Stock latex particles were vortexed and sonicated prior to use. The particles were then washed and resuspended in 0.1 M MES, pH 6.1 (Teknova, M225). The beads were covalently coupled to the antibodies in a two-step process. First, the beads are activated using freshly prepared EDC and NHS in MES. After 30 minutes, the beads were washed and resuspended in PBS pH 7.2. Antibodies were added at the ratios described above, and the activated beads were mixed with the antibodies for 3 hours with end-over-end mixing.