A new nanogel indicator (NGI) for ratiometric fluorescent detection of intracellular pH values has been reported. In aqueous solution, the NGI can be used for ratiometric sensing of pH changes with a large hypsochromic shift of 100 nm in the green–red region and reversible. Furthermore, the NGI has been used to calibrate the cytosol pH value in living cells.

Chem. Commun.,2014

 (a) Mechanism of emission changes with pH. (b) Photography of fluorescence of NGIs at different pH values.

Confocal microscopy images of NGIs (HPC, 1.0 μM) in NIH/3T3 fibroblast cells clamped at pH 6 (a–d), 7 (e–h), 8 (i–l) and 9 (m–p). The excitation wavelength was 458 nm and the images were collected at 470–510 nm (first row) and 570–630 nm (second row). The corresponding contrast images (third row) and ratio images obtained from the green and red channels (fourth row). The bottom color strip represents the pseudocolor change with pH. Scale bar: 20 μm.