A colorimetric strategy for ascorbic acid sensing based on the peroxidase-like activity of core-shell Fe3O4/CoFe-LDH hybrid

Tunable Structured 2D Nanobiocatalysts: Synthesis, Catalytic Properties and New Horizons in Biomedical Applications

2D materials have offered essential contributions to boosting biocatalytic efficiency in diverse biomedical applications due to the intrinsic enzyme-mimetic activity and massive specific surface area for loading metal catalytic centers. Since the difficulty of high-quality synthesis, the varied structure, and the tough choice of efficient surface loading sites with catalytic properties, the artificial building of 2D nanobiocatalysts still faces great challenges. Here, in this review, a timely and comprehensive summarization of the latest progress and future trends in the design and biotherapeutic applications of 2D nanobiocatalysts is provided, which is essential for their development. First, an overview of the synthesis-structure-fundamentals and structure-property relationships of 2D nanobiocatalysts, both metal-free and metal-based is provided. After that, the effective design of the active sites of nanobiocatalysts is discussed. Then, the progress of their applied research in recent years, including biomedical analysis, biomedical therapeutics, pharmacokinetics, and toxicology is systematically highlighted. Finally, future research directions of 2D nanobiocatalysts are prospected. Overall, this review to provide cutting-edge and multidisciplinary guidance for accelerating future developments and biomedical applications of 2D nanobiocatalysts is expected.

Application of cobalt-cerium-iron ternary layered double hydroxide for extraction of perfluorooctane sulfonate followed by HPLC-MS/MS analysis

Herein, Ce-doped CoFe layered double hydroxide (LDH), noted as CoCeFe ternary LDH, was prepared using the co-precipitation route. Prosperous synthesis of CoFe LDH and successful partial replacement of iron cations with cerium cations in CoCeFe ternary LDH were confirmed by X-ray diffraction patterns, energy-dispersive X-ray spectroscopy, and elemental dot-mapping images. Nanosheet morphology was recognized for both CoFe LDH and CoCeFe ternary LDH from scanning electron microscopy and transmission electron microscopy micrographs. In the following, a dispersive solid phase extraction (DSPE) method was developed using the synthesized CoCeFe ternary LDH as a sorbent for extracting perfluorooctanesulfonic acid (PFOS) from wastewater samples. For the selective analysis of PFOS, high-performance liquid chromatography-tandem mass spectroscopy (HPLC-MS/MS) in multiple reaction monitoring mode was used. Analytical parameters such as the limit of detection equal to 0.02 μg/L, with a linear range of 0.05-300 μg/L, the limit of quantification equal to 0.05 μg/L, and an enrichment factor equal to 23.3 were achieved for PFOS at the optimized condition (sorbent: 5 mg of CoCeFe ternary LDH, eluent type and volume: 150 μL mobile phase, pH: 3, adsorption time: 3 min, and desorption time: 5 min). The developed strategy for the analysis of PFOS was tested in real wastewater samples, including copper mine and petrochemical wastewater. The amount of analytes in real samples was calculated using the standard addition method, and good relative recovery in the range of 86%-105% was obtained. The main novelty of this research is the application of CoCeFe ternary LDH to extract the PFOS from wastewater using the DSPE method for determination by HPLC-MS/MS.

Fe3O4 nanoparticles entrapped in the inner surfaces of N-doped carbon microtubes with enhanced biomimetic activity

Tubular structured composites have attracted great interest in catalysis research owing to their void-confinement effects. In this work, we synthesized a pair of hollow N-doped carbon microtubes (NCMTs) with Fe3O4 nanoparticles (NPs) encapsulated inside NCMTs (Fe3O4@NCMTs) and supported outside NCMTs (NCMTs@Fe3O4) while keeping other structural features the same. The impact of structural effects on the catalytic activities was investigated by comparing a pair of hollow-structured nanocomposites. It was found that the Fe3O4@NCMTs possessed a higher peroxidase-like activity when compared with NCMTs@Fe3O4, demonstrating structural superiority of Fe3O4@NCMTs. Based on the excellent peroxidase-like catalytic activity and stability of Fe3O4@NCMTs, an ultra-sensitive colorimetric method was developed for the detection of H2O2 and GSH with detection limits of 0.15 μM and 0.49 μM, respectively, which has potential application value in biological sciences and biotechnology.

Activation of peroxydisulfate via BiCoFe-layered double hydroxide for effective degradation of aniline

The sulfate radical-based advanced oxidation processes (SR-AOPs) is a promising method for the degradation of pollutants, with the development of highly efficient catalysts for persulfate activation has been widely concerned. The novel BiCoFe-LDH (BCF-x) was synthesized successfully by coprecipitation method, which can activate peroxydisulfate (PDS) efficiently to degrade aniline. Comparative analysis with pure CoFe-LDH revealed a remarkable increase in reaction rate constant by approximately 14.66 times; the degradation rate of aniline (10 mg/L) was 100% in 60 min with the condition of 0.5 g/L BCF-1.5 and 0.5 g/L PDS, due to BCF-1.5 which was characterized as a complex of CoFe-LDH and Bi2O2CO3, promoting electron transport to improve the efficiency of activated PDS. In the reaction system, SO4•-, ·OH, and 1O2 were responsible for the aniline degradation and ·OH was the primary one. Furthermore, this work proposes a reaction electron transfer catalytic mechanism, which provided a new insight and good application prospect for efficient activation of PDS for pollutant degradation.

Co-based Nanozymatic Profiling: Advances Spanning Chemistry, Biomedical, and Environmental Sciences

Nanozymes, next-generation enzyme-mimicking nanomaterials, have entered an era of rational design; among them, Co-based nanozymes have emerged as captivating players over times. Co-based nanozymes have been developed and have garnered significant attention over the past five years. Their extraordinary properties, including regulatable enzymatic activity, stability, and multifunctionality stemming from magnetic properties, photothermal conversion effects, cavitation effects, and relaxation efficiency, have made Co-based nanozymes a rising star. This review presents the first comprehensive profiling of the Co-based nanozymes in the chemistry, biology, and environmental sciences. The review begins by scrutinizing the various synthetic methods employed for Co-based nanozyme fabrication, such as template and sol-gel methods, highlighting their distinctive merits from a chemical standpoint. Furthermore, a detailed exploration of their wide-ranging applications in biosensing and biomedical therapeutics, as well as their contributions to environmental monitoring and remediation is provided. Notably, drawing inspiration from state-of-the-art techniques such as omics, a comprehensive analysis of Co-based nanozymes is undertaken, employing analogous statistical methodologies to provide valuable guidance. To conclude, a comprehensive outlook on the challenges and prospects for Co-based nanozymes is presented, spanning from microscopic physicochemical mechanisms to macroscopic clinical translational applications.

