The darkness density increased with the increasing CGOD/CHRP ratio (shown in Fig. 1). Then, it reached the maximum and kept the constant after adding certain ratio of GOD/HRP. The experimental results suggest that the optimized CGOD/CHRP ratio is 20 while the concentrations of GOD and HRP are 1.2 and 0.06 mg/mL, respectively, in the determination of glucose. When adding CGOD/CHRP ratio is lower than the optimized value, the color signal reduced, while the color signal nearly remains at the same level when introducing CGOD/CHRP ratio is higher than the optimized value.