Polymerase chain reaction device including ejection nozzles

Examples include polymerase chain reaction (PCR) devices. Example PCR devices comprise a fluid input, ejection nozzles, and a set of microfluidic channels that fluidly connect the fluid input and the ejection nozzles. Each microfluidic channel comprises a reaction chamber, and examples further comprise at least one heating element, where the at least one heating element is positioned in the reaction chamber of each microfluidic channel. The at least one heating element is to heat fluid in the reaction chamber of each fluid channel. The device may eject fluid via the ejection nozzles.

BACKGROUND

Polymerase chain reaction (PCR) is a process by which a deoxyribonucleic acid (DNA) molecule may be amplified (replicated) into thousands, millions, or billions of copies of the molecule. In a PCR process, a sample DNA template, primer, polymerase, reaction buffer, and deoxynucleotide (dNTP) may be included in a PCR mixture. The PCR mixture may be cycled through various temperatures in a PCR process such that the included DNA template is amplified.

DESCRIPTION

Examples provided herein include devices, methods, and processes for polymerase chain reaction (PCR) processing. Some examples include polymerase chain reaction devices that comprise a fluid input, a set of ejection nozzles, a set of microfluidic channels, and at least one heating element. In such examples, the set of microfluidic channels fluidly connect the fluid input and the ejection nozzles. As will be appreciated, in some examples, the set of microfluidic channels may refer to a plurality of microfluidic channels that may be concurrently operated. Furthermore each microfluidic channel of the set comprises a reaction chamber. At least one heating element is positioned in each reaction chamber. The at least one heating element may heat fluid in the reaction chamber of each fluid channel. Furthermore, the at least one heating element may pump fluid to the reaction chamber and pump fluid from the reaction chamber of each microfluidic channel. In some examples, the at least one heating element may also cause fluid to eject via the ejection nozzles.

An ejection nozzle, as described herein, may comprise a fluid ejector positioned proximate an orifice of the nozzle. The fluid ejection may cause ejection of at least one drop of fluid from the orifice of the nozzle. In some examples, a fluid ejector may comprise a thermal ejector, where the thermal ejector may heat fluid proximate the thermal ejector to cause formation of a bubble in such fluid. Formation of the bubble in turn causes displacement of fluid proximate the orifice. Displacement of the fluid may cause ejection of some of the fluid in the form of at least one fluidic drop. Ejection of fluid by a thermal ejector may be referred to as thermal ejection and/or thermal jetting. In other examples, a fluid ejector may comprise a piezoelectric ejector, where the piezoelectric ejector may be physically deformed by actuation to cause a displacement of fluid proximate the orifice. Displacement of fluid proximate the orifice by the piezoelectric actuator may cause ejection of some of the fluid in the form of at least one fluidic drop. As will be appreciated, ejection nozzles implemented in some examples may be similar to ejection nozzles used in inkjet printing.

A polymerase chain reaction process facilitates amplification (i.e., replication) of a target DNA molecule by causing performance of a denaturing reaction, an annealing reaction, and an extension reaction in a PCR mixture that includes the target DNA molecule, where the reactions may be repeated. A denaturing reaction corresponds to separation of the double helix structure of the target DNA molecule to create single stands of the target DNA molecule. An annealing reaction facilitates binding of primers included in the PCR mixture with corresponding parts of the single strands of the target DNA molecule. An extension reaction includes binding of polymerase to the primer and synthesizes a new DNA strand that is complementary to the DNA template strand. Example devices described herein may be used to perform a PCR process by electrically actuating a heating element in a reaction chamber to cause at least one reaction of the PCR process.

In some examples described herein, a PCR mixture corresponding to a fluid may be pumped to a reaction chamber of each microfluidic channel with the at least one heating element. In some examples, a fluid may be a liquid. The PCR mixture in the reaction chamber may be heated for amplification of a DNA template included in the PCR mixture with the at least one heating element, and the PCR mixture may be pumped from the reaction chamber of each microfluidic channel with the at least one heating element. Therefore, as will be appreciated, examples described herein may comprise at least one heating element that may be used for heating of fluid and pumping of fluid to reaction chambers and from reaction chambers. In particular, in some examples, the at least one heating element may be heated to a fluid pumping temperature to thereby cause pumping of fluid to the reaction chamber and/or from the reaction chamber. To heat fluid for an operation associated with a polymerase chain reaction, the at least one heating element may be heated to a fluid reaction temperature. Furthermore, in some examples, the at least one heating element may be heated to a fluid ejection temperature to thereby cause at least one drop of fluid to eject from an ejection nozzle. In some examples, the fluid pumping temperature and the fluid ejection temperature of a heating element may be approximately equal.

For operations corresponding to a polymerase chain reaction process, example devices may heat fluid to various temperatures. For example, a heating element of a reaction chamber may be heated to a fluid reaction temperature to thereby heat a volume of PCR mixture in the reaction chamber to a temperature of approximately 94° C. to approximately 96° C. such that a denaturation reaction may occur in the PCR mixture in the reaction chamber. As another example, a heating element of a reaction chamber may be heated to a fluid reaction temperature to thereby heat a volume of PCR mixture in the reaction chamber to approximately 55° C. to approximately 60° C. such that an annealing reaction may occur in the PCR mixture in the reaction chamber. In another example, a heating element of a reaction chamber may be heated to a fluid reaction temperature to heat a volume of PCR mixture to a temperature of approximately 75° C. to approximately 80° C. such that and an extension reaction may occur in the PCR mixture in the reaction chamber. The term “approximately” when used with regard to a value may correspond to a range of ±10%.

