Physical Society Colloquium

Bringing electrostatics to light: Electrometry probes a new dimension at the molecular scale

Madhavi Krishnan

Department of Chemistry
Oxford University

The desire to “freely suspend the constituents of matter” in order to study their behavior can be traced back over 200 years to the diaries of Lichtenberg. From radio-frequency ion traps to optical tweezing of colloidal particles, methods to trap matter in free space or solution rely on the use of external fields that often strongly perturb the integrity of a macromolecule in solution. We recently introduced the ‘electrostatic fluidic trap’, an approach that exploits equilibrium thermodynamics to realise stable, non-destructive confinement of a single macromolecule in a room temperature fluid, and represents a paradigm shift in a nearly century-old field. The spatio-temporal dynamics of a trapped molecule reveals important information on its properties, e.g., size and electrical charge. We have demonstrated the ability to measure the electrical charge of a single macromolecule in solution with a precision much better than a single elementary charge. Since the electrical charge of a macromolecule in solution is in turn a strong function of its 3D conformation, our approach enables for the first time precise, general measurements of the relationship between 3D structure and electrical charge of a single macromolecule. I will present our most recent advances in this emerging area of molecular measurement and demonstrate how high-precision interaction energy measurements may be opening up a unique view of molecular-scale matter in solution.