Developing a polarity-specialized TICT fluorescent probe for wash-free and long-term monitoring lipid droplets dynamics

Lipid droplets (LDs) are dynamic and multifunctional organelles that play a crucial role in energy storage, metabolism and lipid signaling. Monitoring the dynamics of LDs is essential for understanding their functions. Twisted intramolecular charge transfer (TICT)-based fluorescent molecules have been widely utilized for LD imaging. However, conventional TICT dyes exhibit sensitivity to both polarity and viscosity, which results in unclear sensing mechanisms for LDs. Additionally, current LD imaging techniques face challenges such as complex washing procedures and limited long-term imaging capabilities. This study presented a far-red coumarin framework designed to modulate the TICT-ICT equilibrium, resulting in the development of two fluorophores that exhibit specialized sensitivity to either polarity or viscosity. The findings suggested that sensitivity to polarity is a crucial factor for LD imaging, as high signal-to-noise ratios (SNR) enable wash-free imaging, while suitable lipophilicity supports long-term imaging. This polarity-specialized TICT probe had the potential to revolutionize LD imaging, facilitating wash-free and extended studies of LD dynamic behaviors and functions during lipolysis.