An efficient thin-walled Pd/polypyrrole hybrid nanotube biocatalyst for sensitive detection of ascorbic acid.

Controllable fabrication of novel and uniform noble metal nanoparticles on a specific support with a superior catalytic or electrocatalytic performance is of significantly importance for practical applications. In this report, we demonstrated an effective way to fabricate uniform thin-walled Pd/polypyrrole (PPy) hollow nanotubes. The prepared Pd/PPy hybrid nanotubes exhibited an excellent peroxidase-like activity to oxidize a typical peroxidase substrate such as 3,3',5,5'-tetramethylbenzidine in comparison with traditional Pd/C and Pd black catalysts. The outstanding catalytic activity of the Pd/PPy hybrid nanotubes for peroxidase mimicking could be resulting from their unique hollow characteristic and an interfacial effect between PPy and Pd components. Based on the favorable catalytic property of the Pd/PPy hybrid nanotubes, a convenient and rapid colorimetric way to sensitively determine ascorbic acid has been presented. The detection limit was around 0.062 µM and an excellent selectivity was also achieved. The developed detection system in this study could be extended to the fields of bioscience and biotechnology with promising prospects.

Fabrication of oxidase-like polyaniline-MnO2 hybrid nanowires and their sensitive colorimetric detection of sulfite and ascorbic acid.

Recently, nanomaterials-based oxidase-like artificial enzymes have attracted much attention due to their unique catalytic efficiency, high environmental stability and low-cost. In this study, we for the first time show the application of polyaniline (PANi)-MnO2 hybrid nanowires for oxidase mimicking. The PANi-MnO2 hybrid nanowires are prepared via a redox reaction between PANi nanowires and KMnO4. The as-prepared PANi-MnO2 hybrid nanowires exhibit an enhanced oxidase-like catalytic activity compared with individual PANi nanowires and MnO2 alone due to the synergistic catalytic effect between the two components. Based on the above findings, we construct PANi-MnO2 hybrid nanowires-based colorimetric assay for sensitive and selective detection of sulfite and ascorbic acid (AA). The detection limits of sulfite and AA are as low as 79 and 26 nM, respectively, which is much lower than many previous reported enzyme mimics-based colorimetric sensors. This work demonstrates a broad potential prospect of PANi-MnO2 hybrid nanowires in biotechnology, environmental science and food safety.

Fabrication of ternary MoS2-polypyrrole-Pd nanotubes as peroxidase mimics with a synergistic effect and their sensitive colorimetric detection of l-cysteine.

Over the past few years, nanomaterials-based enzymatic mimics have attracted tremendous attention due to their excellent catalytic activity and environmental stability. In this work, ternary MoS2-polypyrrole (PPy)-Pd nanotubes have been prepared through a hydrothermal reaction and in situ redox polymerization process between pyrrole monomer and Na2PdCl4. The prepared MoS2-PPy-Pd nanotubes exhibited a higher peroxidase-like catalytic activity than individual MoS2, MoS2-PPy, PPy-Pd and MoS2-Pd nanocomposites due to the synergistic catalytic effect between the three components. The catalytic kinetic of MoS2-PPy-Pd nanotubes follows Michaelis-Menten behaviors, exhibiting a good affinity to both 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2 substrates. On the basis of high peroxidase-like catalytic efficiency of the MoS2-PPy-Pd nanotubes, a simple and convenient colorimetric strategy for the rapid and sensitive detection of l-cysteine with a detection limit of 0.08 µM has been developed. In addition, a high selectivity towards the detection of l-cysteine is achieved. This work present an opportunity of the prepared ternary MoS2-PPy-Pd nanotubes for promising potential applications in biosensing, environmental monitoring, and medical diagnostics.

Controlled synthesis of titanium dioxide/molybdenum disulfide core-shell hybrid nanofibers with enhanced peroxidase-like activity for colorimetric detection of glutathione.

Synergistic effects play a crucial role in improving the catalytic activity of enzyme-like reactions. The preparation of hybrid nanomaterials for enzyme mimicking that display synergistic enhanced catalytic activity remains a formidable challenge. Titanium dioxide (TiO2)/molybdenum disulfide (MoS2) core-shell hybrid nanofibers were synthesized as efficient peroxidase mimics via a three-step approach involving electrospinning, calcination, and hydrothermal treatment. The resulting TiO2/MoS2 hybrid nanofibers exhibited synergistically enhanced peroxidase-like catalytic activity relative to the TiO2 nanofibers or MoS2 nanosheets alone. Based on the high peroxidase-like activity of the TiO2/MoS2 hybrid nanofibers, a simple colorimetric approach for the detection of l-glutathione (GSH) was developed, with a detection limit as low as 0.05 µM. This study provides a simple and sensitive sensing platform for the detection of GSH, with prospective applications in colorimetric sensing, environmental monitoring, and medical diagnosis.

