Interference and Selectivity in Portable Chemical Sensors
Chemical sensors can be loosely classified into those that use light to extract information about chemical concentration (optical sensors) and those that do not (nonoptical sensors). Optical chemical sensors tend to use multiple stages of transduction and require large amounts of system and signal processing overhead to convert target analyte information into a useful output. These sensors often become complex systems or entire pieces of equipment in their final, commercialized form. For this reason, optical chemical sensors are not frequently found in portable, handheld, or field-monitoring units. Nonoptical chemical sensors, on the other hand, especially those that are integrated into an electronic device, are much better suited to portable and related applications. In the interests of evaluating chemical “sensors,” where the bulk of the complete system is the sensor itself, this chapter focuses on nonoptical chemical sensors. While compact, low-cost, small in size, and suitable for field or portable monitoring applications compared to other types of chemical sensors, nonoptical sensors are often hampered by (a) insufficient selectivity or chemical interference where a sensor responds to nuisance analytes in addition to target analytes and (b) nonchemical interference (from both physical/environmental and electronic influences). Advances in materials, sensor design, and signal measurement have made a significant impact on interference and selectivity barriers; however, barriers to commercialization remain. This chapter explains the basic issues associated with selectivity and interference and highlights some of the most promising advances in enhancing selectivity and reducing interference that support continued commercialization of chemical sensor products.