Integrated droplet-digital microfluidic system for on-demand droplet creation, mixing, incubation, and sorting of droplets in a cell trapping array

A method of employing a microfluidic device to trap a cell and perform droplet operations associated with the trapped cell, the method comprising:

• providing the microfluidic device, wherein the microfluidic device comprises:
• a first layer having a plurality of electrodes formed thereon;
• a second layer having an elongate channel defined therein;
• an intermediate dielectric layer residing between the first layer and the second layer;
• and
• a cell trap formed in the second layer, the cell trap extending laterally from a first region of the elongate channel to a second region of the elongate channel that is longitudinally separated, along the elongate channel, from the first region of the elongate channel, the cell trap having a first side in fluid communication with the first region of the elongate channel, the first side being sized to permit entry of the cell into the cell trap, the cell trap having a second side in fluid communication with the second region of the elongate channel, the second side being sized to prevent passage of the cell from the cell trap into the second region of the elongate channel;
• the plurality of electrodes comprising a plurality of cell trap electrodes residing proximal to the cell trap;
• the elongate channel and the cell trap being dimensioned to produce a hydrodynamic resistance through the cell trap, prior to trapping of the cell, that is less than a hydrodynamic resistance through a longitudinal portion of the elongate channel residing between the first region and the second region, to promote fluid flow through the cell trap to facilitate trapping of the cell within the cell trap;
• flowing a first fluid through the elongate channel, the first fluid being an aqueous cell suspension comprising the cell, the first fluid flowing through the elongate channel in a direction such that:
• the first region is encountered prior to the second region, the cell passes from the first region of the elongate channel into the cell trap due to the hydrodynamic resistance, and the cell is trapped by the cell trap;
• after trapping the cell within the cell trap, flowing a second fluid through the elongate channel, the second fluid being immiscible with the aqueous phase of the aqueous cell suspension;
• as the second fluid reaches the first region of the elongate channel, actuating at least a first subset of the cell trap electrodes to maintain the first fluid and the cell within the cell trap and form a first aqueous droplet within the cell trap, the first aqueous droplet encapsulating the cell;
• flowing a second aqueous droplet through the elongate channel;
• and
• as the second aqueous droplet reaches the first region of the elongate channel, actuating at least a second subset of the cell trap electrodes to merge, within the cell trap, at least a portion of the second aqueous droplet with the first aqueous droplet to generate a merged aqueous droplet within the cell trap.