile synthesis of 2DMOF-based hybrid nanozymes remains challenging due to the difficulty in precisely controlling interactions between 2DMOFs and other functional nanocomponents. In this work, a trifunctional surface ligand-mediated strategy was developed to rationalize these interactions and promote the general synthesis of 2DMOF hybrid nanozymes. The surface ligand not only prevents the nanocomponents from self-aggregation and keeps 2DMOF monodispersed to form ultrathin nanosheets, but also drives the assembly of 2DMOF and nanocomponent to form composite nanostructures. Using this strategy, a series of customizable hybrid nanozymes exhibiting synergistically catalytic activity, recyclability, cascade catalysis, and photo-enhanced catalysis were fabricated, respectively. Moreover, these hybrid nanozymes displayed excellent performance in H2O2 detection, glucose sensing, and pollutant degradation. The successful demonstration of a general and facile strategy for synthesizing two-dimensional metal-organic framework (2D MOF) hybrid nanozymes paves the way for the development of 2D MOF-based nanomaterials and nanozymes with customizable functions. These materials hold significant potential in various applications, including catalysis, biosensing, disease diagnosis, and energy conversion.

Defect-regulated reduced graphene oxide anchored Prussian blue and platinum nanoparticles peroxidase for electrochemical detection of mesenchymal circulating tumor cells

The precise analysis of mesenchymal circulating tumor cells (mCTCs), known for their enhanced migratory behavior in peripheral blood, is essential for cancer diagnosis and predicting metastasis. Nevertheless, the rarity and heterogeneity of mCTCs present significant challenges in both their capture and subsequent enumeration. Therefore, designing and realizing a high-performance and adaptable cytosensor platform are crucial for the accurate analyzing various mCTCs. Defect engineering is used to enhance the synthesis of a peroxidase mimic enzyme, achieving significantly higher activity than natural enzymes. This was accomplished by anchoring Prussian blue (PB) and platinum (Pt) nanoparticles onto reduced graphene oxide (rGO), forming rGO@PB/Pt. An electrochemical cytosensor was subsequently constructed based on rGO@PB/Pt linked with aptamers to capture mCTCs and degrade the trace hydrogen peroxide (H2O2) secreted by mCTCs. Specifically, the presence of Fe2+ vacancies creates numerous active Fe3+ sites, resulting in an enlarged specific surface area and a microporous structure with pore diameters of approximately 0.8 nm and 1.3 nm. These structural features enable the effective encapsulation of H2O2, enhancing its rate of decomposition. The cytosensor demonstrated a linear response within the range of 1 to 104 cells/mL, with a detection limit (LOD) as low as 0.1 cells/mL (S/N = 3). Moreover, the cytosensor can quantify mCTCs solely based on cell membrane epitopes, making it applicable to almost all types of CTCs by altering the capture aptamer. In addition, the analysis of mCTCs in human blood additionally validates it as a promising candidate for the precise detection of mCTCs in clinical settings.

On-Chip Electrochemical Sensor Based on 3D Graphene Assembly Decorated Ultrafine RuCu Alloy Nanocatalyst for In Situ Detection of NO in Living Cells

In this work, we developed 3D ionic liquid (IL) functionalized graphene assemblies (GAs) decorated by ultrafine RuCu alloy nanoparticles (RuCu-ANPs) via a one-step synthesis process, and integrated it into a microfluidic sensor chip for in situ electrochemical detection of NO released from living cells. Our findings have demonstrated that RuCu-ANPs on 3D IL-GA exhibit high density, uniform distribution, lattice-shaped arrangement of atoms, and extremely ultrafine size, and possess high electrocatalytic activity to NO oxidation on the electrode. Meanwhile, the 3D IL-GA with hierarchical porous structures can facilitate the efficient electron/mass transfer at the electrode/electrolyte interface and the cell culture. Moreover, the graft of IL molecules on GA endows it with high hydrophilicity for facile and well-controllable printing on the electrode. Consequently, the resultant electrochemical microfluidic sensor demonstrated excellent sensing performances including fast response time, high sensitivity, good anti-interference ability, high reproducibility, long-term stability, as well as good biocompatibility, which can be used as an on-chip sensing system for cell culture and real-time in situ electrochemical detection of NO released from living cells with accurate and stable characteristics in physiological conditions.

