Abstract

A stable layer of 4-phenyl isothiocyanate (4-PITC) was successfully electrografted on glassy carbon electrode (GCE). The electrode modification process was performed in three sequential steps in a single solution: (1) reduction by chronoamperometry of the nitro groups of 4-NITC to amino moieties (2) in situ reaction of amino with nitrous acid to obtain unstable diazonium functional groups and (3) electrografting by chronopotentiometry of diazonium. A thin optimal layer with minimum surface fouling was obtained. The formation of the organic film was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrode was used for detection of Pb(II) and Fe(II) by differential pulse voltammetry (DPV). Under optimal conditions, the limit of detection 1.2 mu g L-1 for Pb(II) and of 2.0 mu g L-1 for Fe(II) were achieved. The developed electrode was successfully applied to detect Pb(II) and Fe(II) in injectable iron pharmaceuticals used to treat iron deficiency anemia simultaneous with investigation of contamination by Pb(II).

Abstract

We have developed a bienzymatic biosensor that contains acetylcholinesterase together with butyrylcholinesterase co-immobilized on the same electrode modified with a stabilized copper containing Prussian blue electrodeposited on electrodes coated with 4-aminothiophenol monolayer using diazonium chemistry and copper nanoparticles for improved sensitivity. There are organophosphorus and carbamate neurotoxic insecticides that inhibit only one of the two enzymes, e.g., pirimicarb inhibits butyrylcholinesterase at much lower concentrations than acetylcholinesterase while methomyl inhibits only acetylcholinesterase. Our system is simple and in a single measurement provides a sensitive signal for insecticides’ presence based on the inhibition of the enzyme with the highest affinity for each toxic compound. The limits of detection are 50 ng/mL pirimicarb for the bienzymatic biosensor in comparison with 400 ng/mL pirimicarb for the acetylcholinesterase biosensor and 6 ng/mL methomyl for the bienzymatic biosensor, while inhibition is obtained for the butyrylcholinesterase biosensor at 700 ng/mL. Graphical Abstract: (Figure presented.) © The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature 2024.

Abstract

Ultrasound generates cavities in liquids with high-energy behaviour due to large pressure variations, leading to (bio)chemical effects and material modification. Numerous cavity-based treatments in food processes have been reported, but the transition from research to industrial applications is hampered by specific engineering factors, such as the combination of several ultrasound sources, more powerful wave generators or tank geometry. The challenges and development of cavity-based treatments developed for the food industry are reviewed with examples limited to two representative raw materials (fruit and milk) with significantly different properties. Both active compound extraction and food processing techniques based on ultrasound are taken into consideration.

Abstract

Sensitive and stable electrodes modified with 4-aminothiophenol were developed for heavy metal detection based on coordination bonds between thiol moieties and analyte. The electrodes were modified using diazonium chemistry in one step modification protocol. The presence of 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) in the electrodeposition media avoids the formation of multilayers and improves the performances due to low surface passivation and good electrochemical transfer at the interface with the solution. Electrodeposition of the organic layer on the electrode surface by chronopotentiometry allowed a good control of the electrode modification process, avoids passivation, and leads to reproducible layers with improved characteristics in comparison with modifications carried out by cyclic voltammetry or chronoamperometry. The electrode was able to detect Pb(II) by differential pulse voltammetry with a linear range of 2.5-400 mu g l(-1) and the detection limit of 1.2 mu g l(-1) and Cd(II) with the calibration line in the range of 2.5-400 mu g l(-1) and a detection limit of 1.5 mu g l(-1). Low interferences were observed and the electrodes were applied for analysis of real samples: fruits pomace and waters. (C) 2022 The Electrochemical Society (ECS). Published on behalf of ECS by IOP Publishing Limited.

Abstract

A rapid, simple, and precise electrochemical method was developed for the determination of the total content of antibiotics containing a 5-nitrofuran ring with antibacterial activity including furazolidone, nitrofurazone, nitrofurantoin, and furaltadone in several samples. Boron-doped diamond electrode was used as the working electrode. The electrochemical properties of these compounds were evaluated by cyclic voltammetry. A differential pulse voltammetric method based on the cathodic reduction at high potentials was used for the determination of the total nitrofuran content in a mixture at pH 6.47. The voltammetric measurements showed that the proposed electrochemical method was able to identify the nitrofurazone from a mixture of antibiotics based on its anodic oxidation in alkaline medium (pH 10.6). This method presented good accuracy (between 94.5 and 102.5%) and precision (less than 3.94%), with calibration graphs starting from 50 nmol L-1. The method was applied with success for the determination of total content of compounds with 5-nitrofuran ring and for the selective determination of nitrofurazone in pharmaceutical tablets and food products (milk and honey) without pretreatment of the samples.

Abstract

A stable and reproducible layer of Prussian blue (PB) modified with copper was electrodeposited on carbon paper electrodes for the multiple detection of ester flavorants with a bienzymatic biosensor. Carbon fiber composite paper was investigated as high-surface, low-cost substrate for biosensor development. The pre-activation of the electrode surface by cyclic voltammetry was necessary to improve the electrochemical properties before the electrochemical deposition of Prussian blue-copper film (PB-Cu). The stability and the reproducibility of the obtained PB-Cu carbon paper electrode was demonstrated at pH 7.4, optimum for biosensor development. The developed biosensor is based on the immobilization of two enzymes (carboxyl esterase and alcohol oxidase) by cross-linking with glutaraldehyde onto PB-Cu carbon paper electrode. A mixture of key aroma ester compounds (methyl butyrate, ethyl butyrate, methyl cinnamate and ethyl cinnamate) was detected in several food samples with low interferences.

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Prussian blue modified with copper was electrodeposited on a platinum microelectrode for the amperometric determination of hydrogen peroxide at -50 mV. The Prussian blue-copper layer was stable for 2 h at pH 7.4 and a storage period of 2 months. The Prussian blue-copper modified microelectrodes were used to develop oxidase based microbiosensors for ethanol and lactate. Lactate and alcohol oxidases were immobilized by cross-linking with glutaraldehyde. No interferences were observed from possible interfering compounds up to a concentration of 0.5 mM. The calibration plot of the lactate microbiosensor was linear between 0.005 and 0.2 mM with a limit of detection of 0.0035 mM lactate. The linear dynamic range of the alcohol microbiosensor was between 0.05 and 2 mM and the limit of detection was 0.02 mM ethanol. The developed microbiosensors were used for the analysis of pickled cucumber juice, yogurt, and wine.