Gold-copper nanostars as photo-thermal agents: synthesis and advanced electron microscopy characterization

First Cu-nanostar as a sustainable catalyst realized through synergistic effects of bowl-shaped features and surface activation of sporopollenin exine

Recently, nanostar-shaped structures, including gold nanostars (NS), have drawn much attention for their potential use in surface-enhanced Raman spectroscopy (SERS) and catalysis. Yet, very few studies have been conducted on Cu-Au hybrid NS, and there are none for Cu-based NS. Herein, we describe an effective method for controlling copper-oxide nanostar (ESP-PEI-CuI/IIO-NS) growth using sporopollenin as a sustainable template material. However, ESP-PEI-CuI/IIO-NS growth depends on sporopollenin surface functionalization. Sporopollenin surface activation was done by amine functionalization with polyethyleneimine (PEI), without which ESP-PEI-CuI/IIO-NS growth was not observed. The sporopollenin's exine (outer wall) has a bowl-like structure, which mediates the growth of Cu nanorods, resulting in an NS morphology. Furthermore, due to their increased surface area, ESP-PEI-CuI/IIO-NS showed excellent catalytic activity for Huisgen 1,3-dipolar cycloadditions even when used in H2O and without additives under green conditions. This approach utilising biomass as a sustainable template would pave the way for developing controlled growth of nanostructures for SERS-related and catalytic applications.

Highly controlled synthesis of symmetrically branched tripod and pentapod nanocrystals with enhanced photocatalytic performance

Anisotropic nanostructures with tunable optical properties induced by controllable size and symmetry have attracted much attention in many applications. Herein, we report a controlled synthesis of symmetrically branched AuCu alloyed nanocrystals. By varying Au:Cu atom ratio in precursor, Y-shaped tripods with three-fold symmetry and star-shaped pentapods with five-fold symmetry are synthesized, respectively. The growth mechanism of AuCu tripods from icosahedral seeds and AuCu pentapods from decahedral seeds is revealed. Aiming to excellent photocatalytic performance, CdS nanocrystals are controlled grown onto the sharp tips of AuCu tripods and pentapods. In addition, a carrier-selective blocking layer of Ag2S is introduced between AuCu and CdS, for achieving effective charge separation in AuCu-Ag2S-CdS nanohybrids. Through evaluating the photocatalytic performance by hydrogen generation experiments, the AuCu-Ag2S-CdS tripod nanocrystals exhibit an optimized hydrogen evolution rate of 2182 μmol·g-1·h-1. These findings will contribute greatly to the understanding of complex nanoparticle growth mechanism and provide a strategy for the design of anisotropic nanoalloys for widely photocatalytic applications.

Cu2+-Assisted Synthesis of Ultrasharp and Sub-10 nm Gold Nanostars. Applications in Catalysis, Sensing, and Photothermia

Gold nanostars have shown enormous potential as the main enablers of advanced applications ranging from biomedicine to sensing or catalysis. Their unique anisotropic structure featuring sharp spikes that grow from a central core offers enhanced optical capabilities and spectral tunability. Although several synthesis methods yield NSs of different morphologies and sizes up to several hundred nanometers, obtaining small NSs, while maintaining their plasmonic properties in the near-infrared, has proven challenging and elusive. Here, we show that Cu2+ addition during NS synthesis in polyvinylpyrrolidone/dimethylformamide generates more crystallographic defects and promotes the directional growth, giving rise to NSs with a larger number of much sharper spikes. They are also formed at smaller volumes, enabling the generation of ultrasmall nanostars, with a volume as small as 421 nm3 (i.e., 9.2 nm of volume-equivalent diameter), while maintaining a plasmon resonance in the near-infrared. To this end, we systematically evaluate the influence of synthesis parameters on the nanostar size and optical characteristics and demonstrate their properties for applications in catalysis, surface-enhanced Raman spectroscopy sensing, and hyperthermia. The ultrasmall nanostars show excellent attributes in all of them, leveraging their small size to enhance properties related to a higher surface-to-volume ratio or colloidal diffusivity.

