MNPs@anionic MOFs/ERGO with the size selectivity for the electrochemical determination of H2O2 released from living cells

Metalation of metal-organic frameworks: fundamentals and applications

Metalation of metal-organic frameworks (MOFs) has been developed as a prominent strategy for materials functionalization for pore chemistry modulation and property optimization. By introducing exotic metal ions/complexes/nanoparticles onto/into the parent framework, many metallized MOFs have exhibited significantly improved performance in a wide range of applications. In this review, we focus on the research progress in the metalation of metal-organic frameworks during the last five years, spanning the design principles, synthetic strategies, and potential applications. Based on the crystal engineering principles, a minor change in the MOF composition through metalation would lead to leveraged variation of properties. This review starts from the general strategies established for the incorporation of metal species within MOFs, followed by the design principles to graft the desired functionality while maintaining the porosity of frameworks. Facile metalation has contributed a great number of bespoke materials with excellent performance, and we summarize their applications in gas adsorption and separation, heterogeneous catalysis, detection and sensing, and energy storage and conversion. The underlying mechanisms are also investigated by state-of-the-art techniques and analyzed for gaining insight into the structure-property relationships, which would in turn facilitate the further development of design principles. Finally, the current challenges and opportunities in MOF metalation have been discussed, and the promising future directions for customizing the next-generation advanced materials have been outlined as well.

Ultrasensitive Electrochemical Platform for Dopamine Detection Based on CoNi-MOF@ERGO Composite

An electrochemical sensor applied for dopamine (DA) detection was constructed. An easy static way was used to synthesize bimetallic CoNi-MOF. Next, it was mixed with graphene oxide (GO) under ultrasound to get a uniform suspension. Subsequently, the solution was coated on the glassy carbon electrode (GCE) to form CoNi-MOF@ERGO/GCE by the electrochemical reduction method. The interaction between CoNi-MOF and electrochemically reduced graphene oxide (ERGO) enhances the electrocatalytic performance for DA detection. CoNi-MOF@ERGO/GCE has a wider linear range (0.1-400 μM) and a lower detection limit (0.086 μM) under optimum conditions. Furthermore, it has been applied to test DA in human serum samples. The results reveal that the DA sensor shows excellent performance, which will provide a novel idea for more sensitive and quicker DA detection.

Co(II)-Based Metal-Organic Framework Derived CA-CoNiMn-CLDHs with Peroxidase-like Activity for Colorimetric Detection of Phenol

Given the serious harm of toxic phenol to human health and the ecological environment, it is urgent to develop an efficient, low-cost and sensitive nanoenzyme-based method to monitor phenol. MOF-derived nanozyme has attracted wide interest due to its hollow polyhedra structure and porous micro-nano frameworks. However, it is still a great challenge to synthesize MOF-derived multimetal synergistic catalytic nanoenzymes in large quantities with low cost. Herein, we reported the synthetic strategy of porous hollow CA-CoNiMn-CLDHs with ZIF-67 as templates through a facile solvothermal reaction. The prepared trimetallic catalyst exhibits excellent peroxidase-like activity to trigger the oxidative coupling reaction of 4-AAP and phenol in the presence of H2O2. The visual detection platform for phenol based on CA-CoNiMn-CLDHs is constructed, and satisfactory results are obtained. The Km value for CA-CoNiMn-CLDHs (0.21 mM) is lower than that of HRP (0.43 mM) with TMB as the chromogenic substrate. Because of the synergistic effect of peroxidase-like activity and citric acid functionalization, the built colorimetric sensor displayed a good linear response to phenol from 1 to 100 μM with a detection limit of 0.163 μM (3σ/slope). Additionally, the CA-CoNiMn-CLDHs-based visual detection platform possesses high-chemical stability and excellent reusability, which can greatly improve economic benefits in practical applications.

