Figure 4.

Lanthanide-encoded beads used for the MFA, where the capture probe is identified by the lanthanide-derived optical code of the bead to which it is attached, are optically encoded ratiometrically with multiple lanthanide emitters (in this case Er, Sm, and Tm) creating “optical bins” into which the beads are sorted for identification. The individual beads are shown enclosed by a tetragon representing the optical bin. As the beads are identified from the ratio of emission intensity of multiple lanthanide emitters, and not the absolute intensity of the emission, the measured ratios are independent of the bead size, excitation source brightness, angle of illumination, sample–detector distance, detector efficiency, etc.; thus, many bead sizes may be used (Figure 2g). The optical bins and bead data points are falsely colored for clarity as most encoded beads with three or more lanthanide emitters appear whitish to the eye.