Notes: IPG-4 TMA is a cell-impermeable fluorescent potassium indicator that has been used to detect extracellular potassium in B. subtilis biofilms.{61811} It binds to potassium (Kd = 7 mM) and displays excitation/emission maxima of 525/545 nm, respectively. IPG-4 TMA is also available in a cell-permeable form (Item No. 35541).