Thermal cycler for PCR

• US 20050145273A1
• Filed: 02/15/2005
• Published: 07/07/2005
• Est. Priority Date: 03/28/1997
• Status: Active Grant

• Current Assignee: Adrian Fawcett, Charles M. Wittmer, Douglas E. Olsen, John G. Atwood, John R. Widomski, Keith S. Ferrara, Paul M. Hetherington, Richard W. Noreiks
• Original Assignee: Adrian Fawcett, Charles M. Wittmer, Douglas E. Olsen, John G. Atwood, John R. Widomski, Keith S. Ferrara, Paul M. Hetherington, Richard W. Noreiks
• Inventors: Fawcett, Adrian, Atwood, John G., Hetherington, Paul M., Wittmer, Charles M., Widomski, John R., Olsen, Douglas E., Ferrara, Keith S., Noreiks, Richard W.
• Granted Patent: US 7,537,377 B2
• Time in Patent Office: Days
• US Class Current: 136/201
• CPC Class Codes: B01L 2300/0829 Multi-well plates; Microtitration plates
• CPC Class Codes: B01L 2300/1822 using Peltier elements
• CPC Class Codes: B01L 2300/1827 using resistive heater
• CPC Class Codes: B01L 3/50853 with covers or lids
• CPC Class Codes: B01L 7/52 with provision for submitting samples to a predetermined sequence of different temperatures, e.g. for treating nucleic acid samples amplification or hybridisation processes per se C12Q1/68; controlling sequential reactions for synthesis B01J19/0046
• CPC Class Codes: C12Q 1/686 Polymerase chain reaction [PCR]
• CPC Class Codes: F25B 21/04 reversible
• CPC Class Codes: F25B 2321/021 Control thereof
• CPC Class Codes: G01R 27/205 Measuring contact resistance of connections, e.g. of earth connections
• CPC Class Codes: G05D 23/1919 characterised by the type of controller
• CPC Class Codes: H10N 10/13 characterised by the heat-exchanging means at the junction
• CPC Class Codes: Y10T 137/1516 Thermo-electric

Abstract

An instrument for performing highly accurate PCR employing an assembly, a heated cover and an internal computer. The assembly is made up of a sample block, a number of Peltier thermal electric devices and heat sink, clamped together. The sample block temperature is changed exclusively by the thermoelectric devices controlled by the computer. The sample block is of low thermal mass and is constructed of silver. The Peltier devices are designed to provide fast temperature excursions over a wide range. The heat sink has a perimeter trench to minimize edge losses and is adjacent to a continuously variable fan. A perimeter heater is used to improve the thermal uniformity across the sample block to approximately ±0.2° C. A heated platen pushes down onto the tube caps to apply a minimum acceptable force for seating the tubes into the block, ensuring good thermal contact with the block. The force is applied about the periphery of the tube caps to prevent distortion of the caps during thermal cycling. The platen is heated to provided thermal isolation from ambient conditions and to prevent evaporation from the surface of the sample into the upper portion of the sample tube. A control algorithm manipulates the current supplied to the thermoelectric coolers such that the dynamic thermal performance of the block can be controlled so that pre-defined thermal profiles for the sample temperature can be executed. The sample temperature is calculated instead of measured using a design specific model and equations. The control software includes calibration diagnostics which permit variation in the performance of thermoelectric coolers from instrument to instrument to be compensated for such that all instruments perform identically. The block/heat sink assembly can be changed to another of the same or different design. The assembly carries the necessary information required to characterize its own performance in an on-board memory device, allowing the assembly to be interchangeable among instruments while retaining its precision operating characteristics. The instrument has a graphical user interface. The instrument monitors the thermoelectric devices and warns of changes in resistance that may result in failure.

Claims

1. A method for measuring the AC resistance of a thermoelectric device having a first heating and cooling surface and a second heating and cooling surface, said method comprising:

measuring the temperature of said first heating and cooling surface;

measuring the temperature of said second heating and cooling surface;

applying power to said thermoelectric device to cause said first heating and cooling surface and said second heating and cooling surface to attain the same temperature;

applying an AC voltage across said thermoelectric device;

measuring said AC voltage across said thermoelectric device;

measuring said AC current through said thermoelectric device;

calculating the AC resistance of said thermoelectric device from said measured AC voltage and said measured AC current.

2. The method of claim 1, further comprising:

performing a calculation for compensating for ambient temperature error to calculate a compensation AC resistance measurement; and

storing said compensated AC resistance measurement.

3. A method for achieving linear temperature transitions utilizing a thermoelectric device having a Seebeck coefficient, at least a first heating and cooling surface and a second heating and cooling surface and being operated in a manner causing said first surface to be higher in temperature and said second surface to be lower in temperature relative to each other, said method comprising:

determining a desired heat flow from said lower temperature surface;

determining electrical resistance of said thermoelectric device as a function of temperature;

determining the Seebeck coefficient of said thermoelectric device as a function of temperature;

determining the conductance of said thermoelectric device as a function of temperature;

measuring temperature of said lower temperature surface;

measuring temperature of said higher temperature surface;

calculating an average temperature of said lower temperature surface and said higher temperature surface; and

calculating a current required to achieve said desired heat flow as a function of said electrical resistance of said thermoelectric device as a function of temperature, said Seebeck coefficient of said thermoelectric device as a function of temperature, said conductance of said thermoelectric device as a function of temperature, said temperature of said lower temperature surface, said temperature of said higher temperature surface, and said average of said lower temperature surface and said higher temperature surface.

4. A method for determining the temperature of a mixture in a sample vial, said vial having an upper portion and a lower portion and being contained in an apparatus comprising:

as assembly for cycling said vials through a series of temperature excursions, said assembly further comprising a sample block for receiving said vials;

a cover for applying a seating force on said vials and for applying a constant temperature to the upper portion of said vials; and

a computing apparatus for controlling said temperature excursions of said assembly and said constant temperature of said cover;

said method comprising;

measuring temperature of said sample block;

measuring temperature applied by said cover;

determining thermal resistance of said vial between said sample block and said mixture;

determining thermal resistance of air in parallel with said vial between said mixture and said cover;

determining thermal capacitance of said mixture;

determining thermal capacitance of said vial between said mixture and said cover; and

calculating temperature of said mixture as a function of said temperature of said sample block, said temperature applied by said cover, said thermal resistance of said vial between said sample block and said mixture, said thermal resistance of air in parallel with said vial between said mixture and said cover, said thermal capacitance of said mixture and said thermal capacitance of said vial between said mixture and said cover.

5. A method for calibrating an assembly for cycling samples through a series of temperature excursions comprising a sample block for receiving vials, a plurality of thermoelectric devices, a heat sink, a clamping mechanism positioned so as to clamp said thermoelectric devices between said sample block and said heatsink, and a memory device capable of storing data related to said assembly, said method comprising:

applying power to said thermoelectric devices, causing said assembly to cycle through a desired series of temperature excursions;

measuring the actual temperature excursions;

comparing said actual temperature excursions with said desired temperature excursions;

adjusting said power applied to said thermoelectric devices so that said actual temperature excursions match said desired temperature excursions; and

recording said adjusted power in said memory device located on said assembly for further utilization in obtaining said desired series of temperature excursions.