IUPAP’s General Assembly

By PoreLab12 October, 2017Uncategorized

The International Union of Pure and Applied Physics is in some sense the “Physics United Nations.” Alex Hansen is participating at the triannual General Assembly (October 9-13, 2017) in Sao Paulo as outgoing vice president at large. IUPAP President Bruce McKellar has just written this article for Physics Today describing what IUPAP is doing: Commentary: International Union of Pure and Applied Physics and you.

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Our guest, Dr. Erika Eiser, Reader in Soft Matter Physics, Cavendish Laboratory, University of Cambridge will give a presentation on “Microrheology of DNA hydrogels” on October the 22nd at PoreLab premises (PTS2, 2nd floor), starting at 13:15. Welcome!

Abstract. The specificity of DNA-hybridization allows us to form multi-valent nanostars similar to molecules with a given valency. However, different to regular molecules we can assign to each arm in the DNA-nanostar a given binding strength by varying the length and sequence of the single-stranded DNA terminating the arms. Such specificity has been used to self-assemble short DNA oligomers into 2D and 3D origamis with prescribed nanostructures. Here I will introduce Y-shaped DNA nanostars that can self-assemble into a continuous, viscoelastic hydrogel. Using Diffusing-Wave Spectroscopy (DWS), we were able to monitor the change of the viscoelastic modulus G*(w) of our solution of Y-shaped DNA nanostars goes from a completely fluid to predominantly elastic system over a wide range of frequencies and function of temperature [1,2]. Our micro- rheological measurements reveal that these hydrogels behave like transient networks made of flexible polymers, when building in some flexible linkers. But differently to most (bio)polymeric networks we can form and melt our DNA hydrogels reversibly by cooling or heating the systems. Moreover, by changing the strength of the sticky overhangs of the Y-shapes we can control the temperature at which the liquid to gel transitions occurs. Finally, our measurements allow us to associate the melting temperature at which this transition occurs as the system’s percolation transition.

[1] Z. Xing et al. ‘Microrheology of DNA hydrogels’, PNAS 115, no. 32 (2018),

[2] I. Stoev et al. ‘Single-Beam Optical Tweezers for the Passive Microrheology of Complex Fluids’ SPIE proceedings, paper 10723-91 (2018)