A single$-$molecule microscopy slide is prepared with $950$ molecules each of magenta, teal,

crimson, and amber fluorescent proteins $($MFP$,$ TFP$,$ CrFP$,$ and AFP$).$ At a concentration of

$3$ nM antibody, results show $870$ molecules of MFP$,12$ of TFP$,3$ of CrFP$,$ and $6$ of AFP are

bound. a$.$ What is the antibody specificity for MFP$?$ b$.$ Determine the KD of the

MFP$$antibody interaction.