Other examples may implement a two-step thermal cycling process. In such examples, a PCR mixture may be cycled between a first temperature of approximately 55° C. to approximately 60° C. and a second temperature of approximately 85° C. to approximately 90° C. In such examples, the extension and anneal operations may occur at the first temperature and the denaturation operation may occur at the second temperature. As will be appreciated, examples that implement the two-step thermal cycling process may perform replication/amplification in less time as compared to the three operation process described above.

To pump fluid to a reaction chamber and from a reaction chamber, an example heating element may be heated to a fluid pumping temperature, where a fluid pumping temperature may correspond to a temperature at which a bubble may form in fluid proximate the heating element. Formation and subsequent collapse of such bubble may generate circulation flow of the fluid. As will be appreciated, asymmetries of the expansion-collapse cycle for a bubble may generate such flow for fluid pumping, where such pumping may be referred to as “inertial pumping.” In some examples, a fluid pumping temperature may correspond to a temperature of the heating element that may cause fluid proximate the heating element to be heated to approximately 200° C. to approximately 300° C. In some examples in which a fluid may be an aqueous solution, the fluid pumping temperature may be approximately 280° C. to approximately 300° C. Heating a heating element of a reaction chamber may be performed by electrically actuating the heating element. For example, if the heating element is a resistive component, the heating element may be heated by electrical actuation of a particular current level. In examples described herein, a fluid pumping temperature is relatively greater than a fluid reaction temperature.

In some examples, a heating element may be a fluid ejector. In such examples, the heating element may be proximate an ejection nozzle. The heating element may be heated to a fluid ejection temperature. Heating of the heating element to a fluid ejection temperature may cause formation of a bubble in fluid proximate the heating element such that fluid may be displaced, which in turn may cause ejection of at least one drop of the fluid from the proximate nozzle. In some examples, a fluid ejection temperature may correspond to a temperature of the heating element that may cause fluid proximate the heating element to be heated to approximately 200° C. to approximately 300° C. In some examples in which a fluid may be an aqueous solution, the fluid ejection temperature for the heating element may be approximately 280° C. to approximately 300° C. As will be appreciated, the fluid ejection temperature may be similar to the fluid pumping temperature. In addition, for fluid ejection, a heating element may be heated to the fluid ejection temperature for a relatively short duration (i.e., on the microsecond scale) such that fluid thermally impacted by the heating element is proximate the heating element. In some examples, a heating element thermally impacts fluid within approximately 1 micrometer of the heating element.

Different levels of electrical actuation and a duration of such electrical actuation may correspond to pumping of fluid by a heating element or heating of a fluid for a PCR process by the heating element. In particular, in some examples, fluid may be pumped by a heating element positioned in a reaction chamber by rapidly heating the heating element to the fluid pumping temperature to cause formation and collapse of a bubble in fluid to be pumped. In such examples, the heating element may be electrically actuated with a first current level to cause pumping of fluid with the heating element, and the heating element may be electrically actuated with second current level to cause heating of fluid for a PCR process. In some example devices, the first current level is greater than the second current level. Similarly, a duration of the electrical actuation of the heating element with the first current level may be shorter as compared to electrical actuation of the heating element with the second current level for the PCR process.

For example, for pumping of fluid, the heating element may be electrically actuated at a first current level for an actuation duration of approximately 0.001 milliseconds (mS), where the electrical actuation may be repeated at a frequency in the kilohertz scale. For heating of fluid for the PCR process, the heating element may be electrically actuated at a second current level for an actuation duration of approximately 10-100 mS for a denaturation reaction, approximately 0.5 to approximately 10 seconds for an extension or anneal reaction. As discussed above, the fluid pumping temperature and the fluid ejection temperature may be similar. However, in such examples, the actuation duration may be different. In particular, when electrically actuating a heating element for fluid ejection, the duration of electrical actuation is greater than the duration of electrical actuation for fluid pumping. For fluid ejection, the heating element may be electrically actuated at a third current level for an actuation duration of approximately 0.001 to approximately 0.006 milliseconds, where the electrical actuation may be repeated at a frequency in the kilohertz scale.

Examples described herein include polymerase chain reaction devices that may be lab-on-a-chip implementations. In such examples, a polymerase chain reaction device may comprise a substrate into which microfluidic channels, reaction chambers, and/or ejection chambers may be formed. The substrate may comprise a silicon based wafer or other such similar materials used for microfabricated devices (e.g., glass, gallium arsenide, plastics, etc.). Furthermore, the at least one heating element may be a resistor component (which may be referred to as simply a “resistor”), such as a thin-film resistor. Accordingly, in some examples, the at least one heating element may be formed on the substrate, where at least a portion of the heating element is positioned in each reaction chamber of each microfluidic channel. As will be appreciated therefore, microfluidic channels and/or reaction chambers may be defined by surfaces fabricated in the substrate. Furthermore, ejection nozzles may be microfabricated devices that may be formed on the substrate or bonded to the substrate through various microfabrication processes.

