•A Fe3O4NPs magnetic molecularly imprinted polymer (MMIPs) nanozyme was constructed.•The nanozyme was prepared by polymerization of dopamine on Fe3O4NPs in the presence of thionine.•The Fe3O4NPs MMIPs showed good selectivity toward thionine.•A highly selective and sensitive electrochemical H2O2 biosensor was proposed.•The biosensor was also used to detect AChE, choline oxidase and acetylcholine.Here, a new nanoenzyme of Fe3O4 nanoparticles (NPs) magnetic molecularly imprinted polymers (MMIPs) was prepared by polymerizing dopamine on the Fe3O4NPs surface in the presence of templated thionine (Thi) for the first time. The results showed that uniform spherical and core-shell structured Fe3O4NPs MMIPs which were about 600 nm in diameter were successfully formed and the imprinting sites improved the selectivity of Fe3O4NPs MMIPs greatly. The as-prepared Fe3O4NPs MMIPs could catalyze the reduction of Thi selectively, which could be enhanced by H2O2 owing to the peroxidase-like activity of Fe3O4NPs. Accordingly, a highly selective and sensitive H2O2 electrochemical biosensor was proposed based on the Fe3O4NPs MMIPs-modified glassy carbon electrode. The electrochemical biosensor based on the Fe3O4NPs MMIPs nanoenzyme exhibited low detection limit of 1.58 nM and high selectivity. Since acetylthiocholine chloride (AChl) could be hydrolyzed into choline with the help of acetylcholinesterase (AChE) and simultaneously the choline oxidase (ChOx) could reduce choline into betaine accompanied by the production of H2O2, the proposed electrochemical H2O2 biosensor could be further used to detect AChl, AChE and ChOx. The results also exhibited wide linear range (2.85–160 μM for AChl, 0.53–20000 ng mL−1 for AChE and 22.76–400 ng mL−1 for ChOx), low detection limit (0.86 μM for AChl, 0.16 ng mL−1 for AChE and 6.83 ng mL−1 for ChOx) and high selectivity. Therefore, the Fe3O4NPs MMIPs should be a promising nanoenzyme for electrochemical biosensors.Download high-res image (79KB)Download full-size image

•The flexible PANI-CNT@ZIF-67-CC with hierarchical porous structure was constructed.•The PANI-CNTs@ZIF-67-CC was used as supercapacitor electrode directly.•The PANI-CNTs@ZIF-67-CC showed high specific capacitance.•At 0.5 mA cm−2, the specific capacitance maintained 83% after 1000 charging/discharging cycles.Polyaniline (PANI)-carbon nanotubes (CNT)@zeolite imidazolate framework-67 (ZIF-67) −carbon cloth (CC) (PANI-CNT@ZIF-67-CC) was constructed as supercapacitor electrode. Herein, the PANI-CNT@ZIF-67 was used as active materials and the flexible CC was employed as flexible collector electrode. The obtained PANI-CNT@ZIF-67-CC supercapacitor electrode was carefully characterized with scanning electron microscopy, N2 adsorption-desorption isotherms, X-ray powder diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and electrochemical techniques. It was found that porous ZIF-67 was enclosed by a large number of CNT and partial CNT went through the ZIF-67, which improved the electroconductivity of the nanocomposites greatly. The CNT@ZIF-67 nanocomposites was covered by lots of PANI. Originating from the synergistic effect of PANI (including excellent electrical activity, well pseudo capacitance and good chemical doping/undoping) and CNT@ZIF-67-CC (including large specific surface area, hierarchical porous nanostructures and good electroconductivity), the obtained PANI-CNT@ZIF-67-CC supercapacitor electrode showed good performances. Under the sweep rate of 10 mV s−1, the PANI-CNTs@ZIF-67-CC supercapacitor electrode exhibited a specific capacitance of 3511 mF cm−2. At the current density of 0.5 mA cm−2, the specific capacitance maintained 83% after 1000 charging/discharging cycles.Download high-res image (132KB)Download full-size image

