Organic and Inorganic Material-Based Functional Surfaces for Sensors and Biosensors: Synthesis and Design

Abstract

The aim of this thesis is the realization of integrated optic sensors based on fiber grating devices. In order to obtain chemical and biological sensors, a Long Period Gratings transducer was used as transduction platform. Different organic and inorganic materials were used as sensitive elements at the interface between the LPGs and the external environment. Since the selectivity and sensitivity of a LPGs based sensor depend upon the interface materials, careful study of the sensing materials, as well as of the deposition process was done. Results of this PhD work has been obtained thanks to the integration of interdisciplinary knowledges in different scientific and technological areas, such as optical engineering, biochemistry, polymer materials, synthetic chemistry. Within the framework of the OPTOFER Project, a GPL sensor based on LPGs coated with a-PS thin films was developed and manufactured. This polymeric film was considered for the physical affinity among hydrophobic polystyrene chains and short aliphatic molecules that constitute GPL. Preliminary results have shown good sensitivity of the device in presence of unknown GPL concentrations: the signal is stable and the sensor is characterized by fast response time and reversibility (absence of hysteresis in consecutive gas on/gas off cycles). An accurate study, of both material and interaction between the LPG transducer and the a-PS film, has allowed the development of a device capable to detect clearly GPL concentration between 1000 and 30000 ppm. These sensors have been installed and tested under the railway tunnel of Porta Rufina station, in Benevento. “Relative humidity fiber optic sensors based on Long Period Gratings” is the name of the collaboration agreement with CERN during which have been designed, developed and manufactured humidity sensors resistant to radiation and to cryogenic temperature. LPGs, used as transducers, were coated with thin film of sol-gel synthesized titania, an inorganic oxide that shows different interesting features: 1) hygrosensitive characteristics, 2) ageing and high energy radiation resistance and 3) thermal stability. The sol-gel synthesis and the deposition process optimization has led to the development of humidity sensors with good sensibility and reversibility, and the inorganic nature of the titania coating guarantees the mechanical and thermal stability of the device. Within the framework of the OPTOBACTERIA Project, has been developed a highly- sensitive reflection-type LPG biosensor, useful to detect antibiotic resistance bacteria. The reflection-type LPG was coated by a primary a-PS layer and by a secondary very thin overlay of PMMA-co-MA. a-PS was used as HRI layer in order to tune the LPG to be able to operate within the transition region. PMMA-co-MA has been employed as thin film to provide carboxylic groups on the external surface of the fiber. A standard linkage chemistry has been carried out to anchor the bioreceptors onto the probe surface. Preliminary experimental results demonstrate the capability of the fabricated LPG biosensor to monitor successfully all steps of the biochemical immobilization strategy as well as to detect the β-Lactamase binding to its functionalized surface.