Unraveling Molecular Assembly and Tracking Lipid Droplet Dynamics Using Fluorescent Phenanthroimidazole Derivatives

Abstract

Small strategic perturbations of the molecular structures impart significant variation in the evolution dynamics and properties of supramolecular self-assembled architectures. However, probing the in situ evolution dynamics of molecular assembly remains a challenge. Herein, we unraveled the real-time, early stage environment-sensitive dynamic molecular self-assembly processes and stimuli-induced reversible morphological transformation between supramolecular fibers and spherical nanoaggregates of alkyl chain-substituted phenanthroimidazole-based luminogen (BPIB1) through fluorescence lifetime imaging microscopy (FLIM). The presence of an octyl chain and basic nitrogen centers in BPIB1 led to a distinct self-assembly pattern. The gradual progression in the fluorescence lifetime provides a unique strategy for elucidating the dynamics of the self-assembly process leading to distinct nano/microarchitectures. Among the varied self-assembled structures, the smaller-sized (diameter ∼ 20–30 nm), highly photostable, water-dispersible, and biocompatible fluorescent nanoaggregates of BPIB1 were employed for tracking the dynamics of lipid droplets in live cells and a model organism, C. elegans, using fluorescence correlation spectroscopy and FLIM. Thus, a combined microscopic and spectroscopic approach demonstrated in the present study opens up new avenues to explore the formation pathways of diverse molecular aggregates and their use to decipher complex organelle dynamics.

Fluorescence correlation spectroscopy and fluorescence lifetime imaging microscopy for deciphering the morphological evolution of supramolecular self-assembly

“…7(a)). 53 BPIB1, with both an octyl chain and basic nitrogen centers, formed an emissive organogel in a binary solvent mixture of 20% chloroform–80% methanol. The green emission ( λ em ≈ 530 nm) of the gel contrasted with the blue emission when in solution, resulting a red shift of ∼30 nm, which could be due to the formation of a supramolecular self-assembled structure.…”

“…Thus, this study justifies the crucial role of FLIM as an emerging microscopic technique to probe the morphological evolution of a diverse range of micro- and nanoarchitectures. 53…”

“…83 Through FCS analysis, Patra and co-workers probed the variation of local microenvironments during the motion of lipid droplets in cancer cells. 53 As the translational diffusion of the particle depends on the size of the probe, thus, the growth kinetics and morphological transformation of the supramolecular self-assembled structures, which includes nano-and microaggregates, can also be analyzed through FCS in the dispersion state in terms of the translational diffusion time (t d ) and the diffusion coefficient (D t ). 62,84 Patra and co-workers deciphered the evolution of supramolecular nanofibers in dispersions using FCS employing a thiophene-based small organic molecule, TPAn (Fig.…”

“…1). [48][49][50][51][52][53] However, a focused deliberation that demonstrates the use and promising scope of FCS-and FLIMbased investigations to decipher complex self-assembly pathways is missing in the literature. In this article, we have highlighted the salient features and the growing need for FCS and FLIM to elucidate the intriguing morphological transformations and the complex dynamics of molecular self-assembled structures, using a few recent reports and breakthrough literature.…”

“…1). [42][43][44][49][50][51][52][53] FCS enables the dynamic processes to be interpreted with singlemolecule sensitivity in the solution or dispersion state, which is often advantageous over ensemble measurements (Fig. 2).…”