Georges Istamboulie

Screen-printed poly(3,4-ethylenedioxythiophene) (PEDOT): A new electrochemical mediator for acetylcholinesterase-based biosensors

This work describes the use of a PEDOT:PSS-based conductive polymer for designing AChE-based biosensors. The transducers were obtained directly by screen-printing a PEDOT:PSS suspension on the surface of thick film carbon electrodes. The obtained working electrodes showed a high conductivity when compared with electrodes modified with conventional mediators like cobalt phthalocyanine or tetracyanoquinodimethane. The PEDOT:PSS polymer was shown to be suitable for thiocholine oxidation, allowing the measurement of AChE activity at 100 mV vs Ag/AgCl. The high conductivity of PEDOT:PSS allowed the accurate detection of the organophosphate insecticide chlorpyrifos-oxon at concentrations as low as 4x10(-9)M, corresponding to an inhibition ratio of 5%.

Sensitive quantitation of Ochratoxin A in cocoa beans using differential pulse voltammetry based aptasensor

In this work, we propose for the first time a sensitive Ochratoxin A (OTA) detection in cocoa beans using competitive aptasensor by differential pulse voltammetry (DPV). In the proposed method, biotin labeled and free OTA competed to bind with immobilized aptamer onto the surface of a screen printed carbon electrode (SPCE), and percentage binding was calculated. The detection was performed after adding avidin-ALP to perform avidin-biotin reaction; the signal was generated through a suitable substrate 1-naphthyl phosphate (1-NP), for alkaline phosphatase (ALP). The cocoa samples were extracted and purified using molecular imprinted polymer (MIP) columns specifically designed for OTA. The developed aptasensor showed a good linearity in the range 0.15-5 ng/mL with the limit of detection (LOD) 0.07 ng/mL and 3.7% relative standard deviation (RSD). The aptasensor displayed good recovery values in the range 82.1-85% with 3.87% RSD, thus, demonstrated the efficiency of proposed aptasensor for such matrices.

Computational and experimental investigation of molecular imprinted polymers for selective extraction of dimethoate and its metabolite omethoate from olive oil.

This work presents the development of molecularly imprinted polymers (MIPs) for the selective extraction of dimethoate from olive oil. Computational simulations allowed selecting itaconic acid as the monomer showing the highest affinity towards dimethoate. Experimental validation confirmed modelling predictions and showed that the polymer based on IA as functional monomer and omethoate as template molecule displays the highest selectivity for the structurally similar pesticides dimethoate, omethoate and monocrotophos. Molecularly imprinted solid phase extraction (MISPE) method was developed and applied to the clean-up of olive oil extracts. It was found that the most suitable solvents for loading, washing and elution step were respectively hexane, hexane-dichloromethane (85:15%) and methanol. The developed MIPSE was successfully applied to extraction of dimethoate from olive oil, with recovery rates up to 94%. The limits of detection and quantification of the described method were respectively 0.012 and 0.05 μg g(-1).

Development of an impedimetric aptasensor for the determination of aflatoxin M1 in milk

An aptasensor was designed for the determination of aflatoxin M1 (AFM1) in milk based on DNA-aptamer recognition and electrochemical impedance spectroscopy detection. A hexaethyleneglycol-modified 21-mer oligonucleotide was immobilized on a carbon screen-printed electrode through carbodiimide immobilization, after diazonium activation of the sensing surface. Cyclic voltammetry and electrochemical impedance spectroscopy in the presence of ferri/ferrocyanide redox probe were used to characterize each step of the aptasensor development. Aptamer-AFM1 interaction induced an increase in electron-transfer resistance, allowing the determination of AFM1 in buffer in the range 2-150 ng/L (LOD=1.15 ng/L). Application to milk analysis showed that a preliminary treatment was mandatory. A simple filtration through a 0.2 µm PTFE membrane allowed determination of AFM1 in milk for concentrations ranging from 20 to 1000 ng/kg. These performances are compatible with the AFM1 levels set in European Union for milk and dairy products for adults (50 ng/kg) and infants (25 ng/kg).

Phosphotriesterase: A complementary tool for the selective detection of two organophosphate insecticides : Chlorpyrifos and chlorfenvinfos

This work shows the possibility of combining the high sensitivity of genetically-modified Drosophila melanogaster acetylcholinesterase (B394) with the ability of phosphotriesterase (PTE) to hydrolyse organophosphate compounds, in the aim of developing a biosensor selective to two insecticides of interest: chlorpyrifos and chlorfenvinfos. The studies clearly demonstrate that chlorfenvinfos is a substrate that acts as competitive inhibitor of PTE, therefore preventing the efficient hydrolysis of other pesticides, including chlorpyrifos. A bi-enzymatic sensor was designed by immobilizing both B394 and PTE in a polyvinylalcohol matrix. The sensor was shown to be able to discriminate between chlorpyrifos and chlorfenvinfos inhibitions.

The use of Artificial Neural Networks for the selective detection of two organophosphate insecticides: chlorpyrifos and chlorfenvinfos.

