Ag Nanowire‐Ag Nanoparticle Hybrids for the Highly Enhanced Fluorescene Detection of Protoporphyrin IX Based on Surface Plasmon‐Enhanced Fluorescence

In this study, we developed an approach to fabricate novel 1D Ag NWs‐Ag NPs hybrid substrate for enhanced fluorescene detection of protoporphyrin IX (PpIX) based on surface plasmon‐enhanced fluorescence. The Ag NWs‐Ag NPs hybrid was synthesized by combining the hydrothermal method and self‐assembly method with the asisstance of polyvinylpyrrolidone (PVP). When the Ag NWs‐Ag NPs hybrid was deposited on the glass substrate and employed as active substrate to detect PpIX, the fluorescence intensity of PpIX was enhanced greatly due to the coupling effect of localized surface plasmon‐localized surface plasmon (LSP‐LSP) and localized surface plasmon‐surface plasmon propagation (LSP‐SPP) which induced great enhancement of the electromagnetic field. Furthermore, the enhancement effect was approximately linear when the concentration of PpIX was ranged from 1×10^?7 mol/L to 2×10^?5 mol/L, and the photobleaching phenomenon of PpIX was reduced greatly, indicating that the fabricated Ag NWs‐Ag NPs hybrid substrate had well performance for PpIX imaging. This work provides an effective approach to prepare highly sensitive and stable fluorescence enhancement substrate, and has great potential application in fluorescence imaging.     

SiO2/TiO2 Hollow Nanoparticles Decorated with Ag Nanoparticles: Enhanced Visible Light Absorption and Improved Light Scattering in Dye‐Sensitized Solar Cells

Hollow SiO₂/TiO₂ nanoparticles decorated with Ag nanoparticles (NPs) of controlled size (Ag@HNPs) were fabricated in order to enhance visible‐light absorption and improve light scattering in dye‐sensitized solar cells (DSSCs). They exhibited localized surface plasmon resonance (LSPR) and the LSPR effects were significantly influenced by the size of the Ag NPs. The absorption peak of the LSPR band dramatically increased with increasing Ag NP size. The LSPR of the large Ag NPs mainly increased the light absorption at short wavelengths, whereas the scattering from the SiO₂/TiO₂ HNPs improved the light absorption at long wavelengths. This enabled the working electrode to use the full solar spectrum. Furthermore, the SiO₂ layer thickness was adjusted to maximize the LSPR from the Ag NPs and avoid corrosion of the Ag NPs by the electrolyte. Importantly, the power conversion efficiency (PCE) increased from 7.1 % with purely TiO₂‐based DSSCs to 8.1 % with HNP‐based DSSCs, which is an approximately 12 % enhancement and can be attributed to greater light scattering. Furthermore, the PCEs of Ag@HNP‐based DSSCs were 11 % higher (8.1 vs. 9.0 %) than the bare‐HNP‐based DSSCs, which can be attributed to LSPR. Together, the PCE of Ag@HNP‐based DSSCs improved by a total of 27 %, from 7.1 to 9.0 %, due to these two effects. This comparative research will offer guidance in the design of multifunctional nanomaterials and the optimization of solar‐cell performance.     

Cofluorescence of dyes in nanoparticles from metal ion complexes with diketones

Nanoparticles (NPs) from diketonates of Al³⁺, Sc³⁺, In³⁺ and Ln³⁺ doped with dye molecules are synthesized. The appearance of sensitized fluorescence (cofluorescence) of dye molecules due to energy transfer from the ensemble of complexes forming NPs is revealed in aqueous solutions of these NPs. It is shown that the dye cofluorescence in NPs from Eu complexes occurs as a result of two distinct processes of energy transfer (ET) to dye molecules: from singlet levels of ligands and from Eu³⁺ ions. It is found that the efficiency of ET from Eu³⁺ ions to dyes in NPs from Eu(DBM)₃phen is one order of magnitude higher than the efficiency of ET from S₁-levels of ligands to dyes in NPs from Al complexes with the same ligands. It is shown that the excitation of dye molecules through ligands of NPs results in the enhancement of the intensity of their fluorescence by a factor of 1.5–2 orders of magnitude compared to the excitation of their own first band of absorption.     

