Patent Description:
Point-of-care ("POC") in vitro diagnostics tests ("IVDT") have traditionally had two major categories, nucleic acid amplification tests ("NAAT") or immunoassay-based tests. The former directly detects a pathogen's DNA or RNA, while the latter detects antibodies or antigens generated by a patient's (human or animal) immune system response to the pathogen.

Current POC diagnostic immunoassays lack the high sensitivity and specificity of nucleic acid amplification methods. This becomes more pronounced during the initial stages of infection, often within <NUM> hours. Taking the case of Dengue virus in whole blood, immunoglobulin M ("IgM") and immunoglobulin G ("IgG") remain undetectable in the majority of patients until <NUM> and <NUM> days post-infection, respectively, whereas nucleic acid can be found as early as <NUM> to <NUM> days. Moreover, many immunoassay tests are unable to detect infectious agents until <NUM> months after the initial onset of the infection. This delay is due to the time it takes for the body's immune system to respond to an infection.

POC diagnostic assays developed utilizing NAATs have very high sensitivities and specificities, matching those of currently accepted laboratory tests. The primary mechanism of NAAT based systems is to directly detect an infectious agent's nucleic acid, lending to the test's ability to detect diseases within the first few days of the onset of infection. In addition, by careful primer design, NAATs also have the ability to have very high specificity and sensitivity compared to immunoassay based testing. The largest drawback of NAATs compared to immunoassay-based tests is the complicated equipment and/or processes required to prepare a sample for testing.

Some known POC immunoassay testing systems analyze a patient sample during early stages of infection by causing a polymerase chain reaction ("PCR") within a test card. To cause the PCR, the patient sample has to be mixed with one or more reagents, such as a primer (e.g., oligonucleotides), a DNA polymerase, and/or a modified DNA polymerase. In addition, to cause the PCR, the reagent-patient sample mixture has to be heated on the test card. One issue that exists with test card screen-printed heaters is thermal uniformity, where a large temperature gradient results from a non-uniform current density. For example, a temperature gradient can be as large as <NUM> degrees over a <NUM> square area, which may cause major issues for PCR's, which require precise temperature control. <CIT> discloses a test card for analysing a fluid sample, comprising a channel layer bonded to a first substrate layer, the channel layer including a microchannel, a second substrate layer bonded to the channel layer, the second substrate layer having electrodes printed adjacent to a target zone of the microchannel of the channel layer and wherein the electrodes are configured to raise the temperature of the fluid sample within the target zone of the microchannel when a current is applied thereto. <CIT> discloses a polymerase chain reaction microfluidic device wherein the temperature at the reaction site is kept uniform by adjusting the areas of the heating bars. <CIT> discloses an electrophoretic chip comprising printed electrodes on a non-conductive substrate.

Described herein is a screen-printed heater that is capable of uniformly raising a temperature of a fluid sample within a microchannel to cause a PCR. In a general example embodiment, which may be used in combination with any other embodiment disclosed herein, a test card for analyzing a fluid sample includes at least one substrate layer including a microchannel extending through at least a portion of one of the substrate layers, and a printed substrate layer that is bonded to or printed on one substrate layer of the at least one substrate layer. The printed substrate layer includes a heater printed on the printed substrate layer so as to align with at least a portion of the microchannel. The heater includes two electrodes aligned on opposite sides of the microchannel, and a plurality of heater bars electrically connecting the two electrodes. The plurality of heater bars includes a central heater bar disposed between outer heater bars. The central heater bar is thinner than the outer heater bars in a direction approximately parallel to the microchannel.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the at least one substrate layer includes a plurality of bonded layers.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the electrodes are printed onto the printed substrate layer with a silver ink.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the plurality of heater bars is printed onto the printed substrate layer with a carbon ink.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the plurality of heater bars includes the central heater bar, a pair of first outer heater bars, and a pair of second outer heater bars, the central heater bar is disposed between the first outer heater bars, the first outer heater bars are disposed between the second outer heater bars, the central heater bar is thinner than the first outer heater bars in the direction approximately parallel to the microchannel, and the first outer heater bars are thinner than the second outer heater bars in the direction approximately parallel to the microchannel.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the central heater bar is thinner than the outer heater bars at a central point between the two electrodes.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the central heater bar is thinner than the outer heater bars at respective points of contact with at least one of the two electrodes.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the central heater bar is thinner than the outer heater bars at respective portions aligned with the microchannel.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the plurality of heater bars each includes a central diamond shape and two protruding ends, and the protruding ends overlap with the two electrodes to place the two electrodes in electrical communication with each other.