Self-templated fabrication of FeMnO3 nanoparticle-filled polypyrrole nanotubes for peroxidase mimicking with a synergistic effect and their sensitive colorimetric detection of glutathione.

A self-templated approach has been developed for the preparation of FeMnO3 nanoparticles filled in the hollow core of polypyrrole (PPy) nanotubes by an in situ polymerization process accompanied by the etching of FeMnO3 nanofibers. The prepared FeMnO3@PPy nanotubes exhibited a superior peroxidase-like activity. The catalytic reaction system has been used for the sensitive colorimetric detection of glutathione with a low detection limit and good selectivity.

Synthesis of hierarchical Co3O4@NiO core-shell nanotubes with a synergistic catalytic activity for peroxidase mimicking and colorimetric detection of dopamine.

Fabrication of core-shell nanostructured catalyst is a promising way for tuning its catalytic performance due to the highly active interface and rich redox properties. In this work, hierarchical Co3O4@NiO core-shell nanotubes are fabricated by the deposition of NiO shells via a chemical bath treatment using electrospun Co-C composite nanofibers as templates, followed by a calcination process in air. The as-prepared Co3O4@NiO core-shell nanotubes exhibit a uniform and novel hollow structure with Co3O4 nanoparticles attached to the inner wall of NiO nanotubes and excellent catalytic activity toward the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. Due to the synergistic effect, the peroxidase-like activity of the Co3O4@NiO core-shell nanotubes is much higher than that of individual Co3O4 and NiO components. Owing to the superior peroxidase-like activity, a simple and rapid colorimetric approach for the detection of dopamine with a detection limit of 1.21µM and excellent selectivity has been developed. It is anticipated that the prepared Co3O4@NiO core-shell nanotubes are promising materials applied for biomedical analysis and environmental monitoring.

General synthesis of hierarchical C/MOx@MnO2 (M=Mn, Cu, Co) composite nanofibers for high-performance supercapacitor electrodes.

Improving the conductivity and specific surface area of electrospun carbon nanofibers (CNFs) is beneficial to a rapid realization of their applications in energy storage field. Here, a series of one-dimensional C/MOx (M=Mn, Cu, Co) nanostructures are first prepared by a simple two-step process consisting of electrospinning and thermal treatment. The presence of low-valence MOx enhances the porosity and conductivity of nanocomposites to some extent through expanding graphitic domains or mixing metallic Cu into the CNF substrates. Next, the C/MOx frameworks are coated with MnO2 nanosheets/nanowhiskers (C/MOx@MnO2), during which process the low-valence MOx can partly reduce KMnO4 so as to mitigate the consumption of CNFs. When used as active materials for supercapacitor electrodes, the obtained C/MOx@MnO2 exhibit excellent electrochemical performances in comparison with the common CNFs@MnO2 (CM) core-shell electrode due to the combination of desired functions of the individual components and the introduction of extra synergistic effect. It is believed that these results will provide an alternative way to further increase the capacitive properties of CNFs- or metal oxide-based nanomaterials and potentially stimulate the investigation on other kinds of C/MOx composite nanostructures for various applications.

Fabrication of cobalt ferrite/cobalt sulfide hybrid nanotubes with enhanced peroxidase-like activity for colorimetric detection of dopamine.

The development of highly sensitive and low-cost biosensors for the detection of dopamine is of paramount importance for medical diagnostics. Herein, we report the preparation of a new peroxidase-like catalyst with a uniform heterostructure by using a technique involving electrospinning, annealing and solvothermal reaction. In this catalyst system, cobalt sulfide (CoS) nanoparticles were homogenously distributed and supported on the surface of cobalt ferrite (CoFe2O4) nanotubes. The as-prepared CoFe2O4/CoS hybrid nanotubes showed remarkably high catalytic efficiency as peroxidase mimics toward the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2. Owing to the synergistic effect between the CoFe2O4 and CoS component, the prepared CoFe2O4/CoS hybrid nanotubes exhibited enhanced peroxidase-like activity, exceeding that of either the CoS nanoparticles or CoFe2O4 nanotubes alone. Dopamine has been widely investigated due to its unique function in the nervous system. Consequently, various approaches have been developed for the sensitive determination of dopamine. In this work, a simple and sensitive colorimetric route for the detection of dopamine was established based on the ability of dopamine to induce the reduction of oxidized TMB to TMB with consequent fading of the blue color. This method shows a wide linear range (0-50µM) and a low detection limit of 0.58µM. The unique heterostructure with spinel/sulfide interfaces represents a new concept for the construction of highly efficient and multifunctional biocatalysts.

Hierarchical CNFs/MnCo2O4.5 nanofibers as a highly active oxidase mimetic and its application in biosensing.

