Synthesis of single-crystal silver slices with predominant (111) facet and their SERS effect

Highly Efficient Photoinduced Enhanced Raman Spectroscopy (PIERS) from Plasmonic Nanoparticles Decorated 3D Semiconductor Arrays for Ultrasensitive, Portable, and Recyclable Detection of Organic Pollutants

Semiconductor materials have become competitive candidates for surface-enhanced Raman scattering (SERS) substrates; however, their limited SERS sensitivity hinders the practical applications of semiconductors. Here, we develop a hybrid substrate by integrating anatase/rutile TiO₂ heterostructure with dense plasmonic hotspots of Ag nanoparticle (AgNPs) for efficient photoinduced enhanced Raman spectroscopy (PIERS). The PIERS mechanism is systematically investigated by means of a portable Raman instrument. When ultraviolet (UV) light irradiates the substrate, the TiO₂-Ag hybrid arrays produce remarkable charge-transfer enhancement, which can be ascribed to the highly efficient charge separation driven by heterojunction and transfer from TiO₂ heterostructure to AgNPs. This platform allows for the rapid detection of multifold organic species, including malachite green (MG), crystal violet (CV), rhodamine 6G (R6G), thiram, and acephate, and as high as 27.8-fold enhancement over the normal SERS is achieved, representing the highest PIERS magnification up to the present time. The intensive PIERS enhancement makes it ultrasensitively detect analyte concentration of an order of magnitude lower than that of SERS method. The improved sensitivity and resolution can be readily realized by simple UV irradiation, which represents a major advantage of our PIERS methodology. Besides, the integration of uniform TiO₂ heterostructure arrays with AgNPs generates superior signal reproducibility with relative standard deviation (RSD) value of less than 14%. In addition, the detected molecules on the substrate can be eliminated by photocatalytic degradation after PIERS measurements by using UV irradiation, which makes the substrate reusable for 15 cycles. The ultrahigh sensitivity, superior reproducibility, and excellent recyclability displayed by our platform may provide new opportunities in field detection analysis coupled with a portable Raman instrument.

Synthesis of Clean Cabbagelike (111) Faceted Silver Crystals for Efficient Surface-Enhanced Raman Scattering Sensing of Papaverine

Clean cabbagelike (111) faceted silver crystals were synthesized via a facile galvanic replacement reaction of [Ag(NH₃)₂]OH and a commercial aluminum foil, a surfactant-free formation process. The cabbagelike silver crystals consisted of interconnected nanoplates and exhibited a single-crystal structure along with preferential (111) facet oriented growth. These silver crystals showed high and reliable surface-enhanced Raman scattering (SERS) activity due to electromagnetic mechanism, and they could be easily transferred onto other rigid or flexible surfaces, making their SERS applications more versatile. Since Ag (111) with low surface energy could preferentially adsorb papaverine molecules, which was verified by molecular dynamics simulation, the cabbagelike silver crystals were further employed as a promising SERS assay for efficient sensing of papaverine, a nonnarcotic alkaloid. A linear range of 0.1-1000 μM was achieved, along with a detection limit of 10 nM and good selectivity relative to other excitability drugs. This SERS assay has successfully been used to determine the concentration of papaverine in hot pot seasonings and drugs with satisfactory recoveries and relative standard deviations.

Rationally Designed Graphene/Bilayer Silver/Cu Hybrid Structure with Improved Sensitivity and Stability for Highly Efficient SERS Sensing

A simple and cost-effective strategy was rationally designed to fabricate a special sandwich structure consisting of graphene, bilayer silver, and a copper plate, which was used as a surface-enhanced Raman scattering (SERS) substrate for highly efficient SERS sensing and detection of trace molecules. Silver dendrite (AgD) nanostructures were subsequently grown on a silver nanosphere (AgNS)/Cu surface to form a bilayer silver/Cu structure, which showed a 1.5-fold Raman enhancement compared to that of the AgNS/Cu substrate. After depositing graphene on the bilayer silver/Cu substrate to obtain a sandwich structure, a higher SERS enhancement and better durability were enabled. The SERS performances, measured by a portable Raman instrument, showed that the optimized sandwich structure substrate exhibited high SERS sensitivity to crystal violet (CV) and rhodamine 6G (R6G) with low limit of detection of 10^-9 and 10^-8 M, respectively. Such a sandwich-structured substrate exhibited good reproducibility across the entire detection areas with an average relative standard deviation less than 5.9%, which permits its reliable quantitative detection of CV and R6G molecules. In addition, graphene both effectively improved the SERS performances and protected Ag nanocrystals from oxidation, which endowed the sandwich structure a long-term stability with deviation of characteristic peaks' intensity lower than 3.6% after 25 days. This study indicates that the graphene/bilayer silver/Cu sandwich structure as a SERS substrate has a great potential in detecting environmental pollutants.

