Luigia Sabbatini

Multi-parameter gas sensors based on organic thin-film-transistors

Abstract In this communication, evidence is provided that an organic thin-film-transistor (OTFT) can be used as a novel gas sensor. When exposed to chemical species at room temperature, four parameters can be measured: the bulk conductivity of the organic thin film, the field-induced conductivity, the transistor threshold voltage and the field effect mobility. Measurements of these parameters may allow for recognition of molecular species.

Synthesis, analytical characterization, and osteoblast adhesion properties on RGD-grafted polypyrrole coatings on titanium substrates

The covalent attachment of an Arg-Gly-Asp (RGD) containing peptide to polypyrrole(PPy)-coated titanium substrates has been investigated in order to develop a bioactive material of potential use in orthopedic fields. Polypyrrole has been employed as the coating polymer because of its suitability to be electrochemically grown directly onto metallic substrates of different shapes, leading to remarkably adherent films. The synthetic peptide Cys-Gly-(Arg-Gly-Asp)-Ser-Pro-Lys, containing the cell-adhesive region of fibronectin(RGD), has been grafted to the polymer substrate via the cysteine residue using a procedure recently developed in the authors laboratory. The effectiveness of grafting was monitored by X-ray photoelectron spectroscopy (XPS), which assessed the presence of the peptide grafted onto the polymer surface exploiting the cysteine sulfur as target element. Neonatal rat calvarial osteoblasts were attached to RGD-modified PPy-coated Ti substrates at levels significantly greater than on unmodified PPy-coated Ti and glass coverslip substrates.

NEW FINDINGS ON POLYPYRROLE CHEMICAL STRUCTURE BY XPS COUPLED TO CHEMICAL DERIVATIZATION LABELLING

Abstract Polypyrrole electrosynthesised from aqueous solutions has been investigated by XPS, both in the conducting (PPY) and in the so-called overoxidised (PPYox) state. An accurate analysis of high resolution spectra, including cross-checking between the independent fittings of different though related signals (e.g. C1s and O1s), is presented, enlightening novel findings on polypyrrole structure. In particular, it suggested, for the first time, that overoxidation breaks polymer chains, producing new oxygen function on α-C (mainly CO). The application of a new chemical derivatization (CD) method to the labelling of this key functional group (CO) would confirm this feature.

Electrosynthesis and characterisation of nanostructured palladium–polypyrrole composites

Abstract Palladium–polypyrrole composite thin films have been synthesised using three different bottom-up procedures all comprising the electrochemical synthesis of palladium nanoparticles that are subsequently potentiostatically deposited or embedded into an electrochemically produced polypyrrole thin film. Transmission electron micrographs of the resulting composites show that the metallic inclusions have a mean diameter of about 5 nm with a homogeneous size distribution. Experimental evidence is also provided that both the nanoparticles and the composite thin films are electroactive. Preliminary results on the extendibility of this approach to the electrosynthesis of other metal–polypyrrole materials (namely Ag–PPy composites) are also presented.

Antifungal activity of polymer-based copper nanocomposite coatings

Eukaryotes, such as fungi, can be harmful pathogen agents, and the control of their bioactivity is critical as humans are eukaryote organisms, too. Here, copper∕polymer nanocomposites are proposed as antifungal spinnable coatings with controlled copper-releasing properties. The tests of the bioactivity show that fungal growth is inhibited on the nanocomposite-coated plates, and the antifungal activity can be modulated by controlling the Cu nanoparticle loading.

Electropolymerization of pyrrole on titanium substrates for the future development of new biocompatible surfaces

Titanium and its alloys are widely used in load-bearing implants as a result of their excellent mechanical properties and corrosion resistance. In order to improve their performances with respect to osseointegration, the use of bioactive coatings has been suggested. Polypyrrole (PPy) has been chosen as coating polymer because of its ability to be electrochemically grown directly onto metallic substrates, of any shape and dimension, leading to remarkably adherent overlayers. This polymer, in addition to protecting the metal implant against corrosion, could be surface modified with biologically active molecules able to stimulate positive interactions with bone tissue. In this work, PPy electrosynthesis on both titanium and Ti-Al-V substrates has been investigated. The chemical composition and the morphology of the polymeric films, deposited under different conditions, were evaluated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), respectively.