Example PCR devices described herein may comprise a plurality of microfluidic channels in a respective set. Each microfluidic channel may include at least one reaction chamber. In some examples, each microfluidic channel may include more than one reaction chamber. Some example PCR devices may comprise reaction chambers that each have a reaction chamber volume such that the reaction chamber is sized to process a single DNA template molecule for a PCR process. For example, the reaction chambers of each microfluidic channel may have a reaction chamber volume within a range of approximately 1 picoliter (pL) to approximately 1 nanoliter (nL). In some examples, the reaction chamber volume may be such that a relatively low number of DNA template molecules (i.e., approximately 2 molecules to approximately 50 molecules) may be processed in each reaction chamber. In examples in which a single DNA template molecule may be processed and replicated with each reaction chamber, the polymerase chain reaction device may be implemented in a digital polymerase chain reaction (dPCR) process. Accordingly, such examples may be referred to as digital polymerase chain reaction devices. As will be appreciated, in an example dPCR device implemented in a dPCR process, some reaction volumes may process a single DNA template molecule, while some reaction volumes may not contain a DNA template molecule. In such examples, the absence of DNA template molecules in some reaction chambers (due in part to the volume of the reaction chambers) may facilitate quantification of the molecular sample in the PCR mixture for the PCR process.

Turning now to the figures, and particularly toFIG. 1, this figure provides a block diagram that illustrates some components of an example polymerase chain reaction device10. In this example, the device10comprises a fluid input12and a set of ejection nozzles14. In this example, the nozzles14are located adjacent to and form a surface of an ejection chamber15. The device10comprises a set of microfluidic channels16fluidly connecting the fluid input12and the ejection nozzles14. Each microfluidic channel16includes a reaction chamber18. In this example, a heating element20is positioned in each reaction chamber18. The heating element20is illustrated in dashed line for clarity and to illustrate that, in this example, the heating element20is an elongated component in which a respective portion of the heating element20is positioned in each reaction chamber18. In the example implementation illustrated inFIG. 1, it will be appreciated that using an elongated heating element20that is partially positioned in each reaction chamber18may simplify fabrication of the device10.

Furthermore, in this particular example, each microfluidic channel16comprises a first channel portion22athat fluidly connects the fluid inlet12and the reaction chamber18, and each microfluidic channel16comprises a second channel portion22bthat fluidly connects the reaction chamber18and a respective ejection nozzle14of the set. In this example, a length of the first channel portion22aof each microfluidic channel16is less than a length of the second channel portion22b. Accordingly, the reaction chambers18may be described as asymmetrically arranged relative to the fluid input12and the ejection nozzles14. In examples similar to the example device10ofFIG. 1, asymmetric arrangement of the reaction chambers relative to the fluid input and ejection nozzles may facilitate pumping of fluid to and from such reaction chambers. While in the example provided inFIG. 1, the example device10is illustrated with three microfluidic channels16, it will be appreciated that other examples may include more or less microfluidic channels16. Moreover, while in this example, the length of the first channel portion22ais illustrated as being relatively less than the length of the second channel portion22b, it will be appreciated that other examples may have different arrangements.

During performance of a PCR process, the example device10ofFIG. 1may pump a PCR mixture in the form of fluid from the first channel portion22aof each microfluidic channel to the reaction chamber18. To pump the PCR mixture to the reaction chamber18of each microfluidic channel16, the heating element20may be heated to a fluid pumping temperature. A volume of PCR mixture pumped to the reaction chamber18may be heated by the heating element20to a fluid reaction temperature to facilitate denaturing, annealing, and/or extension of a target DNA in the PCR mixture. After heating of the PCR mixture for a PCR related process, the PCR mixture may be pumped from the reaction chamber18to the second channel portion22bby heating the heating element20to the fluid pumping temperature. In addition, fluid may be pumped from the second channel portion22bto the ejection nozzles14, and fluid may be ejected from the ejection nozzles14. In examples similar to the example device10ofFIG. 1, pumping of fluid with a heating element20may be performed concurrently with ejection of fluid via nozzles14.

FIG. 2provides a block diagram that illustrates some components of an example PCR device50that comprises a fluid input52and a set of ejection nozzles54to eject fluid. The device50further comprises a set of microfluidic channels56that fluidly connect the fluid input52and the ejection nozzles54. Each microfluidic channel56includes a reaction chamber58. In this example, the device50comprises a respective heating element60for each reaction chamber58. Accordingly, as compared to the example device10ofFIG. 1, which implements an elongated heating element20that is partially positioned in each reaction chamber18, the example device50ofFIG. 2implements individual heating elements60. In this example, fluid may be pumped to and from each reaction chamber58concurrent with ejection of fluid via the nozzles54. In addition, the respective heating element60may heat fluid in the reaction chamber58. As will be appreciated, heating of fluid in the reaction chamber58may be performed for a PCR process. Furthermore, the respective heating element60may thermally eject fluid from a respective nozzle54.

In the example shown inFIG. 2, it will be appreciated that the nozzle54to which the microfluidic channel is fluidly connected is positioned adjacent the respective reaction chamber58of the microfluidic channel56. In particular, as the reaction chamber may be defined by surfaces formed in a substrate, a first surface of the respective reaction chamber58may correspond to the nozzle54. In such examples, the heating element60of a respective reaction chamber58may be on a second surface of the reaction chamber58. The first surface may be opposite the second surface. As will be appreciated in examples similar to the device50ofFIG. 2, the heating element60of a respective reaction chamber58may be used as a thermal ejector to cause ejection of fluid via the ejection nozzle54adjacent the respective reaction chamber58.

FIGS. 3A-Bprovide block diagrams of some components of an example polymerase chain reaction devices100,120. In particular, inFIG. 3A, a microfluidic channel102may fluidly connect a fluid input104and an ejection nozzle106. As shown, the ejection nozzle106has an orifice108through which fluid may be ejected. In the example shown inFIG. 3A, a heating element110is positioned proximate the nozzle106such that the heating element110may be used to thermally eject fluid out of the orifice108of the nozzle106. In this particular example, the nozzle106is positioned adjacent to a reaction chamber112of the microfluidic channel102—i.e., the ejection nozzle106defines a top surface of the reaction chamber112.