In a general embodiment, which may be used in combination with any other embodiment disclosed herein, a test card for analyzing a fluid sample includes at least one substrate layer including a microchannel extending through at least a portion of one of the substrate layers, and a printed substrate layer that is bonded to or printed on one substrate layer of the at least one substrate layer. The printed substrate layer includes a heater printed on the printed substrate layer so as to align with at least a portion of the microchannel. The heater includes two electrodes aligned on opposite sides of the microchannel, and a plurality of heater bars electrically connecting the two electrodes. The plurality of heater bars include a central heater bar disposed between outer heater bars, where the central heater bar has a higher resistance than the outer heater bars.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the at least one substrate layers includes a plurality of bonded layers.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the plurality of heater bars includes the central heater bar, a pair of first outer heater bars, and a pair of second outer heater bars, the central heater bar is disposed between the first outer heater bars, the first outer heater bars are disposed between the second outer heater bars, the central heater bar is thinner than the first outer heater bars in a direction approximately parallel to the microchannel, and the first outer heater bars are thinner than the second outer heater bars in the direction approximately parallel to the microchannel.

In another general embodiment, which may be used in combination with any other embodiment disclosed herein, a heater for a substrate includes two electrodes spaced apart from each other in a first direction, and a plurality of heater bars connecting the two electrodes, the plurality of heater bars including a central heater bar disposed between outer heater bars, the central heater bar being thinner than the outer heater bars in a second direction approximately perpendicular to the first direction.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the outer heater bars are progressively thicker in the second direction as the distance from the central heater bar increases in the second direction.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the plurality of heater bars are each shaped to be thickest at a central point between the two electrodes in the first direction.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the electrodes are printed onto the substrate with a silver ink.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the plurality of heater bars is printed onto the substrate with a carbon ink.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the plurality of heater bars includes the central heater bar, a pair of first outer heater bars, and a pair of second outer heater bars, the central heater bar is disposed between the pair of first outer heater bars, the first outer heater bars are disposed between the second outer heater bars, the central heater bar is thinner than the first outer heater bars in the second direction, and the first outer heater bars are thinner than the second outer heater bars in the first direction.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the heater is printed onto the substrate with conductive ink.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, a heater for a substrate includes two electrodes spaced apart from each other in a first direction, and a plurality of heater bars connecting the two electrodes, the plurality of heater bars including a central heater bar disposed between outer heater bars, the central heater bar having a higher resistance than the outer heater bars.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the outer heater bars have progressively less resistance as the distance from the central heater bar increases in a second direction approximately perpendicular to the first direction.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the plurality of heater bars are each shaped to be thickest at a central point between the two electrodes.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the plurality of heater bars includes the central heater bar, a pair of first outer heater bars, and a pair of second outer heater bars, the central heater bar is disposed between the first outer heater bars, the first outer heater bars are disposed between the second outer heater bars, the central heater bar is thinner than the first outer heater bars in a second direction approximately perpendicular to the first direction, and the first outer heater bars are thinner than the second outer heater bars in the second direction.

