Electrochemical impedance modelling of the reactivities of dendrimeric poly(propylene imine) DNA nanobiosensors

Philosophiae Doctor - PhDIn this thesis, I present the electrochemical studies of three dendrimeric polypropylene imine (PPI) nanomaterials and their applications as a platform in the development of a novel label free DNA nanobiosensor based on electrochemical impedance spectroscopy. Cyclic voltammetry (CV), differentia pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivities of the nanomaterials on glassy carbon electrode (GCE) as the working electrode.South Afric

Carbon Nanofibers Provide a Cationic Rectifier Material::Specific Electrolyte Effects, Bipolar Reactivity, and Prospect for Desalination

We demonstrate that ionic current rectification effects are observed with a film of negatively charged carbon nanofibers (CNFs) deposited as a film or mat onto a 10 μm diameter microhole in poly-ethylene-terephthalate (PET). CNFs are synthesized by using a chemical vapor deposition (CVD) method, followed by oxidation with hydrogen peroxide to introduce carboxyl moieties (providing negative surface charges). CNFs are characterized with transmission electron microscopy, scanning electron microscopy, elemental analysis, and zeta potential measurements. When drop-dried asymmetrically onto a 10 μm diameter cylindrical channel on a 6 μm thick PET substrate and placed as a membrane between two electrolyte compartments, ionic current rectification is observed. Effects of pH, ionic strength, and nature of electrolyte are investigated. Bipolar reactivity of iodide is demonstrated. Potential for future applications in water purification are discussed.</p

Electrochemical studies and sensing of iodate, periodate and sulphite ions at carbon nanotubes/ Prussian blue films modified platinum electrode

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An electrochemical cholesterol biosensor based on a CdTe/CdSe/ZnSe quantum dots—poly (Propylene Imine) dendrimer nanocomposite immobilisation layer

Abstract: We report the preparation of poly (propylene imine) dendrimer (PPI) and CdTe/CdSe/ZnSe quantum dots (QDs) as a suitable platform for the development of an enzyme-based electrochemical cholesterol biosensor with enhanced analytical performance. The mercaptopropionic acid (MPA)-capped CdTe/CdSe/ZnSe QDs was synthesized in an aqueous phase and characterized using photoluminescence (PL) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), X-ray power diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy. The absorption and emission maxima of the QDs red shifted as the reaction time and shell growth increased, indicating the formation of CdTe/CdSe/ZnSe QDs. PPI was electrodeposited on a glassy carbon electrode followed by the deposition (by deep coating) attachment of the QDs onto the PPI dendrimer modified electrode using 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC), and N-hydroxysuccinimide (NHS) as a coupling agent. The biosensor was prepared by incubating the PPI/QDs modified electrode into a solution of cholesterol oxidase (ChOx) for 6 h. The modified electrodes were characterized by voltammetry and impedance spectroscopy. Since efficient electron transfer process between the enzyme cholesterol oxidase (ChOx) and the PPI/QDs-modified electrode was achieved, the cholesterol biosensor (GCE/PPI/QDs/ChOx) was able to detect cholesterol in the range 0.1–10 mM with a detection limit (LOD) of 0.075 mM and sensitivity of 111.16 µA mM−1 cm−2. The biosensor was stable for over a month and had greater selectivity towards the cholesterol molecule

Switching Anionic and Cationic Semi-Permeability in Partially Hydrolyzed Polyacrylonitrile:A pH-Tunable Ionic Rectifier

Membrane materials with semipermeability for anions or for cations are of interest in electrochemical and nanofluidic separation and purification technologies. In this study, partially hydrolyzed polyacrylonitrile (phPAN) is investigated as a pH-switchable anion/cation conductor. When switching from anionic to cationic semipermeability, also the ionic current rectification effect switches for phPAN materials deposited asymmetrically onto a 5, 10, 20, or 40 μm diameter microhole in a 6 μm thick polyethylene-terephthalate (PET) film substrate. Therefore, ionic rectifier behavior can be tuned and used to monitor and characterize semipermeability. Effects of electrolyte type and concentration and pH (relative to the zeta potential at approximately 3.1) are investigated by voltammetry, chronoamperometry, and impedance spectroscopy. A computational model provides good qualitative agreement with the observed electrolyte concentration data. High rectification effects are observed for both cations (pH > 3.1) and anions (pH < 3.1) but only at relatively low ionic strengths

Correction: Baker, P. et al. Electrochemical Aptasensor for Endocrine Disrupting 17β-Estradiol Based on a Poly(3,4-ethylenedioxylthiopene)-Gold Nanocomposite Platform. Sensors 2010, 10, 9872–9890

Herewith please find corrected structures for Figure 8 in our paper published in Sensors in 2010. [...

