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 dis-tance, 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 moni-toring and imaging in living cells and in vivo. Therefore, it has promising application for the early diagnosis and treatment of some diseases.

Automated summary

A cellulose nanocrystal-based upconversion ratiometric fluorescent nanoprobe was developed for pH monitoring and imaging by chemically bonding upconversion nanoparticles, fluorescein isothiocyanate, and rhodamine B acceptors using cellulose nanocrystals as a bridge. The probe addressed issues such as aggregation-caused quenching of dye, long donor-to-acceptor distance, and poor water dispersibility. It exhibited excellent selectivity, sensitivity, and visualization for intracellular pH levels of 5.0-7.4 with 980 nm excitation. The biocompatible probe inspired by chameleons enhanced penetration depth and showed promising results for pH monitoring and imaging in living cells and in vivo.