Impact of Spacer and Strand Length on Oligonucleotide Conjugation to the Surface of Ligand-Free Laser-Generated Gold Nanoparticles

Gold nanoparticles conjugated to nucleic acids are widely used for biomedical targeting and sensing applications; however, little is known about the conjugation chemistry covering the impact of steric dimension and strand orientation of single-stranded oligonucleotides (ssO) on the conjugation process and binding efficiencies. In this context, we present an extensive investigation concerning the attachment of thiolated ssO to the surface of laser-generated gold nanoparticles, altering both strand length and binding orientation by the insertion of different spacer types at either the 3' or 5' ssO terminus. A significant reduction of conjugation efficiency of about 30-50% is determined for spacer-prolonged bionanoconjugates due to coiling effects of the flexible ssO strand on the particle surface which increases deflection angle of oligonucleotides and limits the number of biomolecules attached to the nanoparticles.