An Innovative Trimetallic-MOF mediated Catalytic Cleavage activity of FAM tagged Ag10/T-rich DNAzyme as an Ultra-Sensitive and Selective Fluorescent Biosensor for Subsequent Recognition of Ag+ and Hg2+ Ions

• A novel Trimetallic-MOF was synthesized as an efficient fluorescent quencher and DNA adsorbent. • The catalytic cleavage process-based specific FAM tagged Ag10/T-rich DNAzyme was innovatively designed for the recognition of Ag + and Hg 2+ ions. • The proposed bio-sensing system can achieve low detection limits of Ag + (0.29 nM) and Hg 2+ (0.10 nM). In this work, specific and sensitive recognition of the dual metal ions (Ag + & Hg 2+ ) through the FAM tagged Ag10/T-rich DNAzyme mediated Trimetallic-MOF (Ni/Zn with K 3 [Co (CN) 6 ]) as a biochemical sensing platform. Interestingly, the fluorescence probe of the FAM tagged specific Ag10/T-rich DNAzyme, and the Trimetallic-MOF demonstrated excellent analytical response towards subsequent recognition of the Ag + & Hg 2+ ions compared to the other coexisting targets. More precisely, the silver enzyme oligomer (EO) and FAM tagged thymine rich substrate oligomer (SO) were hybridized to form the Ag10/T-rich DNAzyme structure. When the Ag + ion is induced into the Trimetallic-MOF with the FAM tagged Ag10/T-rich DNAzyme complex caused higher efficient internal catalytic cleavage at RNA site of FAM tagged substrate oligomer (SO). The released FAM tagged T-rich SO sequence was adsorbed on the Trimetallic-MOF surface through π-π stacking and electrostatic interactions, which diminished (Turn-OFF) the fluorescent signal. Surprisingly, the subsequent addition of the Hg 2+ ions into the above-quenched system (Trimetallic-MOF/cleaved FAM tagged SO, and EO with Ag + ) resulted in an enhancement of the fluorescence intensity (Turn-ON) due to the creation of the double-strand structure (T-Hg 2+ -T). By utilizing this sensor, susceptible and discriminating recognition of the Ag + and Hg 2+ ions is attained through the subsequent processes of catalytic cleavage of the DNAzyme and the FRET mechanism. As a result, the proposed biosensor achieved low detection limits of Ag + (0.29 nM) and Hg 2+ (0.10 nM), respectively. The utility of the developed fluorescence biosensor was established due to the subsequent recognition of the Ag + and Hg 2+ in actual water samples with satisfactory regaining and good reproducibility.