Patent Application
20130137144
1. Field of the Invention
This invention relates to sequential chemical reactions of which the polymerase chain reaction (PCR) is one example. In particular, this invention addresses methods and apparatus for performing chemical reactions simultaneously in a multitude of reaction mixtures while closely controlling the temperature in each mixture.
2. Description of the Prior Art
PCR is one of many examples of chemical processes that require a high level of temperature control of reaction mixtures with rapid temperature changes between different stages of the procedure. PCR itself is a process for amplifying DNA, i.e., producing multiple copies of a DNA sequence from a single strand bearing the sequence. PCR is typically performed in instruments that provide reagent transfer, temperature control, and optical detection of the product in a multitude of reaction vessels such as wells, tubes, or capillaries. The process includes a sequence of stages that are temperature-sensitive, different stages being performed at different temperatures and the temperature sequence being repeated in successive cycles.
While PCR can be performed in any reaction vessel, multi-well reaction plates, multi-channel microfluidics devices, and similar structures in which the process is performed concurrently in a multitude of samples, are the reaction vessels of choice. Each sample receptacle, whether it be a well of a multi-well plate or a channel of a multi-channel microfluidics device, will retain a separate sample, and all samples are simultaneously equilibrated to a common thermal environment at each stage of the process.
A 96-well plate, for example, can be used in high-throughput PCR by placing a sample in each well and placing the plate in contact with a metal block, commonly referred to as a “thermal block,” and heating and cooling the metal block according to an established protocol, either by a Peltier (thermoelectric) heating/cooling element or by a closed-loop liquid heating/cooling system that circulates a heat transfer fluid through channels machined into the block. While Peltier elements are widely described for this use, the efficiency of a Peltier element can be improved by increasing the heat transfer between the element and the thermal block and by reducing the heat load on the element.
The present invention resides in a thermal block with one or more Peltier elements built into the block. The terms “Peltier element” and “thermoelectric heating/cooling element” are used herein interchangeably. As is well known among those familiar with these elements, they operate as heating or cooling elements depending on the direction of electric current passing through them. With Peltier elements built into the thermal block, the resulting construction has fewer thermal interfaces than conventional arrangements where the Peltier elements and the thermal block are separate components that must be joined together for use. Where the conventional Peltier element is a laminated structure whose outer layers are ceramic materials that are thermally conducting, the thermal block of the present invention utilizes the metal piece of conventional thermal blocks as the outer layer on the side of the Peltier element that faces the reaction plate. The layers that form the thermal block, from the top down, are therefore (i) a metal piece whose upper surface is contoured to match the contour of the underside of the reaction plate, and thereby to provide maximal contact with each sample receptacle of the sample plate when the plate is lowered onto the metal piece, (ii) a thin layer of an electrically insulating material on the lower surface of the metal piece, (iii) the electrically conductive strips that join together the P-doped and N-doped semiconductor blocks that are the operative components of the Peltier element; (iv) the semiconductor blocks themselves; (v) electrically conductive strips at the bottoms of the semiconductor blocks, and (vi) a heat sink. An optional additional layer included in certain embodiments of the invention is an electrically insulating layer between the lower layer of electrically conductive strips, and the heat sink. The electrically conductive strips referred to above as layer (v) are thermally coupled to the heat sink, the term “thermally coupled” being used herein to denote that heat readily passes from the electrically conductive strips to the heat sink and vice versa, either directly or through the electrically insulating layer when the latter is present. In certain embodiments of the invention, layers (ii), (iii), (iv), and (v) and the heat sink form a single piece permanently joined together that is then joinable to the metal block by removable attaching means such as screw fasteners, clamps, or the like. In other embodiments, all six layers are permanently joined together as a single piece. Conventional permanent joining means such as an adhesive can be used in these latter embodiments.
These and other embodiments, objects and advantages of the invention will be apparent from the attached drawings and the description that follows.