Biocompatible Triplex Ag@SiO2@mTiO2 Core–Shell Nanoparticles for Simultaneous Fluorescence‐SERS Bimodal Imaging and Drug Delivery

Herein, we report the synthesis of biocompatible triplex Ag@SiO₂@mTiO₂ core–shell nanoparticles (NPs) for simultaneous fluorescence‐surface‐enhanced Raman scattering (F‐SERS) bimodal imaging and drug delivery. Stable Raman signals were created by typical SERS tags that were composed of Ag NPs for optical enhancement, a reporter molecule of 4‐mercaptopyridine (4‐Mpy) for a spectroscopic signature, and a silica shell for protection. A further coating of mesoporous titania (mTiO₂) on the SERS tags offered high loading capacity for a fluorescence dye (flavin mononucleotide) and an anti‐cancer drug (doxorubicin (DOX)), thereby endowing the material with fluorescence‐imaging and therapeutic functions. The as‐prepared F‐SERS dots exhibited strong fluorescence when excited by light at 460 nm whilst a stable, characteristic 4‐Mpy SERS signal was detected when the excitation wavelength was changed to longer wavelength (632.8 nm), both in solution and after incorporation inside living cells. Their excellent biocompatibility was demonstrated by low cytotoxicity against MCF‐7 cells, even at a high concentration of 100 μg mL^?1. In vitro cell cytotoxicity confirmed that DOX‐loaded F‐SERS dots had a comparable or even greater therapeutic effect compared with the free drug, owing to the increased cell‐uptake, which was attributed to the possible endocytosis mechanism of the NPs. To the best of our knowledge, this is the first proof‐of‐concept investigation on a multifunctional nanomedicine that possessed a combined capacity for fast and multiplexed F‐SERS labeling as well as drug‐loading for cancer therapy.     

Matrices based on meso antibacterial framework

In this paper, the synthesis of three types of porous materials (PMs) (porous Fe₃O₄, MIL-101 metal-organic framework (MOF), and MCM-41 mesoporous silica) by hydrothermal method was performed. The incorporation of Ag nanoparticles (Ag NPs) was carried out after the synthesis reaction of supports in MCM-41 and MIL-101 MOF. Ag core@ porous Fe₃O₄ core–shell system was prepared via a one-pot hydrothermal method. Ag-MIL-101 was obtained using Urtica dioica leaf extract as the green solvent and reducing agent. The antibacterial activity of Ag-PM nanocomposites (NCs) was investigated on both Gram-negative and Gram-positive bacteria. The size of the silver NPs was determined to be 12 and 30 nm in MCM-41 and MIL-101 MOF, respectively. The diameter of Ag core in Ag@Fe₃O₄ shell was ~135 nm. The antibacterial activity of Ag-PMs was in the order Ag-MCM-41 > Ag-MIL-101 > Ag core@Fe₃O₄ shell. The loading percent of Ag NPs in MCM-41 (84%) was more than that in MIL-101 (53%) and Fe₃O₄ (31%). The release of Ag⁺ ions from Ag-MCM-41, Ag-MIL-101, and Ag@Fe₃O₄ NCs was 46, 2, and 1 ppm, respectively. The release of the Ag⁺ ions and, consequently, the antibacterial activity of NCs depend on the uniform distribution, particles size, and the absence of aggregation of Ag NPs in PMs.     

Charge Separation and Catalytic Activity of Fe3O4@Ag “Nanospheres”

Nanospheres of Ag‐coated Fe₃O₄ were successfully synthesized and characterized. Photocatalytic properties of Fe₃O₄@Ag composites have been investigated using steady‐state studies and laser pulse excitations. Accumulation of the electrons in the Ag shell was detected from the shift in the surface plasmon band from 430 to 405 nm, which was discharged when an electron acceptor such as O₂, Thionine (TH) or C₆₀ was introduced into the system. Charge equilibration with redox couple such as C₆₀^●–/C₆₀ indicated the ability of these core–shell structures to carry out photocatalytic reduction reactions. As well, outer Ag layer could boost charge separation in magnetic core through dual effects of Schottky junction and localized surface plasmonic resonance (LSPR)‐powered band gap breaking effect under sunlight irradiation; resulted in higher photocatalytic degradation of diphenylamine (DPA). The maximum photocatalytic degradation rate was achieved at optimum amount of Ag‐NP loading to products. Adsorption studies confirmed that degradation of DPA dominantly occurred in solution. Moderately renewability of the nanocatalysts under sunlight was due to oxidation and dissolution of the outer Ag layer.     

