  We observe that sub-GeV Dark Matter (DM) induces Casimir-Polder forces
between nucleons, that can be accessed by experiments from nuclear to molecular
scales. We calculate the nucleon-nucleon potentials arising in the DM effective
theory and note that their main features are fixed by dimensional analysis and
the optical theorem. Molecular spectroscopy and neutron scattering turn out be
DM search experiments, and are found to be complementary to nucleon-based DM
direct detection. Existing data set limits on DM with mass up to $\sim 3-50$
MeV and with effective interaction up to the $O(10-100)$ MeV scale,
constraining a region typically difficult to reach for other experiments.
