A thermal block assembly for use in a biological analysis system includes a sample block, a heating and cooling element, a heat sink including a surface, the surface including a plurality of projections for engaging the heating and cooling element to hold the heating and cooling element on the heat sink. A thermal block assembly for use in a biological analysis system includes a heating and cooling element, a sample block including a lower surface configured to be thermally coupled to the heating and cooling element, one or more temperature sensors configured to extend through the one or more slots of the lower surface of the sample block, and one or more thermal pads between the one or more temperature sensors and heating and cooling element.