Lipid droplet-targeting carbonized polymer dots for intracellular polarity visualization under wash-free conditions

For an extended period, lipid droplets (LDs) have been regarded to be the storage depots for metabolic lipids. As a key to energy storage and regulation, lipid droplets (LDs) have been found to perform crucial functions in various physiological processes such as oxidative stress and cell migration. Abnormal polarity variations of LDs are associated with various pathological conditions, including lipid metabolism disorders, the development of atherosclerosis and cancer. Therefore, developing LD-targeting polarity-sensitive probes and effectively monitoring the variations in the LDs microenvironment is highly meaningful.

A highly specific LD-targeting carbonized polymer dot (LD-CPD)-based fluorescent probe with amphiphilicity was designed and synthesized under mild conditions. The new probe exhibits high polarity-sensitivity, low viscosity crosstalk, strong solvatochromic and high photobleaching resistance. The solvatochromic responses of LD-CPD are attributed to hydrogen bonding and solvent dipole-dipole interactions, with hydrogen bonding exerting a stronger influence. In addition, it demonstrates a turn-off response to water, which makes it effective for LDs washing-free imaging. Moreover, as a solvatochromic probe, the proposed CPD can well achieve ratiometric imaging of subtle polarity changes within LDs during starvation and oxidative stress, indicating its capability to observe physiological dynamic changes.

All the features remind that the developed LD-CPD probe has great potential for diagnosis in LDs monitoring and analysis. It will serve as a robust monitoring platform for identifying diseases associated with abnormal LDs polarity. It also expands the application of CPDs in bioanalysis.