Naked-eye sensor for rapid methamphetamine screening with analyte recovery

The feasibility of a simple and rapid test to detect trace amounts of methamphetamine (MA) based on host–guest molecular interactions is demonstrated. The macrocyclic host molecule, cucurbit[7]uril (CB[7]), encapsulates a single guest molecule of the indicator fluorescent dye, acridine orange (AO). Addition of MA to the mixture shifts the equilibrium by replacing the guest molecule, as reflected by the changes in AO fluorescence. Notably, the colors of 0 and 20 µM MA can be distinguished by the naked eye, and the sensitivity is 135 times higher than that of the conventional Simon’s reagent. Similar fluorescence changes have been observed in the AO•CB[7] assay between 15 and 3 °C in the pH range 6–8 in phosphate buffer. The CB[7] system can detect MA while excluding bulky amines and sugars. However, it is also sensitive to other MA-related compounds such as N-isopropylbenzylamine and dimethylsulfone. MA recovery from the host–guest complex solution was greater than 94 %, allowing more accurate analysis of valuable evidence after this rapid screening. These results indicate that the CB[7] supramolecular system for MA detection has the advantages of operational simplicity, rapidity, high sensitivity, and minimal sample consumption and is suitable for initial drug screening during field analysis.