A novel non-enzymatic nitrite sensor was fabricated by immobilizing MnOOH-PANI nanocomposites on a gold electrode (Au electrode). The morphology and composition of the nanocomposites were investigated by transmission electron microscopy (TEM) and Fourier transform infrared spectrum (FTIR). The electrochemical results showed that the sensor possessed excellent electrocatalytic ability for NO2− oxidation. The sensor displayed a linear range from 3.0 μmol•L−1 to 76.0 mmol•L−1 with a detection limit of 0.9 μmol•L−1 (S/N = 3), a sensitivity of 132.2 μA•L•mol−1•cm−2 and a response time of 3 s. Furthermore, the sensor showed good reproducibility and long-term stability. It is expected that the MnOOH-PANI nanocomposites could be applied for more active sensors and used in practice for nitrite sensing.

Au nanoparticles supported on nickel hydroxide nanowires with multiple cavities (Au/m-Ni(OH)2) were synthesized and used for the enhanced electrochemical sensing of dopamine (DA). m-Ni(OH)2 nanowires were first fabricated based on an anion exchange strategy and then chosen as supports for Au nanoparticles without an additional stabilizer and surfactant. The morphology and composition of the nanocomposites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). TEM observations revealed that Au nanoparticles were uniformly embedded in the cavities of m-Ni(OH)2 nanowires, with a high dispersion and a narrow size of 2 nm. Electrochemical investigations indicated that the as-prepared sensor exhibited fascinating performance towards the oxidation of DA. The linear range for DA detection was 0.45 μM to 1.78 mM with a low detection limit of 0.09 μM (S/N = 3). Additionally, the DA sensor possessed an excellent selectivity in the presence of potentially interfering substances such as ascorbic acid (AA), uric acid (UA) and glucose (Glu). Therefore, it is expected that Au/m-Ni(OH)2 nanocomposites could be used as electroactive materials for developing DA sensors.

•MnO2 nanoflowers were synthesized by one-step method.•Acidification of MnO2 was performed to modify its catalytic reactive and active crystalline facets.•H2O2 electrochemical sensor was fabricated based on acidized MnO2 to detect H2O2 released from living cancer and normal cells.•The obtained sensor exhibited remarkable catalytic performance for H2O2 detection.Nanomaterials have been used widely for electrochemical analysis in biological system in recent years. In order to cover the shortage of singular materials, composite nanomaterials were provided, but in the meanwhile laborious synthetic procedures and complex analytic mechanism has to be faced. In this work, for the first time, one-step acidification of flower-like manganese dioxide (MnO2) was performed to modify its catalytic reactive and active crystalline facets, and nonenzymatic electrochemical sensor was fabricated based on the singular materials to detect hydrogen peroxide (H2O2) released from living cancer and normal cells. According to the SEM, XRD characterizations and electrochemical investigations, it was found that 001 and 002 facets probably be the reactive facets while 111 and 020 facets are active facets. Meanwhile, the obtained sensor exhibited a low detection limit of 0.02 μM, a fast response and a wide linear range of 0.00008-12.78 mM which can be applied successfully for quantitative detection of H2O2 released from living cells in stimulation of AA. The work provides a simple and efficient electrochemical biosensing platform based on modification of crystalline facets of metal oxide. Considering the good sensing property, simple catalyst synthesis and analytic mechanism, its potential uses can be exploited for analytic, catalytic, physiological and pathological studies.

•Gold nanoprisms–chitosan composite film as immobilizing matrix realized the direct electrochemistry of glucose oxidase.•Gold nanoprisms accelerated the direct electron transfer rate between glucose oxidase and the substrate electrode.•The GOD–Gold nanoprisms–chitosan composite film modified electrode was successfully applied in glucose detection.Gold nanoprism (AuNP) was used for immobilization of glucose oxidase (GOD), and the direct electrochemistry of GOD–AuNP–chitosan modified GCE and glucose biosensing were studied. Transmission electron microscopy, UV–vis spectroscopy and electrochemical impendence spectroscopy were employed to confirm the morphology and film modification changes of the prepared biosensor. Results showed that the AuNP can provide a favorable and biocompatible microenvironment for facilitating the direct electron transfer between proteins and electrode surface. It was found that the special structure of gold nanoprism exhibited enhanced performances in direct electron transfer of GOD and glucose sensing. The adsorbed GOD displayed an apparent electron transfer rate constant (ks) of 24.92 s−1. The constructed biosensor exhibited a good response to glucose with linear range from 0.05 to 1.2 mM (R2 = 0.9975), low detection limit of 0.01 mM and high sensitivity of 11.83 μA mM−1 cm−2. The proposed biosensor offers an alternative method for the determination of glucose in real samples and has potential applications in the fabrication of other biosensors with redox proteins.A pair of distinct and well-defined redox peaks is observed at the GOD–AuNP–chitosan/GCE (curve c) with the formal potential of −0.460 V (vs. SCE) and the peak to peak separation was 52 mV.Download high-res image (103KB)Download full-size image

