(283c) Particle Dynamics in Solutions Containing DNA

abstract: Double-stranded DNA, fundamental to life, exhibits unusual properties compared to those of synthetic polymers. Because the ratio of Kuhn length to width is of order 50, its ratio of excluded volume to occupied volume is large. As a result, DNA entangles at finite concentration, enabling exploration of the transitions from dilute to semidilute to entangled regimes. Here, I will describe experiments examining how particles of different shapes and sizes diffuse in solutions of DNA at low ionic strengths (10^-3 mM to 10¹ mM) across these regimes. We find that the dynamics of semiflexible M13 viruses couple directly to the dynamics of DNA, whereas those of spherical particles couple to the bulk viscosity. Surprisingly, the particle (and hence DNA) dynamics are insensitive to ionic strength across this range. Subsequently, we examine the microrheology of solutions containing both DNA and a synthetic polyelectrolyte, sodium (polystyrene sulfonate) (NaPSS), of comparable coil size under the low salt conditions. Because the DNA dynamics but not the NaPSS dynamics are insensitive to ionic strength in this range, we are able to span from semidilute to entangled regimes and from polyelectrolyte to neutral polymer behavior, with independent tuning knobs governing these transitions. These studies thus provide a first step towards leveraging the polymer physics of DNA to tailor solution viscoelasticity.