Maximum oxidation currents are recorded for different geometries S0, S1, S2, I1, I2 as recorded in phosphate buffer with pH = 7.8. Data are shown for detection of 4AP (cfg. Figure 4), p APP (cfg. Additional File 1), and detection of 4AP after enzymatic degradation of p APP with ALP (cfg. Figure 5). In the case of the enzymatic reaction also the Michaelis-Menten constant KM is given.