Dual pH and oxygen luminescent nanoprobes based on graft polymers for extracellular metabolism monitoring and intracellular imaging

Abstract

Cellular pH and oxygen are the two important parameters to evaluate cell metabolism and functions of subcellular structures. Herein, we developed graft copolymers-based dual pH and oxygen luminescent nanoprobes with excellent sensitivity and quantum yields for both extracellular sensing and intracellular imaging. The oxygen probe platinum(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl)-porphyrin (PtTFPP) was encapsulated into the hydrophobic core formed by poly(ε-caprolactone) (PCL), while pH sensitive fluorescein moieties were polymerized in hydrophilic chains of poly(oligo(ethylene glycol) methacrylate) (POEGMA). The quantum yield of oxygen and pH probe in the nanoprobes was separately achieved to be ˜0.15 under nitrogen and ˜0.78 at pH 8. Through tuning the polymer structures, the nanoprobes without the [2-(methacryloyloxy)ethyl] trimethylammonium chloride (MATMA) components (M1) was demonstrated to be extracellular probes; while the other nanoprobes with the MATMA moieties (M2) was demonstrated to be intracellular probe. Both nanostructured probes (＜150 nm) exhibited fast, highly sensitive and reproducible responses to pH and dissolved oxygen (DO). Clear cell density dependent extracellular acidification and oxygen consumption were observed by using M1 during the growth of macrophages and E.coli. Whereas, M2 showed the ability for analysis of pH and DO in the macrophage cells through bioimaging. Clear emission intensity changes under confocal were observed between hypoxia and normoxia conditions as well as between pH 4.5 and 7.5, suggesting that these nanoprobes are capable of cell metabolism monitoring and intracellular pH and DO analysis. This study provided a feasible way to design extracellular or intracellular multi-parameters sensing systems, simultaneously with excellent optical and sensing properties for biological applications.