MSE 298 Seminar: DNA Liquids

Abstract: Liquid droplets of biomolecules (aka "condensates") serve as organizers of the cellular interior and are of interest in biosensing and biomaterials applications. Here, I discuss a particular model system of biomolecules formed from multi-armed DNA particles ("nanostars") that can condense into liquid phases through interactions of single-stranded sticky ends that decorate each arm. These phases are analogous to biological condensates but are more colloidal, with each nanostar in the dense phase solely occupying its pervaded volume, rather than entangling in a polymeric fashion with its neighbors. As a result, nanostar liquids are tenuous and highly programmable through control of the sticky-ends, along with being functionalizable through sequence-specific interactions with solutes. I will discuss various aspects of these colloidal DNA liquids, including recent work on the role of finite particle valence in controlling nanostar phase and viscoelastic behavior; the formation of multi-phase droplets and the creation of novel multi-chambered liquid structures; and means to activate nanostar droplets through enzymatic interactions.

Bio: Professor Omar A. Saleh is a physicist and materials scientist with broad expertise in biomolecular and polymer science. Saleh received his B.S. in physics from MIT in 1997, and his Ph.D. in physics from Princeton in 2003. His graduate studies were supported by a Hertz Fellowship. He was a post-doctoral fellow at the École Normale Supérieure in Paris, France, where he developed single-molecule experimental techniques to study motor protein/DNA interactions. He came to UC Santa Barbara in 2005, where he is now a full professor with appointments in the Materials and Physics Departments, along with a minority appointment in the Biomolecular Science and Engineering (BMSE) Program. He served as director of the BMSE program from 2013 to 2017, and was an elected member of the Executive Committee of the Division of Biological Physics of the American Physical Society from 2013 to 2016. Since the summer of 2023, he is the chair of the Materials Department. Saleh's research is focused on the molecular physics underlying biological systems, with particular experience in nucleic acids, protein/DNAinteractions, motor proteins, biomolecular elasticity and self-assembled biomolecular systems. His research achievements were recognized by an NSF CAREER award in 2008, by a Bessel Research Award from the Alexander von Humboldt Society in 2017, and by his selection as a Fellow of the American Physical Society in 2019 by the Division of Biological Physics. More details are available in his CV, linked to the right.