Carbon based materials for electronic bio-sensing

Bio-sensing represents one of the most attractive applications of carbon material based electronic devices; nevertheless, the complete integration of bioactive transducing elements still represents a major challenge, particularly in terms of preserving biological function and specificity while maintaining the sensors electronic performance. This review highlights recent advances in the realization of field-effect transistor (FET) based sensors that comprise a bio-receptor within the FET channel. A birds-eye view will be provided of the most promising classes of active layers as well as different device architectures and methods of fabrication. Finally, strategies for interfacing bio-components with organic or carbon nano-structured electronic active layers are reported.

Interfacial electronic effects in functional biolayers integrated into organic field-effect transistors

Biosystems integration into an organic field-effect transistor (OFET) structure is achieved by spin coating phospholipid or protein layers between the gate dielectric and the organic semiconductor. An architecture directly interfacing supported biological layers to the OFET channel is proposed and, strikingly, both the electronic properties and the biointerlayer functionality are fully retained. The platform bench tests involved OFETs integrating phospholipids and bacteriorhodopsin exposed to 1–5% anesthetic doses that reveal drug-induced changes in the lipid membrane. This result challenges the current anesthetic action model relying on the so far provided evidence that doses much higher than clinically relevant ones (2.4%) do not alter lipid bilayers’ structure significantly. Furthermore, a streptavidin embedding OFET shows label-free biotin electronic detection at 10 parts-per-trillion concentration level, reaching state-of-the-art fluorescent assay performances. These examples show how the proposed bioelectronic platform, besides resulting in extremely performing biosensors, can open insights into biologically relevant phenomena involving membrane weak interfacial modifications.

Analytical characterization of laser-generated copper nanoparticles for antibacterial composite food packaging

AbstractA new type of nanomaterial has been developed as antibacterial additive for food packaging applications. This nanocomposite is composed of copper nanoparticles embedded in polylactic acid, combining the antibacterial properties of copper nanoparticles with the biodegradability of the polymer matrix. Metal nanoparticles have been synthesised by means of laser ablation, a rising and easy route to prepare nanostructures without any capping agent in a liquid environment. As prepared, nanoparticle suspensions have been easily mixed to a polymer solution. The resulting hybrid solutions have been deposited by drop casting, thus obtaining self-standing antibacterial packages. All samples have been characterized by UV–Vis spectroscopy, X-ray photoelectron spectroscopy and electro-thermal atomic absorption spectroscopy. Ion release data have been matched with bioactivity tests performed by Japanese Industrial Standard (JIS) method (JIS Z 2801:2000) against Pseudomonas spp., a very common Gram-negative microbial group able to proliferate in processed food. Online abstract figureAnalytical characterization of copper nanoparticles: an XPS spectrum and a TEM image

Nanostructured palladium–polypyrrole composites electrosynthesised from organic solvents

Abstract Palladium–polypyrrole nanostructured composite films can be easily synthesised using a two-step procedure comprising the electrochemical synthesis of palladium nanoparticles (Pd-NPs) that are subsequently potentiostatically deposited onto a polypyrrole thin film electrosynthesised from an acetonitrile solution. The composite thin films have good conductivity and their transmission electron micrographs show that the metallic inclusions have a mean diameter of about 5 nm with a homogeneous size distribution. X-ray photoelectron spectroscopy (XPS) analysis reveals the presence of two surface oxidation states for the as-synthesised Pd-NPs as well as for those deposited on the films. On the basis of experimental findings, a structural model for the Pd-NPs is proposed.