Electronic Chemical Sensors Based on Conductive Framework Materials

The development of portable electronic chemical sensors is key to solving a number of challenges, including monitoring environmental and industrial hazards, as well as understanding and improving human health. Framework materials possess several desirable characteristics that make them well-suited for electroanalytical applications, including high surface area, atomically precise distribution of active sites, and tunable properties that can be leveraged through modular reticular chemistry. This review highlights the emergence of conductive framework materials as active components in electrically transduced chemical sensors, including the development of new materials for the detection of a wide variety of analytes in both gas and liquid phase. The efforts to gain fundamental understanding of the molecular interactions and sensing mechanisms between framework materials and analytes are described, along with applications of these materials on portable and flexible substrates. The review suggests areas for further study, including the study of material-analyte interactions at the molecular level and the continued development of scalable methods for the integration of framework materials into low-power, portable sensing devices.

An Electrochemical Immunosensor for Sensitive Detection of Exosomes Based on Au/MXenes and AuPtPdCu

Exosomes are important biomarkers for liquid biopsy in early cancer screening which play important roles in many biological processes, including apoptosis, inflammatory response, and tumor metastasis. In this study, an electrochemical aptamer immunosensor based on Au/MXene and AuPtPdCu was constructed for the sensitive detection of colorectal cancer-derived exosomes. AuNPs were deposited in situ on the surface of MXenes as a sensing platform due to their large specific area, excellent conductivity, and higher number of active sites for aptamer immobilization. The aptamer CD63 immobilized on Au/MXene can specifically capture target exosomes. Therefore, the AuPtPdCu-Apt nanoprobe further enhanced the sensitivity and accuracy of the immunosensor. A low limit of detection of 19 particles μL-1 was achieved in the linear range of 50 to 5 × 104 particles μL-1 under optimal conditions. The immunosensor developed herein showed satisfactory electrochemical stability and anti-interference ability for the detection of exosomes in real serum samples.

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.

Trends in conductive MOFs for sensing: A review

Metal-organic frameworks (MOFs) are porous, ordered arrays formed by coordination bonds between organic ligands and metal ions or clusters. The highly tunable properties of the MOF structure and performance make it possible to meet the needs of many applications. Conductive MOFs are essential in the domain of sensing due to their electrical conductivity, porosity, and catalytic properties, offering an effective platform for detection. Numerous sensing devices that utilize conductive MOFs have been created. This text presents a thorough overview of the diverse applications of conductive MOFs within the sensing field. The results of this work provide insights into the properties and synthesis methods of conductive MOFs and the working mechanisms of sensors based on conductive MOFs, which will help to deepen the study of such materials, provide a new vision for the design and production of novel functional materials, and promote the development and application of sensors based on conductive MOFs.

Recent Advances in Biosensors Using Enzyme-Stabilized Gold Nanoclusters

Recently, gold nanoclusters (AuNCs) have been widely used in biological applications due to their ultrasmall size, ranging within a few nanometers; large specific surface area; easy functionalization; unique fluorescence properties; and excellent conductivity. However, because they are unstable in solution, AuNCs require stabilization by using ligands such as dendrimers, peptides, DNA, and proteins. As a result, the properties of AuNCs and their formation are determined by the ligand, so the selection of the ligand is important. Of the many ligands implemented, enzyme-stabilized gold nanoclusters (enzyme-AuNCs) have attracted increasing attention for biosensor applications because of the excellent optical/electrochemical properties of AuNCs and the highly target-specific reactions of enzymes. In this review, we explore how enzyme-AuNCs are prepared, their properties, and the various types of enzyme-AuNC-based biosensors that use optical and electrochemical detection techniques. Finally, we discuss the current challenges and prospects of enzyme-AuNCs in biosensing applications. We expect this review to provide interdisciplinary knowledge about the application of enzyme-AuNC-based materials within the biomedical and environmental fields.

Propelling gold nanozymes: catalytic activity and biosensing applications

Recently, gold nanomaterials have been rapidly developed owing to their high stability, good biocompatibility, and multifunctionality. The unique catalytic activity of gold nanomaterials has driven the emergence of the concept for a "gold nanozyme." Understanding the characteristics of gold nanozymes is crucial for improving their catalytic performance as well as expanding their applications. In this review, we provide an overview of the intrinsic enzyme-like activities of gold nanozymes, including peroxidase-, catalase-, superoxide dismutase-, and glucose oxidase-like activities, and the catalytic mechanisms involved. In addition, strategies for modulating the catalytic activity of gold nanozymes and their applications in biosensing were discussed in detail. Moreover, we highlight the current challenges of gold nanozymes and look forward to attracting more attention for propelling the developments in this field.

