A composition and size controllable approach for Au-Ag alloy nanoparticles

Fast synthesis of nanoporous Cu/Ag bimetallic triangular nanoprisms via galvanic replacement for efficient 4-nitrophenol reduction

We report the synthesis of nanoporous Cu/Ag bimetallic triangular nanoprisms (BTNPs) using a galvanic replacement method. Based on ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS) analyses, the structure of Cu/Ag BTNPs was characterized. The prepared Cu/Ag BTNPs exhibited excellent catalytic activity and good cycling stability for the reduction of 4-nitrophenol (4-NP) due to the synergistic effect between Cu and Ag elements. The kinetic rate constant (k) and turnover frequency (TOF) values reached 331 × 10-3 s-1 and 500 × 10-3 s-1, respectively, which were higher than those of previously reported Cu, Ag, Au, Cu/Ag or Cu/Au-based catalysts. We hope that the development of promising routes for high-quality BTNPs can broaden their applications in catalysis and environmental sustainability.

Multiwavelength SERS of Magneto-Plasmonic Nanoparticles Obtained by Combined Laser Ablation and Solvothermal Methods

The present study introduces a novel method for the synthesis of magneto-plasmonic nanoparticles (MPNPs) with enhanced functionality for surface-enhanced Raman scattering (SERS) applications. By employing pulsed laser ablation in liquid (PLAL) to synthesize plasmonic nanoparticles and wet chemistry to synthesize magnetic nanoparticles, we successfully fabricated chemically pure hybrid Fe3O4@Au and Fe3O4@Ag nanoparticles. We demonstrated a straightforward approach of an electrostatic attachment of the plasmonic and magnetic parts using positively charged polyethylenimine. The MPNPs displayed high SERS sensitivity and reproducibility, and the magnetic part allowed for the controlled separation of the nanoparticles from the reaction mixture, their subsequent concentration, and their precise deposition onto a specified surface area. Additionally, we fabricated alloy based MPNPs from AgxAu100-x (x = 50 and 80 wt %) targets with distinct localized surface plasmon resonance (LSPR) wavelengths. The compositions, morphologies, and optical properties of the nanoparticles were characterized by using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-vis spectroscopy, and multiwavelength Raman spectroscopy. A standard SERS marker, 4-mercaptobenzoic acid (4-MBA), validated the enhancement properties of the MPNPs and found an enhancement factor of 2 × 108 for the Fe3O4@Ag nanoparticles at 633 nm excitation. Lastly, we applied MPNP-enhanced Raman spectroscopy for the analysis of the biologically relevant molecule adenine and found a limit of detection of 10-7 M at 785 nm excitation. The integration of PLAL and wet chemical methods enabled the relatively fast and cost-effective production of MPNPs characterized by high SERS sensitivity and signal reproducibility that are required in various fields, including biomedicine, food safety, materials science, security, and defense.

Charge Transfer Surface-Enhanced Raman and Absorption Spectra of the Zwitterionic Form of Cysteine Adsorbed on M@Au12 (M = Au, Ag, Pt, and Pd) Nanoclusters

The effect of the core atom type of the M@Au₁₂ nanocluster (M = Au, Ag, Pt, and Pd) on the normal (NR) and charge-transfer surface-enhanced Raman spectroscopy (CT-SERS) of the zwitterion form of l-cysteine (ZWCYS) adsorbed on two different sites (D1 and D2) of the nanocluster is investigated separately in the gas phase and water. Because SERS requires the calculation of the absorption spectrum, the effect of the core atom type on the absorption spectrum of M@Au₁₂ and its complex with the ZWCYS has also been investigated. The vibrational bands that show the intensity enhancement in the CT-SERS of the ZWCYS interacting with the D1 site of M@Au₁₂ nanocluster in water are O─C═O asymmetric stretching (M = Au and Ag), NH₂ bending (M = Ag), S-H stretching (M = Ag, Pt, and Pd), CH₂ bending (M = Pt), and CH₂ symmetric stretching (M = Pt and Pd). The ZWCYS at the D₂ site of the M@Au₁₂ nanocluster in water exhibits intensity enhancement for O─C═O asymmetric stretching (M = Pt), NH₃ wagging (M = Au), and S-H stretching (M = Pd). The intensity of the vibrational bands of ZWCYS does not increase for M = Ag but decreases for O─C═O asymmetric stretching, S-H stretching, CH₂ symmetric stretching, CH₂ asymmetric stretching, and especially NH₂ symmetric stretching.

