DNAzyme-Triggered Dual-MOF Ratiometric Electrochemical Platform for Ultrasensitive Detection of Copper Ion

Aberrant copper (II) homeostasis is intimately linked to numerous neurodegenerative pathologies, yet ultrasensitive detection of Cu 2+ in complex biological matrices remains a challenge due to its trace-level concentrations and pervasive interference. Here, we introduce a novel ratiometric electrochemical sensor that couples Cu 2+ activated DNAzyme with a metal-organic framework (2D MOF) as an intrinsic internal reference and methylene blue loaded in MIL-101(MB@MIL-101) as an external reporting element. Upon Cu 2+ binding, an interfacial DNAzyme cleaves its substrate strand, triggering the release of MB@MIL-101 from the electrode while concomitantly exposing additional electroactive sites on the MOFs. This results in an antiparallel dual-signal response: the MB current ( I MB $I_{\mathrm{MB}}$ ) decreases, and the 2D MOFs current ( I MOFs $I_{\mathrm{MOFs}}$ ) increases, enabling Cu 2+ quantification by the ratio I MB / I MOFs $I_{\mathrm{MB}}/I_{\mathrm{MOFs}}$ . The developed ratiometric platform demonstrates a wide linear range from 10 -12 to 10 -4   M and a remarkable detection limit of 2.37 × 10 -13   M. Furthermore, it demonstrates reliable performance in complex samples such as sweat and serum. Beyond Cu 2+ sensing, this work establishes electroactive MOFs as intrinsic ratiometric calibrants and provides new avenues for DNAzyme-based dual-signal electrochemical biosensing.