Lindsay Wilson

Application on Gold Nanoparticles-Dotted 4-Nitrophenylazo Graphene in a Label-Free Impedimetric Deoxynivalenol Immunosensor

In this paper, we report a new concept to construct a label-free electrochemical inhibition-based immunosensor for the detection of the mycotoxin deoxynivalenol (DON) in cereal samples. The electrochemical impedance spectroscopy of tris(bipyridine) ruthenium (II) chloride was used as a marker enhanced with gold nanoparticles-dotted 4-nitrophenylazo functionalized graphene (AuNp/G/PhNO2) nanocatalyst mediated in Nafion on a glassy carbon electrode. Under the optimized conditions, the formation of immunocomplexes inhibited electron flow and increased the charge transfer resistance of the sensing interface linearly. The change in impedance was proportional to DON concentrations in the range of 6–30 ng/mL with a sensitivity and detection limit of 32.14 ΩL/ng and 0.3 μg/mL, respectively, which compares favorably with the ELISA result. The proposed sensor had a stability of 80.3%, good precision and selectivity in DON standard solution containing different interfering agents, indicating promising application prospect for this strategy in designing impedimetric, electrochemiluminescent, voltammetric or amperometric sensors.

A Fumonisins Immunosensor Based on Polyanilino-Carbon Nanotubes Doped with Palladium Telluride Quantum Dots

An impedimetric immunosensor for fumonisins was developed based on poly(2,5-dimethoxyaniline)-multi-wall carbon nanotubes doped with palladium telluride quantum dots onto a glassy carbon surface. The composite was assembled by a layer-by-layer method to form a multilayer film of quantum dots (QDs) and poly(2,5-dimethoxyaniline)-multi-wall carbon nanotubes (PDMA-MWCNT). Preparation of the electrochemical immunosensor for fumonisins involved drop-coating of fumonisins antibody onto the composite modified glassy carbon electrode. The electrochemical impedance spectroscopy response of the FB1 immunosensor (GCE/PT-PDMA-MWCNT/anti-Fms-BSA) gave a linear range of 7 to 49 ng L−1 and the corresponding sensitivity and detection limits were 0.0162 kΩ L ng−1 and 0.46 pg L−1, respectively, hence the limit of detection of the GCE/PT-PDMA-MWCNT immunosensor for fumonisins in corn certified material was calculated to be 0.014 and 0.011 ppm for FB1, and FB2 and FB3, respectively. These results are lower than those obtained by ELISA, a provisional maximum tolerable daily intake (PMTDI) for fumonisins (the sum of FB1, FB2, and FB3) established by the Joint FAO/WHO expert committee on food additives and contaminants of 2 μg kg−1 and the maximum level recommended by the U.S. Food and Drug Administration (FDA) for protection of human consumption (2–4 mg L−1).

Electrochemical Aptatoxisensor Responses on Nanocomposites containing electro-deposited silver nanoparticles on poly(propyleneimine) dendrimer for the detection of microcystin-lr in freshwater

A sensitive and reagentless electrochemical aptatoxisensor was developed on cobalt (II) salicylaldiimine metallodendrimer (SDD–Co(II)) doped with electro-synthesized silver nanoparticles (AgNPs) for microcystin-LR (L, l-leucine; R, l-arginine), or MC-LR, detection in the nanomolar range. The GCE|SDD–Co(II)|AgNPs aptatoxisensor was fabricated with 5’ thiolated aptamer through self-assembly on the modified surface of the glassy carbon electrode (GCE) and the electronic response was measured using cyclic voltammetry (CV). Specific binding of MC-LR with the aptamer on GCE|SDD–Co(II)|AgNPs aptatoxisensor caused the formation of a complex that resulted in steric hindrance and electrostatic repulsion culminating in variation of the corresponding peak current of the electrochemical probe. The aptatoxisensor showed a linear response for MC-LR between 0.1 and 1.1 µg·L−1 and the calculated limit of detection (LOD) was 0.04 µg·L−1. In the detection of MC-LR in water samples, the aptatoxisensor proved to be highly sensitive and stable, performed well in the presence of interfering analog and was comparable to the conventional analytical techniques. The results demonstrate that the constructed MC-LR aptatoxisensor is a suitable device for routine quantification of MC-LR in freshwater and environmental samples.

Label Free Poly(2,5-dimethoxyaniline)–Multi-Walled Carbon Nanotubes Impedimetric Immunosensor for Fumonisin B1 Detection

An impedimetric immunosensor for fumonisin B1 (FB1) was developed from a poly(2,5-dimethoxyaniline)-multi-walled carbon nanotube (PDMA-MWCNT) composite on the surface of glassy carbon electrode (GCE). The composite was prepared electrochemically and characterized using cyclic voltammetry. The preparation of the FB1 immunosensor involved the drop-coating of a bovine serum albumin mixture of the anti-fumonisin antibody (anti-Fms) onto the composite polymer-modified GCE. The electrochemical impedance spectroscopy (EIS) responses of the FB1 immunosensor (GCE/PDMA-MWCNT/anti-Fms) have a linear range of 7 to 49 ng·L−1, and the corresponding sensitivity and detection limits are 0.272 kΩ L·ng−1 and 3.8 pg·L−1, respectively. The limit of detection of the immunosensor for certified corn sample (i.e., certified reference material) is 0.014 ppm FB1, which is in excellent agreement with the value published by the vendors and significantly more accurate than that obtained with enzyme-linked immunosorbent assay (ELISA).

