Year: 2012
Type: book-chapter
Abstract: The area of chemical sensors is one of the fastest growing both in research and in commercial fields.Most of the research work in this area is concentrated towards reducing the size of sensors and the identification and quantification of multiple species.Quick response, minimum hardware requirement, good reversibility, sensitivity, and selectivity are expected from an excellent sensor, and hence there is a need for further research.The applications of chemical sensors include quality and process control, biomedical analysis, medical diagnostics, environmental pollution control, continuous and long term monitoring of pollutants and hazardous substances.There are however several outstanding problems hindering applications of chemical sensors based on optical readout.It is widely accepted that in many instances the sensitivity is not the limitation of the sensor.Indeed many sensors display over-sensitivity at the expense of specificity and are vulnerable to noise.In real applications the environment in which sensors are located is not sterile: additional substances present will cause spurious readouts, and moreover, the substances may react over the sensor's surface and readouts will be then cross-correlated.Methods to overcome these hindrances are addressed in this chapter using porous silicon as a testbed.They are based on signal or statistical analyses of the data acquired and take advantage of the possibility of multi-sensing with properly modified sensor arrays.Several new configurations for optical multi-sensing are presented in this chapter, and demonstrated for ammonia detection.The methods are however generic for optical remote sensing of multiple gas components and can be applied to industrial and environmental gas supervision as well as biomedical applications.The detection of ammonia is based on chemical reaction between ammonia-sensitive dye and the detected molecules.These reactions are accompanied by changes in optical absorption spectrum within the VIS-NIR range.pH sensitive dyes have been widely used for ammonia detection (Malins et al., 1999;Malins et al., 1998;Potyrailo et al., 1994).For these sensors, the response to ammonia vapour is highly dependent upon the level of humidity in the environment since the acid-base reaction of the dye materials is always mediated by water, and therefore calibrating for atmospheric humidity is required for determining true values of ammonia concentration. www.intechopen.comAdvances in Chemical Sensors 48 Porous sliconPorous silicon (PSi) is typically produced by electrochemical etching of bulk crystalline silicon.The porosity of the produced material is directly proportional to the applied current density during the etching process, providing therefore a simple means to control its refractive index (Vial and Derrien, 1995).Various optical components such as Bragg and rugate reflectors have been successfully fabricated with porous silicon (Lorenzo et al., 2005).PSi can be used as smart transducer material in sensing applications, and in particular in the detection of vapours (De Stefano et al., 2004a).Upon exposure to chemical substances, several physical quantities, such as refractive index, photoluminescence, and electrical conductivity change drastically.A key feature of a physical transducer, being sensitive to chemical molecules, either in vapour and liquid state, is a high surface area to volume ratio.Moreover, PSi is an available, low cost material, compatible with standard microelectronics processes, so that it can be successfully employed in the realization of smart sensors and microsystems. How to referenceIn order to correctly reference this scholarly work, feel free to copy and paste the following:
Source: InTech eBooks
DOI: 10.5772/31538
Authors: Tanya Hutter, Shlomo Ruschi
Institutions: University of Cambridge, Tel Aviv University
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W1595981248