Correlative SEM SERS for quantitative analysis of dimer nanoparticles

Abstract

A Raman microscope integrated with a scanning electron microscope was used to investigate plasmonic structures by correlative SEM-SERS analysis. The integrated Raman-SEM microscope combines high-resolution electron microscopy information with SERS signal enhancement from selected nanostructures with adsorbed Raman reporter molecules. Correlative analysis is performed for dimers of two gold nanospheres. Dimers were selected on the basis of SEM images from multi aggregate samples. The effect of the orientation of the dimer with respect to the polarization state of the laser light and the effect of the particle gap size on the Raman signal intensity is observed. Additionally, calculations are performed to simulate the electric near field enhancement. These simulations are based on the morphologies observed by electron microscopy. In this way the experiments are compared with the enhancement factor calculated with near field simulations and are subsequently used to quantify the SERS enhancement factor. Large differences between experimentally observed and calculated enhancement factors are regularly detected, a phenomenon caused by nanoscale differences between the real and 'simplified' simulated structures. Quantitative SERS experiments reveal the structure induced enhancement factor, ranging from ∼200 to ∼20 000, averaged over the full nanostructure surface. The results demonstrate correlative Raman-SEM microscopy for the quantitative analysis of plasmonic particles and structures, thus enabling a new analytical method in the field of SERS and plasmonics.

Plasmonic Optical Tweezers for Particle Manipulation: Principles, Methods, and Applications

“…Then the time-harmonic or frequency-domain form of Maxwell’s equations can be written as Then we can obtain Different numerical methods have been proposed to solve the above-mentioned time-domain or frequency-domain equations, among which, the most commonly used numerical methods include the finite element method, finite-difference time-domain method, boundary element method, discrete dipole approximation, T matrix method, etc . These can be executed using commercial software, such as Comsol Multiphysics and Lumerical, or open-source code like DDSCAT and MNPBEM. − Due to the convenience of numerical simulations, the simulated results are often used as a guide for the geometry design or material selection for the plasmonic structures. In the case of an experimental approach, the localized electromagnetic field is extremely hard to directly detect or observe.…”

Polarization- and Angular-Resolved Optical Response of Molecules on Anisotropic Plasmonic Nanostructures

“…Efforts to make use of the enhancement capability of dimers are still very lively in literature, which can be documented by numerous studies from the last years [ 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 ], benefiting from extremely high enhancement between two adjacent metallic NPs or between a metallic NP and a substrate. A very promising analytical tool for biosensing applications include DNA origami, [ 75 , 76 , 77 ] where NPs with defined distance can be constructed.…”

SERSTEM: An app for the statistical analysis of correlative SERS and TEM imaging and evaluation of SERS tags performance

“…Even though the correlation between SERS and TEM can in principle be achieved by using hybrid instruments, [28,29] such combined imaging facilities are not commonly available. Correlated SERS studies have been reported to determine the SERS enhancement by measuring the same single, dimer, or cluster Ag NPs on a Raman microscope and correlating with either scanning electron microscopy (SEM) [30][31][32][33] or TEM. [34][35][36][37] Statistical analysis to correlate SERS intensity and NP cluster size has also been reported by SERS and SEM imaging.…”