Surfactant-tail control of CsPbBr3 nanocrystal morphology

CsPbBr3 nanocrystals (NCs) are promising optoelectronic and catalytic materials. Manipulating their morphology can improve their properties and stability. In this work, an alkene-derived zwitterionic ligand was used to control the morphology of CsPbBr3 NCs to yield the highly unusual rhombicuboctahedron morphology, showcasing the first example of a surfactant-tail controlled growth.

PDDA induced step-pyramidal growth of nickel-platinum (Ni-Pt) nanoparticles for enhanced 4-nitrophenol reduction

Herein, we report the synthesis of novel platinum-based nanoparticles with step-pyramidal growth induced by poly(diallyldimethylammonium chloride) (PDDA). The complex stepped pyramidal shape became the central point for outstanding catalytic reduction of 4-nitrophenol, overcoming the activity of bare Pt nanoparticles. These results are valuable for the catalytic degradation of reactive molecules.

Engineering the degree of concavity of one-dimensional Au-Cu alloy nanorods with partial intermetallic compounds by facile wet chemical synthesis

Finely modulating the morphology of bimetallic nanomaterials plays a vital role in enhancing their catalytic activities. Among the various morphologies, concave structures have received considerable attention due to the three advantageous features of high-index facets, high surface areas, and high curvatures, which contribute greatly to enhancing the catalytic performance. However, concave morphologies are not the products generated from thermodynamically controlled growth with minimized surface energy. Additionally, most nanocrystals with concave shapes are currently in the state of mono-metals or alloys with disordered arrangements of atoms. The synthesis of alloy structures with ordered atom arrangements, intermetallic compounds, which tend to display superior catalytic performance on account of their optimal geometric and electronic effects, has rarely been reported as high-temperature annealing is usually needed, which constrains the modulation of morphology and surface structure. In this work, concave one-dimensional Au-Cu nanorods with a partially ordered intermetallic structure were synthesized via a facile wet chemical method. By simply adjusting the reaction kinetics via the concentrations of the corresponding metal precursors, the degree of concavity of the one-dimensional Au-Cu nanorods could be regulated. In both the p-nitrophenol reduction and CO₂ electro-reduction reactions, the concave-shaped Au-Cu nanorods demonstrated superior catalytic activity compared to corresponding non-concave samples with the same structure due to the morphological advantages provided by the concave structure.

Tuning the Surface Plasmon Resonance of Gold Dumbbell Nanorods

Gold has always fascinated humans, occupying an important functional and symbolic role in civilization. In earlier times, gold was predominantly used in jewelry; today, this noble metal's surface properties are taken advantage of in catalysis and plasmonics. In this article, the plasmon resonance of gold dumbbell nanorods is investigated. This unusual morphology was obtained by a seed-mediated growth method. The concentration of chemical precursors such as cetyltrimethylammonium bromide and silver nitrate plays a significant role in controlling the shape of the nanorods. Indeed, the aspect ratio of dumbbell nanostructures was varied from 2.6 to 4. UV-visible absorption spectra revealed a shift of the longitudinal surface plasmon resonance peak from 669 to 789 nm. Having the plasmon resonance in the near infrared region helps to use those nanostructures as photothermal agents.

Gold Nanoclusters, Gold Nanoparticles, and Analytical Techniques for Their Characterization

Many reliable and reproducible methods exist for manufacturing gold nanoparticles with the desired and specific compositions, structures, arrangements, and physicochemical properties. In this report, we review the key principles guiding the formation and growth of nanoclusters, their evolution into nanoparticles, and the role and contribution of coatings. We describe a range of imaging methods for characterization of nanoparticles at atomic resolution and a range of spectroscopy methods for structural and physicochemical characterization of such nanoparticles. This chapter concludes with a short review of the emergent applications of nanoparticles in biosciences.

