Phthalocyanines and Porphyrins/Polyaniline Composites (PANI/CuPctBu and PANI/TPPH2) as Sensing Materials for Ammonia Detection.

We combined a conducting polymer, polyaniline (PANI), with an organic semiconducting macrocyclic (MCs) material. The macrocycles are the phthalocyanines and porphyrins used to tune the electrical properties of the PANI, which benefits from their ability to enhance sensor response. For this, we proceeded by a simple ultrasonically assisted reaction involving the two components, i.e., the PANI matrix and the MCs, to achieve the synthesis of the composite nanostructure PANI/MCs. The composite nanostructure has been characterized and deposited on interdigitated electrodes (IDEs) to construct resistive sensor devices. The isolated nanostructured composites present good electrical properties dominated by PANI electronic conductivity, and the characterization reveals that both components are present in the nanostructure. The experimental results obtained under gas exposures show that the composite nanostructures can be used as a sensing material with enhanced sensing properties. The sensing performance under different conditions, such as ambient humidity, and the sensor's operating temperature are also investigated. Sensing behavior in deficient humidity levels and their response at different temperatures revealed unusual behaviors that help to understand the sensing mechanism. Gas sensors based on PANI/MCs demonstrate significant stability over time, but this stability is highly reduced after experiments in lower humidity conditions and at high temperatures.

Effect of roughness on surface plasmons propagation along deep and shallow metallic diffraction gratings.

The roughness of shallow or deep metallic diffraction gratings modifies the propagation of surface plasmon mode along the metallic-air interface. The scattering losses lead to a spectral or angular broadening of the surface plasmon resonance (SPR) and to a shift of the resonance wavelength and coupling angle. This mechanism is deeply analyzed both experimentally and theoretically to overcome these effects when such structures, in particular deep ones, are used as SPR-based sensors.

Nanomaterials for the Selective Detection of Hydrogen Sulfide in Air.

This paper presents a focused review on the nanomaterials and associated transduction schemes that have been developed for the selective detection of hydrogen sulfide. It presents a quite comprehensive overview of the latest developments, briefly discusses the hydrogen sulfide detection mechanisms, identifying the reasons for the selectivity (or lack of) observed experimentally. It critically reviews performance, shortcomings, and identifies missing or overlooked important aspects. It identifies the most mature/promising materials and approaches for achieving inexpensive hydrogen sulfide sensors that could be employed in widespread, miniaturized, and inexpensive detectors and, suggests what research should be undertaken for ensuring that requirements are met.

Electrochemical Sensors Based on Screen-Printed Electrodes: The Use of Phthalocyanine Derivatives for Application in VFA Detection.

Here, we report on the use of electrochemical methods for the detection of volatiles fatty acids (VFAs), namely acetic acid. We used tetra-tert-butyl phthalocyanine (PcH2-tBu) as the sensing material and investigated its electroanalytical properties by means of cyclic voltammetry (CV) and square wave voltammetry (SWV). To realize the electrochemical sensing system, the PcH2-tBu has been dropcast-deposited on carbon (C) orgold (Au)screen-printed electrodes (SPEs) and characterized by cyclic voltammetry and scanning electron microscopy (SEM). The SEM analysis reveals that the PcH2-tBu forms mainly aggregates on the SPEs. The modified electrodes are used for the detection of acetic acid and present a linear current increase when the acetic acid concentration increases. The Cmodified electrode presents a limit of detection (LOD) of 25.77 mM in the range of 100 mM-400 mM, while the Aumodified electrode presents an LOD averaging 40.89 mM in the range of 50 mM-300 mM. When the experiment is realized in a buffered condition, theCmodified electrode presents a lower LOD, which averagesthe 7.76 mM. A pronounced signal decay attributed to an electrode alteration is observed in the case of the gold electrode. This electrode alteration severely affects the coating stability. This alteration is less perceptible in the case of the carbon electrode.

Indigo molecules adsorbed on carbonaceous nanomaterials as chemical filter for the selective detection of NO2 in the environment.

In order to enhance the durability of chemical filters for ozone molecules, devoted to microsystem for the selective detection of NO2 in the environment, the adsorption of indigo molecules onto the surface of carbonaceous nanomaterials (multi-walled carbon nanotubes, a mixture of nanodisks/nanocones, nanofibres) was investigated. The surface of the multi-walled carbon nanotubes was coated by π-stacking with adsorbed indigo molecules. An excess of indigo has resulted in a biphasic sample where nanotubes covered with indigo coexist with free indigo particles. Although similar filtering yields toward O3 (close to 100%) and NO2 (around 0%) were obtained as compared to individual materials, the indigo/MWCNTs samples exhibit enhanced durability as chemical filter at high ozone concentration (1 ppm).

The use of nanocarbons as chemical filters for the selective detection of nitrogen dioxide and ozone.

The gas filtering abilities of different nanocarbon materials such as nanocones/nanodiscs, and nanofibres, either as-prepared or modified by physical (annealing, grinding) or chemical (fluorination) treatment are reported. The aptitude to filter nitrogen dioxide and ozone, two of the most significant gaseous pollutants of the atmosphere, have been correlated to both the BET specific surface area studied by N2 adsorption at 77 K, and the presence of chemical functional groups at the surface. Valuable information regarding the mechanisms of gas-nanocarbon interaction has been obtained, in terms of chemisorption and physisorption. A prototype microsystem is proposed for the selective measurement of nitrogen dioxide and ozone concentration by means of organic semiconductor gas sensors.