In another general embodiment, which may be used in combination with any other embodiment disclosed herein, a method of providing a heater on a substrate includes printing two electrodes spaced apart from each other in a first direction, and printing a plurality of heater bars connecting the two electrodes, the plurality of heater bars including a central heater bar disposed between outer heater bars, the central heater bar being thinner than the outer heater bars in a second direction approximately perpendicular to the first direction.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the outer heater bars to be progressively thicker as the distance from the central heater bar increases in the second direction.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the plurality of heater bars to each be shaped to be thickest in the first direction at a central point between the two electrodes.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the electrodes onto the substrate with a silver ink.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the plurality of heater bars onto the substrate with a carbon ink.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the plurality of heater bars so as to include the central heater bar, a pair of first outer heater bars, and a pair of second outer heater bars, the central heater bar is disposed between the first outer heater bars, the first outer heater bars are disposed between the second outer heater bars, the central heater bar is thinner than the first outer heater bars in the second direction, and the first outer heater bars are thinner than the second outer heater bars in the second direction.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the central heater bar to be thinner than the outer heater bars at a central point between the two electrodes.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the central heater bar to be thinner than the outer heater bars at respective points of contact with at least one of the two electrodes.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the two electrodes and/or the plurality of heater bars onto the substrate with conductive ink.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the two electrodes so as to be aligned on opposite sides of a microchannel extending through at least a portion of the substrate.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the plurality of heater bars so as to overlap a microchannel extending through at least a portion of the substrate.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the plurality of heater bars so as to overlap the microchannel in a direction approximately perpendicular to the direction of the microchannel.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the plurality of heater bars before printing the two electrodes.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the two electrodes to at least partially overlap the plurality of heater bars.

In another general embodiment, which may be used in combination with any other embodiment disclosed herein, a method of providing a heater on a substrate includes printing two electrodes spaced apart from each other in a first direction, and printing a plurality of heater bars connecting the two electrodes, the plurality of heater bars including a central heater bar disposed between outer heater bars, the central heater bar having a higher resistance than the outer heater bars.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the outer heater bars to have progressively less resistance as the distance from the central heater bar increases in a second direction substantially perpendicular to the first direction.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the plurality of heater bars to each be shaped to be thickest at a central point between the two electrodes.

In another embodiment, which may be used in combination with any other embodiment disclosed herein, the method includes printing the plurality of heater bars so as to include the central heater bar, a pair of first outer heater bars, and a pair of second outer heater bars, the central heater bar is disposed between the first outer heater bars, the first outer heater bars are disposed between the second outer heater bars, the central heater bar is thinner than the first outer heater bars in a second direction substantially perpendicular to the first direction, and the first outer heater bars are thinner than the second outer heater bars in the second direction.

Embodiments of the present disclosure will now be explained in further detail by way of example only with reference to the accompanying figures, in which:.

Before describing in detail the illustrative system and method of the present disclosure, it should be understood and appreciated herein that the present disclosure relates to a test card for use with a rapid, high sensitivity and high specificity, low complexity diagnostic system using nucleic acid amplification and capable of operating in low resource settings with minimal user training. The system is configured, for example, to cause and analyze a polymerase chain reaction ("PCR") within the test card, particularly in the early stages of infection, using a low-cost microfluidic platform employing PCR with a modified DNA polymerase. In an embodiment, the test card is configured to receive about <NUM>µL of whole blood, the equivalent to a drop of blood obtained from a finger stick. In another embodiment, the fluid sample can be serum, urine, saliva, tears and/or the like.

<FIG> illustrate an example embodiment of a test card <NUM> according to the present disclosure. As illustrated, test card <NUM> includes an inlet port <NUM>/mixing chamber <NUM>, a capture port <NUM>, an outlet port <NUM>, and a fluid microchannel <NUM>. In use, a fluid sample can be placed into inlet port <NUM>, mixed with one or more reagent in mixing chamber <NUM>, and then pulled though fluid microchannel <NUM>, so that the fluid sample can be analyzed through an analysis port <NUM> while residing within fluid microchannel <NUM> as a PCR occurs, in part, due to heat applied from a heater <NUM>, according to the present disclosure.

