Abstract
Mercury is a highly toxic element that is found both naturally and as an introduced contaminant in the environment. In light of its severe toxicity, a variety of adverse effects, such as the disruption of cell membranes, the impairment of mitochondrial function, and the inhibition of DNA replication in a cell, are considered highly relevant to Hg2+. In addition, it can also damage the normal functions of organs, like brain, heart, kidney, stomach, and intestines. Generally, the concentration of mercury in natural waters is extremely low. Therefore, it should be desirable to develop a sensitive and selective method for the determination of Hg2+ in the environmental water. In the present study, a new method was developed using oligonucleotide−gold nanoparticle conjugates coupled with ET-AAS to determine mercury ion in water samples. To “sandwich” structure, three complementary sequences were designed with two thymine- thymine (T-T) mismatches. Meanwhile, two particles－magnetic microparticle (MMP) and 20 nm gold nanoparticle (AuNPs)－were used as capture and reporter probes after their conjugation with certain oligonucleotide sequences. In our developed analytical procedure, mercury could be tightly bound by the thymine – thymine (T-T) mismatches by the way of the formation of T-Hg2+-T complex and the melting temperature of this double helix structure (56.6℃) could be increased significantly. To separate the “sandwich” structures containing T-T and T-Hg2+-T, individually, a higher hybridization temperature (59℃) was used to remove through the dissociation of multiplexes containing T-T structure. Thereafter, the AuNPs–oligonucleotide sequences conjugates containing T-Hg2+-T base pairs were collected and determined by ET-AAS through the gold signal. Under the optimized condition, we found that mercury concentration of 0.5 nM(0.1 □g/L) could be measured with sufficient reliability, and a limit of detection (LOD) of 93 ng/L. In addition, larger gold nanoparticles (60 nm) were also employed in this experiment for the purpose to enhance the analysis system sensitivity. We found out using larger gold nanoparticles not only let ∆Tm(T-T and T-Hg2+-T) largely, but also let the melting temperature curve much more sharply. The two properties could enhance the analysis system more selectively, in addition, We found out using larger gold nanoparticles add in aqua regia, we could get more gold ion signal than using 20 nm gold nanoparticles. Finally, under the optimized condition, we found out that mercury concentration of 50 pM (0.01 □g L-1) could be measured with sufficient reliability, and a limit of detection (LOD) of 5.6 ng/L.