Hierarchical NiCo2O4@MnMoO4 core–shell nanomaterial on nickel foam was designed via a facile hydrothermal method. A possible growth mechanism of the MnMoO4 is in which the molybdenum acid radical captures part manganese ions of the MnMoO4 nanoflowers. When regarded as binder-free electrodes for supercapacitors (SCs), such special NiCo2O4@MnMoO4 core–shell hybrid electrodes exhibit ultra-high specific capacitances several times larger than a pristine NiCo2O4 electrode. The electrodes possess high specific capacitance of 1118 F g−1 at a current density of 1 A g−1 and excellent cycling stability (5000 cycles). This remarkable electrochemical performance is ascribed to the effective combination of two electroactive materials and the rational array configuration.

In this paper, hierarchical MnCo2O4@MnO2 core–shell nanowire arrays (MnCo2O4@MnO2 NWAs) with mesoporous and large surface area are synthesized on 3D nickel foam via a facile, two-step hydrothermal approach without any adscititious surfactant and binder. The electrode architecture takes advantage of the synergistic effects contributed from both the porous MnCo2O4 nanowire core and the MnO2 shell layer. The fabricated MnCo2O4@MnO2 NWA electrode for supercapacitors in aqueous electrolyte exhibits a significantly enhanced specific capacitance (858 F g−1 at 1 A g−1), high energy density (36.0 Wh kg−1 at 252 W kg−1) and long-life cycling stability (retaining 88% of the initial capacitance after 5000 cycles). Then, a symmetrical supercapacitor is fabricated by assembling two MnCo2O4@MnO2 NWA-based electrodes, which shows a high specific capacitance of 678 F g−1 at 1 A g−1 and a high energy density of 135.6 Wh kg−1 at 513 W kg−1. Thereby, the hierarchical core–shell MnCo2O4@MnO2 NWAs are very promising as next generation high-performance long-life cycling supercapacitors.

Because of the intrinsic importance of transcription factors (TFs) as targets in clinical diagnosis and drug development, the simple and sensitive detection of TFs is very essential for biological studies and medical diagnostics. However, most of the reported methods involve complicated operations or labelling processes and in addition, an electrochemiluminescence (ECL) method with various distinct advantages hasn't been developed for TF detection until now. In this work, we describe a novel simple and efficient strategy for label-free ECL detection of transcription factors with hybridization chain reaction (HCR) signal amplification. Based on the Ag+-stabilized self-assembly triplex DNA, in the presence of TFs, TFs specifically bond to the duplex DNA (dsDNA) recognition probes, resulting in the separation of target DNA from the triplex structure. With the SH-capture probe DNA assembled gold electrode, the presence of the target DNA and helper DNA-1 and helper DNA-2 leads to the formation of long chain dsDNA polymers on the gold electrode surface through hybridization chain reaction, which allows the intercalation of numerous ECL indicators Ru(phen)32+ (phen = 1,10-phenanthroline) into the dsDNA grooves, resulting in significantly amplified ECL signal output. The proposed strategy combines the amplification power of the HCR and the inherent high sensitivity of the ECL technique, resulting in the sensitive detection of transcription factors with a detection limit of as low as 0.017 nM and a broad dynamic range from 0.05 to 2 nM. The distinct advantage of the method is that it is label-free, has high sensitivity and requires no separation of the signal generation strand, which boosts the potential application for real sample detection.

In the present study, based on the mimic oxidase catalytic character of nucleic-acid-stabilized silver nanoclusters (DNA/AgNCs) and hybridization chain reactions for signal amplification, the fabrication of a label-free sensitive “turn-on” electrochemical aptasensor for the amplified determination of lysozyme was demonstrated. First, the designed DNA duplex was modified on the electrode. With the specific binding of the target, lysozyme and its aptamer, the lysozyme-binding DNA sequence was liberated, exposing the induced DNA sequence, which in turn triggered the formation of the supersandwich DNA structure. Because the cytosine-rich sequence was designed ingeniously on the DNA sequence, DNA/AgNCs were formed on the supersandwich DNA structure. The peroxidase-like character of DNA/AgNCs produced detectable electrochemical signals for the lysozyme aptasensor, which showed a satisfying sensitive detection of lysozyme with a low detection limit of 42 pM and a wide linear range of 10−10 M to 10−5 M.

