The detection of the DNA hybridization mechanism using monodispersed gold nanoparticles as labels is an interesting alternative to increase the sensitivity of the SPR imaging technique. DNA-modified Au nanoparticles (DNA-Au NPs) containing single-stranded (ss) portions of DNA were prepared by monitoring their monolayer formation by UV-vis spectroscopy. The hybridization process between specific thio-oligonucleotides immobilized on the DNA-Au NPs and the corresponding complementary strands is reported and compared with the traditional hybridization process on properly self-assembled thin gold films deposited on glass substrates. A remarkable signal amplification is observed, following the incorporation of colloidal Au into a SPR biosensing experiment, resulting in an increased SPR response to DNA-DNA interactions. In particular Fusarium thiolated DNA (5'HS poly(T)(15)ATC CCT CAA AAA CTG CCG CT-3) and trichothecenes complementary DNA (5'-AGC GGC AGT TTT TGA GGG AT-3') sequences have been explored due to their possible application to agro-industry for the control of food quality.

Matrix-assisted pulsed laser evaporation (MAPLE) was used to deposit layers of poly(9,9-dioctylfluorene) (PFO) to study the relation between the solvent properties (laser light absorption, boiling temperature and solubility parameters) and the morphology of the deposited films. To this end, the polymer was diluted (0.5 wt%) in tetrahydrofuran-THF, toluene and toluene/hexane mixtures. The thickness of the films was equal to 70 +/- 20 nm. The morphology and uniformity of the films was investigated by Atomic Force Microscopy and by the photoluminescence emission properties of the polymer films, respectively. It is shown that, although the solubility parameters of the solvents are important in controlling the film roughness and morphology, the optical absorption properties and boiling temperature play a very important role, too. In fact, for matrices characterized by the same total solubility parameter, lower roughness values are obtained for films prepared using solvents with lower penetration depth of the laser radiation and higher boiling temperatures.

In this paper we report on the effects of the insertion of Cr atoms on the electrical and optical properties of indium tin oxide (ITO) films to be used as electrodes in spinpolarized light-emitting devices. ITO films and ITO(80 nm)/Cr-doped ITO(20 nm) bilayers and Cr-doped ITO films with a thickness of 20 nm were grown by pulsed ArF excimer laser deposition. The optical, structural, morphological wand electrical properties of ITO films and ITO/Cr-doped structures were characterized by UV-Visible transmission and reflection spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM) and Hall-effect analysis. For the different investigations, the samples were deposited on different substrates like silica and carbon coated Cu grids. ITO films with a thickness of 100 nm, a resistivity as low as similar to 4 x 10(-4) Omega cm, an energy gap of similar to 4.3 eV and an atomic scale roughness were deposited at room temperature without any post-deposition process. The insertion of Cr into the ITO matrix in the upper 20 nm of the ITO matrix induced variations in the physical properties of the structure like an increase of average roughness (similar to 0.4-0.5 nm) and resistivity (up to similar to 8x10(-4) Omega cm). These variations were correlated to the microstructure of the Cr-doped ITO films with particular attention to the upper 20 nm.

IntroductionSemiconducting metal oxides belong to the frequently used materials in gas sensing both in environmental protection and in medicine [1]. Amongst the broad variety of well established oxides, like SnO2, TiO2, WO3, ZnO, iron oxide ?-Fe2O3 and cobalt - iron oxide CoFe2O4 attract now attention because of complex magnetic and electric properties and high chemical reactivity. Moreover, innovative sensors are built from nanoparticle (NP) arrays. In comparison with continuous films these devices with high surface/volume ratio are more sensitive [2]. Our sensors are appropriate for oxidizing NO2 gas. With ?-Fe2O3 the response R = Iair/Igas (the ratio of the device current in dry air vs. in air mixed with the analysed gas) is 38 at NO2 concentration Cg = 500 ppb and working temperature Tw = 350oC [3]. This result is comparable with the top published sensitivities, e.g. R = 8 at Cg = 500 ppb and Tw =250oC [4]. With CO and acetone (studied as a marker of diabetes in the patient's breath) the sensitivities are lower [2]. With CO R = 2.8 at Cg = 100 ppm and Tw = 350oC, with acetone R = 1.8 at Cg = 5 ppm at Tw = 500oC. (CO and acetone are reducing gases, hence here R = Igas/Iair). High sensitivity of NP sensors to oxidizing gases and lower sensitivity to reducing gases was explained by charge carrier self-exhaustion of NPs by surface traps [5]. For the further progress in the field the mechanism of conductivity of NP arrays is of considerable interest. In this paper we summarize the results obtained as a by product of ?-Fe2O3 and CoFe2O4 sensors testing.

