Dual Stimuli-Responsive BSA-Protected Silver Nanocluster-Driven “FRET On–Off” within the Niosomal Membrane: An Amalgamation of Restoration of Aggregation-Induced Quenched Fluorescence and Energy Transfer

Ion-aided inclusion of protein-coated nanoparticles inside the liposomal membranes is frequently used in drug delivery. However, the stability of the liposomes depends heavily on the nature of the interaction. Herein, we have used a niosomal membrane made from a 1:1 Triton X-100 (TX-100)/cholesterol mixture to incorporate bovine serum albumin (BSA)-coated silver nanoclusters (AgNCs) to impart stability driven by the specific interaction between TX-100 and BSA. Such an assembly is found to be sensitive to external stimuli, such as temperature and UV radiation. This composite is used here to observe and analyze the dynamics of Förster resonance energy transfer (FRET) between the AgNCs and a coumarin dye (coumarin 6 or C6), the photoluminescence (PL) of which, otherwise, shows aggregation-caused quenching (ACQ). Moreover, the dynamics of FRET is considerably slowed down by the niosomal membrane inclusion, which helped us in obtaining the detail of the phenomenon. The quantitative and regulative stimuli-responsive analysis helped us in constructing a “FRET on–off” system and an energy antenna.