Branched CuAu nano-alloy for N2H4 oxidation-assisted H2 production and nitrite detection in water solution

The H2 production using N2H4 splitting (OHzS) was often constrained by the requirement for insufficient stability, distinct catalysts at the anode and cathode, and the high-cost electrocatalyst associated with confined activity. This work verified the efficacy of surfactant-free branched CuAu nano-alloy as a bifunctional electrocatalyst for H2 production. Benefiting from its favorable electronic structure and surfactant-free surface, surfactant-free CuAu nano-alloy demonstrated a reduced over-potential compared with pure Cu, pure Au, and CuAu nano-alloy prepared by surfactant. When using branched CuAu nano-alloy as both cathodic and anodic electrodes, a cell voltage of 0.768 V was required to drive a current density of 10 mA/cm2. After 2550 min of H2 generation, the amplitude of the working potential for anodic reactions was found to be less than 0.92%. The enhanced electrocatalytic activity could be also applied to H2O2 and NaNO2 sensors. The CuAu nano-alloy exhibited a 2.35-folds increase in sensitivity compared to pure Au nano-crystals in the detection of H2O2. Moreover, the detection of NaNO2 in water solution has been successfully achieved. The detection range 0-175.0 mM was much wider than that of sensors in previous works.

Metal-organic frameworks for biomedical applications: A review

Metal-organic frameworks (MOFs) are emergent materials in diverse prospective biomedical uses, owing to their inherent features such as adjustable pore dimension and volume, well-defined active sites, high surface area, and hybrid structures. The multifunctionality and unique chemical and biological characteristics of MOFs allow them as ideal platforms for sensing numerous emergent biomolecules with real-time monitoring towards the point-of-care applications. This review objects to deliver key insights on the topical developments of MOFs for biomedical applications. The rational design, preparation of stable MOF architectures, chemical and biological properties, biocompatibility, enzyme-mimicking materials, fabrication of biosensor platforms, and the exploration in diagnostic and therapeutic systems are compiled. The state-of-the-art, major challenges, and the imminent perspectives to improve the progressions convoluted outside the proof-of-concept, especially for biosensor platforms, imaging, and photodynamic therapy in biomedical research are also described. The present review may excite the interdisciplinary studies at the juncture of MOFs and biomedicine.

Facile and efficient synthesis of sweater-ball shaped metal-organic framework/nickel sulfide nanoheterojunction for boosting electrochemical glucose sensing

The synthesis of heterojunction materials is regarded as an efficient way to enhance catalytic activities in various catalytic reactions. However, the existing fabrication approaches often rely on complex multi-step synthesis process. In this work, we fabricate sweater-ball shaped nanostructured MOF/TMS (Ni-MOF/NiS1.03) heterojunction by one-pot, one-step solvothermal method. According to the results of discrete Fourier transform (DFT) calculations and experiments, the formation of Ni-MOF/NiS1.03 heterojunction interfaces improves electron transfer and charge redistribution, and increases the adsorption energy of glucose molecules as well, which is conducive to enhance electrochemical activity of electrode materials. The as-prepared Ni-MOF/NiS1.03 heterojunction exhibit enhanced glucose sensitivity, wide detection range and low detection limit. This study paves the way towards the development of MOF-based heterojunctions for electrochemical applications.

Ordered mesoporous hairbrush-like nanocarbon assembled microfibers for solid-phase microextraction of benzene series in oilfield sewage

The development of advanced functional nanomaterials for solid-phase microextraction (SPME) remains an imperative aspect of sample pretreatment. Herein, we introduce a novel SPME fiber consisting of graphene fibers modified with ordered mesoporous carbon nanotubes arrays (CNTAs) tailored for the determination of benzene series in oilfield wastewater, which is synthesized by an ionic liquid-assisted wet spinning process of graphene nanosheets, followed by a precisely controlled growth of metal-organic framework and subsequent pyrolysis treatment. The resulting robust microfiber structure resembles a "hairbrush" configuration, with a crumpled graphene fiber "stem" and high-order mesoporous CNTAs "hairs". This unique architecture significantly enhances the SPME capacity, as validated by gas chromatography-mass spectrometry. The hairbrush-like nanocarbon assembled microfibers possess structural characteristics, a high specific surface area, and numerous binding sites, offering efficient enrichment of benzene series compounds in oilfield wastewater, including benzene, ethylbenzene, m-xylene, p-xylene, and toluene. Our analysis demonstrates that these microfibers exhibit broad linear ranges (0.2-600 μg L-1), low detection limits (0.005-0.03 mg L-1), and excellent repeatability (3.2-5.5% for one fiber, 2.1-6.7% for fiber-to-fiber) for detection. When compared to commercial alternatives, these hairbrush-like nanocarbon-assembled microfibers exhibit significantly enhanced extraction efficiency for benzene series compounds.

