(A) Percentage of antibodies and antigens providing accurate detection as a function of target protein concentration. An antibody or antigen was considered to provide qualitatively correct detection at a given concentration if the fluorescence ratio measured at 100% of the replicate spots was above a threshold value. The threshold was calculated by averaging the Cy5/Cy3 fluorescence ratio measured at the lowest tested concentration of the target antibody or antigen and adding two times the standard deviation of these spots. (T = X + 2S, where T = the threshold, X = the average, and S = the standard deviation.) (B) Percentage of antibodies or antigens yielding quantitatively correct results as a function of target protein concentration. An antibody or antigen measurement was considered quantitatively accurate if it both fulfilled the accurate detection criterion in Figure 5A and, in addition, the measured R/G fluorescence ratio was within a factor of two of the true concentration ratio.