•An AA novel ratiometric biosensor based on PCN-333 (Al) MOFs-KB-Thi was prepared.•PCN-333 (Al) MOFs could effectively avoid the cohesion or aggregation of KB and Thi on electrode surface.•PCN-333 (Al) MOFs could selectively accumulate target analytes into their pores to enhance the selectivity.•The ratometric biosensor could improve the accuracy and reproducibility.•The AA ratiometric biosensor showed good performance toward AA detection.In this work, a novel ascorbic acid (AA) ratiometric biosensor was prepared by using the PCN-333 (Al) metal-organic frameworks (MOFs) (PCN stands for porous coordination network) to encapsulate Ketjen black (KB) as catalyst for catalyzing oxidation of AA and thionine (Thi) as an internal reference signal simultaneously. The encapsulation of KB and Thi in the pores of PCN-333 (Al) MOFs not only improved efficiency of KB and Thi greatly because PCN-333 (Al) MOFs could effectively avoid the cohesion or aggregation of KB and Thi on electrode surface but also enhanced the stability of biosensors because they were immobilized in the pore firmly. Furthermore, PCN-333 (Al) MOFs could also selectively accumulate target analytes into their pores to enhance the selectivity of biosensors. The oxidation peak current of AA catalyzed by KB at −0.05 V increased with the increasing concentration of AA, while the oxidation peak current of Thi at −0.24 V kept constant, which resulted in a novel ratiometric biosensor for AA detection. The ratiometric biosensor exhibited a wider linear range from 14.1 ± 0.2 to (5.5 ± 0.1) х103 μM (R2 = 0.998) and a lower detection limit of 4.6 ± 0.1 μM with high accuracy, selectivity, reproducibility and sensitivity. The ratiometric electrochemical approach is not only a new method for AA detection but also opens a new way for sensitive detection of other analytes.

•A hybrid Cu-hemin MOF/CS-rGO with a unique peroxidase-like activity was prepared.•The CS-rGO improved electrical conductivity of the nanocomposites greatly.•The 3D porous structure enhanced the catalytic activity of hemin for H2O2.•A novel sensitive electrochemical biosensing for H2O2 detection was achieved.Herein, a Cu-hemin metal-organic-frameworks (MOFs)/chitosan (CS)-reduced graphene oxide (CS-rGO) nanocomposite with unique peroxidase-like bioactivity and good electrical conductivity was prepared for electrochemical H2O2 sensing for the first time. The prepared Cu-hemin MOFs/CS-rGO nanocomposites were well characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray powder diffraction, UV–vis spectroscopy and electrochemical techniques. The results showed that after the Cu-hemin MOFs were formed on the CS-rGO surface, the crystalline structure of the Cu-hemin MOFs was kept while the size of Cu-hemin MOFs was decreased and the electrical conductivity of the nanocomposites was enhanced greatly as compared with that of Cu-hemin MOFs. The unique peroxidase-like bioactivity and good electrical conductivity as well as some novel properties of Cu-hemin MOFs/CS-rGO nanocomposites resulted in perfect electrochemical performances towards the reduction of hydrogen peroxide (H2O2), superior to some mimic enzymes. The Cu-hemin MOF/CS-rGO was used to construct a novel H2O2 electrochemical sensor which exhibited wide linear range (0.065–410 μM) and low detection limit (0.019 μM). The study might provide a new proposal for preparing perfect hemin-based materials as mimetic peroxidase in the electrochemical sensing.A simple, sensitive and effective method to detect hydrogen peroxide based on a hybrid Cu-hemin metal-organic-frameworks (MOFs)/chitosan-functionalized reduced graphene oxide (CS-rGO) nanocomposite was achieved via Cu-hemin MOFs constructing with CS-rGO in room temperature. The Cu-hemin MOFs/CS-rGO nanomaterials exhibited a unique peroxidase-like activity and good electrical conductivity as well as some novel properties. And the as-prepared electrode resulted in a perfect electrochemical performance towards reduction of hydrogen peroxide which was superior to natural enzymes and some inorganic mimic enzymes.