Hybridizing Ti3C2Tx Layers with Layered Double Hydroxide Nanosheets at the Molecular Level: A Smart Electrode Material for H2O2 Monitoring in Cancer Cells

Vertically stacked artificial 2D superlattice hybrids fabricated through molecular-level hybridization in a controlled fashion play a vital role in scientific and technological fields, but developing an alternate assembly of 2D atomic layers with strong electrostatic interactions could be much more challenging. In this study, we have constructed an alternately stacked self-assembled superlattice composite through integration of CuMgAl layered double hydroxide (LDH) nanosheets having positive charge with negatively charged Ti₃C₂T_x layers using well-controlled liquid-phase co-feeding protocol and electrostatic attraction and investigated its electrochemical performance in sensing early cancer biomarkers, i.e., hydrogen peroxide (H₂O₂). The molecular-level CuMgAl LDH/Ti₃C₂T_x superlattice self-assembly possesses superb conductivity and electrocatalytic properties, which are significant for obtaining a high electrochemical sensing aptitude. Electron penetration in Ti₃C₂T_x layers and rapid ion diffusion along 2D galleries have shortened the diffusion path and enhanced the charge transferring efficacy. The electrode modified with the CuMgAl LDH/Ti₃C₂T_x superlattice has demonstrated admirable electrocatalytic abilities in H₂O₂ detection with a wide linear concentration range and low real-time limit of detection (LOD) of 0.1 nM with signal/noise ratio (S/N) = 3. Practically, an electrochemical sensing podium based on the CuMgAl LDH/Ti₃C₂T_x superlattice has been effectively applied in real-time in vitro tracking of H₂O₂ effluxes excreted from different live cancer cells and normal cells after being encouraged by stimulation. The results exhibit that molecular-level heteroassembly holds great potential in electrochemical sensors to detect promising biomarkers.

pH-responsive dual-enzyme mimics based on hollow metal organic framework-derivatives β-Co(OH)2 for multiple colorimetric assays

A hollow metal organic framework derivative β-Co(OH)₂ has been prepared, which possesses oxidase and peroxidase-like activities. Oxidase-like activity is derived from the generation of free radicals, and peroxidase-like activity is related to the electron transfer process. Unlike other nanozymes with dual enzyme-like activities, β-Co(OH)₂ possesses pH-responsive enzyme-like activities, among which the β-Co(OH)₂ exhibits superior oxidase and peroxidase-like activities under pH of 4 and 6, respectively, which could avoid mutual interference between multiple enzymes. Based on the phenomenon that enzyme-like activities of β-Co(OH)₂ can catalyze colorless TMB to generate blue oxidized TMB (oxTMB) with absorption peak at 652 nm, the sensors integrating total antioxidant capacity and H₂O₂ quantification were developed. The oxidase-like activity-based colorimetric system has a sensitive response to ascorbic acid, Trolox, and gallic acid, in which the limit of detection for those antioxidant substances was 0.54 μM, 1.26 μM, and 14.34 μM, respectively. The sensors based on peroxidase-like activity had low limit of detection of 1.42 μM for H₂O₂ and a linear range of 5-1000 μM. The proposed method can be well applied to the detection of the total antioxidant capacity of kiwi, Vc tables, orange and tea extract with high accuracy, and H₂O₂ determination in milk and glucose detection in beverages with satisfactory recovery (within 97-106%).

Phosphate-driven H2O2 decomposition on DNA-bound bio-inspired activated carbon-based sensing platform for biological and food samples

Hydrogen peroxide (H₂O₂) is one of the most important reactive oxygen species (ROS). Increased endogenous H₂O₂ levels indicate oxidative stress and could be a potential marker of many diseases, including Alzheimer's, cardiovascular diseases, and diabetes. However, consuming H₂O_2-incorporated food has adverse effects on humans and is a serious health concern. We used salmon testes DNA with bio-inspired activated carbon (AC) as an electrocatalyst for developing a novel H₂O₂ sensor. The phosphate backbone of DNA contains negatively charged oxygen groups that specifically attract protons from H₂O₂ reduction. We observed a linearity range of 0.01-250.0 μM in the H₂O₂ reduction peak current with a detection limit of 2.5 and 45.7 nM for chronoamperometric and differential pulse voltammetric studies. High biocompatibility of the sensor was achieved by the DNA, facilitating endogenous H₂O₂ detection. Moreover, this non-enzymatic sensor could also help in the rapid screening of H₂O₂-contaminated foods.

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.

