Abstract
Mercury is a toxic element that exists in metallic, inorganic, and organic forms. Among which, the toxicity of Hg2+ is well-known and can cause the disruption of cell membranes, the impairment of mitochondrial function, and the inhibition of DNA replication in a cell. In addition, it also damages the organs like brain, heart, kidney, stomach, and intestines. Hg2+ is easily ingested by human beings due to its high water solubility; therefore, it should be desirable to develop a sensitive and selective method which is able to detect and quantify Hg2+ existing in environmental waters. To explore the possibility of using nanosensing techniques for the detection of trace Hg2+ ions in aqueous samples, we have developed two independent methods in this study. In the first experiment, a sandwich structure containing magnetic microparticles (MMPs), duplex sequences, and gold nanoparticle (AuNPs) coupled with UV/Vis spectrophotometric and ET-AAS was employed to determine mercuric ion. In which, the duplex sequence was designed with one thymine-thymine (T-T) mismatch for the purpose to specific recognize the mercuric ions. Based on our observations, as higher concentration of mercuric ion is present in the samples, the melting temperature (Tm) of duplex hybrids in the sandwich structure would shift to higher temperature; moreover, different concentrations of mercuric ions could result in different Tm. To utilize this phenomenon to determine mercuric ion and improve its sensitivity, we altered the positions of the T-T mismatch within the duplex to enhance the Tm shift with the participation of Hg2+ as well. In our developed analytical procedure, we found the utility of 1078-4th double helix structure can reach the largest melting temperature shift (5.3℃). To separate the “sandwich” structures containing T-T and T-Hg2+-T, individually, a higher hybridization temperature (60℃) 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 UV/Vis spectrophotometry through the AuNPs absorption. Under the optimized condition, we found that Hg2+ concentration of 0.67 nM (0.134 □g L-1) could be measured with sufficient reliability. In the second experiment, we demonstrate that functional DNA-linked gold nanoparticles (AuNPs) can quickly, simply detect Hg2+ ions in aqueous solution. A linker DNA molecule which contains thymine residues and is complementary to the DNA sequences on the AuNPs was designed to form sandwich structures by react with magnetic microparticle probes. When Hg2+ ions were present in the sample, Hg2+ ions can cause the Hg2+ aptamer DNA sequences to fold by forming thymine-Hg2+-thymine bonds. Thereafter, the folding of Hg2+ aptamer DNA can unwind the AuNPs probe rapidly and disassemble the sandwich structure. To detection the released AuNPs probes, we tried to use UV/Vis spectrophotometer and ET-AAS as the end-determination means. Based on the experimental results, the lowest distinguishable concentration was 20 nM (4.0 □g L-1) through the use of ET-AAS.