A Novel Polydopamine Grafted 3D MOF Nanocubes Mediated GR-5/GC DNAzyme Complex with Enhanced Fluorescence Emission Response toward Spontaneous Detection of Pb(II) and Ag(I) Ions

[Image: see text] In this work, we have proposed a novel DNAzyme/MnCoPBAs-PDANCs complex-based fluorescence biosensor for subsequent detection of Pb(2+) and Ag(+) ions. The GR-5/GC-rich DNAzymes are strongly anchored or quenched on the surface of polydopamine hybridized 3D metal–organic framework MnCoPBAs-PDANCs by π–π stacking interaction. Addition of Pb(2+) ions has exhibited a catalytic inner cleavage of DNAzyme complex and disturbs to release shorter GC-rich sequence over the surface of MnCoPBAs-PDANCs complexes. Later on, addition of intercalating dye ThT interacts with free GC-rich substrate strand to form a G-quadruplex-ThT structure and thereby effectively enhanced the fluorescence intensity (“turn-on”). Interestingly, subsequent addition of Ag(+) ions has an uncoiled GQ-ThT structure to provide a robust double-stranded DNA featuring C–Ag(+)–C, which diminishes (“turn-off”) the fluorescence intensity. This improved hybrid sensor exhibited a linear response in a concentration range of 3–9 nM for Pb(2+), while 4–20 nM for Ag(+) ions with a lower detection limit of 1.6 and 4.2 nM, respectively. Further, the method was successfully implemented for the analysis of Pb(2+) and Ag(+) ions in real water samples with a good regaining and high efficacy for practical analysis.