Surface modified carbon nanomats provide cationic and anionic rectifier membranes in aqueous electrolyte media

Carbon nanofibers (CNFs) are converted into anionic current rectifiers by surface modification with amine functional groups using hydrothermal means (forming modified CNFs, with generation-3 poly (propylene imine) dendrimer, urea and boric acid). To confirm surface charge, morphological changes and carbon nanomat thickness, zeta potential analysis, transmission electron microscopy (TEM) and scanning electron microscopy (SEM), were used. When a dispersion of surface modified carbon nanofibers in DMF is drop-cast asymmetrically to form nanomats onto laser drilled microholes (5, 10, or 20 µm diameter) of poly (ethylene terephthalate) substrates and immersed into aqueous electrolyte solutions, anionic diode behaviour is observed (in contrast to pristine carbon nanofibers, which exhibit cationic diode behaviour). The effects of electrolyte type, ionic strength, and microhole diameter on ionic diode performance were investigated using cyclic voltammetry, chronoamperometry, and impedance spectroscopy. Future applications in desalination are proposed

Electrochemical Aptasensor for Endocrine Disrupting 17β-Estradiol Based on a Poly(3,4-ethylenedioxylthiopene)-Gold Nanocomposite Platform

A simple and highly sensitive electrochemical DNA aptasensor with high affinity for endocrine disrupting 17β-estradiol, was developed. Poly(3,4-ethylenedioxylthiophene) (PEDOT) doped with gold nanoparticles (AuNPs) was electrochemically synthesized and employed for the immobilization of biotinylated aptamer towards the detection of the target. The diffusion coefficient of the nanocomposite was 6.50 × 10−7 cm2 s−1, which showed that the nanocomposite was highly conducting. Electrochemical impedance investigation also revealed the catalytic properties of the nanocomposite with an exchange current value of 2.16 × 10−4 A, compared to 2.14 × 10−5 A obtained for the bare electrode. Streptavidin was covalently attached to the platform using carbodiimide chemistry and the aptamer immobilized via streptavidin—biotin interaction. The electrochemical signal generated from the aptamer–target molecule interaction was monitored electrochemically using cyclic voltammetry and square wave voltammetry in the presence of [Fe(CN)6]−3/−4 as a redox probe. The signal observed shows a current decrease due to interference of the bound 17β-estradiol. The current drop was proportional to the concentration of 17β-estradiol. The PEDOT/AuNP platform exhibited high electroactivity, with increased peak current. The platform was found suitable for the immobilization of the DNAaptamer. The aptasensor was able to distinguish 17β-estradiol from structurally similar endocrine disrupting chemicals denoting its specificity to 17β-estradiol. The detectable concentration range of the 17β-estradiol was 0.1 nM–100 nM, with a detection limit of 0.02 nM

Voltammetric and impedance studies of phenols and Its derivatives at carbon nanotubes/Prussian bluefilms platinum modified electrode

The electrochemical oxidation of phenol (Ph), 4-chlorophenol (4-ClPh) and 4-nitrophenol (4-NPh) at a platinum electrode modified with and without multi-walled carbon nanotubes/Prussian blue nanocomposite in a pH 7.0 phosphate buffer electrolyte was investigated by cyclic voltammetry (CV) and impedance measurements. The modified electrodes were characterised using techniques such as transmission electron microscopy (TEM), electron X-ray dispersive spectroscopy (XRD), cyclic voltammetry (CVs) and electrochemical impedance spectroscopy (EIS)..

Bio-adsorbents for the Removal of Heavy Metals from Water

The work represents the bio-adsorption of arsenic(III) from standard solutions and real water samples using a powdered avocado seed as a bio-adsorbent. The adsorbent was synthesized, demineralized, and characterized by X-ray diffraction (XRD), scanning electron microscope coupled with energy dispersive spectroscopy (SEM-EDS), Fourier transformation infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) theory. Batch adsorption studies were carried out by using avocado seed, and AsIII was analyzed by using inductively coupled plasma optical emission spectroscopy (ICPOES) after optimizing the following parameters: pH 6, analyte concentration 2 mg L−1, bio-adsorbent dosage 0.8 g, contact time 120 min between analyte and adsorbent, and temperature from 22 to 40°C. The adsorption capacity of 93.75 mg/g was obtained, and the Langmuir isotherm was adopted by the adsorbent due to the chemisorption that occurs on the surface between the functional groups of the bio-adsorbent and AsIII