A non-enzymatic, biocompatible electrochemical sensor based on N-doped graphene quantum dot-incorporated SnS2 nanosheets for in situ monitoring of hydrogen peroxide in breast cancer cells

The current study reports the design and construction of enzyme-free sensor using N-doped graphene quantum dots (N-GQDs)-decorated tin sulfide nanosheets (SnS₂) for in situ monitoring of H₂O₂ secreted by human breast cancer cells. N-GQDs nanoparticles having a size of less than 1 nm were incorporated into SnS₂ nanosheets to form an N-GQDs@SnS₂ nanocomposite using a simple hydrothermal approach. The resulting hybrid material was an excellent electrocatalyst for the reduction of H₂O₂, owing to the combined properties of highly conductive N-GQDs and SnS₂ nanosheets. The N-GQDs@SnS₂-based sensing platform demonstrated substantial sensing ability, with a detection range of 0.0125-1128 µM and a limit of detection of 0.009 µM (S/N = 3). The sensing performance of N-GQDs@SnS₂ was highly stable, selective, and reproducible. The practical application of the N-GQDs@SnS₂ sensor was successfully demonstrated by quantifying H₂O₂ in lens cleaner, human urine, and saliva samples. Finally, the N-GQDs@SnS₂ electrode was successfully applied for the real-time monitoring of H₂O₂ released from breast cancer cells and mouse fibroblasts. This study paves the way to designing efficient non-enzymatic electrochemical sensors for various biomolecule detection using a simple method.

Improving the sensitivity for hydrogen peroxide determination with active V2O5 nanocubes incorporated on mesoporous TiO2

The capacity to generate a constant signal response from an enzyme on an electrode surface has been a fascinating topic of research from the past three decades. To nourish the enzymatic activity during electrochemical reactions, the immobilization of dual enzymes on the electrode surface could prevent the enzymatic loss without denaturation and thus long-term stability can be achieved. For effective immobilization of dual enzymes, mesoporous materials are the ideal choice because of its numerous advantages such as 1. The presence of porous structure facilitates high loading of enzymes 2. The formation of protective environment can withstand the enzymatic activity even at acidic or basic pH values and even at elevated temperatures. Herein, we develop bienzymatic immobilization of horseradish peroxidase (HRP) and cholesterol oxidase (ChOx) on mesoporous V₂O₅-TiO₂ based binary nanocomposite for effective sensing of hydrogen peroxide (H₂O₂) in presence of redox mediator hydroquinone (HQ). The utilization of redox mediator in second-generation biosensing of H₂O₂ can eliminate the interference species and reduces the operating potential with higher current density for electrochemical reduction reaction. Using this mediator transfer process approach at HRP/ChOx/V₂O₅-TiO₂ modified GC, the H₂O₂ can be determined at operating potential (-0.2 V) with good linear range (0.05-3.5 mM) higher sensitivity (1040 μAμM^-1 cm^-2) and lower detection limit of about 20 μM can be attained, which is due to higher mediation of electrons were transferred to the enzyme cofactors. These interesting characteristics could be due to mesoporous structure of V₂O₅-TiO₂ can induce large immobilization and facilitate higher interaction with enzymes for wide range of biosensing applications.

Recent advances in metal-based nanoporous materials for sensing environmentally-related biomolecules

Highly sensitive, stable, selective, efficient, and short reaction time sensors play a substantial role in daily life/industry and are the need of the day. Due to the rising environmental issues, nanoporous carbon and metal-based materials have attracted significant attention in environmental analysis owing to their intriguing and multifunctional properties and cost-effective and rapid detection of different analytes by sensing applications. Environmental-related issues such as pollution have been a significant threat to the world. Therefore, it is necessary to fabricate highly promising performance-based sensor materials with excellent reliability, selectivity and good sensitivity for monitoring various analytes. In this regard, different methods have been employed to fabricate these sensors comprising metal, metal oxides, metal oxide carbon composites and MOFs leading to the formation of nanoporous metal and carbon composites. These composites have exceptional properties such as large surface area, distinctive porosity, and high conductivity, making them promising candidates for several versatile sensing applications. This review covers recent advances and significant studies in the sensing field of various nanoporous metal and carbon composites. Key challenges and future opportunities in this exciting field are also part of this review.

