1,721,088 research outputs found
Oxygen optical gas sensing by reversible fluorescence quenching in photo-oxidized poly(9,9-dioctylfluorene) thin films
Full text linkWe 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 on FL quenching. The sensing sensitivity of Keto defects is comparable with the state of the art organic oxygen sensors based on phosphorescence quenching
Metallophthalocyanines thin films in array configuration for electronic optical nose applications.
No full textThe interaction between some ambient reactive compounds and organic or inorganic thin layers can cause variations in the physical properties of the chemically interactive layers. Molecules in the gas phase, which are adsorbed onto the surface or absorbed in the bulk of the thin layer, generally modify the electrical or optical or mass properties of the gas-sensitive material giving rise to a number of different kinds of chemical sensors based on different working principles. This work reports and discusses the experimental results obtained with optical absorbance measurements in ITV-Vis spectral range onto these optical sensitive layers in controlled atmosphere containing vapours. In particular, very interesting results have been obtained by optical absorption measurements carried out in the region of the typical Q band of phthalocyanines and a selectivity toward different vapours, depending both on the metal and the peripheral substituents of the macrocycle, was found. The as-manufactured sensors have been arranged in an array configuration and examples of applications for "electronic optical nose" to the analysis of some volatile organic compounds (VOC) which are of interest in food analysis are reported in this work
Practical strategy to realistically measure the swelling ratio of poly(dimethylsiloxane) without underestimation due to the solvent volatility
No full textWe present an experimental method for measuring “realistically” the swelling ratio in terms of weight (SRW) of PDMS, where “realistically” means without the underestimation involved by the standard protocol (weight-measurements in open environment with time-delay incompatible with fast solvent evaporation rate). Comparison with the literature demonstrates that misleading conclusions can result under application of the standard protocol to very volatile solvents. To discuss this point, we develop a mathematical expression of SRW including solvent properties and the effective amount of sorbed solvent determining a weight gain, consider two solvents with different volatility that severely swell PDMS (i.e., toluene and dichloromethane), check that the results of our measurements are consistent with theoretical predictions, demonstrate that our protocol rules out any dependence of SRW on the solvent volatility and its reliability to measure and compare SRW values of PDMS (or any swelling polymer/soft material) in the case of solvents with very different volatility
Au Nanoparticles Prepared by Physical Method on Si and Sapphire Substrates for Biosensor Applications
No full textGold nanoparticles heavily functionalized with oligonucleotides have been used in a variety of DNA detection methods. The optical properties of three-dimensional aggregates of Au nanoparticles in solution or deposited onto suitable surfaces have been analyzed to detect hybridization processes of specific DNA sequences as possible alternatives to fluorescent labeling methods. This paper reports on the preparation of gold nanoparticles directly deposited onto the surface of silicon (Si) and sapphire (Al2O3) substrates by a physical methodology,
consisting in the thermal evaporation of a thin Au film and its successive annealing. The method guarantees the preparation of monodispersed single-crystal Au nanoparticles with a strong surface plasmon resonance (SPR) peak centered at about 540 nm. We show that the changes of SPR excitation before and after DNA functionalization and subsequent hybridization of Au nanoparticles immobilized onto Si and Al2O3 substrates can be exploited to fabricate specific biosensors devices in solid phase
"C-Nitroso-compounds as novel promising substances for the deposition of Langmuir-Blodgett films "
No full text"Langmuir-Blodgett films of Cu(II) - Tetrakis (3.3 dimethylbutoxycarbonyl) phthalocyanine: a spectrophotometric and TEM analysis of their structure and morphology"
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Protocol of thermal aging against the swelling of poly(dimethylsiloxane) and physical insight in swelling regimes
No full textIn this paper, an unprecedented inspection of the effects of thermal aging on swelling and wettability of PDMS as a function of the interplay between temperature (from 100 to 180 °C) and duration (from 20 min to 24 h) of the treatment is presented. Dichloromethane was used as sample swelling solvent and the swollen weight was measured by a method properly designed to avoid underestimation related to the volatility of the solvent. This study: i) provides practical guidelines for performing optimal thermal aging treatments of PDMS against swelling (for example, in microfluidic platforms to synthesize cancer tracers), and ii) contributes to the fundamental understanding of the swelling process of soft matter systems. An interpretative model has been developed of the observed swelling regimes based on heating-promoted crosslinking and chain reorganization (inter-chain mobility) at short-lasting heating timescales and conformational changes (intra-chains transitions) at long-lasting heating timescales
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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