Abstract:
In a preferred embodiment, a polymerase chain reaction temperature control system, including: a first tank into which a multiwell sample carrier may be placed; apparatus to introduce first temperature controlled heat transfer medium into the first tank for a first predetermined length of time; and apparatus to subsequently introduce at least a second second temperature controlled heat transfer medium into the first tank for at least a second predetermined length of time.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation-in-part of copending application Ser. No. 09/198,018, filed Nov. 23, 1998, and titled ULTRA HIGH THROUGHPUT BIOASSAY SCREENING SYSTEM, which application claims the benefit of filing dates of Provisional Patent Applications Nos. 60/067,895, filed Dec. 8, 1997, and titled ULTRA HIGH THROUGHPUT BIOASSAY SCREENING SYSTEM AND METHOD; Ser. No. 60/073,329, filed Feb. 2, 1998, and titled ULTRAHIGH THROUGHPUT BIOASSAY SYSTEM AND METHOD; and Ser. No. 60/095,497, filed Aug. 6, 1998, and titled USE OF CONTINUOUS CARRIER TAPE FOR POLYMERASE CHAIN REACTIONS, the disclosures of which applications are incorporated by reference hereinto. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to temperature control systems for polymerase chain reactions generally and, more particularly, but not by way of limitation, to a novel temperature control system for polymerase chain reactions that is simple and affords an improved degree of control. 
     2. Background Art 
     Polymerase chain reaction (PCR) is a technique that is commonly used in genomic studies and other areas of biotechnology. It consists of taking biological samples through different temperature cycles multiple times to amplify the DNA. Typically, three different temperatures are used: T 1 , T 2 , and T 3 . The sample or samples are cycled through the three temperatures in a set sequence of times for each specific reaction protocol. 
     A typical protocol might be as follows: Hold the samples at 95 degrees Centigrade for five minutes to start the sequence. Then, sequentially, hold the sample(s) at 95 degrees Centigrade for 15 seconds, hold the samples(s) at 55 degrees Centigrade for 15 seconds, and hold the sample(s) at 72 degrees Centigrade for 30 seconds. This one-minute cycle is repeated 10 times. Then, sequentially, the samples are held at 89 degrees Centigrade for 15 seconds, held at 55 degrees Centigrade for 15 seconds, and held at 72 degrees Centigrade for 30 seconds. The second temperature sequence is repeated 20 times. The samples are then held at 72 degrees Centigrade for 10 minutes as a final step. The samples may then be held at four degrees Centigrade for a longer period of time until used. 
     The conventional method of conducting such protocols is to place multiple DNA samples in a 96-or 384-well microplate and then the plate is robotically switched between liquid baths, held at predetermined temperatures, for the indicated periods of time. In addition to being relatively expensive, such method suffers from not being able to control the ramp rate of temperature change. 
     Accordingly, it is a principal object of the present invention to provide a system for conducting PCR studies that is simple and economical. 
     It is an additional object of the invention to provide such a system that permits for accurate temperature control of the heat transfer medium in the system. 
     It is a further object of the invention to provide such a system that provides control of the ramp rate of temperature change between steps in the reaction protocol. 
     Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures. 
     SUMMARY OF THE INVENTION 
     The present invention achieves the above objects, among others, by providing, in a preferred embodiment, a polymerase chain reaction temperature control system, comprising: a first tank into which a multiwell sample carrier may be placed; means to introduce first temperature controlled heat transfer medium into said first tank for a first predetermined length of time; and means to subsequently introduce at least a second second temperature controlled heat transfer medium into said first tank for at least a second predetermined length of time. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Understanding of the present invention and the various aspects thereof will be facilitated by reference to the accompanying drawing figure, submitted for purposes of illustration only and not intended to define the scope of the invention, on which: 
     FIG. 1 is schematic representation of a PCR temperature control system according to the present invention. 
     FIG. 2 is an isometric view of a roll of carrier tape useful in practicing the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The above-referenced patent applications describe the use of a carrier tape for use in bioassays. The carrier tape has a large number of wells formed therein into which wells various materials may be introduced for reaction and/or incubation. The wells may be sealed with a sealing member and then the carrier tape is formed into a roll. A roll of such carrier tape four inches wide by 16 inches in diameter will hold approximately 100,000 discrete samples. The applications describe the tape and the methods of filing, sealing, and handling the tape. 
     Such a sealed carrier tape is especially useful in practicing the present invention. However, suitably sealed conventional microplates having 96 or 384 or any other number of wells may be employed in the invention as well. 
     FIG. 2 illustrates a suitable roll of such carrier tape, the roll being generally indicated by the reference numeral  4 . Roll  4  includes a plurality of patterns of wells, as at  6 , and may be wound on a reel  8 . 