In an embodiment, a vacuum source can be applied to the outlet port <NUM>. When a negative pressure is applied to the outlet port <NUM>, the vacuum pressure pulls the fluid sample from the mixing chamber <NUM> through fluid microchannel <NUM> so that the fluid sample can be analyzed through analysis port <NUM> while residing within a target zone of the microchannel <NUM>. The capture port <NUM> is configured to capture fluid from the fluid sample before the fluid flows to the outlet port <NUM>. In the illustrated embodiment, the capture port <NUM> is sized to allow fluid to build up before it can reach the outlet port <NUM> to prevent the fluid from being sucked out of the outlet port <NUM> by the vacuum pressure applied to the outlet port <NUM>. In an embodiment, the capture port <NUM> can include a porous material, which can act like a sponge to absorb any excess fluid and prevent fluid from escaping from test card <NUM> due to mishandling.

As illustrated in <FIG> and <FIG>, the test card <NUM> may include one or more substrate layers including a bottom substrate layer <NUM>, a channel layer <NUM>, a middle substrate layer <NUM>, an adhesive layer <NUM>, a top substrate layer <NUM>, and a printed circuit layer <NUM>. In an embodiment, the bottom substrate layer <NUM>, the channel layer <NUM>, the middle substrate layer <NUM>, the adhesive layer <NUM>, and the top substrate layer <NUM> may be bonded together to form inlet the port <NUM>/mixing chamber <NUM>, the capture port <NUM>, the outlet port <NUM>, and the fluid microchannel <NUM>. The printed substrate layer <NUM> may include ink that is printed on a bottom surface of bottom substrate layer <NUM>. Example dimensions of the layers of the test card <NUM>, as well as methods of forming and bonding the layers, are described in more detail in <CIT>.

<FIG> and <FIG> illustrate a top view of a printing arrangement of the printed substrate layer <NUM>, while <FIG> illustrates a bottom view of the same printing arrangement of the printed substrate layer <NUM>. In <FIG>, only conductive ink <NUM> is shown, and dielectric ink <NUM> has been omitted for simplicity. <FIG> shows the top view of <FIG> with dielectric ink <NUM> underneath conductive ink <NUM>. <FIG> illustrates a bottom view of a printing arrangement of the printed substrate layer <NUM>, with dielectric ink <NUM> printed over conductive ink <NUM>.

In the illustrated embodiment, the printed substrate layer <NUM> is printed onto the bottom surface of bottom substrate layer <NUM>, before or after the bottom substrate layer <NUM> is bonded to one or more of channel layer <NUM>, middle substrate layer <NUM>, adhesive layer <NUM>, and top substrate layer <NUM>. As illustrated, the printed substrate layer <NUM> may be printed with a conductive ink <NUM> and a dielectric ink <NUM>. The conductive ink <NUM> forms the electrical components of test card <NUM>, whereas the dielectric ink <NUM> serve as protective, non-conductive coating to encapsulate the electrical components. The conductive ink <NUM> may become the electrical components once it is cured, for example, by heat or ultraviolet light. In an embodiment, one or more layers of conductive ink <NUM> is printed and then cured, and then one or more layers of dielectric ink <NUM> is printed and cured. In another embodiment, both the conductive ink <NUM> and the dielectric ink <NUM> are printed, and then both the conductive ink <NUM> and the dielectric ink <NUM> are cured. In another embodiment, several alternating layers of conductive ink <NUM> and dielectric ink <NUM> are printed to create multiple levels of conductive elements.

In an embodiment, the printed circuit layer <NUM> is screen printed on the bottom surface of bottom substrate layer <NUM> through a screen made of a stainless steel or a polymer mesh. A hardened emulsion can be used to block out all areas of the screen except for the desired print pattern for the conductive ink <NUM> and/or dielectric ink <NUM>, so that the conductive ink <NUM> and/or dielectric ink <NUM> is pushed through the screen in the desired print pattern.

