Yolk-shell nanostructured Fe3O4@C magnetic nanoparticles with enhanced peroxidase-like activity for label-free colorimetric detection of H2O2 and glucose

Ru-containing magnetic yolk-shell structured nanocomposite: a powerful, recoverable and highly durable nanocatalyst

A novel method was used to prepare a magnetic phenylene-based periodic mesoporous organosilica nanocomposite with yolk-shell structure (Fe3O4@YSPMO). The Fe3O4@YSPMO nanomaterial was prepared by using easily accessible pluronic-P123 and cetyltrimethylammonium bromide (CTAB) surfactants under basic conditions. This material was employed for effective immobilization of potassium perruthenate to prepare an Fe3O4@YSPMO@Ru nanocatalyst for the aerobic oxidation of alcohols. The physiochemical properties of the designed Fe3O4@YSPMO@Ru nanocomposite were studied using PXRD, FT-IR, TGA, SEM, TEM, ICP, VSM and XPS analyses. Fe3O4@YSPMO@Ru was effectively employed as a highly recoverable nanocatalyst in the selective aerobic oxidation of alcohols.

Novel hierarchical CuNiAl LDH nanotubes with excellent peroxidase-like activity for wide-range detection of glucose

Novel hierarchical CuNiAl layered double hydroxide (CuNiAl LDH) nanotubes were prepared with in situ transformation of Al₂O₃ produced using the atomic layer deposition (ALD) method. Based on the characterizations using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), FT-IR spectrometry, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), CuNiAl LDH displays a typical nanotube-like structure consisting of uniform ultrathin nanoflakes. It is also confirmed that nitrate precursors play a crucial role in the formation of the LDH hierarchical structure. The unique hierarchical tube-like structure for CuNiAl LDH can supply more active sites and higher surface areas, leading to outstanding peroxidase mimicking property. The kinetic analyses indicate that the catalytic behavior of CuNiAl LDH follows classic Michaelis-Menten models and the affinity of CuNiAl LDH to the substrate is significantly higher than horseradish peroxidase. A simple and label-free method was developed for the colorimetric detection of glucose. As low as 2.9 μM of glucose can be detected with a broad linear range from 10 to 200 μM. The established method is also proved to be suitable for glucose detection in juice samples.

A silicon nanoparticle-based nanoprobe for ratiometric fluorescence and visual detection of glucose

We synthesized SiNPs by a one-step method and established, for the first time, a novel SiNP-based nanoprobe (denoted as SiNPs/OPD/HRP/GOx) for ratiometric fluorescence and visual detection of glucose in serum samples.

Insights into the Formation of DNA-Magnetic Nanoparticle Hybrid Structures: Correlations between Morphological Characterization and Output from Magnetic Biosensor Measurements

Understanding the binding mechanism between probe-functionalized magnetic nanoparticles (MNPs) and DNA targets or amplification products thereof is essential in the optimization of magnetic biosensors for the detection of DNA. Herein, the molecular interaction forming hybrid structures upon hybridization between DNA-functionalized magnetic nanoparticles, exhibiting Brownian relaxation, and rolling circle amplification products (DNA-coils) is investigated by the use of atomic force microscopy in a liquid environment and magnetic biosensors measuring the frequency-dependent magnetic response and the frequency-dependent modulation of light transmission. This approach reveals the qualitative and quantitative correlations between the morphological features of the hybrid structures with their magnetic response. The suppression of the high-frequency peak in the magnetic response and the appearance of a new peak at lower frequencies match the formation of larger sized assemblies upon increasing the concentration of DNA-coils. Furthermore, an increase of the DNA-coil concentration induces an increase in the number of MNPs per hybrid structure. This study provides new insights into the DNA–MNP binding mechanism, and its versatility is of considerable importance for the mechanistic characterization of other DNA-nanoparticle biosensor systems.

Norfloxacin detection based on the peroxidase-like activity enhancement of gold nanoclusters

The use of nanomaterials as mimic enzymes provides a promising way to implement bio-molecule detection in living systems. However, to achieve highly efficient catalytic processes with gold nanocluster-based nanozymes is still challenging. In this study, a facile reduction method was utilized to synthesize gold nanoclusters with 1-methyl-D-tryptophan as the reducing and capping agent. The obtained gold nanoclusters exhibited a peroxidase-mimicking property in the redox reaction of 3,3',5,5'-tetramethylbenzidine to blue oxidized 3,3',5,5'-tetramethylbenzidine in the presence of H₂O₂. The addition of norfloxacin endowed the nanozymes with a 10-fold enhancement in catalytic efficiency due to the surface charge-controlled electron transfer modulation. The colorimetric sensing system presented a high selectivity toward norfloxacin. The good linear relationship of norfloxacin monitoring was gained in the range of 1.25~8.0 μM (R² = 0.996), with a detection limit of 0.2 μM. The practical application of the proposed protocol for the measurement of norfloxacin in capsules was realized. This demonstrates that on account of their significant catalytic efficiency enhancement, the gold nanocluster-based nanozymes hold great promise in realizing the selective detection of drugs. Graphical Abstract.

