I am trying to design a primer using NCBI's Primer Blast for real time PCR. I limited my product size from 70 bp to 200 bp. I also choose "Primer must span on exon-exon junction". Since all of the exons are larger than 200 bp, I did not get any primer that match my criteria.
I am just wondering if I do not design primer on exon-exon junction for my qPCR, what other measure can be taken to rule out/ discriminate DNA contamination?