Accordingly, in this example, the heating element110may be heated to a fluid ejection temperature to eject fluid from the reaction chamber112and concurrently pump fluid into the reaction chamber112. The heating element110may be heated to fluid reaction temperatures to facilitate a denaturing reaction, an annealing reaction, and/or an extension reaction for a PCR mixture in the form of fluid in the reaction chamber112. After facilitating at least one reaction of a PCR process, the heating element may be heated to a fluid ejection temperature to cause ejection of some of the fluid in the form of a fluid drop via the orifice108of the ejection nozzle106.

Turning toFIG. 3B, in this example polymerase chain reaction device120, a microfluidic channel122fluidly connects a fluid input124and an ejection nozzle126. The ejection nozzle124has an orifice128through which drops of fluid may be ejected. As shown, the microfluidic channel includes a reaction chamber130and a heating element132positioned in the reaction chamber130. Furthermore, the device120includes a fluid ejector134positioned proximate the ejection nozzle126that may cause fluid displacement to thereby eject fluid through the orifice128of the ejection nozzle126. In some examples similar to the example ofFIG. 3B, the fluid ejector134may be a piezoelectric ejector, and, in other examples, the fluid ejector134may be a thermal ejector. Moreover, in some examples in which the fluid ejector134is a thermal ejector, the fluid ejector may be used as a heating element for pumping fluid as well as heating fluid for at least one operation of a PCR process.

FIG. 4provides a block diagram that illustrates some components of an example PCR device150. In this example, the device150comprises a first fluid input152a, a second fluid input152b, and ejection nozzles154. The device further comprises a set of microfluidic channels156that fluidly connect the fluid inputs152a,152band the ejection nozzles154. Each microfluidic channel156comprises a respective reaction chamber158. Furthermore, the device150comprises a heating element160that is positioned in the respective reaction chamber158of each microfluidic channel156. In this example, the nozzle154connected to each microfluidic channel156is positioned adjacent to the respective reaction chamber158. Therefore, in this example, the heating element160of each respective reaction chamber158may be used as a thermal ejector to cause fluid to eject via the connected ejection nozzle154. As will be appreciated, in examples similar to the example device150ofFIG. 4, the heating element160of each reaction chamber158may be used to pump fluid, heat fluid for operations associated with a PCR process, and thermally eject fluid via a proximate ejection nozzle154.

Moreover, because the example device150includes two fluid inputs152a,152b, different types of fluid may be input to the reaction chambers158. For example, fluid including PCR master mix and/or PCR primer may be provided via the first fluid input152aand a fluid including a PCR sample and/or PCR buffer may be provided via the second fluid input152b. In such examples, mixing of provided fluids may occur in the reaction chambers158. The mixed fluids may be heated to cause at least one reaction corresponding to a PCR process, and drops of the PCR process resultant fluid may be ejected via the ejection nozzles154. In such examples, the heating element160of each respective reaction chamber158may be thermally cycled via electrical actuation to facilitate mixing of the different types of fluid in the respective reaction chamber160.

InFIG. 5, some components of an example polymerase chain reaction device200are provided. The device200comprises a fluid input202and a set of ejection nozzles204. As shown, each of a first set of microfluidic channels206fluidly connects the fluid input202to a respective fluid ejection nozzle204of the set, and each of a second set of microfluidic channels208fluidly connects the fluid input202to a respective fluid ejection nozzle204. Each microfluidic channel206,208of the first set and the second set include a respective reaction chamber210. Furthermore, the device200comprises a first heating element212that is positioned in each respective reaction chamber210of the first set of microfluidic channels206, and the device comprises a second heating element214that is positioned in each respective reaction chamber210of the second set of microfluidic channels208. In this example, the first heating element212and the second heating element214are illustrated in dashed line for clarity. As shown, the first and second heating elements212,214are elongated heating elements. For the first heating element212, a respective portion is positioned in the reaction chamber210of each microfluidic channel of the first set206. Similarly, a respective portion of the second heating element214is positioned in the reaction chamber210of each microfluidic channel of the second set208. While in this example, an elongated heating element overlaps each reaction chamber of a set of microfluidic channels, it will be appreciated that in other examples more than one elongated heating element may implemented for a reaction chambers of a set of microfluidic channels.

In this example, the reaction chambers210of the first set of microfluidic channels206are located proximate the fluid input202, and the reaction chambers of the second set of microfluidic channels208are a greater distance from the fluid input202such that the reaction chambers210of the first set of microfluidic channels206and the reaction chambers210of the second set of microfluidic channels208are arranged in an interdigitated manner. The example interdigitated manner ofFIG. 5may be implemented to facilitate a compact layout for a polymerase chain reaction device and improved utilization of substrate area.

Turning toFIG. 6, this figure provides a block diagram that illustrates some components of an example polymerase chain reaction device250. In this example, the device250comprises a fluid input252and a set of ejection nozzles253. Each of a first set of microfluidic channels254fluidly connects the fluid input252and an ejection nozzle253of the set. Similarly, each of a second set of microfluidic channels256fluidly connects the fluid input252and an ejection nozzle253of the set. Furthermore, each microfluidic channel254,256is connected to a respective reaction chamber258, and the device250comprises a heating element260positioned in each respective reaction chamber258. In this example, each ejection nozzle253is positioned adjacent a reaction chamber258such that the ejection nozzle253defines a surface of the reaction chamber258. Furthermore, in this example, the fluid input252comprises a first side and a second side that is opposite the first side. The first set of microfluidic channels254, the corresponding reaction chambers258, and ejection nozzles253are positioned on a first side of the fluid input252. The second set of microfluidic channels256, corresponding reaction chambers258, and ejection nozzles253are positioned on the second side of the fluid input252. As will be appreciated, in this example, the microfluidic channels254of the first set and the microfluidic channels256of the second set may be offset from each other on the opposite sides of the fluid input252.