Design and Application of Electrochemical Sensors with Metal-Organic Frameworks as the Electrode Materials or Signal Tags

Metal-organic frameworks (MOFs) with fascinating chemical and physical properties have attracted immense interest from researchers regarding the construction of electrochemical sensors. In this work, we review the most recent advancements of MOF-based electrochemical sensors for the detection of electroactive small molecules and biological macromolecules (e.g., DNA, proteins, and enzymes). The types and functions of MOF-based nanomaterials in terms of the design of electrochemical sensors are also discussed. Furthermore, the limitations and challenges of MOF-based electrochemical sensing devices are explored. This work should be invaluable for the development of MOF-based advanced sensing platforms.

Applications of metal-organic framework-based bioelectrodes

Metal-organic frameworks (MOFs) are an emerging class of porous nanomaterials that have opened new research possibilities. The inherent characteristics of MOFs such as their large surface area, high porosity, tunable pore size, stability, facile synthetic strategies and catalytic nature have made them promising materials for enormous number of applications, including fuel storage, energy conversion, separation, and gas purification. Recently, their high potential as ideal platforms for biomolecule immobilization has been discovered. MOF-enzyme-based materials have attracted the attention of researchers from all fields with the expansion of MOFs development, paving way for the fabrication of bioelectrochemical devices with unique characteristics. MOFs-based bioelectrodes have steadily gained interest, wherein MOFs can be utilized for improved biomolecule immobilization, electrolyte membranes, fuel storage, biocatalysis and biosensing. Likewise, applications of MOFs in point-of-care diagnostics, including self-powered biosensors, are exponentially increasing. This paper reviews the current trends in the fabrication of MOFs-based bioelectrodes with emphasis on their applications in biosensors and biofuel cells.

Electrochemical Sensors for the Detection of Reactive Oxygen Species in Biological Systems: A Critical Review

Reactive oxygen species (ROS) involving superoxide anion, hydrogen peroxide and hydroxyl radical play important role in human health. ROS are known to be the markers of oxidative stress associated with different pathologies including neurodegenerative and cardiovascular diseases, as well as cancer. Accordingly, ROS level detection in biological systems is an essential problem for biomedical and analytical research. Electrochemical methods seem to have promising prospects in ROS determination due to their high sensitivity, rapidity, and simple equipment. This review demonstrates application of modern electrochemical sensors for ROS detection in biological objects (e.g., cell lines and body fluids) over a decade between 2011 and 2021. Particular attention is paid to sensors materials and various types of modifiers for ROS selective detection. Moreover, the sensors comparative characteristics, their main advantages, disadvantages and their possibilities and limitations are discussed.

Metal–Organic Frameworks for Electrocatalytic Sensing of Hydrogen Peroxide

The electrochemical detection of hydrogen peroxide (H₂O₂) has become more and more important in industrial production, daily life, biological process, green energy chemistry, and other fields (especially for the detection of low concentration of H₂O_2). Metal organic frameworks (MOFs) are promising candidates to replace the established H₂O₂ sensors based on precious metals or enzymes. This review summarizes recent advances in MOF-based H₂O₂ electrochemical sensors, including conductive MOFs, MOFs with chemical modifications, MOFs-composites, and MOF derivatives. Finally, the challenges and prospects for the optimization and design of H₂O₂ electrochemical sensors with ultra-low detection limit and long-life are presented.

Copper-based metal-organic frameworks for biomedical applications

Metal-organic frameworks (MOFs) are a class of important porous, crystalline materials composed of metal ions (clusters) and organic ligands. Owing to the unique redox chemistry, photochemical and electrical property, and catalytic activity of Cu^2+/+, copper-based MOFs (Cu-MOFs) have been recently and extensively explored in various biomedical fields. In this review, we first make a brief introduction to the synthesis of Cu-MOFs and their composites, and highlight the recent synthetic strategies of two most studied representatives, three-dimensional HKUST-1 and two-dimensional Cu-TCPP. The recent advances of Cu-MOFs in the applications of cancer treatment, bacterial inhibition, biosensing, biocatalysis, and wound healing are summarized and discussed. Furthermore, we propose a prospect of the future development of Cu-MOFs in biomedical fields and beyond.