In this work, hierarchical Co3O4@CoMoO4 core/shell nanowire arrays on nickel foam are fabricated by a facile hydrothermal ion exchange method. The Co3O4 nanowires are fully covered by ultrathin mesoporous CoMoO4 nanosheets. A possible growth mechanism for the CoMoO4 involves the capturing of the part of the cobalt ions of the Co3O4 nanowires by the molybdenum acid radical without annealing. When investigated as binder-free electrodes for supercapacitors (SCs), such unique Co3O4@CoMoO4 core/shell hybrid electrodes exhibited ultrahigh areal capacitances, which are several times larger than the pristine Co3O4 electrode. The electrode exhibits a high specific capacitance of 1040 F g−1 at a current density of 1 A g−1 and an excellent cycling stability (5000 cycles). The remarkable electrochemical performance is attributed to the rational combination of two electroactive materials and the array configuration.

Integrated nanodevices with the capability of storing energy are widely applicable and thus have been studied extensively. To meet the demand for flexible integrated devices, asymmetric supercapacitors that simultaneously realize energy storage were fabricated by growing NiCo2O4@NiMoO4 hybrid nanowires on nickel foam, thus obtaining the positive electrode, and employing active carbon as the negative electrode. The as-assembled integrated systems were characterized by their improved energy storage (areal specific capacitance of 6.30 F cm−2 at 60 mA cm−2 and specific capacitance up to 1242 F g−2 at a current density of 10 mA cm−2), enhanced power density and energy density by increasing the potential window from 0 V to 1.6 V. Such flexible integrated devices might be used in smart and self-powered sensory, wearable, and portable electronics.

In this study, a hierarchical ZnCo2O4@MnO2 core–shell nanotube arrays electrode was developed by a facile two-step method. The electrode exhibits high specific capacitance of 1981 F g−1 (2.38 F cm−2) at a current density of 5 A g−1 and excellent cycling stability (5000 cycles). Furthermore, a low-cost, high-performance asymmetric supercapacitor (ASC) with ZnCo2O4@MnO2 core–shell nanotube arrays on Ni foam (as positive electrode) and 3D porous α-Fe2O3 on Fe foil (as negative electrode) was successfully designed. The as-designed ASC device with an extended operating voltage window of 1.3 V achieved a specific capacitance of 161 F g−1 at 2.5 mA cm−2 with a maximum energy density of 37.8 W h kg−1 and excellent stability with a capacitance retention of 91% after 5000 cycles. Furthermore, after being charged for dozens of seconds, the ZnCo2O4@MnO2//α-Fe2O3-ASC can easily light up a LED. These fascinating performances indicate that the present ZnCo2O4@MnO2 core–shell nanotube arrays with remarkable electrochemical properties could be considered as potential electrode materials for next generation supercapacitors in high energy density storage systems.

With only graphene oxide and KMnO4, the luminescent graphene quantum dots (GQDs) in high quantum yield were prepared by one-step synthesis using ultrasonication, and applied in the label-free, simple and fast fluorescence assay of alkaline phosphatase (ALP).

Flexible supercapacitors have recently attracted increasing attention as they show unique promising advantages, such as flexibility and shape diversity, and they are light-weight and so on. Herein, we designed a series of 3D porous spinous iron oxide materials synthesized on a thin iron plate through a facile method under mild conditions. The unique nanostructural features endow them with excellent electrochemical performance. The electrochemical properties of the integrated electrodes as active electrode materials for supercapacitors have been investigated using different electrochemical techniques including cyclic voltammetry, and galvanostatic charge–discharge in Na2SO4 and LiPF6/EC:DEC electrolyte solutions. These integrated electrodes showed high specific capacitance (as high as 524.6 F g−1 at the current density of 1 A g−1) in 1.0 M Na2SO4 (see Table S1). Moreover, the integrated electrodes also show high power densities and high energy densities in a LiPF6/EC:DEC electrolyte solution; for example, the energy densities were 319.3, 252.5, 152.1, 74.13 and 38.6 W h kg−1 at different power densities of 8.81, 21.59, 56.65, 92.09 and 152.64 kW kg−1, respectively. Additionally, the flexible superior electrode exhibited excellent stability with capacitance retention of 92.9% after 5000 cycles. Therefore, such flexible integrated devices might be used in smart and portable electronics.

