Md. Abdul Aziz

Gold nanoparticle-modified graphite pencil electrode for the high-sensitivity detection of hydrazine.

A novel gold nanoparticle-modified graphite pencil electrode (AuNP-GPE) is prepared just by immersing a bare GPE in AuNP solution, followed by heating for 15 min. The bare and modified GPEs are characterized by FE-SEM imaging and cyclic voltammetry. The AuNP-GPEs showed excellent electrocatalytic activities with respect to hydrazine oxidation, with good reproducibility. To reduce the quantification and detection limits, and increase the hydrazine sensitivity, the pH and square wave voltammetry parameters are optimized. A square wave voltammetry study as a function of the hydrazine concentration showed that the AuNP-GPE detectors quantification limit was 100 nmol L(-1) hydrazine, much lower than the value obtained using amperometry (10 µmol L(-1)). The limits of detection (at 3σ) for hydrazine sensing at AuNP-GPEs using square wave voltammetry and amperometry were 42 nmol L(-1) and 3.07 µmol L(-1). Finally, the modified electrode was used to determine the hydrazine concentration in drinking water, and satisfactory results are obtained. This simple, rapid, low-cost method for fabricating a modified electrode is an attractive approach to the development of new sensors.

Optimization of Phosphatase- and Redox Cycling-Based Immunosensors and Its Application to Ultrasensitive Detection of Troponin I

The authors herein report optimized conditions for ultrasensitive phosphatase-based immunosensors (using redox cycling by a reducing agent) that can be simply prepared and readily applied to microfabricated electrodes. The optimized conditions were applied to the ultrasensitive detection of cardiac troponin I in human serum. The preparation of an immunosensing layer was based on passive adsorption of avidin (in carbonate buffer (pH 9.6)) onto indium-tin oxide (ITO) electrodes. The immunosensing layer allows very low levels of nonspecific binding of proteins. The optimum conditions for the enzymatic reaction were investigated in terms of the type of buffer solution, temperature, and concentration of MgCl(2), and the optimum conditions for antigen-antibody binding were determined in terms of incubation time, temperature, and concentration of phosphatase-conjugated IgG. Very importantly, the antigen-antibody binding at 4 °C is extremely important in obtaining reproducible results. Among the four phosphatase substrates (L-ascorbic acid 2-phosphate (AAP), 4-aminophenyl phosphate, 1-naphthyl phosphate, 4-amino-1-naphthyl phosphate) and four phosphatase products (L-ascorbic acid (AA), 4-aminophenol, 1-naphthol, 4-amino-1-naphthol), AAP and AA meet the requirements most for obtaining easy dissolution and high signal-to-background ratios. More importantly, fast AA electrooxidation at the ITO electrodes does not require modification with any electrocatalyst or electron mediator. Furthermore, tris(2-carboxyethyl)phosphine (TCEP) as a reducing agent allows fast redox cycling, along with very low anodic currents at the ITO electrodes. Under these optimized conditions, the detection limit of an immunosensor for troponin I obtained without redox cycling of AA by TCEP is ca. 100 fg/mL, and with redox cycling it is ca. 10 fg/mL. A detection limit of 10 fg/mL was also obtained even when an immunosensing layer was simply formed on a micropatterned ITO electrode. From a practical point of view, it is of great importance that ultralow detection limits can be obtained with simply prepared enzyme-based immunosensors.

Effect of surface modification of indium tin oxide by nanoparticles on the electrochemical determination of tryptophan.

The effect of surface modification of indium tin oxide (ITO) by multi wall carbon nanotube (MWNT) and gold nanoparticles attached multi wall carbon nanotube (AuNP-MWNT) has been studied to determine tryptophan, an important and essential amino acid for humans and herbivores. A detailed comparison has been made among the voltammetric response of bare ITO, MWNT/ITO and AuNP-MWNT/ITO in respects of several essential analytical parameters viz. sensitivity, detection limit, peak current and peak potential of tryptophan. The AuNP-MWNT/ITO exhibited a well defined anodic peak at pH 7.2 at a potential of ∼ 669 mV for the oxidation of tryptophan as compared to 760 mV at MWNT/ITO electrode. Under optimum conditions linear calibration curve was obtained over tryptophan concentration range 0.5-90.0 μM in phosphate buffer solution of pH 7.2 with detection limit and sensitivity of 0.025 μM and 0.12 μA μM(-1), respectively. The oxidation of tryptophan occurred in a pH dependent, 2e(-) and 2H(+) process and the electrode reaction followed adsorption controlled pathway. The method has been found selective and successfully implemented for the determination of tryptophan in human urine and plasma samples using standard addition method. The electrode exhibited an efficient catalytic response with good reproducibility and stability.