•Ag@SiO2@Ag core-shell structure nanomaterial was synthesized by a simple one-step method.•The core-shell structure Ag@SiO2@Ag nanomaterial has a uniform size and AgNPs were distributed on the surface of Ag@SiO2.•The new sensor exhibited good electrocatalytic activities toward H2O2 reduction with wide linear range and high sensitivity.Ag@SiO2@Ag core-shell structure nanomaterial was synthesized by a simple one-step method, and applied to electrochemical sensing detection of H2O2. The results of transmission electron microscope (TEM), X-ray diffraction (XRD) and energy dispersive spectrometry (EDS) verified the morphology, structure and composition of Ag@SiO2@Ag nanomaterial. The current response of the Ag@SiO2@Ag sensor was linearly toward to concentration of H2O2 between 0.005 mM and 24.0 mM with a detection limit of 1.7 μM at a signal-to-noise ratio of 3. The sensitivity was 56.07 μA mM−1 cm−2. The Ag@SiO2@Ag/GCE exhibited wide linear range and high sensitivity for electrochemical detection of H2O2.Ag@SiO2@Agcore-shellstructurenanomaterialwassynthesizedbyasimpleone-stepmethod.(*) The H2O2 electrochemical sensor was fabricated by immobilizing Ag@SiO2@Ag nanomaterial on GCE. The electrochemical investigations for this sensor exhibited excellent sensing properties.Download high-res image (110KB)Download full-size image

Nickel–cobalt layered double hydroxides (NiCo-LDHs) were synthesized using a facile hydrothermal method and then wrapped around amorphous Ni(OH)2 nanoboxes with intact shell structures. The morphology and shape of the Ni(OH)2/NiCo-LDHs nanocomposites were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Cyclic voltammetry (CV) was used to evaluate the electrochemical performance of the Ni(OH)2/NiCo nanocomposites modified electrode towards dopamine. With a potential of 0.22 V, the Ni(OH)2/NiCo-LDHs modified electrode was used to determine dopamine by amperometry, showing a significant current response and a linear dependence (R = 0.9997) in the concentration up to 1.08 mM with a sensitivity of 83.48 μA mM−1 cm−2 and a low detection limit of 17 nM (signal-to-noise ratio of 3). In particular, the fabricated dopamine sensor showed excellent reproducibility, long-term stability and favorable anti-interference.

The authors describe a method to anchor gold nanoparticles (AuNPs) on carboxy-functionalized multi-walled carbon nanotubes (c-MWCNTs) utilizing chitosan as dispersing and protective agent. A sensor for the simultaneous determination of hydroquinone and catechol was then fabricated by placing this nanocomposite on a glassy carbon electrode (GCE). The morphology and composition of the nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray powder diffraction. The electrochemical behavior of the modified GCE was studied by electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. The modified GCE exhibits good electrooxidative activity towards hydroquinone and catechol and therefore was used for simultaneous determination of both, with typical voltages of 30 and 130 mV (vs. SCE). A linear reponse is found for the 0.5 μM to 1.5 mM hydroquinone concentration range, and for the 5.0 μM to 0.9 mM catechol concentration range. The respective lower detection limits are 0.17 and 0.89 μM (at an S/N ratio of 3). The sensitivity is 644.44 μA mM−1 cm−2 for hydroquinone and 770.98 μA mM−1 cm−2 for catechol.

Herein, a novel dopamine (DA) electrochemical sensor was developed by combining carbon nanospheres (CNSs) and sulfonated polyaniline (SPANI) with their own excellent characteristics. The sensing materials SPANI/CNSs were prepared through a green and economical approach under hydrothermal treatment, in situ chemical oxidative polymerization, and sulfonation. Scanning electron microscopy and Fourier transform infrared spectroscopy were employed to characterize the morphology and composition of the nanocomposites. Moreover, electrochemical activities of the sensor were investigated by cyclic voltammetry, differential pulse voltammetry, and amperometry. Investigation of the sensor indicated that it had excellent properties towards DA oxidation, with a linear range from 0.50 μM to 1.78 mM, a detection limit of 0.0152 μM (S/N = 3), and a sensitivity of 113.9 μA mM−1 cm−2. Moreover, the sensor exhibited intriguing anti-interference to co-existing substances such as ascorbic acid (AA), uric acid (UA), and glucose (Glu). These electrochemical results could be attributed to the enhanced electron transfer rates and abundant functional groups with negative charges possessed by the nanocomposites. Therefore, the SPANI/CNS nanocomposites showed great application potential for the construction of a DA sensor.

