Simona-Carmen Litescu

Disposable biosensor based on platinum nanoparticles-reduced graphene oxide-laccase biocomposite for the determination of total polyphenolic content

A disposable amperometric biosensor was developed for the detection of total polyphenolic compounds from tea infusions. The biosensor was designed by modifying the surface of a carbon screen-printed electrode with platinum nanoparticles and reduced graphene oxide, followed by the laccase drop-casting and stabilization in neutralised 1% Nafion solution. The obtained biosensor was investigated by scanning electron microscopy and electrochemical techniques. It was observed that platinum nanoparticles-reduced graphene oxide composite had synergistic effects on the electron transfer and increased the electroactive surface area of the carbon screen-printed electrode. The constructed analytical tool showed a good linearity in the range 0.2-2 μM for caffeic acid and a limit of detection of 0.09 μM. The value of Michaelis-Menten apparent constant was calculated from the electrochemical version of Lineweaver-Burk equation to be 2.75 μM. This disposable laccase biosensor could be a valuable tool for the estimation of total polyphenolic content from tea infusions.

VOLTAMMETRIC DETERMINATION OF COENZYME Q10 AT A SOLID GLASSY CARBON ELECTRODE

This paper reports a simple, sensitive, and accurate voltammetric method for the coenzyme Q10 electroanalytical determination on a glassy carbon electrode (GCE) from commercially available capsules, compared with a UV-VIS spectrophotometric method. Cyclic (CV), linear sweep (LSV), and square-wave (SWV) voltammetry on GCE was employed to explore the coenzyme Q10 behaviour, using as supporting electrolyte, 0.12 M H2SO4 (in methanol) in hexane/methanol (1:2 vol.) mixture. The voltammograms showed the characteristic reduction peaks at potential values in the range of 0.190– 0.300 V vs. Ag/AgCl, depending on the technique that was used. A linear dependence of the reduction peak height on the analyte concentration was obtained using LSV and SWV techniques in the domains 5 × 10−6 −7 × 10−4 mol L−1,and 5 × 10−7 −7 × 10−4 mol L−1 coenzyme Q10 concentration. The detection limit was 10−7 mol L−1 for SWV. The coenzyme Q10 determination from commercially available capsules required four consecutive steps of compound extraction in hexane, followed by the appropriate dilution. The voltammetric analysis was performed by the standard addition method, a 97.33 % recovery from the declared content being obtained. The UV-VIS spectra of coenzyme Q10 in hexane showed three maxima at 396 nm, 329 nm, and 272 nm, respectively, with a linear dependence of absorbances on the analyte concentrations. The spectrophotometric determination of the extracted coenzyme Q10 material from capsules was carried out at 396 nm wavelength, since the excipients strongly interfered at 272 nm and 329 nm. The recoveries were 93.7–97.5 %.

Development of a nanocomposite system and its application in biosensors construction

AbstractThe present work describes the development of a nanocomposite system and its application in construction of a new amperometric biosensor applied in the determination of total polyphenolic content from propolis extracts. The nanocomposite system was based on covalent immobilization of laccase on functionalized indium tin oxide nanoparticles and it was morphologically and structural characterized. The casting of the developed nanocomposite system on the surface of a screen-printed electrode was used for biosensor fabrication. The analytical performance characteristics of the settled biosensor were determined for rosmarinic acid, caffeic acid and catechol (as laccase specific substrate). The linearity was obtained in the range of 1.06×10−6 − 1.50×10−5 mol L−1 for rosmarinic acid, 1.90×10−7 − 2.80×10−6 mol L−1 for caffeic acid and 1.66×10−6 − 7.00×10−6 mol L−1 for catechol. A good sensitivity of amperometric biosensor 141.15 nA µmol−1 L−1 and fair detection limit 7.08×10−8 mol L−1 were obtained for caffeic acid. The results obtained for polyphenolic content of propolis extracts were compared with the chromatographic data obtained by liquid-chromatography with diode array detection.

Spectrochemical Characterization of Thin Layers of Lipoprotein Self-Assembled Films on Solid Supports Under Oxidation Process

Low density lipoprotein self-assembled layers on gold support, proposed as model for oxidation studies, were subjected to oxidation processes using different oxidative agents: 2,2′-Azobis(2methylpropionamidine)dihydrochloride, atmospheric oxygen, and metal-induced oxidation. The freshly prepared and the oxidized layers were characterized by X ray photoelectron spectroscopy (XPS), Fourier-Transformed infrared spectroscopy, and Matrix-Assisted Laser Desorption/Ionization-Time of Flight (MALDI-ToF) mass spectrometry to discriminate the effects of oxidative reagents. Data obtained from FTIR and MALDI spectra proved the lipoperoxide formation subsequent to reactive oxygen species attack and the opportunity to use the model to discriminate between oxidation toxicity.

