Application Research Of Functional Gold Nanoparticles And Their Optical Imaging In Heavy Metals Detection

Recently, with the continuously rapid development of nano-science andtechnology, lots of progresses have been achieved in the field of nanomaterialfabrication and characterization. Due to the unique chemical and optical properties ofnanomaterials, including large cross sections, low biotoxicity and excellentphotostability, especially AuNPs, they have been utilized in diverse application as achemical or biological sensor, particularly in bio/chemo imaging filed. On the basis ofprevious researchers’ work, we studied the synthesis, optical and physical propertiesof gold nanoparticles, and their applications in direct imaging as chemical sensorsunder dark field microscopy for heavy metal detection direct imaging. In this article,we presented the research in the following three parts:In chapter2, Hg2+is able to specifically bind to the thymine in a DNA, thusproviding a rationale for DNA-based selective detection of Hg2+with various means.Through this approach, we make use of DNA-NP conjugates and thymine-Hg2+-thymine (T-Hg2+-T) coordination to develop a sensor system that efficiently andeffectively detects the Hg2+. The T-Hg2+-T would result the aggregation of AuNPswhich lead to the color change, the degree of assemble is depending on theconcentration of Hg2+, the more Hg2+, the bigger couple diameter. This technique usesthe chrominance of the AuNPs plasmon resonance scattering light that is captured bya dark-field microscope (DFM). The RGB (three primary colors, red, green, and blue)chrominance information from the dark-field image can be directly converted into thediameters of the assembled AuNPs using the relationship between the particle size andthe scattering light peak wavelength, thus distinguishing the different concentration ofHg2+ulteriorly. This method could selectively detect Hg2+as low as12nM.In chapter3, on the basis of the size, shape and composition-dependent opticalproperties of AuNPs, and the fact that Pb2+could enhance the leaching rate of AuNPsby ammoniacal thiosulfate (S2O32-) and2-mercaptoethanol (2-ME), which would leadto the dramatic decrease of scattering maximum. We presented an effective andefficient method for Pb2+detection at single particle level by observing the scatteringintensity of AuNPs probes under dark field microscopy (DFM).In chapter4, by using DFM-based detection of single AuNP scattering intensity,a highly sensitive method for Pb2+sensing was proposed. Different from other target-induced AuNP aggregation-based colorimetric assays, this method tookadvantages of Pb2+induced AuNP size variation. When Pb2+was added into themixture of S2O32-,2-mercaptoethanol and AuNPs, the Pb-Au complexes acceleratedAuNPs dissolving into solution and their size reduction, leading to a sharp decrease inthe LSPR scattering intensity of the AuNPs with little spectral shift. The fact that anindividual AuNP can act as a probe for sensitive detection of Pb2+allowsminiaturization of the sensing system and significant reduction of sample volume. Asa result, Pb2+concentration in homogenous solution was able to be determined assensitive as0.2pM. Further calculation indicated that we were actually detecting thecatalytic activity of just~5Pb2+ions on one AuNP surface when the Pb2+concentration was0.2pM. To our knowledge, this is the first time to use anon-fluorescence SPD technique for lead ion detection. This approach could befurther applied to study real-time single molecule reaction kinetics and catalyticmechanisms.