Notes for trouble-shooting. The figure provides an overview of crucial points of the DPI-ELISA and notes for trouble-shooting. At the bottom of the panel the effects of different OPD-solution buffers are shown: A carbonate buffer will lead to the precipitation of the coloured OPD-reaction product, if it accumulates to high amounts. Interestingly the sediment dissolves slowly after stopping the reaction with hydrochloric acid (data not shown). In contrast, a transparent solution is obtained with the CP-buffer before and after addition of stopping solution.