Unraveling Molecular Assembly and Tracking Lipid Droplets Dynamics using Fluorescent Phenanthroimidazole Derivatives

Abstract

A judicious structural modification of molecular building units imparts significant variation in the evolution dynamics of supramolecular self-assembled architectures and their functional properties. The incorporation of alkyl chains into the rigid and π-conjugated molecular backbone not only directs the self-assembly but also enhances the hydrophobicity of the probe, facilitating specific interactions with hydrophobic organelle like lipid droplets (LDs). Such a fluorescent molecular probe is ideally suited for elucidation of complex self-assembly processes and to decipher the intracellular dynamics of LDs. Invoking the concept, the main skeleton of 1,4-bis(1H-phenanthro[9,10-d]imidazol-2-yl)benzene abbreviated as BPIB, was functionalized with a varying number of octyl chains to obtain BPIB1 and BPIB2. The alkyl chains were crucial to circumvent the π-π stacking leading to the strong fluorescence in aggregates and solid-state. Contrary to BPIB and BPIB2, intermolecular interactions-driven spontaneous self-association of BPIB1 having an amine nitrogen center and a long alkyl chain resulted in a stimuli-responsive fluorescent organogel. We deciphered the reversible morphological transformation between supramolecular fibers and spherical nanoaggregates using fluorescence lifetime imaging microscopy. The gradual progression in the fluorescence lifetime provides a unique strategy for exploring the dynamics of the self-assembly process. Furthermore, BPIB1 was found to be a specific marker for LDs in multiple cell lines. The fluorescence correlation spectroscopy revealed the microenvironments near LDs. Highly photostable BPIB1 was employed for the real-time tracking of the LDs dynamics in live cells. Thus, a combined microscopic and spectroscopic approach demonstrated in the present study opens up new avenues for further exploration of intriguing molecular aggregation and intracellular dynamics.

Molecular to Supramolecular Self-Assembled Luminogens for Tracking the Intracellular Organelle Dynamics

“…Fluorescence lifetime imaging microscopy (FLIM) could indicate the quantitative fluctuations in the lifetime of the probe during the organelle movements. , The state-of-the-art super-resolution microscopic (SRM) techniques, including structured illumination microscopy (SIM), photoactivated localization microscopy (PALM), and stimulated emission depletion (STED) microscopy have been employed to explore the cellular events with nanoscopic resolution. , Along with the dynamics, the structural organization and morphological changes of the organelles have been probed using diverse SRM imaging techniques. To sum up, the combination of an appropriate organelle-targeting photostable probe and SRM could be beneficial in monitoring the intracellular nanoscopic changes with a high spatiotemporal resolution.…”

“…Patra and co-workers employed fluorescence lifetime imaging microscopy (FLIM) to image the lipid droplets in multiple cancerous cell lines. Phenanthroimidazole-based molecular probe, BPIB1, was developed to probe the dynamics of LDs (Figure a) . The hydrophobic long octyl chain in BPIB1 was found to be crucial for the specific targeting of LDs.…”

“…The merged images at two different time points ascertained the dynamic movements of the LDs over time (Figure l–o). Besides, the insets of Figure h–k illustrate the fission and fusion processes and the changes in the size of LDs over time …”

“…Phenanthroimidazole-based molecular probe, BPIB1, was developed to probe the dynamics of LDs (Figure 14a). 76 The hydrophobic long octyl chain in BPIB1 was found to be crucial for the specific targeting of LDs. BPIB1 exhibited a strong blue emission (λ ex ∼ 405 nm; λ em ∼ 475 nm; Q.Y.…”

“…Additionally, BPIB1 showed excellent biocompatibility and high photostability. Thus, BPIB1 was employed as an LD marker for multiple cell lines such as HeLa, A549, CHO, and HEK293 (Figure 14d 76 The microenvironments such as polarity and viscosity have a profound impact on the dynamics of LDs. In this view, Patra and co-workers developed thiophene and 2-pyridoacetonitrilebased acceptor−π−donor−π−acceptor molecular probe, TPAn, to investigate the microenvironments in LDs (Figure 15a).…”