Study On The Novel Bisensors For Recognition Of Mercury (Ⅱ) Based On Gold Nanoparticles And Their Applications

Mercury is an extremely toxic and widespread global pollutant with lethal effects on the environment and human health. Most of mercury emissions arise from solid waste incineration and the combustion of fossil fuels. The emitted elementary mercury vapors are easily transported in the atmosphere, often across continents and oceans, and are eventually oxidized to Hg (Ⅱ). Atmospheric deposition of Hg (Ⅱ) results in its accumulation on plants, in topsoil, and in water. Irrespective of the source and initial site of deposition, Hg (Ⅱ) ultimately enters freshwater and marine ecosystems. Furthermore, bacteria living in the marine environment convert Hg (Ⅱ) into methylmercury, which enters the food chain and biomagnifies in higher organisms, especially in the muscles of large predatory fish, including tuna, swordfish, and whales, and is subsequently ingested by humans. Neurological problems associated with methylmercury intoxication are manifold and include prenatal brain damage, cognitive and motion disorders, vision and hearing loss, and death. Hence, it is very essential to develop the fast, sensitive, and selective analytical methods for monitoring trace Hg (Ⅱ) in environment and food.Traditional quantitative approaches to Hg (Ⅱ) analysis in water samples employ a number of analytical techniques that include atomic absorption spectroscopy, cold vapor atomic fluorescence spectrometry, and gas chromatography. Many of these methods require complicated, multistep sample preparation and/or sophisticated instrumentation. More recently, it has been reported that mercury ions can selectively bind thymine-thymine pairs in DNA sequences to form T-Hg2+-T complexes. Several sensors of Hg2+ based on T-Hg2+-T complexes have been developed and showed great selectivity and sensitivity.The goal of the present study is to design the novel sensors for recognition of mercury (Ⅱ) with high sensitivity and selectivity based on the complexes of T-Hg2+-T and gold nanoparticles. This paper combines the excellent characteristics of gold nanoparticles, the high specificity of biomolecules, the simplicity of colorimetric thechniques, and the sensitivity of electrochemical methods. The proposed sensors open novel perspectives for determination of Hg (Ⅱ) in biological and environmental samples. The dissertation includes four parts:Chapter One:IntroductionIn the beginning of this dissertation, we introduced the sources of mercury pollution and its harm to human briefly. And then the analysis of mercury were systematically reviewed, especially the design of mercury biosensors was introduced, together with the development of mercury biosensors.Chapter Two:Polythymine oligonucleotide-modifide gold electrode for voltammetric determination of mercury (Ⅱ) in aqueous solutionWe have successfully prepared the polythymine oligonucleotide (PTO)-modified gold electrode (PTO/Au) for voltammetric determination of Hg2+ based on thymine-Hg2+-thymine complexes chemistry. The PTO/Au electrode integrates the sensitivity of electrochemical methods with the high specificity of biomolecules. The differential pulse voltammetry (DPV) of the modified electrode showed a linear response of the mercury oxidation signal with increase of Hg2+ concentration in the range between 0.2 and 1 nmol/L with a detection limit of 60 pM which is 4 orders of magnitude lower than the U. S. Environmental Protection Agency (EPA) limit of Hg2+ for drinkable water. Also, this assay has high selectivity which allows determination of Hg2+ in the presence of excess (200-fold) of other metal ions. The proposed electrode opens novel perspectives for determination of Hg2+ in biological and environmental samples, and holds great promise in electro-analysis as a type of green electrode. Chapter Three:Simple and rapid colorimetric mercury sensing assay using mercury specific DNA-functionalized gold nanoparticlesWe have designed a simple and rapid colorimetric assay for mercury using mercury specific DNA functionalized gold nanoparticles (AuNPs) based on the complexes of T-Hg2+-T and the excellent optical property of AuNPs. The thiolated mercury specific DNA (MSD) was bonded to AuNPs via Au-S bonds to form the colorimetric probes (Au-MSD) of mercury. The detection could be done within 5 min with a detection limit of 60 nM (S/N=3), which is below that of the other colorimetric assays based on oligonucleotide fuctionalized AuNPs. The probes are capable of discriminating Hg2+ ions from 8 other environmentally relevant metal ions. Moreover, the assay only relied on the UV/Vis spectrophotometer at room temperature. These results indicated our proposed method for colorimetric mercury detection is simple, sensitive, and highly selective. It was expected that this cost-effective colorimetric sensor might hold considerable potential in on-site applications of Hg2+ detection.Chapter Four:A simple, rapid, colorimetric mercury sensing assay based on trithiocyanuric acid (TCA)-capped gold nanoparticlesWe have developed a simple, rapid, colorimetric method for the detection of Hg2+ in aqueous solution based on trithiocyanuric acid-capped gold nanoparticles (Au-TCA). Trithiocyanuric acid (TCA) is a star-shape trithiol molecule that can spontaneously attach to citrate-capped gold nanoparticles (AuNPs) through the displacement of the weakly bound citrate ions and the formation of the Au-S covalent bond. The resulting Au-TCA can be dispersed in aqueous solution owing to the high negative charge density of TCA on each AuNP surface. Hg2+ induces the aggregation of Au-TCA through Hg-S recognition, thereby resulting in a color change from red to blue-gray. Linear correlations were found over the range of 0-1.7μM and 2.0～6.5μM respectively, with a detection limit of 50 nM (S/N=3). Also, when the 70μM other environmentally related mental ions were used in place of Hg2+ respectively, only Pb2+ could induce the aggregation of Au-TCA. However, the masking agent pyridine-2,6-dicarboxylic acid (PDCA) could eliminate Pb2+ interference with Hg2+ detection. The proposed colorimetric sensor is sensitive, selective, simple and rapid which could be detected Hg2+ within a minute. The method is attractive for potential point-of-use applications due to its high throughput, convenient readout, and portability.