Cube-like Fe3O4@SiO2@Au@Ag magnetic nanoparticles: a highly efficient SERS substrate for detection of pesticide

As a novel SERS nanocomposities, cube-like Fe3O4@SiO2@Au@Ag magnetic nanoparticles have been synthesized for the first time. Cube-like α-Fe2O3 NPs with uniform size can be achieved by optimizing reaction temperature and time. Firstly, the cube-like Fe3O4@SiO2 with good dispersity were achieved by calcining α-Fe2O3@SiO2 NPs in hydrogen atmosphere at 360 °C for 2.5 h, followed by self-assembling PEI shell via sonication. Furthermore, the Au@Ag particles can be densely assembled on the Fe3O4@SiO2 NPs to form the Fe3O4@SiO2@Au@Ag composite structure via strong Ag-N interaction. The obtained nanocomposites exhibit an excellent surface-enhanced Raman (SERS) behavior, reflected from low detection of limit (p-ATP) at 5×10-14 M level. Moreover, these nanocubes are used for detection of thiram and the detection limit can reach up to 5×10-11 M, while the rule of U.S. Environmental Protection Agency specifies that the residue in fruit must be lower than 7 ppm. Hence, the resulting substrate with high SERS activity has great practical potential applications in rapid detection of chemical, biological and environment pollutants with a simple portable Raman instrument at trace level.

A Simple Route to Synthesize Cu@Ag Core-Shell Bimetallic Nanoparticles and Their Surface-Enhanced Raman Scattering Properties

Water-dispersed Cu@Ag core-shell nanoparticles (NPs) with 15 nm-diameter Cu core and 5 nm-thick Ag shell can be synthesized by a facile one-step chemical reduction at room temperature without any protective atmosphere. To obtain a homogeneous Ag coating on Cu, the influence of [Cu/Ag] molar ratio was investigated. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed that Ag formed a dense coating on the surface of Cu, and that phase-pure spherical Cu@Ag core-shell bimetallic NPs were prepared when the [Cu/Ag] molar ratio was between 1/0.5 and 1/0.75. The time dependence of ultraviolet-visible (UV-Vis) spectra and XRD patterns of six-month stored Cu@Ag NPs showed that the as-prepared Cu@Ag NPs have a long-term antioxidant activity. Also, the surface-enhanced Raman scattering (SERS) signals had a high stability and reproducibility for the substrates. Hence, the as-prepared Cu@Ag nanostructures can be used as an efficient substrate for SERS signals.

Carbamide promoted polyol synthesis and transmittance properties of silver nanocubes

Ag nanocubes of different sizes were rapidly synthesized via a polyol approach promoted by CO(NH₂)₂ and the transmittance properties have been detected.

Localized Surface Plasmon Resonance of Silver Nanotriangles Synthesized by a Versatile Solution Reaction

The surface plasmon resonance (SPR) of silver nanoparticles can be tuned throughout the visible and near-infrared region by their shape and size. Considering SPR applications, an easy and controllable method for preparing the silver nanocrystals with defined shape and size, is necessary. In this work, the triangular silver nanoplates were synthesized by reducing Ag(+) ions with ascorbic acid in the presence of silver seeds and poly(vinylpyrrolidone) (PVP) at room temperature. Both the seeds (as the nucleation sites) and PVP (as the capping reagent) played an important role in determining the edge length of the silver nanotriangles. The SPR of silver nanotriangles showed three distinct bands corresponding to the in-plane dipole, quadrupole, and out-plane quadrupole plasmon resonance, and the SPR shifted to shorter wavelengths with the decreased edge length of the silver nanotriangles as the theoretical calculation.

Effect of metal ions on the morphology of silver nanocrystals

Ag nanoplates were obtained in our developed benzyl alcohol system in the presence of Al³⁺ ions or Fe³⁺ ions.

Generalized green synthesis of diverse LnF3–Ag hybrid architectures and their shape-dependent SERS performances

Diverse LnF₃–Ag hybrid architectures as substrates exhibit superior SERS performance and excellent detection sensibility for analytes.