Nazeem Jahed

Metallo-Graphene Nanocomposite Electrocatalytic Platform for the Determination of Toxic Metal Ions

A Nafion-Graphene (Nafion-G) nanocomposite solution in combination with an in situ plated mercury film electrode was used as a highly sensitive electrochemical platform for the determination of Zn2+, Cd2+, Pb2+ and Cu2+ in 0.1 M acetate buffer (pH 4.6) by square-wave anodic stripping voltammetry (SWASV). Various operational parameters such as deposition potential, deposition time and electrode rotation speed were optimized. The Nafion-G nanocomposite sensing platform exhibited improved sensitivity for metal ion detection, in addition to well defined, reproducible and sharp stripping signals. The linear calibration curves ranged from 1 μg L−1 to 7 μg L−1 for individual analysis. The detection limits (3σ blank/slope) obtained were 0.07 μg L−1 for Pb2+, Zn2+ and Cu2+ and 0.08 μg L−1 for Cd2+ at a deposition time of 120 s. For practical applications recovery studies was done by spiking test samples with known concentrations and comparing the results with inductively coupled plasma mass spectrometry (ICP-MS) analyses. This was followed by real sample analysis.

Electrochemical Immunosensor Based on Polythionine/Gold Nanoparticles for the Determination of Aflatoxin B1

An aflatoxin B1 (AFB1) electrochemical immunosensor was developed by the immobilisation of aflatoxin B1-bovine serum albumin (AFB1-BSA) conjugate on a polythionine (PTH)/gold nanoparticles (AuNP)-modified glassy carbon electrode (GCE). The surface of the AFB1-BSA conjugate was covered with horseradish peroxidase (HRP), in order to prevent non-specific binding of the immunosensors with ions in the test solution. The AFB1 immunosensor exhibited a quasi-reversible electrochemistry as indicated by a cyclic voltammetric (CV) peak separation (ΔEp) value of 62 mV. The experimental procedure for the detection of AFB1 involved the setting up of a competition between free AFB1 and the immobilised AFB1-BSA conjugate for the binding sites of free anti-aflatoxin B1 (anti-AFB1) antibody. The immunosensors differential pulse voltammetry (DPV) responses (peak currents) decreased as the concentration of free AFB1 increased within a dynamic linear range (DLR) of 0.6 - 2.4 ng/mL AFB1 and a limit of detection (LOD) of 0.07 ng/mL AFB1. This immunosensing procedure eliminates the need for enzyme-labeled secondary antibodies normally used in conventional ELISA–based immunosensors.

Electrochemical detection of glyphosate herbicide using horseradish peroxidase immobilized on sulfonated polymer matrix.

This paper describes the use of horseradish peroxidase (HRP) based biosensor for novel detection of glyphosate herbicide. The biosensor was prepared by electrochemically depositing poly(2,5-dimethoxyaniline) (PDMA) doped with poly(4-styrenesulfonic acid) (PSS) onto the surface of a gold electrode followed by electrostatic attachment of the enzyme HRP onto the PDMA-PSS composite film. Fourier transform infrared (FTIR) and UV-Vis spectrometry inferred that HRP was not denatured during its immobilization on PDMA-PSS composite film. The biosensing principle was based on the determination of the cathodic responses of the immobilized HRP to H(2)O(2), before and after incubation in glyphosate standard solutions. Glyphosate inhibited the activity of HRP causing a decrease in its response to H(2)O(2). The determination of glyphosate was achieved in the range of 0.25-14.0 microg L(-1) with a detection limit of 1.70 microg L(-1). The apparent Michaelis-Menten constant (calculated for the HRP/PDMA-PSS biosensor in the presence and absence of glyphosate was found to be 7.73 microM and 7.95 microM respectively.

