Real‐Time Imaging of Ammonia Release from Single Live Cells via Liquid Crystal Droplets Immobilized on the Cell Membrane

Tumor cells exhibit prominent metabolic alterations through which they acclimatize to their stressful microenvironment. These cells have a high rate of glutaminolysis and release ammonia (NH3) as a byproduct, which may function as a diffusible signal among cancer cells and can reveal cellular heterogeneity. E7, a nematic liquid crystal (LC), is doped with 4‐pentyl‐4′‐biphenyl carboxylic acid (PBA) and encapsulated in polymeric microcapsules (P‐E7PBA), which are then immobilized on cells in a microfluidic channel. Normal human umbilical vein endothelial cells (HUVECs) and myeloma, human primary glioblastoma (U87), human colon carcinoma (Caco‐2), and human breast adenocarcinoma (MCF‐7) cells are investigated for the release of NH3. The P‐E7PBA is able to visualize NH3 release from the cell via a radial‐to‐bipolar (R‐B) orientation change, observed through a polarized optical microscope. The various cell lines significantly differ in their response time required for an R‐B change. The mean response times for Caco‐2, U87, and MCF‐7 cells are 277, 155, and 121 s, respectively. NH3 release from a single cell captured in a microwell flow chip shows a similar R‐B change. The P‐E7PBA droplets technology could be applied to other multiple targets by functionalizing LCs with different probes. Ammonia (NH3) diffuses from the cell to the cellular microenvironment. With a dissociation constant (pKa) of 9.3, the NH3 + NH4+ content is 99% composed of NH4+ ions. The NH4+ ions interact with the COO−‐functionalized liquid‐crystals (LCs), which results in a radial‐to‐bipolar change of the LC droplet. The dashed lines in the droplets show the orientation of the LC molecules.