Precious Metal Nanostructure Assembly and Application of Surface-enhanced Raman Scattering
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(a) Scanning electron microscope (SEM) photographs of nanotube arrays assembled from silver nanosheets; (b) SEM photographs of broken nanotubes; (c) SERS spectra of R6G with different concentrations; (d) 20 μM polychlorinated biphenyl-77 A mixture solution of (PCB-77) and 10 μM polychlorinated biphenyl-1 (PCB-1) (curve I) and a SERS spectrum of 30 μM PCB-1 solution (curve II).
Recently, the research team of the Institute of Solid State Physics of the Chinese Academy of Sciences and the Researcher of the Institute of Solid State Physics, Bangguo Bang, teamed up with Professor Wu Nianqiang of the University of West Virginia in the United States to make new advances in the assembly of precious metal nanostructures and the application of surface-enhanced Raman scattering (SERS). The results were published in a cover paper in Nano Res. 2015, 8, 957-966.
Due to the electromagnetic enhancement, the Raman signal of the molecules located on the surface of the noble metal nanostructures is enhanced by orders of magnitude, resulting in surface-enhanced Raman scattering effects. Surface-enhanced Raman scattering technology has the ability of molecular "fingerprint" recognition, and has a wide range of application prospects in chemical and biological analysis and other fields. The surface of noble metal nanostructures with a large enhancement of the local electromagnetic field (generally located at the <10 nm gap) is called surface-enhanced Raman scattering “hot spot†and is the main source of surface-enhanced Raman scattering signals.
Therefore, increasing the concentration of "hotspots" in three-dimensional space will effectively increase the surface-enhanced Raman scattering sensitivity. Currently, the main way to construct a three-dimensional SERS substrate is to assemble spherical noble metal particles onto a non-metal nanostructure array. Relevant theoretical and experimental studies have shown that noble metal nanostructures with edges or corners can generate stronger localized electromagnetic fields than spherical noble metal nanoparticles, and thus the assembly is more likely to generate “hot spots†at the gaps. If these nanostructures are assembled into a three-dimensional SERS substrate, a high-sensitivity SERS substrate can be expected.
The research team used a ZnO nanocones array as a sacrificial template, using an electrolyte containing precious metal ions and a specific surfactant, and using electrodeposition methods to construct a variety of nanotube arrays assembled from noble metal nanostructure units, such as silver nanosheets and gold nanocrystals. Nanotube arrays assembled from structural elements such as rods, platinum nano-thorns, and palladium nano-cones.
These nanostructured elements have sharp corners and/or tips; nanotube arrays assembled from it have a large number of gaps, creating a high density of "hot spots" in three dimensions. Therefore, the constructed nanotube array has a high surface-enhanced Raman scattering sensitivity. For example, silver nanoplate assembled nanotube arrays can sensitively detect rhodamine 6G (R6G) at concentrations as low as 10 fM. This silver nanosheet-assembled three-dimensional SERS substrate also exhibits high surface-enhanced Raman scattering sensitivity for highly toxic organic contaminants, polychlorinated biphenyls, and is capable of detecting a mixture of two polychlorinated biphenyls, indicating that the three-dimensional SERS substrate is detected There are prospects for the use of highly toxic organic contaminants in the environment.
Relevant work was supported by the "973" Program of the Ministry of Science and Technology, the "China Academy of Sciences, the National Foreign Experts Bureau Innovation Team International Partner Program" and the National Natural Science Foundation.
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