FIG. 7is a block diagram that illustrates some components of an example polymerase chain reaction device300. In this example, the device300comprises a first fluid input302aand a second fluid input302b. A set of microfluidic channels304fluidly connect the first fluid input302ato a set of ejection nozzles305, and the set of microfluidic channels304fluidly connect the second fluid input302bto the set of ejection nozzles305. In this example, each microfluidic channel304includes a first reaction chamber306, a second reaction chamber308, and a third reaction chamber310. In this example, the nozzle305connected to each microfluidic channel304is positioned adjacent the second reaction chamber308. Furthermore, the device300comprises a heating element312positioned in each reaction chamber306-310.

In this example, fluid may be pumped from the first fluid input302ato the first reaction chamber306of each microfluidic channel with the heating element312of the first reaction chamber306, the second reaction chamber308, and/or the third reaction chamber310. In addition, fluid may be pumped from the second fluid input302bto the third reaction chamber310of each microfluidic channel304with the heating element312of the first reaction chamber306, the second reaction chamber308, and/or the third reaction chamber310. In the first reaction chamber306and the third reaction chamber310fluid may be heated to facilitate reactions associated with a PCR process with the heating elements312thereof. For each microfluidic channel304, fluid may be pumped from the first reaction chamber306to the second reaction chamber308with the heating element312of the first reaction chamber306and/or second reaction chamber308. Similarly, for each microfluidic channel304, fluid may be pumped from the third reaction chamber310to the second reaction chamber308with the heating element312of the third reaction chamber310and/or second reaction chamber308. Fluid may be heated in the second reaction chamber308of each microfluidic channel304with the heating element312thereof to facilitate a reaction associated with a PCR process. Furthermore, drops of fluid may be ejected from the second reaction chambers308via the ejection nozzles305with the heating elements312thereof.

FIG. 8provides a block diagram that illustrates some components of an example polymerase chain reaction device350. In this example, the device350comprises a fluid input352and a set of microfluidic channels354fluidly connected to the fluid input352. Each microfluidic channel354is fluidly connected to a respective ejection nozzle356of a set. In this example, the ejection nozzle356is positioned adjacent an ejection chamber358. While not shown inFIG. 8, the device350may comprise a fluid ejection in the ejection chamber to cause ejection of fluid via the ejection nozzles356. In addition, each microfluidic channel354comprises a first reaction chamber360, a second reaction chamber362, and a third reaction chamber364. A heating element366is positioned in each reaction chamber360-364.

In the example provided inFIG. 8, a PCR mixture in the form of a fluid may be pumped from the fluid input352to the reaction chambers360and to the ejection chamber358with the heating elements366. At each reaction chamber, the PCR mixture may be heated with the heating element366thereof to facilitate at least one reaction for a PCR process (e.g., a denaturing reaction, an annealing reaction, and/or an extension reaction) in the PCR mixture. After pumping the PCR mixture to the ejection chamber358, the PCR mixture may be ejected as drops of fluid via the ejection nozzles356.

InFIG. 9, some components of an example polymerase chain reaction device400are illustrated in a block diagram. Similar to other examples described herein, the device400comprises a fluid input402and a set of ejection nozzles404. In this example, each ejection nozzle404is positioned adjacent an ejection chamber406. While not shown, the ejection chamber may comprise a fluid ejector positioned in the ejection chamber. The device400further comprises microfluidic channels407that fluidly connect the fluid input402and the ejection nozzles404. Furthermore, each microfluidic channel407comprises a first reaction chamber408, a second reaction chamber410, and a third reaction chamber412. The device further comprises a heating element414positioned in each reaction chamber408-412. As discussed previously, each heating element414is to pump fluid to/from the reaction chambers408-412, and each heating element414is further to heat fluid in the reaction chambers408-412. In this particular example, each ejection nozzle404is fluidly connected to two microfluidic channels407. As will be appreciated, other examples may have different arrangements of microfluidic channels, reaction chambers, and ejection nozzles.

FIG. 10is a block diagram that illustrates some components of an example polymerase chain reaction device450. As shown, the example device450comprises a fluid input452that is fluidly connected to a set of microfluidic channels454. The microfluidic channels454are fluidly connected to an ejection die456that includes a set of ejection nozzles458. The ejection die456is positioned adjacent an ejection chamber460such that fluid in the ejection chamber460may be ejected via the ejection nozzles458of the ejection die458. While not shown, the ejection die456may comprise fluid ejectors located proximate the ejection nozzles458, where a particular fluid ejector may cause displacement of fluid proximate an ejection nozzle458to thereby cause a drop of fluid to be ejected via the ejection nozzle458. In this example, the ejection die456may be a microfabricated ejection die456similar to an ejection die implemented in an inkjet printing device. Furthermore, as shown, the ejection nozzles458of the ejection die456are arranged in a staggered manner along a length of the ejection die456.

In addition, each microfluidic channel454of the device450comprises a first reaction chamber462, a second reaction chamber464, and a third reaction chamber466. The device further comprises a heating element468positioned in each respective reaction chamber462-466. As discussed, the heating elements468may pump fluid to/from the reaction chambers462-466, and the heating elements468may heat fluid in the reaction chambers462-466to facilitate at least one reaction of a PCR process.