An Electrochemical DNA Biosensor Developed on a Nanocomposite Platform of Gold and Poly(propyleneimine) Dendrimer

An electrochemical DNA nanobiosensor was prepared by immobilization of a 20mer thiolated probe DNA on electro-deposited generation 4 (G4) poly(propyleneimine) dendrimer (PPI) doped with gold nanoparticles (AuNP) as platform, on a glassy carbon electrode (GCE). Field emission scanning electron microscopy results confirmed the co-deposition of PPI (which was linked to the carbon electrode surface by C-N covalent bonds) and AuNP ca 60 nm. Voltammetric interrogations showed that the platform (GCE/PPI-AuNP) was conducting and exhibited reversible electrochemistry (E°′ = 235 mV) in pH 7.2 phosphate buffer saline solution (PBS) due to the PPI component. The redox chemistry of PPI was pH dependent and involves a two electron, one proton process, as interpreted from a 28 mV/pH value obtained from pH studies. The charge transfer resistance (Rct) from the electrochemical impedance spectroscopy (EIS) profiles of GCE/PPI-AuNP monitored with ferro/ferricyanide (Fe(CN)63-/4-) redox probe, decreased by 81% compared to bare GCE. The conductivity (in PBS) and reduced Rct (in Fe(CN)63-/4-) values confirmed PPI-AuNP as a suitable electron transfer mediator platform for voltammetric and impedimetric DNA biosensor. The DNA probe was effectively wired onto the GCE/PPI-AuNP via Au-S linkage and electrostatic interactions. The nanobiosensor responses to target DNA which gave a dynamic linear range of 0.01 - 5 nM in PBS was based on the changes in Rct values using Fe(CN)63-/4- redox probe.

Novel therapeutic biosensor for indinavir—A protease inhibitor antiretroviral drug

An amperometric drug metabolism biosensor consisting of cytochrome P450-3A4 (CYP3A4) encapsulated in a didodecyldimethylammonium bromide (DDAB) vesicular system on a Pt disk electrode was developed for the determination of indinavir, a protease inhibitor antiretroviral drug. Cyclic, square wave and pulse voltammetric responses of the bioelectrode showed quasi-reversible electrochemistry of the Fe(3+)/Fe(2+) redox species of the heme thiolate CYP3A4 enzyme under aerobic and anaerobic conditions. The biosensor exhibited excellent response to indinavir with a detection limit and response time of 6.158 x 10(-2)mgL(-1), and 40s, respectively. The detection limit is well below the plasma concentration of indinavir (8h after intake) which range from 0.13 to 8.6mgL(-1).

Characterization of α,ω-dihydroxypolystyrene by gradient polymer elution chromatography and two-dimensional liquid chromatography

Gradient polymer elution chromatography (GPEC) and GPEC × size-exclusion chromatography (SEC) two-dimensional liquid chromatography (2D-LC) techniques were employed to characterize functionality of hydroxy-telechelic polystyrene (polySt) prepared by two different methods. The first method involved the synthesis of hydroxy-functionalized polySt via atom transfer radical polymerization (ATRP) using a hydroxy-containing initiator and subsequent atom transfer radical coupling (ATRC). For the second method, α,ω-dibromo-polySt was synthesized by ATRP using a dibromo-containing initiator, followed by nucleophilic substitution with azide and click reactions. Utilizing GPEC analysis, the polymers were separated according to their hydroxy functionality. The polySt chains containing less hydroxy groups eluted faster. GPEC analysis successfully separated dihydroxy-polySt from monohydroxy- and nonhydroxy-polySt. For the hydroxy-telechelic polySt obtained from ATRC, GPEC analysis provided quantitative information of the termination by coupling during ATRP and the efficiency of ATRC. During the post-polymerization modification of bromotelechelic polySt by nucleophilic substitution and click reactions, the chain-end functionality of the polySt was changed, while the molecular weight of the polymer remained constant. The powerful ability of GPEC was further demonstrated by sufficiently separating polymers with similar molecular weight but different hydroxy functionality.

