Derivatization of WGA with a small-molecule fluorescent pH sensor and cell surface labeling to visualize plasma membrane proton fluxes. (A) Synthetic scheme of WGA-pHRho. Using the degree of labeling equation (Materials and methods) on average, one WGA monomer is labeled with one pHRho molecule that is activated with N,N,N′,N′-tetramethyl-O-(N-succinimidyl) uronium tetrafluoroborate (TSTU). The doubly labeled WGA homodimer is shown. (B) Cartoon depiction of the whole-cell patch-clamp fluorometry approach to visualize proton fluxes with WGA-pHRho.