Fabrication of triple-labeled polyelectrolyte microcapsules for localized ratiometric pH sensing

• Triple-labeled polyelectrolyte microcapsule pH sensors were fabricated.
• The capsules can be used for ratiometric pH sensing with a wide dynamic pH measurement range.
• The capsules can report the local pH environment when ingested by cells.
• The capsules are finally accumulated in acidic environments in cells.

Encapsulation of pH sensitive fluorophores as reporting molecules provides a powerful approach to visualize the transportation of multilayer capsules. In this study, two pH sensitive dyes (fluorescein and oregon green) and one pH insensitive dye (rhodamine B) were simultaneously labeled on the microcapsules to fabricate ratiometric pH sensors. The fluorescence of the triple-labeled microcapsule sensors was robust and nearly independent of other intracellular species. With a dynamic pH measurement range of 3.3–6.5, the microcapsules can report their localized pH at a real time. Cell culture experiments showed that the microcapsules could be internalized by RAW 246.7 cells naturally and finally accumulated in acidic organelles with a pH value of 5.08 ± 0.59 (mean ± s.d.; n = 162).

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