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.

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.

Amorphization-Modulated Metal Sulfides with Boosted Active Sites and Kinetics for Efficient Enzymatic Colorimetric Biodetection

Colorimetric biosensing has become a popular sensing method for the portable detection of a variety of biomarkers. Artificial biocatalysts can replace traditional natural enzymes in the fields of enzymatic colorimetric biodetection; however, the exploration of new biocatalysts with efficient, stable, and specific biosensing reactions has remained challenging so far. Here, to enhance the active sites and overcome the sluggish kinetics of metal sulfides, the creation of an amorphous RuS₂ (a-RuS₂ ) biocatalytic system is reported, which can dramatically boost the peroxidase-mimetic activity of RuS₂ for the enzymatic detection of diverse biomolecules. Due to the existence of abundant accessible active sites and mildly surface oxidation, the a-RuS₂ biocatalyst displays a twofold V_max value and much higher reaction kinetics/turnover number (1.63 × 10^-2 s^-1 ) compared to that of the crystallized RuS₂ . Noticeably, the a-RuS₂ -based biosensor shows an extremely low detection limit of H₂ O₂ (3.25 × 10^-6 m), l-cysteine (3.39 × 10^-6 m), and glucose (9.84 × 10^-6 m), respectively, thus showing superior detection sensitivity to many currently reported peroxidase-mimetic nanomaterials. This work offers a new path to create highly sensitive and specific colorimetric biosensors in detecting biomolecules and also provides valuable insights for engineering robust enzyme-like biocatalysts via amorphization-modulated design.

Porous-nanozyme-based colorimetric sensor for rapid detection of kanamycin in foods under neutral condition

Most colorimetric methods based on nanozymes need to have excellent performance under acidic condition, so they are currently facing some challenges in the field of food hazard detection. Herein, a facile and rapid colorimetric sensor for kanamycin (KAN) detection in foods under neutral condition has been designed using the peroxidase-mimic activity of porous nanozyme like Co₃ O₄ nanodisk. Further investigations showed that the interaction mechanism between porous Co₃ O₄ nanodisk and substrates belongs to a ping-pong model, and the inhibition type of KAN on the peroxidase-mimic activity is noncompetitive inhibition. The constructed sensor has good sensitivity for KAN with the limit of 57 nM, and the color changes can be discerned visually when KAN exceeds 0.5 µM. Besides, the colorimetric sensor obtains excellent recovery results in chicken serum, milk, honey, and pork, which shows that the proposed sensing strategy can provide a rapid and convenient detection method for KAN in foods under neutral condition. PRACTICAL APPLICATION: The established sensing strategy can rapidly distinguish whether KAN residue exceeds the permissible level within 10 min, which meets the requirement for on-site monitoring of antibiotics in foods, and also open up a new idea for other hazards detection under neutral condition.

Effect of Hydrogen Peroxide on the Soil Microbial Community Structure and Growth of Malus hupehensis Rehd. Seedlings under Replant Conditions

Apple replant disease (ARD) is common in apple production, which seriously affects the growth and development of apples. In this study, hydrogen peroxide with a bactericidal effect was used to treat the replanted soil, and the effects of different concentrations of hydrogen peroxide on replanted seedlings and soil microbiology were investigated in order to seek a green, clean way to control ARD. Five treatments were set up in this study: replanted soil (CK1), replanted soil with methyl bromide fumigation (CK2), replanted soil + 1.5% hydrogen peroxide (H1), replanted soil + 3.0% hydrogen peroxide (H2), and replanted soil + 4.5% hydrogen peroxide (H3). The results showed that hydrogen peroxide treatment improved replanted seedling growth and also inactivated a certain number of Fusarium, while the Bacillus, Mortierella, and Guehomyces also became more abundant in relative terms. The best results were obtained with replanted soil + 4.5% hydrogen peroxide (H3). Consequently, hydrogen peroxide applied to the soil can effectively prevent and control ARD.

