Rosanna Ciriello

Assessment of riboflavin and flavin content in common food samples by capillary electrophoresis with laser-induced fluorescence detection

To routinely assay the flavin contents in foodstuffs, a rapid and sensitive method was developed, in which the powerful separation capabilities of high-performance capillary electrophoresis (CE) were exploited. The method is based on a simple sample preparation, electrophoretic separation and laser induced fluorescence (LIF) detection. The average content of water-soluble riboflavin vitamers in raw natural products (i.e. vegetables, wheat flours and tomatoes) and bakers yeasts was evaluated without interferences from the sample matrices. Such an accurate and highly sensitive CE-LIF technique represents a significant improvement over previous analytical methods in terms of sensitivity, simplicity and efficiency. Indeed, it is well suited to satisfy the demands for accurate and sensitive detection with minimal sample preparation and clean-up.

Permselective Behavior of an Electrosynthesized, Nonconducting Thin Film of Poly(2‐naphthol) and Its Application to Enzyme Immobilization

The electrooxidation of 2-naphthol in phosphate buffer at pH 7 leads to the formation of a nonconducting polymer of poly(2-naphthol) on a platinum electrode. Such a resulting thin film displays an interesting permselective behavior, which proved useful in minimizing the interference of ascorbate, acetaminophen, cysteine, and urate sample molecules. Electrochemical detection in flowing streams was used to investigate the relevance of permselectivity for sensor development. Nonconducting poly(2-naphthol) film demonstrated useful also as a novel permselective membrane for glucose oxidase immobilization. The glucose response time, t0.95, evaluated in batch addition experiments, was lower than 4 s. The calibration plot was linear up to 15 mM of glucose with a sensitivity of 2.2 nA/mM.

Permselective and enzyme-entrapping behaviours of an electropolymerized, non-conducting, poly(o-aminophenol) thin film-modified electrode: a critical study.

Non-conducting polymeric films synthesised by the electrooxidation of o-aminophenol on a platinum electrode in acetate or phosphate buffer displayed an interesting permselective behaviour, which proved valuable in minimising the electrochemical interferences from ascorbate, acetaminophen, cysteine and urate sample molecules in amperometric detection mode. The electrosynthesis of poly(o-aminophenol) (p(oAP)) film showed also useful as permselective membrane for enzyme immobilization as demonstrated by the production of an interference-free glucose oxidase biosensor. In this respect, the glucose response time, t(0.95), evaluated in batch addition experiments, was lower than 5s while the calibration curve was linear up to 10mM of glucose with a sensitivity of 69.7nA/mM. Both the permselective behaviour and the enzyme-entrapping property of the film were critically compared with the relevant studies until now reported. With respect to the sophisticated but complex approaches described elsewhere, this study shows that simply a proper optimization of p(oAP) electrosynthesis and its permselective behaviour is the key to improve significantly the selectivity of the resulting analytical devices.

Analysis by X-ray photoelectron spectroscopy of ruthenium stabilised polynuclear hexacyanometallate film electrodes

Abstract The role and effects of ruthenium on the electrochemical stabilisation of some metal-hexacyanometallate film electrodes was investigated by X-ray photoelectron spectroscopy (XPS). The following inorganic films were studied, cobalt(II)-hexacyanoferrate(II/III) (CoHCFe), nickel(II)-hexacyanoferrate(II/III) (NiHCFe), and iron(II/III)-hexacyanorutenate(II/III) (FeHCRu), and their corresponding ruthenium stabilised ones, Ru-CoHCFe, Ru-NiHCFe and Ru-FeHCRu. A mass increase of CoHCFe, NiHCFe, and FeHCRu, during continuous redox cycles (75–90 times) in a millimolar solution of RuCl3, was monitored by an electrochemical quartz crystal microbalance. Detailed XPS analysis of C 1s, O 1s, Fe 2p, Ni 2p, Co 2p, and Ru 3d peaks has allowed a comprehensive description of changes that occurred. The results obtained demonstrate that the insertion of ruthenium oxo species (e.g., Ru2O63+) was effective for the increase in lifetimes and for the electrocatalytic properties of ruthenium-modified metal-hexacyanometallate film electrodes. Three possible models of stabilisation are discussed.

Quantification of l-lysine in cheese by a novel amperometric biosensor

Lysine quantification in cheese by a novel, highly selective amperometric biosensor is reported. Based on l-lysine-α-oxidase immobilized by co-crosslinking onto Platinum (Pt) electrodes modified by overoxidized polypyrrole, the sensor proved almost specific to lysine, sensitive and stable. The pure enzymatic nature of current signals was confirmed by a control electrode modified without enzyme. The precision of the method showed relative standard deviations of 4.7% and 9.2% respectively for Parmigiano Reggiano and Grana Padano cheese (n=5). The recovery data on various cheese, spiked with lysine at 50-100% of the measured content, ranged from 85% to 99%. Different types of cheese were analysed showing lysine concentrations related to the ripening time and the manufacture technology, in agreement with literature data. Within dairy products, no appreciable lysine was detected in yogurts. The method adopted revealed suited to satisfy the demands for precise and sensitive detection of lysine with minimal sample preparation and clean-up.

