Antonella Curulli

Green synthesis of gold-chitosan nanocomposites for caffeic acid sensing.

In this work, colloidal gold nanoparticles (AuNPs) stabilized into a chitosan matrix were prepared using a green route. The synthesis was carried out by reducing Au(III) to Au(0) in an aqueous solution of chitosan and different organic acids (i.e., acetic, malonic, or oxalic acid). We have demonstrated that by varying the nature of the acid it is possible to tune the reduction rate of the gold precursor (HAuCl(4)) and to modify the morphology of the resulting metal nanoparticles. The use of chitosan, a biocompatible and biodegradable polymer with a large number of amino and hydroxyl functional groups, enables the simultaneous synthesis and surface modification of AuNPs in one pot. Because of the excellent film-forming capability of this polymer, AuNPs-chitosan solutions were used to obtain hybrid nanocomposite films that combine highly conductive AuNPs with a large number of organic functional groups. Herein, Au-chitosan nanocomposites are successfully proposed as sensitive and selective electrochemical sensors for the determination of caffeic acid, an antioxidant that has recently attracted much attention because of its benefits to human health. A linear response was obtained over a wide range of concentration from 5.00 × 10(-8) M to 2.00 × 10(-3) M, and the limit of detection (LOD) was estimated to be 2.50 × 10(-8) M. Moreover, further analyses have demonstrated that a high selectivity toward caffeic acid can be achieved without interference from catechin or ascorbic acid (flavonoid and nonphenolic antioxidants, respectively). This novel synthesis approach and the high performances of Au-chitosan hybrid materials in the determination of caffeic acid open up new routes in the design of highly efficient sensors, which are of great interest for the analysis of complex matrices such as wine, soft drinks, and fruit beverages.

Oxidase enzyme immobilisation through electropolymerised films to assemble biosensors for batch and flow injection analysis

Glucose oxidase, lactate oxidase, L-aminoacid oxidase and alcohol oxidase were immobilised on new films based on 2,6-dihydroxynaphthalene (2,6-DHN) copolymerised with 2-(4-aminophenyl)-ethylamine (AP-EA) onto the Pt electrodes. The electropolymerisation was performed by cyclic voltammetry. Different scan rates and scan potential ranges were investigated and selected according to the monomers used. These sensors were tested for hydrogen peroxide, ascorbic acid and acetaminophen by cyclic voltammetry and amperometry. The amperometric studies were carried out in batch as well as in a flow injection analysis (FIA) system. Analytical parameters such as reproducibility, interference rejection, response time, buffer, storage and operational time of the sensors have been studied. These films were also characterised by X-ray photoelectron spectroscopy (XPS). Different strategies for enzyme immobilisation were performed and discussed: enzyme entrapment in the film during the electropolymerisation and covalent attachment of the enzyme to the film via a carbodiimide (1-ethtl-3-(3-dimethylaminopropyl)carbodiimide, EDC) or glutaraldehyde. Different parameters were considered in order to optimise the immobilisation procedures. Results provide a guide to design high sensitive, stable and interference-free biosensors. In addition, studies were performed using these probes in an original FIA based on solenoidal valves. Sensor stability, life time and dynamic range were also optimised in these conditions.

Electropolymerization of hydroxybenzene and aminobenzene isomers on platinum electrodes to assemble interference-free electrochemical biosensors

Abstract Hydroxybenzene and aminobenzene isomers have been electropolymerized on platinum electrodes together with oxidase enzymes for preparation and analytical evaluation of electrochemical biosensors. A conventional three electrode system was assembled for the electropolymerization of these compounds which led to the formation of poly(hydroxybenzene) and poly(aminobenzene). Different scan rates and scan ranges of potential were investigated and selected according to the monomer used. The time of electropolymerization was from 7 min to 4h. All the electrodes with the polymer films formed were tested for H 2 O 2 by cyclic voltammetry. Compounds as ascorbate, urate and acetaminophen, which are a common source of interferences in electrochemical biosensors analysis, based on H 2 O 2 detection, were tested. Results showed an oxidation peak of H 2 O 2 at the bare electrode and in all the electropolymerized probes, whereas for the interfering compounds the oxidation peak at electropolymerized probes was considerably reduced or not observed. When the electropolymerization was carried out in presence of the enzyme glucose oxidase, again the probe did not respond to the interferents, but gave a current signal to glucose in the range of 0.05 to 5mmol/L.