Controlled Overgrowth of Five-Fold Concave Nanoparticles into Plasmonic Nanostars and Their Single-Particle Scattering Properties

Growth of anisotropic nanostructures enables the manipulation of optical properties across the electromagnetic spectrum by fine morphological tuning of the nanoparticles. Among them, stellated metallic nanostructures present enhanced properties owing to their complex shape, and hence, the control over the final morphology becomes of great importance. Herein, a seed-mediated method for the high-yield production of gold_rich-copper concave branched nanostructures and their structural and optical characterization is reported. The synthesis protocol enabled excellent control and tunability of the final morphology, from concave pentagonal nanoparticles to five-fold branched nanoparticles, named "nanostars". The anisotropic shape was achieved via kinetic control over the synthesis conditions by selective passivation of facets using a capping agent and assisted by the presence of copper chloride ions, both having a crucial impact over the final structure. Optical extinction measurements of nanostars in solution indicated a broad spectral response, hiding the properties of the individual nanostars. Hence, single-particle scattering measurements of individual concave pentagonal nanoparticles and concave nanostars were performed to determine the origin of the multiple plasmon bands by correlation with their morphological features, following their growth evolution. Finite-difference time-domain calculations delivered insights into the geometry-dependent plasmonic properties of concave nanostars and their packed aggregates. Our results uncover the intrinsic scattering properties of individual nanostars and the origin of the broad spectral response, which is mostly due to z-direction packed aggregates.

Structural characterization of Au nano bipyramids: reshaping under thermal annealing, the capping agent effect and surface decoration with Pt

Anisotropic gold nanoparticles offer potential applications due to their functionalities and shape-dependent properties. Reshaping noble metal nanoparticles is an interesting field with optical, surface-enhanced Raman spectroscopy, catalytic applications and potential application as a photothermic therapy. This work comprises a structural study on gold nano bipyramids (Au NBPs) and nanodumbbells, and the evolution of Au NBPs capped with cetyltrimethylammonium bromide and dodecanethiol through an in situ and ex situ heating process in high vacuum. Also, we study the reshaping of Au NBPs by the addition of Pt to study the surface modification and the strain generated on a single particle by geometric phase analysis.

Advances in nanomaterials for use in photothermal and photodynamic therapeutics (Review)

Nanomaterials play crucial roles in the diagnosis and treatment of diseases. Photothermal and photodynamic therapy, as two minimally invasive therapeutic methods, have promising potential in the diagnosis and prevention of cancer. Recently, many photothermal materials (such as noble metal material, transition metal sulfur oxides, carbon material and upconversion nanomaterial) and photodynamic materials (such as phthalein cyanogen, porphyrins and other dye molecules) have been applied in photothermal therapy (PTT) and photodynamic therapy (PDT). Moreover, as nanomaterials have suitable biocompatibility, these materials have been applied in cancer therapy. In the present review, we summarized the effects of different material types, synthesis methods, material morphologies and surface modifications on the outcomes of cancer therapy. The application of nanomaterials in PTT and PDT was introduced and the advantages and disadvantages of PTT and PDT in the prevention of cancer were discussed. Finally, we discussed the application of nanomaterials in the combination of PTT and PDT in cancer treatment.

A protein corona study by scattering correlation spectroscopy: a comparative study between spherical and urchin-shaped gold nanoparticles

The study of protein interactions with gold nanoparticles (GNP) is a key step prior to any biomedical application. These interactions depend on many GNP parameters such as size, surface charge, chemistry, and shape. In this work, we propose to use a sensitive technique named scattering correlation spectroscopy or SCS to study protein interactions with GNP. SCS allowed the investigation of the GNP hydrodynamic radius with a very high sensitivity before and after interaction with proteins. No labeling is needed. As a proof-of-concept, two of the most used morphologies of GNP-based nanovectors have been used within this work: spherical-shaped GNP (GNS) and branched-shaped GNP (GNU). The measurement of several parameters such as the number of proteins binding to one GNP, the binding affinity and the cooperativeness of binding for three different plasma proteins on the GNP surface was carried out. While GNS showed an increase in the hydrodynamic radius, indicating that each kind of protein binds on the GNS in a specific orientation, GNU showed different orientations of proteins due to their multi-oriented surfaces (tips) with a higher surface to volume area. Quantitative data based on the Hill model were extracted to obtain the affinity of the proteins to both GNS and GNU surfaces. Data variations can be understood in terms of the electrostatic properties of the proteins, which interact differently with the negatively charged GNP surfaces.

