Microfluidic device with constant heater uniformity
Inventors
Raghunathan, Ashwin • Lee, Steve • Revilla, Ryan Alan • Patel, Tej Rushikesh
Assignees
Publication Number
US-12064764-B2
Publication Date
2024-08-20
Expiration Date
2040-01-24
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Abstract
A heater for a microfluidic test card is disclosed herein. In a general example embodiment, 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.
Core Innovation
The invention disclosed is a screen-printed heater design for a microfluidic test card, wherein the heater is printed on a printed substrate layer aligned with a microchannel. The heater includes two electrodes aligned on opposite sides of the microchannel and a plurality of heater bars that electrically connect these electrodes. Among these heater bars, a central heater bar is disposed between outer heater bars and has a higher resistance than the outer heater bars to achieve temperature uniformity.
The problem addressed by the invention concerns the lack of thermal uniformity in existing test card screen-printed heaters used in polymerase chain reaction (PCR). Conventional heaters can exhibit large temperature gradients, for example, up to 20 degrees over a 6 mm square area due to non-uniform current density, which adversely affects the precision needed for PCR that requires highly controlled temperatures.
The invention solves this by designing heater bars with progressively varying widths in a direction approximately parallel to the microchannel, where the central heater bar is thinner than the first outer heater bars, and the first outer heater bars are thinner than the second outer heater bars. This configuration forces the current density and temperature distribution to be uniform across the microchannel, thereby enabling precise temperature control required for effective PCR within the test card.
Claims Coverage
The patent includes multiple independent claims focusing on the design and method of providing a heater on a substrate with particular structural features for thermal uniformity.
Heater design with central heater bar having higher resistance
A test card comprising at least one substrate layer including a microchannel and a printed substrate layer with a heater aligned to the microchannel, wherein the heater comprises two electrodes on opposite sides of the microchannel and a plurality of heater bars electrically connecting the electrodes. The plurality of heater bars includes a central heater bar disposed between outer heater bars. The central heater bar has higher resistance than outer heater bars by being thinner than first outer heater bars, which are thinner than second outer heater bars in a direction approximately parallel to the microchannel.
Heater structure with progressively varying heater bar thickness
A heater with two electrodes spaced apart in a first direction and a plurality of heater bars connecting them, including a central heater bar disposed between outer heater bars. The central heater bar is thinner than the first outer heater bars, which are thinner than the second outer heater bars, in a direction approximately parallel to the microchannel. The outer heater bars have progressively less resistance as the distance from the central heater bar increases in a second, approximately perpendicular direction.
Heater bars shaped to be thickest at central point between electrodes
The plurality of heater bars are each shaped to have a central diamond shape with a largest width at a central point between the two electrodes for improved current distribution and temperature uniformity.
Use of conductive materials for electrodes and heater bars
The electrodes are printed on the substrate with silver ink, and the plurality of heater bars are printed with carbon ink or other conductive inks to implement the heater structure.
Method of printing heaters with variable heater bar thickness and alignment
A method comprising printing two electrodes spaced apart in a first direction and printing a plurality of heater bars connecting them including a central heater bar thinner than the outer heater bars in a direction approximately perpendicular to the first direction. The method may include printing outer heater bars progressively thicker with increasing distance from the central heater bar, and aligning the heater bars and electrodes relative to a microchannel on the substrate.
The claims provide coverage for a microfluidic test card heater design featuring a plurality of heater bars with a central heater bar of higher resistance achieved via thinner width, progressive thickness variation of outer heater bars to ensure uniform heating, and methods of printing such a heater aligned with a microchannel, using specific conductive inks.
Stated Advantages
The heater design ensures constant heater uniformity, leading to substantially uniform temperature distribution across the fluid microchannel.
The design reduces power consumption due to lower total resistance of the heater.
Improved thermal uniformity enables precise temperature control critical for performing polymerase chain reactions (PCR) within the test card.
Documented Applications
Use of the heater in a microfluidic test card for analyzing fluid samples by causing and analyzing PCR within a fluid microchannel.
The test card is configured for point-of-care (POC) diagnostics, enabling rapid, high sensitivity, and high specificity nucleic acid amplification tests (NAATs) operating with small fluid volumes such as a finger stick drop of whole blood.
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