In the illustrated embodiment, the conductive ink <NUM> is printed to form a heater <NUM>, as well as electrodes <NUM>, <NUM> upstream and downstream of the heater <NUM> along microchannel <NUM>. The conductive ink <NUM> may also form electrodes <NUM>, which receive current from an analyzer device for controlling activation of the electrodes <NUM>, <NUM> and the heater <NUM>. The conductive ink <NUM> may further form electrical lines <NUM> connecting the electrodes <NUM> with the electrodes <NUM>, <NUM> and/or the heater <NUM>. The electrodes <NUM> and the electrodes <NUM> may be used to determine whether a fluid sample has flowed through fluid microchannel <NUM> so that the heater <NUM> may be used to heat the fluid to cause a PCR within the microchannel. In an embodiment, the electrodes <NUM>, <NUM> utilize a changing dielectric constant as fluid flows through microchannel <NUM> to determine whether fluid has flowed therethrough, as the dielectric constant differs considerably when there is liquid in the microchannel at the electrodes <NUM>, <NUM>. Test card <NUM> also includes screen printed electrodes <NUM>, which are in electrical communication with heater <NUM> and electrodes <NUM>,<NUM> via electrical lines <NUM>. By placing a current source (from the analyzer device) in conductive communication with the electrodes <NUM>, the current source can activate heater <NUM> and/or electrodes <NUM>,<NUM>.

As illustrated in <FIG>, dielectric ink <NUM> has been printed over the majority of the electrical components formed by conductive ink <NUM>. The dielectric ink <NUM> serves as protective, non-conductive coating to encapsulate the electrical components. In the illustrated embodiment, the only electrical components visible from the bottom of test card <NUM> are electrodes <NUM> because the electrodes <NUM> are the only electrical components intended to contact corresponding electrodes or contacts of an outside source of current (e.g., an analyzer device). By applying current from the outside source to the electrodes <NUM>, all other electrical components of the test card <NUM> can be powered and controlled. As illustrated, the electrodes <NUM> can be separated from each other (e.g., not be electrically connected to each other on the test card <NUM>) so that each of the heater <NUM> and the electrodes <NUM>,<NUM> can be controlled independently of each other.

<FIG> shows a top view of a fully assembled test card <NUM>. Because the bottom substrate layer <NUM>, channel layer <NUM>, middle substrate layer <NUM>, adhesive layer <NUM>, and top substrate layer <NUM> are transparent in the illustrated embodiment, the printed circuit layer <NUM> is visible from the top view. In <FIG>, the dielectric ink <NUM> on the bottom of test card <NUM> has been omitted for simplicity.

<FIG> illustrates the alignment of the heater <NUM> on printed circuit layer <NUM> in relation to fluid microchannel <NUM>, while <FIG> illustrates a detailed view of the heater <NUM>. In the illustrated embodiment, the heater <NUM> includes two electrodes <NUM> electrically connected by a plurality of heater bars <NUM>. As illustrated in <FIG>, electrodes <NUM> are aligned on opposite sides of the microchannel <NUM>, with the plurality of heater bars <NUM> aligned so as to cross the microchannel <NUM> in a direction approximately perpendicular to the microchannel <NUM>. By applying current to the electrodes <NUM>, the fluid within the microchannel <NUM> may be heated by the heater bars <NUM> to cause a PCR. The disclosed heater <NUM> is therefore particularly useful in causing a PCR within a fluid microchannel due to the way that the electrodes <NUM> align on the sides of the microchannel and the heater bars <NUM> cross the microchannel. In <FIG>,the microchannel <NUM> is shown in broken lines to illustrate this alignment.

In an embodiment, the electrodes <NUM> may be formed of silver ink, while the heater bars <NUM> may be formed of carbon ink. In an alternative embodiment, the electrodes <NUM> and the heater bars <NUM> may be formed of the same or a different material, for example, silver ink, carbon ink, another conductive ink, or another electrically conductive material besides a cured ink.

