Supplementary Figures

Supplementary Fig. S1: Normalized excitation and emission spectra of Alexa488N, TAC-Rh and Alexa647N.

Supplementary Fig. S2: UV-Vis absorption spectrum of ssDNA-TAC-Rh.

Supplementary Fig. S8: 2-IM profiles of HEK 293T cells clamped at pH 6.0.

Supplementary Fig. S9: Comparison of in vitro and in cellulo clamping. A-B, In vitro and in cellulo response of pHlicKer given by fold change (FC) of (A) D/A from pH 6.0 - 6.6 at 0.1 mM [K⁺] and (B) O/R ratios from 0.1 - 140 mM [K⁺] at the indicated pH. C, In vitro and in cellulo Kd values of pHlicKer determined at the indicated pH. D, O/R values of pHlicKer at pH 6.6 as a function of [K⁺] obtained in vitro and in cellulo. 

Supplementary Fig. S10:  A) Normalized ratio of fluorescence intensity of donor to that of acceptor (D/A) of pHlicKer^Biotin on beads as a function of pH. B) pHlicKer^Biotin Kd as a function of pH. 

Supplementary Fig. S11B: Pearson’s correlation coefficient (PCC) of colocalization (CL) and pixel shift (PS) of HEK 293T cells expressing Kv11.1 immunostained for anti-Kv_11.1 and anti-58K that marks the trans Golgi network.  .   

Supplementary Fig. S12B: Pearson’s correlation coefficient (PCC) of colocalization (CL) and pixel shift (PS) of HEK 293T cells expressing Kv_11.1 immunostained for anti-Kv_11.1 and anti-Transferrin receptor that marks recycling endosomes.

Supplementary Fig. S13: A-B, [K⁺]_RE and C-D, [K⁺]_TGN values in UT cells in the absence and presence of cisapride. 

Supplementary Fig. S14: [K⁺]_TGN values in UT and WT cells.

Supplementary Table 1:  Propagation of error assessed by a blind test.