Ag@C core–shell structure composites were successfully synthesized by hydrothermal method, and then Ag nanoparticles were decorated on the surface of Ag@C by reduction of AgNO3. The morphology, composition and structure of the Ag@C@Ag composites were characterized by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). Cyclic voltammetry and amperometry were used to evaluate the electrocatalytic performance of the Ag@C@Ag/GCE for detection of H2O2. Meanwhile, a new electrochemical method of zero current potentiometry was used for electrochemical detection of H2O2. The linear range and the detection limit were from 0.2 to 10, and 0.07 μM, respectively.

In this paper, platinum (Pt) nanomaterials with controlled morphologies are grown on the surface of flowerlike manganese dioxide (MnO2) respectively based on gas–liquid reaction. Then flowerlike three-dimensional (3D) nanostructures are formed, with successful synthesis of corresponding Pt/MnO2 nanocomposites. The obtained nanocomposites are characterized by scanning electron microscopy, energy-dispersive X-ray spectrum, transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. In addition, an interesting color-change phenomenon appeared with the Pt nucleation and growth progress which may be due to variation of the Mn valence state triggered by the reduction of Pt. This phenomenon can be used for naked-eye observation of materials’ growth states which is beneficial for investigation of synthetic mechanisms. At last, the Pt/MnO2 3D nanostructure exhibits perfect electrocatalytic properties toward oxidation of methanol. The four kinds of Pt/MnO2 composites are all used for electrochemical catalytic sensing of methanol respectively which indicates that the morphology of nanomaterials determines the catalytic properties. This research provides a new platform for controllable synthesis of nanomaterials and investigation of electrocatalysis based on morphology controlled nanomaterials.Keywords: 3D nanostructure; Electrocatalysis; Gas−liquid reaction; Manganese dioxide; Platinum nanoparticle

In this paper, we report a novel morphology-controlled synthetic method. Platinum (Pt) nanoparticles with three kinds of morphology (aggregation-like, cube-like and globular) were grown on the surface of graphene oxide (GO) using a simple gas–liquid interfacial reaction and Pt/GO nanocomposites were obtained successfully. According to the experimental results, the morphology of the Pt nanoparticles can be controlled by adjusting the reaction temperature with the protection of chitosan. The obtained Pt/GO nanocomposites were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR). Then the Pt/GO nanocomposites with the three kinds of morphology were all used to fabricate electrochemical sensors. The electrochemical experimental results indicated that compared with various reported electrochemical sensors, the Pt/GO modified sensors in this work exhibit a low detection limit, high sensitivity and an extra wide linear range for the detection of nitrite. In addition, the synthesis of Pt particles based on a gas–liquid interfacial reaction provides a new platform for the controllable synthesis of nanomaterials.

Herein, we report a simple and attractive self-assembly strategy for preparing graphene oxide–multiwalled carbon nanotube–(1-pyrenemethylamine)–gold (GO–MWCNT–PMA–Au) nanocomposites using 1-pyrenemethylamine (PMA) as a coupling agent. The morphology and composition of the nanocomposites were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). Further, a non-enzymatic nitrite sensor was fabricated by immobilizing GO–MWCNT–PMA–Au nanocomposites on a glassy carbon electrode (GCE). To obtain the optimal electrochemical experimental conditions, the effects of pH value and the volume of the as-prepared Au nanoparticle suspension were carefully investigated. Its electrochemical sensing properties were studied by cyclic voltammetry and differential pulse voltammetry. The electrochemical investigation showed that the GO–MWCNT–PMA–Au nanocomposites exhibited good catalytic performance for the oxidation of nitrite. The nitrite electrochemical sensor presented a wide linear range from 2.0 × 10−6 to 1.0 × 10−2 mol L−1, a high sensitivity of 483.51 μA mM−1 cm−2 and a low detection limit of 0.67 μmol L−1 at a signal-to-noise ratio of 3 (S/N = 3). It also exhibited good anti-interference capability and stability. This paper provides a self-assembly strategy for preparing nanocomposites which are used to construct improved electrochemical sensors.

A sandwich structured nanocomposite consisting of mildly reduced graphene oxide modified with silver nanoparticles supported on Co3O4 was synthesized and used for fabricating a nonenzymatic sensor for H2O2. The morphology and composition of the nanocomposite was characterized by transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction and FTIR. The composite was placed on a glassy carbon electrode which then displayed excellent performance in terms of electroreduction of H2O2. The H2O2 sensor, if operated at pH 7.4 at a working potential of 0.4 V (vs. SCE) has the following features: (a) linearity in the 0.1 μM to 7.5 mM concentration range; (b) a sensitivity of 146.5 μA∙mM‾1∙cm‾2; (c) a 35 nM detection limit at a signal-to-noise ratio of 3, and (d) a response time of 2 s. The sensor is long-term stable, well reproducible and selective.

