Selection of Aptamers for Sensing Caffeine and Discrimination of Its Three Single Demethylated Analogues.

TLDR: Four high-quality aptamers for caffeine with dissociation constants ranging from 2.2 to 14.6 μM were isolated using isothermal titration calorimetry, highlighting the effect of the molecular symmetry of the arrangement of the three methyl groups in caffeine.

Abstract: With the growing consumption of caffeine-containing beverages, detection of caffeine has become an important biomedical, bioanalytical, and environmental topic. We herein isolated four high-quality aptamers for caffeine with dissociation constants ranging from 2.2 to 14.6 μM as characterized using isothermal titration calorimetry. Different binding patterns were obtained for the three single demethylated analogues: theobromine, theophylline, and paraxanthine, highlighting the effect of the molecular symmetry of the arrangement of the three methyl groups in caffeine. A structure-switching fluorescent sensor was designed showing a detection limit of 1.2 μM caffeine, which reflected the labeled caffeine concentration within 6.1% difference for eight commercial beverages. In 20% human serum, a detection limit of 4.0 μM caffeine was achieved. With the four aptamer sensors forming an array, caffeine and the three analogues were well separated from nine other closely related molecules.