Figure 4.

Inverse linear relationship between the number of thermal cycles it takes for enough amplicons to be synthesized for a significant fluorescent signal to appear (threshold cycle) and the logarithm of the number of retroviral target molecules originally present in a sample. The threshold cycle for each fluorophore was reached when the intensity of the fluorescent signal was 10 times as great as the standard deviation of the background fluorescence. The results demonstrate that quantitative determinations can be made over an extremely wide range of target concentrations, and they show that the assay is sufficiently sensitive to detect as little as 10 molecules of retroviral DNA.