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.

The work reports on theoretical and nanoscale characterization of Au/Co/Au multilayers used as transducers in Magneto-optical Surface Plasmon Resonance (MOSPR) biosensors. Different aspects related to the optimization of transducers are discussed. In particular, optimized sensitivity is demonstrated to depend on the full multilayer total thickness, on the Co layer thickness and its position within the film, as well as on the discrepancy between the optical constants in very thin layers with respect to bulk values. Co layer thickness and position in the trilayer are optimized to provide the best compromise between magneto-optic (MO) activity and optical losses as well as to ensure large electromagnetic (EM) fields at the Au-dielectric interface. In this sense surface sensitivity can be maximized with respect to variations in the bulk properties of the measuring fluid and ensure higher performances with respect to traditional SPR biosensors. In parallel, a comprehensive study on the structural, morphological, chemical, magnetic and optical properties of layers composing the realized magneto-plasmonic (MP) transducers is reported by comparing the results of experimental and theoretical investigations. High resolution TEM (HR-TEM) images provided a deep insight on the interfaces morphologies thus revealing a significant discrepancy between modelled and real samples basically due to sizable roughness at each metal interface. As highlighted by hysteresis loop measurements, this parameter results having a critical role in tailoring the magnetic and consequently magneto-plasmonic properties of the trilayer transducers. As a proof of concept, a simple immunoassay relative to the study of an antibody-antigen interaction in liquid phase has been investigated.

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.

Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique was used to deposit films of Poly(9,9-dioctylfluorene) - PFO and Methoxy Ge Triphenylcorrole [Ge(TPC)OCH3]. The PFO was dissolved in different matrices, like chloroform-CHCl3, tetrahydrofuran - THF and toluene with a 0.5 wt % concentration, while Ge(TPC)OCH3 was diluted in THF with a concentration of 0.01 wt %. The frozen targets were irradiated with a KrF excimer laser. The, films presented good emission properties to be exploited in light emitting devices and gas sensors based on luminescence quenching. The working principle of the MAPLE technique was used for the deposition of colloidal nanoparticles and nanorods, too. TiO2 colloidal nanoparticles (diameter: similar to 10 nm) and nanorods (diameter: 5 nm; length: 50 nm) were diluted in deionised water (0.02 wt %) and toluene (0.016 wt %) respectively. The deposited nanostructures preserved dimensions and structural properties of the starting particles and the films showed very interesting electrical responses when exposed to oxidizing gases for sensing applications.

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).

We report on nitrogen dioxide (NO2) sensing measurements by means of zinc oxide films presenting different morphologies. The variation in the photoluminescence emission of the films is employed as transduction mechanism to detect the presence of NO2 gas molecules at room temperature. The significant role of film morphology on the sensing properties is presented and possible limits in the use of ZnO nanostructures for NO2 detection at high gas concentration (>20 ppm) and low gas flow (50 ml/min), where a worsening of the sensor response is observed, are discussed. These features are ascribed to a likely incomplete reversibility of the NO2 adsorption process and examined in connection with the mechanisms of interaction between NO2 molecules and ZnO.

We investigated the fluorescence (FL) dependence on the environment oxygen content of poly(9,9-dioctylfluorene) (PF8) thin films. We show that the PF8 interactions with oxygen are not limited to the known irreversible photo-oxidation, resulting in the formation of Keto defects, but also reversible FL quenching is observed. This effect, which is stronger for the Keto defects than for the PF8, has been exploited for the realization of a prototype oxygen sensor based oil FL quenching. The sensing sensitivity of Keto defects is comparable with the state of the art organic oxygen sensors based on phosphorescence quenching.

The optical response by NO2 gas adsorption at different concentrations has been investigated, at room temperature, in ZnO nanostructured films grown by controlled vapor phase deposition. The variation (quenching) in the photoluminescence signal from excitonic and defects bands, due to the interactions between the oxidizing gas molecules and the sample surface, has been detected and dynamic responses and calibration curves as a function of gas concentration have been obtained and analyzed for each band. We showed that the sensing response results larger in excitonic band than in defect one and that the emission signal rises from two different quenchable and unquenchable states. A simple model was proposed in order to explain the quenching processes on the emission intensity and to correlate them to the morphological features of the samples. Finally, the reversibility of the quenching effects has also been tested at high gas concentration. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3700251]

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.

An immunosensor for highly sensitive detection of Salmonella spp has been developed using Surface Plasmon Resonance (SPR) as transducing technique. S.enteritidis spp, of various serotypes are major pathogens present in foodstuff and one of the causes of enteric diseases in humans. Most of the severe foodborne diseases are caused by nontyphoidal Salmonella serovars, with nearly 1.4 million cases of illnesses. The conventional methods of detecting foodborne pathogens require time-consuming preparation procedures including pre-enrichment, selective enrichment and colony isolation, and biochemical testing before the organism can be identified. To overcome these problems, label-free biosensors for this pathogen are highly desirable. SPR technique is a widely used optical technique for biosensing purposes. The reason of such interest is that it allows real-time monitoring of chemical and bio-chemical interactions occurring at the interface between a thin gold film and a dielectric interface, without the need for labeling the reagents. In this work, a high performance SPR device provided with a miniaturised microfluidics system, has been realized for the proposed application. A self-assembled layer of protein A was realized onto a typical SPR transductor via 11-MUA cross linker to achieve uniform, stable, and sterically accessible antibodies coating. The subsequent binding of polyclonal anti-Salmonella spp antibodies (Pab) Pabs have been characterized by Elisa assay to determine the specificity inter species and cross reactions against other pathogens such as E. coli and P. aeruginosa. The presented data showed that SPR allowed to attain a good and remarkable detection of bacteria, with improvement of sensibility. Exploitation of the proposed application for food safety is envisaged.

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.

Various kinds of zinc oxide (ZnO) nanostructures, such as columns, pencils, hexagonal pyramids, hexagonal hierarchical structures, as well as smooth and rough films, were grown by pulsed laser deposition using KrF and ArF excimer lasers, without use of any catalyst. ZnO films were deposited at substrate temperatures from 500 to 700A degrees C and oxygen background pressures of 1, 5, 50, and 100 Pa. Quite different morphologies of the deposited films were observed using scanning electron microscopy when different laser wavelengths (248 or 193 nm) were used to ablate the bulk ZnO target. Photoluminescence studies were performed at different temperatures (down to 7 K). The gas sensing properties of the different nanostructures were tested against low concentrations of NO(2). The variation in the photoluminescence emission of the films when exposed to NO(2) was used as transduction mechanism to reveal the presence of the gas. The nanostructured films with higher surface-to-volume ratio and higher total surface available for gas adsorption presented higher responses, detecting NO(2) concentrations down to 3 ppm at room temperature.