Interfacial pH Behavior at a Cell/Gate Insulator Nanogap Induced by Allergic Responses

[Image: see text] In this paper, we clarify the interfacial pH behavior induced by allergic responses at a mast cell/gate insulator nanogap detected by laser scanning confocal fluorescence microscopy. In a previous work, the change in interfacial pH detected on the basis of allergic responses was monitored at a mast cell/gate insulator nanogap interface using a cell-cultured gate ion-sensitive field-effect transistor (ISFET), but the interfacial pH behavior at a mast cell/gate insulator nanogap has not been clarified using other methods. Here, the phospholipid fluorescein is employed as the extracellular pH indicator, which is fixed to the external side of the plasma membrane of mast cells cultured on a substrate. As a result, the interfacial pH at the mast cell/substrate nanogap increases after mast cells with IgE on their membrane are activated by the interaction between IgE and an allergen. This is due to the basicity of histamine molecules released from mast cells. Moreover, the change in the interfacial pH at the mast cell/substrate nanogap is larger than that at the mast cell/bulk solution interface. That is, molecules of substances secreted as a result of allergic responses are assumed to accumulate around the cell/substrate nanogap. The data obtained in this study support the idea that potentiometric ion sensors such as ISFETs can detect a cellular-function-induced change in pH at a cell/electrode nanogap in real time.