Microenvironment Sensitive Charge-Transfer Dye for Tandem Sensing of Multiple Analytes at Mesoscopic Interfaces

Abstract

An easy to synthesize amphiphilic dye is developed whose sensing behavior in surfactant assemblies can be modulated through surface-charge, micropolarity, and local pH, etc. Thus, the micelle-bound probe shows remarkable ion-dependent bathochromic shifts in the charge-transfer band, enabling simultaneous ratiometric detection of four different metal ions, such as Cu2+, Ni2+, Hg2+, and Zn2+, at parts per billion (ppb) level in water. This is indeed a striking observation since naked-eye sensing of multiple metal ions at the mesoscopic interface is not known to date. Moreover, the probe even shows distinct color response against copper ion in different oxidation states, which is also unheard of. Further, the in situ formed metal complexes can be employed for naked-eye screening of three different amino acids, such as histidine, cysteine, and aspartic acid, in aqueous medium. Probes of this class, which are capable of multiplexing, offer new ways of efficiently screening multiple analytes in complex, real-life samples (e.g., wastewater management, analysis of pharmaceutical drugs, etc.). Further, low-cost reusable dye-coated paper discs were also developed as an ecofriendly method for on-site sensing of metal ions.