Design Of Surface-enhanced Raman Scattering Substrates Research Articles

Surface-Enhanced Raman Scattering on Silver Sinusoidal Nanograting: Impact of Interactions of Grating-Coupled Surface Plasmon Polaritons

In this study, we reported a silver sinusoidal nanograting used in microchannels, forming H2O/Ag/NOA/SiO2 heterostructure and studied the impact of interactions of grating-coupled surface plasmon polaritons (SPPs) on surface-enhanced Raman scattering (SERS). There are two modes of \(E_{x} (z)\) in the Ag grating, namely, the anti-symmetric mode (AM) at the high SPP resonance frequency and the symmetric mode (SM) at the low-SPP resonance frequency. When the refractive indices of the upper and lower dielectrics of the thin Ag grating are close, there will be a strong coupling between the SPPs of the two interfaces, which will increase the transmittance but reduce the maximum electromagnetic (EM) of the SERS substrate. Additionally, the thinner the Ag grating, the stronger the coupling, accompanied by the frequency shift of the two coupling modes. Our experimental results are supported by FDTD calculations, which have corroborated the importance of the interactions of grating-coupled SPPs in the design of SERS substrate.

Study on surface enhanced Raman scattering of Au and Au@Al2O3 spherical dimers based on 3D finite element method

In this paper, the surface enhanced Raman scattering (SERS) characteristics of Au and Au@Al2O3 nanoparticle dimers were calculated and analyzed by using finite element method (3D-FEM). Firstly, the electric field enhancement factors of Au nanoparticles at the dimer gap were optimized from three aspects: the incident angle of the incident light, the radius of nanoparticle and the distance of the dimer. Then, aluminum oxide is wrapped on the Au dimer. What is different from the previous simulation is that Al2O3 shell and Au core are regarded as a whole and the total radius of Au@Al2O3 dimer is controlled to remain unchanged. By comparing the distance of Au nucleus between Au and Au@Al2O3 dimer, it is found that the electric field enhancement factor of Au@Al2O3 dimer is much greater than that of Au dimer with the increase of Al2O3 thickness. The peak of electric field of Au@Al2O3 dimer moves towards the middle of the resonance peak of the two materials, and it is more concentrated than that of the Au dimer. The maximum electric field enhancement factor 583 is reached at the shell thickness of 1 nm. Our results provide a theoretical reference for the design of SERS substrate and the extension of the research scope.

Recent advances in surface-enhanced Raman scattering technique for pollutant detection in Chinese medicinal material

Chinese medicinal material is the foundation of traditional Chinese medicine(TCM) industry. Its quality is not only closely related to the health of residents but also the key to the development of the TCM industry. Pesticide residues, heavy metals and mycotoxins are the major pollutants of Chinese medicinal materials. In recent years, quite a number of rapid detection methods for pollutants have been constructed. Among them, surface-enhanced Raman scattering(SERS), which has been widely used in food chemistry, environmental analysis, and other fields because of its speediness and non-destructiveness, shows its great potential in the pollutant detection in Chinese medicinal material. This paper firstly reviews the application of SERS for the detection of common pollutants in Chinese medicinal material. We then discussed the characteristics and advantages of SERS technique for pesticide detection, including the principle, SERS substrate design, specific recognition, etc. Finally, simultaneous detection of multiple pesticide residues in Chinese medicinal material was explored.

Surface Enhanced Raman Scattering on Regular Arrays of Gold Nanostructures: Impact of Long-Range Interactions and the Surrounding Medium.

Long-range interaction in regular metallic nanostructure arrays can provide the possibility to manipulate their optical properties, governed by the excitation of localized surface plasmon (LSP) resonances. When assembling the nanoparticles in an array, interactions between nanoparticles can result in a strong electromagnetic coupling for specific grating constants. Such a grating effect leads to narrow LSP peaks due to the emergence of new radiative orders in the plane of the substrate, and thus, an important improvement of the intensity of the local electric field. In this work, we report on the optical study of LSP modes supported by square arrays of gold nanodiscs deposited on an indium tin oxyde (ITO) coated glass substrate, and its impact on the surface enhanced Raman scattering (SERS) of a molecular adsorbate, the mercapto benzoic acid (4-MBA). We estimated the Raman gain of these molecules, by varying the grating constant and the refractive index of the surrounding medium of the superstrate, from an asymmetric medium (air) to a symmetric one (oil). We show that the Raman gain can be improved with one order of magnitude in a symmetric medium compared to SERS experiments in air, by considering the appropriate grating constant. Our experimental results are supported by FDTD calculations, and confirm the importance of the grating effect in the design of SERS substrates.

