Nitrobenzoxadiazole based lipid droplets specific probes for atherosclerosis imaging

Fluorescence probes have shown great potential in lipid droplets (LDs) imaging, whereas the imaging performance of the present commercial dyes is far from ideal. In addition, there still is lack of an effective strategy for designing LDs specific probes with satisfactory imaging performance. In this work, we have provided a novel method and probes based on donor (D)-acceptor (A) structure with nitrobenzoxadiazole (NBD) as the A unit and benzene derivatives as the D units, which are expected to show strong emission in lipid environment. Four probes (N–B, N–MeB, N–MeOB and N–Me2NB) with increasing electron-donating ability were prepared, whose fluorescence-emission changed from aggregation-induced emission (AIE) (N–B and N–MeB) to aggregation-caused quenching (ACQ) (N–MeOB and N–Me2NB). Intriguingly, the emission of these probes in oil changed from blue region to red (652 nm) with the increase of electron-donating ability from N–B to N–Me2NB, indicating the great emission regulable ability of this strategy. Moreover, these probes could specifically stain the intracellular and tissular LDs, which had shown considerable performance in the studying of LDs spatial distributions in mice and human atherosclerosis plaques. Impressively, N–Me2NB with the strongest electron-donating group of N-dimethylaniline showed negligible emission in aqueous solution but remarkable enhanced emission in oil, which could still efficiently stain the intracellular LDs at 200 nM. This novel construction strategy would provide new ideas for preparation of LDs specific probes.