FIELD OF THE INVENTION

The present disclosure generally relates to a digital microfluidic system and methods for making and using the same, and in particular, to a digital microfluidic system and methods useful for, e.g., quick polymerase chain reaction.

BACKGROUND OF THE INVENTION

Polymerase chain reaction (PCR) is the kernel of modern molecular biology and diagnostics. This temperature-dependent technique amplifies DNA in an exponential way by cycles of heating and cooling. A typical PCR often takes 1-2 hours in a bulky thermal cycler. In clinical point-of-care diagnostics, especially for infectious diseases, both reaction time and specificity of the reaction are vital to clinical decisions. Many quick PCR methods have been developed, exploiting the miniaturization feature of microfluidics or capillary reactors. However, these methods still require large accessories to support the thermal cycling process. Other fast PCR setups using laser or plasmonic techniques are costly because they need expensive light instrument for the light source.

Digital microfluidics (DMF) is an emerging technology to manipulate individual microliter-sized to nanoliter-sized droplets on an array of electrodes by electro-wetting force. Its features of electric driving and miniature footprint render it a promising technology for point-of-care diagnostics.

However, the existing DMF systems for PCR take longer than 10 min.

Therefore, there is a need for developing a cost effective and robust DMF system for conducting quick PCR in less than 10 min.

SUMMARY OF THE INVENTION

Provided herein is a digital microfluidic device that enables, e.g. quick PCR. Other applications that require heating and cooling cycles are also within the contemplation of the present disclosure.

The digital microfluidic device of the present disclosure is capable of conducting quick PCR and the PCR thereof can successfully amplify detectable DNA products as early as 60 cycles (342 s), less than 6 minutes. Moreover, the configuration of the digital microfluidic device of the present disclosure ensures a robust system for thermal cycles, without the breakdown of any of the materials used for the device, such as dielectric layers, during the process of repeatedly heating and cooling.

In certain embodiments, the present disclosure relates to a digital microfluidic device100for conducting quick polymerase chain reaction in at least one droplet600generated from a loading fluid, the device100comprising an upper layer200, a lower layer300, a lateral wall400positioned between the upper layer200and the lower layer300to form a chamber, an inlet for receiving the loading fluid and providing the loading fluid to the chamber, and an outlet for releasing trapped air and extra loading fluid during a loading process, wherein: the lower layer300comprises: a first substrate303; an array of electrodes comprising at least one thermal electrode307formed on an inner side of the first substrate303, an individual thermal electrode comprising a heater electrode305and a sensor electrode306; at least one first coating302covering each electrode of the array of electrodes such that all electrodes of the array of electrodes are electrically insulated from one another; and a first hydrophobic layer301formed on the at least one first coating302to provide a first hydrophobic working surface301-1.

In certain embodiments, the upper layer200comprises: a second substrate202, at least one top heater204formed by at least one second coating201covering an outer side of the second substrate202, and a second hydrophobic layer203being formed on an inner side of the second substrate202to provide a second hydrophobic working surface203-1.

In certain embodiments, the at least one second coating201is an indium tin oxide coating.

In certain embodiments, the at least one first coating302is an ultraviolet curable resin.

In certain embodiments, the at least one first coating302is a dielectric layer.

In certain embodiments, an individual thermal electrode307is positioned right below a corresponding top heater204to create a space in the chamber with the space between the individual thermal electrode307and the corresponding top heater204capable of contacting a corresponding droplet600located between the second hydrophobic working surface203-1and the first hydrophobic working surface301-1such that the corresponding droplet receives heat from both the upper and lower layers.

In certain embodiments, the heater electrode305is serpentine-shaped having an inner ring (308) and an outer ring309.

In certain embodiments, the inner ring308is wider than the outer ring309.

In certain embodiments, the inner ring308has a width of about 300 μm to about 400 μm, and the outer ring309has a width of about 200 μm to about 300 μm.

In certain embodiments, the inner ring308has a width of about 349 μm, and the outer ring309has a width of about 279 μm.

In certain embodiments, the at least one sensor electrode306is fork-shaped being positioned between the inner ring308and the outer ring309.

In certain embodiments, the at least one heater electrode305and the at least one sensor electrode306have a distance of larger than about 100 μm.

In certain embodiments, the at least one heater electrode305and the at least one top heater204can be connected to an adjustable direct current (DC) power supply to form a first mode for providing heat to the at least one droplet600.

In certain embodiments, the at least one heater electrode305can be connected to an alternating current (AC) power supply to form a second mode for transporting the at least one droplet600from the inlet to the at least one thermal electrode307.

In certain embodiments, the at least one sensor electrode306can be connected to a direct current (DC) power supply and a voltage indicator or voltage meter to form a third mode for recording temperature of the at least one droplet600.

In certain embodiments, the present disclosure also relates to a method for conducting quick polymerase chain reaction, comprising steps of: a) providing a digital microfluidic device100; b) transporting at least one droplet600generated from a loading fluid to the at least one thermal electrode307of the digital microfluidic device100; c) repeatedly heating the at least one droplet600for a first length of time and cooling the at least one droplet600for a second length of time followed by heating the at least one droplet600for a third length of time and cooling the at least one droplet600for a fourth length of time; and d) imaging the at least one droplet600.

In certain embodiments, the method further comprises between the step a) and the step b) a step e): calibrating the at least one sensor electrode306to obtain a linear relationship between temperature sensed by the at least one sensor electrode306and voltage measured by a voltage indicator connected to the at least one sensor electrode306.

In certain embodiments, the loading fluid comprises at least one primer, at least one DNA indicator, and at least one target DNA sequence.

In certain embodiments, the first length of time is time for increasing temperature from about 50° C. to about 95° C., and the second length of time is time for reducing temperature from about 95° C. to about 50° C.

In certain embodiments, the third length of time is obtained by reducing the first length time by 0.1-0.5 seconds, and the fourth length of time is obtained by increasing the second length of time by 0.1-0.5 seconds.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described.

The invention includes all such variation and modifications. The invention also includes all of the steps and features referred to or indicated in the specification, individually or collectively, and any and all combinations or any two or more of the steps or features.

Other aspects and advantages of the invention will be apparent to those skilled in the art from a review of the ensuing description.

