Fig. 7

Time-dependent UV-vis spectrum and corresponding k1 values of Nip with a 0.025 mg, b 0.05 mg, and c 0.1 mg of S2; the inset in a is the diagram for reaction of Nip to Amp, and the inset in b is the color change of Nip solution after catalytic reaction. d Normalized concentration change of Nip for 5 cycles in the presence of 0.05 mg of S2