The Application of Metal-Organic Frameworks and Their Derivatives for Supercapacitors

Supercapacitors (SCs), one of the most popular types of energy-storage devices, present lots of advantages, such as large power density and fast charge/discharge capability. Being the promising SCs electrode materials, metal-organic frameworks (MOFs) and their derivatives have gained ever-increasing attention due to their large specific surface area, controllable porous structure and rich diversity. Herein, the recent development of MOFs-based materials and their application in SCs as the electrode are reviewed and summarized. The preparation method, the morphology of the materials and the electrical performance of various MOFs and their derivatives (such as carbon, metal oxide/hydroxide and metal sulfide) are briefly discussed. Most of recent works concentrate on Ni-, Co- and Mn-MOFs and their composites/derivatives. Conclusions and our outlook for the researches are also given, which would be a valuable guideline for the rational design of MOFs materials for SCs in the near future.

Tuning Atomically Dispersed Fe Sites in Metal-Organic Frameworks Boosts Peroxidase-Like Activity for Sensitive Biosensing

Although nanozymes have been widely developed, accurate design of highly active sites at the atomic level to mimic the electronic and geometrical structure of enzymes and the exploration of underlying mechanisms still face significant challenges. Herein, two functional groups with opposite electron modulation abilities (nitro and amino) were introduced into the metal-organic frameworks (MIL-101(Fe)) to tune the atomically dispersed metal sites and thus regulate the enzyme-like activity. Notably, the functionalization of nitro can enhance the peroxidase (POD)-like activity of MIL-101(Fe), while the amino is poles apart. Theoretical calculations demonstrate that the introduction of nitro can not only regulate the geometry of adsorbed intermediates but also improve the electronic structure of metal active sites. Benefiting from both geometric and electronic effects, the nitro-functionalized MIL-101(Fe) with a low reaction energy barrier for the HO* formation exhibits a superior POD-like activity. As a concept of the application, a nitro-functionalized MIL-101(Fe)-based biosensor was elaborately applied for the sensitive detection of acetylcholinesterase activity in the range of 0.2-50 mU mL^-1 with a limit of detection of 0.14 mU mL^-1. Moreover, the detection of organophosphorus pesticides was also achieved. This work not only opens up new prospects for the rational design of highly active nanozymes at the atomic scale but also enhances the performance of nanozyme-based biosensors.

A Colorimetric Immunosensor Based on Hemin@MI Nanozyme Composites, with Peroxidase-like Activity for Point-of-care Testing of Pathogenic E. coli O157:H7

Recently, nanozymes have become a topic of particular interest due to their high activity level, stability and biocompatibility. In this study, a visual, sensitive and selective point-of-care immunosensor was established to test the pathogen Escherichia coli O157:H7 (E. coli O157:H7). Hemin and magainin I (MI) hybrid nanocomposites (Hemin@MI) with peroxidase-mimicking activities were synthesized via a "one-pot" method, involving the simple mixing of an antimicrobial peptide (MI) against E. coli O157:H7 and hemin in a copper sulfate sodium phosphate saline buffer. Hemin@MI nanocomposites integrating target recognition and signal amplification were developed as signal probes for the point-of-care colorimetric detection of pathogenic E. coli O157:H7. Hemin@MI nanocomposites exhibit excellent peroxidase activity for the chromogenic reaction of ABTS, which allows for the visual point-of-care testing of E. coli O157:H7 in the range of 10² to 10⁸ CFU/mL, with a limit of detection of 85 CFU/mL. These data suggest this immunosensor provides accessible and portable assessments of pathogenic E. coli O157:H7 in real samples.

Synthesis, Catalytic Properties and Application in Biosensorics of Nanozymes and Electronanocatalysts: A Review

The current review is devoted to nanozymes, i.e., nanostructured artificial enzymes which mimic the catalytic properties of natural enzymes. Use of the term "nanozyme" in the literature as indicating an enzyme is not always justified. For example, it is used inappropriately for nanomaterials bound with electrodes that possess catalytic activity only when applying an electric potential. If the enzyme-like activity of such a material is not proven in solution (without applying the potential), such a catalyst should be named an "electronanocatalyst", not a nanozyme. This paper presents a review of the classification of the nanozymes, their advantages vs. natural enzymes, and potential practical applications. Special attention is paid to nanozyme synthesis methods (hydrothermal and solvothermal, chemical reduction, sol-gel method, co-precipitation, polymerization/polycondensation, electrochemical deposition). The catalytic performance of nanozymes is characterized, a critical point of view on catalytic parameters of nanozymes described in scientific papers is presented and typical mistakes are analyzed. The central part of the review relates to characterization of nanozymes which mimic natural enzymes with analytical importance ("nanoperoxidase", "nanooxidases", "nanolaccase") and their use in the construction of electro-chemical (bio)sensors ("nanosensors").