Electrochemically reduced graphene oxide/Cu-MOF/Pt nanoparticles composites as a high-performance sensing platform for sensitive detection of tetracycline

A promising sensing platform was constructed based on an electrochemically reduced graphene oxide (ErGO)/copper metal-organic framework (Cu-MOF)/platinum nanoparticles (ErGO/Cu-MOF/PtNPs) modified glassy carbon electrode for the detection of tetracycline. The ErGO/Cu-MOF/PtNPs composite electrode possessed an excellent electrochemical performance to tetracycline detection mainly due to the synergistic effect of ErGO, Cu-MOF and PtNPs. The electrochemical kinetics and catalytical mechanism of tetracycline were systematically studied, showing that tetracycline's electrocatalytic oxidation reaction was an absorption-controlled two-step process involving two electrons and one proton transfer, respectively. Low concentration of tetracycline was detected by amperometry with the a linear range of 1 ~ 200 μM (R² = 0.9900) and a detection limit of 0.03 μM (S/R = 3). The proposed sensor was successfully applied to the detection of tetracycline in the real water samples with recoveries of 93.5% ~ 106%, and relative standard deviations (RSD) of 4.65% ~ 5.21% (n = 3). Furthermore, acceptable stability, repeatability and reproducibility were verified for continuous determination of tetracycline under optimized conditions. The ErGO/Cu-MOF/PtNPs composite electrode also demonstrated better anti-interference performance compared to other types of antibiotics than that of similar structural tetracyclines. Therefore, the proposed ErGO/Cu-MOF/PtNPs composites might provide a potential sensing platform for detecting analogous tetracyclines or total tetracyclines in the environment.

High-activity daisy-like zeolitic imidazolate framework-67/reduced grapheme oxide-based colorimetric biosensor for sensitive detection of hydrogen peroxide

Colorimetric biosensors, based on enzyme-like nanomaterials, have come into the spotlight in virtue of their visual detection. Herein, a daisy-like zeolitic imidazolate framework-67/reduced grapheme oxide (ZIF-67/rGO) nanozyme with unique 3D hierarchical structures has been designed to realize visual detection of hydrogen peroxide (H₂O₂) that is recognized as a strong oxidizing agent or reactive oxygen species associated with oxidative stress in biological systems. The daisy-like ZIF-67/rGO is prepared by a facile one-step liquid-phase method conducted under room temperature. The successful introduction of rGO endows the daisy-like ZIF-67/rGO nanozyme with abundant porous structure, high specific surface area, and good charge transfer capability, which significantly accelerates the adsorbability and recognition towards the substrates and the oxidation rate of TMB-H₂O₂ reaction, and thus improving the nanozyme activity observably. It is conductive to nanozyme-modulated H₂O₂ determination. The established colorimetric biosensor platform based on ZIF-67/rGO nanozyme exhibits remarkable sensitivity and high specificity for the application in visual detection of H₂O₂. The detection limit of ZIF-67/rGO-based biosensor platform is as low as 3.81 μM, which is nearly 8 times lower than that of ZIF-67-based biosensor platform. Moreover, its potential applicability as an ideal platform for colorimetric biosensors is demonstrated by testing the concentration of H₂O₂ in milk samples, which sheds light on the promising application of the proposed biosensing system in point-of-care detection.

Binder free 3D core-shell NiFe layered double hydroxide (LDH) nanosheets (NSs) supported on Cu foam as a highly efficient non-enzymatic glucose sensor

Rational design with fine-tuning of the electrocatalyst material is vital for achieving the desired sensitivity, selectivity, and stability for an electrochemical sensor. In this study, a three-dimensional (3D) hierarchical core-shell catalyst was employed as a self-standing, binder-free electrode for non-enzymatic glucose sensing. The catalyst was prepared by decorating the shell of NiFe layered double hydroxide (LDH) nanosheets (NSs) on the core of Cu nanowires (NWs) grown on a Cu foam support. The optimized 3D core-shell Cu@NiFe LDH sensor demonstrated higher sensitivity (7.88 mA mM^-1cm^-2), lower limit of detection (0.10 µM) and wider linear range (1 µM to 0.9 mM) in glucose sensing with a low working potential (0.4 V). The applied sensor also showed excellent stability, reproducibility, interference ability as well as practicability in real environment. The detection of real samples further suggests its great feasibility for practical applications. The superior electrocatalytic performance is collectively ascribed to the excellent electro-conductivity of the Cu substrate, the distinct self-standing 3D porous nanostructure, the ultrathin homogenous architecture, and the appropriate loading amount of NiFe LDH NSs. This study then provides a non-enzymatic glucose sensor with 3D Cu@NiFe LDH electrode for ultrahigh sensitivity and stability.

