Fig. 6. Absorption (A) and emission spectra (B) of HR-PiAC (5 μM, MOPS 30 mM, 100 mM KCl) at different pH (excitation wavelength = 535 nm), inset is the titration curve fitted with the Hill equation providing a pKa of 7.68 ± 0.09 and an enhancement of fluorescence of ∼80-fold. Scheme of bead-based pH sensor, containing pH-sensitive dye HR-PiAC and pH-insensitive Alexa Fluor 647 (C); titration curve of the pH beads measured by flow cytometry (D).
