Multifunctional Au@Ag@SiO2 Core-Shell-Shell Nanoparticles for Metal-Enhanced Fluorescence, Surface-Enhanced Raman Scattering, and Photocatalysis Applications

Au@Ag@SiO₂ core-shell-shell nanoparticles (NPs) were prepared by a facile one-pot synthetic technique. The Au@Ag core size and SiO₂ shell thicknesses are readily controlled by adjusting the precursor concentration. The multilayered NPs with dielectric SiO₂ outer shells and bimetallic Au@Ag cores exhibited both the chemical stability of Au with the high scattering efficiency of Ag. Furthermore, the SiO₂ shell is beneficial to the metal-enhanced fluorescence for biomedical applications. Metal-enhanced fluorescence, surface-enhanced Raman scattering, and photocatalytic activities of silica-coated Au@Ag, Ag, Au, and Au/Ag core-shell NPs were compared and discussed. The size and structure of Au@Ag@SiO₂ core-shell-shell NPs were optimized to maximize their optical and catalytic activities.

Injectable Fiducial Marker for Image-Guided Radiation Therapy Based on Gold Nanoparticles and a Body Temperature-Activated Gel-Forming System

Injectable fiducial markers are crucial in image-guided radiation therapy (IGRT) due to their minimally invasive operations and improved patient compliance. This study presents the development of a ready-to-use injectable fiducial marker utilizing alginate stabilized-gold nanoparticles (alg-Au NPs) and a body temperature-activated in situ gel-forming system. Gram-scale alg-Au NPs were prepared in an hour by a green microwave-induced plasma-in-liquid process (MWPLP). Sodium alginate was introduced in this process to avoid aggregation between Au NPs, which ensured their stability and injectability. The gelation behavior of alginate with divalent cations and a temperature-dependent release of calcium source (glucono-delta-lactone (GDL) and CaCO3) served as the foundation of the body temperature-activated in situ gel-forming system. The injectable fiducial marker GDL/CaCO3/alg-Au NPs could maintain a liquid state at a low temperature for a higher injectability. After injection, on the other hand, Ca2+ would be released due to the body temperature-activated hydrolysis of GDL and the subsequent reaction with CaCO3, which would initiate the gelation of alginate. The injectable fiducial marker can be therefore delivered via injection and form gel at target site to avoid marker movement or Au NPs leakage after injection. Rheological measurements demonstrate the stability and gelation behavior of GDL/CaCO3/alg-Au NPs at different temperatures. Furthermore, the injectability and imaging ability of GDL/CaCO3/alg-Au NPs were also examined. In summary, ready-to-use injectable fiducial marker GDL/CaCO3/alg-Au NPs were developed via a green and facile method for IGRT.

Alginate-Stabilized Gold Nanoparticles Prepared Using the Microwave-Induced Plasma-in-Liquid Process with Long-Term Storage Stability for Potential Biomedical Applications

A one-step preparation of alginate-stabilized gold nanoparticles (Au NPs) using the microwave-induced plasma-in-liquid process (MWPLP) was reported. Effects of alginate with various concentrations on the preparation and properties of the synthesized Au NPs, including reaction rate, morphology, size, and optical absorption property, were studied. The introduction of alginate (1) accelerated the reaction rate, (2) prevented aggregation and precipitation due to long time discharge in MWPLP, and (3) provided long-term colloidal stability. An abnormal size change (from large to small) of Au NPs during particle growth, which was opposite to the typical change in bottom-up chemical reduction, was observed and a possible mechanism was proposed based on the dynamical and thermodynamical instability of particles during growth. The strategy of drying and redispersion of Au NPs in alginate solution was also studied. The drying and redispersion process had an imperceptible effect on the Au NPs. As a consequence, this strategy might be an effective technique for the long-term storage of Au NPs and other metal NPs. The alginate-stabilized Au NPs without the addition of toxic reducing or stabilizing agents can be appropriate to biomedical applications.

Control of nanoparticles synthesized via vacuum sputter deposition onto liquids: a review

Sputter deposition onto a low volatile liquid matrix is a recently developed green synthesis method for metal/metal oxide nanoparticles (NPs). In this review, we introduce the synthesis method and highlight its unique features emerging from the combination of the sputter deposition and the ability of the liquid matrix to regulate particle growth. Then, manipulating the synthesis parameters to control the particle size, composition, morphology, and crystal structure of NPs is presented. Subsequently, we evaluate the key experimental factors governing the particle characteristics and the formation of monometallic and alloy NPs to provide overall directions and insights into the preparation of NPs with desired properties. Following that, the current understanding of the growth and formation mechanism of sputtered particles in liquid media, in particular, ionic liquids and liquid polymers, during and after sputtering is emphasized. Finally, we discuss the challenges that remain and share our perspectives on the future prospects of the synthesis method and the obtained NPs.

Microplasmas for Advanced Materials and Devices

Microplasmas are low-temperature plasmas that feature microscale dimensions and a unique high-energy-density and a nonequilibrium reactive environment, which makes them promising for the fabrication of advanced nanomaterials and devices for diverse applications. Here, recent microplasma applications are examined, spanning from high-throughput, printing-technology-compatible synthesis of nanocrystalline particles of common materials types, to water purification and optoelectronic devices. Microplasmas combined with gaseous and/or liquid media at low temperatures and atmospheric pressure open new ways to form advanced functional materials and devices. Specific examples include gas-phase, substrate-free, plasma-liquid, and surface-supported synthesis of metallic, semiconducting, metal oxide, and carbon-based nanomaterials. Representative applications of microplasmas of particular importance to materials science and technology include light sources for multipurpose, efficient VUV/UV light sources for photochemical materials processing and spectroscopic materials analysis, surface disinfection, water purification, active electromagnetic devices based on artificial microplasma optical materials, and other devices and systems including the plasma transistor. The current limitations and future opportunities for microplasma applications in materials related fields are highlighted.

Highly Correlated Size and Composition of Pt/Au Alloy Nanoparticles via Magnetron Sputtering onto Liquid

Pt/Au alloy nanoparticles (NPs) in a wide composition range have been synthesized by room-temperature simultaneous sputter deposition from two independent magnetron sources onto liquid PEG (MW = 600). The prepared NPs were alloyed with the face-centered cubic (fcc) structure. In addition, the particle sizes, composition, and shape are strongly correlated but can be tailored by an appropriate variation of the sputtering parameters. No individual particle but large agglomerates with partial alloy structure formed at Pt content of less than 16 atom %. Highly dispersed NPs with no agglomeration were observed in PEG when the quantity of Pt is more than 26 atom %. On the other hand, a small amount of Pt could terminate the agglomeration of Au when sputtering on the grids for transmission electron microscope observation. Our experiment and computer simulation carried out by two different methods indicate that the composition-dependent particle size of Pt/Au can be explained by the atomic concentration, formation energy of the cluster, and interaction between different metal atoms and the PEG molecule.

Strong optical limiting properties of Ormosil gel glasses doped with silver nano-particles

Ag NP Ormosil gel glasses show good optical limiting performance with nonlinear optical response in the visible and NIR region.