Giorgio Serra

A comparative study of protein immobilization techniques for optical immunosensors.

This paper presents the results of a study of a number of antibody immobilization techniques for application to optical immunosensors. In particular, well-known methods such as covalent binding and physical adsorption have been extended to the Langmiur-Blodgett method in an attempt to improve the density and possibly the uniformity of orientation of monoclonal antibodies on an optical surface. The surface density of active immobilized antibodies was determined from enzyme immunoassay and their thickness and refractive index were deduced from ellipsometry. It is shown that, although high surface densities (500 ng/cm2) of antibody can be obtained, the major obstacle to the detection of low concentrations of antigens or haptens is the non-specific binding of foreign molecules to the sensing surface.

Helical dielectric elastomer actuators

This paper presents a new type of contractile polymer-based electromechanical linear actuator. The device belongs to the class of dielectric elastomer actuators, which are typically capable of undergoing large deformations induced by an applied electric field. It is based on a novel helical configuration, suitable for the generation of electrically driven axial contractions and radial expansions. The architecture, the principle of operation, a fabrication method and results of a preliminary prototype testing of the new device are described. An axial strain of −5% at about 14 V µm −1 was obtained from first prototypes. (Some figures in this article are in colour only in the electronic version)

Characterisation of olive oil by an electronic nose based on conducting polymer sensors

Abstract The selection and test of an array of conducting polymer sensors with extra-virgin olive oil samples is presented in this paper as a first step towards the development of an electronic nose dedicated to the detection of olive oil aroma. Different sensors produced by both electrochemical and chemical techniques were initially exposed to a set of pure substances present in the headspace of extra-virgin olive oil and meaningful for the evaluation of its overall organoleptic characteristics. Four sensors showing the best sensitivity to these standard substances were chosen to carry out further experiments on samples of commercial olive oil. Two different experimental set-ups and protocols for olive oil sampling were tested and compared, providing evidence on the best procedure needed to handle this foodstuff and on the possibility of using a dedicated sensing system for practical purposes in the olive oil industry. Three different extra-virgin Italian types of olive oil can be easily distinguished with an array of four sensors and it is also possible to detect changes in the aromatic content of the headspace after handling of the samples. Different samples of the same oil show reproducible responses.

Microfabrication of conducting polymer devices by ink-jet stereolithography

An ink-jet stereolithographic technique for polymer device microfabrication is described. It exploits the simple working principle of an ink-jet printing head in order to build conjugated polymer devices for electronic, sensing, or actuating applications. The polymer, dissolved in a volatile solvent, is ejected drop by drop onto the substrate. This mechanism allows the deposition of polymeric patterns onto different surfaces without the drawbacks, in terms of time, cost, and process flexibility, that could derive from other classical techniques (spin-coating and photolithography). In addition, three-dimensional structures can be fabricated by means of this technique, by simply depositing different layers of polymer, one on top of the other.

Highly active rhodium catalysts for the [2+2+2] cycloaddition of acetylenes

Abstract The catalytic activity of the complexes [Rh(π 5 -indenyl)L 2 ] (L = ethylene or cyclooctene; L 2 = 1,5-cyclooctadiene), ( I ) - ( III ), and [Rh(π 5 -fluorenyl) (1,5-cyclooctadiene)], ( IV ), in the cyclotrimerization reaction of alkynes to benzene derivatives has been investigated. Compounds I - IV were very active in comparison with the isostructural cyclopentadienyl rhodium complexes. The catalytic activity depended markedly upon the nature of the substituents attached to the carbon-carbon triple bond, decreasing in the order: dimethyl acetylenedicarboxylate > methyl propiolate > diphenylacetylene > 1-hexyne > 3-hexyne > 1-octyne. In almost all cases the reaction has shown a high chemoselectivity. Some influence of the nature of the cyclopentadienyl-like ligand on both the catalytic activity and the regioselectivity has been observed. By reacting diphenylacetylene (dpa) with roughly stoichiometric amounts of I and III , the complexes [Rh 2 π 5 -indenyl) 2 (dpa) 2 ], ( VI ), and [Rh(π 5 -indenyl)(π 4 -tetraphenylcyclobutadiene)], ( VII ), have been obtained, respectively. VI was poorly active and VII inactive in dpa cyclotrimerization. The mechanism of these cyclotrimerization reactions is discussed with reference to the role played by the indenyl and fluorenyl ligands in determining the activity of the catalyst precursors I - IV .