Asymmetric Dichroic Colors in Stretchable Film with Embedded Au/Ag Alloy Nanoparticles

We present a new type of stretchable dichroic film in which Au and Ag alloy nanoparticles (NPs) are dispersed in polydimethylsiloxane (PDMS). The alloy NPs are synthesized with different atomic compositions and sizes to modulate their plasmonic resonance frequencies and absorption and scattering cross sections. The PDMS dichroic film in which 100 nm alloy NPs with a Au/Ag ratio of 7:3 are dispersed shows exotic optical properties under tensile strain. When 40% tensile strain is applied, the film exhibits a strain-sensitive transmission and strain-insensitive reflection behavior in which the transmittance is increased up to 2.6 times, whereas the reflectance remains unchanged. Moreover, we demonstrate a stretchable anticounterfeiting film and a flexible dichroic sculpture fabricated with the PDMS composite. This work demonstrates a new type of plasmonic application that has great potential in various applications, such as special-purpose optical films, security patterns, and smart windows.

Accelerated Development of Colloidal Nanomaterials Enabled by Modular Microfluidic Reactors: Toward Autonomous Robotic Experimentation

In recent years, microfluidic technologies have emerged as a powerful approach for the advanced synthesis and rapid optimization of various solution-processed nanomaterials, including semiconductor quantum dots and nanoplatelets, and metal plasmonic and reticular framework nanoparticles. These fluidic systems offer access to previously unattainable measurements and synthesis conditions at unparalleled efficiencies and sampling rates. Despite these advantages, microfluidic systems have yet to be extensively adopted by the colloidal nanomaterial community. To help bridge the gap, this progress report details the basic principles of microfluidic reactor design and performance, as well as the current state of online diagnostics and autonomous robotic experimentation strategies, toward the size, shape, and composition-controlled synthesis of various colloidal nanomaterials. By discussing the application of fluidic platforms in recent high-priority colloidal nanomaterial studies and their potential for integration with rapidly emerging artificial intelligence-based decision-making strategies, this report seeks to encourage interdisciplinary collaborations between microfluidic reactor engineers and colloidal nanomaterial chemists. Full convergence of these two research efforts offers significantly expedited and enhanced nanomaterial discovery, optimization, and manufacturing.

Ligand free green plasma-in-liquid synthesis of Au/Ag alloy nanoparticles

Au/Ag alloy nanoparticles were successfully prepared by a microwave-induced plasma in liquid process without any organic protecting or reducing agents.

Bioplasmonic Alloyed Nanoislands Using Dewetting of Bilayer Thin Films

Unlike monometallic materials, bimetallic plasmonic materials offer extensive benefits such as broadband tuning capability or high environmental stability. Here we report a broad range tuning of plasmon resonance of alloyed nanoislands by using solid-state dewetting of gold and silver bilayer thin films. Thermal dewetting after successive thermal evaporation of thin metal double-layer films readily forms AuAg-alloyed nanoislands with a precise composition ratio. The complete miscibility of alloyed nanoislands results in programmable tuning of plasmon resonance wavelength in a broadband visible range. Such extraordinary tuning capability opens up a new direction for plasmonic enhancement in biophotonic applications such as surface-enhanced Raman scattering or plasmon-enhanced fluorescence.

