Ion-selective electrodes have been widely used for inorganic ion detection; however, conventional micrometer-tipped electrodes cannot meet the growing demand for calcium imaging with high spatial resolution. Here, we report a sub-100 nm calcium-selective electrode based on a quartz nanopore. A classical calcium ionophore IV membrane cocktail was introduced into a 50 nm laser-pulled quartz conical nanopore by centrifugation, constructing a nanoscale ion-sensing interface. The electrode exhibited a linear potentiometric response of 19.14 mV/dec over the calcium concentration range from 1×10−7 mol/L to 1×10−2 mol/L, with a detection limit of approximately 100 nmol/L (the lowest concentration tested), and showed favorable selectivity against Na+, Mg2+, ascorbic acid, and dopamine. The aperture size significantly influenced the response: when reduced to 20 nm, the response slope decreased to 12.98 mV/dec. To the best of our knowledge, 20 nm represents the smallest aperture reported for quartz-nanopore-based ion-selective electrodes, while the 50 nm aperture still exhibits a sub-Nernstian response, offering a promising tool for ion detection in even smaller nanoscale spaces.
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Jilin University, The Editorial Department of Chemical Research in Chinese Universities and Springer-Verlag GmbH
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