Unraveling near-field and far-field relationships for 3D SERS substrates – a combined experimental and theoretical analysis

Abstract

Simplicity and low cost has positioned inkjet paper- and fabric-based 3D substrates as two of the most commonly used surface-enhanced Raman spectroscopy (SERS) platforms for the detection and the identification of chemical and biological analytes down to the nanogram and femtogram levels. The relationship between far-field and near-field properties of these 3D SERS platforms remains poorly understood and warrants more detailed characterization. Here, we investigate the extremely weak optical scattering observed from commercial and home-fabricated paper-, as well as fabric-based 3D SERS substrates. Using wavelength scanned surface-enhanced Raman excitation spectroscopy (WS-SERES) and finite-difference time-domain (FDTD) calculations we were able to determine their near-field SERS properties and correlate them with morphological and far-field properties. It was found that nanoparticle dimers, trimers, and higher order nanoparticle clusters primarily determine the near-field properties of these substrates. At the same time, the far-field response of 3D SERS substrates either originates primarily from the monomers or cannot be clearly defined. Using FDTD we demonstrate that LSPR bands of nanoparticle aggregates near perfectly overlap with the maxima of the near-field surface-enhanced Raman scattering responses of the 3D SERS substrates. This behaviour of far-field spectroscopic properties and near-field surface-enhanced Raman scattering has not been previously observed for 2D SERS substrates, known as nanorod arrays. The combination of these analytical approaches provides a full spectroscopic characterization of 3D SERS substrates, while FDTD simulation can be used to design new 3D SERS substrates with tailored spectral characteristics.

Gold Nanoparticles from Vegetable Extracts Using Different Plants from the Market: A Study on Stability, Shape and Toxicity

“…The SERS activity of the six samples was estimated by adding thiophenol at 10 −4 M concentration (Figure , right panel). The resulting SERS spectra of thiophenol are in agreement with the literature . In spite of its high affinity for Au surfaces and relatively high concentration, thiophenol could displace the adsorbed species only to a limited extent (< 20%), confirming the strong interactions between capping agents and the NPs, which determined their long‐term stability.…”

Common Aspects Influencing the Translocation of SERS to Biomedicine

“…Key for multiplexing is the analyte specific ultrasensitive fingerprint-like information provided by SERS. Although SERS methodologies have a proven capacity to resolve analytes within complex media [20d, 52], multi-analyte systems are still challenging especially when both sample identification and quantification is intended. One should evaluate several factors when designing multiplex experiments using for example reporter molecules.…”

“…Noble metal colloids in suspension or immobilized in solid templates (glass, silicon wafer, organic or inorganic colloids) are, by far, the most used SERS-active substrates as their LSPRs can be easily excited in the vis or NIR regions [20]. Isolated particles, spherical-shaped colloids, mostly made of gold (Au) and silver (Ag), produce moderate EFs on the order of 10 2 -10 3 .…”

Detection of the conformational changes of Discosoma red fluorescent proteins adhered on silver nanoparticles-based nanocomposites via surface-enhanced Raman scattering

“…The simulations give an idea on the plasmonic enhancement factor of the Raman scattering but more importantly they allow determining the spatial distribution of the plasmonic field and its dependence on the nanoparticles morphology, interaction and location with respect to the sample surface. of the calculated near-field at 532 nm wavelength, which gives the magnitude of the SERS EM enhancement factor [28][29][30]. It can be noticed that the hot spots form in the gap regions between the AgNPs (figure 4(c)) and are uniformly distributed across the substrate (figure 4(d)).…”

“…A large variety of metallic nanostructure morphologies and arrangements (nanosphere, nanotriangles, nanodisks, nanorods, nanocubes, etc) and different coupling geometries (dimers, trimers, arrays, etc) have been developed up to date for SERS platforms [16,[26][27][28][29]. However, their conversion to macroscopic plasmonic substrates relies generally on the NPs volunteer arrangement on dielectric surfaces (mainly through applying chemical methods), thus often resulting in nonuniform distribution on large areas, without a well-defined control of the spacing between the metallic nanostructures and the probed molecules, high point-to-point variability, scarce reproducibility and stability under irradiation conditions (due to photothermal and photodegradation processes) [30]. To overcome the limitations in producing solid SERS substrates various physical approaches, like thermal evaporation [31], combined nanoimprint lithography-shadow evaporation [32], gas aggregation source (GAS) [33], pulsed laser deposition [34], low-energy ion beam synthesis [35][36][37], and plasma-based deposition processes [38,39], have been proposed in the literature.…”