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In neurotransmission process, dopamine (DA) is the key molecule. Hence, the detection of dopamine plays a vital role in the primary diagnosis of diseases which is related to the irregular levels of dopamine. In this study, we proposed the electrochemically deposited Graphene Nanosheets-Polydiphenylamine-Silica (GRNS-PDPA-SiO2) modified nanohybrid electrode for an amperometric detection of dopamine. The electrochemical oxidation of DA ensures the catalytic activity of the prepared nanohybrid composites by chronoamperometry (CA) method. The nanohybrid electrode shows linear response towards DA (1–5 μM) in the presence of phosphate buffer solution (PBS at pH 7.0) with the regression co-efficient (R2) of 0.98. Low detection limit with superior sensitivity of dopamine was achieved as 0.1 μM and 0.66 μA μM−1cm−2 respectively. The structural morphology and the chemical homogeneity of the materials were confirmed by scanning electron microscope with EDX analysis. The molecular vibration and electrochemical performances were recorded through Fourier-transform infrared spectroscopy (FTIR) and cyclic voltammetry (CV). The adopted GRNS-PDPA-SiO2 modified electrode resulted in excellent sensitivity, high selectivity claims its realistic applications in the highly clinical diagnostics.

Amperometric sensor of polydiphenylamine (PDPA)/phosphotungstic acid (PTA)/zinc oxide (ZnO) on glassy carbon (GC) nanohybrid composite electrode (GC/PDPA/PTA/ZnO) fabricated via facile electrochemical deposition method. The structural geometry and surface morphology were recorded by X-ray diffraction spectrometer (XRD) and scanning electron microscopy (SEM). Electro-catalytic properties and performances of nanohybrid composite were recorded by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA) methods. PTA-assisted PDPA/ZnO-ME shows linear steady-state response towards glucose with superior sensitivity of 20.30 μA μM−1 cm−2, lowest detection limit 0.1 μM, and rapid response less than 2 s. The improved electro-catalytic performance towards glucose by GC/PDPA/PTA/ZnO is due to the combined existence of diphenoquinone diamine (DPDI2+) and phosphotungstic acid anion which provides a higher electro-catalytic active spots leads to more electron transport pathway for the oxidation of glucose. Interference analyses confirm the prepared nanohybrid sensor is best apt for glucose detection claims its practical biomedical application.

An amperometric urea biosensor was fabricated using Indium tin oxide (ITO) coated Polydiphenylamine (PDPA)/ Phosphotungstic acid (PTA)/Graphene (Gra) hybrid nanocomposites modified electrode (ITO/PDPA/PTA/Gra-ME) by an electrochemical-deposition technique. Scanning Electron Microscopy (SEM) and Atomic Force microscopy (AFM) techniques were used to capture the surface morphology and surface coating thickness of nanocomposite sandwiched electrodes. Electro-catalytic performances of modified hybrid electrodes were examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) techniques. ITO/PDPA/PTA/Gra-ME exhibits a good linear response to urea concentration over the range of 1–13 μM along with a correlation coefficient of 0.999, good sensitivity (1.085 μA/μM cm2) and at a low response time (5 s). The enhanced electro-catalytic activity of ITO/PDPA/PTA/Gra-sandwich towards urea was owing to the synergistic contribution of tungsten atoms (phosphotungstic acid anion), diphenoquinone diamine (DPDI2+) form of PDPA/Graphene that enhances the fast electron transfer rate. Also, interfering analytes were studied to ensure the fabricated sensor is best suitable for practical applications.

Electrochemical-deposition method was engaged to prepare Fluorine doped Tin oxide (FTO) modified Polydiphenylamine (PDPA)/Phosphotungstic acid (PTA)/Manganese dioxide (MnO2) nanohybrid (FTO/PDPA/PTA/MnO2-ME) Electrode. Nanocomposites structural analysis, morphology, and molecular vibrational studies were characterized through X-ray diffractometer (XRD), Scanning Electron Microscope (SEM) and Fourier Transform Infra read Spectroscopy (FTIR). Recorded XRD and FTIR pattern authenticates the existence of PDPA, PTA, and MnO2 structures. Cyclic voltammetry (CV) studies performed using electrochemical workstation shows very high specific capacitance value of 514.77 Fg−1 at 5 mVs−1 for the modified hybrid electrode system. The superior capacitive performance, cyclic stability of FTO/PDPA/PTA/MnO2 electrode was attributed due to the existence and fast reversible multi‐electron redox response of tungsten atoms in PTA along with PDPA-MnO2 synergistic interaction that augments the electron transfer processes.