Recently, three-dimensional (3D) zinc oxide nanoarchitectures (3D ZnO NAs) have drawn significant research attention due to their excellent stability, environmental friendliness and low cost. However, many of the synthesis methods are complicated, such as the two-step method. Hence, it is crucial to develop a facile hydrothermal approach. We report 3D firecracker-like zinc oxide nanoarchitectures on Zn piece that were fabricated via a facile, one-step hydrothermal approach without any surfactants. The as-prepared 3D firecracker-like ZnO nanoarchitectures/Zn piece are investigated as an integrated electrode (called 3D ZnO NA/ZPIE) and show high electrocatalytic performance to hydrazine, suggesting that 3D ZnO NA/ZPIE has potential applications in the catalytic field. At the same time, the photocatalytic activities of the prepared samples were evaluated by photocatalytic degradation of methyl orange (MO) aqueous solution at ambient temperature under UV-light irradiation. The results exhibit strong UV-light absorption capability, high degradation rate, and greatly enhanced photocatalytic (PC) activity toward degradation of methyl orange (MO) aqueous solutions under UV-light irradiation.

Thioflavin T (ThT), as one of the most exciting fluorogenic molecules, boasts the “molecular-rotor” ability to induce DNA sequences containing guanine repeats to fold into G-quadruplex structures. It has been demonstrated to sense this change by its remarkable fluorescence enhancement. In this work, taking T4 polynucleotide kinase (PNK) as a model, the ThT/G-quadruplex based platform and λexonuclease (λexo) cleavage reaction were combined to design a label-free “turn-on” strategy for fast, simple and accurate detection of T4 PNK activity and its inhibition. In the presence of T4 PNK, the designed thioflavin T based molecular beacon (TMB) DNA probe could be phosphorylated and then digested by the cleavage of λexo, releasing the G-quartets. These then bound to ThT to form ThT/G-quadruplexes with an obvious fluorescence generation, for the “turn-on” detection of T4 PNK. In comparison to traditional methods, the proposed TMB probe is convenient, requiring no sophisticated labeling and separation processes and displaying high analytical performance. It exhibits a satisfying detection result for the activity of T4 PNK with a low detection limit of 0.001 U mL−1. This is not only meaningful for further research on disease-related biochemical processes, but also valuable for molecular-target therapies.

In this paper, we report CoNi2S4 nanowire arrays (NWAs) on 3D nickel foams based on an anion-exchange reaction which involved the pseudo Kirkendall effect. Due to the low electronegativity of sulfur, CoNi2S4 NWAs exhibit higher conductivity compared with Ni–Co oxide NWAs when used as active materials in supercapacitors. The electrochemistry tests show that these self-supported electrodes are able to deliver ultrahigh specific capacitance (1250 F g−1 at a current density of 5 mA cm−2), together with a considerable areal capacitance (2.5 F cm−2 at a current density of 5 mA cm−2), Furthermore, a capacitance retention of 72% after 5000 charge–discharge cycles at 5 mA cm−2 is obtained, indicating the excellent cycling stability of the CoNi2S4 NWA/nickel foam electrode. The superior electrochemistry capacity demonstrates that CoNi2S4 NWAs are promising electrode materials for supercapacitor applications.

In this paper, ZnO@MnO2@PPy ternary core–shell nanorod arrays (NRAs) were fabricated through the layer-by-layer process. In this process, the incorporation of polypyrrole, a highly conductive material, on the surface of a binary ZnO@MnO2 core–shell structured composite is adopted to optimize the charge transfer process to further improve the electrochemical performance. Because of enhanced electron transfer capability, charge transfer resistances of the ZnO@MnO2@PPy ternary core–shell nanorod arrays are reduced and the electrochemical performances are improved. The electrochemistry tests show that these self-supported electrodes are able to deliver ultrahigh specific capacitance (1281 F g−1 at a current density of 2.5 A g−1), together with a considerable areal capacitance (1.793 F cm−2 at a current density of 3.5 mA cm−2). Furthermore, a capacitance retention of 90% after 5000 charge–discharge cycles at 5 A g−1 is obtained, indicating the excellent cycling stability of the ZnO@MnO2@PPy ternary core–shell electrode. The superior electrochemical capacity demonstrates the potential of ZnO@MnO2@PPy ternary core–shell NRAs to further improve the performance in supercapacitor electrodes.

Miniaturized energy storage devices have attracted considerable research attention due to their promising applications in various smart electronic devices. In this work, a high performance asymmetric supercapacitor (ASC) device was designed and fabricated wherein a novel nanocomposite consisting of manganese oxide (NiMn2O4) nanosheets with carbon nanotubes (CNTs) was used as the active material. High capacitance of 151 F g−1 and energy density of 60.69 W h kg−1 were achieved for the CNT@NiMn2O4 nanocomposites ASC at a current density of 1 A g−1, which attributing to the widen operation voltage window ranging from 0 to 1.7 V. Moreover, the CNT@NiMn2O4 nanocomposites ASC also showed remarkable cycling stability with 96.3% energy density retention after 5000 cycles. As a result, the CNT@NiMn2O4 nanocomposite is a possible contender materials for next generation supercapacitors in high energy density storage systems.

