Fumagalli L, Esteban-Ferrer D, Cuervo A, Carrascosa JL, Gomila G.
Label-free detection of the material composition of nanoparticles could
be enabled by the quantification of the nanoparticles’ inherent
dielectric response to an applied electric field. However, the
sensitivity of dielectric nanoscale objects to geometric and non-local
effects makes the dielectric response extremely weak.
Here we show that
electrostatic force microscopy with sub-piconewton resolution can
resolve the dielectric constants of single dielectric nanoparticles
without the need for any reference material, as well as distinguish
nanoparticles that have an identical surface but different inner
composition. We unambiguously identified unlabelled ~10 nm nanoparticles
of similar morphology but different low-polarizable materials, and
discriminated empty from DNA-containing virus capsids. Our approach
should make the in situ characterization of nanoscale dielectrics and biological macromolecules possible.