Yolk-Shell Fe3 O4 @Void@N-Carbon Nanostructures Based on One-Step Deposition of SiO2 and Resorcinol-3-Aminophenol-Formaldehyde (R-APF) Cocondensed Resin Dual Layers onto Fe3 O4 Nanoclusters

Yolk-shell magnetic nanoparticles@nitrogen-enriched Carbon nanostructures with a magnetic core and a hollow nitrogen-enriched carbon shell exhibit considerable promise in various applications, such as drug delivery, heterogenous catalysts, removal of metal ions and organic pollutants, and screening of biomolecules, due to their strong magnetic response, unique cavities, and the selective absorption ability of nitrogen-enriched groups. However, their complicated synthesis always involves possible surface modification, layer-by-layer deposition of a sacrificial middle layer and an outer nitrogen-enriched layer on magnetic nanoparticles, subsequent carbonization, and final removal of the sacrificial middle layer. Herein, yolk-shell Fe₃ O₄ @nitrogen-enriched carbon nanostructures are constructed based on NH₄ ⁺ ion-induced one-step deposition of SiO₂ and Resorcinol-3-aminophenol-formaldehyde cocondensed resin (R-APF) dual layers onto poly acrylic acid-modified Fe₃ O₄ nanoclusters without any extra surface modification. The N-Carbon shell thickness of the yolk-shell Fe₃ O₄ @Void@N-Carbon nanostructure can be finely tailored though tailoring the feeding amount of aminophenol and resorcinol to tune the thickness of the outer R-APF resin shell onto Fe₃ O₄ @SiO₂ intermediate particles. This NH₄ ⁺ ion-induced one-pot deposition of double layers can effectively promote synthesis efficiency of this kind of yolk-shell nanostructure.

Development of Magnesium Oxide-Silver Hybrid Nanocatalysts for Synergistic Carbon Dioxide Activation to Afford Esters and Heterocycles at Ambient Pressure

Multi-metallic hybrid nancatalysts consisting of a porous metal oxide host and metal satellite guests serve as a scaffold for multi-step transformations of divergent and energy-challenging substrates. Here we have developed a 3D porous MgO framework (Lewis basic host) with Ag⁰ nanoparticles (noble metal guest) for ambient pressure activation and insertion of CO₂ into unsaturated alkyne substrates. The hybrid MgO@Ag-x (x = 2, 5, 7, 8 at % Ag) catalysts are synthesized by impregnating Ag⁺ ions in porous MgO cubes followed by reduction using NaBH₄. Morphological (SEM, TEM, EDX mapping) and structural (PXRD, XPS) characterization reveal that the micron-sized hybrid cubes derive from self-assembly of ~100 nm (edge length) MgO cubes decorated with ~ 5 to 25 nm Ag⁰ NPs. Detailed XPS analysis illustrates Ag⁰ is present in two forms, <10 nm NPs and ~25 nm aggregates. The MgO@Ag-7 catalyst is effective for inserting CO₂ into aryl alkynes followed by S_N2 coupling with allylic chlorides to afford a wide range of ester and lactone heterocycles in excellent yields (61-93%) and with low E-factor (2.8). The proposed mechanism suggests a CO₂ capture and substrate assembly role for 3D porous MgO while Ag⁰ performs the key activation of alkyne and CO₂ insertion steps. The catalyst is recyclable (5x) with no significant loss of product yield. Overall, these results demonstrate viable approaches to hybrid catalyst development for challenging conversions such as CO₂ utilization in a green and sustainable manner.