Bienzyme Amperometric Probes for Choline and Choline Esters Assembled with Nonconducting Electrosynthesized Polymers

Different nonconducting polymers have been synthesized on the surface of a platinum (Pt) electrode to assemble fast-response and sensitive amperometric biosensors for choline, butyrylcholine, and acetylcholine, based on choline oxidase (ChOx) and acetylcholinesterase (AchE) or butyrylcholinesterase (BuchE), co-immobilized by crosslinking with bovine serum albumin (BSA) and glutaraldehyde (GLT). Also the electropolymerization conditions as scan rate and time were optimized for each monomer in order to obtain the best permselectivity, the highest interferences rejection and stability. The procedure of immobilization was proven to be fast and simple and resulted in a better long-term stability and in a higher loading of the enzyme than that obtained by the co-electropolymerization. Studies on reproducibility, lifetime of the immobilized enzymes, pH, temperature, interferences, buffers, response time, storage and operational time of the biosensors have been carried out. The optimized biosensors allowed rapid quantitative assay of cholinesterase inhibitor paraoxon, with a detection limit of 0.1 ppb and a response time of less than ten seconds.

Amperometric Nitric Oxide Sensors: a Comparative Study

A comparative study among different types of modified electrodes for nitric oxide (NO) determination has been carried out. Detection limit, response time, reproducibility and selectivity versus some interferents as ascorbic acid, nitrite and dopamine were evaluated. Platinum (Pt) and glassy carbon (GC) electrodes have been assembled with homemade cellulose acetate membranes, commercially available membranes, Nafion and nonconducting polymers electrosynthesized directly onto the electrode surface. The most interesting results were obtained with a cellulose acetate membrane modified electrode and a Pt/poly[4,4′-dihydroxybenzophenone (4,4′-DHB)] electrode. The NO probes assembled showed a detection limit of 20 nmol/L and 40 nmol/L, respectively, for the cellulose acetate membrane modified electrode and for the Pt/poly[4,4′-dihydroxybenzophenone (4,4′-DHB)] electrode. A biological test on washed platelets stimulated by collagen was performed using the Pt/poly(4,4′-DHB) electrode.

A new interference-free lysine biosensor using a non-conducting polymer film

An electrochemical biosensor for the determination of lysine to be used for rapid evaluation of food quality has been developed. Platinum electrodes have been coated by electropolymerisation with 1,2-diaminobenzene (1.2-DAB) using cyclic voltammetry. The reduction in the oxidation of interferents compared with the bare platinum electrode was 100% for ascorbic acid, 99% for acetaminophen and 99% for cysteine. The enzyme L-lysine-alpha-oxidase was then immobilised onto the polymer layer by passive adsorption and a calibration curve for lysine constructed. This gave a linear range of 1 x 10(-5) mol/l to 1 x 10(-3) mol/l and a limit of detection of 2 x 10(-7) mol/l.

Nonconducting polymers on Prussian Blue modified electrodes: improvement of selectivity and stability of the advanced H/sub 2/O/sub 2/ transducer

An approach to improve the analytical performance of a Prussian Blue (PB)-based hydrogen peroxide transducer is described. In support of this objective, both the stabilizing and anti-interferent properties of nonconducting films were used. Electropolymerization on the top surface of PB modified electrodes is possible due to the high oxidizing ability of Berlin Green, and the growth of nonconductive polymers may be independently monitored by investigating the redox activity of the inorganic polycrystal. The best performance characteristics, which are advantageous over existing H/sub 2/O/sub 2/ sensors, were obtained for PB electrodes covered with electropolymerized o-phenylenediamine (1,2-diaminobenzene). The reported transducer remained at the 100% response state for more than 20 h under continuous flow of 0.1-mM hydrogen peroxide (flow rate 1 mlmin/sup -1/), which improves the stability level among the selective H/sub 2/O/sub 2/ sensors by one order of magnitude. The selectivity factor of the PB-poly (1,2-diaminobenzene) based transducer relative to ascorbate is nominally 600. PB-poly(1,2-diaminobenzene) modified electrode allows the detection hydrogen peroxide in the flow-injection mode down to 10/sup -7/ M with sensitivity of 0.3 AM/sup -1/cm/sup -2/, which is two times lower compared to the uncovered PB-based transducer.