In this work, ultrathin porous nickel–cobalt layered double hydroxide (Ni–Co LDH) hybrid nanosheets on metal nickel sheets are synthesized via a facile hydrothermal method without any adscititious surfactant. The fabricated Ni–Co LDH hybrid nanosheet-based electrodes for supercapacitors in aqueous electrolyte exhibit a significantly enhanced specific capacitance (2184 F g−1 at 1 A g−1) and energy density (91.76 W h kg−1 at 825.84 W kg−1) due to the pronounced synergistic effect between Ni2+ and Co2+. Meanwhile, the Ni–Co LDH hybrid nanosheets as electrode materials have excellent long-life cycling stability, retaining 88.5% of the initial capacitance after 2000 cycles. Thereby, the Ni–Co nanocomposites are promising electrode materials for high-energy-density long-life cycling supercapacitors.

•Photoinduced electron transferred between Ag nanoclusters and HRP-DNAzyme.•A label-free fluorescent aptasensor was fabricated for PDGF-BB.•A logic gate of hemin and PDGF-BB also shows satisfying result.•The process only involved one-step incubation.Platelet-derived growth factor-BB (PDGF-BB) is often overexpressed in human malignant tumors as an indicator for tumor angiogenesis. Here by the photoinduced electron transfer (PET) between DNA-Ag fluorescent nanoclusters (NCs) and G-quadruplex/hemin complexes, we present a sensitive label-free fluorescent sensor for PDGF-BB. In the presence of PDGF-BB, the specific conjugation with its aptamer induced the conformational change of the duplex-like DNA sequence, releasing the G-quadruplex sequence part. Then in the presence of hemin and K+, the horseradish peroxidase mimicking DNAzyme (HRP-DNAzyme) was formed. With the electron transfer between the DNA-Ag NCs to the hemin Fe (III) center of HRP-DNAzyme, the PET occurred with a decrease in the fluorescence intensity of the DNA-Ag NCs. The detection performance such as selectivity, linear dynamic range, sensitivity, and the quenching capability of HRP-DNAzyme were estimated. The detection range for PDGF-BB is from 5×10−13 to 1×10−8 M and the detection limit is 1×10−13 M. The experimental results confirmed that the novel fluorescent aptasensor possessed a good sensitivity and high selectivity for PDGF-BB. In addition, the developed probe is nontoxic, label-free only involving one-step hybridization without sophisticated fabrication process. Furthermore, based on this quenching mode occurred by PDGF-BB and hemin, using PDGF-BB and hemin as inputs and the fluorescence signal as an output, a logic gate has been fabricated.

With exonuclease III activity on DNA hybrids containing thymine–Hg2+–thymine, a label-free ultrasensitive “turn-on” fluorescent sensor involving “quenching” and “reappearing” processes based on a carbon nanotube–Ag nanoclusters system is demonstrated for amplified determination of Hg2+.

Ultrathin ZnO nanofilms based on Zn substrate were synthesized through a facile one-pot hydrothermal method. Then this prepared Zn-ZnO integrated electrode was directly used as work electrode to detect glucose and hydrazine in the solution, respectively. Exhilaratingly, the results show that the prepared Zn-ZnO integrated electrode has significant electrocatalytic activity toward the oxidation of glucose and reduction of hydrazine. As a result, Zn-ZnO integrated electrode exhibits a wide linear range from 1 uM to 19.2 mM for the detection of glucose with a low detection limit of 1 uM (S/N = 3) and a wide linear range from 0.5 uM to 14.2 mM for the detection of hydrazine with a linear range from with a low detection limit of 0.5 uM (S/N = 3). What's more, the proposed sensor displays excellent selectivity, good stability, and satisfying repeatability.

Luminescent silver nanoclusters (AgNCs) were anchored by designed oligonucleotides, acting as fluorescent labels. They hybridized with specific nucleic acid targets to form a supersandwich structure resulting in the fluorescence intensity of the DNA/AgNCs decreasing linearly with respect to the concentration of the target DNA.

