Determination of post-amplification DNA labeling efficiency via streptavidin (SA) gel shift. (A) Labeling strategy (illustrated for dTPT3PA-dNaM; B = biotin). (B) Labeling with unnatural base pair centrally located in 134mer duplex. The faster and slower migrating bands corresponds to dsDNA, and the 1:1 complex between dsDNA and streptavidin, respectively. (C) Labeling with unnatural base pair positioned at first, ninth, or eleventh positions, corresponding to duplexes 1–3, respectively.