GB2250581A

GB2250581A - Temperature control for sample incubator

Info

Publication number: GB2250581A
Application number: GB9125908A
Authority: GB
Inventors: Peter John Cox-Smith
Original assignee: COX SMITH PETER JOHN
Current assignee: COX SMITH PETER JOHN
Priority date: 1990-12-05
Filing date: 1991-12-05
Publication date: 1992-06-10
Also published as: GB9125908D0; GB9026517D0

Abstract

In an incubator incubating biological samples in a temperature controlled environment a compartment 12 is heated or cooled by a Peltier device 14 and air is pumped around a recirculating path 28 by a fan 30. The air passes through a region 34 beneath a microplate 22 accommodating biological samples. The air is turbulent in the region 34 to promote even temperature distribution within the airflow. The Peltier device 14 is controlled to maintain the compartment temperature at the required level. Alternatively a block has recesses to accommodate tubes containing the samples, and temperature control is by a recirculating flow of liquid which passes through channels in the block and is turbulent both below the block and in the channels. <IMAGE>

Description

Title: Temperature Control Apparatus Field of the Invention This invention relates generally to temperature control apparatus and in particular to an incubator for incubating biological samples in a temperature controlled environment.

Background to the Invention Many analysis methods include incubation of biological samples which are generally contained in the wells or recesses of microplates. The microplates containing the samples are incubated in a temperature controlled environment for periods of between 10 minutes and two hours or more. For example, microplates are used for immuno-assay diagnosis of conditions such as HIV and Hepatitis and in endocrinology laboratories for measurement of progesterone levels. Known incubators for these purposes tend to have large enclosures across which there can sometimes be large temperature differences which mitigate against accurate temperature control of the samples. The invention aims to provide apparatus in which this disadvantage is substantially overcome.

Disclosure of the Invention According to the invention apparatus for controlling the temperature of a sample comprises a compartment, support means for supporting the sample within the compartment, a heating and/or cooling device for varying the temperature of the compartment, means for forcing a flow of fluid around the compartment such that the fluid flow adjacent the support means is turbulent, and control means for controlling the device to maintain a substantially uniform temperature throughout the compartment. The turbulence of the fluid promotes an even temperature across the fluid flow and promotes heat exchange between the turbulent fluid and the sample on the support means. The fluid may be a gas, such as air, or a liquid.

The heating and/or cooling device may be a simple resistance heating element, but a preferred embodiment of the invention is capable of cooling as well as heating, and incorporates a Peltier device to achieve this.

A Peltier device comprises a junction of two dissimilar metals such that when an electric current flows across the junction in one direction there is a heating effect and when an electric current flows in the other direction there is a cooling effect. Hence, the Peltier device provides an extremely simple and convenient way of providing either a heating or a cooling effect, by control of the magnitude and direction of the DC electric current passing across the junction of the two metals of the Peltier device. This, combined with the forced flow of fluid around the compartment, means that the temperature of the compartment can be maintained uniform and controlled within close limits.

Preferably, the control means include at least one temperature sensor which is located within the compartment and the output from which is maintained substantially constant by means of feedback control of the device.

The means for forcing a flow of fluid around the compartment preferably include a fan, and the support means may include a mounting to support a microplate for holding samples to be incubated. In this case, the compartment is conveniently shaped to produce, in at least one region where the fluid flows past the plate, a turbulent flow of fluid so as to promote heat exchange between the turbulent fluid and the microplate.

Said region is preferably arranged underneath the mounting for the microplate, and in a preferred embodiment the apparatus includes a top plate which in use covers the microplate so as to prevent fluid flow over the microplate and minimise evaporation from the microplate contents.

The top plate is conveniently made of a material of high thermal conductivity.

The compartment is preferably dimensioned so as to accommodate a single standard microplate or a predetermined plurality of microplates, preferably two or three. The apparatus may include a number of such compartments (preferably stacked one above the next) capable of operating at selected individual temperatures and times. Control of each compartment may be from a front panel in manual operation or via a computer port for control by a single microprocessor.

The support means may alternatively include a block formed with a plurality of recesses to receive tubes containing the samples, the block having channels through which the fluid passes.

Two incubators according to the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a diagrammatic sectional view, taken on a vertical plane, through the first incubator, employing air circulation, Figure 2 is a view similar to that of Figure 1 but shows the second incubator, employing liquid circulation, Figure 3 is a fragmentary view of the line III-III of Figure 2, and Figure 4 shows a control loop for controlling the internal temperature of the incubator.

