Synthesis of Small Au-Ag Core-Shell Cubes, Cuboctahedra, and Octahedra with Size Tunability and Their Optical and Photothermal Properties

Plasmonic Superlattice Membranes Based on Bimetallic Nano-Sea Urchins as High-Performance Label-Free Surface-Enhanced Raman Spectroscopy Platforms

On the basis of an abundance of elemental plasmonic nanocrystals identifiable by their unique morphology and intrinsic optoelectronic properties, it is necessary to rationally tailor the structural parameters to optimize the functionalities of nanoassemblies for application as plasmonic circuits/devices. Among them, the plasmonic superlattice membrane has emerged as a novel optically active metamaterial, which is constructed by nanocrystals at a two-dimensional (2D) plane with a highly ordered structure and strong plasmonic coupling interactions. Here, we report on the fabrication of a novel plasmonic superlattice membrane using bimetallic core-shell nano-sea urchins (Nano-SEUs) as meta-atoms. Under the guidance of soft-ligand balancing in conjugation with drying-mediated self-assembly at the air/water interface, well-defined giant 2D superlattices with total lateral dimensions of up to 5 mm wide and 80 nm thick have been synthesized, corresponding to an aspect ratio of 62 500. Programmable morphology control over the Nano-SEUs has been achieved in high yield by rationally tuning the spiky branches as well as the thickness of the silver shell, allowing systematic variation of the plasmonic properties of the membrane. Such superlattice membranes exhibited a strong and reproducible surface-enhanced Raman spectroscopy (SERS) signal that originates from interparticle coupling and electric (E)-field enhancement, enabling an enhancement factor of up to 10⁶. We also demonstrated that the fabricated membrane allows the label-free SERS detection of dopamine from 0.1 nM to 1 μM. Thus, this giant Nano-SEU assembled superlattice membrane can be used as a SERS substrate for on-spot biomarker detection, which paves a robust and inexpensive avenue for highly sensitive and reliable biomedical sensing and diagnostics.

Mussel bioinspired morphosynthesis of substrate anchored core-shell silver self-assemblies with multifunctionality for bioapplications

Core-shell nanoparticles (CSNs) have numerous intriguing properties for advanced device applications, while it remains challenging to directly grow them from a solid substrate. Here, we report a simple mussel-bioinspired solid chemistry strategy for in-situ synthesis of CSNs that are substrate anchored and morphologically tunable for wide-ranging biotechnological applications. Briefly, silver titanate was hydrothermally grown on template titanium and subjected to reaction with mussel-derived dopamine. The synergistic reactivity between silver titanate and dopamine prompted nanosilver/polydopamine (nAg/PD) CSNs to spontaneously assemble and grow on substrate. These CSNs possessed reaction time-dependent dimensions and morphologies, which were related to differing physiochemical properties and biological behaviors. Specifically, the CSNs-modified substrates demonstrated enhanced protein affinity and durable radical scavenging properties. In addition, they manifested remarkable yet robust release-killing and anti-biofilm activities against pathogenic Staphylococcus aureus bacteria. More delightedly, the surface-engineered substrates guaranteed the victory of the anti-infective battle of osteoblastic cells during cell/bacteria coculture, promising applications in implantable medical devices. The adaptability of this strategy was demonstrated by modifying complicated 3D-printed macroporous tissue engineering scaffolds. Intriguingly, the CSNs-modified scaffolds exhibited photothermal performances that bode well for phototherapy. To sum, our strategy combines the simplicity of synthesis modality, the controllability of core-shell silver structures, and the versatility of material functions. The resulting assemblies can enrich the library of nAg-based core-shell engineered nanomaterials.

Designing heterostructured core@satellite Prussian Blue Analogue@Au–Ag nanoparticles: Effect on the magnetic properties and catalytic activity

Prussian Blue Analogue@Au–Ag nanoparticles: Effect on the magnetic properties and catalytic activity.

One-pot synthesis of dumbbell shaped PbS–Te hybrids with promising photothermal properties

The development of multi-component photothermal agents has attracted increasing attention due to their potential applications in energy conversion, medical treatments, etc. Herein, a dumbbell shaped PbS–Te heterostructure was prepared via a one-pot microwave-assisted decomposition of lead dimethyl dithiocarbamate and tellurium diethyl dithiocarbamate. The as-obtained PbS–Te hybrids exhibit excellent photothermal stability and strong optical absorption over a broad wavelength range spanning from ultraviolet to near-infrared, where the photothermal conversion efficiency could reach as high as 12.1%. Such promising photothermal performance demonstrates the advantages of one-pot synthesis that results in more intimate contacts among individual components.