A comparison between sensing performance of traditional SPR (Surface Plasmon Resonance) and magnetooptic SPR (MOSPR) transducing techniques is presented in this work. MOSPR comes from an evolution of traditional SPR platform aiming at modulating Surface Plasmon wave by the application of an external magnetic field in transverse configuration. Previous work demonstrated that, when the Plasmon resonance is excited in these structures, the external magnetic field induces a modification of the coupling of the incident light with the Surface Plasmon Polaritons (SPP). Besides, these structures can lead to an enhancement in the magneto-optical (MO) activity when the SPP is excited. This phenomenon is exploited in this work to demonstrate the possibility to use the enhanced MO signal as proper transducer signal for investigating biomolecular interactions in liquid phase. To this purpose, the transducer surface was functionalized by thiol chemistry and used for recording the binding between Bovine Serum Albumin molecules immobilized onto the surface and its complementary target. Higher sensing performance in terms of sensitivity and lower limit of detection of the MOSPR biosensor with respect to traditional SPR sensors is demonstrated. (c) 2014 Elsevier B.V. All rights reserved.

Ethane-bridged Zn porphyrins dimers (ZnPP) have been deposited by Langmuir-Schafer (LS) deposition technique onto proper transducer layers for surface plasmon resonance (SPR) and magneto-optical surface plasmon resonance (MO-SPR) characterization techniques performed in controlled atmosphere. This last tool has emerged as a novel and very performing sensing technique using as transducer layers a combination of noble and magnetic layers deposited onto glass substrates. A magnetic actuation allows recording a magneto optical SPR signal which ensures best gas sensing performances in terms of signal to noise ratio, sensitivity and limit of detection parameters. Primary and secondary amines in vapour phase have been used as sensing analytes and a possible explanation of the mechanism as well as of the dynamics of the interaction with the sensing Zn Porphyrin layers is provided.

Brookite titanium dioxide (TiO2) nanorods. synthesized by a surfactant-assisted aminolysis route, were used as precursors for the fabrication of thin films by using the matrix-assisted pulsed-laser deposition (MAPLE) technique. Thin films with controllable thickness were grown on a variety of substrates for different characterizations. High-resolution scanning and transmission electron microscopy investigations evidenced the formation of rough TiO2 films incorporating individually distinguishable nanocrystals with different shapes. Suitable alumina substrates equipped with interdigitated electrical contacts (IDC) and heating elements were used to fabricate gas-sensing devices based on resistive transduction mechanism. Electrical characterization measurements in controlled environment were carried out. Typical gas sensor parameters (such as gas response, sensitivity, stability and detection limit) towards selected oxidizing and reducing gases, namely NO2 and CO, respectively, were extracted in dark condition. Very interesting optically activated enhancement of the response towards NO2 oxidizing gas was achieved in controlled atmosphere upon irradiating the sensing layer with UV light with low energy close to the TiO2 sensing layer band-gap width. (C) 2011 Elsevier B.V. All rights reserved.

This work reports on the structural and spectroscopic properties, as well as the gas-sensing performance, of ethane-bridged Zn porphyrin dimers (ZnPP) in Langmuir-Schafer (LS) thin films toward volatile organic compounds in a magneto optical surface plasmon resonance (MOSPR) configuration. Structural and spectroscopic properties of ethane bridged ZnPP thin films deposited onto proper Au/Co/Au magneto-optical substrates were inspected in dry air conditions and after exposure to amine vapors by means of IR spectroscopy, scanning probe microscopy, and MOSPR techniques. The molecular organization of the thin films deposited by the LS technique is investigated. The overall results suggest the presence in all cases of mainly the anti-conformer of the investigated porphyrin dimers. The strong interaction between n-butylamine vapors at high concentration and Zn porphyrin thin layers leads to a great conformational change in the porphyrin structure, which is linked to a change in the optical anisotropy of the realized LS layer.

