Heavy water: a simple solution to increasing the brightness of fluorescent proteins in super-resolution imaging.

Photoactivatable fluorescent proteins (PA-FPs) are widely used in live single-molecule super-resolution imaging but emit substantially fewer photons than organic dyes do. Herein, we show that in heavy water (D2O) instead of H2O, common PA-FPs emit 26-54% more photons, effectively improving the localization precision in super-resolution imaging.