Application Of Nanoprobes In Detection Of Heavy Metal Ions

Heavy Metal is a great hazard of pollutants, it can not be degraded in vivo long-term accumulation, the content can be shown minimal toxicity great. Once it accumulate in human body through the food chain, it cause various diseases,even affect the next generation. Therefor, heavy metal detection is very important for medicine, food and environment. Traditional trance heavy metal detection methods which is based on expensive instrument, wasting of money and time , unsensitive or undetectable for some metal ions ,and need for specialist operator are not competent for these days. Thus new methods with simple instrument,speediness and high sensitivity is need for qualitatively and quantitatively detect heavy metals in samples.Random-coil DNA molecules adsorb onto Au NP surfaces through electrostatic attraction.In the presence of salt, T-rich oligonucleotides on the surface of Au NPs remains in a random-coil structure as a result of electrostatic repulsion between DNA molecules. Owing to the high negative charge density of DNA on each Au NP surface, monodisperse Au NPs exist in the salt solution. Upon formation of Hg²⁺-DNA complexes the conformation of the T-rich oligonucleotides changes to folded structures. As a result of the decreased zeta potential on each Au NP and the reduced degree of electrostatic repulsion between Au NPs, aggregation of the Au NPs occurs and, hence, the color of the solution changes from red to purple in a process that is detectable by the naked eye. Th is mercury sensor is found to be have high sensitivity and selectivity,as it allows a fast(in minutes)identification of 5.0nmol/L Hg²⁺ without any detectable perturbation by a spectrum of non-specific metal ions.A simple and sensitive detection method for mercury ions was developed with quartz crystal microbalance (QCM), based on the specific T-Hg²⁺-T structure and gold nanoparticles. The gold nanoparticles were prepared by the citrate reduction method. In a self-assembled way, the particle surface was modified with the probe oligonucleotides which were partially replaced by 6-Mercaptohexan-1-ol (MCH) to reduce the steric hindrance of hybridization. The sensitivity was optimized by the oligonucleotide with a strand length of 9bp and a T number of 7. The linear range was 5.0～100 nmol·L^-1 with a detection limit of 2.0 nmol·L^-1. And Ca²⁺,Mg²⁺ and other metal ions had no significant interferences. This method was successfully applied for the detection of Hg²⁺ in environmental water samples, with RSD less than 2. 92% and recoveries of 97. 3%～ 101. 2%.An innovative scheme for signal amplification using random tetramer-modified gold nanoparticles, termed"nanoamplicons,"has been developed for Pb²⁺ assay . It is based on the 8-17 DNAzyme selected by several groups that have shown the DNAzyme to be highly specific for Pb²⁺.In the presence of Pb²⁺, the substrate strand was cleaved under the catalysis of enzyme strand,the release of single stranded DNA hybridize to nanoamplicons, These hybridizations cause aggregation of gold nanoparticles and result in the color change from red to blue that can be observed with naked eyes. hence, Pb²⁺could be rapidly detected at room temperature based on this principle,and the limits of detection were 3 .0nmol·L^-1.For divalent metal ions, such as Zn²⁺,Mn²⁺,Co²⁺,Cd²⁺,Cu²⁺,Mg²⁺ and Ni²⁺,the sensor responds only in the presence of Pb²⁺,It is demonstrated that the nove1lead biosensor has a good selectivity to Pb²⁺.Au nanoparticle prepared by reduction of HAuCl4 with citratewas found to show pH-dependent response to Pb²⁺ ion. The citrate capped Au nanoparticles show response to a variety of heavy metal ions which have strong affinity to the carboxyl groups of citrate ligand, such as Pb²⁺, Cu²⁺, Fe³⁺ etc. At pH value of 11.5, other heavy metal ions with strong affinity to the carboxyl groups become less effective to induce the color change of the Au nanoparticles due to their suppressed coordination with the ligand on the particle surface upon increased concentration of hydroxyl group. However, the Au nanoparticles are still sensitive to Pb²⁺ ion under the pH of 11.5 due to its amphoteric character. Such pH-dependent response character of the Au nanoparticles allows the selective detection of Pb²⁺ ion at the pH of 11.5, for example, the citrate capped Au nanoparticles are qualified for the quantitative detection of Pb²⁺ ions , the limits of detection were 50 nmol·L^-1...