     FIG. 1 illustrates a PCR temperature control system, generally indicated by the reference numeral  10 . System  10  includes a thermally insulated tank  20  into which is placed a multiwell sample carrier  22 . Tank  20  may be made of a thermally insulating material such as polypropylene. In the case where sample carrier  22  is a roll of carrier tape as described above, the inside of insulated tank  20  would be about 17 inches in diameter and about five inches deep. A water inlet  30  is supplied at the bottom of insulated tank  20  for the introduction of water thereinto, while top  32  of the insulated tank is designed to permit the outlet water to overflow around the perimeter thereof. A gutter  40  defined around and surrounding top  32  collects the overflow and returns it through outlet  42 . Circulation of the water is effected by pump  50  and its associated variable speed drive  52 . 
     Separate, vented or open, temperature controlled water tanks  60 ,  61 , and  62  are provided to supply circulating water to insulated tank  20  though pump  50 . Tanks  60 - 62  are held, respectively, at temperatures T- 1 , T- 2 , and T- 3  by means of electrical heating coils  70 - 72  and cooling coils  74 - 76 , the latter being supplied with recirculated brine from a chiller unit  80 . Temperatures T- 1 , T- 2 , and T- 3  in tanks  60 - 62  are sensed, respectively, by temperature sensing elements  90 - 92  and a master controller  94  connected to receive outputs from the temperature sensing elements closely controls the temperatures by controlling electrical heating coils  70 - 72  and brine control valves  96 - 98  connected in the lines from cooling coils  74 - 76 . The temperature in insulated tank  20  is similarly sensed by temperature sensing element  100  and the output thereof passed to master controller  94 . 
     Water from water tank  60  is circulated by pump  50  through insulated tank  20  and returned thereto by means of master controller  94  opening valves  110  and  112 . Similarly, water from water tank  61  is circulated by pump  50  through insulated tank  20  and returned thereto by means of master controller  94  opening valves  120  and  122  and from and to water tank  62  by means of the master controller opening valves  130  and  132 . Of course, the respective valves on those of tanks  60 - 62  from which water is not being recirculated will be closed. 
     In operation, valves  110  and  112  are opened by master controller  94  and water at temperature T- 1  from water tank  60  is recirculated through insulated tank  20 . When the temperature in insulated tank  20  stabilizes at T- 1 , pump  50  stops and valve  112  is closed. When the protocol calls for temperature T- 2  in insulated tank  20 , pump  50  is started and valve  122  on water tank  61  is opened, permitting water from tank  61  to be pumped to the insulated tank. Water at temperature T- 1  continues to exit insulated tank  20  and return to water tank  60 . When water from insulated tank  20  at temperature T- 2  begins to exit that tank, valve  110  is closed, valve  120  is opened, and the water returns to water tank  61 . When the temperature in insulated tank  20  stabilizes at T- 2 , valve  122  is closed and pump  50  is stopped. In a similar manner, water at temperature T- 3  is supplied from water tank  62 . The sequence is used in such manner as to match the temperature cycles and times called for by the protocol. 
     Some PCR protocols require controlling the ramp time from one temperature to the next. This is accomplished by the present invention by varying the speed of pump  50  through master controller  94  controlling variable speed drive  52 . Pump  50  and its top speed are matched to the fastest rise time required by the desired protocols. Variable speed drive  52  on pump  50  permits the pump to be set to match the slowest ramp time. 
     Water tanks  60 - 62  are sized to provide a storage capacity in excess of the volume of insulated tank  20 . Typically, each of water tanks  60 - 62  is about three times the size of insulated tank  20 . In addition, electrical coils  70 - 72  and cooling coils  74 - 76  are sized to have a fast response time and to quickly control the temperature in their respective water tanks. This excess capacity and fast response time are designed to assure that the desired temperatures are maintained in water tanks  60 - 62  and then delivered to insulated tank  20 . 
     While three water tanks have been illustrated, it will be understood that the present invention may employ only two water tanks or it may employ a number greater than three water tanks, depending on the protocol being used. 
     In the embodiments of the present invention described above, it will be recognized that individual elements and/or features thereof are not necessarily limited to a particular embodiment but, where applicable, are interchangeable and can be used in any selected embodiment even though such may not be specifically shown. 
     Terms such as “upper”, “lower”, “inner”, “outer”, “inwardly”, “outwardly”, and the like, when used herein, refer to the positions of the respective elements shown on the accompanying drawing figures and the present invention is not necessarily limited to such positions. 
     It will thus be seen that the objects set forth above, among those elucidated in, or made apparent from, the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown on the accompanying drawing figures shall be interpreted as illustrative only and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.