Methods and devices for electrical sample preparation
Devices and methods are provided for electrically lysing cells and releasing macromolecules from the cells. A microfluidic device is provided that includes a planar channel having a thickness on a submillimeter scale, and including electrodes on its upper and lower inner surfaces. After filling the channel with a liquid, such that the channel contains cells within the liquid, a series of voltage pulses of alternating polarity are applied between the channel electrodes, where the amplitude of the voltage pulses and a pulse width of the voltage pulses are effective for causing irreversible electroporation of the cells. The channel is configured to possess thermal properties such that the application of the voltage produces a rapid temperature rise as a result of Joule heating for releasing the macromolecules from the electroplated cells. The channel may also include an internal filter for capturing and concentrating the cells prior to electrical processing.
1. A method of electrically processing a cell-containing liquid within a microfluidic device, the method comprising:
flowing the liquid into a microfluidic channel of the microfluidic device;
closing the microfluidic channel, such that the liquid is confined within the closed volume of the microfluidic channel;
while maintaining the microfluidic channel in a closed state, applying bipolar voltage pulses across the microfluidic channel; and
while applying the bipolar voltage pulses:
measuring an electrical current within the microfluidic channel; and
controlling one or more properties of the bipolar voltage pulses, according to feedback based on the electrical current, to achieve conditions within the channel that are sufficient to effect lysis of the at least one cell.
2. The method according to claim 1 wherein the one or more properties of the bipolar voltage pulses are controlled according to a feedback parameter associated with the electrical current.
3. The method according to claim 2 wherein the feedback parameter is one of the electrical current and an impedance of the microfluidic channel.
4. The method according to claim 2 wherein the bipolar voltage pulses are modified after detecting that the feedback parameter associated with the electrical current has reached a pre-selected value.
5. The method according to claim 4 wherein, after detecting that the feedback parameter has reached the pre-selected value, modifying the delivery of the bipolar voltage pulses to maintain the feedback parameter at the pre-selected value.
6. The method according to claim 1 wherein the one or more properties of the bipolar voltage pulses are controlled, according to the feedback from the electrical current, to prevent a phase change from a liquid phase to a vapour phase.
7. The method according to claim 1 wherein the one or more properties of the bipolar voltage pulses are controlled, according to the feedback from the electrical current, to maintain the liquid in a superheated state.
8. The method according to claim 1 wherein the one or more properties of the bipolar voltage pulses that are controlled based on feedback from the electrical current include one or more of voltage pulse train amplitude, pulse density, duty cycle, and pulsewidth.
9. The method according to claim 1 wherein a known temperature dependence of an electrical conductivity of the liquid within the microfluidic device is employed to infer a temperature of the liquid based on the electrical current, and wherein the one or more properties of the bipolar voltage pulses are controlled based on the temperature.
10. The method according to claim 9 wherein the one or more properties of the bipolar voltage pulses are controlled to maintain the liquid at a pre-selected temperature for a pre-selected residence time.
11. The method according to claim 1 wherein the one or more properties of the bipolar voltage pulses are controlled, according to the feedback from the electrical current, such that delivery of the bipolar voltage pulses is maintained after having detected a feature in the electrical current.
12. The method according to claim 11 wherein the feature comprises one or more of a peak, a maximum, and a minimum.
13. The method according to claim 1 wherein the bipolar voltage pulses are applied such that an electric field generated across a thickness of the microfluidic channel is between approximately 2 kV/cm and 30 kV/cm such that the liquid is heated with a heating rate of at least 250 degrees Celsius per second.