Co, Fe Dual-Doped MoS2 Nanosheets on Polypyrrole Microtubes as Effective Peroxidase Mimics for Glutathione Sensing

Heteroatom doping is considered an effective way to enhance the catalytic activity of MoS2 nanosheets (NSs). In the paper, dual-metal doping was proposed to incorporate Fe and Co into hierarchical MoS2 ultrathin NSs, which grew directly on polypyrrole microtubes (Fe, Co-MoS2@PPy), for the enhanced enzyme-like catalytic reaction. The particular hollow tubular structure realized effective electron transfer. The doped Fe and Co tuned the electronic architecture of the MoS2 NSs to enhance the enzyme-like catalytic activity. The abundant exposed void spaces facilitated ion diffusion/penetration between the PPy interlayer and Fe-Co doped MoS2 shell, leading to heterostructured synergistic effects. Therefore, the synthesized Fe and Co-MoS2@PPy composites showed remarkable catalytic activity. The high catalytic efficiency of Fe and Co-MoS2@PPy was confirmed with the reaction of tetramethylbenzidine (TMB) and H2O2 for visible detection. The blue color disappeared after adding glutathione (GSH). Thus, this procedure was used as a convenient way to detect GSH with a detection limit of 0.76 μM. The dual-metal-doped strategy was confirmed to improve the performance of MoS2 nanocomposites and could be used as a promising matrix for other applications, such as electrochemical energy conversion, medical diagnosis, and others.

Design and application of histidine-functionalized ZnCr-LDH nanozyme for promoting bacteria-infected wound healing

Excessive use of antibiotics can lead to an increase in antibiotic-resistant bacteria, which makes it a serious health threat. Therefore, developing new materials with antibacterial activity, such as nanozymes, has gained considerable attention. Reactive oxygen species (ROS) produced by nanozymes have rapid and effective antibacterial efficacy. Here, histidine (His) modified ZnCr layered double hydroxide (LDH) was synthesized inspired by the natural enzyme, and the enzyme-like activity of His/ZnCr-LDH was tested using a colorimetric method. Then, we developed an acid-enhanced antibacterial method based on the high peroxidase-like activity of His/ZnCr-LDH, and its ROS-generating capability in the presence of glucose oxidase (GOx) and glucose (Glu) as a source of hydrogen peroxide (H2O2). Gluconic acid (GA), the main product of the GOx reaction, provides an acidic environment and promotes ROS generation. The mentioned strategy shows high antibacterial activity at a low minimum inhibitory concentration (MIC) which represents the potential of His/ZnCr-LDH for effective bacterial elimination (3.5 μg mL-1 for S. aureus and 6 μg mL-1 for E. coli). In addition, animal experiments illustrated that the His/ZnCr-LDH can successfully boost the curing of infected wounds. The outcomes indicate that amino acid modified LDHs offer a new strategy for effective bacterial removal in different medical applications.

PEG mediated NiMn2O4 nanomaterials as a nano catalyst for peroxidase mimetic activity and photocatalytic degradation

Artificial peroxidases have garnered a lot of attention owing to their tremendous superiority over their natural counterparts. Here, NiMn2O4 nanoparticles have been successfully prepared through PEG assisted hydrothermal method. The varied PEG concentrations significantly altered the morphology and particle size of the synthesizedmaterials. We demonstrate the improved peroxide-like assay of different NiMn2O4 nanoparticles for the first time. Among them, Ni4 nanoparticles exhibit good peroxidase-like activity by generating the oxidation of chromogenic substrate 3, 3', 5, 5'-tetramethylbenzidine (TMB) in the presence of H2O2 and a blue color charge transfer product with an absorption maximum is positioned at 652 nm. These observations led to the development of a method for assessingH2O2 that can be read visually and photometrically. The Ni4 nanoparticles show enhanced kinetics compared to the natural enzyme horse radish peroxidase (HRP) with a lower Km (0.168 mM) value. Additionally, this Ni4 nanosphere applies as a visible light photocatalyst for the degradation of methylene blue (MB) and rhodamine B (Rh B) dyes under visible-light irradiation. Under optimized conditions, the degradationrates of MB and Rh B are 68 and 80.7 %, respectively, after 210 min, and recyclable efficiency is about 99 % for Rh B photocatalytic degradation in the first test and 98 % for five cycles, and about 98 % for MB photocatalytic degradation in the first test and 97 % for five cycles.

A robust and facile label-free method for highly sensitive colorimetric detection of ascorbic acid in fresh fruits based on peroxidase-like activity of modified FeCo-LDH@WO3 nanocomposite

Many compounds such as amino acids and oligonucleotides have been shown to effectively change peroxidase-like activity of nanoparticles. While a few studies have focused on mimicking the active site of natural enzymes on nanozymes and thus increasing their substrate affinity. Therefore, in this work, the surface of FeCo@WO3 nanocomposite was modified using guanosine triphosphate (GTP) to mimic the histidine of peroxidase enzyme's active site and its modification was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FT-IR). Then, the peroxidase-mimicking activity of the modified nanocomposite was tested using a colorimetric method, based on the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2). It was found that GTP improves the activity of FeCo@WO3 as a natural peroxidase active site's distal histidine residue. Ascorbic acid (AA) is a powerful antioxidant that induces the reduction of blue color (oxidized TMB) ox-TMB to colorless TMB. The colorimetric method was applied for the sensitive detection of AA in common fruits. The linear range of AA was 10-100 μM with a limit of detection (LOD) of 0.27 μM, which provides a rapid and sensitive method for testing AA in the field of food analysis.