Synthesis and Properties of the Self-Assembly of Gold-Copper Nanoparticles into Nanoribbons

We report the efficient wet-chemical production of self-assembled gold-copper bimetallic nanoparticles (diameter of ∼2 nm) into two-dimensional flexible ribbonlike nanostructures. The direct observation of a layered arrangement of particles into nanoribbons was provided through high-resolution transmission electron microscopy and electron tomography. These nanoribbons showed photoluminesce and efficient photocatalytic activity for the conversion of 4-nitrophenol. The thermal stability of the nanoribbons was also measured by in situ heat treatment in the electron microscope, confirming that the self-assembled gold-copper nanoribbons efficiently supported up to 350 °C. The final morphology of the nanoparticles and their ability to self-assemble into flexible nanoribbons were dependent on concentration and the ratio of precursors. Therefore, these experimental factors were discussed. Remarkably, the presence of copper was found to be critical to triggering the self-assembly of nanoparticles into ordered layered structures. These results for the synthesis and stability of self-assemblies of metallic nanoparticles present a potential extension of the method to producing materials with catalytic applications.

Inverse Stellation of CuAu-ZnO Multimetallic-Semiconductor Nanostartube for Plasmon-Enhanced Photocatalysis

One-dimensional (1D) metallic nanocrystals constitute an important class of plasmonic materials for localization of light into subwavelength dimensions. Coupled with their intrinsic conductive properties and extended optical paths for light absorption, metallic nanowires are prevalent in light-harnessing applications. However, the transverse surface plasmon resonance (SPR) mode of traditional multiply twinned nanowires often suffers from weaker electric field enhancement due to its low degree of morphological curvature in comparison to other complex anisotropic nanocrystals. Herein, simultaneous anisotropic stellation and excavation of multiply twinned nanowires are demonstrated through a site-selective galvanic reaction for a pronounced manipulation of light-matter interaction. The introduction of longitudinal extrusions and cavitation along the nanowires leads to a significant enhancement in plasmon field with reduced quenching of localized surface plasmon resonance (LSPR). The as-synthesized multimetallic nanostartubes serve as a panchromatic plasmonic framework for incorporation of photocatalytic materials for plasmon-assisted solar fuel production.

Scalable Super-Resolution Synthesis of Core-Vest Composites Assisted by Surface Plasmons

The behavior of composite nanostructures depends on both size and elemental composition. Accordingly, concurrent control of size, shape, and composition of nanoparticles is key to tuning their functionality. In typical core-shell nanoparticles, the high degree of symmetry during shell formation results in fully encapsulated cores with severed access to the surroundings. We commingle light parameters (wavelength, intensity, and pulse duration) with the physical properties of nanoparticles (size, shape, and composition) to form hitherto unrealized core-vest composite nanostructures (CVNs). Unlike typical core-shells, the plasmonic core of the resulting CVNs selectively maintains physical access to its surrounding. Tunable variations in local temperature profiles ≳50 °C are plasmonically induced over starburst-shaped nanoparticles as small as 50-100 nm. These temperature variations result in CVNs where the shell coverage mirrors the temperature variations. The precision thus offered individually tailors access pathways of the core and the shell.