Effect of gold nanoparticle attached multi-walled carbon nanotube-layered indium tin oxide in monitoring the effect of paracetamol on the release of epinephrine.

A gold nanoparticle attached multi-walled carbon nanotube-layered indium tin oxide (AuNP/MWNT/ITO) electrode has been used for monitoring the effect of paracetamol (PAR) on the release of epinephrine (EPI) in human urine. The modified electrode shows an excellent electrocatalytic activity for the oxidation of EPI and PAR with acceleration of electron transfer rate as compared to MWNT/ITO and AuNP/ITO. An apparent shift of the oxidative potential towards less positive potential with a marked increase in peak currents is observed in square wave voltammetry at AuNP/MWNT/ITO electrode. The calibration curves for the simultaneous determination of PAR and EPI showed an excellent linear response, ranging from 5.0×10(-9) mol L(-1) to 80.0×10(-9) mol L(-1) for both the compounds. The detection limits for the simultaneous determination of PAR and EPI were found to be 46×10(-10) mol L(-1) and 42×10(-10) mol L(-1) respectively. The proposed method has been successfully applied for the simultaneous determination of PAR and EPI in human urine. It is observed that gold nanoparticles attached with multi-wall carbon nanotube catalyze the oxidation of EPI and PAR.

The rhodium complex of bis(diphenylphosphinomethyl)dopamine-coated magnetic nanoparticles as an efficient and reusable catalyst for hydroformylation of olefins

A new bis(diphenylphosphinomethyl)dopamine (bpd) ligand has been prepared and anchored on the surface of magnetic nanoparticles (MNPs). The obtained ligand and the surface functionalized nanoparticles of type MNP@bpd have been characterized by various analytical techniques, such as NMR, IR, TEM, XRD, and VSM. TEM shows homogeneous distribution of the particles with the size ranging 5–7 nm. XRD Rietveld analysis confirms the formation of a pure and single Fe3O4 phase with high crystallinity. The ligands anchored on the magnetic nanoparticle surface have been confirmed by the shift of the characteristic Fe–O vibration band in the FT-IR spectrum, and have been supported by the stepwise weight loss in TGA as a function of temperature. The phosphorus content determined by ICP-MS is approximately 0.39 mmol of phosphine per gram of the nanoparticles. Magnetization-field curves recorded at room temperature reveal superparamagnetic behavior. MNP@bpd materials have proven to be excellent catalysts after in situ addition of the rhodium (Rh) metal precursor for the hydroformylation reaction of styrene and its derivatives. The extent of reusability of the catalyst has been tested and was found to be active even after seven consecutive cycles.

Manganese dioxide–vulcan carbon@silver nanocomposites for the application of highly sensitive and selective hydrazine sensors

Manganese dioxide (MnO2)–vulcan carbon (VC)@silver (Ag) (core@shell) nanocomposites were synthesized through a simple wet chemical method without using hazardous organic reagents, polymeric micelles, templates or catalysts. The synthesized MnO2–VC@Ag exhibited a MnO2–VC core and Ag shell, and the thickness of shell was found to be 23 nm. The obtained diffraction patterns confirmed that the prepared nanocomposite consists of tetragonal and face-centred cubic structures of MnO2 and Ag nanostructures, respectively. Cyclic voltammetry and amperometric techniques were adopted to electrochemically characterize the MnO2–VC@Ag nanospheres for hydrazine oxidation in phosphate buffer solution. Under the optimized conditions, the fabricated sensor exhibited a good electrochemical performance toward hydrazine oxidation, offering a broad linearity of 0.1 to 350 μM, with a relatively low detection limit of 100 nM and a high sensitivity of 0.33 μA μM−1 cm−2. In addition, anti-interference properties, good reproducibility, long term performance, good repeatability and real sample analysis were achieved for the constructed sensor, owing to the synergetic effects of the Ag and MnO2–VC nanostructures. The aforesaid attractive analytical performance and facile preparation of the MnO2–VC@Ag core–shell nanospheres are new features for electrocatalytic materials and may hold promise for the design and development of effective hydrazine sensors.