Electrochemical Ultra-Low Detection of Isoniazid Using a Salicylaldamine Functionalised G1-DAB-(NH2)4 Dendritic Sensor vs. UV-VIS Spectrophotometric Detection

A poly(propyleneimine) based dendrimer was synthesised and successfully functionalised with a copper centre within its branches. The dendrimer and corresponding metallodendrimer were successfully characterised using FTIR, HR-TEM and HR-SEM in order to determine the effect of the inclusion of copper into the dendritic structure. The incorporation of copper caused crystallinity as revealed in the HR-TEM and a sheet-like morphology as shown in the HR-SEM images. The resulting metallodendrimer was then applied as an electrocatalytic platform for the sensing of a first line TB drug called isoniazid. This method was compared to a routine laboratory detection using UV-Vis and was found to be much more sensitive to trace amounts of isoniazid in solution. The electrochemical detection was found to have a limit of detection (LOD) of 0.233 nM compared to 11.47 nM using the Ultraviolet-visible spectroscopy method.

A Novel Polyaniline Nanocomposite with Doping Effects of Poly(Methyl Methacrylate) and TiO2 Nanoparticles

Polyaniline (PANI) is a globally investigated conductive polymer with a variety of applications in various fields due to its ease of synthesis and modification. One method of enhancing the physico-chemical properties and processability of PANI is the incorporation of polymers and nanoparticles to form composite and hybrid materials with new features. This study reports the electrochemical synthesis of a polyaniline nanocomposite that incorporates titanium dioxide nanoparticles (TiO2) and poly (methyl methacrylate) (PMMA). The significant effects of PMMA and TiO2 nanoparticles on structural, morphological, optical and electrochemical properties of native polyaniline were investigated using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, cyclic voltammetry (CV) and square wave voltammetry (SWV). The formation and deformation of relevant peaks observed from the FTIR spectra confirm the intrusion of PMMA and TiO2 into PANI while the voltammetric results show that the incorporation of both dopants significantly enhanced the electroactivity of PANI in a neutral pH medium.

Cytochrome P450-3A4/Copper-Poly(Propylene Imine)-Polypyrrole Star Co-Polymer Nanobiosensor System for Delavirdine - A Non-Nucleoside Reverse Transcriptase Inhibitor HIV Drug

HIV and AIDS are among the world’s pandemics that pose serious concern to almost every individual in the world. With the current level of availability of anti-retroviral (ARV) drugs and the ease of accessibility of treatment in many countries such as South Africa, the disease can be controlled by suppressing the viral load of an infected individual. These anti HIV drugs such as delavirdine are metabolised by enzymes which are found in the liver microsomes, particularly those of the cytochrome P450 family. Due to the fact that the metabolic rate of a patient determines the effect of the drug, the drug could either have a beneficial or an adverse effect once it is administered. It is therefore imperative that the metabolic profile of a patient is determined to ensure proper dosing of the ARV drugs. In this study a nanobiosensor system was devised and used for the determination of the metabolism of delavirdine (DLV), a non-nucleoside reverse transcriptase inhibitor (NNRTI) ARV drug. The nanobiosensor was prepared by the entrapment of the isoenzyme CYP3A4 into a pre-formed electro active carrier matrice consisting of a dendrimeric copper generation-2 poly(propylene imine)-co-polypyrrole star copolymer (Cu(G2PPI)-co-PPy). The metallo-dendrimer was used as a host for the enzyme and provided the necessary bio-compatible environment that allowed the direct transfer of electrons between the enzyme’s active centres and platinum electrode surface. (Cu(G2PPI)-co-PPy) was prepared by the incorporation of the copper metal into the G2PPI and the electropolymerization of pyrrole onto the Cu(G2PPI). The incorporation of Cu into G2PPI was determined by Fourier transform infrared (FTIR) spectroscopy which did not show the presence of the Cu but showed an increase in the intensities of the peaks after the incorporation. The surface morphology of Cu(G2PPI-2Py) was confirmed by the use of high resolution scanning electron microscopy (HRSEM) which showed a difference in the surface morphology of the dendrimer moiety with the addition of the copper metal. The HRSEM images after Cu incorporation resulted in the change from rough surface to smooth surface with open cavities which were essential for the entrapment of the biological systems (CYP3A4). The energy band gap of (Cu(G2PPI)-co-PPy) were determined to be 3.85 eV, signifying that the copolymer is characteristic of a biocompatible semiconductive platform for applications in biosensors. The star copolymer (Cu(G2PPI)-co-PPy) was characterized using cyclic voltammetry where it was confirmed that the material was electroactive and conducting due to electron movement along the polymer chain. A diffusion co-efficient (Do) value of 8.64 x 10-5 cm2/s was determined for the material indicating a slow electron transfer kinetics within the diffusion layer. The resultant nanobiosensor parameters include a dynamic linear range (DLR) of 0.01-0.06 nM, a limit of detection (LOD) of 0.025 nM and a sensitivity value of 0.379 μA/nM.