Amperometric acetylcholinesterase (AChE) biosensors have been developed to resolve mixtures of chlorpyrifos oxon (CPO) and chlorfenvinfos (CFV) pesticides. Three different biosensors were built using the wild type from electric eel (EE), the genetically modified Drosophila melanogaster AChE B394 and B394 co-immobilized with a phosphotriesterase (PTE). Artificial Neural Networks (ANNs) were used to model the combined response of the two pesticides. Specifically two different ANNs were constructed. The first one was used to model the combined response of B394+PTE and EE biosensors and was applied when the concentration of CPO was high and the other, modelling the combined response of B394+PTE and B394 biosensors, was applied with low concentrations of CPO. In both cases, good prediction ability was obtained with correlation coefficients better than 0.986 when the obtained values were compared with those expected for a set of six external test samples not used for training.

Molecularly imprinted polymer cartridges coupled to high performance liquid chromatography (HPLC-UV) for simple and rapid analysis of fenthion in olive oil

A combination of molecular modelling and a screening of the library of non-imprinted polymers (NIPs) was used to identify acrylamide as a functional monomer with high affinity towards fenthion, organophosphate insecticide, which is frequently used in the treatment of olives. A good correlation was found between the screening tests and modelling of monomer-template interactions performed using a computational approach. Acrylamide-based molecularly imprinted polymer (MIP) and non-imprinted polymer (NIP) were thermally synthesised in dimethyl formamide (porogen) using ethylene glycol dimethacrylate as a cross-linker and 1,1-azo-bis (isobutyronitrile) as an initiator. The chemical and physical properties of the prepared polymers were characterised. The binding of fenthion by the polymers was studied using solvents with different polarities. The developed MIP showed a high selectivity towards fenthion, compared to other organophosphates (dimethoate, methidathion malalthion), and allowed extraction of fenthion from olive oil samples with a recovery rate of about 96%. The extraction of fenthion using MIPs was much more effective than traditional C18 reverse-phase solid phase extraction and allowed to achieve a low detection limit (LOD) (5 µg L(-1)).

Determination of Mycotoxins in Food: A Review of Bioanalytical to Analytical Methods

Abstract This review highlights methods for the detection of the main mycotoxins: aflatoxins, fumonisins, ochratoxin, patulin, trichothecene, zearalenone, citrinin. Detection methods such as competitive or noncompetitive immunoassays, different biosensors, and the use of optoelectronics devices to miniaturize the equipment in a portable way, are described. The importance of spectroscopic techniques are underlined and the maxima permissible by various committees are indicated.

Chronoamperometric determination of lead ions using PEDOT:PSS modified carbon electrodes.

A new simple chronoamperometry methodology was developed for the ultrasensitive determination of lead ions using a PEDOT:PSS coated graphite carbon electrode. The polymer was directly coated on a graphite carbon electrode and characterized using simple cycle voltammetric measurements. The presence of lead ions induced a cathodic peak starting at -550 ± 10 mV vs. Ag/AgCl, and an anodic peak starting at -360 ± 10 mV vs. Ag/AgCl. Electroaccumulation of lead ions onto the PEDOT:PSS modified electrode was performed at -650 mV vs. Ag/AgCl for 30s in a pH 2.2 hydrochloric acid solution. Chronoamperometry measurements were carried out at -350 mV vs. Ag/AgCl allowing the oxidation of accumulated lead. Using this method, lead ions were detected for concentrations ranging between 2.0 nmol L(-1) and 0.1 μmol L(-1) (R(2)=0.999). The detection limit was calculated to be 0.19 nmol L(-1) and the quantification limit of 0.63 nmol L(-1). The method was shown to be highly precise and sensitive, negligible interference was detected from other metal ions. The proposed method was successfully applied for the detection of lead ions in vegetables.

Development of structure switching aptamer assay for detection of aflatoxin M1 in milk sample

The discovery of in-vitro systematic evolution of ligands by exponential enrichment (SELEX) process has considerably broaden the utility of aptamer as bio-recognition element, providing the high binding affinity and specificity against the target analytes. Recent research has focused on the development of structure switching signaling aptamer assay, transducing the aptamer- target recognition event into an easily detectable signal. In this paper, we demonstrate the development of structure switching aptamer assay for determination of aflatoxin M1 (AFM1) employing the quenching-dequenching mechanism. Hybridization of fluorescein labelled anti-AFM1 aptamer (F-aptamer) with TAMRA labelled complementary sequences (Q-aptamer) brings the fluorophore and the quencher into close proximity, which results in maximum fluorescence quenching. On addition of AFM1, the target induced conformational formation of antiparallel G-quadruplex aptamer-AFM1 complex results in fluorescence recovery. Under optimized experimental conditions, the developed method showed the good linearity with limit of detection (LOD) at 5.0ngkg(-1) for AFM1. The specificity of the sensing platform was carefully investigated against aflatoxin B1 (AFB1) and ochratoxin A (OTA). The developed assay platform showed the high specificity towards AFM1. The practical application of the developed aptamer assay was verified for detection of AFM1 in spiked milk samples. Good recoveries were obtained in the range from 94.40% to 95.28% (n=3) from AFM1 spiked milk sample.