A composite material obtained by ultrasonication of graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) was loaded with manganese dioxide (MnO2), poly(diallyldimethylammonium chloride) and gold nanoparticles (AuNPs), and the resulting multilayer hybrid films were deposited on a glassy carbon electrode (GCE). The microstructure, composition and electrochemical behavior of the composite and the modified GCE were characterized by transmission electron microscopy, Raman spectra, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The electrode induces efficient electrocatalytic oxidation of dopamine at a rather low working voltage of 0.22 V (vs. SCE) at neutral pH values. The response is linear in the 0.5 μM to 2.5 mM concentration range, the sensitivity is 233.4 μA·mM‾1·cm‾2, and the detection limit is 0.17 μM at an SNR of 3. The sensor is well reproducible and stable. It displays high selectivity over ascorbic acid, uric acid and glucose even if these are present in comparable concentrations.

•Novel graphene oxide/chitosan/platinum nanocomposite was successfully synthesized by using chitosan as protective agent and dispersant.•Chitosan was used to disperse platinum nanoparticles, and then the aggregation of platinum nanoparticles was avoided.•A hydrazine electrochemical sensor were constructed via immobilizing graphene oxide/chitosan/platinum nanocomposites on a glassy carbon electrode.•Compared with the previous reports, this hydrazine sensor showed a low catalytic potential and high sensitivity.In this paper, a novel graphene oxide/chitosan/platinum (GO/CTS/Pt) nanocomposite was successfully synthesized by using CTS as protective agent and dispersant. Further, a hydrazine electrochemical sensor was constructed by immobilizing GO/CTS/Pt nanocomposites on a glassy carbon electrode (GCE). The morphology and composition of the nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The electrochemical investigations indicated that the GO/CTS/Pt modified GCE showed excellent electrocatalytic ability towards the oxidation of hydrazine. The current responses of the GO/CTS/Pt modified GCE towards the addition of hydrazine showed a wide linear range from 2.0 × 10−5 to 1.0 × 10−2 mol L−1 at a low applied potential of 0 V (versus SCE), and the low detection limit was 3.6 μmol L−1 at the signal-to-noise ratio of 3. Moreover, the sensor also exhibited good reproducibility, stability and selectivity for hydrazine sensing. This study suggests that the GO/CTS/Pt nanocomposites might be further applied to other fields with great potential.

In this work, a nonenzymatic reduced glutathione (GSH) sensor was constructed based on the electrodepoition of Ni–Al layered double hydroxides (Ni–Al LDHs) on multiwall carbon nanotubes (MWCNTs) modified glassy carbon electrode (GCE). The morphologies and compositions of Ni–Al LDHs/MWCNTs nanocomposite were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Cyclic voltammetry and amperometry were employed to explore the electrochemical properties and performance of Ni–Al LDHs/MWCNTs nanocomposites in sensing and detection. The results indicated that the response current of GSH oxidation at the Ni–Al LDHs/MWCNTs/GCE was obviously higher than that at the MWCNTs/GCE or the Ni–Al LDHs/GCE. The amperometric current of the sensor is proportional to the concentration of GSH in a linear range of 1.2 to 1630.0 μM with a detection limit of 0.7 μM at a signal-to-noise ratio of 3. In addition, the sensor exhibits easy preparation, low cost, good stability and anti-interference.

In this work, a nonenzymatic reduced glutathione (GSH) sensor was constructed based on the electrodepoition of Ni–Al layered double hydroxides (Ni–Al LDHs) on multiwall carbon nanotubes (MWCNTs) modified glassy carbon electrode (GCE). The morphologies and compositions of Ni–Al LDHs/MWCNTs nanocomposite were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Cyclic voltammetry and amperometry were employed to explore the electrochemical properties and performance of Ni–Al LDHs/MWCNTs nanocomposites in sensing and detection. The results indicated that the response current of GSH oxidation at the Ni–Al LDHs/MWCNTs/GCE was obviously higher than that at the MWCNTs/GCE or the Ni–Al LDHs/GCE. The amperometric current of the sensor is proportional to the concentration of GSH in a linear range of 1.2 to 1630.0 μM with a detection limit of 0.7 μM at a signal-to-noise ratio of 3. In addition, the sensor exhibits easy preparation, low cost, good stability and anti-interference.