Nickel-cysteine nanoparticles: Synthesis, characterization and application for direct electron transfer studies.

Nickel-cysteine nanostructures (Ni-CysNSs) are prepared by a simple wet chemistry procedure under mild conditions, in which l-cysteine acts both as precursor and structure directing agent. This method involves the reaction of nickel chloride with l-cysteine, followed by simultaneous adjusting the pH in the range of 6-8.5 by addition of an aqueous NaOH solution. The structure and morphology of the prepared products are characterized using various techniques, including X-ray powder diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, CHNS elemental analysis, Field emission scanning electron microscopy (FESEM) and Transmission electron microscopy (TEM). The effects of a variety of synthetic conditions on the structure and morphology of the Ni-CysNSs are studied, including the molar ratio of precursors, dispersing solvent, pH value of the reaction solution, reaction time and reaction temperature. FT-IR measurements reveal that synthesized Ni-CysNSs contain many free carboxylic groups on the surface, which could be used as binding sites to anchor biological molecules in order to develop various bioelectronic devices. In this work, the applicability of synthesized nanostructure in biosensing is studied by using Ni-CysNSs as a platform for covalently immobilization of GOx, as a model enzyme, on the surface. Cyclic voltammetric measurements reveal that the direct electron transfer from the active center of GOx to the glassy carbon electrode facilitated upon its immobilization on the Ni-CysNSs film. More importantly, GOx preserves its native structure and catalytic activity for the oxidation of glucose after immobilization on the Ni-CysNSs surface. The electrocatalytic characteristics of the GC/NiCysNS/GOx electrode toward the oxidation of glucose are investigated by cyclic voltammetry, which displayed acceptable electrical and sensing performance. Simple preparation of Ni-CysNPs and their biocompatibility make them attractive platforms for integration of various biomolecules such as proteine/enzymes with surface.

Shape-dependent electron transfer kinetics and catalytic activity of NiO nanoparticles immobilized onto DNA modified electrode: fabrication of highly sensitive enzymeless glucose sensor.

Herein we describe improved electron transfer properties and catalytic activity of nickel oxide nanoparticles (NiONPs) via the electrochemical deposition on DNA modified glassy carbon electrode (DNA/GCE) surface. NiONPs deposited on the bare and DNA-coated GCE showed different morphologies, electrochemical kinetics and catalytic activities. The atomic force microscopy (AFM) images revealed the formation of triangular NPs on the DNA/GCE that followed the shape produced by the DNA template, while the electrodeposition of NiONPs on the bare GCE surface led to the formation of spherical nanoparticles. Electrochemical impedance spectroscopy (EIS) measurements revealed lower charge-transfer resistance (Rct) of triangular NiONPs compared to spherical NPs. Furthermore, the electrocatalytic activity of triangular NiONPs compared to spherical NPs toward glucose oxidation in alkaline media was significantly improved. The amperometric oxidation of glucose at NiONP-DNA/GCE, yielded a very high sensitivity of 17.32 mA mM(-1)cm(-2) and an unprecedented detection limit of 17 nM. The enhanced electron transfer properties and electrocatalytic activity of NiONP-DNA/GCE can be attributed to the higher fraction of sharp corners and edges present in the triangular NiONPs compared to the spherical NPs. The developed sensor was successfully applied to the determination of glucose in serum samples.

Electrocatalytic activity of nickel oxide nanoparticles as mediatorless system for NADH and ethanol sensing at physiological pH solution.

The glassy carbon (GC) electrode modified by nickel oxide nanoparticles (NiOxNPs) is proposed as a novel electrocatalytic system for the oxidation of NADH without using any electron transfer mediator. Here, chronoamperometry was used not only as a simple method for the deposition of NiOxNPs onto the GC electrode but also as an efficient tool in the controlling of nanoparticles size and efficient electrocatalytic activity. The surface morphology and electrochemical properties of the NiOxNPs/GC electrode was investigated using scanning electron microscopy and cyclic voltammetry techniques, respectively. The NPs are deposited uniformly across the GC surface and the size of NiOxNPs varies from 20 to less than 100 nm. The NiOxNPs/GC electrode shows excellent electrocatalytic activity toward oxidation of NADH at reduced overvoltage. The detection limit and sensitivity of the modified electrode toward NADH were estimated to be 106 nM (S/N=3) and 0.052 µAµM(-1), respectively at a concentration range up to 1mM. Due to the biocompatibility of NiOxNPs toward biomolecules, this modified electrode can be used as an efficient transducer in the design of an ethanol biosensor based on the coupled alcohol dehydrogenase enzyme(ADH). Hydrodynamic amperometric detection of ethanol on the ADH-Nafion/NiOxNPs/GC modified electrode gives linear responses over the concentration range of 0.2-6mM with a detection limit of 6.4 µM and sensitivity of 36 nA mM(-1). Applicability of the proposed biosensor for ethanol detection in real samples, easy and simple preparation, being mediator free, high sensitivity and biocompatibility are the major advantages of the proposed biosensor.

