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.

Reduced graphene oxide-chitosan-aptamer interface as new platform for ultrasensitive detection of human epidermal growth factor receptor 2.

The present work describes an ultrasensitive electrochemical aptamer-based assay for detection of human epidermal growth factor receptor 2 protein (HER2) cancer biomarker as a model analyte. Results show that the reduced graphene oxide-chitosan (rGO-Chit) film as a suitable electrode material possesses great favorable properties including high homogeneity, good stability, large surface area and high fraction of amine groups as aptamer binding sites. Various steps of aptasensor fabrication were characterized using microscopic, energy-dispersive X-ray spectroscopy (EDAX), Fourier transform infrared (FTIR) spectroscopy and electrochemical techniques. Using methylene blue (MB) as an electrochemical probe and differential pulse voltammetry (DPV) technique, two linear concentration ranges of 0.5-2ngml-1 and 2-75ngml-1 were obtained with a high sensitivity of 0.14µAng-1ml and a very low detection limit of 0.21ngml-1 (very lower than the clinical cut-off). The fabricated aptasensor showed excellent selectivity for detection of HER2 in complex matrix of human serum samples. The sensitive detection of HER2 can be attributed to the multiple signal amplification of MB during its accumulation to the modified electrode surface via both affinity interaction to aptamer molecules and electrostatic adsorption to the HER2 analyte as well as high charge transfer kinetic properties of the applied rGO-Chit film. The rapid and simple preparation of the proposed aptasensor as well as its high selectivity, stability and reproducibility provided a promising protocol for non-invasive diagnosis for various points of care application. The proposed aptasensor showed excellent analytical performance in comparison with current HER2 biosensors.

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.

Fabrication of a highly sensitive adenosine aptasensor based on covalent attachment of aptamer onto chitosan-carbon nanotubes-ionic liquid nanocomposite.

The present study describes the fabrication of a novel electrochemical aptasensor for the label-free determination of adenosine. The immobilization surface is prepared by the modification of a glassy carbon (GC) electrode with a robust nanocomposite containing multiwalled carbon nanotubes, ionic liquid and chitosan(MWCNTs-IL-CHIT). Amine-terminated 12-mer capture probe(ssDNA1) is covalently attached onto the nanocomposite using glutaraldehyde (GA) as the linking agent, a 32-mer adenosine-specific aptamer (ssDNA2) immobilized onto the electrode surface through hybridization with the ssDNA1 and methylene blue (MB) used as the redox probe. The peak current of MB decreased linearly with increasing adenosine concentration due to the formation of aptamer-adenosine complex and displacement of the aptamer from the modified electrode surface. The aptasensor showed a low detection limit of 150 pM and high sensitivity of 0.67 µAnM⁻¹ at a concentration range of up to 0.4 µM. Through the control experiments performed by using some other nucleosides such as guanosine, cytidine and uridine, the excellent specificity of this sensor toward adenosine detection is demonstrated. The potential applicability of the aptasensor is successfully applied for measuring adenosine concentration in blood serum and drug formulation samples.The herein described methodology may hold great promise for fabrication of other aptasensors and immunosensors.

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.

Immobilization of glucose oxidase on electrodeposited nickel oxide nanoparticles: direct electron transfer and electrocatalytic activity.

For the first time glucose oxidase (GOx) was successfully co-deposited on nickel-oxide (NiO) nanoparticles at a glassy carbon electrode. In this paper we present a simple fabrication method of biosensor which can be easily operated without using any specific reagents. Cyclic voltammetry was used for electrodeposition of NiO nanoparticle and GOx immobilization. The direct electron transfer of immobilized GOx displays a pair of well defined and nearly reversible redox peaks with a formal potential (E(0')) of -0.420 V in pH 7 phosphate buffer solution and the response shows a surface controlled electrode process. The surface coverage and heterogeneous electron transfer rate constant (k(s)) of GOx immobilized on NiO film glassy carbon electrode are 9.45 x 10(-13)mol cm(-2) and 25.2+/-0.5s(-1), indicating the high enzyme loading ability of the NiO nanoparticles and great facilitation of the electron transfer between GOx and NiO nanoparticles. The biosensor shows excellent electrocatalytical response to the oxidation of glucose when ferrocenmethanol was used as an artificial redox mediator. Furthermore, the apparent Michaelis-Menten constant 2.7 mM, of GOx on the nickel oxide nanoparticles exhibits excellent bioelectrocatalytic activity of immobilized enzyme toward glucose oxidation. In addition, this glucose biosensor shows fast amperometric response (3s) with the sensitivity of 446.2nA/mM, detection limit of 24 microM and wide concentration range of 30 microM to 5mM. This biosensor also exhibits good stability, reproducibility and long life time.

Direct electrochemistry and electrocatalytic activity of catalase immobilized onto electrodeposited nano-scale islands of nickel oxide.

Cyclic voltammetry was used for simultaneous formation and immobilization of nickel oxide nano-scale islands and catalase on glassy carbon electrode. Electrodeposited nickel oxide may be a promising material for enzyme immobilization owing to its high biocompatibility and large surface. The catalase films assembled on nickel oxide exhibited a pair of well defined, stable and nearly reversible CV peaks at about -0.05 V vs. SCE at pH 7, characteristic of the heme Fe (III)/Fe (II) redox couple. The formal potential of catalase in nickel oxide film were linearly varied in the range 1-12 with slope of 58.426 mV/pH, indicating that the electron transfer is accompanied by single proton transportation. The electron transfer between catalase and electrode surface, (k(s)) of 3.7(+/-0.1) s(-1) was greatly facilitated in the microenvironment of nickel oxide film. The electrocatalytic reduction of hydrogen peroxide at glassy carbon electrode modified with nickel oxide nano-scale islands and catalase enzyme has been studied. The embedded catalase in NiO nanoparticles showed excellent electrocatalytic activity toward hydrogen peroxide reduction. Also the modified rotating disk electrode shows good analytical performance for amperometric determination of hydrogen peroxide. The resultant catalase/nickel oxide modified glassy carbon electrodes exhibited fast amperometric response (within 2 s) to hydrogen peroxide reduction (with a linear range from 1 microM to 1 mM), excellent stability, long term life and good reproducibility. The apparent Michaelis-Menten constant is calculated to be 0.96(+/-0.05)mM, which shows a large catalytic activity of catalase in the nickel oxide film toward hydrogen peroxide. The excellent electrochemical reversibility of redox couple, high stability, technical simplicity, lake of need for mediators and short preparations times are advantages of this electrode. Finally the activity of biosensor for nitrite reduction was also investigated.