In the illustrated embodiment, the plurality of heater bars <NUM> includes a central heater bar 112a, first outer heater bars 112b, and second outer heater bars 112c. In the illustrated embodiment, each of central heater bar 112a and outer heater bars 112b, 112c is formed with a central diamond shape <NUM> (shown as 114a, 114b, 114c) and two protruding ends <NUM> (shown as 116a, 116b, 116c). The protruding ends <NUM> overlap with the electrodes <NUM> (shown as first electrode 110a and second electrode 110b) to place the electrodes <NUM> in electrical communication with each other. Although five heater bars <NUM> are shown in the illustrated embodiment, it should be understood by those of ordinary skill in the art that more or less heater bars may be used. The electrodes <NUM> may be printed either before or after the plurality of heater bars <NUM> so that the electrodes <NUM> and the plurality of heater bars <NUM> overlap.

In the illustrated embodiment, each of the plurality of heater bars <NUM> increases in width in the y-direction from first electrode 110a to a central point <NUM> (shown as 118a, 118b, 118c) and then decreases in width in the y-direction from the central point <NUM> to second electrode 110b, creating a diamond shape with a largest width in the y-direction at central point <NUM>. It is envisioned that other shapes could be used, for example, an oval shape that omits the sharp points at central point <NUM> but maintains a largest width at central point <NUM>. Example embodiments of other shapes are illustrated at <FIG>.

In the illustrated embodiment, central heater bar 112a is thinner in the y-direction than outer heater bars 112b, 112c, giving central heater bar 112a a higher resistance than the outer heater bars 112b, 112c. As illustrated, the central heater bar 112a is thinner in the y-direction at central point 118a of the diamond shape and also at each protruding end 116a than outer heater bars 112b, 112c at 118b, 118c and 116b, 116c, respectively.

In an embodiment, the width W<NUM> of protruding ends 116a of central heater bar 112a in the y-direction may be about <NUM>, the width W<NUM> of protruding ends 116b of outer heater bars 112b in the y-direction may be about <NUM>, and the width W<NUM> of protruding ends 116c of outer heater bars 112c in the y-direction may be about <NUM>. In another embodiment, W<NUM> may be any width greater than W<NUM>, and W<NUM> may be any width greater than W<NUM>. In another embodiment, W<NUM> may be about <NUM>. 5x W<NUM>, and W<NUM> may be about <NUM>. 33x W<NUM> or about 2x W<NUM>. In another embodiment, W<NUM> may be about 1x to 2x W<NUM>, and W<NUM> may be about 1x to 2x W<NUM>. Those of ordinary skill in the art will recognize that other dimensions are possible.

In an embodiment, the width W<NUM> of the diamond or other shape of central heater bar 112a at central point 118a in the y-direction may be about <NUM>, the width W<NUM> of the diamond or other shape of outer heater bars 112b at central point 118b in the y-direction may be about <NUM>, and the width W<NUM> of the diamond or other shape of outer heater bars 112c at central point 118c in the y-direction may be about <NUM>. In another embodiment, W<NUM> may be any width greater than W<NUM>, and W<NUM> may be any width greater than W<NUM>. In another embodiment, W<NUM> may be about <NUM>. 2x W<NUM>, and W<NUM> may be about <NUM>. 1x W<NUM> or about <NUM>. In another embodiment, W<NUM> may be about 1x to 2x W<NUM>, 1x to <NUM>. 5x W<NUM> or <NUM>. 1x to <NUM>. 3x W<NUM>, while W<NUM> may be about 1x to 2x W<NUM>, 1x to <NUM>. 5x W<NUM> or 1x to <NUM>. Those of ordinary skill in the art will recognize that other dimensions are possible.

In an embodiment, each of the heater bars <NUM> may have a same length Li in the x-direction. For example, Li may be <NUM>. In an embodiment, the length L<NUM> of each electrode <NUM> in the x-direction may be about <NUM>, and the width W<NUM> of each electrode <NUM> in the y-direction may be about <NUM>.