As noted above, the term “sample plate” is used herein to denote any device or component that holds samples (reaction mixtures) in individual locations where they can individually undergo chemical reactions without being influenced by or interfering with the reactions occurring in samples at other locations in the plate. While detailed attention is directed herein to multi-well plates and microfluidics devices as examples of sample plates, other examples will be apparent to those of skill in the performance of chemical reactions simultaneously in a multitude of small reaction mixtures. For sample plates that are multi-well plates, the plates will often be of a thin material that heat readily passes through, and the wells will be arranged in a geometrical, often rectangular, array, with adjacent connected by a deck portion of the plate, which in many cases is a continuous flat portion that is joined to the wells at their rims. The deck portion can also consists of filaments joining the wells, or any such structure that holds the wells in fixed positions. The wells themselves will typically extend below the deck portion, with convex undersurfaces that are exposed for direct contact with the thermal block. By “convex” is meant that the undersurfaces are the outer surfaces of the wells, surrounding the well interiors. For rectangular wells, for example, the convex undersurfaces will be the outersurfaces of a rectangular block; for conical or cylindrical wells, the convex undersurfaces will be conical or cylindrical in shape, and for wells with parabolic or hemispherical profiles, the convex surfaces will likewise have parabolic or hemispherical profiles. For sample plates that are microfluidics devices, the channels will generally be cut or etched in the body of the device and may not have undersides that extend below a deck. The undersides of the channels and hence of the device itself may therefore be flat. The device walls will often be thin enough however that rapid heat transfer in and out of each channel is still readily achieved.
In
The upper layer 21 of the block 12 is the metal piece that transmits heat to and from the wells by virtue of its direct contact with the wells and its high thermal conductivity. The thermoelectric element 22 is constructed of conventional components, central to which are the P-doped and N-doped semiconductor blocks 23, 24 and the electrically conductive strips 25, 26 joining the blocks in alternating manner according to conventional Peltier element construction. Between the Peltier element 22 and the metal piece 21 is a layer of electrically insulating material 27, and between the Peltier element 22 and the heat sink 28 is a second layer of electrically insulating material 29. The semiconductor blocks 23, 24 can be of conventional construction and materials. The selection of particular materials of construction may vary with the operating conditions for the reactions that will occur within the wells and the temperature range that the reaction mixtures will be cycled through. An example of a semiconductor material useful for this purpose is bismuth telluride doped with either bismuth selenide (for N-doping) or antimony telluride (for P-doping). With one P-doped block and one N-doped block defined as a couple, four couples are shown, but the number of couples can be as few as one or as many as several hundred. The number is not critical and will vary with the dimensions of the thermal block and the sample plate, although in most cases the number will be no greater than one hundred. The electrically conductive strips 25, 26 can be copper or any other conventional electric lead material. Examples of materials that can be used for the layers of electrically insulating material 27, 29 are ceramics, notably aluminum oxide or beryllium oxide. Alternatively, a thin polyimide sheet can be used. The thicknesses of these layers can vary but will generally be selected to be thick enough to provide both electrical insulation and structural integrity or support, yet thin enough to transmit heat. Additional layers for optional inclusion, although not shown in this Figure, are coatings on the surfaces of the semiconductor blocks to serve as diffusion barriers, for example, or to facilitate the joining of the surfaces to the conductive leads. Shear films can also be included to allow movement, and thereby reduce shear stress, at the interfaces between the semiconductor materials, the thermal block, and the sample plate, such stress often resulting from expansion and contraction of these elements due to temperature changes. These and other optional variations will be readily apparent to those skilled in the use of Peltier elements and familiar with the literature on Peltier elements.
The
The construction and composition of the individual Peltier elements can be the same as those of the embodiment of
Another distinguishing feature of the embodiment of
In the claims appended hereto, the term “a” or “an” is intended to mean “one or more.” The term “comprise” and variations thereof such as “comprises” and “comprising,” when preceding the recitation of a step or an element, are intended to mean that the addition of further steps or elements is optional and not excluded. All patents, patent applications, and other published reference materials cited in this specification are hereby incorporated herein by reference in their entirety. Any discrepancy between any reference material cited herein or any prior art in general and an explicit teaching of this specification is intended to be resolved in favor of the teaching in this specification. This includes any discrepancy between an art-understood definition of a word or phrase and a definition explicitly provided in this specification of the same word or phrase.
This application claims the benefit of U.S. Provisional Patent Application No. 61/494,742, filed Jun. 8, 2011, the contents of which are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61494742 | Jun 2011 | US |
