Microscale flow visualization

Advances in microfluidic and nanofluidic technologies have been paralleled by advances in methods for direct optical measurement of transport phenomena on these scales. A variety of methods for microscale flow visualization have appeared and evolved since the late 1990s. These methods and their applications to date are reviewed here in detail, and in context of the both the fundamental phenomena they exploit and the fundamental phenomena they are applied to measure. Where possible, links to macroflow visualization methods are established, and the physical mechanisms underlying these methods are explained.