Green Synthesis of Au Magnetic Nanocomposites Using Waste Chestnut Skins and Their Application as a Peroxidase Mimic Nanozyme Electrochemical Sensing Platform for Sodium Nitrite

An electrochemical sensor with high sensitivity for the detection of sodium nitrite was constructed based on the peroxidase-like activity of Au magnetic nanocomposites (Au@Fe3O4). The Au@Fe3O4 composite nanoparticles were green-synthesized via the reduction of gold nanoparticles (AuNPs) from waste chestnut skins combined with the sonochemical method. The nanoparticles have both the recoverability of Fe3O4 and the advantage of being able to amplify electrical signals. Furthermore, the synergistic effect of green reduction and sonochemical synthesis provides a functional approach for the preparation of Au@Fe3O4 with significant peroxidase-like activities. The physicochemical properties were characterized using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), the Brunauer-Emmett-Teller (BET) method, and Fourier transform infrared spectroscopy (FT-IR). The electrochemical properties of sodium nitrite were determined with cyclic voltammetry (CV) and chronoamperometry (i-t). The results revealed that Au@Fe3O4 acted as a peroxidase mimic to decompose hydrogen peroxide to produce free radicals, while ·OH was the primary free radical that promoted the oxidation of sodium nitrite. With the optimal detection system, the constructed electrochemical sensor had a high sensitivity for sodium nitrite detection. In addition, the current response had a good linear relationship with the sodium nitrite concentration in the range of 0.01-100 mmol/L. The regression equation of the working curve was y = 1.0752x + 4.4728 (R2 = 0.9949), and the LOD was 0.867 μmol/L (S/N = 3). Meanwhile, the constructed detection system was outstanding in terms of recovery and anti-interference and had a good detection stability of more than 96.59%. The sensor has been successfully applied to a variety of real samples. In view of this, the proposed novel electrochemical analysis method has great prospects for application in the fields of food quality and environmental testing.

Controlled molecular arrangement of easily aggregated deoxycholate with layered double hydroxide

Deoxycholate (DA) is a natural emulsifying agent involved in the absorption of dietary lipids. Due to the facial distribution of hydrophobic-hydrophilic region, DA easily aggregates under ambient conditions, and this property hinders the practical application of DA in clinical applications. In this study, we found that the molecular arrangement of DA molecules could be controlled by using layered double hydroxide (LDH) under a specific reaction condition. The effect of reaction methods such as co-precipitation, ion exchange and reconstruction on the molecular arrangement of DA was investigated by X-ray diffraction, Fourier-transform infrared spectroscopy, high-resolution transmission electron microscopy and differential scanning calorimetry. It was demonstrated that the self-aggregation of DA molecules could be suppressed by the oriented arrangement of DA between the gallery space of LDH. The DA moiety was well stabilized in the LDH layers due to the electrostatic interaction between DA molecules and LDH layers. The most ordered arrangement of DA molecules was observed when DA was incorporated into LDH via a reconstruction method. The DA molecules arranged in LDH via reconstruction did not show significant exothermic or endothermic behaviour up to 400°C, showing that the DA moiety lost its intermolecular attraction in between LDH layers.

Nitrogen-doped porous carbon nanomaterials synthesized using a magadiite template as efficient peroxidase mimics for colorimetric detection of ascorbic acid as an antioxidant

Nanomaterials with intrinsic enzyme-like activity have gained substantial scientific attention as viable substitutes to natural biological enzymes owing to their cheap price and great stability. Numerous artificial enzyme mimics have been employed effectively in sectors such as sensing, environmental processing, and cancer treatment. In this study, novel nitrogen-doped porous carbon nanomaterials (CPs) were produced by modifying polypyrrole with magadiite using chemical oxidative polymerization and calcination methods. The obtained nitrogen-doped porous carbon nanomaterials exhibited improved peroxidase-like activity, which catalyzed the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2) to produce colorful compounds. Kinetic investigation revealed that the affinity for TMB of nitrogen-doped porous carbon peroxidase mimics was higher than that of genuine horseradish peroxidase (HRP). In addition, a sensitive assay with encouraging performance for the colorimetric detection of ascorbic acid (AA) was successfully fabricated employing nitrogen-doped porous carbon nanomaterials as peroxidase mimics. The results were satisfactory and demonstrated its potential application in antioxidant detection.

Exploiting the Potential of Magnetic Nanoparticles for Rapid Diagnosis Tests (RDTs): Nanoparticle-Antibody Conjugates and Color Development Strategies

Magnetic nanoparticles (MNPs) have emerged as a promising material in disease diagnostics due to their potential to enhance detection sensitivity, facilitate concentration and purification of target substances in diverse samples, and enable favorable color-based detection. In this study, antibody-conjugated MNPs were successfully synthesized and validated through two appropriate methods: the measurement of MNPs' size and the use of phosphatase methods. Additionally, three methods were suggested and implemented for developing color in MNPs-based immunoassay, including the formation of MNP aggregations, utilization of MNPs' peroxidase-like activity, and synthesis of dually-conjugated MNPs with both enzyme and antibody. In particular, color development utilizing nanoparticle aggregations was demonstrated to result in a more yellowish color as virus concentration increased, while the peroxidase activity of MNPs exhibited a proportional increase in color intensity as the MNP concentration increased. This observation suggests the potential applicability of quantitative analysis using these methods. Furthermore, effective concentration and purification of target substances were demonstrated through the collection of MNPs using an external magnetic field, irrespective of factors such as antibody conjugation, dispersion medium, or virus binding. Finally, based on the key findings of this study, a design proposal for MNPs-based immunoassay is presented. Overall, MNPs-based immunoassays hold significant potential for advancing disease diagnostics.

