Abderrazak Maaref

E-Nose and e-Tongue combination for improved recognition of fruit juice samples

There are many important challenges related to food security analysis by application of chemical and electrochemical sensors. One critical parameter is the development of reliable tools, capable of performing an overall sensory analysis. In these systems, as much information as possible is required in relation to smell, taste and colour. Here, we investigated the possibility of using a multisensor data fusion approach, which combines an e-Nose and an e-Tongue, adept in generating combined aroma and taste profiles. In order to shed light on this concept, classification of various Tunisian fruit juices using a low-level of abstraction data fusion technique was attempted. Five tin oxide-based Taguchi Gas Sensors were applied in the e-Nose instrument and the e-Tongue was designed using six potentiometric sensors. Four different commercial brands along with eleven fruit juice varieties were characterised using the e-Nose and the e-Tongue as individual techniques, followed by a combination of the two together. Applying Principal Component Analysis (PCA) separately on the respective e-Nose and e-Tongue data, only few distinct groups were discriminated. However, by employing the low-level of abstraction data fusion technique, very impressive findings were achieved. The Fuzzy ARTMAP neural network reached a 100% success rate in the recognition of the eleven-fruit juices. Therefore, data fusion approach can successfully merge individual data from multiple origins to draw the right conclusions that are more fruitful when compared to the original single data. Hence, this work has demonstrated that data fusion strategy used to combine e-Nose and e-Tongue signals led to a system of complementary and comprehensive information of the fruit juices which outperformed the performance of each instrument when applied separately.

An Electrochemical Immunosensor for Detection of Staphylococcus aureus Bacteria Based on Immobilization of Antibodies on Self-Assembled Monolayers-Functionalized Gold Electrode

The detection of pathogenic bacteria remains a challenge for the struggle against biological weapons, nosocomial diseases, and for food safety. In this research, our aim was to develop an easy-to-use electrochemical immunosensor for the detection of pathogenic Staphylococcus aureus ATCC25923. The biosensor was elaborated by the immobilization of anti-S. aureus antibodies using a self-assembled monolayer (SAMs) of 3-Mercaptopropionic acid (MPA). These molecular assemblies were spontaneously formed by the immersion of the substrate in an organic solvent containing the SAMs that can covalently bond to the gold surface. The functionalization of the immunosensor was characterized using two electrochemical techniques: cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Here, the analysis was performed in phosphate buffer with ferro/ferricyanide as the redox probe. The EIS technique was used for affinity assays: antibody-cell binding. A linear relationship between the increment in the electron transfer resistance (RCT) and the logarithmic value of S. aureus concentration was observed between 10 and 106 CFU/mL. The limit of detection (LOD) was observed at 10 CFU/mL, and the reproducibility was calculated to 8%. Finally, a good selectivity versus E. coli and S. epidermidis was obtained for our developed immunosensor demonstrating its specificity towards only S. aureus.

Impedimetric immunosensor based on SWCNT-COOH modified gold microelectrodes for label-free detection of deep venous thrombosis biomarker

Measurement of D-dimer has subsequently become an essential element in the diagnostics of deep vein thrombosis and pulmonary embolism; in this context microelectrodes with an area of 9×10(-4) cm(2) were used to develop impedimetric immunosensor for detecting deep venous thrombosis biomarker (D-dimer). The biosensor is based on functionalized carbon nanotubes (SWCNT-COOH) where the antibody (anti-D-dimer) was immobilized by covalent binding. The electrical properties and the morphology of the biolayer were characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry and atomic force spectroscopy (AFM). Impedimetric microimmunosensor allows to obtain sensitivity of 40.1 kΩ μM(-1) and detection limit of 0.1 pg/mL (0.53 fM) with linear range from 0.1 pg/mL to 2 μg/mL (0.53 fM to 0.01 μM). We demonstrate that using carbon nanotubes and microelectrodes, high sensitivity and dynamic range were obtained. The biosensor exhibited a short response time of 10 min. Moreover, the studied immunosensor exhibits good reproducibility (R.S.D. 8.2%, n=4).

