Surprises Upon Watching Single Macromolecules in Real Time

This is the age when one risks rolling back Boltzmann’s advances: what can we learn from inspecting individual molecules in favour of the ensemble-average? I will present 2 examples. Using fluorescence correlation spectroscopy in super-resolution mode (STED-FCS) we find that the enhanced diffusivity of enzymes is a “run-and-tumble” process analogous to that performed by swimming microorganisms, executed in this situation by molecules that lack the decision-making machinery of microorganisms. The result is that enzymes display “anti-chemotaxis” when they turn over substrate; they migrate in the direction of lesser reactant concentration. In a second example, we developed methods to image macromolecules in solution using transmission electron microscopy (TEM) in liquid environments where they display interesting properties because of their motions and relaxations. Our recent work shows that liquid samples wrapped between atomically-thin graphene sheets can be imaged so that macromolecules can be imaged one-by-one in real time. A picture emerges in which simple experiments, performed using new experimental methods, lend insight into important matters relevant to soft matter physics.

(work performed in collaboration with Ah-Young Jee, Tsvi Tlusty, Yoon-Kyoung Cho, Sandipan Dutta, Oh-Hoon Kwon, Yejing Kim, Hima Manasa Kandula, and Huan Wang.)