Silver–platinum core–shell nanoparticles for surface-enhanced Raman spectroscopy

Core–shell Ag@Pt nanoparticles have been synthesised by the means of seed-growth reaction including reduction of PtCl₄²⁻ with silver and replacing Ag atoms with Pt. Surface-enhanced Raman scattering (SERS) spectra of pyridine (which gives slightly different spectra when interacting with various metals) adsorbed on synthesised Ag@Pt clusters were measured. SERS measurements have revealed that deposition of the platinum layer causes near elimination of the spectral interferences from pyridine directly interacting with the silver core. The average SERS enhancement factor for pyridine adsorbed on the Ag@Pt clusters was estimated as equal to about 10³–10⁴, significantly higher than the SERS enhancement factor achievable on the pure platinum nanostructures. Using the silver core (instead of the previously used gold cores) allows for measurement of strong SERS spectra on the Pt covered nanostructures for the wider range of the excitation radiation. This procedure of platinum deposition was tested with various silver nanoparticles – produced with borohydride, citrate and citrate/borohydride methods – which substantially differ in size distribution. The application of formed Ag@Pt structures for obtaining intense Raman spectra for molecules adsorbed on only slightly modified platinum surfaces is discussed.     

Porosity‐Controlled Eggshell Membrane as 3D SERS‐Active Substrate

We report on the fabrication of a surface‐enhanced Raman scattering (SERS) platform, comprised of a three‐dimensional (3D) porous eggshell membrane (ESM) scaffold decorated with Ag nanoparticles (NPs). Both native and treated ESM were used, where the treated ESM pore size and fiber crossing density was controlled by timed exposure to hydrogen peroxide (H₂O₂). Ag NPs were synthesized in situ by reduction of silver nitrate with ascorbic acid. Our results demonstrate that H₂O₂‐treated Ag‐ESM provides a more densely packed 3D network of active material, which leads to consistently higher SERS enhancement than untreated Ag‐ESM substrates.     

Fabrication of Ag Nanoparticles Embedded in TiO2 Nanotubes: Using Electrospun Nanofibers for Controlling Plasmonic Effects

Composites of electrospun poly(ethylene oxide) (PEO) fibers and silver nanoparticles (Ag NPs) were used as a soft template for coating with TiO₂ by atomic layer deposition (ALD). Whereas the as‐deposited TiO₂ layers on PEO fibers and Ag NPs were completely amorphous, the TiO₂ layers were transformed into polycrystalline TiO₂ nanotubes (NTs) with embedded Ag NPs after calcination. Their plasmonic effect can be controlled by varying the thickness of the dielectric Al₂O₃ spacer between Ag NPs and dye molecules by means of the ALD process. Electronic and spectroscopic analyses demonstrated enhanced photocurrent generation and solar‐cell performance due to the intense electromagnetic field of the dye resulting from the surface plasmon effect of the Ag NPs.     

Enhanced upconversion emission in Er3+-doped tellurite glass containing silver nanoparticles

Er³⁺-doped tellurite glass containing silver nanoparticles (NPs) has been synthesized. Detailed structural and optical characterizations have been carried out. Infrared to visible frequency upconversion (UC) emission has been observed in Er³⁺-doped tellurite glass on pumping with the 976 nm radiation. Further, an enhancement in UC emission intensity of green bands (²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2) of Er³⁺ ion has been observed up to four times in presence of silver NPs in the glass annealed at 240 °C for 40 h. Though, there is enhancement in intensity in the red band (⁴F_9/2 → ⁴I_15/2) also but it is smaller. The enhancement in fluorescence intensity is attributed to local field effect due to the silver NPs.     