Herein, a novel Poly (melamine) have been successively electrodeposited on glassy carbon electrode and decorated by Pd nanoparticles (Pd NPs) subsequently to fabricate Poly (melamine) – Pd nanocomposite. Structural geometry, morphological view, and elemental composition analysis were ensured by X-ray diffractogram, scanning electron microscope, and X-ray photoelectron spectroscopy. The electrodeposited Poly (melamine) (PME) material depicts an interconnected nano rod (50 nm) morphology leads to a nano exploder (~150 nm) arrangement. Spherical shaped Pd decorated PME morphology was obtained for GC\PME-Pd NPs composite (150 nm). The electrocatalytic activity of the fabricated anode electrocatalyst was examined by cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry methods. The modified GC\PME-Pd NPs composite electrode validates superior electrocatalytic behaviour towards methanol and ethanol oxidation in alkaline background. Besides, the electrochemical surface area and electrocatalytic behaviour make it a greater anode catalyst towards methanol and ethanol oxidation. The synergic effects amid the Poly (melamine)-Pd NPs composite enhances the catalytic activity, mechanical stability on the electrocatalysis of methanol and ethanol oxidation reaction superior than modified Poly (melamine) electrode. Hence, the fabricated anode electrocatalyst is proficient to get realistic approach towards the progression in the direct alcohol (methanol and ethanol) oxidation reaction in direct alcohol fuel cells (DAFCs) applications.

Polyaniline (PANI) is one of the important materials in conducting polymers (CPs) for significant applications in devices due to its unique properties such as high electrical conductivity, flexibility, and economical price. In this work, novel and eco-friendly green synthesis of polyaniline Nanorod (PANI-NR) were developed by solar irradiation approach in acidic medium without the aid of any surfactant and template. As characterized by morphology studies, the average diameter of PANI-NR is approximately 200–250 nm and length is 2–2.5 µm. The elemental analysis and structural geometry of PANI-NR are examined through EDX, Mapping, and XRD studies. The electrochemical properties were investigated using CV, GCD, and EIS techniques. The electrochemical performance of Cyclic voltammetry analysis shows the redox peaks which confirms the PANI-NR has excellent electrical conductivity. A specific capacitance of 25 F/g at 10 mV/s scan rate by CV studies and 106 F/g at 1 A/g current density by GCD studies is observed for One-Dimensional (1D) PANI-NR as an electrode material for supercapacitor. Also, it shows remarkable cyclic retention and stability. These results indicate that PANI-NR is expected to have better electrochemical performance in energy storage applications.

In this work, a copolymer (polyaniline(PANI)-copolymer(co)-polydiphenylamine (PDPA)) hybrid impregnated on graphene (Gra) nanosheets was examined. At first, graphene was synthesized by the oxidation of natural graphite employing modified Hummer’s method and subsequently reduced using hydrazine monohydrate. Then, interfacial chemical oxidative polymerization was engaged to synthesize PANI, PDPA, and copolymer (PANI/PDPA) along with graphene nanosheets in liquid–liquid (CHCl3/HCl) interface individually. During the polymerization process, PANI and PDPA chain grown well and dispersed homogeneously on the graphene nanosheets. Morphological and molecular vibrational analyses were confirmed by field emission scanning electron microscopy (FESEM) and Fourier transform infra red spectroscopy (FTIR). In addition, the electrochemically modified Gra-PDPA, Gra-PANI, and Gra-copolymer hybrids show good electrical conductivity ensured via cyclic voltammetry (CV). The enhanced electro-catalytic activity of Gra-PANI-co-PDPA-ME towards glucose with superior sensitivity 0.51 μ A/ μ M at 5 s was achieved. The combined existence and synergistic interaction amid of graphene, aniline and diphenoquinone diamine (DPDI 2 + ) provides enhanced electron transfer for the glucose oxidation. Also, Interference studies ensure that the fabricated sensor is best suitable for glucose sensing performance.

A modified electrode was fabricated by grafting poly(2,5-dimethoxyaniline) (PDMA) onto multiwalled carbon nanotubes (MWNTs) and used for the electrocatalytic oxidation of ascorbic acid (AA). Cyclic voltammetry was used to fabricate the modified electrode and demonstrate the electroactivity of MWNT-g-PDMA-ME towards AA. Field emission scanning electron microscopy (FESEM) of MWNT-g-PDMA-ME revealed the combined presence of MWNT and PDMA. The MWNT-g-PDMA-ME exhibited excellent performance for AA at 320 mV with a high sensitivity (12.78 μA/mM) and linear concentration range of 1 to 5 mM (correlation coefficient of 0.9991). Differential pulse voltammetry (DPVs) showed that MWNT-g-PDMA-ME experiences negligible interference from other electro-active components.

