N.S.K. Gowthaman

Modification of a glassy carbon electrode with gold–platinum core–shell nanoparticles by electroless deposition and their electrocatalytic activity

Gold–platinum (Au@Pt) nanoparticles with a core–shell structure were fabricated on a glassy carbon electrode (GCE) by an electroless deposition method. Initially, gold nanoparticles (AuNPs) were deposited on GCE by reducing HAuCl4 with NH2OH. SEM studies showed that the size of the deposited AuNPs was found to be 30 nm. The deposited AuNPs on GCE act as the nucleation centre for the deposition of platinum nanoparticles (PtNPs) in the presence of H2PtCl6 and NH2OH. The size of the PtNP increases on increasing the electroless deposition time. The SEM studies demonstrated that the electroless deposition of Pt on Au was isotropic and uniform. Further, Au@Pt modified substrates were characterized by X-ray photoelectron spectroscopy (XPS), an X-ray diffraction method (XRD), energy dispersive X-ray analysis (EDAX) and cyclic voltammetry (CV). XPS showed characteristic binding energies at 71.2 and 74.4 eV for PtNPs and 83.6 and 87.3 eV for AuNPs indicating the zero valent nature of both Au and Pt. Further, the electrocatalytic activity of the Au@Pt modified electrode was examined by studying the reduction of dioxygen and oxidation of hydrazine. The modified electrode showed higher electrocatalytic activity towards the oxidation of hydrazine not only by shifting its oxidation potential towards a less positive potential but also enhancing the oxidation peak current. It also exhibited higher electrocatalytic activity towards the reduction of dioxygen by shifting its reduction overpotential by 650 mV towards a less positive potential when compared to bare GCE.

Fabrication of nitrogen-doped carbon dots for screening the purine metabolic disorder in human fluids.

Fabrication of nitrogen-doped carbon dots (N-CDs) electrode for the screening of purine metabolic disorder was described in this paper. Peroxynitrite is a short-lived oxidant species that is a potent inducer of cell death. Uric acid (UA) can scavenge the peroxynitrite to avoid the formation of nitrotyrosine, which is formed from the reaction between peroxynitrite and tyrosine (Try). Scavenging the peroxynitrite avoids the inactivation of cellular enzymes and modification of the cytoskeleton. Reduced level of UA decreases the ability of the body from preventing the peroxynitrite toxicity. On the other hand, the abnormal level of UA leads to gout and hyperuricemia. Allopurinol (AP) is administered in UA lowering therapy. Thus, the simultaneous determination of UA, Try and AP using N-CDs modified glassy carbon (GC) electrode was demonstrated for the first time. Initially, N-CDs were prepared from L-asparagine by pyrolysis and characterized by different spectroscopic and microscopic techniques. The HR-TEM image shows that the average size of the prepared N-CDs was 1.8±0.03nm. Further, the N-CDs were directly attached on GC electrode by simple immersion, follows Micheals nucleophilic addition. XPS of N-CDs shows a peak at 285.3eV corresponds to the formation of C-N bond. The GC/N-CDs electrode shows higher electrocatalytic activity towards UA, Tyr and AP by not only shifting their oxidation potentials toward less positive potential but also enhanced their oxidation currents in contrast to bare GC electrode. The GC/N-CDs electrode shows the limit of detection of 13×10-10M (S/N=3) and the sensitivity of 924μAmM-1cm-2 towards the determination of UA. Finally, the N-CDs modified electrode was utilized for the determination of UA, Tyr and AP in human blood serum and urine samples.

Tuning the composition of gold–silver bimetallic nanoparticles for the electrochemical reduction of hydrogen peroxide and nitrobenzene

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 AuCl4− 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 Michaels 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 × 10−7 cm s−1 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 μM (S/N = 3) for HP and NB, respectively.

