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

Abstract Intracellular pH (pH i ) is a critical factor that governs many physiological and pathological processes. Accurate measurement and visual imaging of pH i 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 ( PTNEt 2 ) 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 PTNEt 2 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 p Ka 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.