Silk fibroin from silk gland of Bombyx mori 5th instar larvae was utilized to fabricate films, which may find possible applications as two-dimensional matrices for tissue engineering. Bombyx mori cocoon fibroin is well characterized as potential biomaterial by virtue of its good mechanical strength, water stability, thermal properties, surface roughness and biocompatibility. The present study aims to characterize the biophysical, thermal, mechanical, rheological, swelling properties along with spectroscopic analysis, surface morphology and biocompatibility of the silk gland fibroin films compared with cocoon fibroin. Fibroin solutions showed increased turbidity and shear thinning at higher concentration. The films after methanol treatment swelled moderately and were less hydrophilic compared to the untreated. The spectroscopic analysis of the films illustrated the presence of various amide peaks and conformational transition from random coil to beta sheet on methanol treatment. X-ray diffraction studies also confirmed the secondary structure. Thermogravimetric analysis showed distinct weight loss of the films. The films were mechanically stronger and AFM studies showed surfaces were rougher on methanol treatment. The matrices were biocompatible and supported L929 mouse fibroblast cell growth and proliferation. The results substantiate the silk gland fibroin films as potential biomaterial matrices.

Perovskite oxide based thin film gas sensors have long been considered as potential alternatives to commonly investigated binary metal oxides based sensors. BiFeO3, which is a prototype of ptype perovskite based semiconducting oxides, has recently drawn significant attention for its promising gas sensing characteristics. In the present work, the hydrogen sensing characteristics of calcium doped BiFeO3 has been reported by varying the film thickness, doping concentration, operating temperature, and test gas concentration. The films were deposited on glass substrates by sol-gel route using spin coating. X-ray diffraction analyses confirmed formation of phase pure films and scanning electron microscopy confirmed their uniform and dense microstructure. The Ca-doped BiFeO3 sensors exhibit higher sensitivity compared to pure BiFeO3 sensors. It is reported that the film thickness and Ca doping concentration play major role to control hydrogen sensing characteristics of the deposited films. The sensor based on 15% Ca-doped BiFeO3 sensor exhibited very high sensitivity (~212 % at 500 ppm H2), and excellent selectivity towards hydrogen at a moderate operating temperature (~250 °C).The enhanced gas sensing response of the doped BiFeO3 films has been attributed to the higher oxygen vacancy concentration induced by incorporation of aliovalent Ca 2+ .

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Selective detection of gases such as nitrogen dioxide (NO 2 ), carbon monoxide (CO), carbon dioxide (CO 2 ), and various volatile organic components (VOCs) is necessary for air quality monitoring. Detection of hydrogen (H 2 ) is equally important as it is a flammable gas and poses serious threat of explosion when exposed to oxygen gas. We have studied the sensing characteristics of these gases using thin film deposited by chemical solution deposition as well as relatively thicker films deposited by atmospheric plasma spray (APS) process. The chapter starts with the sensing mechanism of chemiresistive sensors followed by the definition of gas sensing parameters. Subsequently, we have demonstrated selective NO 2 sensing characteristics of zinc oxide-graphene (ZnO-G) multilayered thin film followed by CO and H 2 sensing characteristics of ZnO thin film and SnO 2 thick film. Cross-sensitivity among CO and H 2 gases has been addressed through the analysis of conductance transients with the determination of activation energy, E a , and heat of adsorption, Q. The concepts of reversible and irreversible sensing have also been discussed in relation to CO and H 2 gases. CO 2 sensing characteristics of LaFe 0.8 Co 0.2 O 3 (LFCO)-ZnO thin film have been elucidated. Interference from CO has been addressed with principal component analyses and the ascertaining of E a and Q values. Additionally, the variation of response with temperature for each gas was simulated to determine distinct parameters for the individual gases. Further, VOC sensing characteristics of copper oxide (CuO) thin film and WO 3 -SnO 2 thick film were investigated. Principal component analysis was performed to discriminate the gases in CuO thin film. The interaction of WO 3 -SnO 2 thick film with various VOCs was found to obey the Freundlich adsorption isotherm based on which E a and Q values were determined.Keywords: air quality monitoring, gas sensing, thin film sensor, thick film sensor, Langmuir adsorption isotherm, Freundlich adsorption isotherm, reversible sensing, irreversible sensing Salient features of semiconducting oxide gas sensorSemiconducting metal oxide (SMO) sensors are attractive for lower cost, smaller size, simpler operation principle, durability, and ease of fabrication together with their low concentration of gas detection limit [9]. These sensors change their conductivity when exposed to test gases of different concentrations [9]. However, the sensor operating temperature ($300°C) needs to be lowered, and cross-sensitivity toward multiple gases needs to be minimized for its wide commercial adaptation. The operating principle and salient features of SMO-based chemiresistive sensors are briefly described as follows:3 Multilayered and Chemiresistive Thin and Thick Film Gas Sensors for Air Quality Monitoring DOI: http://dx.doi.org/10.5772/intechopen.89710

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