•A novel kenaf stem-derived porous carbon/nitrogen-doped carbon nanotubes/polyaniline nanocomposite (KSC/NCNTs/PANI) was constructed.•The NCNTs were densely distributed on the channel walls of the KSC.•The nanocomposites had advantages of both PANI and KSC/NCNTs.•The as-prepared supercapacitor exhibited a high specific capacitance and long-term cycle stability.A novel kenaf stem-derived porous carbon/nitrogen-doped carbon nanotubes/polyaniline (denoted as KSC/NCNTs/PANI) nanocomposite was constructed in this work. Three-dimensional (3D) KSC/NCNTs nanocomposites were firstly constructed through a CVD method. The NCNTs were densely distributed on the channel walls of KSC, which increased both the effective surface area and the active sites greatly. Then, the PANI was grown on the KSC/NCNTs by using in situ chemical oxidation polymerization method. The obtained 3D KSC/NCNTs/PANI nanocomposites were carefully characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and Raman spectra. The nanocomposites were employed as the electrode materials of supercapacitors owing to their unique advantages originating from both PANI (e.g. interesting electroactivity, high pseudocapacitance, unusual doping/dedoping chemistry) and KSC/NCNTs (e.g. large specific surface area, high porosity, good electrical conductivity), and exhibited a high specific capacitance. At the current density of 0.1 A g−1, the KSC/NCNTs/PANI nanocomposites showed a specific capacitance of 1090 F g−1 with a specific energy density around 97 Wh kg−1. Moreover, the specific capacitance remained 96.9% after 1000 charging/discharging cycles at a current density of 0.1 A g−1.

This work reports a one-step synthesis of reduced graphene oxide (rGO) supported platinum–nickel oxide nanoplate arrays (denoted as Pt–NiO/rGO) for nonenzymatic glucose sensing. The prepared Pt–NiO/rGO nanocomposite was characterized by scanning electron microscopy, X-ray energy dispersive spectrometry, and X-ray powder diffraction. The existence of a small quantity of Pt could significantly enhance the catalytic activity of NiO and played an important role in controlling the morphology of Pt–NiO nanoplate arrays. The vertical array structure of the Pt–NiO/rGO nanocomposite increased the effective loading of the Pt–NiO catalyst on the electrode surface to some extent. Therefore, the Pt–NiO/rGO modified glassy carbon electrode (GCE) was successfully used for highly sensitive and selective nonenzymatic glucose detection. The linear range was from 0.008 to 14.5 mM (R2 = 0.9976, n = 41). The sensitivity was 832.95 μA cm−2 mM−1 and the detection limit was 2.67 μM (S/N = 3). The good catalytic activity and high sensitivity and stability make the Pt–NiO/rGO/GCE sensor a new kind of hybrid material for the electrochemical detection of glucose.

A simple and industrially scalable approach to prepare porous carbon (PC) with high surface areas as well as abundant nitrogen element as anode supporting materials for lithium-ion batteries (LIBs) was developed. Herein, the N-doped PC was prepared by carbonizing crawfish shell, which is a kind of food waste with abundant marine chitin as well as a naturally porous structure. The porous structure can be kept to form the N-doped PC in the pyrolysis process. The N-doped PC-Co3O4 nanocomposites were synthesized by loading Co3O4 on the N-doped PC as anode materials for LIBs. The resulting N-doped PC-Co3O4 nanocomposites release an initial discharge of 1223 mA h g–1 at a current density of 100 mA g–1 and still maintain a high reversible capacity of 1060 mA h g–1 after 100 cycles, which is higher than that of individual N-doped PC or Co3O4. Particularly, the N-doped PC-Co3O4 nanocomposites can be prepared in a large yield with a low cost because the N-doped PC is derived from abundant natural waste resources, which makes it a promising anode material for LIBs.Keywords: anode; Co3O4; lithium-ion batteries; N-doped porous carbon; nanocomposites;