Fe3O4/gamma-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.

A theoretical comparison of the optical and electronic properties of metallic nanostructures characterized by complementary geometries is proposed in this work. Periodic array of nanoparticles on glass substrate and nano-holes on metal substrate have been analysed performing finite element analysis with the RF Module of COMSOL Multiphysics. Single and array of gold nanostructures have been studied, exploring several key parameters responsible for sensitivity enhancement of LSPR sensors. The analysed structures show a minimum in their spectral transmittance, confirming that regular arrays of nano-holes in thin metal films as well as nano-disk arrays may support localized surface plasmon resonance. © 2014 Springer International Publishing Switzerland.

Thin film of ethane bridged Zn-Porphyrin dimers have been deposited via Langmuir-Schäfer (LS) technique onto Au/Co/Au transducers fabricated onto glass substrates. They have been tested as sensing layer in a Magneto-optic Surface Plasmon Resonance (MO-SPR) sensor to monitor the controlled adsorption of molecules of a volatile compound such as tert-butylamine vapours. © 2014 Springer Science+Business Media.

In this work we present a theoretical and experimental analysis of a new and cheaper plasmonic material, very attractive for its potential biosensing applications. We investigate the optical properties and the sensing capabilities of a highly disordered system of silica nanowires decorated with spherical gold nanoparticles. These systems present unique light trapping properties due to the combination of the highly diffusivity of transparent silica nanowires, with the selective absorption resonances given by Au nanoparticles deposited along the wires. The enhanced absorption at the LSPR resonances makes our materials excellent candidates to build plasmonic biosensors. The optical properties of these systems have been theoretically investigated by developing appropriate 2D finite element simulations. As proof of concept we have successfully tested the ability of the NP/NW forests to act as refractive index sensors and to detect biomolecular binding of the Protein BSA - AntiBSA bonding. © 2014 AEIT.

In this work a proper combination of metal and ferromagnetic multilayers tailored on the nanoscale is used as novel transducer in propagating SPR-based biosensor coupled with an external magnetic field. The modulation of plasmon moment by an external magnetic field has been demonstrated in literature . The coupling between the incident light and the surface plasma waves is determined by the magneto-optical (MO) properties of the magnetic layer that can be modulated using an external magnetic field. Moreover, such a combination of materials can produce a great enhancement of the MO effects when the Plasmon resonant condition is satisfied. The MO enhancement is strongly localized in the plasmon resonance conditions and critically depends on the refractive index of the dielectric medium. As a consequence, small variations of the refractive index will induce large changes in the MO response, allowing using the proposed platform as novel transducer for optical sensing .

The synthesis of four new complexes based on tridentate bispyrazole ligand by coordination of 4-[bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-amino]phenol with different transition metals such as Cu(NO(3))(2), NiCl(2), CoCl(2) and Cu(BF(4))(2) was reported. Their characterization by means of IR. UV-visible and mass spectroscopy was investigated. Their optical pollutant gases recognition capabilities as solid state thin layer on quartz were investigated. Different analytes have been studied such as SO(2), NO(2), CO, CH(4) and NH(3). The coordinated complex layer presents reversible system sensitivity towards SO(2) and NO(2) with good sequences in function with time. No influence on the optical properties was shown in the presence of CO, CH(4) and NH(3).

The present work focuses on the development of a Surface Plasmon Resonance (SPR) sensor transducer able to measure lubricant degradation in real time. Preliminary, several simulations were performed, by means of a commercial software (Film Wizard), in order to optimize for the specific application the sensor transducers in term of the proper choice and combination of metal layers material and thickness. In order to realize the sensing transducers, metal thin films were deposited onto SF10 glass slabs by e-beam evaporation. 4 sensing devices have been realized, calibrated and tested. They have been used to acquire the experimental reflectance curves of a new (0 km) and partially used synthetic motor oil (5700 km). Measurements proved that alteration of lubricants, which flow in the SPR sensing device, modifies the signal, which reaches the detector. Therefore, the system can be used to observe in real time oil degradation by the measurement of its optical properties, following the variation in surface plasmon resonance curves. Experimental results showed that all sensors provide good responses, variable within the range of 1%.

