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The tumor microenvironment (TME) is a dynamic pseudoorgan that shapes the development and progression of cancers. It is a complex ecosystem shaped by interactions between tumor and stromal cells. Although the traditional focus has been on the paracrine communication mediated by protein messengers, recent attention has turned to the metabolic secretome in tumors. Metabolic enzymes, together with exchanged substrates and products, have emerged as potential biomarkers and therapeutic targets. However, traditional techniques for profiling secreted metabolites in complex cellular contexts are limited. Surface-enhanced Raman scattering (SERS) has emerged as a promising alternative due to its nontargeted nature and simplicity of operation. Although SERS has demonstrated its potential for detecting metabolites in biological settings, its application in deciphering metabolic interactions within multicellular systems like the TME remains underexplored. In this study, we introduce a SERS-based strategy to investigate the secreted purine metabolites of tumor cells lacking methylthioadenosine phosphorylase (MTAP), a common genetic event associated with poor prognosis in various cancers. Our SERS analysis reveals that MTAP-deficient cancer cells selectively produce methylthioadenosine (MTA), which is taken up and metabolized by fibroblasts. Fibroblasts exposed to MTA exhibit: i) molecular reprogramming compatible with cancer aggressiveness, ii) a significant production of purine derivatives that could be readily recycled by cancer cells, and iii) the capacity to secrete purine derivatives that induce macrophage polarization. Our study supports the potential of SERS for cancer metabolism research and reveals an unprecedented paracrine crosstalk that explains TME reprogramming in MTAP-deleted cancers. [ABSTRACT FROM AUTHOR]

Chiral metal nanoparticles (NPs) offer a powerful means of inducing and harnessing optical activity. However, due to the incomplete knowledge of the underlying growth mechanisms, there is still limited control over the achievable morphological detail and, consequently, over the resulting optical activity. Therefore, theoretical modeling is needed to guide experimental development toward optimizing the plasmonic chiroptical response. Toward filling this gap, herein an extensive parametric analysis is presented, via computer‐aided‐design (CAD) models and full‐wave electrodynamic simulations, which aims at systematically analyzing the influence of structural changes on the plasmonic circular dichroism (CD) spectra of rod‐shaped gold NPs comprising helical indentations on achiral nanorod cores. From this analysis, interesting patterns in the plasmon‐mediated resonant behavior are identified and cause–effect relationships are drawn that may serve as a go‐to recipe for the understanding and fabrication of these NPs and their applications, such as spectroscopic (bio)detection including CD spectral shifts and surface‐enhanced Raman optical activity. [ABSTRACT FROM AUTHOR]

Bottom‐up assembly of nanoparticle‐on‐mirror (NPoM) nanocavities enables precise inter‐metal gap control down to ≈ 0.4 nm for confining light to sub‐nanometer scales, thereby opening opportunities for developing innovative nanophotonic devices. However limited understanding, prediction, and optimization of light coupling and the difficulty of controlling nanoparticle facet shapes restricts the use of such building blocks. Here, an ultraprecise symmetry‐breaking plasmonic nanocavity based on gold nanodecahedra is presented, to form the nanodecahedron‐on‐mirror (NDoM) which shows highly consistent cavity modes and fields. By characterizing > 20 000 individual NDoMs, the variability of light in/output coupling is thoroughly explored and a set of robust higher‐order plasmonic whispering gallery modes uniquely localized at the edges of the triangular facet in contact with the metallic substrate is found. Assisted by quasinormal mode simulations, systematic elaboration of NDoMs is proposed to give nanocavities with near hundred‐fold enhanced radiative efficiencies. Such systematically designed and precisely‐assembled metallic nanocavities will find broad application in nanophotonic devices, optomechanics, and surface science. [ABSTRACT FROM AUTHOR]