Multiwalled carbon nanotubes (MWNTs) grafted chitosan (CS) nanowire (NW) was prepared by phase separation method. Glucose oxidase (GOx) was sequentially immobilized into MWNT-CS-NW to obtain MWNT-CS-NW/GOx biosensor. Field emission scanning electron microscopy (FESEM) images of MWNT-CS-NW/GOx reveals the existence of MWNT and CS. Cyclic voltammetry and amperometry were used to evaluate the electrochemical determination of glucose. The MWNT-CS-NW/GOx biosensor shows an excellent performance for glucose at +0.34 V with a high sensitivity (5.03 μA/mM) and lower response time (3 s) in a wide concentration range of 1–10 mM (correlation coefficient of 0.9988). In addition, MWNT-CS-NW/GOx biosensor possesses better reproducibility, storage stability and there is negligible interference from other electroactive components.

Conducting hybrid submicrostructures composed of chitosan (CS and silica-based conducting poly[N-(3-trimethoxysilylpropyl)aniline] (PTMSPA were prepared by graft copolymerization. The spherical and fibrous morphologies of the CS-PTMSPA hybrid submicrostructures could be observed by optical and field emission electron microscopy. Under room temperature conditions, the CS-PTMSPA graft copolymers possessed the uniformly distributed spherical submicroparticles with diameters in the range of ca. 400–1,000 nm. On the other hand, under ice cold conditions (5 °C), CS-PTMSPA showed the development of randomly oriented fiber bundles. The diameter of a single fiber was in the range of ca. 100–500 nm. These CS-PTMSPA fibers were obtained by a temperature-driven template-free self-assembly pathway. Spectroscopic and thermal evaluations confirmed that CS-PTMSPA graft copolymer had been prepared by an oxidative polymerization method. The electrochemical performance of the CS-PTMSPA submicrostructures were compared with CS and PTMSPA by cyclic voltammetry with the Fe(CN)63−/4− system as a redox marker. The CS-PTMSPA submicrostructures showed high electrical conductivity (difference between the anodic and cathodic peaks = 0.24 and 0.29 V for CS-PTMSPA sphere and fiber, respectively compared to those of CS (0.14 V and PTMSPA (0.20 V), which was ascribed to the relatively high surface-to-volume ratios of these submicrostructures. Open image in new window

A novel amperometric cholesterol biosensor was fabricated by the immobilization of ChOx (cholesterol oxidase) onto the chitosan nanofibers/gold nanoparticles (designated as CSNFs/AuNPs) composite network (NW). The fabrication involves preparation of chitosan nanofibers (CSNFs) and subsequent electrochemical loading of gold nanoparticles (AuNPs). Field emission scanning electron microscopy (FE-SEM) was used to investigate the morphology of CSNFs (sizes in the range of ∼50–100 nm) and spherical AuNPs. Cyclic voltammetry, hydrodynamic voltammetry and amperometry were used to examine the performance of CSNF–AuNPs/ChOx biosensor. The CSNF–AuNPs/ChOx biosensor exhibited a wide linear response to cholesterol (concentration range of 1–45 μM), good sensitivity (1.02 μA/μM), low response time (∼5 s) and excellent long term stability. The combined existence of AuNPs within CSNFs NW provides the excellent performance of the biosensor towards the electrochemical detection of cholesterol.

Multiwalled carbon nanotubes (MWNTs) was grafted onto silica network (MWNT–silica-NW) by sol–gel process. MWNT–silica-NW was further electrodeposited with gold nanoparticles (AuNPs). The morphology of the GC/MWNT–silica-NW–AuNPs modified electrode (ME) was analyzed by field emission scanning electron microscopy (FE-SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to evaluate the electrochemical performances of GC/MWNT–silica-NW–AuNPs-ME. Ascorbic acid (AA) was found to be electrocatalytically oxidized at GC/MWNT–silica-NW–AuNPs-ME due to the synergistic influence of MWNTs, silica-NW and AuNPs. The MWNT–silica-NW–AuNPs-ME sensor electrode presents a high sensitivity (8.59 μA/mM) and selectivity for AA in the presence of dopamine (DA). Differential pulse voltammetry revealed that the sensor electrode exhibited excellent selectivity for AA in the presence of large excess of DA with a large potential separation of ∼0.26 V. The effective electrocatalytic activity, excellent peak resolution and ability for independent determination of DA in the presence of AA reveal that MWNT–silica-NW–AuNPs-ME is suitable for simultaneous and selective determination of DA and AA.

