Dual-Targeting into the Mitochondria of Cancer Cells for Ratiometric Investigation of the Dynamic Fluctuation of Sulfur Dioxide and Formaldehyde with Two-Photon Integrated Semiconducting Polymer Dots

Mitochondrial sulfur dioxide (SO₂) and formaldehyde (FA) in cancer cells serve as important signal molecules in mediating multiple physiological and pathological activities. Accurate monitoring of the dynamic fluctuation of SO₂ and FA in the mitochondria of cancer cells is important for insight into their relationships and functions in cancer, understanding cancer mechanism, and the role of mitochondrial homeostasis in cancer invasion and metastasis. Herein, a novel integrated two-photon semiconducting polymer dot (BF@Pdots) with dual-targeting (cancer cells and mitochondrial) and dual-emission in green and red regions, which is rationally designed through a four-step engineering strategy by using two newly synthesized functionalized polymers PFNA and FD-PSMA as precursors, has been developed for accurate tracking of the dynamic variation of SO₂ and FA in the mitochondria of cancer cells. The sensing mechanism is on the basis of the fluorescence resonance energy transfer (FRET) process in BF@Pdots tuned by the reversible Michael addition reaction between the sensing-groups and SO₂ (or FA). The integrated BF@Pdots nanoprobes display excellent performances in the accurate detection of the dynamic fluctuation of SO₂ and FA such as precise positioning in the mitochondria of cancer cells, self-calibrating ratiometric, two-photon emission with long wavelength excitation, and fast reversible response. The BF@Pdots nanoprobes are also applied to the ratiometric detection of the dynamic fluctuation of exogenous and endogenous SO₂ and FA in the mitochondria of cancer cells for the first time with satisfactory results. Taken together, this work will provide an attractive way to develop versatile integrated Pdots-based fluorescent probes through flexible molecular engineering for applications in accurate imaging of biomolecules in living systems.