Ultrasensitive Pd nano catalyst as peroxidase mimetics for colorimetric sensing and evaluation of antioxidants and total polyphenols in beverages and fruit juices

Herein, we developed a new Pd NP from the aq extract of Elsholtzia blanda Benth. flower that showed efficient peroxidase mimetic activity. The catalytic mechanism was confirmed through colorimetric analysis. The optimizations of temperature, concentration, P^H and time were done to find out the best procedure to implement the intrinsic catalytic activity in practical applications. Michaelis-Menten constants were evaluated for both TMB and H₂O₂ substrate to investigate the affinity of Pd NP towards them. K_m was observed to be 42.35 mM for H₂O₂ and 0.0076 mM for TMB. Antioxidants were sensed using the peroxidase mimetic property up to nanomolar levels with a LOD = 0.78 nM for Gallic acid 0.85 nM for Tannic acid. The method was further implemented in comparing the radical scavenging power of different phenolic compounds. Smart-phone based analysis was done for observing the change in colour which could further be utilized as an analytical tool for study the antioxidant activity. R-Square values of 0.97 and 0.96 for detection of gallic acid and tannic acid respectively suggest good linearity of the plot. Lastly, the system was utilized in the evaluation of total antioxidant capacity (TAC) and total phenolic content (TPC) in commercially available juices and beverages.

Keratin-inorganic hybrid nanoflowers decorated with Fe3O4 nanoparticles as enzyme mimics for colorimetric detection of glucose

Fe3O4 magnetic nanoparticles (MNPs) are highly active enzyme-like catalysts. However, low stability is still a big challenge for Fe3O4-based enzyme mimics because the Fe3O4 MNPs can be easily dissolved when exposed to acidic conditions. Inspired by the numerous catalytic sites of a flower-like structure and the biological functions of amino acids in structural proteins, herein, by employing keratin as a protein component, stable Fe3O4-based MNP embedded keratin-Cu3(PO4)2 nanoflowers were constructed, from which hierarchical nanostructures with a three-dimensional petal-like morphology were selected for subsequent studies owing to their excellent enzymic catalytic activity. The keratin-nanoflower@Fe3O4 exhibited significantly enhanced catalytic activity compared with that of keratin-Cu3(PO4)2 nanoflowers and individual Fe3O4 MNPs. Remarkably, keratin-nanoflower@Fe3O4 exhibited superior long-term stability to Fe3O4 MNPs under more acidic conditions and favorable reusability. This method has been successfully exploited for the colorimetric determination of glucose in human serum with satisfactory sensitivity and specificity, offering a novel approach for glucose detection.

Porous Co3O4 nanodisks as robust peroxidase mimetics in an ultrasensitive colorimetric sensor for the rapid detection of multiple heavy metal residues in environmental water samples

The current method for rapid and ultrasensitive detection of multiple heavy metals in environmental water still face challenge. Herein, the porous Co₃O₄ nanodisks with robust peroxidase-mimicking activity were prepared, and its catalytic activity can be significantly inhibited by the heavy metals like Cd(II), Hg(II), Pb(II) and As, which makes us to establish an ultrasensitive and rapid colorimetric sensor for the detection of multiple heavy metals. Further investigation reveals the anticompetitive inhibition effect of heavy metals on peroxidase-mimicking activity. The colorimetric sensor displays excellent sensitivity and selectivity, and the limits of detection (LOD) for Cd(II), Hg(II), Pb(II) and As are 0.085 μg·L^-1, 0.19 μg·L^-1, 0.2 μg·L^-1 and 0.156 μg·L^-1, respectively. Notably, the absorbance variation will be greater than 0.5 as the concentration of heavy metals exceeds 5 μg·L^-1, which can be clearly discriminated by the naked eyes. Moreover, the average recovery range of heavy metals in actual water samples is from 86.9% to 98.3%. The above results indicate that the proposed sensor exhibits excellent practical applicability for the rapid and ultrasensitive detection of multiple harmful heavy metals in several environmental water samples, which has potential bright application in protecting the environment and human health.

