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Rahman Hallaj 's Owned Publications
  • Glucose biosensor prepared by glucose oxidase encapsulated sol-gel and carbon-nanotube-modified basal plane pyrolytic graphite electrode. (2004) A new glucose biosensor has been fabricated by immobilizing glucose oxidase into a sol-gel composite at the surface of a basal plane pyrolytic graphite (bppg) electrode modified with multiwall carbon ...nanotube. First, the bppg electrode is subjected to abrasive immobilization of carbon nanotubes by gently rubbing the electrode surface on a filter paper supporting the carbon nanotubes. Second, the electrode surface is covered with a thin film of a sol-gel composite containing encapsulated glucose oxidase. The carbon nanotubes offer excellent electrocatalytic activity toward reduction and oxidation of hydrogen peroxide liberated in the enzymatic reaction between glucose oxidase and glucose, enabling sensitive determination of glucose. The amperometric detection of glucose is carried out at 0.3 V (vs saturated calomel electrode) in 0.05 M phosphate buffer solution (pH 7.4) with linear response range of 0.2-20 mM glucose, sensitivity of 196 nA/mM, and detection limit of 50 microM (S/N=3). The response time of the electrode is < 5s when it is stored dried at 4 degrees C, the sensor showed almost no change in the analytical performance after operation for 3 weeks. The present carbon nanotube sol-gel biocomposite glucose oxidase sensor showed excellent properties for the sensitive determination of glucose with good reproducibility, remarkable stability, and rapid response and in comparison to bulk modified composite biosensors the amounts of enzyme and carbon nanotube needed for electrode fabrication are dramatically decreased.Show more Salimi A,Compton RG,Hallaj R Analytical biochemistry
  • Catalytic oxidation of thiols at preheated glassy carbon electrode modified with abrasive immobilization of multiwall carbon nanotubes: applications to amperometric detection of thiocytosine, l-cysteine and glutathione. (2005) The performance of preheated glassy carbon electrode modified with carbon nanotubes is described. First glassy carbon electrode is heated for 5min at 50 degrees C, then abrasive immobilization of mult...iwall carbon nanotubes on a preheated glassy carbon electrode was achieved by gentle rubbing of electrode surface on a filter paper supporting carbon nanotubes. Carbon nanotubes (CNTs)-modified glassy carbon electrodes exhibit strong and stable electrocatalytic response toward thiols oxidation in wide pH range. These properties permit an important decrease in over voltage for the oxidation of thiocytosine, glutathione and l-cysteine, as well as a dramatic increase in the peak currents in comparison with bare glassy carbon electrode. Furthermore, the thiols amperometric response of the coated electrodes is extremely stable, with more than 95% of the initial activity after 30min stirring of 0.1mM thiols. The electrocatalytic behavior is further exploited as a sensitive detection scheme for thiols detection by hydrodynamic amperometry. The substantial decrease in the overvoltage of the thiols oxidation associated with a stable amperometric response and antifouling properties of nanotubes films allow the development of highly sensitive thiols sensor without using any redox mediator. Such ability of carbon nanotubes to promote the thiols electron transfer reaction, short response time (5s) and long-term stability, low detection limit, extended linear concentration range, high sensitivity suggest great promise for thiols amperometric sensors and detector for chromatographic analysis of thiol derivatives.Show more Salimi A,Hallaj R Talanta
  • Simultaneous determination of ascorbic acid, uric acid and neurotransmitters with a carbon ceramic electrode prepared by sol-gel technique. (2006) A sol-gel carbon composite electrode (CCE) has been prepared by mixing a sol-gel precursor (e.g. methyltrimethoxysilane) and carbon powder without adding any electron transfer mediator or specific rea...gents. It was demonstrated that this sensor can be used for simultaneous determination ascorbic acid, neurotransmitters (dopamine and adrenaline) and uric acid. Direct electrochemical oxidation of ascorbic acid, uric acid and catecholamines at a carbon composite electrode was investigated. The experimental results were compared with other common carbon based electrodes, specifically, boron doped diamond, glassy carbon, graphite and carbon paste electrodes. It was found that the CCE shows a significantly higher of reversibility for dopamine. In addition, in comparison to the other electrodes used, for CCE the oxidation peaks of uric acid, ascorbic acid and catecholamines in cyclic and square wave voltammetry were well resolved at the low positive potential with good sensitivity. The advantages of this sensor were high sensitivity, inherent stability and simplicity and ability for simultaneous determination of uric acid, catecholamines and ascorbic acid without using any chromatography or separation systems. The analytical performance of this sensor has been evaluated for detection of biological molecules in urine and serum as real samples.Show more Salimi A,Mamkhezri H,Hallaj R Talanta
