Nano-assembled thin film gas sensors. I. Ammonia detection by a porphyrin-based multilayer film

Abstract

A thin film of porphyrin deposited by the layer-by-layer method is employed as the active element for an optical sensor. The usefulness of this film technology and the resulting nanoscale matrix for the detection of volatile organic compounds (VOCs), aromatics and amine-containing substances has been studied. The sensing principle is based on monitoring the optical changes of the Q band at 700 nm, as induced by the analyte in the electrostatic interaction between tetrakis(4-sulfophenyl)porphine (TSPP) and poly(diallyldimethylammonium chloride) (PDDA) layers. Three thin film samples with different thicknesses were prepared to assess the effect of film thickness on the sensitivity. For ammonia, the sensor shows a linear sensitivity in the concentration range 0-100 ppm and the sensor response was within 30 seconds. Sensor response could be regenerated by rinsing in distilled water.

Optical Fibre Long-Period Gratings Functionalised with Nano-Assembled Thin Films: Approaches to Chemical Sensing

“…Figure 12 shows the absorbance spectrum of the PDDA/SiO2 film after infusion of the TSPP compound. As can be seen from Figure 12, the two Soret bands at wavelengths 419 and 482 nm, along with well-pronounced Q-band at 700 nm, are present, which indicates that the TSPP compound forms J-aggregates in the porous silica film [41,42]. It was previously confirmed that nano-assembled thin films with TSPP in J-aggregate state are particularly sensitive to ammonia gas [42].…”

“…In order to study the stability of the PDDA/SiO2 films infused with TSPP in aqueous solutions, they were immersed into water several times, with the resultant changes in absorption spectra shown in Figure 12. The second Soret-band (482 nm) and Q-band (at 700 nm) disappeared when the film was immersed into water, accompanied by a decrease in the absorbance of the first Soret-band (419 nm), which indicates the partial removal of the adsorbed TSPP molecules from the film [42]. We can speculate that this phenomenon is a result of the cleavage of the J-aggregates of TSPP formed in the space between the SiO2 NPs.…”

“…As can be seen from Figure 12, the two Soret bands at wavelengths 419 and 482 nm, along with well-pronounced Q-band at 700 nm, are present, which indicates that the TSPP compound forms J-aggregates in the porous silica film [41,42]. It was previously confirmed that nano-assembled thin films with TSPP in J-aggregate state are particularly sensitive to ammonia gas [42]. In this work, mesoporous SiO2 NPs films infused with TSPP were to be used to detect the presence of ammonia in aqueous solutions.…”

“…Interactions with some chemical species can produce further spectral changes, thus creating the possibility that they can be used in the development of optical sensor systems. For instance, exposure of TSPP that has sulfonic functional groups to ammonia leads to the modification of the absorption spectrum [42].…”

Nanoassembled Thin-Film Gas Sensor II. An Intrinsic Highly Sensitive Fibre Optic Sensor for Ammonia Detection

“…Alternatively, the sensor response can be regenerated by rinsing for a few seconds in distilled water. (25) The calibration curve at each wavelength was plotted from the recorded spectra at given ammonia concentrations. The sensor shows linear responses at all wavelengths for a wide concentration range from 0.1 to 20 ppm and the highest sensitivity was observed at 706 nm (Fig.…”