Atomic structures and electronic properties of Ni or N modified Cu/diamond interface

The interfacial stability of copper/diamond directly affects its mechanical properties and thermal conductivity. The atomic structures and electronic properties of Cu/diamond and Cu/X/diamond interfaces have been identified to investigate the effect of interfacial additive X (X  =  Ni or N) on the low-index interfacial adhesion of copper/diamond composites. For unmodified composites, the interfacial stability decreases in the order of Cu(0 0 1)/diamond(0 0 1)  >  Cu(1 1 1)/diamond(1 1 1)  >  Cu(0 1 1)/diamond(0 1 1). The metallic interfacial additive Ni is found to enhance the Cu(0 1 1)/diamond(0 1 1) interfacial stability and exchange the interfacial stability sequence of (0 1 1) and (1 1 1) composites. The nonmetallic element N will promote the stability of Cu(1 1 1)/diamond(1 1 1) but not alter the stability order of the composites at different interfaces. To explain the origin of interfacial stability, a series of analyses on atomic structures and electronic properties have been carried out, including the identification of the type of formed interfacial boundaries, the measurement of interfacial bond lengths, and the calculations of density of states, bond populations, and atomic charge. The stability of the interface is found to be related to the type of formed interfacial boundary and bond, the interfacial bond populations, and the interfacial bond numbers. The layer-projected density of states reveals that all of the considered interfaces exhibit metal characteristics. The interfacial Ni additive is found to be an electron donor contributing the electrons to its bonded Cu and C atoms while the interfacial N atom is an electron acceptor where it mainly accepts the electrons from its bonded Cu and C.

Multi-triggered and enzyme-mimicking graphene oxide/polyvinyl alcohol/G-quartet supramolecular hydrogels

Supramolecular hydrogels with stimuli-responsive behaviors under aqueous environments are attractive for their potential applications in controlled drug delivery, clinical diagnostics, and tissue engineering. However, there still remain challenges in developing multicomponent hydrogels as a new generation of "smart" soft materials with multiple intelligent functions toward complex biochemical stimuli. In this work, a three dimensional (3D)-nanostructured supramolecular hydrogel was fabricated using a simple and facile strategy via the self-assembly of graphene oxide (GO) nanosheets, poly(vinyl alcohol) (PVA) chains, and G-quartet/hemin (G4/H) motifs. The as-prepared GO/PVA/G4/H hydrogel exhibited a honeycomb-like 3D GO network architecture as well as excellent mechanical properties. Importantly, the hydrogel demonstrated pH-inducing reversible and cyclic phase transitions between solution and hydrogel states, which could be used as "ink" for injectable 3D printing of different shaped patterns. Also, binary AND and OR logic gates were successfully built by encapsulating enzymes into the hydrogels, which responded to a variety of biochemicals. In addition, the hydrogels showed excellent peroxidase-like activity, achieving the ultrasensitive detection of H2O2 at a concentration as low as 100 nM by their deposition on an electrochemical electrode. The design of multicomponent hydrogels opens up an avenue to fabricate novel "smart" soft matter for biological and medical applications.

Rapid colorimetric sensing of ascorbic acid based on the excellent peroxidase-like activity of Pt deposited on ZnCo2O4 spheres

Pt/ZnCo₂O₄ composites were firstly found to act as artificial peroxidases and used to construct colorimetric sensing platforms for detecting H₂O₂ and ascorbic acid.

Self-assembly synthesis of Ag@PANI nanocomposites as a tandem enzyme utilizing a highly efficient label-free SERS method to detect saccharides

Surface Enhanced Raman Scattering (SERS), with good reproducibility and stability, is an analytical testing technique that uses metals or metal nanoparticles as detection substrates, and it can also be used to characterize the information from molecular vibration.

Carbon-supported Ni and MoO2 nanoparticles with Fe3O4 cores as a protein adsorbent

Here we have fabricated hierarchical structures of Fe₃O₄@MoO₂∩C–Ni and Fe₃O₄@C∩MoO₂–Ni composites using two different synthetic strategies, which can be used for histidine-rich protein separation.

The design and characterization of a hypersensitive glucose sensor: two enzymes co-fixed on a copper phosphate skeleton

A new glucose sensor GOx&DhHP-6–Cu₃(PO₄)₂ showed the best catalytic ability at a neutral temperature and pH.

Fabrication of noble metal nanoparticles decorated on one dimensional hierarchical polypyrrole@MoS2 microtubes

Herein, we present a facile strategy to fabricate noble metal (Ag, Au, Pd) decorated on PPy@MoS₂ microtubes. As a proof of application, the ternary PPy@MoS₂@Au hybrids reveal excellent enzyme-like catalytic performance.

Impact of linker functionalization on the adsorption of nitrogen-containing compounds in HKUST-1

