Functionalized alkoxysilane mediated controlled synthesis of noble metal nanoparticles dispersible in aqueous and non-aqueous medium.

The synthesis of amphiphilic noble metal nanoparticles involving the functional role of 3-aminopropyltrimethoxysilane (3-APTMS) and 3-glycidoxypropyltrimethoxy-silane (3-GPTMS) is reported herein. The mechanistic approach on the reactivity of these functional alkoxysilane for the typical controlled synthesis of AuNPs as evidenced from UV-visible spectroscopy and transmission electron microscopy (TEM) is reported. The experimental findings demonstrate the followings; (1) Methanolic solution of 3-GPTMS undergo interaction with 3-APTMS and the same is facilitated in the presence of 3-APTMS treated noble metal ions, (2) The molar ratio of 3-GPTMS/3-APTMS control the nanogeometry as well as the dispersibility of AuNPs in both aqueous and non-aqueous media, (3) the dispersion ability of nanoparticles is found to be based on the hydrophobic alkyl chain of the reaction product of 3-GPTMS and 3-APTMS, and (4) AuNPs shows absorption maxima as a function of polarity and refractive index of the medium. A typical application of as synthesized AuNPs as peroxidase mimetic is reported.

Novel synthesis of super peroxidase mimetic polycrystalline mixed metal hexacyanoferrates nanoparticles dispersion.

Mixed metal-hexacyanoferrates (MHCF) have shown promising applications for technological development particularly in energy storage technologies, ferromagnetic materials, and electrode materials. However, the challenge of controlling their chemical synthesis, solubility, polycrystallinity and nanogeometry have restricted the practical implementation of MHCF in commercial designs. Further, MHCFs have shown potential as peroxidase mimetics. There is still challenging demand to enhance the catalytic efficiency of such materials to the equivalent of biocatalytic activity thereby allowing the precise control of the mimetic character and ultimately leading to the development of new materials as powerful peroxidases i.e. Horseradish peroxidase (HRP) replacement during enzyme and immuno-sensors development. We report herein a new process that allows the controlled synthesis of biocompatible mixed MHCF nanoparticles with a variety of transition metal ions. The resulting polycrystalline mixed MHCF shows enhanced catalytic efficiency to hydrogen peroxide (H2O2) as compared to that of polycrystalline Prussian blue (PB) made under similar conditions with significant increase in catalytic efficiency as a function of respective hetero-transition metal ion of mixed FeHCF in the order of FeHCF < Mn-FeHCF < Ni-FeHCF < Cu-FeHCF justifying as perfect peroxidase replacement.

Size-dependence enhancement in electrocatalytic activity of NiHCF-gold nanocomposite: potential application in electrochemical sensing.

A nanocomposite of nickel hexacyanoferrate (NiHCF) was made with gold nanoparticles (AuNPs) of two different sizes (20 and 80 nm as AuNP(red) and AuNP(blue) respectively), synthesized via 3-glycidoxypropyltrimethoxysilane mediated reduction of 3-aminopropyltrimethoxysilane treated gold chloride and characterized by scanning electron microscopy and UV-VIS spectroscopy. The size of AuNPs was found to influence the two pairs of reversible voltammetric peaks of cation rich and cation deficient NiHCF. Such influence was identified from cyclic voltammetry of nanocomposite modified electrodes and applications during electrochemical sensing of two different analytes hydrazine and glutathione (GSH). Electrochemical sensing of hydrazine was based on cyclic voltammetry and differential pulse voltammetry (DPV) found as a function of sodium deficient NiHCF and was greatly amplified with increasing AuNPs nanogeometry. NiHCF alone is not an efficient electrode material for GSH analysis at the level required, however, the presence of AuNPs introduces size dependent sensitive and selective detection of GSH. GSH sensing based on linear sweep voltammetry (LSV) was found to be mediated by the potassium rich form of NiHCF redox couple in the presence of AuNPs. The results justified electrochemical detection of these analytes based on a mediated mechanism and support the role of AuNPs for facilitated electrochemical activity of NiHCF based systems as a function of nanogeometry.

Substrate dependent structural and magnetic properties of pulsed laser deposited Fe3O4 thin films.