Controlled assembly of gold nanoparticles (AuNPs) into clusters is a promising avenue for the development of sensitive bioimaging and diagnostic tools based on surface‐enhanced Raman scattering (SERS). However, several challenges, such as biocompatibility or colloidal and structural stability in biological environments, remain before AuNPs can be used as a tool for in vivo bioimaging. A versatile strategy for the preparation of colloidally stable and biocompatible AuNP clusters (AuNPCs) is introduced with high SERS signals, which are used as SERS contrast bioimaging agents (SERS tags). By tuning the ligand ratio of Raman reporter molecules to stabilizing polymer on the surface of each AuNP, aggregation can be carefully controlled. The resulting AuNPCs exhibit redshifted surface plasmon resonances in the near‐infrared (NIR) region, as well as distinct electromagnetic hotspots that give rise to SERS analytical enhancement factors above 104, compared to non‐clustered spherical AuNPs. Thanks to the protective polymer shell, high levels of cellular uptake with low cytotoxicity are observed, allowing 3D SERS mapping of cells with sufficiently high spatial resolution to detect AuNPCs within intracellular organelles. [ABSTRACT FROM AUTHOR]

Plasmonic metal‐organic frameworks are composite nanoparticles comprising plasmonic metal nanoparticles (NPs) embedded within a metal‐organic framework (MOF) matrix. As a result, not only the functionalities of the individual components are retained, but synergistic effects additionally provide improved chemical and physical properties. Recent progress in plasmonic MOFs has demonstrated the potential for nanofabrication and various nanotechnology applications. Synthetic challenges toward plasmonic MOFs have been recently addressed, resulting in new opportunities toward practical applications, such as surface‐enhanced Raman scattering, therapy, and catalysis. The impact of key parameters (thermodynamic vs. kinetic) on the synthetic pathways of plasmonic MOFs is reviewed, while providing insight into related progress toward structure‐derived applications. [ABSTRACT FROM AUTHOR]

Lattice plasmons, i.e., diffractively coupled localized surface plasmon resonances, occur in long‐range ordered plasmonic nanostructures such as 1D and 2D periodic lattices. Such far‐field coupled resonances can be employed for ultrasensitive surface‐enhanced Raman spectroscopy (SERS), provided they are spectrally matched to the excitation wavelength. The spectral positions of lattice plasmon modes critically depend on the lattice period and uniformity, owing to their pronounced sensitivity to structural disorder. We report the fabrication of superlattices by templated self‐assembly of gold nanoparticles on a flexible support, with tunable lattice‐plasmon resonances by means of macroscopic strain. We demonstrate that the highest SERS performance is achieved by matching the lattice plasmon mode to the excitation wavelength, by post‐assembly fine‐tuning of long‐range structural parameters. Both asymmetric and symmetric lattice deformations can be used to adapt a single lattice structure to both red‐shifted and blue‐shifted excitation lines, as exemplified by lattice expansion and contraction, respectively. This proof‐of‐principle study represents a basis for alternative designs of adaptive functional nanostructures with mechanically tunable lattice resonances using strain as a macroscopic control parameter. [ABSTRACT FROM AUTHOR]

Raman spectroscopy is becoming increasingly popular as an in vitro bioimaging technique, when coupled with plasmonic substrates such as gold nanoparticles (AuNPs). Plasmonic AuNPs not only display excellent biocompatibility but can also induce the surface‐enhanced Raman scattering (SERS) effect, which can be exploited for cell labeling, as an interesting alternative to fluorescence‐based techniques. SERS bioimaging requires the use of so‐called SERS tags or SERS‐encoded AuNPs. A remaining difficulty toward the general implementation of this method is the difficulty to correlate the SERS signal (spectral intensity) with the number of SERS tags. Therefore, a general correlation method, suitable for arbitrary AuNP morphologies and Raman‐active molecules (Raman reporters or RaRs), should largely improve the quantitative character of SERS as an imaging technique. We propose a protocol, with an associated app (SERSTEM), which enables the user to determine the average SERS intensity per nanoparticle from transmission electron microscopy (TEM) and SERS data. As a proof of concept, we demonstrated the method for Au nanostars and nanorods, carrying four different RaRs, and implemented the SERSTEM app, which is publicly available from an open‐source platform. [ABSTRACT FROM AUTHOR]