Fabricated Metal-Organic Frameworks (MOFs) as luminescent and electrochemical biosensors for cancer biomarkers detection

In the health domain, a major challenge is the detection of diseases using rapid and cost-effective techniques. Most of the existing cancer detection methods show poor sensitivity and selectivity and are time consuming with high cost. To overcome this challenge, we analyzed porous fabricated metal-organic frameworks (MOFs) that have better structures and porosities for enhanced biomarker sensing. Here, we summarize the use of fabricated MOF luminescence and electrochemical sensors in devices for cancer biomarker detection. Various strategies of fabrication and the role of fabricated materials in sensing cancer biomarkers have been studied and described. The structural properties, sensing mechanisms, roles of noncovalent interactions, limits of detection, modeling, advantages, and limitations of MOF sensors have been well-discussed. The study presents an innovative technique to detect the cancer biomarkers by the use of luminescence and electrochemical MOF sensors. In addition, the potential association studies have been opening the way for personalized patient treatments and the development of new cancer-detecting devices.

A facile construction of Ag/MoSe2 composite based non-enzymatic amperometric sensor for hydrogen peroxide

We report an electrochemical non-enzymatic method for hydrogen peroxide (H2O2) detection based on Ag nanoparticle-decorated MoSe2 (Ag/MoSe2-500) hybrid nanostructures. These hybrid nanocomposites are easily prepared by in-situ reduction of Ag+...

Cu(ii)-assisted self-assembly of dicyandiamide-derived carbon dots: construction inspired from chemical evolution and its H2O2 sensing application

In the rapid development of artificial nanomaterials comparable to biological enzymes, we propose herein a novel concept for the construction of functional materials inspired from chemical evolution.

AgPt/MoS2 hybrid as electrochemical sensor for detecting H2O2 release from living cells

A novel non-enzymatic H2O2 biosensor based on a AgPt/MoS2 nanohybrid exhibits high sensitivity and selectivity.

Multi-tailoring of a modified MOF-derived CuxO electrochemical transducer for enhanced hydrogen peroxide sensing

Reasonable control of the redox states within the catalytic units together with the interconnection degrees of the substrate is of great significance in the modulation of a well-performing transducer. Herein, a novel carbon black (CB)-modified copper metal-organic framework nanomaterial (CB@Cu-MOF) prepared at room temperature was utilized as a precursor to synthesize mixed-valent copper-oxide composite catalysts (NC/Cu_xO-T). By tuning the carbonization process of the precursor at different temperatures (T = 100 °C, 200 °C, 300 °C and 400 °C), the different ratio configurations of the redox-alternated Cu_xO portions were successfully controlled with the simultaneous effective tailoring of the defect abundance in the N-doped carbon substrate. As a result, an optimized NC/Cu_xO-300 electrochemical H₂O₂ sensor was able to present a low detection limit (0.26 μM) and decent linear ranges (0.02-1.79 mM and 2.29-9.29 mM). Our strategy using easily available initial materials with mild preparation conditions is expected to promote the practical application of the star materials in laboratories.

Postmodulation of the Metal-Organic Framework Precursor toward the Vacancy-Rich CuxO Transducer for Sensitivity Boost: Synthesis, Catalysis, and H2O2 Sensing

Metal-organic frameworks (MOFs) act as versatile coordinators for the subsequent synthesis of high-performance catalysts by providing dispersed metal-ion distribution, initial coordination condition, dopant atom ratios, and so on. In this work, a crystalline MOF trans-[Cu(NO₃)₂(Him)₄] was synthesized as the novel precursor of a redox-alternating Cu_xO electrochemical catalyst. Through simple temperature modulation, the gradual transformation toward a highly active nanocomposite was characterized to ascertain the signal enhancing mechanism in H₂O₂ reduction. Owing to the proprietary structure of the transducer material and its ensuing high activity, a proof-of-principle sensor was able to provide an amplified sensitivity of 2330 μA mM^-1 cm^-2. The facile one-pot preparation and intrinsic nonenzymatic nature also suggests its wide potentials in medical settings.

