Colorimetric visualization of Cu2+ based on Cu2+-catalyzed reaction and the signal amplification induced by K+-aptamer-Cu2+ complex

In this work, we report an ultrasensitive colorimetric sensing strategy for Cu2+ based on the Cu2+ catalyzed TMB-H2O2 reaction, and the signal amplification induced by aptamer-K+-Cu2+ complex. It is demonstrated that Cu2+ exhibits an intrinsic peroxidase-like catalytic activity. Thus, we utilize the catalytic activity of Cu2+ to TMB-H2O2 reaction for direct colorimetric visualization of Cu2+ for the first time. The limit of detection (LOD) is 2.6 μM. To further improve the sensitivity of Cu2+ detection, we utilized G-quadruplex-Cu2+ metalloenzyme complex formed by K+, G-rich DNA, and Cu2+ to amplify colorimetric signal of TMB-H2O2 reaction. The LOD is as low as 0.076 μM, which is 34-fold lower than that of only Cu2+-catalyzed TMB-H2O2 system (2.6 μM). The LOD shows excellent potential for monitoring ultralow levels of Cu2+ in water samples.