Magnetic nanoparticle-supported ferrocenylphosphine: a reusable catalyst for hydroformylation of alkene and Mizoroki–Heck olefination

We present dopamine (dop) conjugated bis(diphenylphosphino)ferrocenylethylamine (BPPFA) functionalized magnetic nanoparticles (Fe3O4). A ferrocene ({η5-C5H4-PPh2}Fe{η5-C5H3-1-PPh2-2-CH(Me)NH-CH2-CH2-4Ph-1,2-OH}) ligand (dop-BPPF) has been prepared by reaction of (1-[1′,2-bis(diphenylphosphino)-ferrocenyl]ethyl acetate) and dopamine hydrochloride to form dop-BPPF, which was characterized by NMR, IR, FTIR, EA and FAB-MS. This ligand was anchored on ultrasmall (6–8 nm) magnetic nanoparticles (MNP) to yield Fe3O4@dop-BPPF. The resulting ferrocenylphosphine on magnetic nanoparticles was characterized by SEM, EDS, XRD, TEM, TGA, and VSM. The magnetic nature of the materials was investigated. Fe3O4@dop-BPPF exhibits very high catalytic activity for the Pd-catalyzed Mizoroki–Heck reaction and exceptionally high regioselectivity for the Rh-catalyzed hydroformylation reaction with branched aldehydes (up to > 99%). The potential of this Fe3O4@dop-BPPF as a reusable catalyst has been studied for the Mizoroki–Heck reaction, and this catalyst was robustly active even after eleven consecutive cycles.

Pyrolytic preparation of gold nanoparticle-coated taro carbon and its application for the selective detection of dopamine

A highly selective and sensitive electrochemical method was developed for the detection of dopamine (DA), based on a gold nanoparticle (AuNP)-coated taro carbon (TC)-modified glassy carbon electrode (AuNP-TC/GCE). This novel AuNP-TC material was simply prepared by carrying out a pyrolysis of a composite material obtained by treatment of an acid-treated taro stem powder with HAuCl4. Transmission electron microscopy (TEM), Raman spectroscopy, field-emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) were employed to characterize the AuNP-TC material. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to characterize the modified electrode. The modified GCE exhibited a well-defined current response only toward the electrochemical oxidation of DA in a mixture solution of ascorbic acid (AA), DA, and uric acid (UA). This designed electrochemical sensor showed a linear response in the concentration range of 0.5 μM to 250 μM DA and a sensing limit (S/N = 3) of 0.25 μM was found. The sensor was also able to successfully detect DA in a dopamine hydrochloride injection (DAI). Moreover, the sensor exhibited excellent stability and reproducibility.

Electrochemical Investigation of Gold Nanoparticle-Modified Glassy Carbon Electrode and its Application in Ketoconazole Determination

Ketoconazole (KCZ) is an extensively used antifungal compound and is an active ingredient of anti-scaling shampoos, pomades, and skin ointments. In this work, the cyclic voltammetric behaviour of KCZ was studied with a gold nanoparticle (AuNP)-modified glassy carbon (GC) electrode. The conditions for KCZ determination with GC/AuNP were optimised to achieve the best possible response. A pre-adsorption voltage of –1.6 V, a deposition time of 120 s, pH 4.0, and stirring of the KCZ solution during deposition were chosen as the optimum conditions for KCZ determination. The anodic peak at 0.697 V was used for KCZ determination. A linear concentration range of 20–100 μM (R2 = 0.9986) and a detection limit of 2.3 μM (3σ) was achieved for KCZ using the GC/AuNP electrode.

Facile hydrogenation of N-heteroarenes by magnetic nanoparticle-supported sub-nanometric Rh catalysts in aqueous medium

The hydrogenation of nitrogen-containing heterocyclic precursors in aqueous medium at low temperature without imposing molecular hydrogen pressure is quite challenging. Herein, we report the synthesis and performance of a novel catalyst capable of facile hydrogenation (employing tetrahydroxydiboron (THDB) as the reductant) of N-heteroarenes in water at 80 °C with good recyclability. Rhodium particles in the sub-nano range (<1 nm) were produced by in situ reduction of a Rh precursor on freshly prepared superparamagnetic iron oxide nanoparticles (SPIONs, Fe3O4), using aqueous ammonia as a reducing agent at 50 °C. HRTEM and elemental mapping images reveal a homogeneous distribution of <1 nm Rh particles within the matrix of Fe3O4 nanoparticles having an average size within a narrow range of 7–9 nm. The superparamagnetic nature of the composite was confirmed by VSM analysis. The Rh@Fe3O4 catalyst was found to be highly efficient in the heterogeneous hydrogenation of nitrogen-containing heterocyclic compounds with quantitative conversion. It showed selectivity towards the hydrogenation of 1,2,3,4-tetrahydroquinoline (py-THQ) in water using THDB with a high TOF of 1632 h−1. These results are compared with the conversion and selectivity data obtained from reduction with molecular hydrogen gas pressure. The catalytic activity is extended to the successful hydrogenation of simple aromatics like benzene, toluene etc. Isotopic labelling studies were performed to determine the source of hydrogen in quinoline hydrogenation in the presence of THDB. It was found that it could be used for 16 consecutive cycles with gaseous hydrogen, without any undesired by-products; it also retained its original crystallinity.