Oligonucleotide-based fluorescence probe for sensitive and selective detection of mercury(II) in aqueous solution

In this paper we unveil a new homogeneous assay-using TOTO-3 and the polythymine oligonucleotide T-33-for the highly selective and sensitive detection of Hg2+ in aqueous solution. The fluorescence of TOTO-3 is weak in the absence or presence of randomly coiled T-33. After T-33 interacts specifically with Hg2+ ions through T-Hg2+-T bonding, however, its conformation changes to form a folded structure that preferably binds to TOTO-3. As a result, the fluorescence of a mixture of T33 and TOTO-3 increases in the presence of Hg2+. Our data from fluorescence polarization spectroscopy, capillary electrophoresis with laser-induced fluorescence detection, circular dichroism spectroscopy, and melting temperature measurements confirm the formation of folded T-33-Hg2+ complexes. Under optimum conditions, the TOTO-3/T-33 probe exhibited a high selectivity (>= 265-fold) toward Hg2+ over other metal ions, with a limit of detection of 0.6 ppb. We demonstrate the practicality of this TOTO-3/T33 probe for the rapid determination of Hg2+ levels in pond water and in batteries. This approach offers several advantages, including rapidity (< 15 min), simplicity (label-free), and low cost.