Towards the synthesis of chiral isochromanquinones. The use of Corey–Bakshi–Shibata reductions

(1R,3R,4S)-3,4-Dihydro-4-hydroxy-6-methoxy-1,3-dimethylisochroman-5,8-dione has been synthesized in 65% ee from (1R,3R,4S)-5-benzyloxy-3,4-dihydro-4-hydroxy-6-methoxy-1,3-dimethylisochroman by catalytic hydrogenolysis followed by Fremys salt oxidation of the derived phenol. The latter isochroman was synthesized from a mercury(II) mediated oxidative cyclization of (R)-3-benzyloxy-4-methoxy-1-(1′-hydroxyethyl)-2-prop-1′-enylbenzene which in turn was obtained in 75% ee from the chiral reduction of 1-acetyl-3-benzyloxy-4-methoxy-2-prop-1′-enylbenzene with borane–methylsulfide complex in the presence of the Corey–Bakshi–Shibata catalyst.

The synthesis of R-3-alkoxy-1-(1′-hydroxyethyl)-4-methoxy-2-(1″-propenyl)benzenes utilizing Corey–Bakshi–Shibata asymmetric reductions

Pyrolysis of the 3-O-allyl derivative 7 of isovanillin followed by alkylation of the derived allylphenol 8 afforded a series of benzaldehyde derivatives 9-11 each of which was transformed by initial treatment with methylmagnesium bromide followed by oxidation of the corresponding alcohols with activated manganese dioxide into a series of ketones 15-17. Palladium(0) catalysed isomerization of the double bond in the prop-2′-enyl side-chain afforded ketones 36-38 which were subjected to the Corey-Bakshi-Shibata asymmetric reduction protocol to afford the R-3-alkoxy-1-(1′-hydroxyethyl)-4-methoxy-2-(1″-propenyl) benzenes 42-44 in yields of approximately 60% and with ees of 75%.

Polyester Sulphonic Acid Interstitial Nanocomposite Platform for Peroxide Biosensor

A novel enzyme immobilization platform was prepared on a platinum disk working electrode by polymerizing aniline inside the interstitial pores of polyester sulphonic acid sodium salt (PESA). Scanning electron microscopy study showed the formation of homogeneous sulphonated polyaniline (PANI) nanotubes (∼90 nm) and thermogravimetric analysis (TGA) confirmed that the nanotubes were stable up to 230 °C. The PANI:PESA nanocomposite showed a quasi-reversible redox behaviour in phosphate buffer saline. Horseradish peroxidase (HRP) was immobilized on to this modified electrode for hydrogen peroxide detection. The biosensor gave a sensitivity of 1.33 μA (μM)-1 and a detection limit of 0.185 μM for H2O2. Stability experiments showed that the biosensor retained more than 64% of its initial sensitivity over four days of storage at 4 °C.

3-Mercaptopropionic Acid Capped Ga2Se3 nanocrystal-CYP3A4 Biosensor for the Determination of 17-Alpha-Ethinyl Estradiol in Water

Water soluble and biocompatible 3-mercaptopropionic acid capped gallium selenide nanocrystals, were synthesized from hydrated gallium (III) perchlorate and selenide ions. The 3-mercaptopropionic acid capped gallium selenide nanocrystals, was non-fluorescent but showed a sharp UV-vis absorption maximum at 250 nm.The synthesized nanoparticle was used to develop an electrochemical biosensor for the detection of 17-alpha-ethinyl estradiol, an estrogenic endocrine disrupting compound (e-EDC). The biosensor was fabricated by potentiostatic deposition of novel gallium selenide nanocrystals on a L-cystine modified gold electrode, followed by covalent coupling of genetically engineered cytochrome P450-3A4 (CYP3A4), a Heme containing enzyme. The biosensor gave an electrochemical response at about-220 mV. The results revealed that 3-Mecarptopropanoic acid capped Gallium Selenide nanocrystals can be used in conjunction with CYP3A4 as an electrode modifier for the detection of 17-alpha ethinyl estradiol. The 3-Mecarptopropanoic acid capped Gallium Selenide nanoparticles exhibited a semiconductor like behaviour.