Combinatorial selectivity with an array of phthalocyanines functionalized TiO₂/ZnO heterojunction thin film sensors

Abstract

The development of electronic noses requires the control of the selectivity pattern of each sensor of the array. Organic chemistry offers a manifold of possibilities to this regard but in many cases the chemical sensitivity is not matched with the response of electronic sensor. The combination of organic and inorganic materials is an approach to transfer the chemical sensitivities of the sensor to the measurable electronic signals. In this paper, this approach is demonstrated with a hybrid material made of phthalocyanines and a bilayer structure of ZnO and TiO2. Results show that the whole spectrum of sensitivity of phthalocyanines results in changes of the resistance of the sensor, and even the adsorption of compounds, such as hexane, which cannot change the resistance of pure phthalocyanine layers, elicits changes of the sensor resistance. Furthermore, since phthalocyanines are optically active, the sensitivity in dark and visible light are different. Thus, operating the sensor in dark and light two different signals per sensors can be extracted. As a consequence, an array of 3 sensors made of different phthalocyanines results in a virtual array of six sensors. The sensor array shows a remarkable selectivity respect to a set of test compounds. Principal component analysis scores plot illustrates that hydrogen bond basicity and dispersion interaction are the dominant mechanisms of interaction.

Vertical MoS2 Nanosheets via Space-Confined CVD for Room Temperature Photo-Enhanced Highly Selective Triethylamine Sensing

“…All of the measurements were performed at room temperature (25 °C). In our case, the sensor response (relative resistance change) was measured from the following equation R = { R false( normala normali normalr false) − R false( normalg normala normals false) R false( normalg normala normals false) = Δ R R } where R (air) and R (gas) are the resistances of the sensor before and after gas exposure, respectively.…”

Substituent Effect on Stimuli-Responsive Donor–Acceptor Framework-Based 2-Thiohydantoins for Monitoring Nonanal Vapors

“…The functionalized thin film showed a higher selectivity and sensitivity toward TEA detection, which is the major VOC exhaled through breath in patients with liver diseases. 30 On the other hand, Reji and the group reported VOC adsorption studies on the metal-free as well as Fe(II)phthalocyanine, which showed J-aggregation in the solid state. Contrary to the metal-free phthalocyanine, Fe(II)phthalocyanine exhibits a selective photoresponse to nonanal and 1-hexanol under dark and illumination of visible light, respectively.…”

“…Sivalingam and co-workers showed how gas adsorption affects the surface PVT of a phthalocyanine-coated TiO 2 thin film as a biomarker for liver disorders. The functionalized thin film showed a higher selectivity and sensitivity toward TEA detection, which is the major VOC exhaled through breath in patients with liver diseases . On the other hand, Reji and the group reported VOC adsorption studies on the metal-free as well as Fe­(II)­phthalocyanine, which showed J -aggregation in the solid state.…”

Effect of Nb(V) doping on the Structure and Oxygen Chemisorption on Nanocrystalline TiO2

“…Besides, TiO 2 generally demonstrates lower response towards majority of gases and has lower electrical conductance than more commonly used metal oxides – SnO 2 , ZnO, WO 3 , In 2 O 3 etc., which makes it less convenient for practical applications. However, TiO 2 attracts attention due to high selectivity of response, caused by the formation of anatase/rutile homojunctions and heterojunctions with other semiconductor oxides [8–11] . Doping with Nb(V) has been widely exploited for the improvement of electrical, optical and sensor characteristics of TiO 2 [12–18] .…”

“…However, TiO 2 attracts attention due to high selectivity of response, caused by the formation of anatase/rutile homojunctions and heterojunctions with other semiconductor oxides. [8][9][10][11] Doping with Nb(V) has been widely exploited for the improvement of electrical, optical and sensor characteristics of TiO 2 . [12][13][14][15][16][17][18] It has been reported that Nb(V) doping also provides a stabilizing effect by suppressing the temperature induced anatase to rutile phase transformation, leading to a decrease in sensor sensitivity.…”