Using Förster resonance energy transfer (FRET) images we study the possibility of estimating the equilibrium dissociation constant $K_d$ and the intrinsic FRET efficiency $E_m$ from single cells. We model the measurement uncertainty in the acquired images and use the method of total least squares for estimation based on the pixel values in the images. Considering a population of cells we demonstrate a variability in the estimates of $K_d$ and $E_m$ that cannot be explained by measurement noise and therefore points to systematic variation between images.

Keywords: Förster resonance energy transfer; protein-protein interaction; fluorescent proteins.