Highly sensitive and selective spectroscopic detection of mercury(II) in water by using pyridylporphyrin-DNA conjugates

Single-labeled pyridylporphyrin-DNA conjugates are reported as highly sensitive and selective spectroscopic sensors for mercury(II) ions in water. The effects of chemical structure (thymine versus adenine), number of nucleotides (monomer versus octamer), and porphyrin metalation (Zn versus free base) on the sensitivity and selectivity of mercury(II) detection are explored. The results indicated that pyridylporphyrin rather than the nucleobase plays a crucial role in mercury(II) sensing, because porphyrin conjugates with both adenosine and thymidine exhibited excellent mercury(II) detection. Mercury(II) recognition was shown in emission quenching, as well as in a redshift of the porphyrin Soret band absorption. The limit of detection (LOD, 3σ/slope) of zinc(II) pyridylporphyrin-5′-oligodeoxythymidine (ZnPorT8) obtained by fluorescence quenching was calculated to be 21.14 nM. Other metal cations (Zn²⁺, Cd²⁺, Pb²⁺, Mn²⁺, Ca²⁺, Ni ²⁺, Mg²⁺, Fe²⁺, Cu²⁺, and Na ⁺) did not interfere with the emission and absorption sensing of mercury(II). Free-base porphyrin-oligothymine conjugate 2HPorT8 displayed similar sensitivity to ZnPorT8 but different selectivity. The results also implied that the sensing properties of porphyrin-deoxythymidine conjugates could potentially be tuned by porphyrin metalation. Dark H(u)g: Mercury(II) quenches the emission of pyridylporphyrin-DNA conjugates (see figure), which allows its detection in water in the presence of other heavy metals. The effect of chemical structure, number of nucleotides, and porphyrin metalation on the sensitivity and selectivity of detection is explored. The results indicate that porphyrin, rather than thymine, plays a crucial role in mercury(II) sensing.