Higher Surface Enhanced Raman Scattering Intensity Research Articles

Improve optical properties by modifying Ag nanoparticles on a razor clam SERS substrate.

Irregular substrates are inappropriate for enhancing surface enhanced Raman scattering (SERS) due to their poor performances in terms of uniformity, enhancement performance, and polarization characteristics. However, in this work, we purposely employed a natural biological razor clam material with messy and irregular structures to improve the SERS. The rough surface was achieved by magnetron sputtering Ag nanoislands on the prism layer of the razor clams, and the Ag nanoparticles were treated using the method of oil-water interface self-assembly to form relatively uniform structures. Compared to the substrate without Ag nanoparticles, the presented substrate has better reproducibility, polarization-independence, and higher SERS intensity, and the detect limitation of R6G can be decreased from 10-12 M to 10-18 M. The ultrasensitive detection of thiram gives our structures potential for high sensitivity biosensors.

Synthesis of Monolayer Gold Nanorings Sandwich Film and Its Higher Surface-Enhanced Raman Scattering Intensity.

Most previous studies relating to surface-enhanced Raman spectroscopy (SERS) signal enhancement were focused on the interaction between the light and the substrate in the x-y axis. 3D SERS substrates reported in the most of previous papers could contribute partial SERS enhancement via z axis, but the increases of the surface area were the main target for those reports. However, the z axis is also useful in achieving improved SERS intensity. In this work, hot spots along the z axis were specifically created in a sandwich nanofilm. Sandwich nanofilms were prepared with self-assembly and Langmuir-Blodgett techniques, and comprised of monolayer Au nanorings sandwiched between bottom Ag mirror and top Ag cover films. Monolayer Au nanorings were formed by self-assembly at the interface of water and hexane, followed by Langmuir-Blodgett transfer to a substrate with sputtered Ag mirror film. Their hollow property allows the light transmitted through a cover film. The use of a Ag cover layer of tens nanometers in thickness was critical, which allowed light access to the middle Au nanorings and the bottom Ag mirror, resulting in more plasmonic resonance and coupling along perpendicular interfaces (z-axis). The as-designed sandwich nanofilms could achieve an overall ~8 times SERS signals amplification compared to only the Au nanorings layer, which was principally attributed to enhanced electromagnetic fields along the created z-axis. Theoretical simulations based on finite-difference time-domain (FDTD) method showed consistent results with the experimental ones. This study points out a new direction to enhance the SERS intensity by involving more hot spots in z-axis in a designer nanostructure for high-performance molecular recognition and detection.

Effect of layer structures of gold nanoparticle films on surface enhanced Raman scattering

Using a method of collecting nanoparticles at a water/hexane interface in a close-packed monolayer film and transferring such films onto a solid substrate, three-dimensional multilayer films of nanoparticles were formed. The packed nanoparticles were gold nanospheres (NS) with a 26 nm diameter or gold nanorods (NR) with a 31 nm diameter and 74 nm length. We investigated variations in the surface enhanced Raman scattering (SERS) intensities from such nanoparticle films as the layer compositions were changed. The films stacked with NR layers generated much higher SERS intensity than those of NS layers. The SERS intensities from both kinds of films increased as the number of layers were increased. However, when the NR layer and NS layer were stacked alternately, SERS intensity varied in a zigzag fashion. It was found that the structure of top layer plays a distinguishable role in generating strong SERS enhancement while the lower layers contribute to SERS with less dependency on structures. Interlayer coupling as well as intralayer coupling was considered in order to explain the observations.