Colorimetric and SERS dual-mode detection of GSH in human serum based on AuNPs@Cu-porphyrin MOF nanozyme

BACKGROUND

Rapid and accurate detection of glutathione content in human blood plays an important role in real-time tracking of related diseases. Currently, surface-enhanced Raman scattering/spectroscopy (SERS) combined with nanozyme material has been proven to have excellent properties in the detection applications compared to many other methods because of it combines the advantages of trace detection capability of SERS and efficient catalytic activity of nanozymes. However, there are still existing problems in real sample detection, and to achieve quantitative detection is still challenging.

RESULTS

In this study, gold nanoparticles (AuNPs) were synthesized in situ on the surface of two-dimensional Cu-porphyrin metal-organic framework (MOF) nanosheets to produce the AuNPs@Cu-porphyrin MOF nanozyme, which exhibited both oxidase-like activity and SERS detection ability. On one hand, the intrinsic oxidase-like activity of the nanozyme could be inhibited due to the chelation of glutathione (GSH) and Cu, which thus led to the visual color change of the solution. On the other hand, the abundant Raman "hot spots" at the nanogap generated by Au NPs and the internal standard (IS) signal provided by Cu-meso-tetra (4-carboxyphenyl) porphine (Cu-TCPP) MOF improved the sensitivity and quantitative accuracy of detection.

SIGNIFICANCE AND NOVELTY

A dual-mode signal output sensor based on the nanozyme was thus established, which could be used in the trace detection of GSH. Such a dual-mode sensor possesses excellent detection performance, with the advantage of both wide detection range from 1 to 300 μM in the colorimetric detection mode and high sensitivity with LOD of 5 nM in the SERS detection mode, and can be applied to GSH detection in actual serum samples with reliable results.

Flexible Graphene Paper Modified Using Pt&Pd Alloy Nanoparticles Decorated Nanoporous Gold Support for the Electrochemical Sensing of Small Molecular Biomarkers

The exploration into nanomaterial-based nonenzymatic biosensors with superb performance in terms of good sensitivity and anti-interference ability in disease marker monitoring has always attained undoubted priority in sensing systems. In this work, we report the design and synthesis of a highly active nanocatalyst, i.e., palladium and platinum nanoparticles (Pt&Pd-NPs) decorated ultrathin nanoporous gold (NPG) film, which is modified on a homemade graphene paper (GP) to develop a high-performance freestanding and flexible nanohybrid electrode. Owing to the structural characteristics the robust GP electrode substrate, and high electrochemically catalytic activities and durability of the permeable NPG support and ultrafine and high-density Pt&Pd-NPs on it, the resultant Pt&Pd-NPs-NPG/GP electrode exhibits excellent sensing performance of low detection limitation, high sensitivity and anti-interference capability, good reproducibility and long-term stability for the detection of small molecular biomarkers hydrogen peroxide (H2O2) and glucose (Glu), and has been applied to the monitoring of H2O2 in different types of live cells and Glu in body fluids such as urine and fingertip blood, which is of great significance for the clinical diagnosis and prognosis in point-of-care testing.

Hierarchical N-doped porous carbon scaffold Cu/Co-oxide with enhanced electrochemical sensing properties for the detection of glucose in beverages and ascorbic acid in vitamin C tablets

This research focuses on the development of a highly efficient electrocatalyst, CuxO/NPC@Co3O4/NPC-10-7, for detecting glucose and ascorbic acid. In a 0.1 M NaOH solution, the modified electrode exhibits a sensitivity of 3314.29 μA mM-1 cm-2 for glucose detection. The linear range for ascorbic acid sensing is 0.5 μM - 23.332 mM, with a detection limit as low as 0.24 μM. In a 0.1 M PBS solution, the linear range for ascorbic acid detection extends to 43.328 mM, which represents the best performance reported to date by chronoamperometry. Moreover, the electrode demonstrates high accuracy, with a recovery rate of 96.80 % - 103.60 % for glucose detection and a recovery rate of 95.25 % - 104.83 % for ascorbic acid detection. These results suggest that the CuxO/NPC@Co3O4/NPC-10-7 modified electrode shows significant potential for practical applications in food detection.

