Despite a long history, the reaction of creatinine with ferricyanide remains relatively unexplored, and mechanistic studies and parametric optimization are lacking. This knowledge gap exists because the reaction is difficult to incorporate into colorimetric analysis since ferrocyanide requires further reaction steps to generate a measurable color change, e.g., with Fe 3+ to form Prussian blue (Fig. ). By removing this second step, the two-electrode detector format presented here offers an attractive platform for studying the kinetics and mechanisms of this reaction.