Comparative study of conductometric glucose biosensor based on gold and on magnetic nanoparticles.

The aim of this study was to show the feasibility and the performances of nanoparticle biosensing. A glucose conductometric biosensor was developed using two types of nanoparticles (gold and magnetic), glucose oxidase (GOD) being adsorbed on PAH (poly(allylamine hydrochloride)) modified nanoparticles, deposited on a planar interdigitated electrode (IDEs). The best sensitivities for glucose detection were obtained with magnetic nanoparticles (70 μM/mM and 3 μM of detection limit) compared to 45 μM/mM and 9 μM with gold nanoparticles and 30 μM/mM and 50 μM with GOD directly cross-linked on IDEs. When stored in phosphate buffer (20 mM, pH 7.3) at 4 °C, the biosensor showed good stability for more than 12 days.

Study of the silicon nitride/aqueous electrolyte interface on colloidal aqueous suspensions and on electrolyte/insulator/semiconductor structures

Abstract The silicon nitride/aqueous electrolyte interface has been studied on colloidal aqueous suspensions and on electrolyte/insulator/semiconductor (EIS) structures. Electrophoretic mobilities of the colloidal suspensions and capacitances of the EIS structures were measured. Before any previous exposure to water or after hydrogen fluoride etching, the silicon nitride surface shows a linear and Nernstian response for pH and its isoelectric point is 4. This behavior has been explained by the presence of a small fraction of amine groups at the silicon nitride surface. After exposure to water and to alkaline media, the silicon nitride surface behaves just like a silica surface for both systems. This is due to disappearance of the amine groups through a hydrolysis reaction.

Electrochemical sensing of trimethylamine based on polypyrrole–flavin-containing monooxygenase (FMO3) and ferrocene as redox probe for evaluation of fish freshness

Amperometric and impedimetric biosensor for detecting trimethylamine (TMA) which represents good parameters for estimating fish freshness has been developed. The biosensor is based on a conducting polypyrrole substituted with ferrocenyl, where flavin-containing monooxygenase 3 (FMO3) enzyme was immobilised by covalent bonding. FMO3 catalyzes the monooxygenation TMA to trimethylamine N-oxide (TMO). For catalysis FMO require flavin adenine (FAD) as a prosthetic group, NADPH as a cofactor and molecular oxygen as cosubstrate. Ferrocenyl group substituted on the polypyrrole matrix will serve as redox probe for monitoring the response of the biosensor to TMA. The construction of the biosensor was characterized by FT-IR, cyclic voltammetry and impedance measurements. Detection is done through the analysis of the current of oxidation signal of the ferrocenyl groups and compared to the measurement of impedance related to the electrical properties of the layers. Amperometric and impedimetric response were measured as a function of TMA concentration in range of 0.4 μgm L(-1)-80 μgm L(-1) (6.5 μmol L(-1)-1.5 mmol L(-1)). Amperometric measurements show a decrease in current response which is in correlation with the increase of the charge transfer resistance demonstrated by impedance. Calibration curve obtained by impedance spectroscopy shows a high sensitivity with a dynamic range from (0.4 μgm L(-1) to 80 μgm L(-1)). We demonstrated, using ferrocene as redox probe for catalytic reaction of FMO3, that high sensitivity and dynamic range was obtained. The biosensor was stable during 16 days. The biosensor shows high selectivity and its sensitivity to TMA in real samples was evaluated using fish extract after deterioration during storage.

Electrically addressable deposition of diazonium-functionalized antibodies on boron-doped diamond microcells for the detection of ochratoxin A

This work reports the manufacturing procedure for an impedimetric immunosensor for sensitive detection of the mycotoxin, ochratoxin A (OTA), through electroaddressing of diazonium functionalized antibodies on the working electrode of a planar Boron Doped Diamond (BDD) electrochemical microcell. The immunosensor elaboration and the immunochemical reaction between ochratoxin A and the surface-bound antibody were monitored using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The impedance variation due to the specific antibody–OTA interaction was correlated with the OTA concentration in the samples. The increase in electron-transfer resistance values presents a sigmoidal shape versus log concentration of OTA, with a dynamic range between 7 pg mL−1 and 25 ng mL−1. A limit of detection (LOD) of 7 pg mL−1 and a IC50 of 1.2 ng mL−1 were obtained. The immunosensor thus fabricated exhibited high sensitivity, good reproducibility, long-term stability, and was used for the detection of OTA in real coffee samples with a good recovery rate. The reported validated manufacturing procedure is compatible with the production of microarrays for multidetection.