DNA/nickel oxide nanoparticles/osmium(III)-complex modified electrode toward selective oxidation of l-cysteine and simultaneous detection of l-cysteine and homocysteine.

The modification of glassy carbon (GC) electrode with electrodeposited nickel oxide nanoparticles (NiOxNPs) and deoxyribonucleic acid (DNA) is utilized as a new efficient platform for entrapment of osmium (III) complex. Surface morphology and electrochemical properties of the prepared nanocomposite modified electrode (GC/DNA/NiOxNPs/Os(III)-complex) were investigated by FESEM, cyclic voltammetry and electrochemical impedance spectroscopy techniques. Cyclic voltammetric results indicated the excellent electrocatalytic activity of the resulting electrode toward oxidation of l-cysteine (CySH) at reduced overpotential (0.1 V vs. Ag/AgCl). Using chronoamperometry to CySH detection, the sensitivity and detection limit of the biosensor are obtained as 44 µA mM(-1) and 0.07 µM with a concentration range up to 1000 µM. The electrocatalytic activity of the modified electrode not only for oxidation of low molecular-mass biothiols derivatives such as, glutathione, l-cystine, l-methionine and electroactive biological species ( dopamine, uric acid, glucose) is negligible but also for very similar biothiol compound (homocysteine) no recognizable response is observed at the applied potential window. Furthermore, the simultaneous voltammetric determination of l-cysteine and homocysteine compounds without any separation or pretreatment process was reported for the first time in this work. Finally, the applicability of sensor for the analysis of CySH concentration in complex serum samples was successfully demonstrated. Highly selectivity, excellent electrocatalytic activity and stability, remarkable antifouling property toward thiols and their oxidation products, as well as the ability for simultaneous detection of l-cysteine and homocysteine are remarkably advantageous of the proposed DNA based biosensor.

Voltammetric determination of dopamine at a zirconium phosphated silica gel modified carbon paste electrode.

Zirconium phosphated amorphous silica gel (devoted briefly as Si-ZrPH) modified carbon paste electrode (CPE) was used for detection of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA). Cyclic voltammetry demonstrated improved reversibility of the DA on the modified electrode. Cyclic voltammetry of Fe(CN)(6)(3-/4-) as a negatively charged probe revealed that the surface of the Si-ZrPH modified CPE surface had a high density of negative charge. As a result, the modified carbon paste electrode could inhibit the voltammetric response of AA and UA while the redox reaction of dopamine was promoted. Based on this, a selective method has been developed to detect DA in the presence of 2500 and 1000 time higher concentration of AA and UA, respectively. The effect of various experimental parameters on the voltammetric response of dopamine was investigated. Under the chosen conditions, the differential pulse voltammetry peak current was found to be linear with DA concentration in the ranges of 0.04 to 50 microM and 50 to 400 microM. The detection limit of the proposed method in the presence of 100 microM of AA and 40 microM of UA was found to be 0.02 microM for DA determination. Satisfying results are achieved when detecting the DA in injection and human serum samples.

Fabrication of bulk-modified carbon paste electrode containing alpha-PW12O40(3-) polyanion supported on modified silica gel: Preparation, electrochemistry and electrocatalysis.

Alpha-PW(12)O(40)(3-) (PW(12)) supported on the surface of silica gel derivatized by 3-aminopropyl(triethoxy)silane (devoted briefly as SiNH(3)PW(12)) was synthesized and used as bulk modifier to fabricate a renewable three-dimensional chemically modified electrode. The electrochemical behavior of the modified electrode was characterized by cyclic voltammetry. There is an ionic bonding character between PW(12) and the surface amino groups of modified silica, which greatly improves the stability of SiNH(3)PW(12)-modified carbon paste electrode due to insolubility of silica gel in water. The SiNH(3)PW(12) bulk-modified carbon paste electrode not only maintains the electrochemical activity of PW(12), but also exhibits remarkable advantages of renewability, as well as simple preparation and inexpensive material. The modified electrode offers an excellent and stable electrocatalytic response for the reduction of IO(3)(-) and hydrogen peroxide. The SiNH(3)PW(12)-CPE is successfully applied as an electrochemical detector to monitor IO(3)(-) in flow injection analysis (FIA). The catalytic peak current was found to be linear with the IO(3)(-) concentration in the range 5x10(-6) to 1x10(-3)molL(-1). The detection limit of the proposed method was found to be 3.1x10(-6)molL(-1) for IO(3)(-) determination.

