The heart of Thermal Gradient's technology is surprisingly simple. The fundamental principles are the same ones at work in the thermal pane windows used in most houses today. In modern windows, a "thermal gradient" is established within the window structure where the room side is comfortable and the outside is hot (or cold).
All of Thermal Gradient's devices are constructed of multiple layers, some of which are made from materials that conduct thermal energy very well and others that act as insulators. The device in the illustration is an typical example. The front (denaturing) and back (annealing, extension) layers are made from a thermally conductive material. Plastic, which is an excellent thermally insulating material, separates the conductive layers.
When used in Thermal Gradient's systems, the front layer is placed in contact with a heating device that is maintained at the desired denaturing temperature, around 95°C. The system also maintains the back layer at the desired annealing and extension temperature, around 60°C. This establishes a "thermal gradient" within the device. (The actual temperatures are precisely established by the device design as required by the desired PCR protocol.)
Because of the differences in the layer material properties, each of the conductive layers (denaturing, annealing and extension) are uniformly at each of the desired PCR temperatures. The large differences between these temperatures are contained within the insulating layers.
The thermally conducting layers have channel sections in them. The insulating layers have holes or "vias" that connect the channel sections from one layer to another. When assembled, the device contains one long channel (about 2 feet!). The path of the channel goes from the denaturing layer, to annealing and extension, and then back to denaturing. This is repeated for as many PCR cycles as is designed into the device. The device in the illustration has 54 PCR cycles.
In use, the PCR sample is routed into the inlet port of the device and moved through at a constant speed. As the sample moves from layer to layer, it is exposed to each of the temperatures in each PCR cycle.
It is important to note that once the device is secured in Thermal Gradient's instrument and the top and bottom layers are established at the denaturing and annealing temperatures, there is no "thermal cycling" in the system or the device. The only thing that changes temperature is the sample itself as it moves from layer to layer to layer. This is the reason why PCR in Thermal Gradient devices is so incredibly fast and why we say, "PCR as Fast as Nature Will Allow."