title: Equilibrium gels of trivalent DNA-nanostars: Effect of the ionic strength on the dynamics.
abstract: Self-assembling DNA-nanostars are ideal candidates to explore equilibrium gelation in systems composed of limited-valence particles. We present here a light scattering study of the dynamics in a trivalent DNA-nanostars equilibrium gel and of its dependence on ionic strength and concentration. Reversible bonds between different nanostars, whose formation is sensitively dependent on temperature, concentration and ionic strength, are provided by complementary DNA sticky ends. We find that the decay of the density correlations is described by a two-step relaxation process characterised by: i) a slow time scale that varies over nearly four orders of magnitude in a temperature window of less than 30 degrees; ii) an increase of the amplitude (the so-called non-ergodicity factor) of the slow relaxation. The slow process follows an Arrhenius law with temperature. We observe that the activation enthalpy does not depend on the ionic strength and that the dependence of the relaxation time on the ionic strength can be rationalized in terms of the free-energy cost of forming a sticky-end duplex. Finally, we observe that dynamics is insensitive to nanostar concentration, in full agreement with the predicted behaviour in equilibrium gels.
authors.affiliation: Department of Physics, Sapienza Università di Roma, Piazzale Aldo Moro 2, I-00185, Roma, Italy. francesca.bomboi@uniroma1.it.
authors.forename: Francesca
authors.initials: F
authors.lastname: Bomboi
authors.affiliation: Department of Medical Biotechnology and Translational Medicine, Università di Milano, I-20133, Milano, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Biffi
authors.affiliation: Department of Medical Biotechnology and Translational Medicine, Università di Milano, I-20133, Milano, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Cerbino
authors.affiliation: Department of Medical Biotechnology and Translational Medicine, Università di Milano, I-20133, Milano, Italy.
authors.forename: Tommaso
authors.initials: T
authors.lastname: Bellini
authors.affiliation: Department of Physics and CNR-ISC, Sapienza Università di Roma, Piazzale Aldo Moro 2, I-00185, Roma, Italy.
authors.forename: Federico
authors.initials: F
authors.lastname: Bordi
authors.affiliation: Department of Physics and CNR-ISC, Sapienza Università di Roma, Piazzale Aldo Moro 2, I-00185, Roma, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Sciortino
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000737:chemistry*; D005782:Gels / Q000737:chemistry; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D053758:Nanoparticles / Q000737:chemistry*; D009994:Osmolar Concentration
chemical_list: D005782:Gels; D004247:DNA