Table 3.

Process steps of the preprogrammed release of liquid with a single void

Process Step	Experimental Result
Loading – The liquids were loaded through reservoir inlets and stopped at the multilevel stop junctions just before the void. The liquid stopped due to the fluidic resistance levels of the abrupt expansions. The surface tension allowed long storage times (days) without activation or evaporation when maintained in water-saturated ambient.
Air Trap & Equilibration – The trigger liquid (red) was introduced through the main channel, filling the deep branch and the 3 shallow branches. The air was trapped in the void to isolate the 3 liquids from that in the main channel. The red liquid continued through the detection site and the capillary pump.
1st Activation – The branch with the smallest retention burst (blue) was activated when the red liquid in the main channel emptied to the activation resistance component. The downstream capillary pressure provided sufficient suction power to activate the blue liquid. The air in the void was displaced by the pneumatic suction.
2nd Activation – The same principle occurred for the activation of the chamber with the intermediate retention burst (green). When the 1st chamber was emptied, the next π-valve was activated using the next shallow branch available (closest to the reservoir).
3rd Activation – The last release was the one with the highest retention burst (red). The red liquid was activated and flowed into the main channel through the last shallow branch. Backflow or diffusion was not apparent during the sequential release of the liquids.
Detection – The capillary pump provided enough suction power to empty the 3 different fluids. However, it was not strong enough to overcome the activation resistance. Therefore, the liquid remaining in the main channel was not emptied. This phenomenon allowed the measurement to be carried out in wet and homogenous conditions.

The scale bar is 2 mm