Influence of the nature of quantum dot surface cations on interactions with DNA

Quantum dots are semiconductor nanoparticles that are ∼1–10 nm in diameter, similar to small proteins, and their photoluminescence is sensitive to the presence and nature of adsorbates. We have deployed these nanomaterials as luminescent probes of DNA structure. Sequence dependent conformational flexibility of DNA is of great interest due to its implications for drug–DNA and DNA–protein interactions. The counterion atmosphere surrounding DNA plays an important role in its structure, dynamics, and packaging. In this paper, we investigate the effect that various monovalent and divalent cations have on the binding of 4.5 nm CdS quantum dots to oligonucleotides that have sequence-directed intrinsic structure.