The invention provides methods of using a compound as an optical probe or sensor of the activity of at least one cytochrome P450 enzyme, and methods of using the compound to screen candidate drugs, and kits for performing these methods. The taggant composition can be printed or otherwise applied to a material such as fabric to provide a detectable and identifiable indicium. They are most preferably devices of nitinol shape memory alloy, most particularly that is superelastic at normal body temperature.