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[Display omitted] • A new nanozyme Fe 3 O 4 @MoS 2 -Au NPs was designed and synthesized. • The dual-mode sensor based on Fe 3 O 4 @MoS 2 -Au NPs has multiple advantages. • Using the magnetic characteristics of nanozyme, real-time regulation of the catalytic reaction can be achieved. • 4. This research provides a new sensitive and accurate multi-channel analysis strategy for H 2 O 2 detection. Hydrogen peroxide (H 2 O 2) is closely related to many diseases and is often used as a target for disease diagnosis and treatment, so the research of H 2 O 2 detection method has attracted much attention. Compared with the current single-signal detection methods commonly used, dual-mode detection has inherent self-verification and self-correction functions and is expected to provide more reliable and anti-interference detection results. In this work, a novel nanocomposite Fe 3 O 4 @MoS 2 -Au NPs with strong peroxidase activity was constructed for the first time, and on this basis, a colorimetric/electrochemical dual-mode sensor was successfully prepared. Concretely, the Fe 3 O 4 @MoS 2 -Au NPs could catalyze reduction of H 2 O 2 to generate ·OH, leading to a significant electrochemical signal. At the same time, the color reaction of 3, 3′, 5, 5′-tetramethylbenzidine (TMB) by ·OH can be used to build a colorimetric sensor. In colorimetric and electrochemical sensing systems, the linear range was 1–120 μM. The detection limit (LOD) can reach as low as 109 nM and 80 nM, respectively. In addition, the sensor has been favorably used for the detection of H 2 O 2 in normal human serum, and the recovery range was 87.55–113.13 %. In conclusion, this work provides an economical, sensitive and visualized H 2 O 2 detection platform, which has a wide application prospects. [ABSTRACT FROM AUTHOR]

A molecularly imprinted stir bar was constructed based on Fe 3 O 4 @Polyaniline nanoparticles with magnetic field-induced self-assembly process. The monomer, methacrylic acid, was pre-assembled into the pre-polymers with vanillin as template by the formation of hydrogen bonds. After that, the magnetic complexes were generated by the hydrogen bonding, the hydrophobic and π–π interaction between the pre-polymers and Fe 3 O 4 @Polyaniline. The complexes were adsorbed on the surface of magnetic stir bar under the magnetic induction, and the coating of vanillin-molecularly imprinted polymers was generated by the one-step copolymerization basing on the cross linking of ethylene glycol dimethacrylate. The molecular imprinting stir bar showed superior selectivity and fast binding kinetics for vanillin, and was used for the enrichment of vanilla-flavor enhancers (vanillin, ethyl maltol and methyl vanillin) in infant milk powders. The results measured by HPLC-UV exhibited good linear ranges of 0.01–100, 0.02–100 and 0.03–100 μg mL −1 with the limit of detection of 2.5–10.0 ng mL −1 , and the recoveries were 94.7–98.9%, 82.1–96.7% and 84.5–93.2% with RSD < 7.2% for the three enhancers, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A novel electrochemical sensing platform based on magnetic field-induced self-assembly of Fe3O4@Polyaniline nanoparticles (Fe3O4@PANI NPs) has been for the first time fabricated for the sensitive detection of creatinine in biological fluids. The template molecule, creatinine, was self-assembled on the surface of Fe3O4@PANI NPs together with the functional monomer aniline by the formation of N–H hydrogen bonds. After pre-assembled, through the magnetic-induction of the magnetic glassy carbon electrode (MGCE), the ordered structure of molecularly imprinted polymers (MIPs) were established by the electropolymerization and assembled on the surface of MGCE with the help of magnetic fields by a simple one-step approach. The structural controllability of the MIPs film established by magnetic field-induced self-assembly was further studied. The stable and hydrophilic Fe3O4@PANI can not only provide available functionalized sites with which the template molecule creatinine can form hydrogen bond by the abundant amino groups in PANI matrix, but also afford a promoting pathway for electron transfer. The as-prepared molecularly imprinted electrochemical sensor (MIES) shows good stability and reproducibility for the determination of creatinine with the detection limit reached 0.35nmolL−1 (S/N=3). In addition, the highly sensitive and selective MIES has been successfully used for the clinical determination of creatinine in human plasma and urine samples. The average recoveries were 90.8–104.9% with RSD lower than 2.7%. [Copyright &y& Elsevier]

Abstract: Based on magnetic field directed self-assembly (MDSA) of Fe3O4@rGO composites, a novel magnetic molecularly imprinted electrochemical sensor (MIES) was fabricated and developed for the determination of the azo dye amaranth. Fe3O4@rGO composites were obtained by a one-step approach involving the initial intercalating of iron ions between the graphene oxide layers via the electrostatic interaction, followed by the reduction with hydrazine hydrate to deposit Fe3O4 nanoparticles onto the reduced oxide graphene nanosheets. In molecular imprinting, the complex including the function monomer of aniline, the template of amaranth and Fe3O4@rGO was pre-assembled through π–π stacking and hydrogen bonding interactions, and then was self-assembled on the surface of magnetic glassy carbon electrode (MGCE) with the help of magnetic field induction before electropolymerization. The structures and morphologies of Fe3O4@rGO and the doped molecularly imprinted polymers (MIPs) were investigated by Fourier transform infrared spectrometer (FT-IR), Raman spectra and scanning electron microscope (SEM). Besides, the characterization by differential pulse voltammetry (DPV) showed that Fe3O4@rGO composites promoted the electrical conductivity of the imprinted sensors when doped into the MIPs. The adsorption isotherms and adsorption kinetics were employed to evaluate the performances of MIES. The detection of amaranth was achieved via the redox probe K3[Fe(CN)6] by blocking the imprinted cavities, which avoided the interferences of oxidation products and analogs of amaranth. Furthermore, the prepared MIES exhibited good sensitivity, selectivity, reproducibility and efficiency for detecting amaranth in fruit drinks. The average recoveries were 93.15–100.81% with the RSD <3.0%. [Copyright &y& Elsevier]