Pd nanocatalysts adsorbed onto silica nanoparticle coated indium tin oxide: a reusable nanozyme for glucose detection

Nanozymes are nanomaterials that exhibit enzyme-like activity upon exposure to a substrate solution. The use of noble and platinum group metals enhances enzyme-like catalytic activity. However, noble metals are obtained at a high cost; therefore, their recovery after use is of high importance. Herein, we report the fabrication of indium tin oxide-silica nanoparticles decorated with palladium nanoparticles (ITO-SiO2-prS-PdNPs). The ITO-SiO2-prS-PdNPs were evaluated for peroxidase-like activity toward the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. A colour change from clear or colourless TMB to blue colour (oxidized TMB products) was observed confirming the peroxidase-like activity. A typical Michaelis-Menten enzyme-like behaviour is observed with Km values of 0.68 mM for H2O2 and 0.47 mM for TMB, which are better than the reported values for horse-radish peroxidase (HRP) for the same substrate. The peroxidase-like activity of ITO-SiO2-prS-PdNPs was found to proceed via the electron-transfer mechanism. The ITO-SiO2-prS-PdNPs were cleaned successfully after each use by rinsing with water and ethanol solution thus making the surface simple and easy to recover and reuse. A reusable and highly selective colorimetric assay for glucose detection based on the peroxidase-like activity of ITO-SiO2-prS-PdNPs gave excellent results. ITO-SiO2-prS-PdNPs exhibited a good linear range of 5.0-30 μM, a low limit of detection (LOD) of 1.84 μM and a limit of quantification (LOQ) of 6.14 μM. Finally, the nanozyme (ITO-SiO2-prS-PdNPs) was successfully used to detect glucose in a complex newborn calf serum (NCS), representing a real sample.

A colorimetric smartphone-based sensor for on-site AA detection in tropical fruits using Fe-P/NC single-atom nanoenzyme

Ascorbic acid is one of the important vitamins to maintain human life activities and plays an irreplaceable role in regulating human redox metabolism. Fresh fruit can provide plenty of AA to maintain human metabolic balance. Thus, it is great significant to develop a rapid and convenient method for detection of AA to evaluate the freshness and nutritional quality of fruits. In this work, Fe single-atom nanoenzyme (Fe-SAN) based colorimetric sensor assisted with smartphone was designed for rapid and on-site AA detection in tropical fruits. Firstly, Fe-SAN with high oxidase-mimicking activity was synthesized by using green tea leaves as sources of carbon and nitrogen and NaH₂PO₂ as P source to obtain Fe-P/NC SAN, in which P was used to reconstruct the distribution of electronic to enhance the oxidase-mimicking activity of Fe-SAN. Besides, the as-synthesized Fe-P/NC SAN with remarkable oxidase-like activities could oxidize 3,3́,5,5́-tetramethylbenzidine (TMB) to blue colored oxidized TMB. AA could inhibit the oxidation of TMB, leading to blue fading. Based on the above principle, colorimetric sensor integrated with smartphone RGB mode was fabricated and exhibited a good linear detection range (0.5-100 μM) and low detection limit of 0.315 μM for AA detection under optimal conditions. More importantly, the developed sensor could rapidly and accurately detect AA in real sample, such as pineapple, wax apple and mango. Therefore, this research provides a new cost-effective method for the efficient and exact detection of AA in tropical fruit, which has a broad application prospect.

Activation of peroxymonosulfate by Co-Mg-Fe layered doubled hydroxide for efficient degradation of Rhodamine B

Reactive species serve as a key to remediate the contamination of refractory organic contaminants in advanced oxidation processes. In this study, a novel heterogeneous catalyst, CoMgFe-LDH layered doubled hydroxide (CoMgFe-LDH), was prepared for an efficient activation of peroxymonosulfate (PMS) to oxidize Rhodamine B (RhB). The characterization results showed that CoMgFe-LDH had a good crystallographic structure. Correspondingly, the CoMgFe-LDH/PMS process exhibited good capacity to remove RhB, which was equivalent to degradation performance as homogeneous Co(II)/PMS process. The RhB oxidation in the CoMgFe-LDH/PMS process was well described with pseudo-first-order kinetic model. Additionally, the oxidation process presented an excellent stability, and only 0.9% leaching rate was detected after six sequential reaction cycles at pH 5.0. The effects of initial pH, CoMgFe-LDH dosage, PMS concentration, RhB concentration, and inorganic anions on the RhB degradation were discussed in detail. Quenching experiments showed that sulfate radicals (SO₄^•-) acted as the dominant reactive species. Further, the removal of RhB from simulated wastewater was explored. The removal efficiency of RhB (90 μM) could reach 94.3% with 0.8 g/L of catalyst and 1.2 mM of PMS addition at pH 5.0, which indicated the CoMgFe-LDH/PMS process was also effective in degrading RhB in wastewater.

α-MnO2/FeCo-LDH on Nickel Foam as an Efficient Electrocatalyst for Water Oxidation

The ever-expanding human societies on the one hand and the diminishing fossil fuel resources on the other have driven man to find a suitable, cheap, clean, and accessible source of energy. Water splitting is a good solution to this crisis. Because of the slow kinetics of water oxidation reaction, it is important to select efficient and durable electrocatalysts to improve the reaction kinetics. In this research, α-MnO₂/FeCo-LDH catalysts on nickel foam were developed for water oxidation, which exhibited good catalytic performance and stability in a 0.1 M KOH solution. The electrocatalysts were synthesized by hydrothermal methods and characterized by XRD, FTIR, Raman, SEM, TEM, EDS, and MAP techniques. The proposed modified electrode has large exchange current, low overpotential, and small Tafel slope. Here, only an overpotential of 210 mV is required to achieve a current density of 5 mA cm² with a Tafel slope of 70.4 mV dec^-1 in an alkaline solution.

Advances in layered double hydroxide based labels for signal amplification in ultrasensitive electrochemical and optical affinity biosensors of glucose

Since the development of enzyme electrodes, the research area of glucose biosensing has seen outstanding progress and improvement. Numerous sensing platforms have been developed based on different immobilization techniques and improved electron transfer between the enzyme and electrode. Interestingly, these platforms have consistently used innovative nanostructures and nanocomposites. In recent years, layered double hydroxides (LDHs) have become key tools in the field of analytical chemistry owing to their outstanding features and benefits, such as facile synthesis, cost-effectiveness, substantial surface area, excellent catalytic performance, and biocompatibility. LDHs are often synthesized as nanomaterial composites or manufactured with specific three-dimensional structures. The purpose of this review is to illustrate the biosensing prospects of LDH-based glucose sensors and the need for improvement. First, various clinical and conventional approaches for glucose determination are discussed. The definitions, types, and various synthetic methodologies of LDHs are then explained. Subsequently, we discuss the various research studies regarding LDH-based electrochemical and optical assays, focusing on modified systems, improved electron transfers pathways (through developments in surface science), and different sensing designs based on nanomaterials. Finally, a summary of the current limitations and future challenges in glucose analysis is described, which may facilitate further development and applications.