Abstract: Polymers and nanoparticles can be combined into different materials with applications in various fields like catalysis, biotechnology, or drug delivery, to cite just a few. Colloidal composites may vary significantly, ranging from a single nanoparticle stabilized by a polymer shell through a polymeric carrier decorated with hundreds of particles. We review here composite colloids comprising gold nanoparticles, with an emphasis in systems with potential application in surface enhanced Raman scattering (SERS). The focus is on selected strategies for synthesis and functionalization, such as: encapsulation of gold nanoparticles by amphiphilic polymers, polymeric matrices as nanoparticle carriers and smart polymer based composites. We stress the benefits derived from the combination of polymers and metal particles toward SERS, such as chemical and colloidal stabilization in complex environments, and collective optical effects through hot spot generation for optimized SERS enhancement or improved imaging tags. [ABSTRACT FROM AUTHOR]

This feature article focuses on the use of colloid chemistry to engineer metallic nanostructures toward application in surface enhanced Raman scattering (SERS) sensing, in particular for ‘real-life’ applications, where the analyte may be present in complex mixtures. We present a broad summary of the field, including recent advances that have been developed during the past 10 years. Real-life applications require a rational design and we aimed at identifying the key elements involved in it. The discussion is centered around colloidal plasmonic nanoparticles and therefore we start from the library of morphologies that have been reported in the literature. To complete the picture, colloidal self-assembly, surface chemistry and the combination with materials science techniques are highlighted. Considering the progress in the field, SERS may ultimately realize its full potential as an ultrasensitive tool for routine analytical applications. [ABSTRACT FROM AUTHOR]

The incorporation of gold nanoparticles in biodegradable polymeric nanostructures with controlled shape and size is of interest toward different applications in nanomedicine. Properties of the polymer such as drug loading and antibody functionalization can be combined with the plasmonic properties of gold nanoparticles, to yield advanced hybrid materials. This study presents a new way to synthesize multicompartmental microgels, fibers, or cylinders, with embedded anisotropic gold nanoparticles. Gold nanoparticles dispersed in an organic solvent can be embedded within the poly(lactic- co-glycolic acid) (PLGA) matrix of polymeric microstructures, when prepared via electrohydrodynamic co-jetting. Prior functionalization of the plasmonic nanoparticles with Raman active molecules allows for imaging of the nanocomposites by surface-enhanced Raman scattering (SERS) microscopy, thereby revealing nanoparticle distribution and photostability. These exceptionally stable hybrid materials, when used in combination with 3D SERS microscopy, offer new opportunities for bioimaging, in particular when long-term monitoring is required. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Simple wet chemistry has been applied to control the vertical growth of gold nanowires on a glass substrate. As a consequence, the longitudinal localized surface plasmon band position can be tuned from 656 to 1477 nm in a few minutes by simply controlling the growth rate and time. This allowed us to select the optimum conditions for maximum electromagnetic enhancement and performance in surface enhanced Raman scattering (SERS) detection. SERS measurements confirmed the uniform and reproducible distribution of the nanowires on the substrate, with the subsequent high reproducibility of hot spot formation. Detection of malachite green in water and of 1-naphthalenethiol from the gas phase are demonstrated as proof-of-concept applications of these three-dimensional SERS substrates. [ABSTRACT FROM AUTHOR]

No Abstract [ABSTRACT FROM AUTHOR]

Surface enhanced Raman scattering (SERS) spectroscopy is a powerful technique that provides molecular information through greatly enhanced Raman scattering from minute amounts of substance near nanostructured metallic surfaces. SERS is thus a promising technique for ultrasensitive sensing applications. Plasmonic nanostructures including metal nanoparticles and lithographically prepared nanostructures are ideal substrates to produce enhanced Raman signals. Numerous studies have been published on the production of SERS-active substrates for SERS measurements including solution phase methods and solid supports. In SERS applications, hot spots where the electromagnetic field is particularly intense, play a key role. In this review, we provide an overview of techniques designed for the creation of SERS hot spots both in solution and on solid supports. We first introduce the self-assembly of spherical and anisotropic nanoparticles in solution, to then focus on a wide variety of techniques to assemble nanoparticles onto solid supports. We also describe top-down approaches typically based on lithography techniques. Finally, we provide our own view on the current state of the field and the aspects where further development is expected. [ABSTRACT FROM AUTHOR]

