Maria Pia Sammartino

Hydrogen peroxide determination in pharmaceutical formulations and cosmetics using a new catalase biosensor.

The possibility of evaluating the content of hydrogen peroxide in several authentic matrices, such as cosmetic and pharmaceutical formulations, was studied. A new catalase biosensor fabricated using an amperometric gas-diffusion oxygen sensor as electrochemical transducer and the catalase enzyme immobilized in kappa-carrageenan gel and capable of operating in both aqueous and non aqueous solvents was developed and tested for this purpose. Creams, emulsions and disinfectant solutions were analysed. To this end, a preliminary check was needed to establish the best conditions to analyse these matrices; the choice of solvent was one of the most important points studied. The solvents considered included dioxane, water-dioxane mixtures, water saturated chloroform and aqueous solutions. The different solubility properties of the matrices analysed were taken into account.

The effect of organic solvent properties on the response of a tyrosinase enzyme sensor

The use of an enzyme tyrosinase sensor capable of being employed in non aqueous media represents a good opportunity to investigate the effects of the organic solvent on enzyme activity. Six different solvents are considered (n-heptane, n-hexane, n-pentane, toluene, chloroform, acetonitrile) and two properties of these solvents are studied in particular, i.e. hydrophobicity (as log P) and dielectric constant, taking into account their influence on sensor response. Results are generally in agreement with those found by other authors, who determined the behaviour of the enzyme activity as a function of organic solvents using different methods.

Butyrylcholine enzyme sensor for determining organophosphorus inhibitors

Abstract Esterase enzymes play an important role in biology because they are responsible for the hydrolysis of acetylcholine and because, in their absence, (or if their activity is inhibited), the original state of the postsynaptic membranes cannot be re-established. It is therefore of interest to study the inhibiting action exerted by some compounds on this class of enzymes. Among them, pesticides are important because of the potential danger as a result of their large-scale use in agriculture. The behavior of the esterase/pesticide systems, and the analytical possibilities arising from the inhibiting action exerted by pesticides on esterases were examined. Along these guide lines, a biosensor for the determination of pesticides did finally result. This biosensor consists of a Clark oxygen electrode, modified with a dialysis membrane placed over it containing two immobilized biological mediators: butyryl- or acetyl-cholinesterase and choline oxidase. Its application to the analysis of ecologically important matrices is described. A comparison with the results obtained by a similar, previously published procedure, characterized by butyryl- (or acetyl-)cholinesterase free in solution, is also reported.

XPS characterization of (copper-based) coloured stains formed on limestone surfaces of outdoor Roman monuments

Limestone basements holding bronzes or other copper alloys artefacts such as sculptures, decorations and dedicatory inscriptions are frequently met both in modern and ancient monuments. In outdoor conditions, such a combination implies the corrosion products of the copper based alloy, directly exposed to rainwater, will be drained off and migrate through the porous surfaces, forming stains of different colours and intensities, finally causing the limestone structures to deteriorate.In this work we have analysed samples from two modern limestone monuments in Rome, the Botticino surfaces of the ‘Vittoriano’ (by G.Sacconi, 1885-1911- Piazza Venezia) and the travertine basement of the ‘Statua dello Studente’ (by A.Cataldi, 1920- University city, La Sapienza), and focussed our investigation on the chemical composition of the copper-stained zones using XPS (X-ray Photoelectron Spectroscopy) as a surface-specific technique.Based on observations reporting on the structure and bonding at the calcite surfaces we have identified copper complexes and mixed calcium/copper carbonates associated with the stains, as well as the chemical state of other elements therein included, and related the compositional changes with differences in chromatic characteristics and sampling locations.

Determination of phenol in wastes and water using an enzyme sensor

Biosensors for the determination of phenol in real matrices such as oil press and industrial wastes and sea-, lake and river waters are proposed. Optimization of the experimental parameters, especially regarding enzyme immobilization, was performed. The biosensors are based on a Clark oxygen electrode coupled with tyrosinase immobilized by three different methods. Biosensors were also tested in order to verify whether their direct use with environmental samples and in in situ analysis is possible.

Tyrosinase biosensor response as a function of physical properties of organic solvents.

The main aim was to investigate the possibility of developing a fast, easily produced biosensor capable of being used in non-aqueous solvents such as n-hexane, chloroform, mixtures thereof and water-saturated chloroform. The research also provided an experimental confirmation of several concepts, described in the literature, concerning enzymatic activity in different types of non-aqueous solvents. The results are decidedly encouraging as regards future possible uses of this sensor to determine soluble substances in non-aqueous solvents.

Organophosphorus pesticide (Paraoxon) analysis using solid state sensors

A comparison of two new solid-state biosensors for organophosphorus pesticide analysis is presented, both of which employ the inhibiting action of these toxic compounds versus the enzyme butyrylcholinesterase. The indicating sensor used was a graphite electrode, or a FET, coated with an ion-selective polymeric membrane sensitive to pH containing tridodecylamine as exchanger. The former was coupled to the enzyme butyrylcholinesterase immobilised on a functionalized nylon net, while the latter employed the same enzyme coated on the polymeric membrane by means of polyazetidine prepolymer. The responses of the two biosensors to the substrate, i.e. butyrylcholine (BuCh), and to the inhibitor, i.e. Paraoxon, one of the most common organophosphorus pesticides, were tested.

New enzyme sensor for phenol determination in non-aqueous and aqueous medium

Abstract Research was performed in our laboratory, using tyrosinase enzyme, to develop a suitable probe sensitive to phenols, working in non-aqueous media. For this aim were used: a Clark oxygen electrode as indicating sensor, the tyrosinase enzyme immobilised in a dialysis membrane and n-hexane as non-aqueous solvent. A comparison of the response between the sensors, when working in n-hexane, and in aqueous buffer, is also reported.

Suitable ion-selective sensors for lead and cadmium analysis

Abstract Two different chemical sensor assemblies for lead(II) and cadmium(II) ions have been fabricated. The first is based on a traditional ion-selective electrode and the second on a graphite solid-state device. Both chemical sensors have been characterized and tested in standard solutions and also in river water samples. The use of a PVC-PVA-PVAc copolymer as base polymer in the membrane allows us to get a better adhesion on the graphite active surface of the device. The selectivity in the modified membrane is given using derivatives of dioxa diamide or ditioamide. The results obtained by the solid-state chemical sensors are compared with those obtained by ion-selective electrodes. Potentiometric measurements, response time, lifetime, linearity range and selectivity factors have also been reported and discussed.

Enzyme sensor for the determination of choline-containing phospholipids in some biological fluids

A choline enzymatic-amperometric sensor, obtained by physical entrapment of choline oxidase in cellulose triacetate membranes, was used for the determination of choline-containing phospholipids in serum, bile and amniotic fluids. The results obtained are compared with those obtained using an analogous sensor, based on the chemically immobilised enzyme, and with the data obtained by an enzymatic-spectrophotometric method.