  • Amperometric and voltammetric detection of hydrazine using glassy carbon electrodes modified with carbon nanotubes and catechol derivatives. (2008) A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with carbon nanotubes (CNTs) and catechol compounds. First, 25 microL of DMSO-CNTs solutions (0.4 mg/mL) was cast on... the surface of GC electrode and dried in air to form a CNTs film. Then the GC/CNTs modified electrode immersed into a chlorogenic acid, catechine hydrate and caffeic acid solution (electroless deposition) for a short period of time (2-80s). The cyclic voltammogram of the modified electrode in aqueous solution shows a pair of well-defined, stable and nearly reversible redox couple (quinone/hydroquinone) with surface confined characteristics. The combination of unique electronic and electrocatalytic properties of CNTs and catechol compounds results in a remarkable synergistic augmentation on the response. The electrochemical reversibility and stability of modified electrode prepared with incorporation of catechol compound into CNTs film was evaluated and compared with usual methods for attachment of catechols to electrode surfaces. The transfer coefficient (alpha), heterogeneous electron transfer rate constants (k(s)) and surface concentrations (Gamma) for GC/CNTs/catechol compound modified electrodes were calculated through the cyclic voltammetry technique. The modified electrodes showed excellent catalytic activity, fast response time and high sensitivity toward oxidation of hydrazine in phosphate buffer solutions at pH range 4-8. The modified electrode retains its initial response for at least 2 months if stored in dry ambient condition. The properties of modified electrodes as an amperometric sensor for micromolar or lower concentration detection of hydrazine have been characterized.Show more Salimi A,Miranzadeh L,Hallaj R Talanta
  • Immobilization of hemoglobin on electrodeposited cobalt-oxide nanoparticles: direct voltammetry and electrocatalytic activity. (2007) Cyclic voltammetry at potential range -1.1 to 0.5 V from aqueous buffer solution (pH 7) containing CoCl(2) produced a well defined cobalt oxide (CoOx) nanoparticles deposited on the surface of glassy ...carbon electrode. The morphology of the modified surface and cobalt oxide formation was examined with SEM and cyclic voltammetry techniques. Hemoglobin (Hb) was successfully immobilized in cobalt-oxide nanoparticles modified glassy carbon electrode. Immobilization of hemoglobin onto cobalt oxide nanoparticles have been investigated by cyclic voltammetry and UV-visible spectroscopy. The entrapped protein can take direct electron transfer in cobalt-oxide film. A pair of well defined, quasi-reversible cyclic voltammetric peaks at about -0.08 V vs. SCE (pH 7), characteristic of heme redox couple (Fe(III)/Fe(II)) of hemoglobin, and the response showed surface controlled electrode process. The dependence of formal potential (E(0)) on the solution pH (56 mV pH(-1)) indicated that the direct electron transfer reaction of hemoglobin was a one-electron transfer coupled with a one proton transfer reaction process. The average surface coverage of Hb immobilized on the cobalt oxide nanoparticles was about 5.2536x10(-11) mol cm(-2), indicating high loading ability of nanoparticles for hemoglobin entrapment. The heterogeneous electron transfer rate constant (k(s)) was 1.43 s(-1), indicating great of facilitation of the electron transfer between Hb and electrodeposited cobalt oxide nanoparticles. Modified electrode exhibits a remarkable electrocatalytic activity for the reduction of hydrogen peroxide and oxygen. The Michaels-Menten constant K(m) of 0.38 mM, indicating that the Hb immobilized onto cobalt oxide film retained its peroxidases activity. The biosensor exhibited a fast amperometric response <5 s, a linear response over a wide concentration range 5 microM to 700 microM and a low detection limit 0.5 microM. According to the direct electron transfer property and enhanced activity of Hb in cobalt oxide film, a third generation reagentless biosensor without using any electron transfer mediator or specific reagent can be constructed for determination of hydrogen peroxide in anaerobic solutions.Show more Salimi A,Hallaj R,Soltanian S Biophysical chemistry
