Intramolecular cyclization reaction enabling fluorescent probes for dual-color visualization of lysosomes and lipid droplets with prominent spectral shift

Fluorescent probes that enable labeling lipid droplets (LDs) and lysosomes in different emission colors are promising tools to reveal the interaction and interplay of the two organelles. However, currently such fluorescent probes displayed limited spectral difference (no larger than 150 nm) in the two organelles, and the crosstalk signals may hinder clearly visualizing their interplay. In this work, based on the pH-dependent reversible intramolecular cyclization reaction of spiropyran, two fluorescent probes were constructed to visualize LDs and lysosomes in blue and near-infrared (NIR) fluorescent colors with prominent spectral shift up to 290 nm. The probes were designed as simple D-π-A structure, and the change in both conjugated size and ICT effect should be responsible for the extremely large spectral differences. With the probe, the different regulation of LDs and lysosomes amount under two kinds of high-fat conditions was revealed, the dynamic interplays of the two organelles were in-situ monitored, and the distinctive changes of lysosomal pH and LDs amount during autophagy were for the first time revealed.