Hard template synthesis of 2D porous Co3O4 nanosheets with graphene oxide for H2O2 sensing

In this work, we used graphene oxide (GO) as a template that was removed by calcination to finally successfully prepare Co₃O₄ with 2D porous nanostructure. The results show that 2D porous structure Co₃O₄ nanosheets were only prepared at pH = 2. After electrochemical tests, the as-prepared Co₃O₄ nanosheets showed electrochemical properties that are highly suitable for H₂O₂ detection, such as high current response, short response time (less than 3 s), wide linear range (0.388-44.156 mM), low limit of detection (2.33 μM) and high sensitivity (0.0891 mA mM^-1 cm^-2). These excellent properties are mainly due to GO, as a 2D template, which connects Co₃O₄ nanoparticles to each other on a 2D plane, preventing the agglomeration of Co₃O₄ nanoparticles. The abundant pores between Co₃O₄ nanoparticles can greatly increase the reaction between the nanoparticles and H₂O₂ molecules.

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.

Metal–oxygen clusters as peroxidase mimics for their multifarious applications in colorimetric sensors

Metal–oxygen cluster (Fe₂₈) was certified to own inherent peroxidase-like performance, which displayed multi-functional applications in H₂O₂, glucose and dopamine detection.

Porphyrin functionalized Co(OH)2/GO nanocomposites as an excellent peroxidase mimic for colorimetric biosensing

A colorimetric sensor based on the enhanced peroxidase-like activity of Por/Co(OH)₂/GO for the sensitive detection of H₂O₂ and GSH.

Supramolecular self-assemblies of inverted cucurbit[7]uril with biogenic amines

The binding interactions between six biogenic amine guests and the iQ[7] host were investigated. The experimental results have revealed that iQ[7] shows strong binding affinity towards five of the studied biogenic amines, but not histamine, and that the binding sites are different depending on the structure of the biogenic amine.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Protamine-gold nanoclusters as peroxidase mimics and the selective enhancement of their activity by mercury ions for highly sensitive colorimetric assay of Hg(II)

We certify that protamine-gold nanoclusters (PRT-AuNCs) synthesized by one-pot method exhibit peroxidase-like activity. The catalytic activity of PRT-AuNCs followed typical Michaelis-Menten kinetics and exhibited higher affinity to 3,3',5,5'-tetramethylbenzidine (TMB) as the substrate compared to that of natural horseradish peroxidase. Meanwhile, we found that Hg(II) could dramatically and selectively enhance the peroxidase-like activity of PRT-AuNCs, and the enhanced mechanism by Hg(II) was demonstrated to be generation of the cationic Au species and the partly oxidized Au species (Au^δ+) by Hg²⁺-Au⁰/Au⁺ interaction. Based on this finding, quantitative determinations of Hg(II) via visual observation and absorption spectra were achieved. The proposed strategy displays high selectivity that arises from the strong aurophilic interaction of mercury towards gold. Moreover, the developed method is highly sensitive with a wide linear range and low detection limit of 1.16 nM. This strategy is not only helpful to develop effective nanomaterials-based artificial enzyme mimics but also irradiative to discover new applications of artificial mimic enzymes in bio-detection, medical diagnostics, and biotechnology. Graphical abstract Protamine-gold nanoclusters (PRT-AuNCs) synthesized by one-pot method exhibit peroxidase-like activity. Hg(II) can stimulate the peroxidase-like activity of PRT-AuNCs selectively, enhancing their ability to catalyze the chromogenic reaction of TMB by H₂O₂.

Colorimetric Immunoassay for Rapid Detection of Vibrio parahemolyticus Based on Mn2+ Mediates the Assembly of Gold Nanoparticles

Vibrio parahemolyticus ( V. parahemolyticus) is an important food-borne pathogen that causes food poisoning and acute gastroenteritis in humans. Herein, a novel colorimetric immunoassay was presented for rapid detection of V. parahemolyticus using gold nanoparticles (18.1 nm diameter) as chromogenic substrate, whose combination of a magnetic bead-based sandwich immunoassay and an optical sensing system via Mn²⁺ ions mediated aggregation of gold nanoparticles. MnO₂ nanoparticles coated with polyclonal IgG antibodies (7.8 nm diameter) are used to recognize the target and can be etched to generate manganese ions by ascorbic acid. A color change ranging from red to purple to blue can be easily discerned by bare eye, corresponding to V. parahemolyticus concentration in the range between 10 and 10⁶ cfu·mL^-1. The proposed method possesses high specificity with a limit of detection of 10 cfu·mL^-1 and was successfully applied to determination of V. parahemolyticus in oyster samples without pre-enrichment. In our perception, it shows promise in rapid instrumental and on-site visual detection of V. parahemolyticus.