In this paper, we have designed a signal amplified method for the electrochemical determination of polynucleotide kinase activity. It is based on (a) the peroxidase-like activity of magnetite microspheres (MNPs), (b) the specific recognition capabilities of titanium dioxide (TiO2) with the phosphate groups of the capture probe and (c) the DNA dendrimer structure for signal amplification. MNPs coated with TiO2 (TMNPs) were prepared and characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. TMNP–DNA dendrimers were formed by the hybridization of captured nucleic acids with a link probe. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were carried out to study the electrocatalytic process. The formation of the TMNP–DNA dendrimer structures was related to the phosphorylated capture probe and further to the activity of polynucleotide kinase, which was the base of the polynucleotide kinase detection. The TMNP–DNA dendrimer based biosensor showed sensitive detection of polynucleotide kinase with a satisfying result; a low detection of 0.003 U mL−1 and wide linear range of 0.01 to 30 U mL−1 were achieved. Additionally, the present TMNP–DNA dendrimer based biosensor also demonstrated excellent selectivity, stability and reproducibility.

In this paper, horseradish peroxidase-mimicking DNAzyme (HRP-DNAzyme) and Prussian blue (PB)–gold (Au) nanocomposites were designed as versatile electrochemical sensing platforms for the amplified detection of DNA, Hg2+ and adenosine triphosphate (ATP). By the conjugation of the target probe with the capture probe, a conformational change resulted in the formation of HRP-DNAzyme on the PB–Au modified electrode. The redox of HRP-DNAzyme (red) was efficiently carried out in the presence of H2O2, in which PB acted as a mediator stimulating the biocatalytic functions of HRP-DNAzyme and actuated a catalytic cycle bringing an amplified signal. Specific recognition of the target DNA, Hg2+ and ATP allowed selective amperometric detection of the target molecule. The detection limits of DNA, Hg2+ and ATP were 50 nM, 30 pM and 3 nM, respectively. The highlight of this work is that the catalytic cycle between PB–Au nanocomposites and HRP-DNAzyme was adequately utilized in the amplification platform for versatile sensing. The novel electrocatalytic biosensor involving only one-step incubation exhibited a wide linear range, low detection limit, and satisfactory selectivity and operational stability. The proposed approach provided an ease-of-use and universal reporting system with a simple design and easy operations.

•Detection of Ag+ by electrical contacted enzyme is demonstrated.•Cytosine–Ag+–cytosine is in the DNA scaffold.•Carbon nanodots/Au nanoparticles composite is the immobilization platform.•Methyl blue (MB) molecules can act as a relay for electrical contact.In the present study, ultrasensitive detection of Ag+ is demonstrated by a biocatalytic signal amplification system which is realized by only one DNA sequence based electrical contacted enzyme structure and the Au nanoparticles/Carbon nanodots (AuNPs/C-dots) composite immobilization platform. In the presence of Ag+, with the interaction of cytosine–Ag+–cytosine (C–Ag+–C), cytosine-rich DNA sequence labeled with methylene blue (MB) molecules near 5′ end and Glucose Oxidase (GOx) at 3′ end, has a self-hybridization and then forms a duplex-like structure which makes MB and GOx approach the AuNPs/C-dots modified electrode. MB units can then act as a relay that electrically contacts GOx with the AuNPs/C-dots modified electrode and activate the bioelectrocatalyzed oxidation of glucose to glucose acid. In consequence, based on the bioelectrocatalyzed signal amplification on the AuNPs/C-dots platform, Ag+ could be quantitatively detected in the range of 10−11–10−5 M with a low detection limit of 3 pM. Also, there is an excellent selectivity against other interferential metal ions. The detection of Ag+ ions was realized by Ag+ self-induced conformational change of DNA scaffold which involved only one oligonucleotide showing its convenience and availability.

•Au nanoparticles-graphene-silica sol–gel provides a stable immobilization biointerface.•AuNP-polydopamine@carbon nanotubes multiple enzymes amplify the signal.•High sensitivity and low detection limit are obtained.An Interleukin-6 (IL-6) electrochemical immunosensor was fabricated based on the Au nanoparticles (AuNP)-graphene-silica sol–gel as immobilization biointerface and AuNP-polydopamine (PDA)@carbon nanotubes (CNT) as the label of HRP-bound antibodies. The AuNP-graphene-silica sol–gel film was prepared in situ and modified on the ITO electrode, providing a stable network for the immobilization of antibody and exhibiting a dynamic working range of 1–40 pg/mL with a low detection limit of 0.3 pg/mL IL-6 (at 3 s). The results of serum samples with the sensor received an acceptable agreement with the ELISA method. Importantly, this method provided a promising ultrasensitive assay strategy for clinical applications.

