Fluorescent DNA Labeling by PCR Introduction Amplification of DNA using the polymerase chain reaction (PCR)* provides the opportunity to label the resulting product with either modified nucleotides or oligonucleotide primers. Incorporation of fluorescent labels offers the advantages of direct detection, sensitivity, and multicolor capability. Both fluorescently labeled deoxynucleotide triphosphates (dNTPs) and fluorescently end-labeled oligonucleotide primers are available for use in PCR product labeling.