Electroless deposition of Gold-Platinum Core@Shell Nanoparticles on Glassy Carbon Electrode for Non-Enzymatic Hydrogen Peroxide sensing#

AbstractA non-enzymatic hydrogen peroxide sensor was developed using gold@platinum nanoparticles (Au@PtNPs) with core@shell structure fabricated on glassy carbon electrode (GCE) by electroless deposition method. Initially, gold nanoparticles (AuNPs) were deposited on GCE by reducing HAuCl4 in the presence of NH2OH and the deposited AuNPs on GCE act as the nucleation centre for the deposition of platinum nanoparticles (PtNPs) in the presence of H2PtCl6 and NH2OH. SEM and AFM studies demonstrated that the electroless deposition of Pt on Au was isotropic and uniform. Further, Au@PtNP-modified substrates were characterized by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray analysis (EDAX) and cyclic voltammetry (CV). XPS showed characteristic binding energies at 71.2 and 74.4 eV for PtNPs and, 83.6 and 87.3 eV for AuNPs indicating the zero-valent nature in both of them. The electrocatalytic activity of Au@PtNP-modified electrode was investigated towards hydrogen peroxide (HP) reduction. The modified electrode exhibited higher electrocatalytic activity towards HP by not only shifting its reduction potential by 370 mV towards less positive potential but also by enhancing the reduction current when compared to bare and AuNP-modified GCE. The present method shows better sensitivity compared to the reported methods in literature and the detection limit was found to be 60 nM. Graphical AbstractA non-enzymatic hydrogen peroxide sensor was developed using gold@platinum nanoparticles with core@shell structure fabricated on glassy carbon electrode by electroless deposition method.

Highly sensitive interference-free electrochemical determination of pyridoxine at graphene modified electrode: Importance in Parkinson and Asthma treatments

To reduce the side effects in the medication of Parkinson and Asthma, pyridoxine (PY) is administered along with l-3,4-dihydroxyphenyl alanine (l-dopa) and theophylline (TP), respectively. However, excessive dosage of PY leads to nervous disorder. Thus, a sensitive and selective electrochemical method was developed for the determination of PY in the presence of major interferences including TP, l-dopa, ascorbic acid (AA) and riboflavin (RB) using electrochemically reduced graphene oxide (ERGO) film modified glassy carbon electrode (GCE) in this paper. The ERGO fabrication process involves the nucleophilic substitution of graphene oxide at basic pH on amine terminal of 1,6-hexadiamine which was pre-assembled on GCE followed by electrochemical reduction. The electrocatalytic activity of the ERGO modified electrode was examined towards the oxidation of PY. It greatly enhanced the oxidation current of PY in contrast to bare and GO modified GCEs due to facile electron transfer besides π-π interaction between ERGO film and PY. Since TP and l-dopa drugs antagonize the drug action of PY, ERGO modified GCE was also used for the simultaneous determination of PY and l-dopa and PY and TP. Further, the selective determination of PY in the presence of other water soluble vitamins such as ascorbic acid and riboflavin was also demonstrated. Using amperometry, detection of 100nM PY was achieved and the detection limit was found to be 5.6×10(-8)M (S/N=3). The practical application of the present method was demonstrated by determining the concentration of PY in human blood serum and commercial drugs.

Fabrication of different copper nanostructures on indium-tin-oxide electrodes: shape dependent electrocatalytic activity

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 CuSO4 and 0.1 M H2SO4. 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 cm2 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.

Displacement reduction routed Au–Pt bimetallic nanoparticles: a highly durable electrocatalyst for methanol oxidation and oxygen reduction

