Fig. 3.

Independent SICM feedback-controlled scanning and simultaneous 3D pHe mapping of living cells. a A schematic showing the operation of double-barrel nanoprobe for simultaneous SICM imaging and pH measurement. b A pH-sensitive nanomembrane is formed inside one barrel (pH-barrel) of a double-barrel θ quartz glass nanopipette, while the second barrel (SICM imaging -barrel) is kept open via applied back pressure during fabrication. c The ion-currents flowing into two separated barrels of the generated double-barrel nanoprobe show different I–V responses to pH. d SICM imaging and 3D pHe mapping of a group of low-buffered CD44^GFP-high breast cancer MCF7 cells in estradiol-deprived medium (−E2). The SICM topographical images (left), fluorescence image (GFP, middle), and 3D pHe distributions (right) can be simultaneously obtained from a single scan. e Same as d but using a different group of estradiol-deprived (−E2) CD44^GFP-high cells. f Same as d but using a group of CD44^GFP-high cells under estradiol-supplemented culture (+E2). Scale bars represent 20 µm. Intensity of fluorescence images have been normalised.