Digital microfluidics apparatuses and methods for manipulating and processing encapsulated droplets
Air-matrix digital microfluidics (DMF) apparatuses and methods of using them to prevent or limit evaporation and surface fouling of the DMF apparatus. In particular, described herein are air-matrix DMF apparatuses and methods of using them including thermally controllable regions with a wax material that may be used to selectively encapsulate a reaction droplet in the air gap of the apparatus; additional aqueous droplets may be combined with the encapsulated droplet even after separating from the wax, despite residual wax coating, by merging with an aqueous droplet having a coating of a secondary material (e.g., an oil or other hydrophobic material) that may remove the wax from the droplet and/or allow combining of the droplets.
1. A method of performing droplet operations on a droplet at least partially coated in liquid wax within an air-matrix digital microfluidic (DMF) apparatus, the method comprising:
moving, by electrowetting, an aqueous reaction droplet having an outer coating of liquid wax within an air gap of the air-matrix DMF apparatus which is formed between a first plate and a second plate of the air-matrix DMF apparatus;
merging the aqueous reaction droplet with a carrier droplet comprising an aqueous droplet coated with an oil or an organic solvent in the air gap to form a combined droplet; and
moving, by electrowetting, the combined droplet within the air gap.
2. The method of claim 1 , wherein moving, by electrowetting, the aqueous reaction droplet comprises initially transporting the aqueous reaction droplet to a thermal zone of the air gap, the thermal zone comprising a wax and melting the wax within the thermal zone to at least partially encapsulate the aqueous reaction droplet with the wax.
3. The method of claim 2 , further comprising regulating a temperature of the at least partially encapsulated reaction droplet to allow a reaction to proceed within the aqueous reaction droplet before transporting the aqueous reaction droplet having the outer coating of liquid wax within the air gap.
4. The method of claim 2 , wherein melting the wax comprises melting a solid wax formed into a wall or open chamber within the air gap.
5. The method of claim 1 , wherein moving, by electrowetting, the aqueous reaction droplet comprises transferring the aqueous reaction droplet away from away from a thermal zone comprising a wax material so that at least some of the wax is left behind.
6. The method of claim 1 , further comprising detecting a product within the aqueous reaction droplet or the combined droplet.
7. The method of claim 1 , wherein merging the aqueous reaction droplet with the carrier droplet comprises moving one or both of the aqueous reaction droplet and the carrier droplet into contact with each other by electrowetting.
8. The method of claim 1 , further comprising mixing the combined droplet, wherein the combined droplet comprises a plurality of beads.
9. The method of claim 8 , further comprising immobilizing the beads.
10. The method of claim 9 , further comprising moving the combined droplet away from the immobilized beads.
11. The method of claim 10 , further comprising re-suspending the immobilized beads within an aqueous droplet.
12. The method of claim 8 , further comprising separating the beads from the combined droplet by moving a magnetic field away from the combined droplet to magnetically draw the beads away from the combined droplet.