  We address the measurement of density of states within and beyond the
superconducting gap in tunnel-coupled finite-size nanostructures using a
capacitive method. Third-harmonic generation is used to yield the full
differential conductance spectrum without destruction of the low dimensionality
otherwise induced by intimate ohmic coupling to an electrode. The method is
particularly relevant to attempts to discern the presence of the fragile
Majorana quasiparticle at the end of spin-orbit-coupled nanowires in
appropriate magnetic field conditions by their signature mid-gap density of
states.
