Cleaning up polymerase chain reactions: Artificially expanded genetic information systems (AEGIS) add extra nucleotide "letters" to DNA alphabets; oligonucleotides containing AEGIS nucleotides do not bind to natural DNA. This "orthogonality" is exploited here by placing two AEGIS nucleotides (P and Z) in external tags for primers targeting three cancer genes in a nested PCR architecture. AEGIS tags support multiplexed PCR with fewer primer dimers and off-target amplicons than multiplexed PCR without AEGIS components.