As further illustrated, the width of the outer heater bars 112b, 112c in the y-direction at central points 118b, 118c and protruding ends 116b, 116c progressively increases as the distance from central heater bar 112a increases in the y-direction. That is, the width of outer bars 112b in the y-direction at central point 118b and/or protruding end 116b is greater than the width of central bar 112a in the y-direction at central point 118a and/or protruding end 116a, respectively. Likewise, the width of outer bars 112c in the y-direction at central point 118c and/or protruding end 116c is greater than the width of outer bars 112b in the y-direction at central point 118b and/or protruding ends 116b, respectively.

By using a heater with the same or similar structure as shown in <FIG>, it has been determined that the electrical path between electrodes <NUM> can be controlled to ensure constant heater uniformity. Additionally, the disclosed heater uses lower power consumption than alternatives because of a lower total resistance. These advantages are illustrated for example, at <FIG>.

<FIG> show a heater design in which a large square heater bar is placed between two electrodes <NUM>. In the illustration, the large square has a <NUM> square area. <FIG> shows a current density of the square heater bar of <FIG>, while <FIG> shows the temperature profile. With the heater shown, electricity passes through electrodes <NUM>. Once the current passes through electrodes <NUM> into a central region, the path of least resistance for the current is to flow through the center of the central region. As shown in <FIG>, the current density is highest in the center of the central region because this region is the path of least resistance for the current. As shown in <FIG>, the resultant temperature distribution is uneven because the current is maximum in the center and dramatically drops (e.g., up to <NUM> degrees) around the edges. Thus, with the design of <FIG>, neither the current nor the temperature is uniformly distributed, with the non-uniform current density resulting in the uneven temperature distribution. The large temperature gradient may cause major issues for assays such as PCR, which require precise temperature control.

In contrast, <FIG> show the effects of the presently disclosed heater <NUM> design. <FIG> again illustrates the presently disclosed design using progressively thickening heater bars. <FIG> shows the current density, while <FIG> shows the temperature profile. As illustrated, by varying the heater size/resistance in the y-direction, current is forced to travel further from the centerline in the y-direction of the heater. Additionally, the variation in heater dimensions along the x-axis forces maximum current density nearer the electrodes <NUM>. As shown in <FIG>, the temperature is substantially uniform, thereby providing precise temperature control for a PCR on the test card <NUM>.

It should be understood that the disclosed heater design may be utilized with other materials besides cured conductive inks. For example, another conductive material such as a metal may be sized and/or shaped as shown to achieve the same advantages.

<FIG> illustrates an alternative embodiment of a heater <NUM> according to the present disclosure. <FIG> differs from <FIG> in that heater <NUM> includes two central heater bars 212a between outer heater bars 212b, 212c, whereas heater <NUM> only shows one central heater bar 112a between outer heater bars 112b, 112c. Thus, <FIG> illustrates that the number of particular heater bars <NUM>, <NUM> may vary from embodiment to embodiment, and that increasing the number of any particular size or location of a heater bar <NUM>, <NUM> is within the scope of the present disclosure. It should also be understood to those of ordinary skill in the art that the materials, dimensions and other elements described above with respect to heater <NUM> are equally applicable to heater <NUM>.

<FIG> illustrates an alternative embodiment of a heater <NUM> according to the present disclosure. <FIG> differs from <FIG> in that heater <NUM> includes rounded heater bars 312a, 312b, 312c as opposed to the diamond-shaped heater bars of heater <NUM>. Despite this difference, heater <NUM> maintains the progressively-increasing width of heater <NUM>, where the outer heater bars 312b are wider than the central heater bar 312a in the y-direction at the central point between electrodes and at the protruding ends, and the outer heater bars 312c are wider than outer heater bars 312b at the central point between electrodes and at the protruding ends. It should be understood by those of ordinary skill in the art that other shapes can also be used in place of the diamond shape of heater <NUM>. It should also be understood to those of ordinary skill in the art that the materials, dimensions and other elements described above with respect to heater <NUM> are equally applicable to heater <NUM>.

