Chiral
biological and pharmaceutical molecules are analyzed with
phenomena that monitor their very weak differential interaction with
circularly polarized light. This inherent weakness results in detection
levels for chiral molecules that are inferior, by at least six orders
of magnitude, to the single molecule level achieved by state-of-the-art
chirally insensitive spectroscopic measurements. Here, we show a phenomenon
based on chiral quantum metamaterials (CQMs) that overcomes these
intrinsic limits. Specifically, the emission from a quantum emitter,
a semiconductor quantum dot (QD), selectively placed in a chiral nanocavity
is strongly perturbed when individual biomolecules (here, antibodies)
are introduced into the cavity. The effect is extremely sensitive,
with six molecules per nanocavity being easily detected. The phenomenon
is attributed to the CQM being responsive to significant local changes
in the optical density of states caused by the introduction of the
biomolecule into the cavity. These local changes in the metamaterial
electromagnetic environment, and hence the biomolecules, are invisible
to “classical” light-scattering-based measurements.
Given the extremely large effects reported, our work presages next
generation technologies for rapid hypersensitive measurements with
applications in nanometrology and biodetection.