  The detection of extracellular pH at single cell resolution is challenging
and requires advanced sensibility. Sensing pH at a high spatial and temporal
resolution might provide crucial information in understanding the role of pH
and its fluctuations in a wide range of physio-pathological cellular processes,
including cancer. Here, a method to embed silica-based fluorescent pH sensors
into alginate-based three-dimensional (3D) microgels tumour models, coupled
with a computational method for fine data analysis, is presented. By means of
confocal laser scanning microscopy, live-cell time-lapse imaging of 3D alginate
microgels was performed and the extracellular pH metabolic variations were
monitored in both in vitro 3D mono- and 3D co-cultures of tumour and stromal
pancreatic cells. The results show that the extracellular pH is cell
line-specific and time-dependent. Moreover, differences in pH were also
detected between 3D monocultures versus 3D co-cultures, thus suggesting the
existence of a metabolic crosstalk between tumour and stromal cells. In
conclusion, the system has the potential to image multiple live cells types in
a 3D environment and to decipher in real-time their pH metabolic interplay
under controlled experimental conditions, thus being also a suitable platform
for drug screening and personalized medicine.
