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

Mercaptoethanol-capped CdS nanoparticles (CdSnp) 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 CdSnp do precipitate in 0.1 M NaCl and form two different cluster types in 0.1 M NaNO3. As regards the CdSnp/DNA interaction, absorbance and fluorescence titrations, ethidium bromide displacement assays and gel electrophoresis experiments indicate that a non-covalent interaction between DNA and the CdSnp external surface does take place. The binding constant was evaluated to be equal to (2.2 +/- A 0.5) x 10(5) 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 CdSnp or Au-np. Finally, short-time exposure of cultured cells to nanoparticles revealed the ability of CdSnp 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 CdSnp can strongly interact with living cells and nucleic acid while no effects or interactions were observed for Au-np.