Potentiometric pH Nanosensor for Intracellular Measurements: Real-Time and Continuous Assessment of Local Gradients
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We present a pH nanosensor conceived for single intracellular measurements. The sensing architecture consisted of a two-electrode system evaluated in the potentiometric mode. We used solid-contact carbon nanopipette electrodes tailored to produce both the indicator (pH nanosensor) and reference electrodes. The indicator electrode was a membrane-based ion-selective electrode containing a receptor for hydrogen ions that provided a favorable selectivity for intracellular measurements. The analytical features of the pH nanosensor revealed a Nernstian response (slope of −59.5 mV/pH unit) with appropriate repeatability and reproducibility (variation coefficients of <2% for the calibration parameters), a fast response time (<5 s), adequate medium-term drift (0.7 mV h–1), and a linear range of response including physiological and abnormal cell pH levels (6.0–8.5). In addition, the position and configuration of the reference electrode were investigated in cell-based experiments to provide unbia...