Ruggeri, F. et al. Nat. Nanotechnol. http://dx.doi.org/10.1038/nnano.2017.26 (2017).

The electrostatic properties of biological molecules are functionally important, but the direct and precise measurement of molecular charge has remained a challenge. Ruggeri et al. describe single-molecule electrometry, a method to measure the electrical charges of single macromolecules, including proteins and nucleic acids. In this approach, a charged molecule labeled with two fluorescent dyes is electrostatically trapped in solution. The time it takes for the molecule to escape the trap is measured by fluorescence microscopy, and it is used to calculate the molecule's effective electrical charge. The authors demonstrate the application of electrometry for detecting single amino acid substitutions and chemical modifications, and they note that it could be employed more generally to probe the structure and interactions of single biomolecules.