Exploiting Co-solubilization of Warfarin, Curcumin, and RhodamineB for Modulation of Energy Transfer: A Micelle FRET On/Off Switch

Two new FRET pairs, warfarin (WF)-curcumin (CUR) and curcumin-rhodamineB (RhB), are explored by using surfactant-based self-assembled soft systems as scaffolds. The study is extended to design a two-step concurrent FRET system based on these three fluorophores, which is an important mechanism to devise artificial light-harvesting/antenna systems. Surfactant systems of varying nature (cationic, anionic, nonionic, and zwitterionic) are exploited to modulate the energy transfer in different FRET systems. Interestingly, micelle/water interfacial-charge-responsive FRET is observed owing to selective solubilization of the fluorophores during co-solubilization. The step-one FRET (WFCUR) is switched on in cationic and zwitterionic media but switched off in anionic/nonionic media, whereas the step-two FRET from CUR to RhB is switched on in anionic/nonionic and zwitterionic media. However, both the FRET steps (WFCURRhB) are observed to be active only in zwitterionic medium. Co-solubilized, appropriately mixed fluorophores having multistep FRET possibilities can be switched on/off selectively as and when required and energy efficiency can be tuned to an optimal level by varying the nature and geometry of the micellar scaffold. Thus, the two FRET pairs selectively acknowledge all types of media for their anticipated applications in biological systems, as structural tools, and for the development of artificial light-harvesting/antenna systems and lasers.