Development of modified electrode materials for biosensor applications

L'objectif du travail de recherche mené concerne l'élaboration des nouveaux matériaux d'électrodes modifiés pour des applications dans le domaine des biocapteurs. Le travail a été subdivisé en trois parties portant sur le greffage du sel de diazonium pour application immunocapteur, l'électroadressage des d'anticorps et l'électrodépôt d'un espaceur pour application aptacapteur. Dans la première partie de ce travail, nous nous sommes consacrés d'abord à l'électrogreffage du nitrobenzène diazonium sur la surface d'or pour le développement de capteurs immunologiques destinés à la détection de la bactérie Staphylococcus aureus. Une limite de détection de 10 UFC/mL a été atteinte. Dans la deuxième partie, la détection de l'ochratoxine A est présentée, basée sur l'électroadressage covalent de l'anticorps modifié par la fonction diazonium sur des électrodes de Diamant Dopé Bore (BDD). Une limite de détection de 0.007ng/mL a été obtenue et l'immunocapteur a été testé sur des échantillons réels. Enfin, on a développé un aptacapteur basé sur le greffage d'un espaceur (PEG) sur la surface des microcellules BDD pour la quantification de la biotoxine OTA. Une limite de détection de 0,01ng/L a été obtenue et application à un échantillon réel (le riz) a été démontrée. Les résultats obtenus, basés sur des méthodes électrochimiques de détection (variation de l'impédance ou du courant d'une sonde redox) sont encourageantes en termes de sensibilité, limite de détection, reproductibilité et spécificitéThe objective of the research work was to the development of modified electrode materials for biosensor application. The work was devided into three parts: electrografting of diazonium salt for immunosensor application, electroadressing of antibodies and electrodeposition of PEG spacer for aptasensor application. In the first part of this work, the modification of gold surfaces with nitrobenzene diazonium cation was investigated in order to develop an immunosensors for the detection of Staphylococcus aureus. A detection limit of 10 CFU/mL has been obtained. The second part was focused on the electrically addressable deposition of diazonium functionalized antibodies on boron-doped diamond (BDD) microcells for the detection of OTA. A detection limit of 0.007ng/mL has been obtained and the immunosensor was tested on real samples. Finally, we developed an amperometric aptasensor based on electrochemical grafting of a PEG-COOH spacer on a BDD microcell for the detection of OTA biotoxin. A detection limit of 0.01 ng/L has been obtained and application to a real sample (rice) has been demonstrated. The amperometric and impedimetric techniques used in this work lead to promising results in terms of sensitivity, specificity and reproductibilit

Highly stable and ultra-sensitive amperometric aptasensor based on pectin stabilized gold nanoparticles on graphene oxide modified GCE for the detection of aflatoxin M1

Herein, we have elaborated a new electrochemical aptasensor for the detection of ultra-trace amounts of aflatoxin M1 (AFM1) present in cow milk, with regulated low levels. To achieve detection of AFM1, a simple strategy for the deposition of specific aptamers was elaborated, based on their grafting on pectin-reduced gold nanoparticles (AuNPs) electrogenerated on a graphene oxide sheet modified glassy carbon electrode. The elaboration of composite film was confirmed by cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and UV–visible absorption measurements. The aptamer/pectin-AuNPs/GO/GCE exhibited significantly enhancement in the determination of AFM1 in 20 min with a low detection limit 0.2 ng/L, a wide and useful linear range (10–1000 ng/L). An excellent stability, a high sensitivity, and a reproducibility as well as good recovery were obtained by the designed aptasensor. Moreover, the obtained results were tested in real samples. Thus, good electrochemical performance and simple preparation process of the aptamer/pectin-AuNPs/GO/GCE can provide promising potential for the detection of AFM1 in milk samples in a daily use

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

International audienceThis 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 surfacebound 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

An aptasensor for ochratoxin A based on grafting of polyethylene glycol on a boron-doped diamond microcell

International audienceA novel strategy for the fabrication of an electrochemical label-free aptasensor for small-size molecules is proposed and demonstrated as an aptasensor for ochratoxin A (OTA). A long spacer chain of polyethylene glycol (PEG) was immobilized on a boron-doped diamond (BDD) microcell via electrochemical oxidation of its terminal amino groups. The amino-aptamer was then covalently linked to the carboxyl end of the immobilized PEG as a two-piece macromolecule, autoassembled at the BDD surface, forming a dense layer. Due to a change in conformation of the aptamer on the target analyte binding, a decrease of the electron transfer rate of the redox [Fe(CN)(6)](4-/3-) probe was observed. To quantify the amount of OTA, the decrease of the square wave voltammetry (SWV) peak maximum of this probe was monitored. The plot of the peak maximum against the logarithm of OTA concentration was linear along the range from 0.01 to 13.2 ng/L, with a detection limit of 0.01 ng/L. This concept was validated on spiked real samples of ric