Ultrasmall Pt Nanozymes Immobilized on Spherical Polyelectrolyte Brushes with Robust Peroxidase-like Activity for Highly Sensitive Detection of Cysteine

Distinct platinum (Pt) nanozymes as peroxidase mimics have received extensive interest owing to their outstanding catalytic activity, high environmental tolerance, lower consumption, and great potential in replacing natural enzymes. However, easy agglomeration of Pt nanoparticles (Pt NPs) resulting from the high surface free energy significantly decrease their peroxidase-like activity. Herein, spherical polyelectrolyte brush (SPB)-stabilized ultrasmall Pt NPs (SPB@Pt NPs) were prepared by a novel synthetic strategy where the SPB not only performed as a nanoreactor for the synthesis of ultrasmall Pt NPs but also greatly stabilized Pt NPs against aggregation. The well-defined SPB@Pt NP nanozymes exhibited outstanding peroxidase-like activity for the catalytic oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB and were then used to establish a colorimetric sensor for rapid detection of cysteine, giving a limit of detection of 0.11 μM. Moreover, the colorimetric detection system was demonstrated with outstanding performance in sensitive and selective detection of cysteine in the presence of several interference molecules. From these results, SPB@Pt NPs have been regarded as promising peroxidase mimics for a large number of applications such as in biosensing, biomedicine, the food industry, and environmental chemistry.

Recent trends in layered double hydroxides based electrochemical and optical (bio)sensors for screening of emerging pharmaceutical compounds

The rapid expansion of the human population has given rise to new environmental and biomedical concerns, contributing to different advancements in the pharmaceutical industry. In the field of analytical chemistry over the last few years, layered double hydroxides (LDHs) have drawn significant attention, owing to their extraordinary properties. Furthermore, the novel advancement of LDH-based optical and electrochemical platforms to detect different pharmaceutical materials has acquired substantial attention because of their outstanding specificity, actual-time controlling, and user-friendliness. This review aims to recapitulate advanced LDHs-based optical and electrochemical sensors and biosensors to identify and measure important pharmaceutical compounds, such as anti-depressant, anti-inflammatory, anti-viral, anti-bacterial, anti-cancer, and anti-fungal drugs. Additionally, fundamental parameters, namely interactions between sensor and analyte, design rationale, classification, selectivity, and specificity are considered. Finally, the development of high-efficiency techniques for optical and electrochemical sensors and biosensors is featured to deliver scientists and readers a complete toolbox to identify a broad scope of pharmaceutical substances. Our goals are: (i) to elucidate the characteristics and capabilities of available LDHs for the identification of pharmaceutical compounds; and (ii) to deliver instances of the feasible opportunities that the existing devices have for the developed sensing of pharmaceuticals regarding the protection of ecosystems and human health at the global level.

Enhancing enzymatic activity of Mn@Co3O4 nanosheets as mimetic nanozyme for colorimetric assay of ascorbic acid

In nanozyme-based assays, increasing enzymatic activity is very desirable for enhancing sensitivity and lowering the detection limit. In this study, novel Mn doped cobalt oxide nanosheets (Mn@Co₃O₄ NSs) were synthesized by hydrothermal process. The obtained Mn@Co₃O₄ possessed enhanced dual-enzyme mimetic, oxidase and peroxidase, and can catalytically oxidize of 3, 3', 5, 5'-tetramethylbenzidine (TMB), to a blue product of oxidized TMB. The enzyme kinetics were well-described mathematically using a common Michaelis-Menten and Lineweaver Burk model. The enzyme kinetics constant (K_m) was found to be 0.15 mM, which is relatively low comparing with pure Co₃O₄ nanosheets (0.35 mM) and natural enzyme HRP (0.434 mM). Therefore, the efficient colorimetric method was achieved for determination of H₂O₂ and ascorbic acid. The limit of detection (LOD) of H₂O₂ was 8.0 μM and the linear range was 20-200 μM based on direct turn on of the peroxidase-like activity of Mn@Co₃O₄. While, for ascorbic acid detection based on turn-off approach, the linearity range for the ascorbic acid was 1-8 μM with LOD of 0.4 μM. Moreover, the colorimetric system exhibited good stability and selectivity toward the detection of ascorbic acid effectively in real samples (vitamin C tablets) with satisfactorily accuracy and precision.

Cur@SF NPs alleviate Friedreich's ataxia in a mouse model through synergistic iron chelation and antioxidation

Abnormal iron metabolism, mitochondrial dysfunction and the derived oxidative damage are the main pathogeneses of Friedrich's ataxia (FRDA), a single-gene inherited recessive neurodegenerative disease characterized by progressive cerebellar and sensory ataxia. This disease is caused by frataxin (FXN) mutation, which reduces FXN expression and impairs iron sulfur cluster biogenesis. To date, there is no effective therapy to treat this condition. Curcumin is proposed harboring excellent ability to resist oxidative stress through Nrf2 activation and its newly found ability to chelate iron. However, its limitation is its poor water solubility and permeability. Here, we synthesized slow-release nanoparticles (NPs) by loading curcumin (Cur) into silk fibroin (SF) to form NPs with an average size of 150 nm (Cur@SF NPs), which exhibited satisfactory therapeutic effects on the improvement of FRDA manifestation in lymphoblasts (1 μM) derived from FRDA patients and in YG8R mice (150 mg/kg/5 days). Cur@SF NPs not only removed iron from the heart and diminished oxidative stress in general but also potentiate iron-sulfur cluster biogenesis, which compensates FXN deficiency to improve the morphology and function of mitochondria. Cur@SF NPs showed a significant advantage in neuron and myocardial function, thereby improving FRDA mouse behavior scores. These data encourage us to propose that Cur@SF NPs are a promising therapeutic compound in the application of FRDA disease.