Colorimetric and electrochemical dual-mode uric acid determination utilizing peroxidase-mimicking activity of CoCu bimetallic nanoclusters

We present the preparation of CoCu bimetallic nanoclusters (Co@Cu-BNCs) by a hydrothermal and one-step pyrolysis method to build a colorimetric and electrochemical dual-mode sensing platform for uric acid (UA) detection. In the presence of H2O2, Co@Cu-BNCs with peroxidase-mimicking activity may convert colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue-colored oxidized TMB (oxTMB). However, due to the inhibitory effect of uric acid (UA) on the oxidation process of TMB, the characteristic absorption peak intensity of oxTMB decreased when UA was added into a mixed solution. In this approach, a colorimetric assay platform for the detection of UA was demonstrated, with a linear range of 0.1-195 μM and a low limit of detection of 0.06 μM (S/N ratio of 3). In addition, an even wider detection range is achieved in the electrochemical method, due to the pronounced electrocatalytic activity of Co@Cu-BNCs. The surface of the glassy carbon electrode was modified with Co@Cu-BNCs to build an electrochemical sensor for detecting UA. The sensor achieves a wider linear range from 2 to 1000 μM and a limit of detection of 0.61 μM (S/N ratio of 3). Moreover, the detection of UA in a human serum sample showed satisfactory results. The results proved that the colorimetric and electrochemical dual-mode detection platform was sensitive, convenient and accurate.

Nanozymes and carbon-dots based nanoplatforms for cancer imaging, diagnosis and therapeutics: Current trends and challenges

Cancer patients face a significant clinical and socio-economic burden due to increased incidence, mortality, and poor survival. Factors like late diagnosis, recurrence, drug resistance, severe side effects, and poor bioavailability limit the scope of current therapies. There is a need for novel, cost-effective, and safe diagnostic methods, therapeutics to overcome recurrence and drug resistance, and drug delivery vehicles with enhanced bioavailability and less off-site toxicity. Advanced nanomaterial-based research is aiding cancer biologists by providing solutions for issues like hypoxia, tumor microenvironment, low stability, poor penetration, target non-specificity, and rapid drug clearance. Currently, nanozymes and carbon-dots are attractive due to their low cost, high catalytic activity, biocompatibility, and lower toxicity. Nanozymes and carbon-dots are increasingly used in imaging, biosensing, diagnosis, and targeted cancer therapy. Integrating these materials with advanced diagnostic tools like CT scans and MRIs can aid in clinical decision-making and enhance the effectiveness of chemotherapy, photothermal, photodynamic, and sonodynamic therapies, with minimal invasion and reduced collateral effects.

MOF-based nanocomposites as transduction matrices for optical and electrochemical sensing

Metal Organic Frameworks (MOFs), a class of crystalline microporous materials have been into research limelight lately due to their commendable physio-chemical properties and easy fabrication methods. They have enormous surface area which can be a working ground for innumerable molecule adhesions and site for potential sensor matrices. Their biocompatibility makes them valuable for in vitro detection systems but a compromised conductivity requires a lot of surface engineering of these molecules for their usage in electrochemical biosensors. However, they are not just restricted to a single type of transduction system rather can also be modified to achieve feat as optical (colorimetry, luminescence) and electro-luminescent biosensors. This review emphasizes on recent advancements in the area of MOF-based biosensors with focus on various MOF synthesis methods and their general properties along with selective attention to electrochemical, optical and opto-electrochemical hybrid biosensors. It also summarizes MOF-based biosensors for monitoring free radicals, metal ions, small molecules, macromolecules and cells in a wide range of real matrices. Extensive tables have been included for understanding recent trends in the field of MOF-composite probe fabrication. The article sums up the future scope of these materials in the field of biosensors and enlightens the reader with recent trends for future research scope.

Recent Advances in Metallic Nanostructures-assisted Biosensors for Medical Diagnosis and Therapy

The field of nanotechnology has witnessed remarkable progress in recent years, particularly in its application to medical diagnosis and therapy. Metallic nanostructures-assisted biosensors have emerged as a powerful and versatile platform, offering unprecedented opportunities for sensitive, specific, and minimally invasive diagnostic techniques, as well as innovative therapeutic interventions. These biosensors exploit the molecular interactions occurring between biomolecules, such as antibodies, enzymes, aptamers, or nucleic acids, and metallic surfaces to induce observable alterations in multiple physical attributes, encompassing electrical, optical, colorimetric, and electrochemical signals. These interactions yield measurable data concerning the existence and concentration of particular biomolecules. The inherent characteristics of metal nanostructures, such as conductivity, plasmon resonance, and catalytic activity, serve to amplify both sensitivity and specificity in these biosensors. This review provides an in-depth exploration of the latest advancements in metallic nanostructures-assisted biosensors, highlighting their transformative impact on medical science and envisioning their potential in shaping the future of personalized healthcare.