Referring to Figure 1, the incubator includes a casing 10 enclosing a compartment 12 the temperature of which is controlled by a Peltier device 14. The device 14 carries fins 16 projecting into the compartment 12, and the external side of the casing 10 may have fins, as shown in Figure 1. Water cooling (not shown) is used to remove heat extracted by the Peltier device.

The Peltier device 14 comprises a junction of two dissimilar metals. When a DC electric current passes across the junction in one direction the junction is heated and when a DC electric current passes across the junction in the opposite direction the junction is cooled.

Hence, control of the direction and magnitude of the electric current passing into the Peltier device 14 enables the device to provide a controlled heating or cooling effect within the compartment.

The compartment 12 accommodates a mounting 18 carrying a flexible support 20 shaped to accommodate a microplate 22 having therein a number of recesses or wells accommodating biological samples. The upper side of the mounting 18 is closed by a top plate 24 which overlies the microplate 22 and meets upstanding edges of the mounting 18 so as to enclose the biological samples within an inner chamber 26.

A recirculating air flow, generally indicated at 28, is forced to flow within the compartment 12 around the inner chamber 26 by means of a fan 30. The compartment 12 has a raised base 32 and this constricts the air flow in a region 34 where it passes below-the plate 22. This constriction in the air flow ensures that there is turbulent air in the region 34, and this turbulence promotes -an even temperature distribution within the air flow and maximum heat transfer between the air and the plate 22.

Control of the temperature within the compartment is achieved by the use of a first temperature sensor 42 on the internal wall of the compartment and a second temperature sensor 44 in the heat transfer region 34.

These two temperature sensors are linked to a controlling microprocessor into which is set the desired temperature from a front panel or from an RS232 port command. This controls the Peltier device 14 to maintain the compartment temperature at the required level.

The incubator shown in Figure 2 has a dry block 51 mounted on the plate 22. The dry block 51 has an array of recesses 53 for accommodating small tubes containing samples to be incubated. The block 51 is of metal and has a plurality of channels 52 (Figure 3) extending through its length. Liquid is circulated around the path 28 by a pump 30, passing through the regions 34 and 50 where turbulence is created to ensure even temperature distribution. In the region 50, the liquid passes through the channels 52 at high speed, to achieve turbulence.

Figure 4 shows how two control loops operate by feedback action to control the temperature of the compartment of the incubator of Figure 1 or Figure 2. The power output 46 controls the Peltier device 14, and is controlled by feed back (through control loop 2) from the temperature sensor 42 such that the hot side temperature never exceeds 27"C. This prevents excessive heat conduction from the hot to the cold side.

The overall control loop (control loop 1) uses temperature sensor 44 to maintain the fluid temperature around the samples.

The described incubator can be held at a selected steady temperature within the range 0 to 60"C, with a temperature variation over the microplate (Figure 1) or across the block 51 (Figure 2) of less than 1 C. There is a minimal evaporation loss from the microplate wells because the microplate of Figure 1 is supported in a closed chamber 26.

Claims

1. Apparatus for controlling the temperature of a sample comprising a compartment, support means for supporting the sample within the compartment, a heating and/or cooling device for varying the temperature of the compartment, means for forcing a flow of fluid around the compartment such that the fluid flow adjacent the support means is turbulent, and control means for controlling the device to maintain a substantially uniform temperature throughout the compartment.

2. Apparatus according to claim 1, wherein the heating and/or cooling device is a resistance heating element.

3. Apparatus according to claim 1, wherein the heating and/or cooling device is a Peltier device.

4. Apparatus according to claim 1 or 2, wherein the control means include at least one temperature sensor which is located within the compartment and the output from which is maintained substantially constant by means of feedback control of the device.

5. Apparatus according to any of the preceding claims, wherein the means for forcing a flow of fluid around the compartment include a fan or pump.

6. Apparatus according to any of the preceding claims, wherein the support means include a mounting to support a microplate for holding samples to be incubated.

7. Apparatus according to claim 6, wherein the fluid is turbulent in a region underneath the mounting for the microplate.

8. Apparatus according to claim 7, wherein the apparatus includes a top plate which in use covers the microplate so as to prevent fluid flow over the microplate and minimise evaporation from the microplate contents.

9. Apparatus according to any of claims 1 to 5, wherein the support means include a block formed with a plurality of recesses to receive tubes containing the samples, the block having channels through which the fluid passes.

10. Apparatus for controlling the temperature of a sample, substantially as herein particularly described with reference to Figures 1 and 4, or Figures 2, 3 and 4, of the accompanying drawings.