An immunosensor for pathogenic staphylococcus aureus based on antibody modified aminophenyl-Au electrode

International audienceThe objective of this work is to elaborate an immunosensing system which will detect and quantify Staphylococcus aureus bacteria. A gold electrode was modified by electrografting of 4-nitrophenyl diazonium, in situ synthesized in acidic aqueous solution. The immunosensor was fabricated by immobilizing affinity-purified polyclonal anti S. aureus antibodies on the modified gold electrode. Cyclic voltammetry (CV) and Faradaic Electrochemical Impedance Spectroscopy (EIS) were employed to characterize the stepwise assembly of the immunosensor. The performance of the developed immunosensor was evaluated by monitoring the electron-transfer resistance detected using Faradaic EIS. The experimental results indicated a linear relationship between the relative variation of the electron transfer resistance and the logarithmic value of S. aureus concentration, with a slope of 0.40 ± 0.08 per decade of concentration. A low quantification limit of CFU per ml and a linear range up to CFU per mL were obtained. The developed immunosensors showed high selectivity to Escherichia coli and Staphylococcus saprophyticus

An electrochemical immunosensor for detection of staphylococcus aureus bacteria based on immobilization of Aantibodies on self-assembled monolayers-functionalized gold electrode

International audienceThe 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

PEG-templated synthesis of ultramicroporous n-ZIF-67 nanoparticles with high selectivity for the adsorption and uptake of CO2 over CH4 and N2

International audienceChallenges remain concerning the development of rapid and low-cost adsorbents that combine good separation performance with high adsorption capacity, especially for CO2. Herein, we report for the first time a new polyethylene glycol templated synthesis method to obtain a nanocrystalline zeolitic imidazolate framework (n-ZIF-67) at room temperature in 5 min. The n-ZIF-67 nanoparticles were characterized using X-ray powder diffraction with Rietveld refinement (space group = I-43 m, a = 17.0545(4) Å), Fourier-transform infrared, transmission electron microscopy, thermogravimetric analysis, and N2 adsorption (Brunauer-Emmett-Teller) measurements and exhibited excellent properties, including a total pore volume of 0.86 cm³/g, a high surface area equal to 1891 m²/g, and 0.64 nm size ultramicropores.). The highly porous ZIF-67 nanoparticles were explored for the adsorption and desorption of CH4, CO2, and N2 gases at pressures up to 40 bar and isotherm temperatures of 273, 298, 323, and 353 K. The adsorption isotherms revealed a high capacity for CO2 of 681 mg/g at 298 K and an adsorption enthalpy of 29.19 to 34.44 KJ/mol, in part linked to the ultramicroporous structure. The n-ZIF-67 particles exhibited gas uptake values for CH4 and N2 of 241 mg/g and 219 mg/g, respectively. As far as the authors are concerned, these are the highest capacities ever reported for zeolitic framework metal organic frameworks such as ZIF-67 and ZIF-8. The Langmuir adsorption isotherm was employed to obtain the maximum adsorption capacity, qm, and adsorption equilibrium constant, KL. The isosteric heat of adsorption data sheds light on a CO2 physisorption process. The n-ZIF-67 also exhibited high CO2/N2 and CO2/CH4 mixed gases selectivity, with the preferential adsorption of CO2 over N2 or CH4 confirmed by breakthrough experiments. The n-ZIF-67 with ultramicropores is therefore an effective new adsorbent for greenhouse gas capture with high CO2 gas selectivity over competing gases. Zeolitic framework MOFs merit further development as low-cost and easy-to-synthesize adsorbents to help address the pressing need to mitigate CO2 emissions

Trifluoromethylated Flavonoid-Based Isoxazoles as Antidiabetic and Anti-Obesity Agents: Synthesis, In Vitro α-Amylase Inhibitory Activity, Molecular Docking and Structure–Activity Relationship Analysis