Functionalization of metal-organic framework (MOF) ligands can tune the adsorption properties of MOFs. The adsorptions of NO, NO2, NH3, C5H5N, C4H5N, and C4H4O on pristine and five X-functionalized HKUST-1, i.e. Cu3(BTC)2 (BTC = 1,3,5-benzenetricarboxylate) (X = CH3, CH3O, NH2, NO2, and Br) are evaluated by van der Waals corrected density functional theory calculations. Despite the fact that the open metal center is the energetically preferred adsorption site for most of them, the functional group site can yield a comparable adsorption ability with the open metal center. This is particularly true for pyrrole C4H5N adsorption on CH3O-functionalized HKUST-1 where the functional group site shows stronger adsorption stability than the open metal center site, probably due to the formed hydrogen bond between pyrrole and the CH3O functional group. While the CH3- or CH3O-functionalized organic linker in these MOFs strengthens the adsorption of all the considered species, that of NO2-, Br-, or NH2-functional groups reduces, which is associated with their topologies. Among them, only CH3- or CH3O-functionalized HKUST-1 presents the fmj (orthorhombic crystal system) topology while all the others are isostructural to the pristine HKUST-1 with the tbo (twisted boracite-type, cubic) topological structure. Among six adsorbates, two basic adsorbates, C5H5N and NH3, always yield the strongest bonding strength upon adsorption on the pristine and five functionalized HKUST-1. Electronic properties including the Bader charges, electron density differences, and electron localization function were investigated to comprehend their adsorption behaviors. This work provides guidance for the proper functionalization of HKUST-1 with improved adsorption properties for specific adsorbates.

Two-dimensional iron MOF nanosheet as a highly efficient nanozyme for glucose biosensing

A 2D Fe-BTC nanosheet was preparedviaa cation exchange route. Its peroxidase-like activity is 2.2 times that of 3D MIL-100(Fe) due to highly accessible surface active sites. This is helpful for substrate contact with the catalyst during the catalytic reaction.

Nanostructured MnO2 nanosheets grown on nickel foam: an efficient and readily recyclable 3D artificial oxidase for the colorimetric detection of ascorbic acid

.An efficient and readily recyclable 3D artificial oxidase (NF@MnO₂) for the colorimetric detection of ascorbic acid was well constructed with nickel foam as the substrate.

Ultrasensitive aptamer-based protein assays based on one-dimensional core-shell nanozymes

In enzyme-based immunoassys, the use of natural enzyme has been remarkably restricted by the inconvenience in preparation and storage, especially for point-of-care testing. Nanozymes, which can mimic the functions of natural enzymes, have been regarded as promising alternatives due to their robust stability and convenience in fabrication. Here we fabricated one-dimensional Fe₃O₄@C core-shell nanostructures via a solvent-thermal method. Thus prepared nanocomposites showed excellent peroxidase-like activity, capable of catalyzing chromogenic substrates into colored products in the presence of H₂O₂. We then developed a nanozyme-linked aptamer sorbent assay (NLASA) in a sandwich format, in which the as-prepared Fe₃O₄@C nanowires were employed as catalytic labels for colorimetric detection by naked eyes. In the detection of platelet-derived growth factor BB (PDGF-BB), this assay reliably exhibited detection limits as low as 10 fM, with a working range from 10 fM to 100 nM. By incorporating G-quadruplex-hemin DNAzyme with Fe₃O₄@C nanowires, the detection limit could be further lowered to 50 aM. The detection limit of PDGF-BB in 50% human serum was 100 fM. This ultrasensitive, cost-effective and easy-to-operate sensing platform offers new opportunities for protein detection in clinical diagnosis.

Molecular imprinting on PtPd nanoflowers for selective recognition and determination of hydrogen peroxide and glucose

PtPd nanoflowers (PtPd NFs) exhibit intrinsic peroxidase-like activity as nanozymes, but the nanozymes lack substrate specificity and have low catalytic activity. Herein, a molecularly imprinted nanogel on PtPd NFs was prepared by using 3,3',5,5'-tetramethylbenzidine (TMB) as the template through the aqueous precipitation polymerization method. After the TMB was washed out, many substrate binding pockets were retained in the PtPd NFs. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) were employed to characterize the molecularly imprinted polymer (MIP) PtPd nanoflowers (T-MIP-PtPd NFs). The obtained T-MIP-PtPd NFs exhibited enhanced catalytic activity and specific recognition for TMB. Compared with PtPd NFs, T-MIP-PtPd NFs showed a linear range from 0.01-5000 μM and a detection limit of 0.005 μM toward the detection of H2O2. Glucose can also be sensitively detected through cascade reaction by the T-MIP-PtPd NFs and glucose oxidase. Therefore, molecular imprinting on nanozymes technology shows promising application in biocatalysis and sensing fields.