A glucose biosensor was fabricated with loading of glucose oxidase (GOx) into a new organic-inorganic hybrid nanocomposite. The preparation involves formation of silica network into a Nafion (perfluorosulfonate ionomer) and subsequent loading of polyaniline grafted multiwalled carbon nanotubes (MWNT-g-PANI) onto Nafion-silica nanocomposite. Field emission scanning electron microscopy (FE-SEM) of Nafion-silica/MWNT-g-PANI composite reveals the presence of spherical silica particles (sizes in the range 250 nm-1 microm) and tubular MWNT-g-PANI particles. Chronoamperometry and cyclic voltammetry were used to evaluate the performance of biosensor towards glucose. The Nafion-silica/MWCNT-g-PANI/GOx biosensor exhibited a linear response to glucose in the concentration range of 1-10 mm with a correlation coefficient of 0.9972, good sensitivity (5.01 microA/mm), a low response time (approximately 6s), repeatability (R.S.D value of 2.2%) and along-term stability. The presence of silica network within Nafion and MWNT-g-PANI synergistically contributes to the performance of the biosensor towards the electrochemical detection of glucose.

A novel amperometric biosensor was fabricated based on the immobilization of cholesterol oxidase (ChOx) into a cross-linked matrix of chitosan (Chi)-room-temperature ionic liquid (IL) (1-butyl-3-methylimidazolium tetrafluoroborate). Initially, the surface of bare electrode (indium tin oxide coated glass) was modified with the electrodeposition of Au particles onto thiol (-SH) functionalized multi-walled carbon nanotubes (MWNTs). The biosensor electrode is designated as MWNT(SH)-Au/Chi-IL/ChOx. Scanning electron microscopy image of MWNT(SH)-Au/Chi-IL/ChOx reveals that Chi-IL exists as the interconnected wires covering the Au particles on the surface of MWNT(SH)-Au. Cyclic voltammetry and chronoamperometry were used for the electrochemical determination of cholesterol at the biosensor electrode, MWNT(SH)-Au/Chi-IL/ChOx. The presence of Au particles in the matrix of CNTs provides an environment for the enhanced electrocatalytic activities. The MWNT(SH)-Au/Chi-IL/ChOx biosensor exhibited a linear response to cholesterol in the concentration range of 0.5-5mM with a correlation coefficient of 0.998, good sensitivity (200 microAM(-1)), a low response time ( approximately 7s), repeatability (R.S.D value of 1.9%) and long term stability (20 days with a decrease of 5% response). The synergistic influence of MWNT(SH), Au particles, Chi and IL contributes to the excellent performance for the biosensor.

We report an ingenious approach for the fabrication of a promising glucose sensor, GOx/Au/CS–IL–MWNT(SH), that exploits the synergistic beneficial characteristics of multiwalled-carbon nanotubes (MWNTs), gold nanoparticles (AuNPs), chitosan (CS) and room temperature ionic liquid (RTIL). Direct electron transfer between glucose oxidase (GOx) and electrode was achieved. Scanning electron microscopy and atomic force microscopy images of GOx/Au/CS–IL–MWNT(SH) reveal that MWNTs and AuNPs are dispersed in CS–IL matrix. Cyclic voltammetry, impedance spectroscopy and chronoamperometry were used to evaluate the performance of biosensor. The GOx/Au/CS–IL–MWNT(SH) biosensor exhibits a linear current response to glucose concentration (1–10 mM) at a low potential of 0.10 V and precludes interferences from uric acid and ascorbic acid. The GOx/Au/CS–IL–MWNT(SH) biosensor has superior performances over GOx/CS–IL–MWNT(SH). Keywords: Direct electrochemistry, Chitosan, Glucose oxidase (GOx), Ionic liquid, Glucose sensor

A simple, rapid and efficient route to prepare polyaniline nanostructures (PANI-NS) by “one-step chemical oxidative polymerization” method is described. This method possesses advantages in terms of good yield, short reaction time, neat conditions and cost-effectiveness. The morphology of the PANI-NS was investigated by field-emission scanning electron microscopy (FE-SEM). The average diameter of single PANI-NS was calculated to be ∼376 nm. Results from UV–visible spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and cyclic voltammetry (CV) reveals the existence of PANI units present in the polymeric nanostructures. Also, electrical conducting property of the PANI-NS was analyzed using four-probe measurement method.