•A dual hairpin-like MB was built for the selective and specific detection of MA.•The sensor was more stable and lower toxicity than typical MB structure.•The system has high quenching efficiency based on contact quenching mechanism.•The detection limit of MA is about 4000 times lower than the MA safety limit.This study presents a novel dual hairpin-like molecular beacon (MB) for the selective and sensitive detection of melamine (MA) based on the conjugation of MA and thymine. In this protocol, the coordination between coralyne and adenosine (A) leaded a dual hairpin-like MB and the fluorophore–quencher pair is close proximity resulting in the fluorescence quenching. With the addition of MA, it conjugated with thymine in the loop part of dual hairpin-like MB by triple H-bonds, triggering the dissociation of the dual hairpin-like MB. The resulting spatial separation of the fluorophore from quencher induced the enhancement in fluorescence emission. Under the optimized conditions, the sensor exhibited a wide linear range of 8×10−9–1.6×10−5 M (R2=0.9969) towards MA, with a low detection limit of 5 nM, approximately 4000 times lower than the Drug Administration and the US Food estimated MA safety limit. The real milk samples were also investigated with a satisfying result.

We report on the detection of trace quantities of melamine (MA) by a colorimetric method that exploits the conformational change of hemin G-quadruplex-DNAzyme. The addition of MA to hemin G-quadruplex-DNAzyme structure containing thymine bases causes the thymine in the DNAzyme to interact with MA via a stable triple H-bond and leads to a conformational change. This, in turn, affects the peroxidase-like activity of hemin which is determined colorimetrically at 450 nm by adding 3,3’,5,5’-tetramethylbenzidine and hydrogen peroxide. The method was applied to the colorimetric determination of MA over a wide range of concentrations (0.2 to 24 μM) with a detection limit of 80 nM. The effect also can be detected with bare eyes. The method was successfully applied to the determination of MA in spiked milk powder.

•Potassium ions sensor was fabricated by the conformational change of DNA.•Signal amplification was achieved by the biocatalytic and mediated co-effect.•Different metal types (iron, nickel and copper) of different sizes were tested and compared first time.•Fc unit stimulated the biocatalysis of HRP-DNAzyme.•The system realized the electrical contact of HRP-DNAzyme by Fc as relay.Sensitive and selective sensors need to be explored to detect the physiological potassium level due to its important role in the living organisms. In the present system, a novel electron transfer mediator actuated electrocatalytical biosensor was demonstrated to assay K+ based on the conformational change of DNA. With the hybridization between the complementary bases and the self-folding of guanine-rich nucleic acid sequence, the horseradish peroxidase-mimicking enzyme (HRP-DNAzyme) was formed and brought to approach the ferrocene (Fc) unit on Au nanoparticles (AuNPs). Thus, in the system, Fc unit acted as the relay, stimulating the electrical contact of HRP-DNAzyme with the electrode to obtain the bioelectrocatalyze reduction signal. Under the Fc actuated catalysis of HRP-DNAzyme and amplification of Au nanoparticles, the obtained biosensor exhibited a sensitive detection for K+. A satisfying result of a wide linear range and low detection limit were obtained with the novel electrocatalytical biosensor which was then applied in real samples.

Silver oxide nanowire arrays (Ag2O NWAs) were first synthesized on a copper (Cu) rod by a simple and facile wet-chemistry approach without using any surfactants. The as-synthesized Ag2O NWA/Cu rod not only can be used as an integrated electrode (called a Ag2O NWA/CRIE) to detect hydrazine (HZ) but also can serve as the catalyst layer for a direct HZ fuel cell. The current density of HZ oxidation on Ag2O NWA (94.4 mA cm–2) is much bigger than that on a bare Cu rod (3.9 mA cm–2) at −0.6 V, and other Ag2O NWAs have the lowest onset potential (−0.85 V). This suggests that a Ag2O NWA integrated electrode has potential application in catalytic fields that contain the HZ fuel cell.Keywords: amperometric sensor; electrocatalysis; hydrazine; integrated electrode; silver oxide;

Ag+ is known to bind very strongly with cytosine–cytosine (C–C) mismatches in DNA duplexes to form C–Ag+–C base pairs. Exonuclease III (Exo III) can catalyze the stepwise removal of mononucleotides of duplex DNA. In this work, we study Exo III activity on DNA hybrids containing C–Ag+–C base pairs. Our experiments show that Ag+ ions could intentionally trigger the activity of Exo III towards a designed cytosine-rich DNA oligonucleotide (C-rich probe) by the conformational change of the probe. Our sensing strategy uses this conformation-dependent activity of Exo III, which is controlled through the cyclical shuffling of Ag+ ions between the solid DNA hybrid and the solution phase. This interesting conversion has led to the development of an ultrasensitive detection platform for Ag+ ions with a detection limit of 0.03 nM and a total assay time possible within minutes. This simple detection strategy could also be used for the detection of other metal ions which exhibit specific interactions with natural or synthetic bases.