Novel Enzyme-Free Multifunctional Bentonite/Polypyrrole/Silver Nanocomposite Sensor for Hydrogen Peroxide Detection over a Wide pH Range

Precise designs of low-cost and efficient catalysts for the detection of hydrogen peroxide (H₂O₂) over wide ranges of pH are important in various environmental applications. Herein, a versatile and ecofriendly approach is presented for the rational design of ternary bentonite-silylpropyl-polypyrrole/silver nanoarchitectures (denoted as BP-PS-PPy/Ag) via the in-situ photo polymerization of pyrrole with salinized bentonite (BP-PS) in the presence of silver nitrate. The Pyrrolyl-functionalized silane (PS) is used as a coupling agent for tailoring the formation of highly exfoliated BP-PS-PPy sheet-like nanostructures ornamented with monodispersed Ag nanoparticles (NPs). Taking advantage of the combination between the unique physicochemical properties of BP-PS-PPy and the outstanding catalytic merits of Ag nanoparticles (NPs), the as-synthesized BP-PS-PPy/Ag shows a superior electrocatalytic reduction and high-detection activity towards H₂O₂ under different pH conditions (from 3 to 10). Intriguingly, the UV-light irradiation significantly enhances the electroreduction activity of H₂O₂ substantially, compared with the dark conditions, due to the high photoelectric response properties of Ag NPs. Moreover, BP-PS-PPy/Ag achived a quick current response with a detection limit at 1 μM within only 1 s. Our present approach is green, facile, scalable and renewable.

Space-confined pyrolysis for fabrication of peacods-like Fe3O4@C-Ni nanostructures for catalysis and protein adsorption

A unique nanostructure of Fe₃O₄ nanoparticles (NPs)-in/carbon layer/out-Ni NPs was developed and proved to be an efficient catalyst and protein adsorbent. This kind of nanostructure was formed through a space-confined pyrolysis procedure using polydopamine-Ni²⁺ coated Fe-NTA nanowires as the precursor. A N-doped carbon interlayer derived from polydopamine (PDA) supported a large amount of Ni NPs and entrapped well-defined Fe₃O₄ NPs, which were obtained through reduction of Ni²⁺, Fe³⁺ by carbonized NTA groups and a PDA layer. The contributions of the unique configuration along with the high density of Ni NPs in Fe₃O₄@C-Ni are significant for improving catalysis and protein adsorption performance, which is expected to be a promising alternative to other conventional catalysts and protein adsorbents. Due to the unique novel nanostructure, this nanocomposite possesses a wide range of applications, not only for catalytic reactions but also for other inhomogeneous reactions.

Trace determination and characterization of ginsenosides in rat plasma through magnetic dispersive solid-phase extraction based on core-shell polydopamine-coated magnetic nanoparticles

Enrichment of trace bioactive constituents and metabolites from complex biological samples is challenging. This study presented a one-pot synthesis of magnetic polydopamine nanoparticles (Fe₃O₄@SiO₂@PDA NPs) with multiple recognition sites for the magnetic dispersive solid-phase extraction (MDSPE) of ginsenosides from rat plasma treated with white ginseng. The extracted ginsenosides were characterized by combining an ultra-high-performance liquid chromatography coupled to a high-resolution mass spectrometry with supplemental UNIFI libraries. Response surface methodology was statistically used to optimize the extraction procedure of the ginsenosides. The reusability of Fe₃O₄@SiO₂@PDA NPs was also examined and the results showed that the recovery rate exceeded 80% after recycling 6 times. Furthermore, the proposed method showed greater enrichment efficiency and could rapidly determine and characterize 23 ginsenoside prototypes and metabolites from plasma. In comparison, conventional methanol method can only detect 8 ginsenosides from the same plasma samples. The proposed approach can provide methodological reference for the trace determination and characterization of different bioactive ingredients and metabolites of traditional Chinese medicines and food.

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The Fe₃O₄@SiO₂@PDA NPs were synthesized through one-pot method.

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The RSM was designed to promote the extraction of trace active ingredients.

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The MDSPE, UPLC-MS and UNIFI software were integrated into an analytical platform.

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The synergetic strategy was applied to enrich ginsenosides from rat plasma.

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The synergetic strategy provided an easy, rapid and sensitive method for analytes.

Enhanced synergistic effects from multiple iron oxide nanoparticles encapsulated within nitrogen-doped carbon nanocages for simple and label-free visual detection of blood glucose

Hollow-structured carbon materials play a crucial role in research of biosensors, energy storage and nanomedicine as a kind of material with advantages like high surface area, tunable pore volume, excellent mechanical properties, and good biocompatibility. Herein, we developed a simple, facile and controllable method for synthesis of Fe₃O₄ nanoparticles encapsulated in hollow carbon nanocages (FNHCs) with SiO₂ nanospheres as a sacrificial template. Owing to the unique structure of multiple Fe₃O₄ nanoparticles cores integrated with N-doped carbon nanocages, the as-synthesized FNHCs exhibited greatly enhanced peroxidase mimicking activity with extremely high signal-to-noise ratio of ∼91 fold. Also, it was found that the FNHCs possessed a higher peroxidase-like activity than that of other similar-structured Fe₃O₄ architectures (e.g. Fe₃O₄@C NPs). The resulting steady-state kinetic curve demonstrated the enzymatic activity of FNHCs with classic Michaelis-Menton kinetics following a ping-pong mechanism. On the basis of the superior enzymatic activity, the FNHCs performed as a high-efficiency peroxidase mimic, realizing facile, label-free, highly sensitive/selective colorimetric detection of H₂O₂ and glucose. Furthermore, the colorimetric sensor successfully determined glucose in patients' serum samples with high accuracy and precision, suggesting great potential for real applications.

