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).

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).

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.

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.

Amperometric nanobiosensor for quantitative determination of glyphosate and glufosinate residues in corn samples

This study presents a simple, sensitive, rapid, and low-cost amperometric method for direct and quantitative determination of glyphosate and glufosinate herbicides. Electrochemical synthesis and characterization of poly(2,5-dimethoxyaniline)-poly(4-styrenesulfonic acid) (PDMA-PSS) nanoparticles was achieved by cyclic voltammetry (CV) and scanning electron microscopy (SEM). The nanobiosensor was constructed by immobilizing the enzyme horseradish peroxidase (HRP) electrostatically onto the surface of a rotating gold disk electrode modified with PDMA-PSS nanoparticles. The biosensing principle was based on determination of the sensor response to glyphosate and glufosinate by amperometric methods. Hydrogen peroxide (H2O2) was used to measure activity of the enzyme before injection of the herbicides into the electrolyte solution. The enzyme electrode was stable for a long period of time and was used for over 60 measurements. Glyphosate and glufosinate analyses were realized on spiked corn samples within a concentration range of 2.0-78.0 μg L-1, corroborating that the nanobiosensor is sensitive enough to detect herbicides in these matrices. Based on a 20-μL sample injection volume, the detection limits were 0.1 μg L-1 (10-10 M) for both glyphosate and glufosinate without sample clean-up or preconcentration.

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 immunosensor's 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.

Modelling of the impedimetric responses of an aflatoxin B1 immunosensor prepared on an electrosynthetic polyaniline platform

Aflatoxins are a group of mycotoxins that have deleterious effects on humans and are produced during fungal infection of plants or plant products. An electrochemical immunosensor for the determination of aflatoxin B(1) (AFB(1)) was developed with AFB(1)antibody (AFB(1)-Ab) immobilized on Pt electrodes modified with polyaniline (PANi) and polystyrene sulphonic acid (PSSA). Impedimetric analysis shows that the electron transfer resistances of the Pt/PANi-PSSA electrode, the Pt/PANi-PSSA/AFB(1)-Ab immunosensor and Pt/PANi-PSSA/AFB(1)-Ab incubated in bovine serum albumin (BSA) were 0.458, 720 and 1,066 kOmega, respectively. These results indicate that electrochemical impedance spectroscopy (EIS) is a suitable method for monitoring the change in electron transfer resistance associated with the immobilization of the antibody. Modelling of EIS data gave equivalent circuits which showed that the electron transfer resistance increased from 0.458 kOmega for the Pt/PANi-PSSA electrode to 1,066 kOmega for the Pt/PANi-PSSA/AFB(1)-Ab immunosensor, indicating that immobilization of the antibody and incubation in BSA introduced an electron transfer barrier. The AFB(1) immunosensor had a detection limit of 0.1 mg/L and a sensitivity of 869.6 kOmega L/mg.

Acetylcholinesterase-polyaniline biosensor investigation of organophosphate pesticides in selected organic solvents

The behavior of an amperometric organic-phase biosensor consisting of a gold electrode modified first with a mercaptobenzothiazole self-assembled monolayer, followed by electropolymerization of polyaniline in which acetylcholinesterase as enzyme was immobilized, has been developed and evaluated for organophosphorous pesticide detection. The voltammetric results have shown that the formal potential shifts anodically as the Au/MBT/PANI/AChE/PVAc thick-film biosensor responded to acetylthiocholine substrate addition under anaerobic conditions in selected organic solvent media containing 2% v/v 0.05 M phosphate buffer, 0.1 M KCl (pH 7.2) solution. Detection limits in the order of 0.147 ppb for diazinon and 0.172 ppb for fenthion in acetone-saline phosphate buffer solution, and 0.180 ppb for diazinon and 0.194 ppb for fenthion in ethanol-saline phosphate buffer solution has been achieved.