Dye-conjugated upconversion nanoparticles for ratiometric imaging of intracellular pH values

A ratiometric pH probe based on Tm3+ doped UCNPs functionalized with dye xylenol orange on the surface was developed, which can realize ratiometric pH sensing and imaging under continuous-wave excitation at 980 nm through the quenching and recovery of upconversion luminescence at 450 nm from UCNPs.