Sorry, but in this case, it's actually N^x. Even running PCR and gel analysis requires steps where the time is dependent on the number of samples (e.g. pipetting, walking to the centrifuge, making multiple gels)
Are you really saying that going from 10 samples to 11 samples causes a doubling (or 1.2x-ing or tripling or whatever) of the time/work required? That's what exponential means.