Numerical Design of Photonic Crystal-Based Nanostructured Substrate for Efficient Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) has emerged as a sensitive and established spectroscopic technique for trace detection in various fields including chemistry, material science, biochemistry, and life sciences. With the rapid progress in nano-fabrication scheme, design of SERS substrate has immensely contributed in the development of biological and biomedical sensors, detectors for explosives and narcotics, besides other applications. The electromagnetic enhancement, which majorly contributes to the SERS phenomena, is enabled by the fabrication of nanostructured substrates with high enhancement factor. The enhancement factor depends on the shape, size, and orientation of the nanostructure pattern. Here, we present a new design that ensures high enhancement factor (~ 107), is polarization independent, robust with respect to various geometrical parameters and excitation wavelength. It can be easily implemented in reflection mode configuration and is spread over a hotspot region of ~ 3200 nm2 (in each periodic unit of the array), yielding an overall emission efficiency of 0.12%. The proposed design can be realized for various SERS applications due to ease of its fabrication using standard techniques.

Optimization of Ag coated hydrogen silsesquioxane square array hybrid structure design for surface-enhanced Raman scattering substrate.

A computer-automated design process for a surface-enhanced Raman scattering (SERS) substrate using a particle swarm optimization algorithm is proposed. Nanostructured Ag coated hydrogen silsesquioxane nanopillar arrays of various sizes for SERS substrate applications are fabricated by direct Ag film deposition on substrates patterned by electron beam lithography and are investigated systematically. Good agreement is demonstrated between experimental and simulation results. The absorption spectra, charge distributions, and electric field distributions are calculated using finite-difference time-domain simulations to explain the field enhancement mechanism and indicate that this enhancement originates from plasmon resonance. Our work provides a guide towards optimum SERS substrate design.

Surface-Enhanced Raman Scattering on Template-Embedded Gold Nanorod Substrates

Surface-enhanced Raman scattering (SERS) of rhodamine 6G was investigated on template-embedded gold nanorods produced by anodic aluminum oxide template-assisted nanofabrication. A signal enhancement of about 106 was obtained. Two-dimensional arrays of gold nanospheres with different diameters and gap sizes were used as simplified model systems. SERS substrate design principles were investigated in order to achieve maximum electromagnetic enhancement of both the incident and Raman scattered fields.

Evanescent field excited plasmonic nano-antenna for improving SERS signal

The purpose of this work is to develop a high-performance surface-enhanced Raman scattering (SERS) substrate with high light harvesting and SERS emitting efficiencies based on the principle of a plasmonic nano-antenna. A prism/Ag nanowell array was designed and constructed based on the Kretschmann configuration. Almost 100% of the incident light can be absorbed at the resonance angle. A strong electromagnetic (EM) field is generated in the near field along the rim and at the center of the nanowells by means of the localized energy of surface plasmons (SPs), resulting in the electric field being enhanced 300 times at the Ag surface. The co-enhancement of localized SPs and propagating SPs was achieved in this substrate. The plasmonic nano-antenna structure can also redirect the SERS, which benefits the SERS collection. The SERS sensitivity on this configuration was improved by about 40 times compared with that on a conventional Kretschmann configuration with a flat Ag film. This SERS substrate design with full consideration on the tuning of the EM field in the near field and SERS space distribution in the far field could give insight into the design of a new generation of SERS substrates.

Hybrid surface-enhanced Raman scattering substrate from gold nanoparticle and photonic crystal: Maneuverability and uniformity of Raman spectra

A novel hybrid surface-enhanced Raman scattering (SERS) substrate based on Au nanoparticles decorated inverse opal (IO) photonic crystal (PhC) is presented. In addition to the enhancement contributed from Au nanoparticles, a desired Raman signal can be selectively further enhanced by appropriately overlapping the center of photonic bandgap of the IO PhC with the wavelength of the Raman signal. Furthermore, the lattice structure of the IO PhC provides excellent control of the distribution of Au nanoparticles to produce SERS spectra with high uniformity. The new design of SERS substrate provides extra maneuverability for ultra-high sensitivity sensor applications.