Ratiometric pH-Responsive and Biomimetic Microparticles for Quantitative Monitoring of Phagosomal Acidification.

We present a modular biomimetic fluorescent sensing platform designed to precisely interrogate the physicochemical mechanisms governing phagosomal acidification. Phagocytosis is an internalization process for micrometric biological objects and the later stages of phagosomal maturation -including acidification- play a pivotal role in pathogen destruction and immune signaling. In vitro studies with particulate pathogen models have shown that these degradation pathways depend on the nature of the internalized object as well as on the type of receptors engaged. To alleviate this variability and gain a finer understanding of the phagosome maturation, microparticulate fluorescent pH sensors with chemically controlled composition and cell-like mechanical properties are thus still lacking. The soft particle-based biosensors presented herein aim at filling this gap by uniquely integrating (i) cell-mimicking properties with a fluid and deformable interface, (ii) receptor-specific uptake and (iii) a ratiometric pH-responsive fluorescence to quantitatively follow the onset and progression of phagosomal acidification. This versatile platform provides a direct means to couple defined interfacial recognition events to intracellular pH measurements, offering new opportunities to unravel phagosomal physiology.