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.

We report the fabrication of silica nanowires (NWs) decorated with Au or Ag nanoparticles (NPs) by dewetting thin metal films evaporated on the NWs. The Au or Ag NPs, displaced along the NWs, form a three-dimensional (3D) ensemble of metallic NPs in a macroporous structure. Their optical behavior results from the combination of the high white-light scattering of silica NWs with the selective absorption of the localized surface plasmon resonances (LSPRs) of the NPs, causing light trapping just at the LSPR wavelengths. Such a 3D plasmonic structure shows a strong dependence of the LSPR wavelength on the refractive index of the environment in which the 3D NP ensemble is immersed, a feature that makes them morphologically and optically peculiar materials appealing for sensing applications.

Detection of legionellae by water sampling is an important factor in epidemiological investigations of Legionnaires' disease and its prevention. To avoid labor-intensive problems with conventional methods, an alternative, highly sensitive and simple method is proposed for detecting L. pneumophila in aqueous samples. A compact Surface Plasmon Resonance (SPR) instrumentation prototype, provided with proper microfluidics tools, is built. The developed immunosensor is capable of dynamically following the binding between antigens and the corresponding antibody molecules immobilized on the SPR sensor surface. A proper immobilization strategy is used in this work that makes use of an important efficient step aimed at the orientation of antibodies onto the sensor surface. The feasibility of the integration of SPR-based biosensing setups with microfluidic technologies, resulting in a low-cost and portable biosensor is demonstrated.

In this paper we report on the growth and structural characterization of very thin (20 nm) Cr-doped ITO films, deposited at room temperature by double-target pulsed laser ablation on amorphous silica substrates. The role of Cr atoms in the ITO matrix is carefully investigated with increasing doping content by transmission electron microscopy (TEM). Selected-area electron diffraction, conventional bright field and dark field as well as high-resolution TEM analyses, and energy dispersive x-ray spectroscopy demonstrate that (i) crystallization features occur despite the low growth temperature and small thickness, (ii) no chromium or chromium oxide secondary phases are detectable, regardless of the film doping levels, (iii) the films crystallize as crystalline flakes forming large-angle grain boundaries; (iv) the observed flakes consist of crystalline planes with local bending of the crystal lattice. Thickness and compositional information about the films are obtained by Rutherford back-scattering spectrometry. Results are discussed by considering the combined effects of growth temperature, smaller ionic radius of the Cr cation compared with the trivalent In ion, doping level, film thickness, the double-target doping technique and peculiarities of the pulsed laser deposition method.

Lubricant systems are fundamental in engines (automotive, aviation, rail etc.) and in any industrial system where surfaces of moving mechanical parts are in contact [1]. An improper lubrication due to oil degradation over a long period of time can lead to unwanted component failure and increased maintenance costs. Present study, unlike methods developed until now for detecting oil degradation (loss of mechanical, physical, chemical and optical properties) focuses on the development of a Surface Plasmon Resonance (SPR) transduction methodology able to measure lubricant degradation in real time observing the change in the refractive index. This approach answers to environmental regulation and user requirements on performance, life-time expectancy and engine efficiency.

In this work, we perform a numerical and experimental comparison of 2D and 3D systems of plasmonic nanostructures in order to explore several key parameters for sensitivity enhancement of traditional LSPR biosensors. The optical properties and the sensing capabilities of planar and three-dimensional distributions of metal nanostructures have been theoretically and experimentally investigated. We developed a numerical model for calculating the absorption spectra and the sensitivity towards increasing refractive indexes of periodic array of plasmonic nanostructures. Our numerical results have been verified performing a sensitivity comparison of 2D and 3D nanostructured systems composed by the same kind of metal nanoparticles. As proof of concept, our experiment were conducted on a planar distribution of gold nano-spheres and an hybrid 3D plasmonic material composed by a disordered system of silica nanowires decorated with spherical gold nanoparticles.