Color‐Controlled Ag Nanoparticles and Nanorods within Confined Mesopores: Microwave‐Assisted Rapid Synthesis and Application in Plasmonic Catalysis under Visible‐Light Irradiation

Color‐controlled spherical Ag nanoparticles (NPs) and nanorods, with features that originate from their particle sizes and morphologies, can be synthesized within the mesoporous structure of SBA‐15 by the rapid and uniform microwave (MW)‐assisted alcohol reduction method in the absence or presence of surface‐modifying organic ligands. The obtained several Ag catalysts exhibit different catalytic activities in the H₂ production from ammonia borane (NH₃BH₃, AB) under dark conditions, and higher catalytic activity is observed by smaller yellow Ag NPs in spherical form. The catalytic activities are specifically enhanced under the light irradiation for all Ag catalysts. In particular, under light irradiation, the blue Ag nanorod shows a maximum enhancement of more than twice that observed in the dark. It should be noted that the order of increasing catalytic performance is in close agreement with the order of absorption intensity owing to the Ag localized surface plasmon resonance (LSPR) at irradiation light wavelength. Upon consideration of infrared thermal effect, wavelength dependence on catalytic activity, and effect of radical scavengers, it can be concluded that the dehydrogenation of AB is promoted by change of charge density of the Ag NP surface derived from LSPR. The LSPR‐enhanced catalytic activity can be further realized in the tandem reaction consisting of dehydrogenation of AB and hydrogenation of 4‐nitrophenol, in which a similar tendency in the enhancement of catalytic activity is observed.     

X-ray and UV photoelectron spectroscopy of Ag nanoclusters

The main purpose of the present work is to analyze a series of Ag nanoparticles (NPs) with different size or ligand functionalization by using X-ray photoelectron spectroscopy (XPS) and to identify the differences in the band-shape and energy peak position of photoemission spectra due to the particle dimension. A transmission electron microscopy characterization was performed, to verify the consistency of the results. Three types of samples were prepared starting from AgNO₃ water solution and adding different capping agents. In the first two cases, the formation of NPs was promoted by the reduction of silver ions Ag⁺¹ to metallic Ag⁰ through the addition of sodium borohydride, whereas in the last case, it was triggered by the exposure to UV light. Depending on the size of the NPs, a different physical behavior can be recognized. NPs with diameter of about 5 nm are characterized by the phenomenon of localized surface plasmon resonance (LSPR). The other type of samples having a diameter of about 1.5 nm presents discrete energy levels instead of electronic bands, and in this case, a typical fluorescence phenomenon can be observed. In the latter case, we can refer to such systems as nanoclusters. The XPS analyses were focused on the Ag 3D spectra looking for the possible shifts of the Ag doublet as a function of the particles size. The ultraviolet photoelectron spectroscopy with He II source was used for the investigation of possible changes in the valence band.     

γ-Ray induced catalytic properties of the silica nanoparticles dispersed in the aerated aqueous solution

Silica nanoparticles (NPs) dispersed in an aerated aqueous solution containing Ag⁺ were irradiated to a dose of 10 kGy using ⁶⁰Co γ-rays. The typical surface plasmon band of Ag NPs was observed around 400 nm, indicating that even in the presence of dissolved oxygen the reduction of Ag⁺ occurred by silica NPs. Transmission electron microscopy images indicated that Ag NPs formed on the surface of the silica NPs. The subtraction spectra showed broad absorption around 500 nm with the absorbance depending on the dose. The electrons generated by charge separation from silica NPs with a size of about 12 nm reduce Ag⁺ to Ag⁰ and form (Ag⁰) _n species on the silica NPs, and the type of (Ag⁰) _n species formed depended on the silica NP, and Ag⁺ contents, and the dose. In the co-presence of organic molecules on the silica NP such as rhodamine, the absorbance of the surface plasmon band of both Ag NPs and rhodamine decreased, indicating the electrons to participate in the reductive decomposition of rhodamine molecules adsorbed on the silica NP. Furthermore, in the case when the silica NPs contained fluorescein molecules, the fluorescein molecules were also decomposed, indicating that the fluorescein molecules adsorbed on the inner surface of the silica NPs. The addition of I₂ as an oxidative reagent prevented the decomposition of the fluorescein molecules, indicating that electrons are the main species emitted from irradiated silica NPs.     

