  Quark number susceptibilities as computed in lattice QCD are commonly
believed to provide insights into the microscopic structure of QCD matter, in
particular its degrees of freedom. We generalize a previously constructed
partonic $T$-matrix approach to finite chemical potential to calculate various
susceptibilities, in particular for configurations containing a heavy charm
quark. At vanishing chemical potential and moderate temperatures, this approach
predicts large collisional widths of partons generated by dynamically formed
hadronic resonance states which lead to transport parameters characteristic for
a strongly coupled system. The quark chemical potential dependence is
implemented into the propagators and the in-medium color potential, where two
newly introduced parameters for the thermal and screening masses are fixed
through a fit to the baryon number susceptibility, $\chi^B_2$. With this setup,
we calculate heavy-light susceptibilities without further tuning; the results
qualitatively agree with the lattice-QCD (lQCD) data for both $\chi^{uc}_{11}$
and $\chi^{uc}_{22}$. This implies that the lQCD results are compatible with a
significant content of broad $D$-meson and charm-light diquark bound states in
a moderately hot QGP.
