Triggered "on/off" micropumps and colloidal photodiode.

We discuss a set of smart micropumps that sense their surrounding environment and respond accordingly. First we show that crystallites of a photoacid generator function as micropumps in the presence of UV light via diffusiophoresis and can be turned "on/off" in a controlled manner. The pump can be restarted multiple times simply by re-illumination. The electroosmotic component was distinguished from the diffusiophoretic component and compared. We also demonstrate patterning. Second, we show that a polymeric imine can also work as a micropump in acidic environment wherein the velocity can be controlled by controlling the pH and, in turn, the ion gradient; the highest velocities are achieved at the lowest pH. Finally, we combined the photoacid and polyimine pumps to create a colloidal photodiode, where we attain both spatial and temporal control over colloidal transport and obtain amplification along with rectification.