High plasma urate is closely related to gout, cardiovascular and other diseases. Therefore, monitoring the content of uric acid (UA) in plasma is of great significance for the treatment of gout and the prevention of other related diseases. Herein, a biosensor based on the biomimetic oxidase Fe 3 O 4 nanoparticles (NPs) @MnO 2 nanosheets (Fe 3 O 4 @MnO 2 NS) was constructed for colorimetric determination of UA. MnO 2 NS is an efficient biomimetic oxidase, and we found that the intrinsic oxidase activity of MnO 2 NS doped with Fe 3 O 4 NPs can be significantly enhanced. The chromogenic substrate TMB can be catalyzed by Fe 3 O 4 @MnO 2 NS to generate blue oxidized TMB, and UA can decompose the MnO 2 NS to inhibit the color reaction of TMB selectively, thereby realizing the quantitative detection of UA. In addition, the UA biosensor can perform colorimetric analysis of UA level through three methods: naked eye, smartphone and ultraviolet-visible (UV–vis) spectrophotometer. The linear ranges of UV–vis spectrophotometry and colorimetry with smartphone were 1–70 μM and 200–650 μM, respectively, and the limits of detection (LOD) were 0.27 μM and 21 μM. The analysis results of human plasma samples showed that the method had good selectivity and practicability. [Display omitted] • Fe 3 O 4 @MnO 2 NS showing significantly enhanced intrinsic oxidase activity. • Colorimetric analysis of UA level by naked eye, smartphone and microplate reader. • Fe 3 O 4 @MnO 2 NS combining the advantages of oxidase and magnetic properties. • The method completing the detection within 1 min at room temperature. [ABSTRACT FROM AUTHOR]

• Construct a coumarin ratio fluorescence sensor with artificial nano enzymes firstly. • Fe 3 O 4 NPs used to conveniently control the catalytic reaction and purification system. • The method for analysis of complex samples with great selectivity and sensitivity. Herein, using Fe 3 O 4 nanoparticles (Fe 3 O 4 NPs) as a magnetic artificial peroxidase, an "on–off" ratiometric photoluminescence sensor with high-sensitivity and high-selectivity for coumarin was constructed based on photoinduced electron transfer (PET) between 7-hydroxycoumarin and rhodamine B (RB). The results showed that Fe 3 O 4 NPs catalyzed H 2 O 2 to generate nucleophilic group ·OH, which attacked the active site of coumarin and produced strong fluorescent 7-hydroxycoumarin molecules. Then, the fluorescence of RB was quenched with 7-hydroxycoumarin through the PET effect. The ratio signal generated in the above process was used for the quantitative detection of coumarin. Under optimized conditions, the linear range 0.5–25 mg/L was acquired for coumarin with the detection limit of 0.016 mg/L. This method had excellent selectivity and the recovery rate was 81.8%−106.8% with the relative standard deviation less than 5.6%, so it can be used for the quantitative analysis of coumarin in complex matrix samples. [ABSTRACT FROM AUTHOR]

• A novel magnetic ternary nanocomposite hemin-Fe 3 O 4 @polypyrrole with stronger peroxidase-like activity was synthesized. • The residual catalytic effect can be removed and the real-time regulation of the catalytic reaction can be realized. • Its excellent stability and reusable characteristics can increase the practicality of this colorimetric sensors. • The analysis of actual samples showed that GSH/GSSG was more significant in clinical diagnosis. At present, artificial mimic enzyme has become a powerful substitute for natural enzyme. In particular, the biosensors based on nano-enzymes have been the focus of current research. Herein, a novel magnetic ternary nanocomposite hemin-Fe 3 O 4 @polypyrrole (h-Fe 3 O 4 @ppy) was synthesized by chemical oxidation polymerization. The results showed that the h-Fe 3 O 4 @ppy had stronger peroxidase activity than Fe 3 O 4 nanoparticles (Fe 3 O 4 NPs) and h-ppy NPs, and was indicated by Michaelis-Menten constant (K m) and maximum initial velocity (V max). Therefore, we used h-Fe 3 O 4 @ppy catalyzing H 2 O 2 to oxidize the chromogenic substrate TMB, and built Hydrogen peroxide (H 2 O 2) and Glutathione (GSH) colorimetric biosensors with the help of signal intrinsic exponential amplification and easy operation. The controllable catalysis was realized by h-Fe 3 O 4 @ppy which was prone to separation. The method of removing h-Fe 3 O 4 @ppy by magnetic separation effectively eliminated the effect of residual catalysis when terminating the reaction. The sensor was then applied to the determination of GSH in biological samples from acute coronary syndrome patients. The linear ranges of H 2 O 2 and GSH were 0.2–100 μM and 0.5–80 μM, respectively. The detection limits of H 2 O 2 and GSH are 0.18 μM and 0.15 μM, respectively. This research not only proposes a new type of nanoenzyme, but also shows the multiple advantages of magnetic nano-enzymes for the construction of biosensors. [ABSTRACT FROM AUTHOR]