  Nanobubbles are observed with optical microscopy using the total internal
reflection fluorescence (TIRF) excitation. We report on TIRF visualization
using Rhodamine 6G at 5$\mu\,$M concentration which results to strongly
contrasted pictures. The preferential absorption and the high spatial
resolution allow to detect nanobubbles with diameters of 230\,nm and above. We
present a study of the nucleation dynamics from the water-ethanol-water
exchange and report the size distributions. Nanobubble nucleation is observed
within 4 min after the exchange, later a stable population of nanobubbles with
a surface density of 0.55 bubbles\,/$\mu$m$^2$ is formed. Interestingly,
unstable, slowly dissolving nanobubbles are observed during the first stage of
water-ethanol exchange; only after the ethanol-water exchange stable
nanobubbles appear.