Recent studies have shown that layered silicate clays can be used to form a nacre-like bioinspired layered structure with various polymer fillers, leading to composite films with good material strength, gas-barrier properties, and high loading capacity. We go one step further by in situ growing metal nanoparticles in nacre-like layered films based on layered silicate clays, which can be used for applications in plasmonic sensing and catalysis. The degree of anisotropy of the nanoparticles grown in the film can be controlled by adjusting the ratio of clay to polymer or gold to clay and reducing agent concentration, as well as silver overgrowth, which greatly enhances the surface enhanced Raman scattering activity of the composite. We show the performance of the films for SERS detection of bacterial quorum sensing molecules in culture medium, and catalytic properties are demonstrated through the reduction of 4-nitroaniline. These films serve as the first example of seedless, in situ nanoparticle growth within nacre-mimetic materials, and open the path to basic research on the influence of different building blocks and polymeric mortars on nanoparticle morphology and distribution, as well as applications in catalysis, sensing, and antimicrobial surfaces using such materials. [ABSTRACT FROM AUTHOR]

We describe the preparation of multibranched gold-silica-molecularly imprinted polymer (bAu@mSiO2@MIP) core-shell nanoparticles, with their specific ability to recognize enrofloxacin (ENRO), and their application as label-free nanosensors for the specific detection of the antimicrobial by surface-enhanced Raman scattering. The use of these nanocomposites results in a large enhancement of the Raman scattering of ENRO upon binding of an antibiotic to the selective recognition sites in the MIP. These are in the proximity of the gold core branches that act as intrinsic hot spots providing highly localized and strongly enhanced electromagnetic fields caused by plasmon resonance. The effect of the multibranched morphology of the gold cores (bAu) on the optical spectroscopic response of the bAu@mSiO2@MIP nanosensors is investigated with the aim of improving ENRO detection. The optimized nanostructures allowed us to achieve a detection limit of 1.5 nM for ENRO, which is 2 orders of magnitude lower than those for previously reported Au@MIP nanosensors, additionally providing negligible cross-reactivity toward other potential interfering species. [ABSTRACT FROM AUTHOR]

Labeled nanoparticles have attracted much interest toward applications in bioimaging and diagnostics. In particular, surface enhanced Raman scattering (SERS) nanotags have been demonstrated to be excellent candidates for multiplexed imaging and biological detection. We propose an alternative, effective method to easily prepare gold nanostars exhibiting plasmon bands in the near-infrared range, encoded with Raman reporter molecules, concomitantly acting as capping agents which are then protected with an amphiphilic polymer. The resulting nanotags are noncytotoxic and display long-term stability against aggregation and reporter leakage, while showing reproducible SERS signals suitable for multiplexing. These tags were used to distinguish five different types of breast cancer cells by imaging of a quintuple cell coculture. Time-lapse SERS imaging of the coculture was additionally performed, demonstrating the applicability of these nanotags for cell tracing over time scales above 24 h. [ABSTRACT FROM AUTHOR]

Wedescribe a simple and efficient methodology for the aqueoussynthesis of stable, uniform, and size tunable Au@Ag core–shellnanoparticles (NPs) that are stabilized by citrate ions. The syntheticroute is based on the stepwise Ag reduction on preformed Au NPs. Thefinal size of the core–shell NPs and therefore their opticalproperties can be modulated at least from 30 to 110 nm by either tuningthe Ag shell thickness or changing the size of the Au core. The opticalproperties of the Au@Ag core–shell NPs resemble those of pureAg NPs of similar sizes, which was confirmed by means of Mie extinctioncalculations. We additionally evaluated the surface-enhanced ramanscattering(SERS) enhancing properties of Au@Ag core–shell NP colloidswith three different laser lines (532, 633, and 785 nm). Importantly,such core–shell NPs also exhibit a higher SERS efficiency thanAg NPs of similar size under near-infrared excitation. The resultsobtained here serve as a basis to select Au@Ag core–shell NPsof specific size and composition with maximum SERS efficiency at theirrespective excitation wavelengths for SERS-based analytical and bioimagingapplications. [ABSTRACT FROM AUTHOR]