Total-internal-reflection-fluorescence microscopy for the study of nanobubble dynamics.

Nanobubbles can be observed with optical microscopy using the total-internal-reflection-fluorescence excitation. We report on total-internal-reflection-fluorescence visualization using rhodamine 6G at 5 μM concentration which results in strongly contrasting pictures. The preferential absorption and the high spatial resolution allow us to detect nanobubbles with diameters of 230 nm and above. We resolve the nucleation dynamics during the water-ethanol-water exchange: within 4 min after exchange the bubbles nucleate and form a stable population. Additionally, we demonstrate that tracer particles near to the nanobubbles are following Brownian motion: the remaining drift flow is weaker than a few micrometers per second at a distance of 400 nm from the nanobubble's center.