FIG. 11is a block diagram that illustrates some components of an example polymerase chain reaction device500. In this example, the device500comprises a first fluid input502a(also labeled ‘FLUID INPUT1’) and a second fluid input502b(also labeled ‘FLUID INPUT2’). The device500includes a first set of microfluidic channels504and a second set of microfluidic channels506. As shown, the first set of microfluidic channels504are fluidly connected to the first fluid input502aand the second fluid input502b. The second set of microfluidic channels506are fluidly connected to the first fluid input502a. Each microfluidic channel504,506includes a reaction chamber508. For each reaction chamber508, the device500comprises ejection nozzles510positioned adjacent to the reaction chamber508. The ejection nozzles510are fluidly connected to the microfluidic channels504,506. While not shown inFIG. 11, the device500may comprise fluid ejectors proximate the nozzles510.

Furthermore, the device500comprises inertial pumps512positioned in each microfluidic channel504,506. Inertial pumps512may comprise fluid actuators that may generate compressive and tensile fluid displacements to thereby cause fluid flow (i.e., movement). As will be appreciated, an inertial pump may be connected to a controller, and electrical actuation of an inertial pump by the controller may thereby control pumping of fluid. Fluid actuators that may be implemented in inertial pumps described herein may include, for example, thermal resistor based actuators, piezo-membrane based actuators, electrostatic membrane actuators, mechanical/impact driven membrane actuators, magneto-strictive drive actuators, and/or other such micro-devices.

The device500comprises heating elements514positioned in each reaction chamber508. In some examples, the heating elements514may be used to heat fluid in the reaction chamber508for a PCR process. In addition, in this example, the device500comprises temperature sensors516positioned in each reaction chamber508.

Furthermore, the device500comprises a mixing actuator518positioned in each microfluidic channel504,506. A mixing actuator may be implemented to mix fluid in a respective microfluidic channel. As will be appreciated, examples described herein correspond to polymerase chain reaction devices. Accordingly, in some examples, a fluid processed with such example devices may correspond to a PCR mixture in the form of a liquid. In such examples, a mixing actuator may be included in a microfluidic channel to mix components included in a PCR mixture. In some examples, different types of fluid may be input into a common microfluidic channel via different fluid inputs (for example the first fluid input and the second fluid input of the device ofFIG. 11). In these examples, a mixing actuator may mix fluids input from different fluid inputs. A mixing actuator that may be implemented in examples described herein may include, for example, thermal resistor based actuators, piezo-membrane based actuators, electrostatic membrane actuators, mechanical/impact driven membrane actuators, magneto-strictive drive actuators, and/or other such micro-devices.

In the example device500ofFIG. 11, the reaction chambers508of the first set of microfluidic channels504are fluidly connected to both fluid inputs502a,502b, while the reaction chambers508of the second set of microfluidic channels506are fluidly connected to only the first fluid input502a. In examples similar to the example device500ofFIG. 11, the first fluid input502amay be used to input PCR mastermix and/or primers, and the second fluid input502bmay be used to input a PCR sample and/or PCR buffer. As will be appreciated, the fluid drops ejected from reaction chambers of the second set of microfluidic channels506may not include a DNA sample for analysis (because the DNA sample is input via the second fluid input502b). Accordingly, fluid drops ejected from the reaction chambers508of the second set of microfluidic channels506may be analyzed for baseline analysis, and drops of ejected from the reaction chambers508of the first set of microfluidic channels504may be analyzed to thereby analyze an input DNA sample.

As will be appreciated, the components of the example device500ofFIG. 11may be electrically connected to a controller. The controller may electrically actuate the heating elements514, inertial pumps512, mixing actuators518, and/or fluid ejectors associated with the ejection nozzles510. In addition, the controller may receive temperature data from the temperature sensors516. As will be appreciated, the controller may electrically actuate the components to thereby pump fluid to reaction chambers508, mix fluid, heat fluid to facilitate at least one reaction for a PCR process, and/or eject drops of fluid via the ejection nozzles510.

FIG. 12provides a block diagram that illustrates some components of an example polymerase chain reaction device550. Example polymerase chain reaction devices may be microfabricated devices, where some components and features of the device may be at least partially formed on a substrate by various microfabrication processes. The example device550ofFIG. 12comprises a substrate552upon which some components of the device are coupled and/or formed. As shown, the device550may comprise a controller554and a machine readable memory556coupled to the substrate552. The machine-readable memory556includes instructions558that may be executed by the controller554.

While the term “controller” may be used herein, it will be appreciated that a controller may comprise various types of data processing resources. A controller may include, for example, at least one hardware based processor. Similarly, a controller may comprise one or more general purpose data processors and/or one or more specialized data processors. For example, a controller may comprise a central processing unit (CPU), an application-specific integrated circuit (ASIC), and/or other such configurations of logical components for data processing. Execution of the instructions558may cause the controller554and/or device550to perform the functionalities, processes, and/or sequences of operations described herein. Furthermore, in the examples, the machine-readable memory556may comprise a machine-readable storage medium, which may be referred to as a memory and/or a memory resource. The machine-readable memory may represent random access memory (RAM) devices as well as other types of memory (e.g. cache memories, non-volatile memory devices, read-only memories, etc.). A machine-readable storage medium may include RAM, ROM, erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory, flash memory or other solid state memory technology, or any other medium that may be used to store executable instructions and information. Furthermore, the machine-readable memory556may be non-transitory.

