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

Abstract

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 Forster resonance energy transfer (FRET) between the AgNCs and a coumarin dye (coumarin 6 or C6), the photoluminescence (PL) of which, otherwise, shows aggregationcaused 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.

Microviscosity-Assisted Disaggregation of a Model Ophthalmic Drug and FRET-Controlled Singlet Oxygen Generation in Lyotropic Liquid Crystals

“…The excited state lifetime gradually increased and showed a rise component in the higher monitoring wavelengths (506 and 590 nm), which consolidated the occurrence of ESICT in the LLC domains (Figure S1a and Table S1). Furthermore, the time-resolved emission spectrum (TRES) of C6 in all of the LLCs clearly showed a slight red-shift with gradually increased delay time that reinforced the manifestation of ICT in the LLC phases (Figure S1b). In time-resolved area normalized emission spectra (TRANES), the occurrence of “ N ” iso-emissive points in the plot signifies the presence of “ N + 1” emissive species in the excited state .…”

“…In this case, we observed one iso-emissive point in each of the LLC phases due to the presence of two emissive states for C6, one for the locally excited state and the other for the ICT state (Figure S1c). The electron donating N , N -diethyl moiety in C6 pushes the electron cloud toward the electron-withdrawing benzothiazole group in the excited state favoring ICT …”

“…22 Coumarin 6 (C6) (Scheme S1) is such an organic fluorophore, which readily loses its fluorescence due to spontaneous aggregation in water at a fairly very low concentration of almost ∼1 μM. 23,24 However, the quenched C6 fluorescence can be effectively revived using host−guest chemistry where the host provides a relatively hydrophobic interior, and the revived energy can be used in various ways. 23,25−29 C6 is not only a useful laser dye but also an ophthalmic drug and a very popular fluorescent biomarker in the ocular system.…”

BSA-Capped Dual-Emissive Silver Nanoclusters for Detection of IO4– and Cu2+ Ions

“…Metal nanoclusters (MNCs) possessing inherent intriguing features, viz., molecule-like discrete energy levels, ultrasmall size, and remarkable fluorescence (Fl), continue gaining attention among researchers. − Their exceptional inherent properties render them an extensive platform for offering various applications like sensing toxic metal ions − and hazardous molecules, , bioimaging, photodynamic theory, catalysis, and optoelectronics . MNCs, particularly with red or near-infrared (NIR) emission, possess remarkable advantages in contrast to lower wavelength emitting MNCs due to their beneficial properties like deep cell penetrating power, minimizing the possibility of light scattering, and bypassing autofluorescence, − augmenting their utilization for various applications ranging from sensing of environmental contaminants to biologically hazardous molecules. − MNCs capped by proteins offer excellent biocompatibility and optical stability. − Following the first report of bovine serum albumin (BSA)-capped gold nanoclusters (AuNCs), several other proteins, e.g., lysozyme (LYS), ovalbumin, insulin, pea protein, and pepsin, have been utilized for capping many other MNCs. Induction of biocompatible reducing agents like dithiothreitol (DTT) in the synthesis further improves their applicability in biological systems .…”

Unveiling the Long-Lived Emission of Copper Nanoclusters Embedded in a Protein Scaffold

“…At present, the facile protein-directed synthesis, especially bovine serum albumin (BSA)-protected nanoclusters having strong red emission, have boosted nanocluster research for their advanced applications. , In this context, although gold (Au) and silver (Ag) nanoclusters have been studied a great deal, , copper nanoclusters (Cu NCs) have gradually attracted more attention due to their chemical similarity with Au and Ag nanoclusters, distinct fluorescent characteristics, low cost, earth abundance, easier accessibility of their precursors, and facile preparation procedures. , Despite the notable progress in terms of practical applications, the specific mechanism behind the emission characteristics of protein-protected Cu NCs remains unclear.…”