Rapid and specific assays for intracellular pH fluctuations based on pH-dependent disassembly-assembly of conjugated polymer nanoparticles

Abstract

Intracellular pH (pHi) is a critical factor that governs many physiological and pathological processes. Accurate measurement and visual imaging of pHi is of importance and in high demand for biological research and clinical diagnosis. In this paper, a novel strategy of pH-dependent disassembly-assembly of conjugated polymer nanoparticles was developed and successfully applied in constructing an efficient fluorescent probe for intracellular pH sensing and imaging. The nanoparticles-based probe (PTNPs) was prepared by reprecipitation method from a polythiophene derivative (PTNEt2) with diethylamine group on its side chains. As the acidity of system increased, the disassembly of PTNPs took place due to the electrostatic repulsion between protonated PTNEt2 chains at low pH. Conversely, once the system recovered to weak alkalinity, the dispersed polymer chains reassembled to form nanoparticles owing to their poor water-solubility at high pH. Thus, PTNPs showed a rapid, highly selective and reversible fluorescence response to pH. Besides, the probe exhibited an ideal pKa value of 5.71, which was suitable for quantification of intracellular pH values with a linearly proportional range of 4.0–8.0. In view of easy modification properties of conjugated polymers, this proposed strategy could offer a general way for quantifying various biological events inside living cells.