Hydrocarbon oxidation catalyzed by vanadium polyoxometalate supported on mesoporous MCM-41 under ultrasonic irradiation.

Vanadium polyoxometalate (PVMo) supported on mesoporous MCM-41, MCM-41-NH(2), as efficient and heterogeneous catalysts, with large surface area, for hydrocarbon oxidation with hydrogen peroxide is reported. Oxidation of the alkenes and alkanes gave product selectivities, which are similar to those observed for corresponding homogeneous catalyst. PVMo-MCM was prepared by introduction of PVMo into the mesoporous molecule sieves of MCM-41 by impregnation and adsorption techniques. The samples were characterized by X-ray diffraction (XRD), thermal gravimetric-differential thermal analysis (TG-DTA), FT-IR, scanning electron microscopy (SEM), UV-Vis and cyclic voltametry (CV). Ultrasonic irradiation has a particular effect on MCM-41 structural uniformity and reduced the reaction times and improved the product yields. In addition, the solid catalysts could be recovered and reused several times without loss of its activity.

Selective response of dopamine in the presence of ascorbic acid on carbon paste electrode modified with titanium phosphated silica gel.

Titanium phosphate grafted on the surface of silica gel (devoted briefly as Si-TiPH) was synthesized and used as bulk modifier to fabricate a renewable three-dimensional chemically modified electrode. The Si-TiPH bulk modified carbon paste electrode was used for the selective determination of dopamine (DA) in the presence of ascorbic acid (AA). The modified electrode offers an excellent and stable response for the determination of DA in the presence of AA. The differential pulse voltammetry peak current was found to be linear with the DA concentration in the range 2 x 10(-7) to 1 x 10(-6) and 2 x 10(-6) to 6 x 10(-5) mol L(-1). The detection limit of the proposed method in the presence of 2.0 x 10(-5) M of AA was found to be 4.3 x 10(-8) mol L(-1) for DA determination. The proposed method was successfully applied for the determination of DA in injections.

Simultaneous determination of copper, bismuth and lead by adsorptive stripping voltammetry in the presence of thymolphthalexone.

A novel, sensitive and selective adsorptive stripping procedure for simultaneous determination of copper, bismuth and lead is presented. The method is based on the adsorptive accumulation of thymolphthalexone (TPN) complexes of these elements onto a hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan using differential pulse modulation. The influences of control variables on the sensitivity of the proposed method for the simultaneous determination of copper, lead and bismuth were studied using the Derringer desirability function. The optimum analytical conditions were found to be TPN concentration of 4.0 microM, pH of 9.0, and accumulation potential at -800 mV vs. Ag/AgCl with an accumulation time of 80 s. The peak currents are proportional to the concentration of copper, bismuth and lead over the 0.4-300, 1-200 and 1-100 ng mL(-1) ranges with detection limits of 0.4, 0.8 and 0.7 ng mL(-1), respectively. The procedure was applied to the simultaneous determination of copper, bismuth and lead in the tap water and some synthetic samples with satisfactory results.

Determination of trace amounts of thallium by adsorptive cathodic stripping voltammetry with xylenol orange.

Trace amounts of thallium(I) can be determined using adsorptive cathodic stripping voltammetry in the presence of Xylenol Orange (XO). The reduction current of the thallium(I)-XO complex ion was measured by square-wave cathodic stripping voltammetry. The peak potential was at -0.44 V vs. Ag/AgCl. The effect of various parameters (pH, ligand concentration, accumulation potential and collection time) on the response are discussed. The response was linearly related to the thallium concentration in the range 0.5-110 ng ml(-1) and 110-2000 ng ml(-1). The limit of detection was 0.2 ng ml(-1). The relative standard deviation for the determination of 80 ng ml(-1) thallium was 2.8%. Many common anions and cations did not interfere with the determination of thallium. The interference of lead was reduced by the addition of 0.003 M sodium carbonate. The voltammetric procedure was then successfully applied to the determination of thallium in various complex samples.