Oligonucleotide adsorption to gold nanoparticles: A surface-enhanced raman spectroscopy study of intrinsically bent DNA

We have examined the adsorption of short 16 base pair DNA to 14 nm protein-sized gold particles using surface-enhanced Raman spectroscopy and electronic absorption spectroscopy. In the presence of KCI, we find greater Raman enhancement of adenine and guanine ring breathing vibrations (per adenine and guanine present in each sequence) for crystallographically "kinked" oligonucleotide than for the DNA-particle interactions for "bent" A-tract and "straight" oligonucleotides. The calculated binding constants are within the range of nonspecific protein-DNA interactions and are nearly the same for each sequence. The difference in the surface plasmon frequency of the gold particles in the presence of either straight, bent, or kinked DNA is attributed to differences in the DNA-mediated aggregation of the nanoparticles. Specifically, the displacement of the gold's stabilizing citrate ions seems to vary with DNA sequence, and this controls the residual interparticle electrostatic interaction and average interparticle separation in the aggregate.