This paper reports the synthesis of gold-silver bimetallic nanoparticles (Au-AgNPs) with different Ag : Au compositions in an aqueous medium and their attachment on a glassy carbon electrode (GCE) via a 1,6-hexadiamine (HDA) linker for the electrochemical reduction of hydrogen peroxide (HP) and nitrobenzene (NB). Initially, silver nanoparticles (AgNPs) were synthesized by the reduction of silver nitrate using trisodium citrate as a capping agent and sodium borohydride as a reducing agent. Then, the Au-AgNPs were prepared by the galvanic displacement of Ag (0) by AuCl 4 À ions. The composition of the Au-AgNPs was varied by changing the mole ratio of Ag : Au in the range of 1 : 0 to 1 : 0.16. TEM images show that the Au-AgNPs were spherical in shape with a diameter of $16 nm. The prepared colloidal solution of Au-AgNPs were then attached on a HDA modified GCE through the Michael's addition reaction and were confirmed by UV-vis diffuse reflectance spectroscopy (DRS), atomic force microscopy (AFM), line scanning analysis, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The AFM image shows that the Au-AgNPs were densely packed on the electrode surface. The Au-AgNPs modified electrode exhibits a higher heterogeneous electron transfer rate constant of 2.77 Â 10 À7 cm s À1 when compared to Ag and AuNPs modified electrodes. Furthermore, the electrocatalytic activity of the Au-AgNPs modified electrode was examined by studying the reduction of HP and NB. It was found that the Au-AgNPs with the Ag : Au mole ratio of 1 : 0.12 showed excellent electrocatalytic activity towards the reduction of both HP and NB by not only shifting their reduction potentials toward less negative potentials but also enhanced their currents compared to the bare GCE, Ag and AuNPs modified electrodes and Au-AgNPs of other molar ratios. The present modified electrode shows the limit of detection of 0.12 and 0.23 mM (S/N ¼ 3) for HP and NB, respectively.Fig. 3 AFM images obtained for (A and B) 2-D and (C and D) 3-D views of AgNPs and Au-AgNPs, modified substrates. (E and F) Line spectra obtained for Au-AgNPs and CV obtained for GC/HDA/Au-AgNPs (Ag : Au ¼ 1 : 0.12) electrode in 0.2 M PB solution (pH 7.2) at a scan rate of 50 mV s À1 . 63438 | RSC Adv., 2016, 6, 63433-63444This journal is

The attachment of nitrogen-doped graphene (NG) on glassy carbon electrode (GCE) followed by electrodeposition of copper nanostructures (CuNSs) is described in this paper. Nitrogen-doped graphene oxide (N-GO) was prepared by intercalating melamine into graphene oxide (GO) by sonication. The doping of nitrogen was confirmed from the characteristic peaks at 285.3 and 399 eV in the XPS corresponding to the C–N bond and nitrogen, respectively. The presence of amine groups on the N-GO was exploited to attach them on GCE via Michael’s reaction. Subsequently, N-GO was electrochemically reduced to form NG by reducing the oxygen functionalities present on the N-GO. Then, the CuNSs on the NG modified electrode was prepared by electrodeposition at various applied potentials with different deposition times. The homogeneous deposition of cubic, spherical, quasidendritic, and dendritic NS at the applied potentials of 0, −0.10, −0.30, and −0.40 V, respectively, was evidenced from scanning electron microscopy (SEM) studies. The surface energy of the system can be reduced by the intercalated nitrogen in the graphene layer via doping. Hence, the NG layers with large surface area act as a robust scaffold for the homogeneous deposition of CuNSs. Further, the electrocatalytic activity of the NG-CuNSs modified GCE toward glucose oxidation was studied. In a comparison with NG and CuNSs, the NG-CuNSs exhibited 2-fold higher oxidation current. Further, it was found that the electrocatalytic activity of the composite electrode depends on the shape of the CuNSs. Among the different CuNSs, the NG-dendritic CuNSs electrode exhibited higher electrocatalytic activity. Finally, the practical applicability of the present sensor was demonstrated by fabricating NG-dendritic CuNSs on screen printed carbon electrode for the determination of glucose in human blood serum and urine samples.

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This paper describes the fabrication of cubic, spherical, dendritic and prickly copper nanostructures (CuNS) on indium-tin-oxide (ITO) substrates by electrodeposition and their electrocatalytic activity towards the oxidation of glucose and hydrazine. CuNS with different shapes were fabricated on ITO substrates by using different applied potentials of +0.10, −0.10, −0.30 and −0.50 V for 400 s in the presence of 10 mM CuSO 4 and 0.1 M H 2 SO 4 . The formed CuNS were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), X-ray photoelectron spectroscopy (XPS) and electrical impedance spectroscopy (EIS). SEM images showed that cubic, spherical, dendritic and prickly CuNS were formed at applied potentials of +0.10, −0.10, −0.30 and −0.50 V, respectively. XPS showed characteristic peaks at 935 and 955 eV corresponding to Cu(0). The dendritic CuNS modified electrode exhibits a higher heterogeneous electron transfer rate constant of 3.70 × 10 −7 cm s −1 and an electroactive area of 51.32 cm 2 when compared to other CuNS modified electrodes. Further, the electrocatalytic activity of the different shaped CuNS modified ITO electrodes was examined towards the oxidation of glucose and hydrazine. Interestingly, the dendritic CuNS modified ITO substrate dramatically enhanced the oxidation currents of both glucose and hydrazine and also shifted their oxidation potential towards less positive potential when compared to bare ITO and other CuNS modified ITO substrates. The formation of dendritic CuNS was optimized with respect to deposition time, anion and pH and was monitored by SEM. Based on the results, a plausible mechanism for dendritic CuNS formation was proposed.

A superparamagnetic graphene-based magnetite nanocomposite (rGO-Fe3O4) was synthesized via a simple in-situ chemical approach. This rGO-Fe3O4 nanocomposite can be used as a drug carrier that is able to be guided by external magnetic fields to the specific site of interest for targeted drug delivery application to treat cancer. Ganoderma lucidum extract (GL) was employed, which successfully stabilized the rGO-Fe3O4 via hydrogen bonding and resulted in enhancement of water dispersibility and stability of the prepared nanocomposite, while Pluronic F-127 (PF) was introduced to reduce the overall cytotoxicity. The presence of both GL and PF on the surface of nanocomposite was successfully validated by cyclic voltammetry (CV). Quercetin (Que), a naturally-available polyphenolic flavonoid with anti-cancer properties was utilized to study the potential of rGO-Fe3O4-GL-PF for controlled drug delivery application. The loading capacity of Que on rGO-Fe3O4-GL-PF was determined to be 11 wt% through UV-visible spectroscopy. The Que was loaded on rGO plane via π-π stacking and hydrophobic interaction, which was validated through CV. Furthermore, the in-vitro cytotoxicity of the synthesized nanocomposite showed obvious cytotoxicity toward A549 cells due to the anti-cancer properties of GL which has high potential to be developed into a targeted drug delivery carrier for cancer therapeutics.

Au@Pt core@shell NPs were synthesized by a galvanic displacement reduction method and fabricated on an electrode surface for the investigation of methanol oxidation and oxygen reduction reactions.