Ni@Ru and NiCo@Ru Core-Shell Hexagonal Nanosandwiches with a Compositionally Tunable Core and a Regioselectively Grown Shell

The development of highly active electrocatalysts is crucial for the advancement of renewable energy conversion devices. The design of core-shell nanoparticle catalysts represents a promising approach to boost catalytic activity as well as save the use of expensive precious metals. Here, a simple, one-step synthetic route is reported to prepare hexagonal nanosandwich-shaped Ni@Ru core-shell nanoparticles (Ni@Ru HNS), in which Ru shell layers are overgrown in a regioselective manner on the top and bottom, and around the center section of a hexagonal Ni nanoplate core. Notably, the synthesis can be extended to NiCo@Ru core-shell nanoparticles with tunable core compositions (Ni₃ Co_x @Ru HNS). Core-shell HNS structures show superior electrocatalytic activity for the oxygen evolution reaction (OER) to a commercial RuO₂ black catalyst, with their OER activity being dependent on their core compositions. The observed trend in OER activity is correlated to the population of Ru oxide (Ru⁴⁺ ) species, which can be modulated by the core compositions.

Experimental Comparison of Photothermal Conversion Efficiency of Gold Nanotriangle and Nanorod in Laser Induced Thermal Therapy

An experimental comparison of the photothermal conversion efficiency (PCE) for gold nanotriangles (GNTs) and nanorods (GNRs) was carried out in the present work. The discrete dipole approximation method was applied to identify the spectral characteristic of GNTs and GNRs with different aspect ratios. On this basis, the PCE of GNTs and GNRs in photothermal therapy were compared theoretically. Afterwards, an in vitro experiment was adopted to investigate the thermal effect of porcine muscle induced by laser irradiation, with and without injected GNTs and GNRs. The influences of laser total power, nanoparticle concentration, and nanoparticle type were investigated. It was found that for the commonly-used wavelengths for photothermal therapy, the PCE of GNTs is higher than that of the GNRs. Furthermore, for GNRs loaded in tissue in vitro, high laser power and high concentration of nanoparticles leads to the degeneration and even carbonization of tissue. However, for the GNTs with the same situation (laser power, nanoparticle volume concentration, and heating time), it could lead to the tissue's evaporation instead of carbonization.

Order-disorder phase transitions in Au-Cu nanocubes: from nano-thermodynamics to synthesis

Catalysts have been widely used in industries and can be optimized by tuning the composition and chemical ordering of the elements involved in the nano-alloy. Among bi-metallic alloys, the Au-Cu system is of particular interest because it exhibits ordered phases at low temperatures. Nevertheless, the temperature at which these ordered structures are formed is totally unknown at the nanoscale. Consequently, to speed up the development of these catalysts, this paper theoretically predicts the structural phase transitions between ordered and disordered phases for the Au-Cu system by using nano-thermodynamics. Following the predictions, the suggested annealing temperatures have been carefully chosen and consequently, Au-Cu ordered nanocubes have been successfully synthesized through a solventless protocol. The results are fully supported by electron microscopy observations.

The roles of surface chemistry, dissolution rate, and delivered dose in the cytotoxicity of copper nanoparticles

The understanding of nanoparticle (NP) cytotoxicity is challenging because of incomplete information about physicochemical changes particles undergo once they come into contact with biological fluids. It is therefore essential to characterize changes in NP properties to better understand their biological fate and effects in mammalian cells. In this paper, we present a study on the effect of particle surface oxidation and dissolution rates of Cu NPs. Particle dissolution, cell-associated Cu doses, and oxidative stress responses in A549 luciferase reporter cells were examined for Cu NPs modified with mercaptocarboxylic acids with different carbon chain lengths and a thiotic acid appended-PEG ligand (TA). We found that these Cu NPs released ionic species together with small particles upon oxidation and that surface chemistry influenced the morphology and dissolution rate. The dissolution rate was also shown to impact both the cellular Cu dosimetry and associated oxidative stress responses. The convergent results from dissolution and dosimetry measurements demonstrate that both intracellular and extracellular (i.e., NP uptake-independent) release of ionic species from Cu NPs greatly affect the cytotoxicity.