Formation of Silver Rhombic Dodecahedra, Octahedra, and Cubes through Pseudomorphic Conversion of Ag2O Crystals with Nitroarene Reduction Activity

Using ethanol as a co-solvent, relatively small-sized Ag₂O octahedra (∼645 nm in opposite corner distance) and rhombic dodecahedra (∼540 and 655 nm in opposite face distance) were synthesized in aqueous solutions. Ag₂O cubes synthesized in an aqueous solution have an edge length of ∼425 nm. Band gaps of these crystals have been obtained, revealing the presence of facet-dependent light absorption properties. The Ag₂O rhombic dodecahedra, octahedra, and cubes were treated with ammonia borane in ethanol at 50 °C for just 10 min to pseudomorphically convert to Ag polyhedra of the corresponding morphologies. Transmission electron microscopy characterization confirms that the Ag cubes, octahedra, and rhombic dodecahedra are bound by the {100}, {111}, and {110} faces, respectively. The Ag rhombic dodecahedra, available for the first time, showed more superior catalytic activity toward 4-nitroaniline reduction at 50 °C than Ag octahedra and cubes, and gave 100% product yield after 1 h of reaction. This work demonstrates the value of forming Ag rhombic dodecahedra, exposing {110} surfaces that may be useful in other organic transformations.

Facet-Dependent Optical Properties of Semiconductor Nanocrystals

Recent observations of facet-dependent electrical conductivity and photocatalytic activity of various semiconductor crystals are presented. Then, the discovery of facet-dependent surface plasmon resonance absorption of metal-Cu₂ O core-shell nanocrystals with tunable sizes and shapes is discussed. The Cu₂ O shells also exhibit a facet-specific optical absorption feature. The facet-dependent electrical conductivity, photocatalytic activity, and optical properties are related phenomena, resulting from the presence of an ultrathin surface layer with different band structures and thus varying degrees of band bending for the {100}, {110}, and {111} faces of Cu₂ O to absorb light of somewhat different wavelengths. Recently, it is shown that the light absorption and photoluminescence properties of pure Cu₂ O cubes, octahedra, and rhombic dodecahedra also display size and facet effects because of their tunable band gaps. A modified band diagram of Cu₂ O can be constructed to incorporate these optical effects. Literature also provides examples of facet-dependent optical behaviors of semiconductor nanostructures, indicating that optical properties of nanoscale semiconductor materials are intrinsically facet-dependent. Some applications of semiconductor optical size and facet effects are considered.

Origin of symmetry breaking in the seed-mediated growth of bi-metal nano-heterostructures

Seed-mediated growth is the most general way to controllably synthesize bimetal nano-heterostructures. Despite successful instances through trial and error were reported, the way for second metal depositing on the seed, namely whether the symmetry of resulted nano-heterostructure follows the original crystal symmetry of seed metal, remains an unpredictable issue to date. In this work, we propose that the thermodynamic factor, i.e., the difference of equilibrium electrochemical potentials (corresponding to their Fermi levels) of two metals in the growth solution, plays a key role for the symmetry breaking of bimetal nano-heterostructures during the seed-mediated growth. As a proof-of-principle experiment, by reversing the relative position of Fermi levels of the Pd nanocube seeds and the second metal Au with changing the concentration of reductant (L-ascorbic acid) in the growth solution, the structure of as-prepared products successfully evolved from centrosymmetric Pd@Au core-shell trisoctahedra to asymmetric Pd-Au hetero-dimers. The idea was further demonstrated by the growth of Ag on the Pd seeds. The present work intends to reveal the origin of symmetry breaking in the seed-mediated growth of nano-heterostructures from the viewpoint of thermodynamics, and these new insights will in turn help to achieve rational construction of bimetal nano-heterostructures with specific functions.

Bimetallic Au/Ag Core-Shell Superstructures with Tunable Surface Plasmon Resonance in the Near-Infrared Region and High Performance Surface-Enhanced Raman Scattering

Due to the larger surface area and the synergistic effects between two noble metals, the bimetallic superstructures exhibit enhanced distinctive optical, catalytic, and photothermal performances and surface-enhanced Raman scattering (SERS) "hot-spot" effect, and thus have attracted great interest in various applications. Compared with the common Pd, Pt hierarchical structures coated onto Au nanoparticles (NPs), easily synthesized via fast autocatalytic surface growth arising from intrinsic properties of Pd and Pt metals, precisely controlling the hierarchical Ag growth onto Au NPs is rarely reported. In our present study, the reducing agent dopamine dithiocarbamate (DDTC) was covalently capped onto the first metal core (Au) to delicately control the growth model of the second metal (Ag). This results in heterogeneous nucleation and growth of Ag precursor on the surface of Au nanorods (NRs), and further formation of cornlike bimetallic Au/Ag core-shell superstructures, which usually cannot be achieved from traditional epitaxial growth. The thickness of the hierarchical Ag shell was finely tuned in a size range from 8 to 22 nm by simply varying the amount of the ratio between Ag ions and DDTC capped on Au NR core. The tunable Ag shell leads to anisotropic bimetallic Au/Ag core-shell superstructures, displaying two distinctive plasmonic resonances in the near-infrared region (NIR). In particular, the longitudinal surface plasmon resonance exhibits a broadly tunable range from 840 to 1277 nm. Additionally, the rich hot spots from obtained Au/Ag superstructures significantly enhance the SERS performance.

