Electrostatically tuned DNA adsorption on like-charged colloids and resultant colloidal clustering

Abstract

The adsorption of λ-DNA on like-charged silica particles and the resultant DNA-colloid complex structures are examined microscopically in this work. Enhanced adsorption of fluorescence labeled DNA on unlabeled silica particles of varied COOH- and NH2-end functionality is observed with the addition of monovalent or divalent salts to aqueous suspensions of constant DNA and colloid concentrations, which results in an apparent fluorescent shell-like structure for DNA-adsorbed silica particles. ζ-potential measurements indicate that the functionalized silica particles have a negative net charge at all varied ionic strengths, suggesting that screened electrostatic repulsion can account for the enhanced adsorption of DNA on like-charged silica particles in high salt aqueous media, despite the possible hydrophobic origin of the adsorption of DNA in low salt media. Additionally, curious DNA-mediated colloid clustering to form colloidal doublets and triplets is observed for the mixed DNA-colloid suspensions. The optimal DNA and salt concentration ranges are explored and a phase diagram is obtained to predict the formation of considerable fractions of DNA-induced colloidal doublet clusters, which could lead to a simple and rapid method for the synthesis of functional colloidal clusters of desirable shape and bio-functionality.