A chromoreactand for optical sensing of amphetamines.

A bisazo dye is presented that undergoes a reversible chemical reaction with amphetamine in thin layers of plasticised PVC and changes its colour from blue to red. The sensitivity of the dye in the polymer layer covers the range from 0.3 to 30 mmol L(-1) amphetamine with a limit of detection of 0.1 mmol L(-1). The maximum signal changes are observed at 630 nm making the dye compatible with cheap light sources and detectors.