Donor–acceptor Stenhouse adduct formation for the simple and rapid colorimetric detection of amphetamine-type stimulants

Widespread abuse of amphetamine-type stimulants (ATS) calls for the development of reliable and rapid on-site analytical methods for their detection and quantitation. A simple, rapid, sensitive, selective, and inexpensive method for the colorimetric detection of ATS using furylidene Meldrum's acid derivative 1 is reported herein. This colorimetric assay is based on the formation of Stenhouse adducts, through a chromogenic ring-opening mechanism upon the reaction of 1 with secondary amines, including methamphetamine (METH), 3,4-methylenedioxymethamphetamine (MDMA), and related illicit drugs. The reaction is accompanied by the formation of a new, red shifted absorption band resulting in a distinct color change from colorless to red. The utility of the colorimetric assay is demonstrated in aqueous solution, spiked drinks, and ‘ecstasy’ tablets. Detection limits of 0.36 μg·mL⁻¹ METH and 0.57 μg·mL⁻¹ MDMA in aqueous solution are achieved, and the naked-eye detection of ATS is also realized within 5 min in multiple matrices. Moreover, this method is resistant to interference from various pharmaceuticals, controlled substances, or common cutting agents found in illicit drugs. Paper-based portable indicators based on 1, suitable detection of ATS by agents in the field, are additionally reported.