Magnetic Cu/Fe3O4@FeOOH with intrinsic HRP-like activity at nearly neutral pH for one-step biosensing

The convenience of colorimetric sensors is useful for practical applications. In this work, we constructed a novel colorimetric sensor with magnetic separation ability that can be operated in nearly neutral conditions and achieve one-step detection of metabolites. Magnetic Cu doped Fe₃O₄@FeOOH magnetic nanocomposite (Cu/Fe₃O₄@FeOOH) with an oxygen vacancy was prepared by a one-step self-assembly hydrothermal method, and fully characterized by different methods. The oxygen vacancy generated by the incorporation of Cu²⁺ cations into the Fe₃O₄@FeOOH structure was confirmed to be a vital reactive site for enhancing the catalytic activity, which opens up a new way of designing highly efficient enzyme mimics. Benefiting from its inherent horseradish-peroxidase-like activity, a simple and selective enzyme-based colorimetric sensor was developed for one-step detection of H₂O₂ and cholesterol, and 3,3',5,5'-tetramethylbenzidine was catalyzed by H₂O₂ to generate a colored product of oxidized 3,3',5,5'-tetramethylbenzidine for signaling. H₂O₂ and cholesterol can be linearly detected in the same range from 0.01 to 0.4 mmol L^-1 with detection limits of 0.0075 mmol L^-1 and 0.0082 mmol L^-1, respectively. The proposed colorimetric sensor has satisfactory reusability, accuracy, and practicability in human serum samples, indicating its potential application for the detection of different metabolites in the fields of life science and analytical science. Graphical abstract.

One-step colorimetric genotyping of single nucleotide polymorphism using probe-enhanced loop-mediated isothermal amplification (PE-LAMP)

Single nucleotide polymorphism (SNP) is the most abundant molecular marker associated with many physiologic and pathologic phenotypes. An isothermal, accurate and cost-effective SNP detection could make a great difference in point-of-care testing (POCT) or on-site diagnosis. However, there are two challenges, the expensive instrument and labor-intensive process, faced by the development of on-site SNP detection. We reported a novel SNP typing method based on the probe-enhanced loop-mediated isothermal amplification (PE-LAMP), which combines the oligonucleotide probe with a conventional LAMP to realize the SNP discrimination by analyzing the great discrepancy in amplification efficiency.

Methods: We firstly constructed the genotyping method by combining the hybridization of the specific probe with the powerful amplification of LAMP. Then we validated the method by genotyping the SNP rs3741219 and we sought to realize one-step visualized typing. Finally, we applied the method to pharmacogenomic testing by genotyping CYP2C19*2 and MDR1 C3435T.

Results: The PE-LAMP was successfully constructed to detect SNP and the sensitivity of our method is as low as 1000 copies of target DNA, which is sufficient to routine diagnosis. The high specificity in detecting mutant in the presence of excess wild-type allele could be achieved. It has shown good performance in helping predict the individual response of antiplatelet drug Clopidogrel through typing simply treated saliva samples.

Conclusions: The proposed method is one-step, colorimetric, specific and sensitive enough to detect crudely treated samples, showing great potential in the pharmacogenomic study and POCT use.

One-pot fabrication of Fe-doped carbon nitride nanoparticles as peroxidase mimetics for H2O2 and glucose detection

Iron-doped carbon nitride nanoparticles (Fe-CNNPs) were prepared from citric acid, urea and ferric chloride through a convenient one-pot solvothermal method. Oleic acid was used as the reaction medium. The morphology and chemical composition of the obtained Fe-CNNPs were characterized by multiple methods including transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). It is interesting to find that the Fe-CNNPs showed higher catalytic activity than horseradish peroxidase (HRP), and tetramethylbenzidine (TMB) can be catalytically oxidized in the presence of H₂O₂ to produce a color change in aqueous solution. As H₂O₂ can be generated in the oxidation process of glucose catalyzed by glucose oxidase (GOD), a novel sensitive method for the detection of glucose with a limit of detection (LOD) of 0.29 μM has been developed combined with the catalytic properties of GOD and Fe-CNNPs. The Fe-CNNPs with peroxidase mimetics activity may have potential applications in biotechnology field.

