Cu²⁺-mediated telomeric dimeric G-quadruplex DNAzyme for highly sensitive colorimetric detection of deferasirox

Deferasirox (DEF) is an important iron chelator for treatment of iron overload-related diseases. Monitoring DEF concentration in human serum will provide some valuable information for clinical diagnosis and therapy of such diseases. In this study, we developed a peroxidase-mimicking colorimetric sensor for the detection of DEF by simple assembly of a telomeric dimeric G-quadruplex DNAzyme with Cu²⁺. The DNAzyme-catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine in the presence of H₂O₂ can generate a quantitative colorimetric signal, and the color change can be discerned by the naked eye. Compared with the reaction rate of the monomeric G-quadruplex-Cu²⁺ DNAzyme, the reaction rate of the dimeric G-quadruplex-Cu²⁺ (G2-Cu²⁺) DNAzyme is significantly accelerated, and the reaction rate gradually increases and then reaches a plateau with increasing number of TTA spacers. Herein, the G2-Cu²⁺ DNAzyme is chosen for the highly sensitive detection of DEF based on the DEF-Cu²⁺ complex-induced inhibition of its peroxidase-mimicking activities. The limit of detection (LOD) of DEF is achieved as low as 0.03 μM, and the linear range is from 0.05 to 1.2 μM. The proposed strategy exhibits excellent selectivity in the presence of potential interferents, such as metal ions and small molecules. Importantly, the G2-Cu²⁺ DNAzyme is further expanded to detect DEF in dispersible tablets and human serum samples. Overall, this G2-Cu²⁺ DNAzyme provides a simple, low-cost, and rapid platform for DEF detection. This novel strategy is the first example of DEF analysis by utilizing signal amplification technology based on the G-quadruplex DNAzyme and holds great potential for DEF quality control and therapeutic drug monitoring.