A SELEX Protocol to Identify ssDNA Biotemplates for Gold Nanoparticle Synthesis

A modified ssDNA SELEX protocol was developed in order to evolve a randomized library of imidazole modified ssDNA sequences towards sequences that mediate the formation of gold nanoparticles from Au precursor ions in aqueous solution. Active sequences bound to nanoparticles were partitioned from inactive sequences based on density via ultracentrifugation through a discontinuous sucrose gradient. Colloidal gold solutions produced by the evolved pool had a distinct absorbance spectra and produced nanoparticles with a narrower distribution of sizes compared to colloidal gold solutions produced by the starting, randomized pool of imidazole modified ssDNA. Sequencing data from the evolved pool shows that conserved 5 and 6 nt motifs were shared amongst many of the isolates, which indicates that these motifs could serve as chelation sites for gold atoms or help stabilize colloidal gold solutions in a base specific manner.