In-Plate and On-Plate Structural Control of Ultra-Stable Gold/Silver Bimetallic Nanoplates as Redox Catalysts, Nanobuilding Blocks, and Single-Nanoparticle Surface-Enhanced Raman Scattering Probes

Noble metal bimetallic nanomaterials have attracted a great deal of attention owing to the strong correlation between their morphology and chemical and physical properties. Even though the synthetic strategies for controlling the shapes of monometallic nanomaterials such as gold (Au) and silver (Ag) are well-developed, limited advances have been made with Au/Ag bimetallic nanomaterials to date. In this work, we demonstrate a highly complex in-plate and on-plate structural control of Au/Ag bimetallic nanoplates (Au/AgBNPLs) in contrast to conventional, simply structured, 1D and 2D, branched, and polyhedral nanomaterials. The polymer used in the synthesis of seeds plays a critical role in controlling the structure of the Au/AgBNPLs. The Au/AgBNPLs exhibit exceptionally high chemical stability against various chemical etchants and a versatile catalytic reactivity with biologically and environmentally relevant chemical species. Significantly, the reversible assembly formation of the Au/AgBNPLs is demonstrated by carrying out the surface-functionalization of the materials with thiol DNA, emphasizing the potential applications of the Au/AgBNPLs in various diagnostic and therapeutic purposes. Finally, the surface-enhanced Raman scattering (SERS) properties of the Au/AgBNPLs are experimentally and theoretically investigated, demonstrating a substantial potential of the Au/AgBNPLs as single-nanoparticle SERS probes. Electron microscopy, UV-vis spectroscopy, selected area electron diffraction (SAED), and energy-dispersive X-ray (EDX) spectroscopy are employed to analyze the structure and composition of the Au/AgBNPLs at the atomic level.

Regulation of size and uniformity of In2O3 nanooctahedra

Rational regulation of the size and uniformity of nanoparticles has drawn great interests and shown widespread application, but this cannot be simply achieved by the vapor route. In this work, by adopting a chemical vapor deposition approach, the growth process was intricately regulated to guide the reagent supersaturation, and the large-scale growth of uniform-sized In2O3 nanooctahedra was realized. A one-time nucleation and synchronous growth mode controlled by the reagent supersaturation ratio is proposed to be responsible for the uniformity of size. Furthermore, a series of comparative experiments were conducted to study the size dependence on reaction duration, and temperature difference between the heating and depositing zones. This study demonstrates a feasible approach to prepare uniform-sized nanoparticles through precisely controlling the crystal growth process, and the developed growth strategy could be generalized to synthesize uniform-sized nanostructures of other material systems.

Seed-Mediated Growth of Silver Nanocubes in Aqueous Solution with Tunable Size and Their Conversion to Au Nanocages with Efficient Photothermal Property

Two seed-mediated approaches for the growth of silver nanocubes in aqueous solution have been developed. Addition of a silver-seed solution to a mixture of cetyltrimethylammonium chloride (CTAC), silver trifluoroacetate, and ascorbic acid and heating the solution at 60 °C for 1.5 h produces uniform Ag nanocubes with tunable sizes from 23 to 60 nm by simply adjusting the volume of silver-seed solution introduced. Alternatively, the silver-seed solution can be injected into a mixture of cetyltrimethylammonium bromide (CTAB), silver nitrate, copper sulfate, and ascorbic acid and heated to 80 °C for 2 h to generate 46 nm silver nanocubes. Plate-like Ag nanocrystals exposing {111} surfaces can be synthesized by reducing Ag(NH3 )2 (+) with ascorbic acid in a CTAC solution. Relatively large Ag nanocubes were converted to cuboctahedral Au/Ag and Au nanocages and nanoframes with empty {111} faces through a galvanic replacement reaction. The nanocages showed a progressive plasmonic band red-shift with increasing Au content. The nanocages exhibited high and stable photothermal efficiency with solution temperatures quickly reaching beyond 100 °C when irradiated with an 808 nm laser for large heat and water vapor generation.