<FIG> illustrates an alternative embodiment of a heater <NUM> according to the present disclosure. <FIG> differs from <FIG> in that heater <NUM> includes straight heater bars 412a, 412b, 412c as opposed to the diamond-shaped heater bars of heater <NUM>. Despite this difference, the heater <NUM> maintains the progressively-increasing width of heater <NUM>. In this example, the outer heater bars 412b are wider than central heater bar 412a in the y-direction at the central point between electrodes and at the protruding ends, and the outer heater bars 412c are wider than outer heater bars 412b at the central point between electrodes and at the protruding ends. Although the heater <NUM> may not function as uniformly as heater <NUM>, it is contemplated that heater <NUM> could still be advantageous over, for example, the heater illustrated at <FIG>. It should also be understood to those of ordinary skill in the art that the materials, dimensions and other elements described above with respect to heater <NUM> are equally applicable to heater <NUM>.

In the illustrated embodiments, the plurality of heater bars <NUM> are printed with the same type of conductive ink and in the same general shape, and the size of the plurality of heater bars is used to cause the central heater bar 112a to have the greatest resistance, with the resistance of the outer heater bars 112b, 112c progressively decreasing as the distance from central heater bar 112a increases. That is, central heater bar 112a has the greatest resistance, first outer heater bars 112b have less resistance than central heater bar 112a, and second outer heater bars 112c have less resistance that first outer heater bars 112b. It is also envisioned, however, that the size of heater bars 112a, 112b, 112c may be the same or similar, and the overall shape or materials for each heater bar may be altered so that central heater bar 112a has the greatest resistance, first outer heater bars 112b have less resistance that central heater bar 112a, and second outer heater bars 112c have less resistance that first outer heater bars 112b. For example, the shape of all heater bars could be the same or similar, and the material used for central heater bar 112a could cause central heater bar 112a to have the greatest resistance, the material used for first outer heater bars 112b could cause first outer heater bars 112b to have less resistance than central heater bar 112a, and the material used for second outer heater bars 112c could cause second outer heater bars 112c to have less resistance that first outer heater bars 112b.

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about. " Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

The terms "a" and "an" and "the" and similar referents used in the context of the disclosure (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. The use of any and all examples, or exemplary language (e.g. "such as") provided herein is intended merely to better illuminate the disclosure and does not pose a limitation on the scope of the disclosure otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the disclosure.

The use of the term "or" in the claims is used to mean "and/or" unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and "and/or.

Preferred embodiments of the disclosure are described herein, including the best mode known to the inventors for carrying out the disclosure. Of course, variations on those preferred embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects those of ordinary skill in the art to employ such variations as appropriate, and the inventors intend for the disclosure to be practiced otherwise than specifically described herein.

Specific embodiments disclosed herein may be further limited in the claims using consisting of or consisting essentially of language. When used in the claims, whether as filed or added per amendment, the transition term "consisting of" excludes any element, step, or ingredient not specified in the claims. The transition term "consisting essentially of" limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s). Embodiments of the disclosure so claimed are inherently or expressly described and enabled herein.

Claim 1:
A test card (<NUM>) for analyzing a fluid sample, comprising:
at least one substrate layer (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) including a microchannel (<NUM>) extending through at least a portion of one of the substrate layers; and
a printed substrate layer (<NUM>) that is bonded to or printed on one substrate layer of the at least one substrate layer, the printed substrate layer (<NUM>) including a heater (<NUM>, <NUM>, <NUM>, <NUM>) printed on the printed substrate layer so as to align with at least a portion of the microchannel (<NUM>), characterized in that the heater (<NUM>, <NUM>, <NUM>, <NUM>) includes:
two electrodes (<NUM>) aligned on opposite sides of the microchannel (<NUM>); and
a plurality of heater bars (<NUM>, <NUM>, <NUM>, <NUM>) electrically connecting the two electrodes (<NUM>), the plurality of heater bars including a central heater bar disposed between outer heater bars, wherein the central heater bar is thinner than the outer heater bars in a direction approximately parallel to the microchannel,
wherein each of the heater bars (<NUM>, <NUM>, <NUM>, <NUM>) includes two protruding ends (<NUM>) that overlap respectively with the two electrodes (<NUM>).