Fibre-optic pH sensor for sea-water monitoring using a single dye

Abstract A sensor for the continuous monitoring of pH in sea water, having the configuration of a probe, is described. The characteristics of this probe, which uses phenol red adsorbed on Amberlite resin as a chemichromatic element on top of an optical fibre, are reported and the effects of interfering parameters (variable salinity and temperature of sea water) are assessed. The possibility of enhancing the working range is discussed, and a procedure for rendering the range suitable for marine monitoring is presented.

Fabrication of conducting polymer patterns for gas sensing by a dry technique

Abstract A dry fabrication technique to form conducting polymer patterns is presented. Such a technique can be particularly suitable for the implementation of conducting polymer arrays for gas sensing. The whole process, from sample preparation up to the polymerization process, is described. It basically consists of an in situ polymerization of the monomer in the vapour phase on a solid oxidizing salt formed on an insulating substrate under controlled conditions. Solid monomers were also polymerized using a purposely designed and realized reactor. The whole process was tested with a solid monomer belonging to the class of polyalkylthiophenes: homogeneous, repeatable conducting polymeric patterns were obtained and the results of their electrical and morphological characterization are reported and sensitivity to alcohol vapours tested. Various technological aspects of the process are discussed and a comparison with the more widely used wet polymerization techniques is reported.

Exploiting conducting polymer fiber radial expansion for bio-inspired actuation

Following the biological paradigm, artificial polymeric systems considered as candidates for actuation applied to biomedical devices and systems were tested taking into account longitudinal strain as a result of energy conversion from external sources. Among them, dielectric elastomers show good mechanical performances, but they require very high voltages for the driving, on the order of kilovolts, which are not suitable for devices that are in contact with biological systems. Conducting polymers work in a voltage range much more reasonable, but they show only few percents of longitudinal strain. On the other hand, it is known that, for instance, in a planar configuration of DBS-doped polypyrrole, the longest dimension undergoes a dimensional change of 0.5% up to 4% while the shortest one has a strain of roughly 35%. In this work, we discuss the latest advances concerning conducting polymer based devices and assess the worth of exploiting the interesting properties characterizing the radial strain of conducting polymer fibers rather than the axial strain. We also describe a possible method able to convert radial to longitudinal strain via a braided mesh acting as a merely mechanical transducer or even as a strain amplifier. The described technical improvements and observations, together with a voltage drop range acceptable for biomedical applications, give conducting polymers a new appeal for this kind of utilization and promise new interesting applications.

Study of the influence of oxidising salt on conducting polymer sensor properties

Abstract Conducting polymer sensors obtained by vapour phase polymerisation are suitable for odour recognition. This work investigates the influence of the precursor oxidising salt on the sensing properties of the polymer and the possibility of producing different sensors from the same monomer polymerised onto different salts. Twenty salts obtained from several metals via exposure to oxidising agents in gas phase have been tested and a set of three salts whose properties are compatible with our dry technique has been selected. The sensors grown on these salts using a monomer of the class of alkoxythiophenes show different sensitivities to a test vapour in terms of percentage variation of resistance.

Conducting polymer as smart interfaces for cultured neurons

This work is part of a research project aimed at realising conducting polymer matrices for interfacing with cultured neurons. The polymer matrix has a dual function, one as a medium for recording electrical activity; the other is chemical stimulation through the release of bioactive molecules. In this work we use poly-3-hexylthiophene as a conducting polymer matrix. To test the polymer’s ability to release molecules upon the application of a potential it was doped with glutamate (GA). GA is an important neurotransmitter, and its controlled release can be important in several medical and tissue engineering applications. Diffusional and controlled release of GA from the polymer were assessed. Biocompatibility of the samples was evaluated at each stage using neuroblastoma cell cultures.