Theoretically, two options have to be discussed: (1) a signal (a) is generated for each phage with at least one unoccupied active site (Eq.11), (2) a signal (a) is generated proportionally to the total concentration of unoccupied active sites (Eq.12). The first variant would be more probable for high TnT surface density (significantly higher capability than phages present in solution) where phages are mostly bound to the layer. According to the second variant, it is also possible that the recognition and binding process is slow enough to make the reaction kinetically limited. In this case, phages with a higher number of free active sites are more likely to be bound than more saturated ones. Nevertheless, the incubation times during ELISA and preincubation are comparable, and an equilibrium state can achieve equilibrium in both stages.