Preparation of porphyrin modified CO9S8 nanocomposites and application for colorimetric biosensing of H2O2

Hydrogen peroxide detection has been widely applied in the fields of biology, medicine, and chemistry. Colorimetric detection of hydrogen peroxide has proven to be a fast and convenient method. In this work, 5,10,15,20-tetrakis(4-chlorophenyl) porphyrin modified Co[Formula: see text]S[Formula: see text] nanocomposites (H[Formula: see text]TClPP-Co[Formula: see text]S[Formula: see text] were prepared via a facile one-step hydrothermal method. H[Formula: see text]TClPP-Co[Formula: see text]S[Formula: see text] nanocomposites were demonstrated to possess an enhanced mimetic peroxidase activity toward the substrate, 3,3[Formula: see text],5,5[Formula: see text]-tetramethylbenzidine (TMB), which can be oxidized to oxTMB (oxidized TMB) in a buffer solution of hydrogen peroxide with a color change from colorless to blue. The catalytic activity of H[Formula: see text]TClPP-Co[Formula: see text]S[Formula: see text] was further analyzed by steady-state kinetics, and H[Formula: see text]TClPP-Co[Formula: see text]S[Formula: see text] had high affinity towards both TMB and H[Formula: see text]O[Formula: see text]. Furthermore, fluorescence and ESR data revealed that the catalytic mechanism of the peroxidase activity of H[Formula: see text]TClPP-Co[Formula: see text]S[Formula: see text] is due to hydroxyl radicals generated from decomposition of H[Formula: see text]O[Formula: see text]. Based on the catalytic activity of H[Formula: see text]TClPP-Co[Formula: see text]S[Formula: see text], a sensitive colorimetric sensor of H[Formula: see text]O[Formula: see text] with a detection limit of 6.803 [Formula: see text]M as well as a range of 7–100 [Formula: see text]M was designed.

Colorimetric Immunosensor by Aggregation of Photochemically Functionalized Gold Nanoparticles

A colorimetric immunosensor based on local surface plasmon resonance by gold nanoparticles is presented, and its application for the detection of human immunoglobulin G (IgG) is demonstrated. The color change of the colloidal solution is produced by nanoparticle aggregation, a process that can be tuned by the presence of the analyte once the nanoparticles are functionalized. In comparison to common functionalization techniques, the procedure described here is simpler, low-cost, and effective in binding antibodies upright on the gold surface. The dose-response curve is similar to that resulting in typical immunoassay platforms and is satisfactorily described by the proposed theoretical model. Human IgG at concentration levels of few hundreds of nanograms per milliliter can be detected by eyes within a few minutes, thereby making the colorimetric immunosensor proposed here a powerful tool in several areas, with urine test in medical diagnostics being the most immediate.

Ultrasensitive point-of-care testing of arsenic based on a catalytic reaction of unmodified gold nanoparticles

Ultrasensitive arsenic detection based on inhibition of a catalytic reaction between Rhodamine B and sodium borohydride.

Colorimetric and optical Hg(ii) ion sensor developed with conjugates of M13-bacteriophage and silver nanoparticles

Hg(ii) produces an AgHg amalgam on a conjugate of Ag nanoparticles and M13-bacteriophage, which effectively quenches the optical absorption of the Ag nanoparticles.

Colorimetric sensor for cimetidine detection in human urine based on d-xylose protected gold nanoparticles

A simple, novel, and rapid colorimetric sensor for cimetidine (Cim) detection based on d-xylose protected gold nanoparticles (d-x@AuNPs) has been developed for the first time.

Synthesis of well-dispersed Fe3O4 nanoparticles loaded on montmorillonite and sensitive colorimetric detection of H2O2 based on its peroxidase-like activity

In this study, a simple strategy for the preparation of Fe₃O₄ nanoparticles (NPs) loaded on montmorillonite as a support is reported.

Cobalt and nickel bimetallic sulfide nanoparticles immobilized on montmorillonite demonstrating peroxidase-like activity for H2O2 detection

In this study, ternary transition metal sulfide (cobalt and nickel sulfides) nanoparticles were anchored on the surface of montmorillonite (MMT) by a facile one-pot hydrothermal method.