𝐾 𝑑 (10) During an ELISA experiment, as proposed by Friguet , a constant concentration of phages is incubated with different concentrations of TnT. Saturation of phages (in solution) by soluble TnT limits the ability of phages to bind to immobilised TnT, and therefore, increasing concentration of TnT causes a decrease in signal from the phages, in our case the M13.