| Noble metal nanoparticles, especially silver and gold nanoparticles (AgNPs and AuNPs) exhibit internal parameters and external condition dependent localized surface plasmon resonance (LSPR) light scattering properties, which enable them to be nice candidates as light scattering probes for analytical purposes. Thus, it is of fundamental importance to study the LSPR property of metal nanoparticles, and it also has practical value to apply them in the field of light scattering analytical chemistry. Presently. noble metal nanoparticles used as light scattering probes have been widely applied in biochemical analytical field. However, it has some shortages such as rare application of highly scattered AgNPs. lack of the facile method to acquire scattering signal of single nanoparticles. and so on. Thus. we focused our investigation on AgNPs and AuNPs to remedy the drabacks of noble metal nanoparticles based light scattering analysis, and carried out following researches.1. One-step preparation of DNA-AgNPs light scattering probes for DNA detection. DNA-AgNPs conjugates with strong scattering light were prepared through a one-step conjugation chemistry method by directly incubating AgNPs with SH-DNA in the presence of1.0mol/L NaCI with assist of FSN-100. This method is a universal and efficient strategy for preparation of DNA-metal nanoparticles conjugates. The DNA-AgNPs conjugates with strong scattering light were then used for the quantitative detection of HIV DNA with a sandwich strategy based on the LSPR light scattering signals. Sandwich hybridization of HIV DNA with probe DNA1and DNA2induced AgNPs to aggregate. The plasmon coupling between close proximity nanoparticles changed the LSPR light scattering signals of AgNPs that can be detected by a Fluorescence Spectrophotometer or observed with naked eye that enables to detect visually. The prepared DNA-AgNPs conjugates have proven to be as robust as their gold counterparts and enable to detect a low concentration (195pmol/L) of a specific DNA sequence based on the LSPR light scattering signals of AgNPs, and exhibited high selectivity.2. Screening highly sensitive sensing units through the investigation of the LSPR of AgNPs of different shapes. This work included three contents.1) AgNPs in multiple shapes with rainbow scattering lights were synthesized, and the shape effect on the scattering light color was determined by combining dark-field microscope (DFM) with scanning electron microscope (SEM). The results showed that AgNPs scatter blue, cyan, yellow, and red lights are Ag nanospheres, nanocubes, triangular bipyramids, and nanorods, respectively, which enable us to directly recognize the shape of AgNPs through a common dark-field microscope rather than electron microscope.2) Following study by examining the LSPR scattering spectral responses of single AgNPs to their surrounding solvents told that the RI sensitivities of AgNPs in different shapes follow the order of rods> cubes> triangular bipyramids> spheres. Ag nanorods have the highest RI sensitivity among the commonly studied AgNPs and they showed higher RI sensitivity as their aspect ratios increase.3) AgNPs of various shapes were used as single nanoparticle sensors for probing the adsorption of thiol molecules. The results confirmed the reliability of the results of shape-dependent RI sensitivity. This study provide the theoretical basis for us to design highly sensitive single nanoparticles analytical platform.3. In-situ and real-time watching the growth of single Ag@Hg nanoalloys. Ag@Hg nanoalloys were formed through the direct amalgamation of Ag nanoparticles with elemental mercury (Hg0). After exposure of Ag nanoparticles to growth solution, the scattering light of all single Ag nanoparticles exhibited noticeable changes, suggesting the growth of Ag@Hg nanoalloys. Further characterizations by scanning electron microscopy (SEM), high-resolution transmit electron microscopy (HRTEM), and energy-dispersive X-ray spectroscopy (EDXS) confirmed the formation of Ag@Hg nanoalloys, and the changes of nanoparticles composition, shape, and size after growth. In this work, growth of Ag@Hg nanoalloys from four typical shaped Ag nanoparticles, rods, triangular bipyramids, cubes, and spheres, was investigated. By combining the single particles spectral data and shape change of single nanoparticles during growth process, the proposed growth process of single Ag@Hg nanoalloys from various shapes undergoes following stages:quick adsorption of Hg0onto Ag nanoparticles, early stage diffusion of HgO into Ag nanoparticles rounding the particle surfaces, continuous diffusion of Hg0to form Ag@Hg nanoalloys. The present work enables to design nanoalloys with given property for single nanoparticles analysis.4. Novel single metal nanoparticles based light scattering analytical methods. Previous studies on single nanoparticles analysis must rely on a standard procedure for scanning the scattering spectrum of a single nanoparticle, which was complicated and time-consuming. In our work by using a commonly used software, we code the colors of the scattering light of individual nanoparticles with the RGB system and thus established single nanoparticles based RGB analytical method. To validate the feasibility to code single nanoparticles with RGB for analysis, we first studied the RGB changes of single AuNPs bathed in various solvents. To extend the analytical use of scattering light colors, herein, we presented RGB analysis for the binding study of thiols to single AuNPs. Dark-field scattering images of single AuNPs before and after thiols binding to their surfaces were taken by a truecolor digital CCD camera. Then, the color spots in the dark-field scattering images were transferred to digital RGB information. RGB values of the scattering light changed after thiol molecules covalently bound to the surface of an AuNP. This forms the basis of RGB analysis by coding individually color-coded plasmonic nanoparticles with the RGB system. In addition, the change of scattering intensity, however, as a basic feature in any spectral investigations and easy to be detected, seems to be neglected by researchers for such applications. Thus, we focus our further concern on the light scattering intensity of single AuNPs. which was handily transferred to digital information for digital analysis through commonly used software and then used for recording the molecular binding. Firstly, above work gives a special view to the scattering light colors and scattering intensity of single plasmonic nanoparticles. to which little attention was paid before. Secondly, comparing with previous works of SNA focused on the scattering spectral shift, our proposed analytical methods are much easier to achieve.In summary, all of our researches are based on the LSPR property of noble metal nanoparticle. which were measured by dark-field light scattering microscopy and single nanoparticle spectroscopy. We investigated the shape-dependent LSPR property of single AgNPs and followed by in situ and real-time watching the growth of single Ag@Hg nanoalloys to study the composition, shape, and size dependent LSPR property of single nanoparticles. Then. AgNPs and AuNPs were use as light scattering probes for analytical purposes. The novel) of our researches exhibit as two aspects. One is the successful observation of the growth of single nanoparticles using dark-field microscopy. The other one is the development of RGB and scattering intensity based single nanoparticles analysis that can be used in common laboratories. |
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