Cell‐permeable f
‐HM‐SiR can be specifically conjugated in live cells by DAinv. a) Prior to reaction with dienophile, f
‐HM‐SiR resides in quenched form. Target‐bound f
‐HM‐SiR spontaneously switches between fluorescent on‐ and off‐form. b) HeLa cells transiently expressing H2A‐HaloTag were incubated with (upper row) or without (lower row) HTL‐BCN (10 μm) for 30 min, washed, and labeled with f
‐HM‐SiR (2 μm, magenta) prior to imaging. Reference images (green) were generated by labeling with HTL‐TMR after incubation with HTL‐BCN. c) HeLa cells transiently expressing TOM20‐HaloTag were incubated with TPP‐BCN (10 μm) and HTL‐TMR (green), washed, and labeled with f
‐HM‐SiR (2 μm, magenta) prior to imaging. d) Background intensity of HeLa cells incubated with various SiR derivatives (2 μm), n=20. Medium was replaced once after incubation with dyes. Note the broken y‐axis and change of scale. e) Representative images for diagram in (d). Settings for image acquisition, processing, and display were identical for all shown images. Outlines of cells indicated by white line. Scale bars: b,c,e) 10 μm.