Herein we present a method for the simultaneous, multiple conjugation of alkynyl-(Gd(III)-DOTA) moieties to a PNA oligomer possessing a domain of azide residues. This is achieved in a single Huisgen type copper-catalyzed azide alkyne cycloaddition (CuAAC) reaction after the oligomer assembly is completed. A triplex formed between the labelled PNA and riboadenylic acid, [(Gd(III)-DOTA)4–PNA]2:poly(rA), displayed higher relaxivities at any field strength compared to the single-stranded probe at the same concentration of Gd3+ ions as determined by nuclear magnetic resonance dispersion (NMRD) studies.