Monitoring of Rosmarinic Acid Accumulation in Sage Cell Cultures using Laccase Biosensor

INTRODUCTION A recently developed laccase based biosensor is used for polyphenols determination from in vitro Salvia cultures, the results being expressed as rosmarinic acid equivalent content. OBJECTIVE The aim of this work was to use a previously developed laccase biosensor for the determination of total phenolic content from in vitro cultivated Salvia, and to support the biosensors further application for the assessment of polyphenols metabolites. METHODOLOGY The biosensor was constructed by drop casting 3 μL of laccase solution and stabilisation with 0.1 % Nafion solution onto a DropSens carbon screen-printed electrode. Electrochemical measurements were carried out in a 0.1 mol/L phosphate buffer (pH 4.50), the applied working potential being -30 mV versus reference electrode. RESULTS The response of the biosensor developed was characterised in terms of repeatability, accuracy and precision; the limit of detection was 7.5 × 10(-7) mol/L, the limit of determination was 9.5 × 10⁻⁷ mol/L, and linear response range for rosmarinic acid was 1 × 10⁻⁶-10⁻⁵ mol/L. CONCLUSION A stable, sensitive and simple biosensor based on laccase-nafion was used for monitoring the total polyphenolic content from two in vitro cultivated plants. The biosensor response was free of electrochemical interferences and of possible interferences from growth media constituents, demonstrating a high sensitivity for rosmarinic acid determination in cell culture suspensions.

Fourier Transform Infrared Spectroscopy - Useful Analytical Tool for Non-Destructive Analysis

It is highly recognized that the use of Fourier Transform Infrared Spectrometry (FTIR) for chemical substances identification it is not a trivial task to be fulfilled by analytical chemists. The complexity of FTIR characterization comes mainly from the high degree of infrared absorption bands overlapping, that are difficult to be accurately ascribed, despite of the fact that up to date computer-searchable databases of spectra are currently available.

Lipid hydroxide determination on a ferrocenemethanol modified electrode

The main products generated by lipid peroxidation are the lipid hydroperoxides, compounds that are involved in the pathology of several diseases and in the process of food rancidification. In this context, simple, fast, and reliable analytical tools for the determination of lipid hydroperoxides are highly required. The present work describes the development of a single use ferrocenemethanol modified carbon screen-printed electrode for the determination of lipid hydroperoxides. The modified electrode is equally applicable to evaluation of peroxidation inhibition degree of two well-known antioxidants. The performance characteristics of the proposed non-enzymatic sensor are: linear working range 6.0 × 10−6 to 2.7 × 10−4 mol L−1, limit of detection 1.7 × 10−6 mol L−1, upper control limit 3 × 10−4 mol L−1 and sensitivity 826.53 nA mM−1; the required time to reach the steady state was 60 s. The sensor was then applied for the determination of lipid hydroperoxide formation from four real samples of vegetal oils, walnut, sunflower, linseed and soybean oils, the results being expressed as linoleic acid equivalents. Furthermore, the efficacy of Trolox and butylated hydroxyanisole in inhibiting lipid hydroperoxide formation was tested.

Assessment of role of rosmarinic acid in preventing oxidative process of low density lipoproteins

This study aimed to assess the antioxidant compound effects on oxidisable substrates, using an effective bio-mimetic system based on human low density lipoproteins (LDL). Thermally generated radicals induce LDL oxidative changes to be identified and quantified. The bio-mimetic system thus developed responded linearly to radicals’ concentration over a range of 10−6-10−5 mol L−1. Cu2+ accentuates lipoperoxidation but, when rosmarinic acid was present, Cu2+ produced an unexpected effect, i.e. increased antioxidant efficiency against lipoperoxidation. Rosmarinic acid inhibits production of lipoperoxides by up to 30 % in the absence of Cu2+ and up to 70 % in its presence when the rosmarinic acid-to-Cu molar ratio is 1: 1.

Spectroscopic studies on lipoprotein structure modification under oxidative stress

Matrix assisted laser desorption-ionization time of flight (MALDI-ToF) and infrared techniques were used to study oxidative modification of low density lipoproteins (LDL), considered to have the key role in biological process that initiates and accelerates the development of cardiovascular disease. The early identification of lipoperoxidation products creates the oppor- tunity of the efficient prevention of eventual oxidative damages. MALDI analysis of LDL subjected to in vitro oxidation process initiated by 2,2-azobis(2-amidinopropane) dihydrochloride revealed that some fragments of lipoprotein changed the molecular weight by 16 and 32 Da due to the oxygen or hydroxyl groups attachment, and peroxide or hydroperoxide formation, while Fourier Transformed Infrared studies proved that lipoprotein changes its protein secondary conformation from predominantly α-helix in predominantly β-turn. The increase in free radicals concentration correlated to structural changes, and the presence of transitional metal ion, copper (II), in the oxidation process lead to an enhancing of the damaging effects of free radicals on lipoprotein substrate. It was shown that the toxic effects of oxidants are delayed by the presence of glutathione (10 mM), an endogenous antioxidant.