Adina Arvinte

Development of a bio-electrochemical assay for AFB1 detection in olive oil.

A novel biosensor assay format for aflatoxin based on acetylcholinesterase (AChE) inhibition by aflatoxin B(1) (AFB(1)) is proposed. The AChE was present in solution and an amperometric choline oxidase biosensor was used for monitoring its residual activity. To create the biosensor, the choline oxidase was immobilized by cross-linking onto screen-printed electrodes modified with Prussian Blue (PB) and these were used to detect the H(2)O(2) at low potential (-0.05V versus a screen-printed internal silver pseudoreference electrode). For the development of the AFB(1) assay, several parameters such as AChE and substrate concentration, the methanol effect, and pH were evaluated and optimized. The linear working range was assessed to be 10-60ppb. Concentrations as low as 2ppb, which correspond to the legal limit of AFB(1) in food for humans, were detected after a pre-concentration step. The suitability of the method was evaluated using commercial olive oil samples. A recovery equal to 78+/-9% for 10ppb of AFB(1) in olive oil samples was obtained.

Carbohydrates electrocatalytic oxidation using CNT-NiCo-oxide modified electrodes.

A new sensor for an amplified electrochemical detection of carbohydrates is proposed, where carbohydrates are oxidized by CNT-NiCo-oxide composite in basic solutions. Cyclic voltammograms of the modified electrode show a stable and well defined redox couple in alkaline media due to the synergy of Ni(II)/Ni(III) system with Co(II)/Co(III). The modified electrode shows excellent electrocatalytic activity towards monosaccharides oxidation at reduced overpotential in alkaline solutions. Six monosaccharides were determined amperometrically at the surface of this modified electrode with high sensitivity over a wide range of concentrations, from 0.02 up to 12.12 mM. Low detection limit of 5 μM for glucose could be obtained.

Synergistic effect of mediator-carbon nanotube composites for dehydrogenases and peroxidases based biosensors.

Very sensitive, low cost and reliable NADH and H(2)O(2) sensors were realised and used for development of enzyme based biosensors. The active surface of the electrodes was modified with a nanocomposite obtained by modification of SWNT with a proper mediator: Meldola Blue (for NADH) and Prussian Blue (for H(2)O(2)). Low applied potential of -50 mV vs. Ag/AgCl reference electrode proved the synergistic effect of nanocomposite materials towards NADH and H(2)O(2) detection. Biosensors for malic acid and alkylphenols have been developed, using mediator-functionalized-SWNT-based electrodes and two different classes of enzymes: NAD(+)-dependent dehydrogenases and peroxidases. Immobilization of the enzymes was realised using a series of different procedures - adsorption, Nafion membrane, sol-gel and glutaraldehyde, in order to find the best configuration for a good operational stability. A higher sensitivity comparing with other reported biosensors of about 12.41 mA/M.cm(2) was obtained for l-malic acid biosensor with enzyme immobilised in Nafion membrane. Phenol, 4-t-octylphenol and 4-n-nonylphenol were used as standard compounds for HRP based biosensor. Fast biosensor response and comparable detection limit with HPLC methods were achieved.

DEVELOPMENT OF A PESTICIDES BIOSENSOR USING CARBON-BASED ELECTRODE SYSTEMS

The biosensors described in this work, for the monitoring of pesticides, are based on acetylcholinesterase immobilized on the surface of screen-printed electrodes. The principle of the biosensor is that the degree of inhibition of an enzyme sensor by a pesticide is dependent on the concentration of that pesticide. The DPV technique was used as a detection method and methyl-paraoxon as a reference pesticide for sensor calibration.

Electrochemical evidence for inclusion complexes of thiotriazinone with cyclodextrins

The formation of the inclusion complexes of thiotriazinone (TTZ) with α-cyclodextrin and β-cyclodextrin was studied by cyclic voltammetry and 1H-NMR. The oxidation and reduction reactions specific to thiotriazinone compounds are irreversible, diffusion controlled processes, and occur in a complex mechanism. The stable inclusion of thiotriazinone in β-cyclodextrin is proved by the significant changes of redox activity characteristic for TTZ and good electrochemical stability of the complex. Moreover, the present study demonstrates that β-cyclodextrin can serve as a carrier system, since the TTZ molecule can be gradually released from the inclusion complex with time.

Multifunctional magnetic cargo-complexes with radical scavenging properties

Core-shell magnetic nanoparticle synthesis offers the opportunity to engineering their physical properties for specific applications when the intrinsic magnetic properties can be associated with other interesting ones. The purpose of this study was to design, synthesize, and characterize core-shell magnetic nanoparticles that mimic superoxide dismutase activity offering the possibility of guidance and therapeutic action. We proposed, for the first time, the synthesis and characterization of the nanocarriers comprised of magnetite nanoparticles functionalized with branched polyethyleneimine of low molecular weight (1.8 kDa) permitting the loading of the protocatechuic acid or its inclusion complex with anionic sulfobutylether-β-cyclodextrin for active drug delivery, in order to combine the useful properties of the magnetite and the protocatechuic acid antioxidant effect. NMR and DSC analyses confirmed the formation of the inclusion complex between sulfobutylether-β-cyclodextrin and protocatechuic acid, while structural and compositional analyses (FT-IR, TEM, XRD) revealed the synthesis of the multifunctional magnetic systems. Due to the possibility of being formulated as blood system injectable suspensions, antioxidant activity (using DPPH test) and cytotoxicity (using MTS assay on normal human dermal fibroblasts cells) were also measured, showing adequate properties to be used in biomedical applications. Moreover, we proposed a nanocarrier that would be able to load unstable active principles and with very low solubility in biological fluids to increase their biological ability.

Ni–Co Bimetallic Nanostructures Based Electrochemical Sensors for Glucose Detection

Electrochemical sensors based on metallic nanoparticles and different forms of carbon have [...]

Electrochemical Deposition of Silver—Gold Nanoparticles for Sensitive Dopamine Detection

Dopamine (DA) is a catecholamine neurotransmitter, which plays a crucial role as chemical messengers in the central nervous system, hormonal, cardiovascular and renal systems. [...]

Crown ether-based structures for sensitive electrochemical detection

N-(2-Hydroxypropyl)methacrylamide-co-N-acryloxysuccinimide with 2-aminomethyl-18-crown-6 (p(HPMA-NAS-18C6)) graft copolymer deposited on the gold (Au) electrode is able to bind heavy metal cations from aqueous solutions. The binding of the lead(II) cations (Pb2+) is monitored by quartz crystal microbalance, cyclic voltammetry, and anodic stripping voltammetry. Electrochemical studies have demonstrated that the presence of p(HPMA-NAS-18C8) on the Au electrode surface resulted in the shift of Pb oxidation wave to less negative potentials, accompanied by the increase of the oxidation peak magnitude. The p(HPMA-NAS-18C6)-modified electrode could sensitively detect Pb2+ cations in a range from 10 ppb to 4.39 ppm with a low detection limit of 0.17 ppb.