Primer and probe sequence designs are among the most critical input factors in real-time polymerase
chain reaction (PCR) assay optimization. In this study, we present the use of statistical design of experiments
(DOE) approach as a general guideline for probe optimization and more specifically focus on design
optimization oflabel-free hydrolysis probes that are designated as mediator probes (MPs), which are used
in reverse transcription MP PCR (RT-MP PCR). The effect of three input factors on assay performance was
investigated: distance between primer and mediator probe cleavage site; dimer stability of MP and target
sequence (influenza B virus); and dimer stability of the mediator and universal reporter (UR). The results
indicated that the latter dimer stability had the greatest influence on assay performance, with RT-MP
PCR efficiency increased by up to 10% with changes to this input factor. With an optimal design configuration,
a detection limit of 3–14 target copies/10 l reaction could be achieved. This improved detection
limit was confirmed for another UR design and for a second target sequence, human metapneumovirus,
with 7–11 copies/10 l reaction detected in an optimum case. The DOE approach for improving oligonucleotide
designs for real-time PCR not only produces excellent results but may also reduce the number
of experiments that need to be performed, thus reducing costs and experimental times.