  • Immobilization of [Cu(bpy)2]Br2 complex onto a glassy carbon electrode modified with alpha-SiMo12O40(4-) and single walled carbon nanotubes: application to nanomolar detection of hydrogen peroxide and bromate. (2009) A simple procedure has been used for preparation of modified glassy carbon electrode with carbon nanotubes and copper complex. Copper complex [Cu(bpy)(2)]Br(2) was immobilized onto glassy carbon (GC) ...electrode modified with silicomolybdate, alpha-SiMo(12)O(40)(4-) and single walled carbon nanotubes (SWCNTs). Copper complex and silicomolybdate irreversibly and strongly adsorbed onto GC electrode modified with CNTs. Electrostatic interactions between polyoxometalates (POMs) anions and Cu-complex, cations mentioned as an effective method for fabrication of three-dimensional structures. The modified electrode shows three reversible redox couples for polyoxometalate and one redox couple for Cu-complex at wide range of pH values. The electrochemical behavior, stability and electron transfer kinetics of the adsorbed redox couples were investigated using cyclic voltammetry. Due to electrostatic interaction, copper complex immobilized onto GC/CNTs/alpha-SiMo(12)O(40)(4-) electrode shows more stable voltammetric response compared to GC/CNTs/Cu-complex modified electrode. In comparison to GC/CNTs/Cu-complex the GC/CNTs/alpha-SiMo(12)O(40)(4-) modified electrodes shows excellent electrocatalytic activity toward reduction H(2)O(2) and BrO(3)(-) at more reduced overpotential. The catalytic rate constants for catalytic reduction hydrogen peroxide and bromate were 4.5(+/-0.2)x10(3) M(-1) s(-1) and 3.0(+/-0.10)x10(3) M(-1) s(-1), respectively. The hydrodynamic amperommetry technique at 0.08 V was used for detection of nanomolar concentration of hydrogen peroxide and bromate. Detection limit, sensitivity and linear concentration range proposed sensor for bromate and hydrogen peroxide detection were 1.1 nM and 6.7 nA nM(-1), 10 nM-20 microM, 1 nM, 5.5 nA nM(-1) and 10 nM-18 microM, respectively.Show more Salimi A,Korani A,Hallaj R,Khoshnavazi R,Hadadzadeh H Analytica chimica acta
  • Electrocatalytic oxidation of NADH at electrogenerated NAD+ oxidation product immobilized onto multiwalled carbon nanotubes/ionic liquid nanocomposite: application to ethanol biosensing. (2012) The multiwalled carbon nanotubes/N-butyl-N-methyl-pyrolydinium-bis(trifluoromethylsulfonyl)imide [C(4)mpyr][NTf(2)] ionic liquid (MWCNTs/IL) modified glassy carbon (GC) electrode has been utilized as ...a platform to immobilize electrogenerated NAD(+) oxidation products (Ox-P(NAD(+))). During potential cycling, the adenine moiety of NAD(+) molecule is oxidized and gives rise to generation of a redox active system that shows great electrocatalytic activity toward NADH oxidation. The cyclic voltammetric results indicated the ability of MWCNTs/IL/Ox-P(NAD(+)) modified GC electrode to catalyze the oxidation of NADH at a very low potential (0.05 V vs. Ag/AgCl) and subsequently, a substantial decrease in the overpotential by about 600 mV compared with the bare GC electrode. This modified electrode thus allowed highly sensitive amperometric detection of NADH with a very low limit of detection (2 × 10(-8) mol L(-1)), low applied potential (+0.05 V) at concentration range up to 4.2 × 10(-5) mol L(-1) and minimum of surface fouling. High ability of MWCNTs/IL/Ox-P(NAD(+)) to promote electron transfer between NADH and the electrode suggested a new promising biocompatible platform for development of dehydrogenase-based amperometric biosensors. With alcohol dehydrogenase (ADH) as a model enzyme, ethanol sensing ability of the proposed system was examined. The amperometric response of the biosensor increased linearly with increasing ethanol concentration in two concentration ranges, 5 × 10(-6)-6 × 10(-5) and 6 × 10(-5)-9 × 10(-4) mol L(-1) with detection limit of 5 × 10(-7) mol L(-1) and rapid response of 10s. Furthermore, the interference effects of redox active species, such as ascorbic acid, uric acid, glucose and acetaminophen for the proposed biosensor are negligible. Finally, the ability of the proposed biosensor for detection of ethanol in real complex samples was successfully demonstrated.Show more Teymourian H,Salimi A,Hallaj R Talanta
