Glass nanopipettes are widely used in scanning ion conductance microscopy (SICM), to measure surface topography and surface charge. However, the ionic current data do not provide quantitative analysis of specific chemical concentrations in complex media. Multifunctional probes have been developed that measure chemical concentration, that usually combine an SICM probe with a second electrochemical or ion conductance probe that measures analyte concentration. In a double-barreled glass nanopipette, one channel is filled with solution and serves as the SICM probe to measure topography and aid in tip-positioning, while the second channel can be functionalized to enable the detection of specific molecules. For example, pH measurement can be achieved using iridium oxide deposited on a carbon filled channel, which provides a potentiometric scanning electrochemical microscopy (SECM) measurement. The glass surface of a nanopipette may also be functionalized with biosensing elements to generate a signal change upon target analyte concentration change. In this work, multifunctional probes were used for topographic mapping of live mammalian cells, with a simultaneous measurement of chemical concentrations, that includes proton concentration (i.e. pH). Furthermore, miniaturized sensors employing structure-switching single stranded DNA aptamer probes were used to add specific molecule sensing capabilities to the imaging probe.

Multifunctional probes for topography mapping and chemical sensing at living cells

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