In this paper, a new galvanic displacement reduction (GDR) approach was demonstrated for Au–PtNPs synthesis with different Pt : Au compositions in an aqueous medium. PtNPs were initially synthesized by the reduction of H2PtCl6 using trisodium citrate and sodium borohydride. Addition of various concentrations of HAuCl4 to PtNPs leads to the formation of Au–PtNPs, which follows the GDR between Pt(0) and AuCl4− ions. The formation of Au–PtNPs was monitored by UV-vis spectroscopy by tuning the mole ratio of Pt : Au. HR-TEM images showed that the Au–PtNPs were spherical with 11 nm diameter. HR-TEM, XRD and XPS analysis showed that the formed Au–PtNPs were in the form of a core–shell structure. The colloidal Au–PtNPs were then attached on a glassy carbon (GC) electrode via a 1,6-hexanediamine linker for the methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). The attachment of Au–PtNPs was further confirmed by XRD, line scanning coupled with energy-dispersive X-ray spectroscopy (EDS) and cyclic voltammetry (CV). The Au–PtNPs modified electrode exhibits a higher heterogeneous electron transfer rate constant of 4.12 × 10−3 cm s−1 than bare (1.01 × 10−4 cm s−1) and PtNP (1.77 × 10−4 cm s−1) modified GC electrodes. Further, the Au–PtNPs modified electrode exhibited a composition dependent activity towards the MOR and ORR. It was found that the modified electrode with a Pt : Au ratio of 1 : 0.09 shows 8 times more sensitive oxidation for the MOR when compared to a commercial Pt/C catalyst. The present Au–PtNPs catalyst exhibits a greatly enhanced catalytic activity in terms of mass activity (132 mA mg Pt−1) and excellent stability relative to the commercial Pt/C catalyst.

Selective and sensitive determination of the antidote of heparin using Ag-GQDs by optical methods

The determination of the polyanionic drug heparin has been reported in the literature by using various spectral techniques at the expense of the polycationic drug protamine. But, the determination of protamine in the presence of heparin by optical methods has not been reported so far. Since the administration of protamine is associated with different side effects its accurate determination is essential in the presence of heparin. The present study reports the sensitive and selective determination of protamine in the presence of heparin by colorimetric, spectrophotometric and spectrofluorimetric methods using GQD capped silver nanoparticles (Ag-GQDs) for the first time. The yellow colour of the Ag-GQD containing heparin immediately turns red while adding 100 ng mL−1 protamine. The obtained color change is due to an increase in the Ag-GQD size from 9 to 15 nm which was confirmed by HR-TEM studies. On the other hand, the surface plasmon resonance (SPR) band of Ag-GQDs at 411 nm decreased and a new peak appeared at 520 nm after the addition of protamine. While adding each 10 ng mL−1 protamine to Ag-GQDs, the emission intensity at 451 nm increases linearly with a correlation coefficient of 0.9910 and the limit of detection was found to be 0.05 × 10−9 g mL−1 (S/N = 3). Furthermore, the selective determination of protamine was achieved in the presence of heparin and other common interferents using Ag-GQDs. The practical application of the present sensor was displayed by determining protamine in blood serum.

Simultaneous growth of spherical, bipyramidal and wire-like gold nanostructures in solid and solution phases: SERS and electrocatalytic applications

Anisotropic growth of gold nanostructures (AuNS) on an indium tin oxide (ITO) substrate and in growth solution was achieved by in situ electrochemical reduction of Au+ ions from the growth solution. Initially, the growth solution was prepared by adding the shape-directing agent Cu2+ into a solution of cetyltrimethylammonium bromide (CTAB), HAuCl4 and ascorbic acid (AA). The Au+–CTAB complex from the solution was electrochemically reduced to deposit AuNPs on ITO, which act as nucleation centers. The HR-TEM and SEM images exhibit spherical, bipyramidal and wire-like AuNS grown both in solution and on ITO after 1, 3 and 6 h, respectively. The crystallite size and lattice strain were calculated and it was found that the lattice strain decreases with an increase in nucleation time. The ITO/Au-nanowires showed a higher surface coverage (10.1%) and electrochemically active surface area (0.69 cm2) than the other AuNS. Further, the ITO/AuNS exhibited shape-dependent surface enhanced Raman scattering enhancement (SERS) towards 4-aminothiophenol adsorbed on the grown AuNS surface. The ITO/Au-nanowires showed a higher enhancement factor of 9.7 × 105 when compared to the other AuNS. Further, the electrocatalytic activity of the different shaped AuNS was examined towards the reduction of hydrogen peroxide (HP). The Au-nanowire modified ITO electrode exhibited higher electrocatalytic activity towards HP reduction by not only shifting its reduction potential towards less positive potential but also by enhancing its reduction current.