Anisotropic metal nanoparticles for surface enhanced Raman scattering

The optimization of the enhancement of Raman scattering by plasmonic effects is largely determined by the properties of the enhancing substrates. The main parameters behind this effect are related to the morphology of plasmonic nanoparticles and their relative distribution within the substrate. We focus this tutorial review on the effects of nanoparticle morphology, for the particular case of anisotropic metal nanoparticles. Anisotropy in silver and gold nanoparticles offers the possibility to tailor their plasmonic properties and intrinsic electromagnetic ‘‘hotspots’’. We describe the effect of varying particle size and shape on the SERS signal, focusing on the most common anisotropic morphologies used for SERS. Especial emphasis is made on existing comparative studies that shed light on the effect of nanoparticle anisotropy on their enhancement capabilities. We aim at providing a general perspective toward understanding the general key factors and highlighting the difficulty in quantitatively determining SERS performance

Plexcitonic nanorattles as highly efficient SERS‐encoded tags

Plexcitonic nanoparticles exhibit strong light‐matter interactions, mediated by localized surface plasmon resonances, and thereby promise potential applications in fields such as photonics, solar cells, and sensing, among others. Herein, these light‐matter interactions are investigated by UV‐visible and surface‐enhanced Raman scattering (SERS) spectroscopies, supported by finite‐difference time‐domain (FDTD) calculations. Our results reveal the importance of combining plasmonic nanomaterials and J‐aggregates with near‐zero‐refractive index. As plexcitonic nanostructures nanorattles are employed, based on J‐aggregates of the cyanine dye 5,5,6,6‐tetrachloro‐1,1‐diethyl‐3,3‐bis(4‐sulfobutyl)benzimidazolocarbocyanine (TDBC) and plasmonic silver‐coated gold nanorods, confined within mesoporous silica shells, which facilitate the adsorption of the J‐aggregates onto the metallic nanorod surface, while providing high colloidal stability. Electromagnetic simulations show that the electromagnetic field is strongly confined inside the J‐aggregate layer, at wavelengths near the upper plexcitonic mode, but it is damped toward the J‐aggregate/water interface at the lower plexcitonic mode. This behavior is ascribed to the sharp variation of dielectric properties of the J‐aggregate shell close to the plasmon resonance, which leads to a high opposite refractive index contrast between water and the TDBC shell, at the upper and the lower plexcitonic modes. This behavior is responsible for the high SERS efficiency of the plexcitonic nanorattles under both 633 nm and 532 nm laser illumination. SERS analysis showed a detection sensitivity down to the single‐nanoparticle level and, therefore, an exceptionally high average SERS intensity per particle. These findings may open new opportunities for ultrasensitive biosensing and bioimaging, as superbright and highly stable optical labels based on the strong coupling effect.Agencia Estatal de Investigación | Ref. PID2019-108854RA-I00Agencia Estatal de Investigación | Ref. PID2019-108954RB-I00Agencia Estatal de Investigación | Ref. PRE2020-096163Agencia Estatal de Investigación | Ref. PRE2020- 094237Fundação para a Ciência e a Tecnologia | Ref. 2022.03164Universidade de Vigo/CISU

Ag2S Biocompatible Ensembles as Dual OCT Contrast Agents and NIR Ocular Imaging Probes

Ag2S nanoparticles (NPs) emerge as a unique system that simultaneously features in vivo near-infrared (NIR) imaging, remote heating, and low toxicity thermal sensing. In this work, their capabilities are extended into the fields of optical coherence tomography (OCT), as contrast agents, and NIR probes in both ex vivo and in vivo experiments in eyeballs. The new dual property for ocular imaging is obtained by the preparation of Ag2S NPs ensembles with a biocompatible amphiphilic block copolymer. Rather than a classical ligand exchange, where surface traps may arise due to incomplete replacement of surface sites, the use of this polymer provides a protective extra layer that preserves the photoluminescence properties of the NPs, and the procedure allows for the controlled preparation of submicrometric scattering centers. The resulting NPs ensembles show extraordinary colloidal stability with time and biocompatibility, enhancing the contrast in OCT with simultaneous NIR imaging in the second biological windowThis work was funded by the Ministry of Science and Innovation (Spain) through the projects PID2020-118878RB-I00, PID2019-106211RB I00, PID2019-109506RB-100, PID2021-127033OB-C21, and PID2019- 108854RA-I00. A.E. acknowledges RYC2020-029282-I contract and R.L.-M. acknowledges FPI PRE2020-96246. Additional funding was provided by the Instituto de Salud Carlos III (PI19/00565), by the Comunidad Autónoma de Madrid (CAM) and the Universidad Autónoma de Madrid (SI3-PJI 2021-00211), the CAM (S2022/BMD-7403 RENIM-CM) co-financed by the European structural and investment fund, and through COST action CA17140, supported by COST (European Cooperation in Science and Tech nology), as well as the Fundación para la Investigación Biomédica del Hos pital Universitario Ramón y Cajal program IMP21_A4 (2021/0427). A.C.acknowledges the JAE-Intro grant from the Nanomedicine Hub CSIC. Mice were housed and handled in accordance with the ARVO statement for the Use of Animals in Ophthalmic and Vision Research and the guidelines of the European Union and the local ethics committees of the CSIC and the Comunidad de Madrid (Ref: PROEX 272.8/21, 01 October 2021