High performance boron doped peroxidase-like nanozyme Cu/B-NC for detection of epinephrine and catalase

Herein, a novel peroxidase-like (POD-like) nanozyme Cu/B-NC was synthesized. The Cu and B co-doped nanozyme Cu/B-NC has competitive POD-like activity but negligible oxidase-like (OXD-like) activity, which is proved to partly benefit from the doping of boron atom. The catalytic activity of Cu/B-NC is high with great affinity for TMB and H2O2 and high reaction velocity. Cu/B-NC was utilized to catalyze the condensation of phenolic substance epinephrine (EP) and 4-aminoantipyrine (4-AAP) to form colored quinone imine in the presence of H2O2. UV-vis absorbance of quinone imine at 492 nm was used for EP determination. Catalase (CAT) could decompose H2O2, so CAT could also be quantified through absorbance variation. The linear ranges of colorimetric detection for EP and CAT were 2-100 μM and 1-30 U mL-1, respectively. The limits of detection (LODs) for EP and CAT were 0.97 μM and 0.57 U mL-1, respectively. The practicability of this sensing platform was further validated by successful application in actual samples.

Signal Amplification Strategy Design in Nanozyme-Based Biosensors for Highly Sensitive Detection of Trace Biomarkers

Nanozymes show great promise in enhancing disease biomarker sensing by leveraging their physicochemical properties and enzymatic activities. These qualities facilitate signal amplification and matrix effects reduction, thus boosting biomarker sensing performance. In this review, recent studies from the last five years, concentrating on disease biomarker detection improvement through nanozyme-based biosensing are examined. This enhancement primarily involves the modulations of the size, morphology, doping, modification, electromagnetic mechanisms, electron conduction efficiency, and surface plasmon resonance effects of nanozymes for increased sensitivity. In addition, a comprehensive description of the synthesis and tuning strategies employed for nanozymes has been provided. This includes a detailed elucidation of their catalytic mechanisms in alignment with the fundamental principles of enhanced sensing technology, accompanied by the presentation of quantitatively analyzed results. Moreover, the diverse applications of nanozymes in strip sensing, colorimetric sensing, electrochemical sensing, and surface-enhanced Raman scattering have been outlined. Additionally, the limitations, challenges, and corresponding recommendations concerning the application of nanozymes in biosensing have been summarized. Furthermore, insights have been offered into the future development and outlook of nanozymes for biosensing. This review aims to serve not only as a reference for enhancing the sensitivity of nanozyme-based biosensors but also as a catalyst for exploring nanozyme properties and their broader applications in biosensing.

Chromogenic Mechanisms of Colorimetric Sensors Based on Gold Nanoparticles

The colorimetric signal readout method is widely used in visualized analyses for its advantages, including visualization of test results, simple and fast operations, low detection cost and fast response time. Gold nanoparticles (Au NPs), which not only exhibit enzyme-like activity but also have the advantages of tunable localized surface plasmon resonance (LSPR), high stability, good biocompatibility and easily modified properties, provide excellent platforms for the construction of colorimetric sensors. They are widely used in environmental monitoring, biomedicine, the food industry and other fields. This review focuses on the chromogenic mechanisms of colorimetric sensors based on Au NPs adopting two different sensing strategies and summarizes significant advances in Au NP-based colorimetric sensing with enzyme-like activity and tunable LSPR characteristics. In addition, the sensing strategies based on the LSPR properties of Au NPs are classified into four modulation methods: aggregation, surface modification, deposition and etching, and the current status of visual detection of various analytes is discussed. Finally, the review further discusses the limitations of current Au NP-based detection strategies and the promising prospects of Au NPs as colorimetric sensors, guiding the design of novel colorimetric sensors.

Development of nanozyme based sensors as diagnostic tools in clinic applications: a review

Since 1970, many artificial enzymes that imitate the activity and structure of natural enzymes have been discovered. Nanozymes are a group of nanomaterials with enzyme-mimetic properties capable of catalyzing natural enzyme processes. Nanozymes have attracted great interest in biomedicine due to their excellent stability, rapid reactivity, and affordable cost. The enzyme-mimetic activities of nanozymes may be modulated by numerous parameters, including the oxidative state of metal ions, pH, hydrogen peroxide (H2O2) level, and glutathione (GSH) concentration, indicating the tremendous potential for biological applications. This article delivers a comprehensive overview of the advances in the knowledge of nanozymes and the creation of unique and multifunctional nanozymes, and their biological applications. In addition, a future perspective of employing the as-designed nanozymes in biomedical and diagnostic applications is provided, and we also discuss the barriers and constraints for their further therapeutic use.

