Ratiometric visualization of lysosomal pH fluctuations during autophagy by two-photon carbonized polymer dots-based...

Monitoring the pH variation in lysosomes is very conducive to studying the autophagy process, and fluorescent ratiometric pH nanoprobes with inherent lysosome targeting ability are highly desirable. Here, a carbonized polymer dots-based pH probe (oAB-CPDs) was developed by self-condensation of o-aminobenzaldehyde and further carbonization at low temperature. The obtained oAB-CPDs display improved performance in pH sensing, including robust photostability, intrinsic lysosome-targeting ability, self-referenced ratiometric response, desirable two-photon-sensitized fluorescence property, and high selectivity. With the suitable pKa value of 5.89, the as-prepared nanoprobe was successfully applied to monitor the variation of lysosomal pH in HeLa cells. Moreover, the occurrence that lysosomal pH decreased during both starvation-induced and rapamycin-induced autophagy was observed by using oAB-CPDs as fluorescence probe. We believe that nanoprobe oAB-CPDs can work as a useful tool for visualizing autophagy in living cells.