A three-dimensional (3D) macroporous carbon (3D-KSCs) derived from kenaf stem (KS) is proposed as a novel supporting material for electrochemical sensing and a biosensing platform. A series of 3D-KSCs/inorganic nanocomposites such as Prussian blue (PB) nanoparticles (NPs)-carboxylic group-functionalized 3D-KSCs (PBNPs-3D-FKSCs), CuNiNPs-3D-KSCs, and CoNPs-3D-KSCs were prepared by a facile two-step route consisting of carbonization and subsequent chemical synthesis or one-step carbonization of KS–metal ion complex. The obtained 3D-KSCs/inorganic nanocomposites were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, and Fourier transform-infrared spectroscopy. A whole piece of 3D-KSCs/nanocomposites was used to prepare an integrated 3D-KSCs/nanocomposite electrode. Compared to the electrode modified by graphene, carbon nanotubes and their derivatives, which can form close-packed structure after assembled on electrode surface, the integrated 3D-KSCs/nanocomposite electrode shows a 3D honeycomb porous structure. Such structure provides a large specific surface area, effectively supports a large number of electro-active species, and greatly enhances the mass and electron transfer. The electrochemical behaviors and electrocatalytic performances of the integrated 3D-KSCs/inorganic nanocomposite electrode were evaluated by cyclic voltammetry and the amperometric method. The resulted PBNPs-3D-FKSCs, CuNiNPs-3D-KSCs, and CoNPs-3D-KSCs electrode show good electrocatalytic performances toward the reduction of H2O2, the oxidation of glucose and amino acid, respectively. Therefore, the low-cost, renewable, and environmentally friendly 3D-KSCs should be promising supporting materials for an electrochemical sensor and biosensor.

The well-ordered assembly of collagen molecules on mica surface has attracted extensive attention because it has great potential applications or can be served as a model system for study on the assembly process. Although the epitaxially guided collagen assembly mediated by potassium ion on mica surface has been reported several times over these years, specific effects of anions in this field has never been surveyed and discussed before now. In this work, atomic force microscopy was employed to visually follow the assembly of collagen on mica surface mediated by three kinds of Mg2+ salts with different anions, including MgAc2, MgSO4, and MgCl2. It was found that at high ionic concentration anions could critically affect the interaction between collagen microfibrils and mica surface and accordingly resulted in different structures. Almost parallelly aligned collagen fibrils in one direction were achieved for acetates, sparse and small fibrils in two main directions rotated by 120° were acquired for sulfate, while flat film with some defects was obtained for chloride, respectively. The Hofmeister series and Collins’ model were used to interpret the results. This study would be useful for controlling the morphologies of assembled collagen on a surface.

•OH-capped (CdS–OH QDs) and CH3-capped (CdS–CH3 QDs) CdS QDs were prepared.•The interaction between EcoRI and these CdS QDs was studied, respectively.•Functional group affects the interaction strength and mode of EcoRI with CdS QDs.•Functional group affects the conformation of EcoRI.•The enzyme activity of EcoRI was preserved in the EcoRI–CdS QDs bioconjugates.In this study, we investigated the interaction between EcoRI and CdS QDs modified with different functional groups as well as the conformational changes of EcoRI in the process. MUD capped (CdS–OH QDs) and UDT capped (CdS–CH3 QDs) CdS QDs were separately prepared and used to react with EcoRI, respectively. The interaction was characterized by various spectroscopic techniques including UV–vis absorption, fluorescence and Fourier transform infrared (FTIR) spectroscopy, together with electrophoresis methods. The strength of interaction for EcoRI with CdS–OH QDs and CdS–CH3 QDs was evaluated and analysed. Relevant thermodynamic parameters such as ΔH, ΔG and ΔS were calculated and a static quenching interaction process was proposed. The conformational change of EcoRI interacted with CdS–OH QDs or CdS–CH3 QDs was also measured and compared. Finally agarose electrophoresis assay was performed and revealed that the enzyme activity of EcoRI was somewhat conserved after interaction with CdS QDs. This study contributed to a better understanding of protein-NPs interaction and created a framework for applications of nanomaterial-biomolecule conjugation in some fields such as nanobiology and nanomedicine.