Smartphone-Based Chemiluminescence Glucose Biosensor Employing a Peroxidase-Mimicking, Guanosine-Based Self-Assembled Hydrogel

Chemiluminescence is widely used for hydrogen peroxide detection, mainly exploiting the highly sensitive peroxidase-luminol-H₂O₂ system. Hydrogen peroxide plays an important role in several physiological and pathological processes and is produced by oxidases, thus providing a straightforward way to quantify these enzymes and their substrates. Recently, biomolecular self-assembled materials obtained by guanosine and its derivatives and displaying peroxidase enzyme-like catalytic activity have received great interest for hydrogen peroxide biosensing. These soft materials are highly biocompatible and can incorporate foreign substances while preserving a benign environment for biosensing events. In this work, a self-assembled guanosine-derived hydrogel containing a chemiluminescent reagent (luminol) and a catalytic cofactor (hemin) was used as a H₂O₂-responsive material displaying peroxidase-like activity. Once loaded with glucose oxidase, the hydrogel provided increased enzyme stability and catalytic activity even in alkaline and oxidizing conditions. By exploiting 3D printing technology, a smartphone-based portable chemiluminescence biosensor for glucose was developed. The biosensor allowed the accurate measurement of glucose in serum, including both hypo- and hyperglycemic samples, with a limit of detection of 120 µmol L^-1. This approach could be applied for other oxidases, thus enabling the development of bioassays to quantify biomarkers of clinical interest at the point of care.

Surface modification strategies and the functional mechanisms of gold nanozyme in biosensing and bioassay

Gold nanozymes (GNZs) have been widely used in biosensing and bioassay due to their interesting catalytic activities that enable the substitution of natural enzyme. This review explains different catalytic activities of GNZs that can be achieved by applying different modifications to their surface. The role of Gold nanoparticles (GNPs) in mimicking oxidoreductase, helicase, phosphatase were introduced. Moreover, the effect of surface properties and modifications on each catalytic activity was thoroughly discussed. The application of GNZs in biosensing and bioassay was classified in five categories based on the combination of the enzyme like activities and enhancing/inhibition of the catalytic activities in presence of the target analyte/s that is realized by proper surface modification engineering. These categories include catalytic activity enhancer, reversible catalytic activity inhibitor, binding selectivity enhancer, agglomeration base, and multienzyme like activity, which are explained and exemplified in this review. It also gives examples of those modifications that enable the application of GNZs for in vivo biosensing and bioassays.

Insights into the multirole CoAl layered double hydroxide on boosting photoelectrochemical activity of hematite: Application to hydrogen peroxide sensing

As an important compound in many industrial and biological processes, hydrogen peroxide (H₂O₂) would cause harmfulness to human health at high concentration level. It thus is urgent to develop highly sensitive and selective sensors for practical H₂O₂ detection in the fields of water monitoring, food quality control, and so on. In this work, CoAl layered double hydroxide ultrathin nanosheets decorated hematite (CoAl-LDH/α-Fe₂O₃) photoelectrode was successfully fabricated by a facile hydrothermal process. CoAl-LDH/α-Fe₂O₃ displays the relatively wide linear range from 1 to 2000 μM with a high sensitivity of 132.0 μA mM^-1 cm^-2 and a low detection limit of 0.04 μM (S/N ≥ 3) for PEC detection of H₂O₂, which is superior to other similar α-Fe₂O₃-based sensors in literatures. The (photo)electrochemical characterizations, such as electrochemical impedance spectroscopy, Mott-Schottky plot, cyclic voltammetry, open circuit potential and intensity modulated photocurrent spectroscopy, were used to investigate the roles of CoAl-LDH on the improved PEC response of α-Fe₂O₃ toward H₂O₂. It revealed that, CoAl-LDH could not only passivate the surface states and enlarge the band bending of α-Fe₂O₃, but also could act as trapping centers for holes and followed by as active sites for H₂O₂ oxidation, thus facilitated the charge separation and transfer. The strategy for boosting PEC response would be help for the further development of semiconductor-based PEC sensors.

Electrochemical aptasensor based on the engineered core-shell MOF nanostructures for the detection of tumor antigens

It is essential to develop ultrasensitive biosensors for cancer detection and treatment monitoring. In the development of sensing platforms, metal-organic frameworks (MOFs) have received considerable attention as potential porous crystalline nanostructures. Core-shell MOF nanoparticles (NPs) have shown different diversities, complexities, and biological functionalities, as well as significant electrochemical (EC) properties and potential bio-affinity to aptamers. As a result, the developed core-shell MOF-based aptasensors serve as highly sensitive platforms for sensing cancer biomarkers with an extremely low limit of detection (LOD). This paper aimed to provide an overview of different strategies for improving selectivity, sensitivity, and signal strength of MOF nanostructures. Then, aptamers and aptamers-modified core-shell MOFs were reviewed to address their functionalization and application in biosensing platforms. Additionally, the application of core-shell MOF-assisted EC aptasensors for detection of several tumor antigens such as prostate-specific antigen (PSA), carbohydrate antigen 15-3 (CA15-3), carcinoembryonic antigen (CEA), human epidermal growth factor receptor-2 (HER2), cancer antigen 125 (CA-125), cytokeratin 19 fragment (CYFRA21-1), and other tumor markers were discussed. In conclusion, the present article reviews the advancement of potential biosensing platforms toward the detection of specific cancer biomarkers through the development of core-shell MOFs-based EC aptasensors.

