Click chemistry-mediated cyclic cleavage of metal ion-dependent DNAzymes for amplified and colorimetric detection of human serum copper (II)

Abstract

The determination of the level of Cu²⁺ plays important roles in disease diagnosis and environmental monitoring. By coupling Cu⁺-catalyzed click chemistry and metal ion-dependent DNAzyme cyclic amplification, we have developed a convenient and sensitive colorimetric sensing method for the detection of Cu²⁺ in human serums. The target Cu²⁺ can be reduced by ascorbate to form Cu⁺, which catalyzes the azide-alkyne cycloaddition between the azide- and alkyne-modified DNAs to form Mg²⁺-dependent DNAzymes. Subsequently, the Mg²⁺ ions catalyze the cleavage of the hairpin DNA substrate sequences of the DNAzymes and trigger cyclic generation of a large number of free G-quadruplex sequences, which bind hemin to form the G-quadruplex/hemin artificial peroxidase to cause significant color transition of the sensing solution for sensitive colorimetric detection of Cu²⁺. This method shows a dynamic range of 5 to 500 nM and a detection limit of 2 nM for Cu²⁺ detection. Besides, the level of Cu²⁺ in human serums can also be determined by using this sensing approach. With the advantages of simplicity and high sensitivity, such sensing method thus holds great potential for on-site determination of Cu²⁺ in different samples.

Graphical abstract