Thermal cycler for PCR

An apparatus for performing the polymerase chain reaction in a plurality of liquid reaction mixtures, said apparatus comprising:

• an assembly adapted for cycling a plurality of vials through a series of temperature excursions, the assembly comprising:
• a sample block for receiving a microtiter plate having the plurality of vials, wherein in a position of the microtiter plate received by the sample block, the vials are optically accessible by an optical reader without opening the vials;
• a heated cover having a platen and a skirt surrounding a perimeter of and extending from the platen, the platen comprising a plurality of recesses sized to allow optical access to the vials, and the skirt being configured to engage and align to the microtiter plate in the position of the microtiter plate received by the sample block;
• a plurality of thermoelectric devices,
• a heatsink, and
• a seal element surrounding and contacting a perimeter of the sample block and configured to seal off the plurality of thermoelectric devices, wherein the seal element is in contact with an inner surface of the heated cover surrounding the sample block;
• and
• a computing apparatus configured for controlling said temperature excursions of said assembly.