Assembling and evaluation of new dehydrogenase enzyme electrode probes obtained by electropolymerization of aminobenzene isomers and PQQ on gold, platinum and carbon electrodes

Pt, Au and graphite electrodes have been coated by electropolymerization of 1,2-, 1,3-, 1,4-diaminobenzene (DAB) and 4-aminobiphenyl in the presence of PQQ using cyclic voltammetry. The activity of the modified electrodes for the oxidation of paracetamol, ascorbic and uric acid was reduced by approximately 90% as compared to the bare electrodes. Polymerization in the presence 4,5-dihydro-4,5-dioxo-1H-pyrrolo(2,3-f)quinoline-2,7,9-tricarboxilic+ ++ acid, pyrroloquinolinequinone (PQQ) led, after optimization, to electrodes capable of catalysing the electrooxidation of beta-nicotinamide adenine dinucleotide, reduced form (NADH), in the range 10(-4)-10(-2) mol/l with a detection limit of 5 x 10(-5) mol/l. Amperometric measurements of NADH have been carried out at +0.2 V and the efficiency of different electrodes based on different materials has been studied. By co-entrapment of dehydrogenase highly selective enzymes, electrodes for glucose, L-lactate and L-glutamate were obtained. Dehydrogenase substrates such as glucose, lactate and glutamate were measured in the range 5 x 10(-5)-1 x 10(-2) mol/l, with detection limits of 10(-5) and 5 x 10(-6) mol/l, respectively. Probe stability under non-dynamic conditions was evaluated over 2 months. All the probes showed a decrease of 10% over 1 month and a residual activity of 50% over 2 months.

Novel route to high-yield synthesis of sp2-hybridized boron nitride nanoplates on stainless steel

The synthesis of randomly distributed sp2-BN nanoplates embedded in a steel matrix was achieved by using boron doped AISI 316 stainless steel as substrates and a dissociated anhydrous NH3 atmosphere at 1070 °C as the nitrogen source. The chemical and morphological nature of the BN nanoplates has been studied by means of the combined use of XPS, FESEM-EDS, FTIR, XRD and SIMS techniques. The BN nanoplates are generally 100–400 nm wide and in many cases are characterised by a triangular or quasitriangular shape with some truncated and broken nanoplates that form a film whose thickness varies from 45 to 60 nm as a function of the boron content. This synthesis has the potential for coating stainless steel vacuum components and vessel walls with a stable film inert to gas adsorption to be used for the production of the next-generation of high performance stainless steel components for vacuum technology such as particle accelerators, thin film deposition and surface analysis equipment and further, as precursors for the fabrication of c-BN nanoplates.

Functionalization and dispersion in a polymer-matrix of single-wall carbon nanotubes: a FT-IR study

The exceptional structural, mechanical, chemical and electronic properties of single-wall carbon nanotubes (SWCNTs) make them suitable for the development of a completely new class of sensors and actuators, biosensors, electrochemical capacitors and supercapacitors. As a result, the study of CNT-based nanostructured and functional materials has become an interesting theme. In particular, the formation of CNT/polymer composites, besides possible improvements in the mechanical and electrical properties of polymers, is considered as a promising approach for the assembling of hybrid CNTs-polymer devices. However, manipulation and processing of SWCNTs is generally limited by their insolubility in most common solvents. Considerable effort has therefore been devoted to the chemical modification and derivation of carbon nanotubes. In this work, we described different treatments of carbon nanotube materials and a FT-IR study to demonstrate the functionalization of SWCNTs.