The present invention discloses a method of harnessing versatile phosphoramidation reactions to regioselectively link a group of alkynyl-/azido-containing compounds to post-synthetic nucleic acids primed with phosphate at the 5′ termini. The method includes steps of: (a) monophosphoramidating H2N(CH2)nNH2 to the 5′ end of the nucleic acid to form an intermediate 1 where n is an integer from 2 to 6, and the intermediate 1 has a formula of: (b) amidating the free —NH2 group of the intermediate 1 with to form an intermediate 2; and (c) reacting the terminal —N3 group of the intermediate 2 with 1-{3-{[4-(2-cyclooctyn-1-ylmethyl)benzoyl]amino}propyl}-4-{2-[4-(dimethylamino)phenyl]ethenyl}pyridinium hexafluorophosphate (Alkyne MegaStokes dye 608) by the SPAAC reaction to form modified nucleic acids. Without the presence of Cu(I), the modified nucleic acids were subjected to azide-alkyne cycloaddition in an aqueous solution to obtain various nucleic acid conjugates with a high yield.