A novel amperometric biosensor based on a co-crosslinked l-lysine-α-oxidase/overoxidized polypyrrole bilayer for the highly selective determination of l-lysine

An amperometric biosensor for the determination of L-lysine based on L-lysine-α-oxidase immobilized by co-crosslinking on a platinum electrode previously modified by an overoxidized polypyrrole film is described. The optimization of experimental parameters, such as pH and flow rate, permitted to minimize significantly substrate interferences even using a low specific, commercial enzyme. The relevant biases introduced in the measurement of lysine were just about 1% for L-arginine, L-histidine and L-ornithine, roughly 4% for L-phenylalanine and L-tyrosine. The developed approach allowed linear lysine responses from 0.02 mM up to 2 mM with a sensitivity of 41 nA/(mM × mm(2)) and a detection limit of 4 μM (S/N=3). No appreciable loss in lysine sensitivity was observed up to about 40 days. Allowing polypyrrole layer to remove interference from electroactive compounds, the present method revealed suitable to detect L-lysine in a pharmaceutical and cheese sample, showing a good agreement with the expected values.

Assessment of the genetic polymorphism and physiological characterization of indigenous Oenococcus oeni strains isolated from Aglianico del Vulture red wine

The aim of this study was a reliable intra-species discrimination and strain biodiversity in Oenococcus oeni populations of two different Aglianico wineries by molecular, biochemical, and physiological characterization. Pulsed field gel electrophoresis (PFGE) analysis revealed a high polymorphism related to the origin (winery) of strains, while differential display PCR (DD-PCR) allowed a further discrimination of strains from the same winery. Moreover, the heterogeneity of these natural populations was investigated by capillary electrophoresis and enzymatic assays. A variability related to a different surface charge distribution was observed among strains, linked to their origin. Malolactic activity study evidenced strain-specific differences in malic acid degradation, and then, only the presence of L(-)-malic acid in the medium induced the mle gene. This study provided evidences on the importance of intra-species biodiversity of malolactic bacterial populations in wine ecosystems, as each wine possess peculiar winemaking conditions and physical–chemical properties which make specific the bacterial survival and growth. This study highlighted a great biodiversity among O. oeni strains that can be also winery specific. Such biodiversity within a certain winery and winemaking area is important for selecting malolactic starters, and strain-specific trait identification is especially important to match individual strains to specific industrial process.

Comparative Spectra Illustrating Degradation of CaC2O4⋅H2O During XPS Analysis

Calcium oxalate monohydrate is found as a by-product of environmental damage to stonework of importance in preserving cultural heritage. XPS (X-ray Photoelectron Spectroscopy) was here used to characterize the standard compound, calcium oxalate monohydrate, RPE, chemically synthesized as provided by Carlo Erba Reagents - Cod. 434004. Degradation occurred during analysis and this is described. Repeat XPS acquisitions have allowed us to monitor the spectral changes of calcium oxalate during the whole process of analysis: its degradation was rationalized by considering the effect of x-ray power; UHV exposure; and thermal effects suffered by the powdered sample after its insertion into the spectrometer and, particularly, during spectra acquisition. Measurement of degradation with time enabled extrapolation to yield the primary composition. It was found that samples will completely dehydrate in ultra high vacuum, UHV. Although dehydrated samples are then stable in UHV, during XPS acquisitions degradation of ca...

A novel approach for the selective analysis of l-lysine in untreated human serum by a co-crosslinked l-lysine–α-oxidase/overoxidized polypyrrole bilayer based amperometric biosensor

An amperometric biosensor based on an l-lysine-α-oxidase (LO) layer immobilized by co-crosslinking onto the surface of an overoxidized polypyrrole modified Pt electrode (Pt/oPPy) and able to analyse l-lysine (Lys) in untreated human serum is described. The sensing electrode has been characterised and a proper enzyme kinetics optimisation permits to use a low specific enzyme as LO from Trichoderma viride for the selective biorecognition of Lys in the presence of other interferent amino acids; a kinetics study of LO evidenced also the allosteric behaviour of this enzyme, a kinetic feature which was never reported before for this enzyme. The biosensor showed a sensitivity of 0.11 μA/mM mm2, linear responses up to 4 mM and a limit of detection of 2 μM; the within-a-day coefficients of variation for replicate (n = 5) were 0.92% and 1.35% at 4 mM and 0.2 mM Lys levels, respectively. The permselective behaviour of Pt/oPPy modified electrode assured an interference- and fouling-free determination of Lys even in untreated serum samples. The determination of Lys in human serum from healthy donors gave Lys levels in good agreement with the expected values so that the use of the proposed biosensor appears promising in the relevant clinical fields.

In Situ Electrochemical–AFM and Cluster-Ion-Profiled XPS Characterization of an Insulating Polymeric Membrane as a Substrate for Immobilizing Biomolecules

The electrochemical oxidation of ortho-aminophenol (oAP) by cyclic voltammetry (CV), on platinum substrates in neutral solution, produces a polymeric film (PoAP) that grows to a limiting thickness of about 10 nm. The insulating film has potential use as a bioimmobilizing substrate, with its specificity depending on the orientation of its molecular chains. Prior investigations suggest that the film consists of alternating quinoneimine and oAP units, progressively filling all the platinum sites during the electrosynthesis. This work concerns the evaluation of the growth orientation of PoAP chains, which until now was deduced only from indirect evidence. Atomic force microscopy (AFM) has been used in situ with an electrochemical cell so that PoAP deposition on a specific area can be observed, thus avoiding any surface reorganization during ex situ transport. In parallel with microscopy, XPS experiments have been performed using cluster ion beams to profile this film, which is exceptionally thin, without damage while retaining molecular information.