Fabrication of Cu-hemin metal-organic-frameworks nanoflower supported on three-dimensional reduced graphene oxide for the amperometric detection of H2O2

A novel electrochemical sensor based on Cu-hemin metal-organic-frameworks nanoflower/three-dimensional reduced graphene oxide (Cu-hemin MOFs/3D-RGO) was constructed to detect H₂O₂ released from living cells. The nanocomposite was synthesized via a facile co-precipitation method using hemin as the ligand, then decorated with 3D-RGO. The prepared Cu-hemin MOFs showed a 3D hollow spherical flower-like structure with a large specific surface area and mesoporous properties, which could load more biomolecules and greatly enhance the stability by protecting the activity of hemin. In addition, the introduction of 3D-RGO effectively enhanced the conductivity of Cu-hemin MOFs. Thus, the proposed sensor (Cu-hemin MOFs/3D-RGO/GCE) showed excellent electrochemical performances towards H₂O₂ with a wide linear range (10-24,400 μM), high sensitivity (207.34 μA mM^-1 cm^-2), low LOD (0.14 μM), and rapid response time (less than 3 s). Most importantly, we prepared a Cu-hemin MOFs/3D-RGO/ITO electrode with cells growing on it. Compared with detecting H₂O₂ in cell suspension by GCE-based electrode, adhesion of cells on ITO could shorten the diffusion distance of H₂O₂ from solution to the surface of the electrode and achieve in situ and a real-time monitor of H₂O₂ released by living cells. This self-supported sensing electrode showed great potential applications in monitoring the pathological and physiological dynamics of cancer cells.

Ultrasensitive Detection of Hydrogen Peroxide Using Bi2Te3 Electrochemical Sensors

Electrochemical sensors, with high accuracy, good selectivity, and linear response, have been widely used for environmental protection, health monitoring, and disease treatment. However, to date, these sensors still have limit sensitivity or otherwise require the use of high-cost materials such as noble metals and enzymes. Here, we report a novel electrochemical sensor using a topological insulator, Bi₂Te₃. Through liquid-phase exfoliation, we prepared nano- and microflakes of Bi₂Te₃ and measured their performance in hydrogen peroxide sensing via electrocatalytic reduction processes. Our devices exhibit a sensitivity of ∼4900 μA mM^-1 cm^-2 and a detection limit of ∼10^-8 molar, both of which are superior to typical noble metal-based electrochemical sensors. Through electrochemical analysis and microkinetic simulations, we extracted the kinetic parameters and gained insights into the reaction mechanism. We attribute the ultrahigh sensitivity to the facile electron transfer at the Bi₂Te₃-aqueous solution interface.

Metal–organic framework derived metal oxide/reduced graphene oxide nanocomposite, a new tool for the determination of dipyridamole

NICo₂O₄/NIO@MOF-5 rGO can detect dipyridamole at trace levels with high selectivity and sensitivity.

Detection of pollutants in water bodies: electrochemical detection or photo-electrochemical detection?

The massive discharge of pollutants including endocrine-disrupting chemicals (EDCs), heavy metals, pharmaceuticals and personal care products (PPCPs) into water bodies is endangering the ecological environment and human health, and needs to be accurately detected. Both electrochemical and photo-electrochemical detection methods have been widely used for the detection of these pollutants, however, which one is better for the detection of different environmental pollutants? In this feature article, different electrochemical and photo-electrochemical detection methods are summarized, including the principles, classification, common catalysts, and applications. By summarizing the advantages and disadvantages of different detection methods, this review provides a guide for other researchers to detect pollutants in water bodies by using electrochemical and photo-electrochemical analysis.

Sn-MOF@CNT nanocomposite: An efficient electrochemical sensor for detection of hydrogen peroxide

