Temperature- and Salt-Dependent Binding of Long DNA to Protein-Sized Quantum Dots: Thermodynamics of “Inorganic Protein”−DNA Interactions

The adsorption of calf thymus DNA to 45 A nanoparticles of Cd(II)-rich CdS has been examined by photoluminescence spectroscopy as a function of temperature. The resulting van't Hoff plot suggests that the driving force for adsorption is entropy, and the enthalpic contribution to DNA−surface binding is slightly unfavorable. A likely source of the increase in entropy upon binding is release of solvent and/or counterions from the interface, analogous to what has been observed for nonspecific protein−DNA interactions. Reverse salt titrations suggest that counterion release is a substantial component of the nanoparticle−DNA interaction.