Engaging Dynamic Surfactant Assemblies in Improving Metal Ion Sensitivity of a 1,4,7-Triazacyclononane-Based Receptor: Differential Optical Response for Cysteine and Histidine

Abstract

Self-assembly as well as metal ion binding property of an amphiphilic, dansylated 1,4,7-triazacyclononane (TACN) probe have been investigated in the presence of various surfactant assemblies in aqueous media. As expected, the receptor molecule shows highly sensitive, but rather nonspecific, interaction with metal ions in the bulk water medium. Thus, to achieve the good specificity without dampening the sensitivity of the probe, we embedded the sensor in different surfactant assemblies, such as micelles and vesicles, and explored their metal ion sensing ability. Change in microenvironment by restricting conformational mobility and increasing local hydrophobicity renders a drastic improvement in selectivity and also sensitivity toward Cu2+. Further, the preformed Cu2+ complex of the probe was utilized for exclusive “turn-on” detection of both cysteine (green fluorescence) and histidine (blue fluorescence). The diverse complexation mode of interactions with these amino acids caused a distinct change in the monomer to aggregate ratio, which was reflected in different spectral response. Furthermore, the dansylated probe was involved in developing reusable paper strips for rapid on-site detection of both Cu2+ and cysteine.