Non-covalent interactions of cadmium sulphide and gold nanoparticles with DNA

Mercaptoethanol-capped CdS nanoparticles (CdS_np) and monohydroxy-(1-mercaptoundec-11-yl)tetraethylene-glycol-capped Au nanoparticles (Au_np) were synthesised, characterised and their interactions with DNA were investigated. Au_np are stable in different aqueous solvents, whereas CdS_np do precipitate in 0.1 M NaCl and form two different cluster types in 0.1 M NaNO₃. As regards the CdS_np/DNA interaction, absorbance and fluorescence titrations, ethidium bromide displacement assays and gel electrophoresis experiments indicate that a non-covalent interaction between DNA and the CdS_np external surface does take place. The binding constant was evaluated to be equal to (2.2 ± 0.5) × 10⁵ M⁻¹. On the contrary, concerning Au_np, no direct interaction with DNA could be observed. Possible interaction with serum albumin was also checked, but no effects could be observed for either CdS_np or Au_np. Finally, short-time exposure of cultured cells to nanoparticles revealed the ability of CdS_np to enter the cells and allocate both in cytosol and nucleus, thus promoting cell proliferation at low concentration (p < 0.005), while longer-time exposure resulted in a significant inhibition of cell growth, accompanied by apoptotic cell death. Au_np neither enter the cells, nor do affect cell proliferation. In conclusion, our data indicate that CdS_np can strongly interact with living cells and nucleic acid while no effects or interactions were observed for Au_np.