A facile and mild approach was used for the controlled synthesis of 3D porous gear-like CuO on a Cu substrate (PGC) based on annealing gear-like Cu(OH)2 (GC) at 200 °C in air. There are 3–10 edges that build up a gear-like structure and a huge number of holes formed on each edge. As an integrated nanostructure, the binder-free PGC can be used as a supercapacitors electrode (SC) directly. Due to its 3D porous structure and the highly conductive Cu substrate as a current collector, the integrated electrode exhibited excellent electrochemical properties. These were demonstrated by excellent specific capacitance as high as 348 F g−1 at a discharge current density of 1 A g−1, which corresponds to the energy density of 43.5 Wh kg−1. The electrochemical tests also showed that the as-synthesized PGC exhibited excellent cycling stability.

In the present study, based on multifunctional Dual-Hairpin DNA structure, a simple, fast and high sensitive assay for the detection of DNA, thrombin and adenosine triphosphate (ATP) was demonstrated. DNA sequence labeled with methylene blue (MB), which was designed as single-stranded DNA (ssDNA) matching with target DNA, thrombin, or ATP aptamer, hybridized to the adjunct probe and formed the dual-hairpin structure on the electrode. With the hybridization of adjunct probe and the hairpin-like capture probe in the stem region, the dual-hairpin was formed with outer and inner hairpins. By the conjugation of the target probe with the adjunct probe in the outer hairpin, the adjunct probe divorced from the dual-hairpin structure. The adjunct probe with signal molecules MB, attaching near or divorcing far from the electrode, produced electrochemical signal change and efficient electron transfer due to the fact that it was in proximity to the electrode. However, upon hybridization with the perfect match target, the redox label with the target probe was forced away from the modified electrode, thus resulting in the change of the Dual-Hairpin DNA conformation, which enables impedance of the efficient electron transfer of MB and, consequently, a detectable change of the electrochemical response. In addition, another highlight of this biosensor is its regenerability and stability owing to the merits of structure. Also, based on this Dual-Hairpin platform, the detection limits of DNA, thrombin, and ATP were 50 nM, 3 pM, and 30 nM, respectively. Moreover, this pattern also demonstrated excellent regenerability, reproducibility, and stability. Additionally, given to its ease-of-use, simplicity in design, easy operations, as well as regenerability and stability, the proposed approach may be applied as an excellent design prompter in the preparation of other molecular sensors.

With exonuclease III activity on DNA hybrids containing thymine–Hg2+–thymine, a label-free ultrasensitive “turn-on” fluorescent sensor involving “quenching” and “reappearing” processes based on a carbon nanotube–Ag nanoclusters system is demonstrated for amplified determination of Hg2+.

Integrated nanodevices with the capability of storing energy are widely applicable and thus have been studied extensively. To meet the demand for flexible integrated devices, asymmetric supercapacitors that simultaneously realize energy storage were fabricated by growing NiCo2O4@NiMoO4 hybrid nanowires on nickel foam, thus obtaining the positive electrode, and employing active carbon as the negative electrode. The as-assembled integrated systems were characterized by their improved energy storage (areal specific capacitance of 6.30 F cm−2 at 60 mA cm−2 and specific capacitance up to 1242 F g−2 at a current density of 10 mA cm−2), enhanced power density and energy density by increasing the potential window from 0 V to 1.6 V. Such flexible integrated devices might be used in smart and self-powered sensory, wearable, and portable electronics.

In this work, hierarchical Co3O4@CoMoO4 core/shell nanowire arrays on nickel foam are fabricated by a facile hydrothermal ion exchange method. The Co3O4 nanowires are fully covered by ultrathin mesoporous CoMoO4 nanosheets. A possible growth mechanism for the CoMoO4 involves the capturing of the part of the cobalt ions of the Co3O4 nanowires by the molybdenum acid radical without annealing. When investigated as binder-free electrodes for supercapacitors (SCs), such unique Co3O4@CoMoO4 core/shell hybrid electrodes exhibited ultrahigh areal capacitances, which are several times larger than the pristine Co3O4 electrode. The electrode exhibits a high specific capacitance of 1040 F g−1 at a current density of 1 A g−1 and an excellent cycling stability (5000 cycles). The remarkable electrochemical performance is attributed to the rational combination of two electroactive materials and the array configuration.

