Design of a cellulose nanocrystal-based upconversion ratiometric fluorescent nanoprobe for pH monitoring and imaging

The monitoring of intracellular pH value is beneficial for the early diagnosis and treatment of some diseases. Here, a cellulose nanocrystal (CNC)-based upconversion ratiometric fluorescent nanoprobe for pH monitoring and imaging was constructed by chemicaliy bonding the upconversion nanoparticles donor and fluorescein isothiocyanate and rhodamine B acceptors using CNC as a bridge. The CNC bridge could improve stability and solve the problems of aggregation-caused quenching of dye on the donor surface, long donor-to-acceptor distance, and poor water dispersibility of the probe. The probe with a double internal reference of donor and rhodamine B acceptor exhibited excellent selectivity, sensitivity and visualization for intracellular pH of 5.0–7.4 with 980 nm excitation. Interestingly, the chameleon-inspired biocompatible probe based on the luminescent resonance energy transfer platform enhanced the depth of penetration and demonstrated excellent pH monitoring and imaging in living cells and in vivo . Therefore, it has promising application for the early diagnosis and treatment of some diseases.