Modified carbon nitride nanozyme as bifunctional glucose oxidase-peroxidase for metal-free bioinspired cascade photocatalysis

Nanomaterials-based biomimetic catalysts with multiple functions are necessary to address challenges in artificial enzymes mimicking physiological processes. Here we report a metal-free nanozyme of modified graphitic carbon nitride and demonstrate its bifunctional enzyme-mimicking roles. With oxidase mimicking, hydrogen peroxide is generated from the coupled photocatalysis of glucose oxidation and dioxygen reduction under visible-light irradiation with a near 100% apparent quantum efficiency. Then, the in situ generated hydrogen peroxide serves for the subsequent peroxidase-mimicking reaction that oxidises a chromogenic substrate on the same catalysts in dark to complete the bifunctional oxidase-peroxidase for biomimetic detection of glucose. The bifunctional cascade catalysis is successfully demonstrated in microfluidics for the real-time colorimetric detection of glucose with a low detection limit of 0.8 μM within 30 s. The artificial nanozymes with physiological functions provide the feasible strategies for mimicking the natural enzymes and realizing the biomedical diagnostics with a smart and miniature device.

A multifunctional mesoporous silica-gold nanocluster hybrid platform for selective breast cancer cell detection using a catalytic amplification-based colorimetric assay

Breast cancer is the most common malignancy and also the second leading cause of cancer mortality in women globally. Strategies for early and precise detection of breast cancer cells are highly desired in breast cancer diagnosis and treatment. Here, we report on the efficient detection of HER2-positive (HER2+) breast cancer cells using an amplified signal scheme enabled by gold nanoclusters entrapped in mesoporous silica nanoparticles (MSNs). The utilization of MSNs as an excellent enzyme immobilization support and gold nanoclusters as an effective peroxidase mimic imparts high sensitivity to this detection platform. In addition, the inclusion of target-specific HER2 antibodies adds excellent selectivity. Determination of HER2+ cancer cells in breast cancer tissue demonstrates the potential application of this biosensor design in clinical diagnosis in particular, and bioanalysis in general.

A Two-Step Strategy for Fabrication of Biocompatible 3D Magnetically Responsive Photonic Crystals

Extremely stable and biocompatible 3D magnetically responsive photonic crystals (MRPCs) are successfully prepared in aqueous solution. Classic hydrothermal synthesis was applied for preparation of the Fe₃O₄@C core. Modified Stöber method was then employed for synthesis of the different size of Fe₃O₄@C@SiO₂. Unlike the traditional magnetic nanoparticles, the highly negative charged superparamagnetic nanospheres (SMNs), i.e., the double-shell structure Fe₃O₄@C@SiO₂ are capable of rapidly self-assembling into 3D MRPCs with full visible and various colors that can be periodically and reversibly tuned under different kinds of external magnetic fields (EMFs) within 1 s. The assembling behavior and mechanism of the 3D MRPCs under EMF were monitored and analyzed. The preparation is simple and the size of the SMN is easily controllable by adjusting the amount of catalyst. Compared with the previous works, the synthesized 3D MRPCs are hydrophilic, and exhibit extremely high stability after 6-month storage. To conclude, our study provides an effective two-step strategy for fabrication of biocompatible 3D MRPCs and it reveals great potentials in biological fields.

Engineering Nanozymes Using DNA for Catalytic Regulation

DNA treatment of metal nanoparticles provides a potent tool for tuning their native properties and constructing advanced materials. However, there have been limited studies on interactions between DNA and nanomaterial-based artificial enzymes (nanozymes) to influence their intrinsic peroxidase-like properties. Here, we present the utilization of DNA as a capping ligand to engineer various bio-nanointerfaces for high-precise and adjustable regulation of catalytic behaviors of nanozymes toward the oxidation of substrates. The treatment of stiff double-stranded DNA only induced a negligible enhancement of the catalytic activity of nanozymes, and both coil-like single-stranded DNA and hairpin DNA-capped nanoparticles produced a medium signal increase. Interestingly, hybridization chain reaction (HCR) product-treated nanoparticles showed the highest peroxidase-like activities among four DNA structures. Furthermore, significant parameters that influence HCR process and the modulation of catalysis, such as the concentration of the hairpin DNA, the ionic strength, and the amount of nanozyme, were also systematically investigated. On the basis of HCR amplification and iron oxide (Fe₃O₄) nanoparticles, we develop a simple, fast, label-free, and sensitive colorimetric strategy for sensing of a Yersinia pestis-relevant DNA sequence with a detection limit as low as 100 pM as well as single nucleotide polymorphism discrimination. These results highlight DNA engineering as a facile strategy to regulate the catalytic activities of nanozymes and understand the interactions between metallic nanoparticles and nucleic acids for biosensing applications.