Optimal Surface-enhanced Raman Scattering Research Articles

Annealing temperature effects on monolayer WS2-veiled Ag nanoparticle array for surface catalytic reaction

Plasmonic-WS2 hybrids have attracted widespread interest for plasmon driven catalytic reactions. In this work, a Ag nanoparticles (NPs)/WS2 hybrid was fabricated by utilizing a one-step anodized Al template-assisted vacuum thermal evaporation technique and wet transfer method. To optimize the catalytic performance, the morphological evolution and corresponding changes in the catalytic properties of the Ag NPs/WS2 hybrid at different thermal annealing temperatures were investigated. It was found that the surface-enhanced Raman scattering (SERS) and catalytic activity of the hybrid were optimized by tuning the annealing temperature, with the optimal SERS and catalytic properties observed at 290 °C. These results may open new avenues for improving the efficiency and expanding the research field of plasmon-driven reactions.

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

The increasing applications of surface-enhanced Raman scattering (SERS) has led to the development of various SERS-active platforms (SERS substrates) for SERS measurement. This work reviews the current optimization techniques available for improving the performance of some of these SERS substrates. The work particularly identifies self-assembled-monolayer(SAM-) based substrate modification for optimum SERS activity and wider applications. An overview of SERS, SAM, and studies involving SAM-modified substrates is highlighted. The focus of the paper then shifts to the use of SAMs to improve analytical applications of SERS substrates by addressing issues including long-term stability, selectivity, reproducibility, and functionalization, and so forth. The paper elaborates on the use of SAMs to achieve optimum SERS enhancement. Specific examples are based on novel multilayered SERS substrates developed in the author’s laboratory where SAMs have been demonstrated as excellent dielectric spacers for improving SERS enhancement more than 20-fold relative to conventional single layer SERS substrates. Such substrate optimization can significantly improve the sensitivity of the SERS method for analyte detection.

Cyclic electroplating and stripping of silver on Au@SiO2 core/shell nanoparticles for sensitive and recyclable substrate of surface-enhanced Raman scattering

A simple and convenient methodology to fabricate silver-coated Au@SiO2 core/shell nanomaterials (Au@SiO2@Ag nanostructures) is developed by cyclic electroplating and stripping of AgNO3 on the surface of Au@SiO2 core/shell nanoparticles, and the proposed nanostructures served as sensitive and reproducible surface-enhanced Raman scattering (SERS) substrates. Silver coverage of nanostructured Au@SiO2@Ag could be easily controlled by electrodeposition time without substrate motion. The Au@SiO2@Ag nanostructures possess a hexagonal array multiplying the hot spots. SERS of the nanostructures was examined at different electrodeposition times using rhodamine B (RdB) as probe molecule and 785 nm excitation. Optimum SERS was observed when silver was electrodeposited at −0.4 V for 1 min. RdB can be detected down to 10−11 M even without the resonance SERS effect, and the enhancement factor was found at 1.03 × 105. Additionally, silver shells could be easily stripped electrochemically when immersed in the H2SO4 solution for rebuilding and recycling the SERS substrates. The results validate the feasibility for quantitative detection of biomolecules in organisms and combine the advantages of recyclability and sensitivity.

Silver nanoparticles self assembly as SERS substrates with near single molecule detection limit

Highly sensitive SERS substrates with a limit of detection in the zeptomole (for Nile blue A and oxazine 720) range were fabricated through a bottom-up strategy. Ag nanoparticles (Ag NPs) were self-assembled onto glass slides by using 3-mercaptopropyltrimethoxysilane (MPTMS) sol-gel as linker. The substrates were characterized by UV-Vis and AFM after each deposition of Ag NPs. It was found that the glass slide presented just a few Ag NPs aggregates scattered throughout the surface after just one deposition. The glass surface was gradually covered by a homogeneous distribution of Ag NPs aggregates as the deposition number increased. Surface-enhanced Raman scattering (SERS) of the substrates was examined at different numbers of Ag NPs deposition using nile blue A and oxazine 720 as probe molecules and two laser excitations (632.8 nm and 785 nm). Optimum SERS was observed after six depositions of Ag NPs. SERS mapping indicated that at lower deposition numbers (less than 3 Ag NPs depositions) the substrates presented a few SERS "hot-spots" randomly distributed at the surface. After 7 Ag NPs depositions, spatial distribution of the SERS signal followed a Gaussian statistics, with a percent relative standard deviation (RSD%) of approximately 19%. In addition, the sample-to-sample reproducibility of the SERS intensities under both laser excitations was lower than 20%. It was also found that these substrates can provide giant Raman signal enhancement. At optimum conditions and with a 632.8 nm laser, the signal from an estimated of only approximately 44 probe molecules (100x objective) can still be detected.