Synthesis, Study, and Discrete Dipole Approximation Simulation of Ag-Au Bimetallic Nanostructures

Water-soluble Ag-Au bimetallic nanostructures were prepared via co-reduction and seed-mediated growth routes employing poly-(4-styrenesulfonic acid-co-maleic acid) (PSSMA) as both a reductant and a stabilizer. Ag-Au alloy nanoparticles were obtained by the co-reduction of AgNO3 and HAuCl4, while Ag-Au core-shell nanostructures were prepared through seed-mediated growth using PSSMA-Au nanoparticle seeds in a heated AgNO3 solution. The optical properties of the Ag-Au alloy and core-shell nanostructures were studied, and the growth mechanism of the bimetallic nanoparticles was investigated. Plasmon resonance bands in the range 422 to 517 nm were observed for Ag-Au alloy nanoparticles, while two plasmon resonances were found in the Ag-Au core-shell nanostructures. Furthermore, discrete dipole approximation theoretical simulation was used to assess the optical property differences between the Ag-Au alloy and core-shell nanostructures. Composition and morphology studies confirmed that the synthesized materials were Ag-Au bimetallic nanostructures.

Chitosan stabilized Ag-Au nanoalloy for colorimetric sensing and 5-Fluorouracil delivery

Fluorescent CS/Ag-Au (chitosan/silver-gold) nanocomposite containing different weight percentage of Ag and Au was synthesized using the chemical reduction method. 5-Fluorouracil (5-FU) encapsulated nanocomposite was also synthesized and its cytotoxicity towards breast cancer cell lines (MCF-7) studied. The XRD pattern of the nanocomposite shows peaks of chitosan, silver and gold. The peaks corresponding to gold and silver indicate the face centered cubic structure of silver and gold nanoparticles. The polymer matrix nanocomposite structure with chitosan as the matrix and silver-gold as the filler phase is evident from the high resolution transmission electron microscopy (HRTEM) images and an increase in particle size from∼5nm to about 12nm is noticeable on encapsulation of 5-Fluorouracil (5-FU). The presence of fluorine in the case of 5-FU encapsulated nanocomposite and the presence of reflections corresponding to 5-FU in the SAED pattern confirms the encapsulation of 5-FU into the nanocomposite, which is also confirmed by elemental mapping. The presence of a single surface plasmon resonance (SPR) peak in the case of the nanocomposite in a position in between the SPR bands of pure silver and gold nanoparticles confirms the formation of Ag-Au alloy and the elemental mapping results obtained for the nanocomposite also supports the UV-vis results. The photoluminescence (PL) spectrum clearly shows an emission peak in the near infrared region (700-900nm), which makes the nanocomposite suitable for use in cellular imaging. The application of the nanocomposite as a colorimetric sensor was also studied and it was found to be useful for the specific detection of mercury (Hg) without much interference and the detection limit was found to be 5.0×10^-8M.

One pot aqueous synthesis of nanoporous Au85Pt15 material with surface bound Pt islands: an efficient methanol tolerant ORR catalyst

For the first time, we are reporting the synthesis of Au100-xPtx nanoporous materials in the size range of 7-10 nm through the galvanic replacement of Ag by Pt from Au100-xAg2x spherical nano-alloys (x = 20, 15, 10 and 5) in an aqueous medium. The galvanic replacement reaction follows the 'Volmer-Weber' growth mode, resulting in the formation of surface bound platinum islands on a nanoporous gold surface. The high angle annular dark field image and low angle X-ray diffraction studies confirm the presence of nanoporous Au100-xPtx NPs. The electrochemical studies using the Au85Pt15/C catalyst show excellent methanol tolerance behaviour and better performance towards oxygen reduction reaction (ORR) in terms of high mass activity, mass-specific activity and figure of merit (FOM) when compared to HiSPEC Pt/C commercial catalyst. Preliminary studies on a full cell using nanoporous Au85Pt15/C (loading 1.0 mg cm(-2)) as the cathode material and Pt-Ru/C (loading: 0.5 mg cm(-2)) as the anode material performed better (38 mW cm(-2)) than the HiSPEC Pt/C cathode material (16 mW cm(-2)).