Nanozymes and nanoflower: Physiochemical properties, mechanism and biomedical applications

Natural enzymes possess several drawbacks which limits their application in industries, wastewater remediation and biomedical field. Therefore, in recent years researchers have developed enzyme mimicking nanomaterials and enzymatic hybrid nanoflower which are alternatives of enzyme. Nanozymes and organic inorganic hybrid nanoflower have been developed which mimics natural enzymes functionalities such as diverse enzyme mimicking activities, enhanced catalytic activities, low cost, ease of preparation, stability and biocompatibility. Nanozymes include metal and metal oxide nanoparticles mimicking oxidases, peroxidases, superoxide dismutase and catalases while enzymatic and non-enzymatic biomolecules were used for preparing hybrid nanoflower. In this review nanozymes and hybrid nanoflower have been compared in terms of physiochemical properties, common synthetic routes, mechanism of action, modification, green synthesis and application in the field of disease diagnosis, imaging, environmental remediation and disease treatment. We also address the current challenges facing nanozyme and hybrid nanoflower research and the possible way to fulfil their potential in future.

Electrochemical-Based Sensing Platforms for Detection of Glucose and H2O2 by Porous Metal-Organic Frameworks: A Review of Status and Prospects

Establishing enzyme-free sensing assays with great selectivity and sensitivity for glucose and H₂O₂ detection has been highly required in biological science. In particular, the exploitation of nanomaterials by using noble metals of high conductivity and surface area has been widely investigated to act as selective catalytic agents for molecular recognition in sensing platforms. Several approaches for a straightforward, speedy, selective, and sensitive recognition of glucose and H₂O₂ were requested. This paper reviews the current progress in electrochemical detection using metal-organic frameworks (MOFs) for H₂O₂ and glucose recognition. We have reviewed the latest electrochemical sensing assays for in-place detection with priorities including straightforward procedure and manipulation, high sensitivity, varied linear range, and economic prospects. The mentioned sensing assays apply electrochemical systems through a rapid detection time that enables real-time recognition. In profitable fields, the obstacles that have been associated with sample preparation and tool expense can be solved by applying these sensing means. Some parameters, including the impedance, intensity, and potential difference measurement methods have permitted low limit of detections (LODs) and noticeable durations in agricultural, water, and foodstuff samples with high levels of glucose and H₂O₂.

Nanozyme and Stimulated Fluorescent Cu-Based Metal-Organic Frameworks (Cu-MOFs) Functionalized with Engineered Aptamers as a Molecular Recognition Element for Thrombin Detection in the Plasma of COVID-19 Patients

An essential tool in the management and control of the COVID-19 pandemic is the development of a fast, selective, sensitive, and inexpensive COVID-19 biomarkers detection method. Herein, an ultrasensitive and label-free biosensing strategy was described for the colorimetric and fluorimetric detection of thrombin. A dual-mode aptasensing method based on integrating engineered ssDNA with a stimulated fluorescent enzyme-mimetic copper-based metal-organic framework (Cu-MOF) as a molecular recognition element for thrombin was investigated. Cu-MOFs displayed stimulated fluorescence and enzyme-mimetic peroxidase activities that oxidize the chromogenic colorless substance TMB to blue-colored oxTMB. The thrombin-based aptamer (ssDNA) can be immobilized on the Cu-MOF surface to form a functionalized composite, ssDNA/MOF, and quench the stimulated fluorescence emission and the enzymatic activity of the Cu-MOF. Later, addition of thrombin recovers the fluorescence and enzymatic activity of the MOF. Thus, a turn-on colorimetry/fluorimetry aptasensing probe was designed for the detection of thrombin. Based on colorimetric assay, 350 pM was recorded as the lower limit of detection (LOD), while based on the fluorescence mode, 110 fM was recorded as the LOD (when S/N = 3). The label-free aptasensing probe was used successfully for the detection of thrombin in COVID-19 patients with satisfactory recoveries, 95-98%. Since the detection time of our aptasensor is relatively rapid (45 min) and due to the low-cost precursors and easy-to-operate characteristics, we believe that it has great potential to be used in point-of-care testing (POCT).