Plasmonic Titanium Nitride Tubes Decorated with Ru Nanoparticles as Photo-Thermal Catalyst for CO2 Methanation

Photo-thermal catalysis has recently emerged as a viable strategy to produce solar fuels or chemicals using sunlight. In particular, nanostructures featuring localized surface plasmon resonance (LSPR) hold great promise as photo-thermal catalysts given their ability to convert light into heat. In this regard, traditional plasmonic materials include gold (Au) or silver (Ag), but in the last years, transition metal nitrides have been proposed as a cost-efficient alternative. Herein, we demonstrate that titanium nitride (TiN) tubes derived from the nitridation of TiO₂ precursor display excellent light absorption properties thanks to their intense LSPR band in the visible–IR regions. Upon deposition of Ru nanoparticles (NPs), Ru-TiN tubes exhibit high activity towards the photo-thermal CO₂ reduction reaction, achieving remarkable methane (CH₄) production rates up to 1200 mmol g⁻¹ h⁻¹. Mechanistic studies suggest that the reaction pathway is dominated by thermal effects thanks to the effective light-to-heat conversion of Ru-TiN tubes. This work will serve as a basis for future research on new plasmonic structures for photo-thermal applications in catalysis.     

Multifunctional Ag‐Decorated Porous TiO2 Nanofibers in Dye‐Sensitized Solar Cells: Efficient Light Harvesting,Light Scattering,and Electrolyte Contact

Designing the photoanode structure in dye‐sensitized solar cells (DSSCs) is vital to realizing enhanced power conversion efficiency (PCE). Herein, novel multifunctional silver‐decorated porous titanium dioxide nanofibers (Ag/pTiO₂ NFs) made by simple electrospinning, etching, and chemical reduction processes are introduced. The Ag/pTiO₂ NFs with a high surface area of 163 m² g^?1 provided sufficient dye adsorption for light harvesting. Moreover, the approximately 200 nm diameter and rough surface of the Ag/pTiO₂ NFs offered enough light scattering, and the enlarged interpores among the NFs in the photoanode also permitted electrolyte circulation. Ag nanoparticles (NPs) were well dispersed on the surface of the TiO₂ NFs, which prevented aggregation of the Ag NPs after calcination. Furthermore, a localized surface plasmon resonance effect by the Ag NPs served to increase the light absorption at visible wavelengths. The surface area and amount of Ag NPs was optimized. The PCE of pTiO₂ NF‐based DSSCs was 27 % higher (from 6.2 to 7.9 %) than for pure TiO₂ NFs, whereas the PCE of Ag/pTiO₂ NF‐based DSSCs increased by about 12 % (from 7.9 to 8.8 %). Thus, the PCE of the multifunctional pTiO₂ NFs was improved by 42 %, that is, from 6.2 to 8.8 %.     

Silver nanocube-enhanced far-red/near-infrared fluorescence of conjugated polyelectrolyte for cellular imaging

We present the study of silver nanocube (Ag NC)-enhanced fluorescence of a cationic conjugated polyelectrolyte (CPE) for far-red/near-infrared fluorescence cell imaging. Layer-by-layer self-assembly of polyelectrolytes on 78 nm Ag NCs is used to control CPE-metal distance and its effect on CPE fluorescence. The highest fluorescence enhancement factor (FEF) is obtained for Ag NCs with two bilayers, corresponding to a CPE-metal spacer thickness of ～6 nm. At the optimal excitation wavelength, the FEF is 13.8 with respect to the control silica nanoparticles (NPs). The fluorescent NPs are further used for cellular imaging studies. The CPE-loaded Ag NCs with two bilayers exhibit excellent image contrast, superior to the control of CPE-silica NP at a similar uptake efficiency. The viability test indicates low cytotoxicity of the CPE-loaded Ag NCs, rendering them as promising cell imaging agents.     

Spectroscopic and fluorescence properties of silver-dye composite nanoparticles

The aim of this work was to investigate the formation of J-aggregates of thiacyanine dye (TC, 5,5′-disulfopropyl-3,3′-dichlorothiacyanine sodium salt) in the presence of 6 nm spherical silver nanoparticles (Ag NPs) using spectrophotometric and fluorescence methods. The formation of J-aggregates was concentration dependent and characterized by the appearance of the new absorption band with the maximum at 481 nm. Spectrophotometric study of J-aggregate formation and time stability suggested that they were formed on the account of monomer form of TC. Moreover, the stability of J-aggregates increased with the lowering AgNPs concentration. The measurements of fluorescence of the NPs—dye assembly clearly indicated that the fluorescence of TC was quenched by Ag NPs on the concentration dependent manner. The spectrophotometric and fluorescence properties of NPs—dye assembly were found to be quantitatively related to the surface coverage of the dye on the Ag NPs.     

