Microfluidic devices containing reversibly pinned droplet samples and methods
A microfluidic device comprising: (a) a plate comprising a substrate, a plurality of electrodes, and a first layer of hydrophobic material applied over the plurality of electrodes; (b) a processing unit operably programmed to perform a method of pinning an aqueous droplet within the microfluidic device; and (c) a controller operably connected to a power source, the processing unit, and the plurality of electrodes. The method of pinning an aqueous droplet comprises: applying an electric field of a first polarity to an aqueous droplet located on the surface of the layer of hydrophobic material and having a first contact angle, to cause the droplet to maintain a second contact angle in the absence of the electric field, wherein the aqueous droplet contains a surfactant and the second contact angle is less than the first contact angle.
1. A microfluidic device comprising:
a first substrate;
a plurality of electrodes;
a first layer of hydrophobic material completely covering the plurality of electrodes;
a plurality of gate line drivers operationally coupled to the plurality of electrodes; and
a plurality of data line drivers operationally coupled to the plurality of electrodes, the plurality of data line drivers and the plurality of gate line drivers responsive to one or more signals to apply a first electric field of a first polarity to an aqueous droplet containing a surfactant located at a location on a surface of the first layer of hydrophobic material during a first time and having a first contact angle, and the plurality of data line drivers and the plurality of gate line drivers responsive to one or more signals to halt application of the first electric field to the aqueous droplet containing the surfactant located at the location on the surface of the first layer of hydrophobic material during a second time, the aqueous droplet having a second contact angle and remaining at the location on the surface of the first layer of hydrophobic material in absence of the first electric field, the second contact angle being less than the first contact angle.
2. The microfluidic device of claim 1 , wherein the first contact angle is greater than or equal to 90 degrees.
3. The microfluidic device of claim 1 , wherein the first contact angle is greater than or equal to 90 degrees and the second contact angle is less than 90 degrees.
4. The microfluidic device of claim 1 , wherein the first contact angle is greater than or equal to 90 degrees and the second contact angle is less than 75 degrees.
5. The microfluidic device of claim 1 , wherein the first polarity is negative.
6. The microfluidic device of claim 1 , wherein the plurality of data line drivers and the plurality of gate line drivers are responsive to one or more signals to apply a second electric field of a second polarity opposite to the first polarity to the aqueous droplet for a third time causing the aqueous droplet to maintain a third contact angle in the absence of the second electric field, the third contact angle being greater than the second contact angle.
7. The microfluidic device of claim 6 , wherein the second polarity is positive.
8. The microfluidic device of claim 1 , wherein the plurality of data line drivers and the plurality of gate line drivers apply droplet actuation parameters associated with the aqueous droplet.
9. The microfluidic device of claim 8 , wherein the droplet actuation parameters account for the surfactant content, or the composition of solvent and solvates.
10. The microfluidic device of claim 8 , wherein the droplet actuation parameters include a frequency or amplitude of a pulse applied to the plurality of electrodes to generate the applied electric field.
11. The microfluidic device of claim 1 , further comprising a dielectric covering the plurality of electrodes.
12. The microfluidic device of claim 11 , wherein the dielectric is adjacent to the first layer of hydrophobic material.
13. The microfluidic device of claim 1 , wherein the surfactant is a non-ionic surfactant.
14. The microfluidic device of claim 1 , wherein the surfactant comprises polyethylene oxide.
15. The microfluidic device of claim 1 , further comprising:
a second substrate;
a continuous conductor,
a second layer of hydrophobic material completely covering the continuous conductor, and
a gap between the first and second layers of hydrophobic material, wherein the aqueous droplet is introduced into the gap.
16. The microfluidic device of claim 15 , wherein the first layer of hydrophobic material on the first substrate and the second layer of hydrophobic material on the second substrate are the same composition.