Nanocrystalline iron oxide thin films have been deposited on various substrates such as quartz, MgO(100), and Si(100) by pulsed laser deposition technique using excimer KrF laser (248 nm). The orientations, crystallite size and lattice parameters were studied using X-ray diffraction. The XRD results show that the films deposited on MgO and Si substrates are highly oriented and show only (400) and (311) reflections respectively. On the other hand, the orientation of the films deposited on quarts substrate changed from (311) to (400) with an increase in the substrate temperature from 400 degrees C to 600 degrees C, indicating thereby that the film growth direction is highly affected with nature of substrate and substrate temperature. The surface morphology of the deposited films was studied using Atomic Force Microscopy (AFM) and spherical ball like regular features of nanometer size grains were obtained. The magnetic properties were studied by Superconducting Quantum Interference Device (SQUID) magnetometer in the magnetic field +/- 6 Tesla. The magnetic field dependent magnetization (M-H) curves of all the Fe3O4 thin films measured at 5 K and 300 K show the ferrimagnetic nature. The electrochemical sensing of dopamine studied for these films shows that the film deposited on MgO substrate can be used as a sensing electrode.

Fabrication of alpha-Fe2O3 nanopowder modified glassy carbon electrode for applications in electrochemical sensing.

In the present study, Fe2O3 nanopowder has been grown by Ultrasonic mist chemical vapor deposition (UM-CVD), which is a promising method for large area deposition at low temperatures taking in to account of its simplicity, inexpensiveness and safety. Room temperature XRD results revealed prominent hematite phase with intense (104) reflection and was also in agreement with the HR-TEM results. In situ high temperature X-ray diffraction (XRD) studies clearly indicated the change of phase from hematite to magnetite as the temperature increases above 300 degrees C. The surface morphology and particle size distribution of Fe2O3 nanopowder were characterized using field emission scanning electron microscope (FE-SEM) and high resolution transmission electron microscope (HR-TEM), which revealed that the particles were spherical in nature and distributed in range of 50-100 nm. SQUID magnetometry results indicate the ferromagnetic nature of the nanopowder with crystallite size of 6 nm as calculated from M-H curve. Transmittance of approximately 55% and estimated direct band gap of 2.5 eV was observed. Further, the nanopowder was used to modify glassy carbon electrode (GCE) and the modified electrode was found to exhibit electrocatalytic activity for the oxidation of dopamine. It is expected that the nanopowder will exhibit promising applications in the development of sensors.

Effect of graphite and metallic impurities of C60 fullerene on determination of salbutamol in biological fluids.

A new method for the determination of salbutamol has been developed using fullerene C60-modified glassy carbon electrode and validated using GC-MS. The presence of graphite and metallic impurities in C60 are found to diminish the peak. The oxidation of salbutamol was observed in a single well-defined, diffusion-controlled process using square wave voltammetry. The peak potential of oxidation peak was dependent on pH and determination was carried out at physiological pH 7.4. The peak current versus concentration plot was linear in the range 100-2000 ng/ml of salbutamol. The detection limit was found to be 40 ng/ml. The determination of salbutamol was carried out in human blood and urine samples and common interferents such as dopamine, ascorbic acid and uric acid do not interfere. The method proved to be specific, rapid, and accurate and can be easily applied for detecting cases of doping. A cross-validation of the observed results with GC-MS indicated a good agreement.

Differential pulse voltammetric determination of methylprednisolone in pharmaceuticals and human biological fluids.

Electrochemical behaviour of methylprednisolone (MP) at the fullerene-C60-modified glassy carbon electrode has been investigated using differential pulse voltammetry. The experimental results suggest that the modified electrode exhibits electrocatalytic effect on the oxidation of MP resulting in a marked enhancement of the peak current response. Under the selected conditions, the oxidation peak current was linearly dependent on the concentration of MP in the range 5.0 nM-1.0 microM with a sensitivity of 0.0107 microA microM(-1). The detection limit was estimated to be 5.6 nM. The electrode showed good sensitivity, selectivity, stability and reproducibility. In addition, the developed method was satisfactorily applied to the determination of MP in pharmaceutical formulations and human serum and urine samples without any necessity for sample treatment or time-consuming extraction steps prior to the analysis. GC-MS method was used to cross-validate the results obtained for the quantitative estimation of MP in biological fluids and the results showed approximately 2% deviation to those obtained using the proposed method.