State of the art: Lateral flow assays toward the point-of-care foodborne pathogenic bacteria detection in food samples

Diverse chemicals and some physical phenomena recently introduced in nanotechnology have enabled scientists to develop useful devices in the field of food sciences. Concerning such developments, detecting foodborne pathogenic bacteria is now an important issue. These kinds of bacteria species have demonstrated severe health effects after consuming foods and high mortality related to acute cases. The most leading path of intoxication and infection has been through food matrices. Hence, quick recognition of foodborne bacteria agents at low concentrations has been required in current diagnostics. Lateral flow assays (LFAs) are one of the urgent and prevalently applied quick recognition methods that have been settled for recognizing diverse types of analytes. Thus, the present review has stressed on latest developments in LFAs-based platforms to detect various foodborne pathogenic bacteria such as Salmonella, Listeria, Escherichia coli, Brucella, Shigella, Staphylococcus aureus, Clostridium botulinum, and Vibrio cholera. Proper prominence has been given on exactly how the labels, detection elements, or procedures have affected recent developments in the evaluation of diverse bacteria using LFAs. Additionally, the modifications in assays specificity and sensitivity consistent with applied food processing techniques have been discussed. Finally, a conclusion has been drawn for highlighting the main challenges confronted through this method and offered a view and insight of thoughts for its further development in the future.

"Three-in-One" Multifunctional Nanohybrids with Colorimetric Magnetic Catalytic Activities to Enhance Immunochromatographic Diagnosis

Colorimetric lateral flow immunoassay (LFIA) with gold nanoparticles (AuNPs) as signal reporters has been widely used in point-of-care testing. Nonetheless, the potential of traditional AuNP-based LFIA for the early diagnosis of disease is often compromised by limited sensitivity due to the insufficient colorimetric signal brightness of AuNPs. Herein, we develop a "three-in-one" multifunctional catalytic colorimetric nanohybrid (Fe₃O₄@MOF@Pt) composed of Fe₃O₄ nanoparticles, MIL-100(Fe), and platinum (Pt) nanoparticles. Fe₃O₄@MOF@Pt displays enhanced colorimetric signal brightness, fast magnetic response, and ultrahigh peroxidase-mimicking activity, which are beneficial to the enhancement of the sensitivity of LFIA by coupling with magnetic separation and catalytic amplification. When integrated with the dual-antibody sandwich LFIA platform, the developed Fe₃O₄@MOF@Pt can achieve an ultrasensitive immunochromatographic assay of procalcitonin with a sensitivity of 0.5 pg mL^-1, which is approximately 2280-fold higher than that of conventional AuNP-based LFIA and superior to previously published immunoassays. Therefore, this work suggests that the proposed catalytic colorimetric nanohybrid can act as promising signal reporters to enable ultrasensitive immunochromatographic disease diagnostics.

Recent Developments in Innovative Magnetic Nanoparticles-Based Immunoassays: From Improvement of Conventional Immunoassays to Diagnosis of COVID-19

During the ongoing COVID-19 pandemic, the development of point-of-care (POC) detection with high sensitivity and rapid detection time is urgently needed to prevent transmission of infectious diseases. Magnetic nanoparticles (MNPs) have been considered attractive materials for enhancing sensitivity and reducing the detection time of conventional immunoassays due to their unique properties including magnetic behavior, high surface area, excellent stability, and easy biocompatibility. In addition, detecting target analytes through color development is necessary for user-friendly POC detection. In this review, recent advances in different types of MNPs-based immunoassays such as improvement of the conventional enzyme-linked immunosorbent assay (ELISA), immunoassays based on the peroxidase-like activity of MNPs and based on the dually labeled MNPs, filtration method, and lateral-flow immunoassay are described and we analyze the advantages and strategies of each method. Furthermore, immunoassays incorporating MNPs for COVID-19 diagnosis through color development are also introduced, demonstrating that MNPs can become common tools for on-site diagnosis.

A bifunctional nanozyme of carbon dots-mediated Co9S8 formation

Controlling the size of nanocrystals and inhibiting their agglomeration are of paramount importance for achieving ideal catalytic performance. Here we discovered that carbon dots (CDs) are not only able to serve as reductants but also as stabilizers of ultrasmall Co₉S₈ nanocrystals by means of their surface terminal groups. As a result, ultrasmall Co₉S₈ nanocrystals are incorporated into porous carbon nanosheets formed by splicing CDs. The resultant nanocomposites display a rich pore structure accompanying with large specific surface area and outstanding bifunctional performances to mimic the catalytic activity of peroxidase and oxidase without exerting any external energy. More importantly, the unique architecture endows Co₉S₈ nanocrystals with high stability and good durability. The nanocomposites have been demonstrated as a colorimetric sensor for detection of ascorbic acid with a superior anti-interference ability as well as a detection limit of 0.2 μM. Our findings open new synthetic opportunities by tuning the interaction of CDs with the surrounding environment and enable advanced applications such as biomedicine and catalytic transformations.

Efficient degradation of Rhodamine B by magnetically recoverable Fe3O4-modified ternary CoFeCu-layered double hydroxides via activating peroxymonosulfate

Environment-friendly nano-catalysts capable of activating peroxymonosulfate (PMS) have received increasing attention recently. Nevertheless, traditional nano-catalysts are generally well dispersed and difficult to be separated from reaction system, so it is particularly important to develop nano-catalysts with both good catalytic activity and excellent recycling efficiency. In this work, magnetically recoverable Fe₃O₄-modified ternary CoFeCu-layered double hydroxides (Fe₃O₄/CoFeCu-LDHs) was prepared by a simple co-precipitation method and initially applied to activate PMS for the degradation of Rhodamine B (RhB). X-ray diffraction (XRD), fourier transform infrared spectrometer (FT-IR), scanning electron microscope (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller method (BET), and vibrating sample magnetometer (VSM) were applied to characterize morphology, structure, specific surface area and magnetism. In addition, the effects of several key parameters were evaluated. The Fe₃O₄/CoFeCu-LDHs exhibited high catalytic activity, and RhB degradation efficiency could reach 100% within 20 min by adding 0.2 g/L of catalyst and 1 mmol/L of PMS into 50 mg/L of RhB solution under a wide pH condition (3.0-7.0). Notably, the Fe₃O₄/CoFeCu-LDHs showed good super-paramagnetism and excellent stability, which could be effectively and quickly recovered under magnetic condition, and the degradation efficiency after ten cycles could still maintain 98.95%. Both radicals quenching tests and electron spin resonance (ESR) identified both HO• and SO₄^•- were involved and SO₄^•- played a dominant role on the RhB degradation. Finally, the chemical states of the sample's surface elements were measured by X-ray photoelectron spectroscopy (XPS), and the possible activation mechanism in Fe₃O₄/CoFeCu-LDHs/PMS system was proposed according to comprehensive analysis.

