Magnetic particle extraction in an EWOD instrument
A method of operating an EWOD device to employs a magnetic field to separate magnetically responsive particles from a polar liquid droplet. The method includes the steps of dispensing a liquid droplet onto an element array of the EWOD device, wherein the liquid droplet includes magnetically responsive particles; performing an electrowetting operation to move the liquid droplet along the element array to a location relative to a magnet element in proximity to that location of the EWOD device; operating the magnet element to apply a magnetic field to the liquid droplet, wherein at least a portion of the magnetically responsive particles aggregate within the liquid droplet in response to the magnetic field; and separating the aggregated magnetically responsive particles from the liquid droplet with the magnetic field, wherein the aggregated magnetically responsive particles move in response to the magnetic field to a location on the element array in proximity to the magnet element. Embodiments of the methods of the present application may be performed by an EWOD control system executing program code stored on a non-transitory computer readable medium.
1 . A method of operating an electrowetting on dielectric (EWOD) device that performs electrowetting operations on liquid droplets dispensed onto an element array of the EWOD device, the method of operating comprising the steps of:
dispensing a liquid droplet onto the element array of the EWOD device, wherein the liquid droplet includes magnetically responsive particles;
performing an electrowetting operation to move the liquid droplet along the element array to a first location on the element array;
operating a magnet element, at a second location of the EWOD device different from the first location, from a first state in which no magnetic field is applied to the liquid droplet to a second state to apply a magnetic field to the liquid droplet,
aggregating at least a portion of the magnetically responsive particles within the liquid droplet in response to the magnetic field; and
separating the aggregated magnetically responsive particles from the liquid droplet with the magnetic field by the aggregated magnetically responsive particles moving in response to the magnetic field to the second location on the element array of the magnet element.
2 . The method of operating of claim 1 , further comprising removing an electrowetting force of the electrowetting operation from the liquid droplet prior to operating the magnet element to apply the magnetic field.
3 . The method of operating of claim 1 , further comprising:
performing an electrowetting operation to orient the actuated droplet with a straight edge facing the magnet element;
while maintaining an electrowetting force on the liquid droplet to maintain the liquid droplet in an actuated state, operating the magnet element to apply the magnetic field to the liquid droplet, wherein at least a portion of the magnetically responsive particles aggregate within the liquid droplet in response to the magnetic field along the straight edge; and
removing the electrowetting force to de-actuate the liquid droplet to effect separation of the aggregated magnetically responsive particles from the liquid droplet with the magnetic field.
4 . The method of operating of claim 1 , further comprising:
performing an electrowetting operation to orient the actuated droplet with a non-straight edge facing the magnet element; and
while maintaining an electrowetting force on the liquid droplet to maintain the liquid droplet in an actuated state, operating the magnet element to apply the magnetic field to the liquid droplet, wherein at least a portion of the magnetically responsive particles aggregate within the liquid droplet in response to the magnetic field along the non-straight edge;
wherein the aggregated magnetically responsive particles separate from the liquid droplet at the non-straight edge in response to the magnetic field.
5 . The method of operating of claim 1 , further comprising:
performing another electrowetting operation to move the liquid droplet along the element array relative to the first magnet element, wherein additional magnetically responsive particles aggregate within the liquid droplet in response to the first magnetic field as the liquid droplet is moved relative to the first magnet element;
operating the first magnet element to remove the first magnetic field from the liquid droplet;
operating a second magnet element of the EWOD device to apply a second magnetic field to the liquid droplet; and
separating the aggregated magnetically responsive particles from the liquid droplet with the second magnetic field, wherein the aggregated magnetically responsive particles move in response to the second magnetic field to a location on the element array in proximity to the second magnet element.
6 . The method of operating of claim 5 , further comprising removing an electrowetting force of the electrowetting operation prior to operating the second magnet element to apply the second magnetic field.
7 . The method of operating of claim 1 , wherein multiple iterations of aggregation and separation of the magnetically responsive particles is performed in response to applying the magnetic field.
8 . The method of operating of claim 7 , further comprising, in response to determining that a number of remaining magnetically responsive particles is insufficient to separate from the liquid droplet in response to the magnetic field, adding additional magnetically responsive particles to the liquid droplet, wherein the aggregated magnetically responsive particles including the additional magnetically responsive particles separate from the liquid droplet in response to the magnetic field.
9 . The method of operating of claim 1 , wherein aggregating the magnetically responsive particles within the liquid droplet in response to the magnetic field does not induce bulk movement of the liquid droplet.
10 . The method of operating of claim 1 , wherein the liquid droplet includes a polar liquid, and the liquid droplet is dispensed into a non-polar liquid on the element array of the EWOD device.
11 . The method of operating of claim 1 , wherein the magnet element is a permanent magnet, and the magnet element is moved by an actuator in the EWOD device relative to the element array from a withdrawn position to an elevated position to apply the magnetic field.
12 . The method of operating of claim 1 , wherein the magnet element is an electromagnet, and the magnet element is operated from an off state to an on state to apply the magnetic field.
13 . The method of operating of claim 1 , wherein the EWOD device further include sensing circuity, and the method further comprises reading the output of the sensing circuitry to determine a location of one of the magnet elements and/or the liquid droplet to position the liquid droplet relative to the one magnet element.
14 . The method of operating claim 13 , further comprising applying a voltage perturbation to the one magnet element of the magnet elements, and reading the output from the sensing circuitry in response to the voltage perturbation applied to the one magnet element.
15 . The method of operating of claim 13 , further comprising preventing return of the separated magnetically responsive particles to the liquid droplet by the steps of:
employing sensor feedback to determine whether the liquid droplet has moved toward the one magnet element; and
performing an electrowetting operation to move the liquid droplet away from the magnet element and/or operating the magnet element to remove the magnetic field.
16 . The method of operating of claim 1 , further comprising, prior to operating the or each magnet element, incubating the magnetically responsive particles for a sufficient time to bind the magnetically responsive particles to target particles.
17 . The method of operating of claim 1 , further comprising increasing a viscosity of the liquid droplet prior to operating the or each magnet element to apply the magnetic field.
18 . The method of operating of claim 1 , further comprising decreasing a surface tension of the liquid droplet prior to operating the or each magnet element to apply the magnetic field.
19 . A microfluidic system configured to perform the method of operating the EWOD device according to claim 1 comprising:
the electro-wetting on dielectric (EWOD) device comprising the element array that receives the liquid droplet, the element array comprising a plurality of individual array elements;
the magnet element operable to apply the magnetic field to the element array; and
a control system configured to control actuation voltages applied to the element array to perform the electrowetting operation to move the liquid droplet along the element array to a first location on the element array, and to control operation of the magnet element from the first state in which no magnetic field is applied to the liquid droplet to the second state to apply the magnetic field to the liquid droplet, to perform the method of operating the EWOD device according to claim 1 .