Rapid Technique for Fabricating Disposable Thermal Chambers to Be Used in Testing Low Temperature USB Powered Thermofoils and Heating Elements

R. Siderits, A. Malik, M Roche


In this project we will describe the steps that we used to make an experimental Thermal Chamber.
We used this thermal chamber to test heating elements that will connect to a USB port.
This project was undertaken in preparation for a USB port powered polymerase chain reaction thermocycler.

This procedure a simple, cost effective and can be accomplished within 5 minutes. The properties and a thermal chamber are described in the following slides.

We used the Computer-Aided Design (CAD) program "trueSpace" developed by Caligari corporation to model the chamber. However, "Sketch-up" (by Google) would have worked equally well for creating a virtual model of the thermal chamber.

These dimensions are arbitrary and correspond to the thickness of the Styrofoam that we used as substrate material.

Thicker Styrofoam can be used and sectioned to provide thinner pieces of materials to work with.

A USB powered mug warmer reaches a temperature of approximately 45-50°C. 

However, a USB powered mug warmer placed in a thermally insulated chamber will reach approximately 65-70°C, within a few minutes. 

We know that the denaturation point for DNA is 100°C, and most PCR thermal cycles are between 95 and 102°C, using an annealing point up to about 54°C. A reasonable assumption would be that the power provided by two USB ports would be sufficient to reach the denaturation point of DNA, in a small thermally isolated chamber.  This, however, will be the subject of a future Instructable.

Equipment that is needed is minimal including some Styrofoam, glue, a saw and various size hole cutters. 

We used some Styrofoam that came as packing material. 

We have provided a closeup image of this type of Styrofoam on the next slide.

You can use more shop equipment if you want but this project can be done with very simple tools.

Q= Thickness/ R

R value represents the insulation property of the material being used.  The R value is 5.  The thickness of the polystyrene foam in this project is 1cm (0.39 inches).  So the Q value which is heat (thermal) conductivity is 0.078. 0.078 being such a small number means that there is not much heat loss which makes polystyrene foam a good insulator. It provides a medium through which there is less transfer of heat.

Read more information on R-value on Wikipedia

This slide provides some background information about the glue that we used for this project. 

There is a wide selection of glues that can be used however Elmer's multi-purpose "Glue-All"  is inexpensive, easily available and works well enough for a series of prototypes.

Hole cutters, such as the one pictured in this slide, are easily available and inexpensive and may be obtained at almost any hardware store. 

It is of course not necessary to use a round contour for this project. 

A thermal chamber created out of straight sides will work just as well, however the radial distribution of heat will be less reliable.

Here is the chamber with two Minco Thermofoils.  Each is attached to a switch and separate USB ports for power.  The USB ports can provide up to 500mA (under specific conditions) at about 4.5 volts.

Here are some of our test results for the thermal chamber.

DISCLAIMER:

We are sharing our experience NOT telling you what to do. 

Do not use Powertools that you have never read the instructions on how to use, maintain or repair.

Do not use anything that spins, heats up, pinches, crushes, shears, dissolves, vaporizes, hyperpolarizes, radiates or otherwise damages human or animal tissues.

If you do anything similar to what we have done it is AT YOUR OWN RISK and the risk of your stuff.

Thanks for viewing this Instructable. 

The next related Instructable will deal with making a USB powered PCR platform. 

The third in this series will deal with a USB powered RT-PCR platform for educational and Field research applications.