Synergy between Plasmonic and Electrocatalytic Activation of Methanol Oxidation on Palladium–Silver Alloy Nanotubes

Localized surface plasmon resonance (LSPR) excitation of noble metal nanoparticles has been shown to accelerate and drive photochemical reactions. Here, LSPR excitation is shown to enhance the electrocatalysis of a fuel‐cell‐relevant reaction. The electrocatalyst consists of Pd_xAg alloy nanotubes (NTs), which combine the catalytic activity of Pd toward the methanol oxidation reaction (MOR) and the visible‐light plasmonic response of Ag. The alloy electrocatalyst exhibits enhanced MOR activity under LSPR excitation with significantly higher current densities and a shift to more positive potentials. The modulation of MOR activity is ascribed primarily to hot holes generated by LSPR excitation of the Pd_xAg NTs.     

Silver overlayer-modified surface-enhanced Raman scattering-active gold substrates for potential applications in trace detection of biochemical species

Because Ag and Au nanoparticles (NPs) possess well-defined localized surface plasmon resonance (LSPR) they are popularly employed in the studies of surface-enhanced Raman scattering (SERS). As shown in the literature and in our previous studies, the advantage of SERS-active Ag NPs is their higher SERS enhancement over Au NPs. On the other hand, the disadvantage of SERS-active Ag NPs compared to Au NPs is their serious decay of SERS enhancement in ambient laboratory air. In this work, we develop a new strategy for preparing highly SERS-active Ag NPs deposited on a roughened Au substrate. This strategy is derived from the modification of electrochemical underpotential deposition (UPD) of metals. The coverage of Ag NPs on the roughened Au substrate can be as high as 0.95. Experimental results indicate that the SERS of Rhodamine 6G (R6G) observed on this developed substrate exhibits a higher intensity by ca. 50-fold of magnitude, as compared with that of R6G observed on the substrate without the deposition of Ag NPs. The limit of detection (LOD) for R6G measured on this substrate is markedly reduced to 2 × 10⁻¹⁵ M. Moreover, aging of SERS effect observed on this developed substrate is significantly depressed, as compared with that observed on a generally prepared SERS-active Ag substrate. These aging tests were performed in an atmosphere of 50% relative humidity (RH) and 20% (v/v) O₂ at 30 °C for 60 day. Also, the developed SERS-active substrate enables it practically applicable in the trace detection of monosodium urate (MSU)-containing solution in gouty arthritis without a further purification process.     

Iron oxide nanoparticles coated with green tea extract as a novel magnetite reductant and stabilizer sorbent for silver ions: Synthetic application of Fe3O4@green tea/Ag nanoparticles as magnetically separable and reusable nanocatalyst for reduction of 4‐nitrophenol

Green tea extract having many phenolic hydroxyl and carbonyl functional groups in its molecular framework can be used in the modification of Fe₃O₄ nanoparticles. Moreover, the feasibility of complexation of polyphenols with silver ions in aqueous solution can improve the surface properties and capacity of the Fe₃O₄@green tea extract nanoparticles (Fe₃O₄@GTE NPs) for sorption and reduction of silver ions. Therefore, the novel Fe₃O₄@GTE NPs nano‐sorbent has potential ability as both reducing and stabilizing agent for immobilization of silver nanoparticles to make a novel magnetic silver nanocatalyst (Fe₃O₄@GTE/Ag NPs). Inductively coupled plasma analysis, transmission and scanning electron microscopies, energy‐dispersive X‐ray and Fourier transform infrared spectroscopies, and vibrating sample magnetometry were used to characterize the catalyst. Fe₃O₄@GTE/Ag NPs shows high catalytic activity as a recyclable nanocatalyst for the reduction of 4‐nitrophenol at room temperature.