  We investigate a model nanopore sensor that is able to detect analyte ions
that are present in the electrolyte solution in very small concentrations. The
nanopore selectively binds the analyte ions with which the local concentrations
of the ions of the background electrolyte (KCl), and, thus, the ionic current
flowing through the pore is changed. Analyte concentration can be determined
from calibration curves. In our previous study (M\'{a}dai et al. J. Chem.
Phys., 147(24):244702, 2017.), we proposed a symmetric model (surface charge is
negative all along the pore). The mechanism of sensing was a competition
between K$^{+}$ and positive analyte ions, so increasing analyte concentration
decreased K$^{+}$ current. Here we allow asymmetric charge patterns on the pore
wall (positive/negative/neutral along the pore), thus, gaining an additional
device function, rectification, resulting in a dual responsive device. We find
that a bipolar nanopore is an efficient geometry with Cl$^{-}$ ions being the
main charge carriers. The mechanism of sensing is that more positive analyte
ions attract more Cl$^{-}$ ions into the pore thus increasing the current. Also
they make the pore less asymmetric and, thus, decrease rectification. We use a
hybrid computer simulation method, where a generalization of the grand
canonical Monte Carlo method to non-equilibrium (Local Equilibrium Monte Carlo)
is coupled to the Nernst-Planck equation with which the flux is computed.