Diabetes mellitus is a major health problem globally. The management of carbohydrate digestion provides an alternative treatment. Flavonoids constitute the largest group of polyphenolic compounds, produced by plants widely consumed as food and/or used for therapeutic purposes. As such, isoxazoles have attracted the attention of medicinal chemists by dint of their considerable bioactivity. Thus, the main goal of this work was to discover new hybrid molecules with properties of both flavonoids and isoxazoles in order to control carbohydrate digestion. Moreover, the trifluoromethyl group is a key entity in drug development, due to its strong lipophilicity and metabolic stability. Therefore, the present work describes the condensation of a previously synthesized trifluoromethylated flavonol with different aryl nitrile oxides, affording 13 hybrid molecules indicated as trifluoromethylated flavonoid-based isoxazoles. The structures of the obtained compounds were deduced from by 1H NMR, 13C NMR, and HRMS analysis. The 15 newly synthesized compounds inhibited the activity of α-amylase with an efficacy ranging from 64.5 ± 0.7% to 94.7 ± 1.2% at a concentration of 50 μM, and with IC50 values of 12.6 ± 0.2 μM–27.6 ± 1.1 μM. The most effective compounds in terms of efficacy and potency were 3b, 3h, 3j, and 3m. Among the new trifluoromethylated flavonoid-based isoxazoles, the compound 3b was the most effective inhibitor of α-amylase activity (PI = 94.7 ± 1.2% at 50 μM), with a potency (IC50 = 12.6 ± 0.2 μM) similar to that of the positive control acarbose (IC50 = 12.4 ± 0.1 μM). The study of the structure–activity relationship based on the molecular docking analysis showed a low binding energy, a correct mode of interaction in the active pocket of the target enzyme, and an ability to interact with the key residues of glycosidic cleavage (GLU-230 and ASP-206), explaining the inhibitory effects of α-amylase established by several derivatives

An Electrochemical Sensor for Sulfadiazine Determination Based on a Copper Nanoparticles/Molecularly Imprinted Overoxidized Polypyrrole Composite

To protect consumers from risks related to overexposure to sulfadiazine, total residues of this antibacterial agent in animal-origin foodstuffs not exceed international regulations. To this end, a new electrochemical sensor based on a molecularly imprinted polymer nanocomposite using overoxidized polypyrrole and copper nanoparticles for the detection of sulfadiazine is elaborated. After optimization of the preparation of the electrochemical sensors, their differential pulse voltammetric signal exhibits an excellent stability and reproducibility at 1.05 V, with a large linear range between 10−9 and 10−5 mol L−1 and a low detection limit of 3.1 × 10−10 mol L−1. The produced sulfadiazine sensor was successfully tested in real milk samples. The combination of the properties of the electrical conduction of copper nanoparticles with the properties of the preconcentration of the molecularly imprinted overoxidized polypyrrole allows for the highly sensitive detection of sulfadiazine, even in real milk samples. This strategy is new and leads to the lowest detection limit yet achieved, compared to those of the previously published sulfadiazine electrochemical sensors

Electrochemical sensor based on gum Arabic nanoparticles for rapid and in-situ detection of different heavy metals in real samples

The key solution to combat trace metal pollution and keep the environment, ecosystem, animals, and humans safe is earlier and rapid trace metal detection. For all these reasons, we propose in this work the design of a simple electrochemical sensor functionalized with green nanoparticles for electrochemical detection of the fourth most dangerous heavy metal ions namely copper, zinc, lead, and mercury. The green nanoparticles are fabricated by a one-step, consisting of reducing platinum nanoparticles by a natural gum Arabic polymer. To guarantee the success of these nanoparticles' design, the nanoparticles have been characterized by Fourier-transform infrared spectroscopy FTIR, and thermogravimetric TGA techniques. While, for the electrochemical characterization, we have adopted cyclic voltammetry CV and electrochemical impedance spectroscopy EIS to control different steps of surface modification, and the differential pulse anodic stripping DPAS was monitored to follow up the electrochemical detection of different heavy metals. Results: have confirmed the good chemical and physical properties of the elaborated nanoparticles. As, the developed sensor showed a specific electrochemical response toward the heavy metal ions separately, with a lower limit of detection lower LOD than that recommended by the World Health Organization, in order of 9.6 ppb for Cu2+, 1.9 ppb for Zn2+, 0.9 ppb for Hg2+, and 4.2 ppb for Pb2+. Impressively, the elaborated sensor has demonstrated also high stability, outstanding sensitivity, and excellent analytical performance.In addition, the elaborated analytical tool has been successfully applied to the determination of various heavy metal ions in real samples, reflecting then its promising prospect in practical application