The device550further comprises a fluid input560, a set of ejection nozzles562, and a set of microfluidic channels564at least partially formed in the substrate552. As shown, the microfluidic channels564may be positioned between the fluid input560and the ejection nozzles562, and the microfluidic channels564fluidly connect the fluid input560and the ejection nozzles562. Each microfluidic channel564comprises a first reaction chamber566and a second reaction chamber568. As shown, the second reaction chamber568of each microfluidic channel564is positioned proximate a respective ejection nozzle562, such that the respective ejection nozzle562defines a surface of the second reaction chamber568. Furthermore, the example device550comprises a heating element570positioned in each reaction chamber566,568. In addition, the example device550comprises a temperature sensor572positioned in each reaction chamber566,568. As shown, the controller554may be connected to the heating elements570and/or the temperature sensors572. In this example, the fluid input560, reaction chambers566,568, and/or microfluidic channels564may be features at least partially formed in the substrate552.

In this example, instructions558may be executable by the controller554, and execution of the instructions558by the controller554may cause the controller554to electrically actuate the heating elements570. In such examples, the controller554may receive temperature data from the temperature sensors572which may facilitate feedback for electrical actuation of the heating elements570. In particular, execution of some instructions558may cause the controller to electrically actuate the heating elements570to thereby cause the heating elements570to pump fluid to/from the respective reaction chambers566,568. In addition, execution of some instructions558may cause the heating elements570to heat fluid in the respective reaction chambers568,568for an operation associated with a PCR process. For example, if the heating elements570are resistive components, the controller554may electrically actuate the heating elements570with a first current level such that the heating elements570are heated to a fluid pumping temperature. Similarly, the controller554may electrically actuate the heating elements570with a second current level such that the heating elements570are heated to a fluid reaction temperature. In addition, the controller554may electrically actuate the heating elements570corresponding to the second reaction chambers568with a third current level such that the heating elements570are heated to a fluid ejection temperature.

In addition, the example device550comprises a detector574that is electrically connected to the controller554. In such examples, the detector574may be a sensor for analyzing DNA samples and performing DNA testing. For example, the detector574may comprise an optical sensor system (that may include an optical sensor for use with an integrated or external light source). As another example, the detector574may comprise an electrical impedance sensor. As will be appreciated, examples incorporating a detector on a common substrate (also referred to as “on-chip”) may be referred to as a lab-on-a-chip device. Some examples described herein may facilitate replication of a DNA sample by performance of a PCR process according to examples described herein, and the example may analyze the DNA sample after replication with an on-chip detector.

FIGS. 13-15provide flowcharts that provide example sequences of operations that may be performed by an example polymerase chain reaction device to perform example processes and methods as described herein. In some examples, some operations included in the flowcharts may be embodied in a memory (such as the machine-readable memory556ofFIG. 12) in the form of instructions that may be executable by a controller to cause a device to perform the operations corresponding to the instructions. Additionally, the examples provided inFIGS. 13-15may be embodied in processes and/or methods. In some examples, the example processes and/or methods disclosed in the flowcharts ofFIGS. 13-15may be performed by a controller implemented in a device, such as the example controller ofFIG. 12.

Turning now toFIG. 13, this figure provides a flowchart600that illustrates an example sequence of operations that may be performed by an example PCR device. The example PCR device may comprise a fluid input, ejection nozzles, and a set of microfluidic channels that fluidly connect the fluid input and the ejection nozzles. In addition, each microfluidic channel may comprise a reaction chamber, and the example device may comprise at least one heating element positioned in the reaction chambers. In this example, a PCR device may pump fluid to each reaction chamber of each microfluidic channel with the at least one heating element (block602). The example device may heat fluid in each reaction chamber with the at least one heating element (block604), and the device may eject fluid from the ejection nozzles (block606).

FIG. 14provides a flowchart650that illustrates an example sequence of operations that may be performed by an example PCR device. In this example, the PCR device may comprise microfluidic channels, where each microfluidic channel comprises a reaction chamber. Furthermore, the device comprises at least one heating element that is positioned in each reaction chamber. The example device may heat the at least one heating element to a fluid pumping temperature to thereby pump fluid to the reaction chamber (block652). The heating element may be heated to a fluid reaction temperature to thereby heat fluid in the reaction chamber of each microfluidic channel (block654). The heating element may then be heated to a fluid ejection temperature to thereby ejection fluid from nozzles fluidly connected to the reaction chamber (block656).

FIG. 15provides a flowchart700that illustrates an example sequence of operations that may be performed by an example PCR device. In this example, the device may comprise a set of microfluidic channels, where each microfluidic channel comprises a reaction chamber. Furthermore, the device comprises at least one heating element positioned in each reaction chamber, and the device comprises a controller connected to the at least one heating element. The device may electrically actuate the at least one heating element with a first current level for a first actuation duration to pump fluid to each reaction chamber (block702). As discussed previously, to pump fluid, a heating element may be rapidly heated to a fluid pumping temperature for a short duration to thereby cause bubble formation and collapse in fluid that causes flow in the fluid. Accordingly, the first current level corresponds to the fluid pumping temperature and the first actuation duration corresponds to the length of time (and frequency) that the first current level is applied to the at least one heating element to cause pumping of fluid.

