CHAPTER 5: Smart Indicator Technologies for Chemical and Biochemical Detection

Chemists have become familiar with a range of chemical indicator reactions which can be used as qualitative, presumptive and/or semi-quantitative tests for the presence of organic or inorganic compounds of interest. For example, the silver mirror test for aldehydes, based on the reduction of ammoniacal silver nitrate to metallic silver, allows discrimination between aldehydes and ketones; the precipitation tests with silver nitrate for the presence of a halide; and universal indicator and litmus papers for pH and colour-changing indicators to mark the end-point of a titration are all examples of quick visual tests which have been used by chemists. The convenience of such visual indicators has also been adopted in the development of a range of bio/chemical tests for the presence of, for example, volatile organic compounds, proteins, bacteria and also metabolites, as well as for presumptive tests of drugs of abuse. This chapter reviews a selection of the chemistries developed to make simple visual indicators for chemical and biological applications. These indicators have far-reaching implications to the layperson, for example in the development of simple tests informative of medical (personal health) and food (the integrity of food packaging, fruit ripeness and food quality) monitoring.