Super-Radiant SERS Enhancement by Plasmonic Particle Gratings

Raman Scattering Enhancements Due to Super- and Subradiant Collective Plasmon Modes on Large-Area 2D-Au Arrays

Ordered metal nanoparticle (MNP) arrays with ultrasmall interparticle gaps S exhibit strong enhancement of the electromagnetic (EM) near-field, known as hotspots, for surface-enhanced Raman spectroscopy (SERS) sensing. These arrays, with uniform gap sizes, are also essential for studying nonlinear Raman scattering effects and surface selection rules. Optical characterization of the fabricated large-area Au arrays with S ≪ r, where r is the MNP radius, revealed the excitation of hybridized-collective plasmon modes with giant EM near-field enhancement. We found that the SERS enhancement associated with a subradiant plasmon mode depends primarily on the interparticle gap distance S, rather than on the ordering of MNPs into arrays. However, arranging MNPs in the form of arrays influenced the far-field scattering of the super-radiant mode excited at a longer wavelength, resulting in lower but highly anisotropic SERS enhancements that depend on the far-field excitation polarization angle σ. This study on ordered MNP arrays with ultrasmall interparticle gaps S ≪ r highlights the roles of S and MNP ordering in SERS enhancement of an analyte. This understanding is pivotal for designing SERS substrates with very small interparticle gaps, as they generate a large number of intense and well-distributed SERS hotspots. Furthermore, an anisotropy-induced SERS dichroism effect was observed. Polarization-dependent SERS intensities varied based on the excitation wavelength λexc and its corresponding Stokes wavelength positions related to the excited plasmon mode. As a result, the SERS dichroism of lower-frequency Stokes-shifted peaks exhibited a cos2(σ) dependence, whereas higher-frequency Stokes-shifted peaks exhibited a sin2(σ) dependence. This observation validates the EM near-field mechanism of SERS. The fabricated large-area 2D-Au arrays meet most of the essential requirements for efficient, robust, and reliable large-area SERS sensing.

Flexible Au@Ag/PDMS SERS imprinted membrane combined with molecular imprinting technology for selective detection of MC-LR

In this study, a core-shell structured bimetallic nano-cube, Au@Ag NCs, was prepared by seed-mediated growth procedure. The array structure of Au@Ag NCs was achieved at the interface through the autonomous assembly technique at the three-phase boundary. Employing polydimethylsiloxane (PDMS) as a flexible carrier, the array structure was effortlessly transferred to the PDMS membrane, bypassing the need for rigid substrates through a simple "pasting" method. This yielded a highly flexible and transparent SERS substrate with an array structure (Au@Ag NCs/PDMS membrane, AAP). In order to promote the selective detection property to the practical samples, molecularly imprinted polymers (MIPs) were coated on the surface of membrane to prepare the imprinted membrane (Au@Ag NCs/PDMS-MIMs, AAP-MIMs). It was demonstrated from the results that the AAP-MIMs exhibited high SERS sensitivity, stability, and uniformity. Furthermore, the flexible substrate possessed commendable mechanical strength, and facilitated the detection of analytes on irregular surfaces. In summary, this substrate held promising potential for practical on-site detection and analysis of specific target substances.

2D wrinkle assisted zigzag plasmonic chains for isotropic SERS enhancement

Template-assisted colloidal self-assembly has gained significant attention due to its flexibility and versatility. By precisely controlling the shape of the template, it is possible to achieve custom-designed nanoparticle assemblies. However, a major challenge remains in fabricating these templates over large areas at a low cost. Recently, one-dimensional (1D) nano-wrinkle structures have been effectively used for the linear assembly of single-chain or multi-chain nanoparticles, which feature abundant interparticle nanogaps that facilitate efficient plasmonic coupling. To further enhance these assemblies by incorporating diffraction modes, we develop two-dimensional (2D) zigzag wrinkle structures that successfully assemble nanoparticles into plasmonic zigzag chains. Micro spectral measurements and FDTD simulations reveal that zigzag assemblies of plasmonic nanoparticle chains offer isotropic behavior and exhibit stronger plasmonic coupling compared to 1D assemblies, which could be highly beneficial for sensing applications. Due to the responsive PANI shell encapsulating the gold nanoparticles, this 2D zigzag assembly enables flexible tuning of plasmonic resonance under pH regulation.

Streamlined Flow Synthesis of Plasmonic Nanoparticles and SERS Detection of Uremic Toxins with Trace-Level Liquid Volumes in a Microchamber

Rapid detection of uremic toxins is crucial due to their severe health risks, including oxidative stress, inflammation, neurotoxicity, cardiovascular complications, and progression of chronic kidney disease. Surface-enhanced Raman spectroscopy (SERS) may provide sensitive, fast, and clinical-grade real-time monitoring of these toxins, enabling effective management with timely dialysis treatments. This study introduces a 3D-printed microchamber that integrates the fabrication of plasmonic metal nanoparticles for the in-flow detection of biological toxins and pharmaceutical drugs using SERS, making it ideal for on-site diagnostics in clinical settings. The microchamber supports quantitative and highly reproducible detection with liquid volumes under 100 μL, which is crucial for trace-level biomarker detection and minimizing cross-contamination. It employs a tunable solvent exchange method for the in situ synthesis of silver nanoparticles (AgNPs) on flexible PDMS or rigid Si wafer substrates, avoiding costly nanofabrication techniques. Ultralow detection limits were achieved for two model compounds and three pharmaceutical drugs: 10-11 M for rhodamine 6G, 10-7 M for adenine, and 10-6 M for the pharmaceutical drugs. A total of 13 biological toxins, including three neurotransmitters, one neuromodulator, five amino acids, two polyamines, and two urea cycle metabolites, were detected with quantitative limits ranging from 10-3 to 10-6 M, all below permissible levels and aligning with physiological conditions. SERS detection within microchambers facilitates rapid on-site analysis, proving ideal for personalized health monitoring, point-of-care diagnostics, and environmental pollution assessment.

Refractiveindex.info database of optical constants

We introduce the refractiveindex.info database, a comprehensive open-source repository containing optical constants for a wide array of materials, and describe in detail the underlying dataset. This collection, derived from a meticulous compilation of data sourced from peer-reviewed publications, manufacturers' datasheets, and authoritative texts, aims to advance research in optics and photonics. The data is stored using a YAML-based format, ensuring integrity, consistency, and ease of access. Each record is accompanied by detailed metadata, facilitating a comprehensive understanding and efficient utilization of the data. In this descriptor, we outline the data curation protocols and the file format used for data records, and briefly demonstrate how the data can be organized in a user-friendly fashion akin to the books in a traditional library.