In situ monitoring of cellular metabolism is useful for elucidating dynamic functions of living cells. In our previous studies, cellular respiration was continuously monitored as a change in pH at the cell/electrode nanoscale interface (i.e., interfacial pH) using an ion-sensitive field-effect transistor (ISFET). However, such interfacial pH behaviour on the nanoscale has not been confirmed using other methods such as fluorescence imaging. In this study, we have clarified the interfacial pH behaviour at a cell/substrate nanogap using a laser scanning confocal fluorescence microscope. The phospholipid fluorescein used as a pH indicator was fixed to the plasma membrane on the external side of a cell by inserting its lipophilic alkyl chain into the membrane, and used to observe the change in interfacial pH. As a result, hydrogen ions generated by cellular respiration were gradually accumulated at the cell/substrate nanogap, resulting in a decrease in pH. Moreover, the interfacial pH between the plasma membrane and the substrate became lower than the pH near the surface of cells not in contact with the substrate. The data obtained in this study support the idea that potentiometric ion sensors such as ISFETs can detect a cellular-metabolism-induced change in pH at a cell/electrode nanogap in real time.

中文翻译：

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阐明了细胞/底物纳米间隙的界面pH行为，可用于细胞呼吸的原位监测†

原位监测细胞代谢对于阐明活细胞的动态功能很有用。在我们以前的研究中，细胞呼吸一直作为细胞/电极纳米级界面的pH值变化进行监测（即，界面pH值）使用离子敏感的场效应晶体管（ISFET）。但是，尚未使用其他方法（例如荧光成像）确认这种纳米级的界面pH行为。在这项研究中，我们已经阐明了使用激光扫描共聚焦荧光显微镜在细胞/基质纳米间隙的界面pH行为。通过将亲脂性烷基链插入膜中，将用作pH指示剂的磷脂荧光素固定在细胞外侧的质膜上，并观察界面pH的变化。结果，细胞呼吸产生的氢离子逐渐积累在细胞/基质纳米间隙中，导致pH降低。而且，质膜和底物之间的界面pH变得低于不与底物接触的细胞表面附近的pH。这项研究中获得的数据支持这样的想法：诸如ISFET的电位离子传感器可以实时检测细胞/电极纳米间隙中细胞代谢引起的pH值变化。