Successive and Specific Detection of Hg2+ and I– by a DNA@MOF Biosensor: Experimental and Simulation Studies

A 2D metal–organic framework (MOF) of {[Cu(Dcbb)(Bpe)]·Cl}n (1, H2DcbbBr = 1-(3,5-dicarboxybenzyl)-4,4′-bipyridinium bromide, Bpe = trans-1,2-bis(4-pyridyl)ethylene)) has been prepared. MOF 1 associates with the thymine-rich (T-rich), single-stranded probe DNA (ss-DNA, denoted as P-DNA) labeled with fluorophore FAM (FAM = carboxyfluorescein) and quenches the FAM emission to give a nonemissive P-DNA@1 hybrid (off state). The P-DNA in the hybrid subsequently captures the Hg2+ to give a rigid double-stranded DNA featuring T–Hg2+–T motif (ds-DNA@Hg2+) and detach from MOF 1, triggering the recovery of the FAM fluorescence (on state). Upon subsequent addition of I–, Hg2+ was further sequestrated from the ds-DNA@Hg2+ duplex, driven by the stronger Hg–I coordination. The released P-DNA is resorbed by MOF 1 to regain the initial P-DNA@1 hybrid (off state). The P-DNA@1 sensor thus detects Hg2+ and I– sequentially via a fluorescence “off–on–off” mechanism. The sensor is highly selective and sensitive, yielding detec...