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 pulsewidth 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 liquid within a microfluidic device to modify the activity of at least one enzyme within the liquid;
the microfluidic device including:
an upper planar substrate;
a lower planar substrate; and
a side wall having a thickness on a submillimeter scale, wherein said upper planar substrate, said lower planar substrate and said side wall define a channel;
an upper electrode provided on an inner surface of said upper planar substrate; and
a lower electrode provided on an inner surface of said lower planar substrate;
the method including:
flowing the liquid into the channel, the liquid having an ionic strength between 0.1 mM and 100 mM;
applying bipolar voltage pulses between the upper electrode and the lower electrode such that the liquid is heated with a heating rate of at least 250 degrees per second;
wherein the voltage pulses are applied such that the liquid is heated to an elevated temperature sufficient to effect modification of the activity of the enzyme.
2. The method according to claim 1 wherein the liquid comprises one or more nucleic acids, and wherein the enzyme is modified under the action of the bipolar voltage pulses without compromising the integrity of the nucleic acids.
3. The method according to claim 1 wherein the liquid is heated to a temperature sufficient for denaturing the enzyme.
4. The method according to claim 1 wherein the enzyme is a nuclease.
5. The method according to claim 4 wherein the nuclease is RNAse.
6. The method according to claim 1 wherein said bipolar voltage pulses are provided such that an electric field between 2 kV/cm and 30 kV/cm is generated across the thickness of the channel.
7. The method according to claim 6 wherein the liquid comprises one or more cells, and wherein at least one cell is lysed under the application of the bipolar voltage pulses.
8. The method according to claim 7 wherein the enzyme is a nuclease released by the at least one cell.
9. The method according to claim 7 wherein the enzyme is modified under the action of the bipolar voltage pulses without compromising the integrity of nucleic acids released by the at least one cell.
10. The method according to claim 8 wherein the nuclease is RNAse.
11. The method according to claim 8 further comprising amplifying a sequence of a nucleic acid released by the at least one cell, wherein the amplification is performed in the absence of a subsequent nucleic acid extraction or purification step.
12. The method according to claim 1 wherein the voltage pulses are applied such that Joule heating of the liquid occurs with a rate of at least 2000 degrees per second.
13. The method according to claim 1 wherein the elevated temperature is between 80 degrees Celsius and 200 degrees Celsius.
14. The method according to claim 1 wherein the elevated temperature greater than or equal to a boiling temperature of the liquid at atmospheric pressure.
15. The method according to claim 1 further comprising monitoring a current flowing between the upper electrode and the lower electrode, and employing the current as a feedback parameter for controlling the temperature of the liquid.
16. The method according to claim 15 wherein the liquid is heated to a phase transition temperature, the method further comprising identifying an initial peak in the current as the onset of the phase transition.
17. The method according to claim 15 further comprising applying the voltage pulses to maintain the temperature for a prescribed time duration, based on the current.
18. The method according to claim 1 further comprising monitoring an impedance of the channel and employing the impedance as a feedback parameter for controlling the temperature of the liquid.
19. The method according to claim 1 wherein the channel is open during application of the voltage pulses.
20. The method according to claim 19 wherein the diameter of a port in fluid communication with the channel is sufficiently restricted in size such that the liquid is superheated during application of the voltage pulses.
21. The method according to claim 1 wherein the microfluidic device comprises a first port in flow communication with a first side of the channel and a second port in flow communication with a second side of the channel, the method further comprising closing the first port and the second port during the application of the voltage pulses such that a pressure within the channel increases while applying the voltage pulses.
22. The method according to claim 1 further comprising the step of regulating a pressure of the liquid within the channel while applying the voltage pulses.
23. The method according to claim 22 wherein the microfluidic device includes a passive pressure regulation device, and wherein regulating the pressure of the liquid includes passively regulating the pressure of the liquid.
24. The method according to claim 22 wherein the microfluidic device includes an expansion chamber equipped with a pressure relief valve in fluid communication with the channel, and wherein regulating the pressure of the liquid includes limiting a maximum pressure of the liquid while applying the voltage pulses.
25. The method according to claim 22 wherein regulating the pressure of the liquid includes maintaining the pressure within the channel while superheating the liquid.
26. The method according to claim 1 further comprising processing the liquid to reduce the ionic strength of the liquid prior to flowing the liquid into the channel.
27. The method according to claim 26 further comprising flowing the liquid through a mixed ion exchange resin prior flowing the liquid into the channel.