Furthermore, the device may electrically actuate the at least one heating element with a second current level for a second actuation duration to heat fluid in the reaction chambers (block704). As discussed, to heat fluid for a PCR process, a heating element may be heated to a fluid reaction temperature. In such examples, the second current level corresponds to the fluid reaction temperature and the second actuation duration corresponds to the length of time that the second current level is applied to the at least one heating element to heat fluid for a PCR process. In some examples, the first current level is greater than the second current level, and the first actuation duration is less than the second actuation duration. In some examples, the device may electrically actuate the at least one heating element with a third current level for a third actuation duration to eject drops of fluid from nozzles fluidly connected to the reaction chambers (block706). In some examples, the first current level and the third current level are approximate each other, as both current levels cause vapor bubble creation in a fluid. In some examples, the duration of actuation as well as the frequency of repetition may be the same for the first current level and the third current level. In other examples, the duration of actuation and/or the frequency of repetition may be different for the first current level and the third current level. Actuation of heating elements for fluid pumping and/or fluid ejection may, in some examples, be characterized as short duration, high-frequency, high-current electrical pulses.

Turning now toFIG. 16, this figure provides a flowchart750that illustrates an example sequence of operations that may be performed by an example polymerase chain reaction device. The example device may heat fluid (such as a PCR mixture) in a reaction chamber with a heating element at least partially positioned in the reaction chamber (block752). As discussed previously, in some examples, fluid pumping may be performed by a fluid ejector and/or a heating element. In particular, in some examples, ejection of fluid via a nozzle by a fluid ejector may cause flow in fluidly connected reaction chambers and microfluidic channels. Fluid flow caused by fluid ejection may be referred to as “pull pumping” or “ejection pumping,” where ejection of droplets of fluid via the fluid ejectors causes flow of fluid due to capillary forces. Accordingly, in this example, with a fluid ejector, fluid may be concurrently ejected via a nozzle and fluid may be pumped to a reaction chamber and/or ejection chamber (block754). In some examples, the fluid ejector may perform fluid pumping due to fluid ejection. In some examples, the heating element may be heated to a fluid pumping temperature to thereby pump fluid, where such operation of the heating element may be approximately concurrent with operation of the fluid ejector to eject fluid.

FIGS. 17A-Fprovide block diagrams that illustrate operation of some components of an example polymerase chain reaction device800. The example provided inFIGS. 17A-Fillustrates pumping and heating of a volume of fluid in a microfluidic channel802that comprises a reaction chamber804. The device800further includes an ejection nozzle806having an orifice808through which drops of fluid may be ejected. In addition, the device810comprises a heating element810positioned in the reaction chamber804, and the device800includes a fluid ejector812positioned proximate the ejection nozzle806. InFIGS. 17A-F, fluid may be pumped and heated by a heating element810positioned in the reaction chamber804. Furthermore, fluid may be pumped and ejected by the fluid ejector812. In these examples, it will be appreciated that pumping of fluid may be performed approximately concurrent with ejection of fluid. As used in this manner, approximately concurrent indicates that the operations may be performed at the same time, in an at least partially overlapping manner, approximately synchronous, and/or in an interleaved manner.

InFIG. 17A, a volume of fluid814may be pumped from a first channel portion of the microfluidic channel802to the reaction chamber804by operation of the heating element810and/or fluid ejector812as described herein. InFIG. 17B, the volume of fluid814may be heated in the reaction chamber804by the heating element810for an operation of the PCR process. InFIG. 17C, the volume of fluid814may be pumped from the reaction chamber804to a second channel portion of the microfluidic channel552by the heating element810and/or fluid ejector812as described herein. InFIG. 17D, the volume of fluid814has been pumped to the second channel portion, and another volume of fluid816may be in the first channel portion for pumping into the reaction chamber804. InFIG. 17E, the volume of fluid814may be pumped to the ejection nozzle806, and the another volume of fluid816may be pumped to the reaction chamber804. InFIG. 17E, pumping of fluid may be performed by the heating element810and/or fluid ejector812. InFIG. 17F, the another volume of fluid816may be heated for a PCR process related reaction in the reaction chamber804. While not shown, when pumping the another volume of fluid816from the reaction chamber804, the volume of fluid814may be ejected via the nozzle806.

As will be appreciated, the operations described above with respect to the flowcharts and example PCR devices may be performed during performance of a PCR process. As such, the fluid may correspond to a PCR mixture, and heating of fluid may correspond to denaturing, annealing, and/or extension operations associated with a PCR process. Furthermore, PCR devices as described herein may be implemented in analysis systems. For example, fluid outputs of the various examples described herein may be further connected to analysis and/or detection components.

Accordingly, the examples described herein provide examples of a polymerase chain reaction device in which at least one heating element may be implemented and used to perform at least two operations. In particular, the at least one heating element may be used to pump fluid in example devices, and the at least one heating element may be used to heat fluid for operations associated with a polymerase chain reaction. In some examples, the at least one heating element may further be used to eject fluid from ejection nozzles. Implementation of such multi-use heating elements in PCR devices may facilitate reduction of components as compared to other types of PCR devices. Moreover, utilization of a heating element for pumping of fluid and heating thereof may facilitate reduction of device size and simplification of electrical connection layouts in such devices. Furthermore, implementation of ejection nozzles in PCR devices may facilitate analysis of drops of ejected fluid as well as controlled ejection of such drops of fluid. Manipulation of small volumes of PCR mixture as well as controlled ejection of drops of such PCR mixture may facilitate drop-on-demand analysis of DNA samples. In addition, example devices as described herein may facilitate manipulation of small volumes of fluid (e.g., approximately 1 nL to approximately 1 pL). Because examples described herein facilitate pumping and heating of such small volumes of fluid (such as small volumes of PCR mixtures), examples described herein may facilitate digital polymerase chain reaction processing of fluid samples.