In this study, a hierarchical ZnCo2O4@MnO2 core–shell nanotube arrays electrode was developed by a facile two-step method. The electrode exhibits high specific capacitance of 1981 F g−1 (2.38 F cm−2) at a current density of 5 A g−1 and excellent cycling stability (5000 cycles). Furthermore, a low-cost, high-performance asymmetric supercapacitor (ASC) with ZnCo2O4@MnO2 core–shell nanotube arrays on Ni foam (as positive electrode) and 3D porous α-Fe2O3 on Fe foil (as negative electrode) was successfully designed. The as-designed ASC device with an extended operating voltage window of 1.3 V achieved a specific capacitance of 161 F g−1 at 2.5 mA cm−2 with a maximum energy density of 37.8 W h kg−1 and excellent stability with a capacitance retention of 91% after 5000 cycles. Furthermore, after being charged for dozens of seconds, the ZnCo2O4@MnO2//α-Fe2O3-ASC can easily light up a LED. These fascinating performances indicate that the present ZnCo2O4@MnO2 core–shell nanotube arrays with remarkable electrochemical properties could be considered as potential electrode materials for next generation supercapacitors in high energy density storage systems.

Hierarchical NiCo2O4@MnMoO4 core–shell nanomaterial on nickel foam was designed via a facile hydrothermal method. A possible growth mechanism of the MnMoO4 is in which the molybdenum acid radical captures part manganese ions of the MnMoO4 nanoflowers. When regarded as binder-free electrodes for supercapacitors (SCs), such special NiCo2O4@MnMoO4 core–shell hybrid electrodes exhibit ultra-high specific capacitances several times larger than a pristine NiCo2O4 electrode. The electrodes possess high specific capacitance of 1118 F g−1 at a current density of 1 A g−1 and excellent cycling stability (5000 cycles). This remarkable electrochemical performance is ascribed to the effective combination of two electroactive materials and the rational array configuration.

Flexible supercapacitors have recently attracted increasing attention as they show unique promising advantages, such as flexibility and shape diversity, and they are light-weight and so on. Herein, we designed a series of 3D porous spinous iron oxide materials synthesized on a thin iron plate through a facile method under mild conditions. The unique nanostructural features endow them with excellent electrochemical performance. The electrochemical properties of the integrated electrodes as active electrode materials for supercapacitors have been investigated using different electrochemical techniques including cyclic voltammetry, and galvanostatic charge–discharge in Na2SO4 and LiPF6/EC:DEC electrolyte solutions. These integrated electrodes showed high specific capacitance (as high as 524.6 F g−1 at the current density of 1 A g−1) in 1.0 M Na2SO4 (see Table S1). Moreover, the integrated electrodes also show high power densities and high energy densities in a LiPF6/EC:DEC electrolyte solution; for example, the energy densities were 319.3, 252.5, 152.1, 74.13 and 38.6 W h kg−1 at different power densities of 8.81, 21.59, 56.65, 92.09 and 152.64 kW kg−1, respectively. Additionally, the flexible superior electrode exhibited excellent stability with capacitance retention of 92.9% after 5000 cycles. Therefore, such flexible integrated devices might be used in smart and portable electronics.

In this paper, hierarchical MnCo2O4@MnO2 core–shell nanowire arrays (MnCo2O4@MnO2 NWAs) with mesoporous and large surface area are synthesized on 3D nickel foam via a facile, two-step hydrothermal approach without any adscititious surfactant and binder. The electrode architecture takes advantage of the synergistic effects contributed from both the porous MnCo2O4 nanowire core and the MnO2 shell layer. The fabricated MnCo2O4@MnO2 NWA electrode for supercapacitors in aqueous electrolyte exhibits a significantly enhanced specific capacitance (858 F g−1 at 1 A g−1), high energy density (36.0 Wh kg−1 at 252 W kg−1) and long-life cycling stability (retaining 88% of the initial capacitance after 5000 cycles). Then, a symmetrical supercapacitor is fabricated by assembling two MnCo2O4@MnO2 NWA-based electrodes, which shows a high specific capacitance of 678 F g−1 at 1 A g−1 and a high energy density of 135.6 Wh kg−1 at 513 W kg−1. Thereby, the hierarchical core–shell MnCo2O4@MnO2 NWAs are very promising as next generation high-performance long-life cycling supercapacitors.

With only graphene oxide and KMnO4, the luminescent graphene quantum dots (GQDs) in high quantum yield were prepared by one-step synthesis using ultrasonication, and applied in the label-free, simple and fast fluorescence assay of alkaline phosphatase (ALP).