A Review on Metal- and Metal Oxide-Based Nanozymes: Properties, Mechanisms, and Applications

Since the ferromagnetic (Fe3O4) nanoparticles were firstly reported to exert enzyme-like activity in 2007, extensive research progress in nanozymes has been made with deep investigation of diverse nanozymes and rapid development of related nanotechnologies. As promising alternatives for natural enzymes, nanozymes have broadened the way toward clinical medicine, food safety, environmental monitoring, and chemical production. The past decade has witnessed the rapid development of metal- and metal oxide-based nanozymes owing to their remarkable physicochemical properties in parallel with low cost, high stability, and easy storage. It is widely known that the deep study of catalytic activities and mechanism sheds significant influence on the applications of nanozymes. This review digs into the characteristics and intrinsic properties of metal- and metal oxide-based nanozymes, especially emphasizing their catalytic mechanism and recent applications in biological analysis, relieving inflammation, antibacterial, and cancer therapy. We also conclude the present challenges and provide insights into the future research of nanozymes constituted of metal and metal oxide nanomaterials.

Magnetic Fe3O4@CoFe-LDH nanocomposite heterogeneously activated peroxymonosulfate for degradation of azo-dye AO7

In this study, a novel core@shell magnetic nanocomposite Fe₃O₄/CoFe-layered double hydroxide (Fe₃O₄@CoFe-LDH) was successfully synthesized by the co-precipitation method, and then employed as an efficient heterogeneous catalyst for activation of peroxymonosulfate (PMS) in removal of azo-dye acid orange 7 (AO7). The as-obtained nanocomposite was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results from these characterizations showed Fe₃O₄@CoFe-LDH to possess good ferromagnetism and a perfect crystalline structure with a typical core@shell morphology. The system of Fe₃O₄@CoFe-LDH11/PMS (cobalt : iron molar ratio of 1 : 1) achieved 95.1% removal rate of AO7 (40 mg L^-1) within 15 min under the optimized conditions, which outperformed bare Fe₃O₄ and raw CoFe-LDH11. Meanwhile, Fe₃O₄@CoFe-LDH11 displayed good adaptability in a wide pH range from 4 to 9 and relatively low PMS activation energy (39.9 kJ mol^-1). The interference tests revealed HCO₃ ^- to possess the strongest restriction effect. Only 57.7% AO7 was removed when 10 mM HCO₃ ^- was introduced, which was ascribed to HCO₃ ^- not only serving as a radical scavenger, but also increasing the pH of the system. The radical quenching tests demonstrated SO₄˙^- as the dominant reactive species during the catalytic reaction. Based on X-ray photoelectron spectroscopy (XPS) analysis, the core structure of Fe₃O₄ served as an electron donor for accelerating the cycle of Co(ii)/Co(iii) at the active site of the LDH outer shell. Also, Fe₃O₄@CoFe-LDH exhibited outstanding stability and recyclability, and maintained high degradation efficiency of AO7 even after five cycles. In sum, the proposed magnetic Fe₃O₄@CoFe-LDH nanocomposite has great potential for remediation of wastewater contaminated with synthetic dyes.

Biosensing platform on ferrite magnetic nanoparticles: Synthesis, functionalization, mechanism and applications

Ferrite magnetic nanoparticles (FMNPs) are gaining popularity to design biosensors for high-performance clinical diagnosis. The fusion of information shows that FMNPs based biosensors require well-tuned FMNPs as detection probes to produce large and specific biological signals with minimal non-specific binding. Nevertheless, there is a noticeable lacuna of information to solve the issues related to suitable synthesis route, particle size reduction, functionalization, sensitivity towards targeted intercellular biological tiny particles, and lower signal-to-noise ratio. Therefore it allows exploring unique characteristics of FMNPs to design a suitable sensing device for intracellular measurements and diseases detection. This review focuses on the extensively used synthesis routes, their advantages and limitations, crystalline structure, functionalization, along with recent applications of FMNPs in biosensors, taking into consideration their analytical figures of merit and range of linearity. This work also addresses the current progress, key factors for sensitivity, selectivity and productivity improvement along with the challenges, future trends and perspectives of FMNPs based biosensors.

Magnetic nanomaterials with unique nanozymes-like characteristics for colorimetric sensors: A review

Colorimetric sensors for the rapid detection of numerous analytes have been widely applied in many fields such as biomedicine, food industry and environmental science due to their highly sensitive and selective response, easy operation and visual identification by naked eyes. In this review, the recent progress of the colorimetric sensors based on the magnetic nanomaterials with unique nanozymes-like catalytic activity (magnetic nanozyme) and their colorimetric sensing applications are presented. Emerging magnetic nanozyme-based colorimetric sensors, such as metal oxide/sulfides-based, metal-based, carbon-based, and aptamer-conjugated magnetic nanomaterials, offer many desirable features for target analytes detection. And due to the unique nanoscale physical-chemical properties, magnetic nanozymes have been used to mimic the catalytic activity of natural enzymes such as peroxidases, oxidases and catalases. This review also highlights the catalytic mechanisms of enzyme-like reactions, and promising colorimetric sensing system for the detection of chemical compounds like H₂O₂, pesticide, ascorbic acid, dopamine, tetracyclines, perfluorooctane sulfonate, phenolic compounds, heavy metal ion and sulfite have been deeply discussed. In addition, the remaining challenges and future directions in utilizing magnetic nanozyme for colorimetric sensors are addressed.

