Plasmonic nanoprobes gauging the length and flexibility of α,ω-Alkanedicarboxylic acids with an optical readout

Discrimination of chemical homologs, compounds differing by the number of repeating units, given their similitude, is non-trivial, and therefore needs unconventional approaches. Herein, by taking advantage of the difference in length and utilizing plasmon coupling, we present the recognition of a sequence of linear saturated carboxylic diacids that occur naturally and accompany us in everyday life. The interactions between these diacids and gold nanoparticles, the surface of which is covered by cationic pillar[n]pyridinium macrocycles, produce a multilevel response, including a color that can be watched with an unaided eye. This method of recognition seems to be universal for anionic species and can be potentially extended to other sorts of molecular similarity and isomerism