Recently, much attention has been paid on the nanomaterial-based artificial enzymes due to their tunable catalytic activity, high stability and low cost compared to the natural enzymes. Different from the peroxidase mimics which have been studied for several decades, nanomaterials with oxidase-like property are burgeoning in the recent years. In this paper, hierarchical carbon nanofibers (CNFs)/MnCo2O4.5 nanofibers as efficient oxidase mimics are reported. The products are synthesized by an electrospinning technique and an electrochemcial deposition process in which the CNFs are used as the working electrode where MnCo2O4.5 nanosheets deposit on. The resulting binary metal oxide-based nanocomposites exhibit a good oxidase-like activity toward the oxidations of 3,3',5,5'tetramethylbenzi-dine (TMB), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium (ABTS) salt and o-phenylenediamine (OPD) without exogenous addition of H2O2. The system of CNFs/MnCo2O4.5-TMB can be used as a candidate to detect sulfite and ascorbic acid via a colorimetric method with a high sensitivity. This work provides the efficient utilization and potential applications of binary metal oxide-based nanocomposites with oxidase activities in biosensors and other biotechnologies.

Strongly coupled CeO2/Co3O4/poly(3,4-ethylenedioxythiophene) nanofibers with enhanced nanozyme activity for highly sensitive colorimetric detection.

In this work, we have prepared CeO2/Co3O4 composite nanofibers via an electrospinning technique followed by a calcination process. Then core-shell structured CeO2/Co3O4/poly(3,4-ethylenedioxythiophene) (PEDOT) composite nanofibers were fabricated through a redox reaction between the 3,4-ethylenedioxythiophene (EDOT) monomer and Co3O4 on the surface of CeO2/Co3O4 composite nanofibers. The morphology and composition of the two composite nanofibers were confirmed by field-emission scanning electron microscopy, transmission electron microscopy, x-ray diffraction, Fourier transform infrared spectroscopy, and x-ray photoelectron spectra measurements. Due to the synergistic effect between CeO2 and Co3O4, the catalytic activity was enhanced compared to that of independent oxide nanofibers. After the growth of PEDOT, the catalytic activity process was further improved, having achieved a secondary synergistic effect. Application of the two prepared composite nanofibers as peroxidase-like catalysts for the colorimetric detection of H2O2 was investigated. It is anticipated that this work can inspire researchers to develop various novel functional nanocomposites for applications in biosensing and environmental monitoring.

Self-Assembly Fabrication of Coaxial Te@poly(3,4-ethylenedioxythiophene) Nanocables and Their Conversion to Pd@poly(3,4-ethylenedioxythiophene) Nanocables with a High Peroxidase-like Activity.

Here, we report a simple one-step procedure to fabricate coaxial Te@poly(3,4-ethylenedioxythiophene) (PEDOT) nanocables via a self-assembly redox polymerization between 3,4-ethylenedioxythiophene monomer and the oxidant of sodium tellurite without the assistance of any templates and surfactants. The as-synthesized Te@PEDOT coaxial nanocables have diameters of center cores in the range of 5-10 nm, and the size of the outer shell from several nanometers to 15 nm. More interestingly, the as-prepared Te@PEDOT nanocables can be converted to Pd@PEDOT nanocables via a galvanic replacement reaction. The center core of the Pd nanowire exhibits a high crystallinity. The application of the synthesized Pd@PEDOT nanocables as peroxidase-like catalysts for the colorimetric detection of H2O2 is reported. The synergistic effect between the Pd nanowire and electrically conducting PEDOT enhances the catalytic activity toward the oxidation of the peroxidase substrate 3,3',5,5'-tetramethylbenzidine in the presence of H2O2. A detection limit toward H2O2 is as low as 4.83 µM, and a linear range from 10 to 100 µM has been achieved. This work offers a potential versatile route for the fabrication of cable-like nanocomposites with conducting polymers and other active components, which display great promise in applications such as catalysis, nanoelectronic devices, and energy storage and conversion.

Electroactive self-doped poly(amic acid) with oligoaniline and sulfonic acid groups: synthesis and electrochemical properties.

A novel poly(amic acid) with pendant aniline tetramer and sulfonic acid groups (ESPAA) was synthesized by ternary polymerization and characterized by Fourier-transform infrared spectra, ((1))H NMR and gel permeation chromatography. The polymer showed good thermal stability and excellent solubility in the common organic solvents. The electrochemical properties were investigated carefully on a CHI 660A Electrochemical Workstation. The polymer displayed good electroactivity in acid, neutral and even in alkaline solutions (pH=1-10) due to the self-doping effect between aniline tetramer and sulfonic/carboxylic acid groups. It also exhibited satisfactory electrochromic performance with high contrast value, acceptable coloration efficiency and fast switching time in the range of pH=1-9.