The autocatalytic kinetic traces collected with P4 over 90 min at pH 8.5 attest of a rather fast autocatalytic reaction (Figure ), approximately 4-fold faster than P3 at the same pH. This gain in analysis time is clearly the result of the better redox cycling properties of 2-MeO-1,4-NQ as compared to 1,4-NQ, compensating thus for the slower H2O2 deprotection rate. This gain in time also almost completely translates into a gain in LOD since the detection limits for P3 and P4 are 0.2 and 0.06 µM H2O2, respectively (Figure ). The fact that the faster kinetics with P4 results in a better LOD is not surprising because, as we had previously demonstrated from theoretical analysis of a crosscatalytic system, 36 reaction time and detection limit are both inversely proportional to the geometric mean of each loop's rate (this corresponds to the limiting case where detection of H2O2 is mainly restricted by the nonspecific response resulting from NADH autoxidation).