Fe3O4/γ-Fe2O3 nanoparticle multilayers deposited by the Langmuir-Blodgett technique for gas sensors application.

Fe3O4/γ-Fe2O3 nanoparticles (NPs) based thin films were used as active layers in solid state resistive chemical sensors. NPs were synthesized by high temperature solution phase reaction. Sensing NP monolayers (ML) were deposited by Langmuir-Blodgett (LB) techniques onto chemoresistive transduction platforms. The sensing ML were UV treated to remove NP insulating capping. Sensors surface was characterized by scanning electron microscopy (SEM). Systematic gas sensing tests in controlled atmosphere were carried out toward NO2, CO, and acetone at different concentrations and working temperatures of the sensing layers. The best sensing performance results were obtained for sensors with higher NPs coverage (10 ML), mainly for NO2 gas showing interesting selectivity toward nitrogen oxides. Electrical properties and conduction mechanisms are discussed.

Sensitive coating for water vapors detection based on thermally sputtered calcein thin films.

In this paper the adsorption properties of thermally sputtered calcein thin films towards water and other polar molecules vapors are studied by different characterization techniques: quartz crystal microbalance, surface plasmon resonance and visible spectroscopy. Sensitivity of calcein thin films to water vapors resulted much higher as compared with those of a number of dyes whose structure was close to that of calcein. All types of sensors with calcein coatings have demonstrated linear concentration dependences in the wide range of water vapor pressure from low concentrations up to 27,000 ppm (close to saturation). At higher concentrations of water vapor all sensors demonstrate the abrupt increase of the response (up to two orders). A theoretical model is advanced explaining the adsorption properties of calcein thin films taking into account their chemical structure and peculiarities of molecular packing. The possibility of application of thermally sputtered calcein films in sensing technique is discussed.

Surface plamon resonance imaging of DNA based biosensors for potential applications in food analysis.

The adsorption processes of oligonucleotides immobilised onto suitable photolithographic patterned gold substrates have been investigated in aqueous buffer solution by using a home made surface plasmon resonance (SPR) imaging equipment. A rapid self-assembled method for the construction of DNA chips to be used in SPR imaging experiments have been followed. The immobilised DNA molecules (probes) adopted in our SPR experiments anchored to a gold surface via thiol group were 5'thiol-modified containing a (CH(2))(15) tail. The hybridisation processes taking place with its complementary sequence have been observed and characterized by monitoring phenomena by a SPR imaging system. The two analysed oligonucleotides (probes and target) are of interest in plant gene biotechnological application and differing for the presence at the 5'-end of a poly T16 spacer. Dynamic investigation of smallest changes in SPR imaging pictures performed in liquid phase in the presence of DNA complementary probes have been performed. Quantitative information in terms of threshold of sensitivity has been extracted by using a specific images treatment.

Liquid phase SPR imaging experiments for biosensors applications.

Surface plasmon resonance (SPR) has recently gained attention as a label-free method for the detection of biological molecules binding onto functionalised surfaces. It is one of the most sensitive detection method for monitor variations in the thickness and refractive index in ultra-thin films. Here, the adsorption processes of oligonucleotides onto gold substrates have been investigated in aqueous buffer solution using SPR imaging measurements. The hybridization of a thiol-modified, single stranded oligonucleotide anchored to a gold surface via thiol group, with its complementary sequence has been observed and characterised monitoring the hybridization process by SPR equipment. In situ investigation of smallest changes in SPR imaging measurements dynamically performed in liquid phase in the presence of DNA complementary probes was performed. Infrared spectroscopy and scanning electron microscopy characterisation of the functionalised gold surfaces of the biosensor were compared with the images obtained by SPR experimental apparatus.