Improving the Fenton-like catalytic performance of MnOx-Fe3O4/biochar using reducing agents: A comparative study

In this work, a Fenton-like system with MnO_x-Fe₃O₄/biochar composite (FeMn/biochar) and reducing agents (RAs) was constructed for pollutant degradation, aiming to enhance Fenton-like performance from both degradation efficacy and operational cost aspects. Batch experiments revealed that five well-characterized RAs (sodium borohydride (SBH), sodium thiosulfate (STS), ascorbic acid (AA), hydroxylamine (HA) and oxalic acid (OA)) could impact performance of FeMn/biochar-H₂O₂ system through multiple mechanisms, including variation of solution pH, competition for H₂O₂, electrostatic attraction and acceleration of metal redox cycle. Significantly, only OA and HA obviously enhanced the catalytic capacity of Fenton-like process and HA increased ciprofloxacin degradation efficiency from 38.2% to 92.8% with a low economic consumption as 4.16 US$/m³, well in agreement with the accelerated Fe(III/II) cycle and Mn(III/II) cycle in FeMn/biochar-H₂O₂-HA system. The accelerated metal redox cycle could enhance the decomposition of H₂O₂ into •OH and •O₂^-, which were verified to be the main reactive oxygen species responsible for ciprofloxacin degradation by radical trapping experiments. Meanwhile, FeMn/biochar-H₂O₂-HA system could also work effectively in real wastewaters, and exhibited favorable catalytic performance towards oxytetracycline, tetracycline, methyl orange, methylene blue, Rhodamine B, and naphthalene, indicating the applicability of FeMn/biochar-H₂O₂-HA system in oxidizing refractory pollutants in wastewaters.

A review on optical sensors based on layered double hydroxides nanoplatforms

In recent years, significant efforts have been devoted towards the fabrication and application of layered double hydroxides (LDHs) due to their tremendous features such as excellent biocompatibility with negligible toxicity, large surface area, high conductivity, excellent solubility, and ion exchange properties. Most impressive, LDHs offer a favorable environment to attach several substances such as quantum dots, fluorescein dyes, proteins, and enzymes, which leads to strengthening the catalytic properties or increasing the sensing selectivity and sensitivity of the resulted hybrids. With the extensive ongoing research on the application of nanomaterials, many studies have led to remarkable achievements in exploring LDHs as sensing nanoplatforms. In optical sensors, for instance, many sensing strategies were tailored based on the enzyme-mimicking properties of LDHs, including colorimetric and chemiluminescence procedures. Meanwhile, others were designed based on intercalating some fluorogenic substrates on the LDHs, whereby the sensing signal can be acquired by quenching or enhancing their fluorescence after the addition of analytes. In this review, we aim to summarize the recent advances in optical sensors that use layered double hydroxides as sensing platforms for the determination of various analytes. By outlining some representative examples, we accentuate the change of spectral absorbance, chemiluminescence, and photoluminescence phenomena triggered by the interaction of LDH or functionalized-LDH with the indicators and analytes in the system. And finally, current limitations and possible future orientation in designing further LDHs-based optical sensors are presented. It is hoped that this review will be helpful in assisting the establishment of more improved sensors based on LDHs features. Optical sensors based on layered double hydroxides (LDHs) nanoplatforms were reviewed. The sensing system and detection approaches were rationally reviewed. Possible future orientations were highlighted.

A colorimetric method for screening α-glucosidase inhibitors from flavonoids using 3,3',5,5'-tetramethylbenzidine as a chromogenic probe

A facile and novel colorimetric method for screening of α-glucosidase inhibitors (AGIs) from flavonoids using 3,3',5,5'-tetramethylbenzidine (TMB) as a chromogenic probe is proposed. This method is based on the colorimetric detection of ascorbic acid (AA) through the TMB oxidation reaction catalyzed by horseradish peroxidase (HRP) in the presence of hydrogen peroxide (H₂O₂). In the TMB/H₂O₂/HRP system, HRP catalyzes the oxidation of H₂O₂ to ‧OH radical which oxidizes TMB to blue-colored oxidized TMB (oxTMB). In the presence of AA, the production of ‧OH radical is suppressed and causes the decrease of oxTMB, resulting in the fading of the blue color and the decrease of absorbance at 652 nm. Based on this, the existence of AA can be facilely identified. In the 2-O-α-d-glucopyranosyl-l-ascorbic acid (AA-2 G)/α-glucosidase (α-Glu) system, the produced AA inhibits the oxidation of TMB to blue-colored oxTMB. In the presence of AGIs, the production of AA is inhibited, which inhibits the reduction of oxTMB, resulting in a blue color recovery and an increase of the absorbance at 652 nm. Based on this, the colorimetric method is developed for screening of AGIs from 7 flavonoids.

Layered Double Hydroxides in Bioinspired Nanotechnology

Layered Double Hydroxides (LDHs) are a relevant class of inorganic lamellar nanomaterials that have attracted significant interest in life science-related applications, due to their highly controllable synthesis and high biocompatibility. Under a general point of view, this class of materials might have played an important role for the origin of life on planet Earth, given their ability to adsorb and concentrate life-relevant molecules in sea environments. It has been speculated that the organic–mineral interactions could have permitted to organize the adsorbed molecules, leading to an increase in their local concentration and finally to the emergence of life. Inspired by nature, material scientists, engineers and chemists have started to leverage the ability of LDHs to absorb and concentrate molecules and biomolecules within life-like compartments, allowing to realize highly-efficient bioinspired platforms, usable for bioanalysis, therapeutics, sensors and bioremediation. This review aims at summarizing the latest evolution of LDHs in this research field under an unprecedented perspective, finally providing possible challenges and directions for future research.

Pt Nanoparticles with High Oxidase-Like Activity and Reusability for Detection of Ascorbic Acid

Noble metal nanoenzymes such as Pt, Au, Pd, etc. exhibit magnificent activity. However, due to the scarce reserves and expensive prices of precious metals, it is essential to investigate their enzyme-like activity and explore the possibility of their reuse. In this work, the oxidase-like activity and reusability of several Pt nanoparticles with different morphologies were detected. We compared the Pt nanoparticles (NPs) with a size of about 30 nm self-assembled by 5 nm Pt nanoparticles and Pt nanoparticles (Pt-0 HCl) with a diameter of about 5 nm, and found that their Michaelis-Menten constants (Km) were close and their initial performance similar, but the Pt NPs had better reusability. This was probably attributed to the stacked structure of Pt NPs, which was conducive to the substance transport and sufficient contact. At the same time, it was found that the size, dispersion, and organic substances adsorbed on the surface of Pt nanoparticles would have a significant impact on their reusability. A colorimetric detection method was designed using the oxidase-like activity of Pt NPs to detect ascorbic acid in triplicate. The limits of detection were 131 ± 15, 144 ± 14, and 152 ± 9 nM, with little difference. This research not only showed that the morphology of the catalyst could be changed and its catalytic performance could be controlled by a simple liquid phase synthesis method, but also that it had great significance for the reuse of Pt nanoenzymes in the field of bioanalysis.