Urease capacitive biosensors using functionalized magnetic nanoparticles for atrazine pesticide detection in environmental samples

A new atrazine pesticide potentiometric biosensor was described using urease biomolecules immobilized onto the insulator–semiconductor electrode and different additional materials such as glutaraldehyde as a cross-linking agent, bovine serum albumin, coated nanoparticles (Fe3O4), cationic poly(allylamine hydrochloride) and anionic poly(sodium 4-styrenesulfonate) polyelectrolytes. The effect of atrazine molecules on the activity of free and immobilized urease was studied using the ion selective electrodes (ISEs) and capacity–potential measurements C(V). The sensitivity of the modified bioelectrode to urea addition was evaluated by the capacitance method via the relationship between the evolution of the flat band potential ΔVFB and the urea concentration for values ranging from 23 to 0.04 mM. The detection of atrazine in solution was performed via its inhibiting action on the urease biosensor. An incubation time of 30 min was chosen to study the inhibition effect of atrazine for different concentrations on the urease biosensor. Under optimal experimental conditions, the enzymatic activity, the inhibition process and the analytical characteristics of the resulting ENFEC (Enzyme Field effect capacitive) system were investigated. As a result, the detection limit of atrazine via the inhibition of urease activity was about 0.13 μM with a dynamic concentration range from 10−2 to 10−7 M.

A novel EIS field effect structures coated with TESUD-PPy-PVC-dibromoaza[7]helicene matrix for potassium ions detection.

In this work, we describe the development of new Aza[7]helicene-containing PVC-based membranes for the K(+) ions quantification. Here, silicon nitride-based structures (Si-p/SiO2/Si3N4) were developed and the surface was activated, functionalized with an aldehyde-silane (11-(Triethoxysilyl)undecanal (TESUD)), functionalized with polypyrrole (PPy), and coated with the polyvinylchloride (PVC)-membrane containing the Aza[7]helicene as ionophore. All stages of functionalization process have been thoroughly studied by contact angle measurements (CAMs) and atomic force microscopy (AFM). The developed ion-selective electrode (ISE) was then applied using electrochemical impedance spectroscopy (EIS) for the detection of potassium ions. A linear range was observed between 1.0 × 10(-8) M to 1.0 × 10(-3) M and a detection limit of 1.0 × 10(-8) M was observed. The EIS results have showed a good sensitivity to potassium ion using this novel technique. The target helicene exhibited good solubility and excellent thermal stability with a high decomposition temperature (Td > 300 °C) and it indicates that helicene may be a promising material as ionophore for ion-selective electrodes (ISEs) elaboration.

Characterization of Urea Biosensor Based on the Immobilization of Bacteria Proteus Mirabilis in Interaction with Iron Oxide Nanoparticles on Gold Electrode

In this work we describe a new urea biosensor, based on the immobilization of bacteria, Proteus mirabilis on gold electrode. To improve the stability of the bio-system, additional materials were used such as functionalized Fe3O4 nanoparticles (NPs), cationic (PAH), anionic (PSS) polyelectrolytes, Bovine Serum Albumin (BSA) and glutaraldehyde as a cross-linking agent. The electrochemical performances of the developed bacteria biosensor was evaluated using the electrochemical impedance spectroscopy (EIS) and cyclic voltammetry measurements. The adhesion of the bacteria cell on gold electrode was evaluated using contact angle measurements. The morphology of bacteria and its interaction with Fe3O4 nanoparticles were evaluated with the atomic force microscopy (AFM). As a result, a sensitive, stable and reproducible urea biosensor was developed.