  • Layer by layer assembly of catalase and amine-terminated ionic liquid onto titanium nitride nanoparticles modified glassy carbon electrode: study of direct voltammetry and bioelectrocatalytic activity. (2012) A novel, simple and facile layer by layer (LBL) approach is used for modification of glassy carbon (GC) electrode with multilayer of catalase and nanocomposite containing 1-(3-Aminopropyl)-3-methylimi...dazolium bromide (amine terminated ionic liquid (NH(2)-IL)) and titanium nitride nanoparticles (TiNnp). First a thin layer of NH(2)-IL is covalently attached to GC/TiNnp electrode using electro-oxidation method. Then, with alternative self assemble positively charged NH(2)-IL and negatively charged catalase a sensitive H(2)O(2) biosensor is constructed, whose response is directly correlated to the number of bilayers. The surface coverage of active catalase per bilayer, heterogeneous electron transfer rate constant (k(s)) and Michaelis-Menten constant (K(M)) of immobilized catalase were 3.32×10(-12) mol cm(-2), 5.28s(-1) and 1.1 mM, respectively. The biosensor shows good stability, high reproducibility, long life-time, and fast amperometric response with the high sensitivity of 380 μA mM(-1)cm(-2) and low detection limit of 100 nM at concentration range up to 2.1 mM.Show more Saadati S,Salimi A,Hallaj R,Rostami A Analytica chimica acta
  • Highly sensitive amperometric sensor for micromolar detection of trichloroacetic acid based on multiwalled carbon nanotubes and Fe(II)-phtalocyanine modified glassy carbon electrode. (2013) A highly sensitive electrochemical sensor for the detection of trichloroacetic acid (TCA) is developed by subsequent immobilization of phthalocyanine (Pc) and Fe(II) onto multiwalled carbon nanotubes ...(MWCNTs) modified glassy carbon (GC) electrode. The GC/MWCNTs/Pc/Fe(II) electrode showed a pair of well-defined and nearly reversible redox couple correspondent to (Fe(III)Pc/Fe(II)Pc) with surface-confined characteristics. The surface coverage (Γ) and heterogeneous electron transfer rate constant (ks) of immobilized Fe(II)-Pc were calculated as 1.26×10(-10) mol cm(-2) and 28.13 s(-1), respectively. Excellent electrocatalytic activity of the proposed GC/MWCNTs/Pc/Fe(II) system toward TCA reduction has been indicated and the three consequent irreversible peaks for electroreduction of CCl3COOH to CH3COOH have been clearly seen. The observed chronoamperometric currents are linearly increased with the concentration of TCA at concentration range up to 20mM. Detection limit and sensitivity of the modified electrode were 2.0 μM and 0.10 μA μM(-1) cm(-2), respectively. The applicability of the sensor for TCA detection in real samples was tested. The obtained results suggest that the proposed system can serve as a promising electrochemical platform for TCA detection.Show more Kurd M,Salimi A,Hallaj R Materials science & engineering. C, Materials for biological applications
  • A highly sensitive prostate-specific antigen immunosensor based on gold nanoparticles/PAMAM dendrimer loaded on MWCNTS/chitosan/ionic liquid nanocomposite. (2014) We have developed a sensitive electrochemical immunosensor for the detection of prostate-specific antigen (PSA), based on covalently immobilizing of anti-PSA and redox mediator (thionine) onto gold na...noparticles-incorporated polyamidoamine dendrimer (AuNPs-PAMAM) and multiwalled carbon nanotubes/ionic liquid/chitosan nanocomposite (MWCNTs/IL/Chit) as the support platform. The MWCNTs/IL/Chit nanocomposite and synthesized AuNPs were characterized using SEM and TEM microscopy techniques. Greatly amplified immunoassay was established by sandwiching the antigen between anti-PSA immobilized on the MWCNTs/IL/Chit/AuNPs-PAMAM interface and anti-PSA labeled with horseradish peroxidase (HRP-labeled anti-PSA) as secondary antibody. Phtaloyl chloride (Ph) was used as linking agent for the subsequent immobilization of AuNPs-PAMAM onto platform and anti-PSA antibody and thionine onto AuNPs-PAMAM dendrimer. The increased electrocatalytic reduction of H2O2 by HRP was monitored by differential pulse voltammetry technique. Under optimized condition the calibration curve for PSA concentration was linear up to 80 ng ml(-1) with detection limit (signal-to-noise ratio of 3) of 1 pg ml(-1). AuNPs-PAMAM dendrimer as platform not only increased the amount of thionine and PSA antibody but also the electron transfer process accelerated by encapsulated AuNPs. Moreover, the proposed PSA immunosensor exhibited excellent stability and reproducibility. Accurate detection of PSA in human serum samples was demonstrated by comparison to standard ELISA assays. In addition, impedance technique was used as simple, rapid, low cost label free analytical method for PSA measurement with detection limit of 0.5 ng ml(-1) at concentration range up to 25 ng ml(-1). The results indicate that the present protocol is quite promising in developing other electrochemical immunosensors.Show more Kavosi B,Salimi A,Hallaj R,Amani K Biosensors & bioelectronics
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