A novel approach for the assembly of Sn-based metal organic framework (Sn-MOF) via solvothermal method and its composite (Sn-MOF@CNT) with electroactive material, carbon nanotubes (CNT) by sonochemical means, is described that is useful for hydrogen peroxide sensing; large surface area and pore volume of Sn-MOF were exploited where in the crystallinity of the Sn-MOF was preserved upon inclusion of CNT over its surface. The surface morphology and structural analysis of Sn-MOF and its composite form, Sn-MOF@CNT, were determined analytically through Fourier-transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), Brunauer-Emmett-Teller and Energy-dispersive X-ray spectroscopy (EDX). The developed Sn-MOF@CNT sensor was expansively used to determine and optimize the effect of scan rate, concentration and detection limits including the EDX and SEM analysis of used Sn-MOF@CNT nanocomposite's post hydrogen peroxide sensing. The electrochemical sensing with Sn-MOF@CNT revealed a lower limit of detection ~4.7 × 10^-3 μM with wide linear range between 0.2 μM and 2.5 mM. This study has explored a new strategy for the deposition of CNT over Sn-MOF via a simple sonochemical methodology for successful electrochemical detection of H₂O₂, an approach that can be imitated for other applications.

"Turn-on" ratiometric electrochemical detection of H2O2 in one drop of whole blood sample via a novel microelectrode sensor

Oxidative stress plays an important role in the pathogenesis of many diseases, while the exact mechanism that hydrogen peroxide (H₂O₂) as one of the most abundant reactive oxygen species (ROS) exerts its influence on oxidative stress remains unclear. We developed a novel turn-on ratiometric electrochemical sensor for the detection of H₂O₂ in blood samples. The electrochemical probe 5-(1,2-dithiolan-3-yl)-N-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pent-anamide (BA) was designed and synthesized for the selective detection of H₂O₂ via a one-step amide reaction. Meanwhile, Nile Blue A (NB) was optimized as an internal reference molecule, thus enabling accurate quantification of H₂O₂ in a complex environment. BA and NB were then co-assembled onto a carbon fiber microelectrode (CFME) coated with Au cones. The oxidation peak current ratio between BA and NB demonstrated good linearity with the logarithm of the H₂O₂ concentration values ranging from 0.5 μM to 400 μM with a low detection limit of 0.02 μM. The developed sensor showed remarkable selectivity against potential interferences in whole blood samples, especially for ascorbic acid, uric acid, and dopamine. In combination with the unique characteristics of CFME, such as a small size and good biocompatibility, the microsensor was used for rapid analysis of one drop of whole blood sample. This sensor not only creates a new platform for the detection of H₂O₂ in whole blood samples, but also provides a new design strategy of other ROS analysis for early diagnosis of ROS-related diseases, drug discovery processes, and pathological mechanisms.

Protein-Supported RuO2 Nanoparticles with Improved Catalytic Activity, In Vitro Salt Resistance, and Biocompatibility: Colorimetric and Electrochemical Biosensing of Cellular H2O2

Protein-supported nanoparticles have a great significance in scientific and nanotechnology research because of their "green" process, low cost-in-use, good biocompatibility, and some interesting properties. Ruthenium oxide nanoparticles (RuO₂NPs) have been considered to be an important member in nanotechnology research. However, the biosynthetic approach of RuO₂NPs is relatively few compared to those of other nanoparticles. To address this challenge, this work presented a new way for RuO₂NP synthesis (BSA-RuO₂NPs) supported by bovine serum albumin (BSA). BSA-RuO₂NPs are confirmed to exert peroxidase-like activity, electrocatalytic activity, in vitro salt resistance (2 M NaCl), and biocompatibility. Results indicate that BSA-RuO₂NPs have higher affinity binding for 3,3',5,5'-tetramethylbenzidine or H₂O₂ than bare RuO₂NPs. Moreover, BSA turns out to be a crucial factor in promoting the stability of RuO₂NPs. Taking the advantages of these improved properties, we established colorimetric (linear range from 2 to 800 μM, a limit of detection of 1.8 μM) and electrochemical (linear range from 0.4 to 3850 μM, a limit of detection of 0.18 μM) biosensors for monitoring in situ H₂O₂ secretion from living MCF-7 cells. Herein, this work offers a new biosynthesis strategy to obtain BSA-RuO₂NPs and sheds light on the sensitive biosensors to monitor the H₂O₂ secreted from living cells for promising applications in the fields of nanotechnology, biology, biosensors, and medicine.

Oxygen vacancy confined nickel cobaltite nanostructures as an excellent interface for the enzyme-free electrochemical sensing of extracellular H2O2 secreted from live cells

Oxygen vacancy (O_V) manufacturing is an effective way to boost the efficiency of a catalyst; therefore, the development of O_V-rich catalysts has attracted substantial research interest.