Diffusive behaviour of PLL–PEG coated colloids on λ-DNA brushes – tuning hydrophobicity

Abstract

We find ‘sticky’ 2D diffusion of poly-L-lysine–polyethylene glycol (PLL–PEG) coated silica colloids sedimented onto a brush of long, double stranded λ-DNA. The interaction is hypothesised to be hydrophobic, due to known physical properties of single and double stranded DNA and the systematic elimination of other known forces. The colloids are found to have variable affinity to the surface when prepared at different pH, even when the electrostatic environment of the brush is kept identical. Varied diffusive behaviour is observed: the diffusivity increases when the incubation pH is higher, and fewer beads are stuck to the brush surface. This sensitivity is found to agree with a simple model for the adsorption conditions of the PLL on the silica spheres. The significance of hydrophobicity is confirmed by capping the ssDNA ‘sticky’ end of the DNA, leading to a drastic enhancement of diffusivity of the particles on the brush.