Silver (Ag) electrodes were roughened by electrochemical oxidation–reduction cycles (ORC) in a KCl solution. The roughened Ag electrode exhibited a powerful electrocatalytic activity for the reduction of hydrogen peroxide (H2O2). Atomic force microscopy and electrochemical experiments confirmed that the electrocatalytic ability mainly resulted from the Ag nanoparticles produced in the process of ORC on the roughened Ag electrode. The electrochemical behaviors of the roughened Ag electrodes toward the reduction of H2O2 and the factors related to that reduction were investigated in detail.

A monolayer of Keggin-type heteropolyanion [SiNi(H2O)W11O39]6− was fabricated by electrodepositing [SiNi(H2O)W11O39]6− on cysteamine modified gold electrode. The monolayer of [SiNi(H2O)W11O39]6− modified gold electrode was characterized by atomic force microscopy (AFM) and electrochemical method. AFM results showed the [SiNi(H2O)W11O39]6− uniformly deposited on the electrode surface and formed a porous monolayer. Cyclic voltammetry exhibited one oxidation peak and two reduction peaks in 1.0 M H2SO4 in the potential range of −0.2 to 0.7 V. The constructed electrode could exist in a large pH (0–7.6) range and showed good catalytic activity towards the reduction of bromate anion (BrO3−) and nitrite (NO2−), and oxidation of ascorbic acid (AA) in acidic solution. The well catalytic active of the electrode was ascribed to the porous structure of the [SiNi(H2O)W11O39]6− monolayer.

•The 3D-KSCs/hierarchical Co3O4 nanoclusters integrated electrode was prepared.•The integrated electrode shows lots of needle-shaped and layered Co3O4 on 3D-KSC.•The integrated electrode shows large specific surface area and good electrical conductivity.•The integrated electrode shows superior performance for the detection of glucose.A novel supporting material named as three-dimensional kenaf stem-derived carbon (3D-KSCs) was used to load hierarchical Co3O4 nanoclusters for electrochemical sensing glucose. The 3D-KSCs/hierarchical Co3O4 nanoclusters were constructed by two steps. Los of acicular precursor nanoclusters firstly grew on the channels of 3D-KSCs densely by hydrothermal method and then the as-prepared 3D-KSCs/hierarchical Co3O4 nanoclusters was obtained by thermal pyrolysis of the 3D-KSCs/precursors nanocomposites at 400 °C. The 3D macroporous configuration of 3D-KSCs resulted in lots of hierarchical Co3O4 nanoclusters arrayed on the surface of 3D-KSCs owing to its large enough specific surface area, which effectively avoided their aggregations and improved the stability of nanocomposites. The obtained 3D-KSCs/hierarchical Co3O4 nanoclusters showed a large number of needle-shaped and layered Co3O4 nanoclusters uniformly grew on the macropore’s walls of 3D-KSC. Due to its unique nanostructures, the 3D-KSCs/hierarchical Co3O4 nanoclusters integrated electrode showed superior performance for nonenzymatic electrochemical glucose sensing, showing wide linear range (0.088–7.0 mM) and low detection limit of 26 μM. It might be a new strategy to prepare nanostructures on 3D-KSC for future applications.

This work reports a one-step synthesis of reduced graphene oxide (rGO) supported platinum–nickel oxide nanoplate arrays (denoted as Pt–NiO/rGO) for nonenzymatic glucose sensing. The prepared Pt–NiO/rGO nanocomposite was characterized by scanning electron microscopy, X-ray energy dispersive spectrometry, and X-ray powder diffraction. The existence of a small quantity of Pt could significantly enhance the catalytic activity of NiO and played an important role in controlling the morphology of Pt–NiO nanoplate arrays. The vertical array structure of the Pt–NiO/rGO nanocomposite increased the effective loading of the Pt–NiO catalyst on the electrode surface to some extent. Therefore, the Pt–NiO/rGO modified glassy carbon electrode (GCE) was successfully used for highly sensitive and selective nonenzymatic glucose detection. The linear range was from 0.008 to 14.5 mM (R2 = 0.9976, n = 41). The sensitivity was 832.95 μA cm−2 mM−1 and the detection limit was 2.67 μM (S/N = 3). The good catalytic activity and high sensitivity and stability make the Pt–NiO/rGO/GCE sensor a new kind of hybrid material for the electrochemical detection of glucose.