  Cells use surface receptors to estimate the concentration of external
ligands. Limits on the accuracy of such estimations have been well studied for
pairs of ligand and receptor species. However, the environment typically
contains many ligands, which can bind to the same receptors with different
affinities, resulting in cross-talk. In traditional rate models, such
cross-talk prevents accurate inference of individual ligand concentrations. In
contrast, here we show that knowing the precise timing sequence of stochastic
binding and unbinding events allows one receptor to provide information about
multiple ligands simultaneously and with a high accuracy. We argue that such
high-accuracy estimation of multiple concentrations can be realized by the
familiar kinetic proofreading mechanism.
