Photoluminescent Gold–Copper Nanoparticle Alloys with Composition-Tunable Near-Infrared Emission

Stable and homogeneous intermetallic alloys by atomic gas-migration for propane dehydrogenation

Intermetallic nanoparticles (NPs) possess significant potentials for catalytic applications, yet their production presents challenges as achieving the disorder-to-order transition during the atom ordering process involves overcoming a kinetic energy barrier. Here, we demonstrate a robust approach utilizing atomic gas-migration for the in-situ synthesis of stable and homogeneous intermetallic alloys for propane dehydrogenation (PDH). This approach relies on the physical mixture of two separately supported metal species in one reactor. The synthesized platinum-zinc intermetallic catalysts demonstrate exceptional stability for 1300 h in continuous propane dehydrogenation under industrially relevant industrial conditions, with extending 95% propylene selectivity and propane conversions approaching thermodynamic equilibrium values at 550-600 oC. In situ characterizations and density functional theory/molecular dynamics simulation reveal Zn atoms adsorb on the particle surface and then diffuse inward, aiding in the formation of ultrasmall and highly ordered intermetallic alloys. This in-situ gas-migration strategy is applicable to a wide range of intermetallic systems.

Constructing Efficient CuAg Nanoalloys on Ce0.90In0.10Oδ for Methanol Deep Oxidation Catalysis at Low Temperature

So far, it is still extremely challenging to develop an efficient catalyst for deep oxidation of methanol at low temperature. Herein, we report the construction of the highly dispersed CuAg alloy on the surface of Ce0.90In0.10Oδ nanorods support for catalyzing methanol deep oxidation. The composition, structure and properties of catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) spectroscopy and X-ray photoelectron spectroscopy (XPS). The results show that the CuxAg100-x/Ce0.90In0.10Oδ alloy catalysts exhibit superior catalytic activity and stability compared to pure Ag/Ce0.90In0.10Oδ, with the highest activity observed for Cu40Ag60/Ce0.90In0.10Oδ, accompanied by the light-off temperature (T50) and full conversion temperature (T90) of 115 and 145 °C, respectively. This is attributed to the synergistic effect of CuAg alloy, which results in electron transfer, generating more Ag0, and enhanced interaction between CuAg alloy and the support, leading to increased Ce3+ content and higher oxygen vacancy concentration. This work successfully applies CuAg alloy catalysts in thermo-catalytic reaction, offering promising prospects for CuAg alloy catalysts in the methanol deep oxidation.

Reactive Oxygen Species Amplifier for Apoptosis-Ferroptosis Mediated High-Efficiency Radiosensitization of Tumors

Insufficient reactive oxygen species (ROS) production and radioresistance have consistently contributed to the failure of radiotherapy (RT). The development of a biomaterial capable of activating ROS-induced apoptosis and ferroptosis is a potential strategy to enhance RT sensitivity. To achieve precision and high-efficiency RT, the theranostic nanoplatform Au/Cu nanodots (Au/CuNDs) were designed for dual-mode imaging, amplifying ROS generation, and inducing apoptosis-ferroptosis to sensitize RT. A large amount of ROS is derived from three aspects: (1) When exposed to ionizing radiation, Au/CuNDs effectively absorb photons and emit various electrons, which can interact with water to produce ROS. (2) Au/CuNDs act as a catalase-like to produce abundant ROS through Fenton reaction with hydrogen peroxide overexpressed of tumor cells. (3) Au/CuNDs deplete overexpressed glutathione, which causes the accumulation of ROS. Large amounts of ROS and ionizing radiation further lead to apoptosis by increasing DNA damage, and ferroptosis by enhancing lipid peroxidation, significantly improving the therapeutic efficiency of RT. Furthermore, Au/CuNDs serve as an excellent nanoprobe for high-resolution near-infrared fluorescence imaging and computed tomography of tumors. The promising dual-mode imaging performance shows their potential application in clinical cancer detection and imaging-guided precision RT, minimizing damage to adjacent normal tissues during RT. In summary, our developed theranostic nanoplatform integrates dual-mode imaging and sensitizes RT via ROS-activated apoptosis-ferroptosis, offering a promising prospect for clinical cancer diagnosis and treatment.

Protein-Templated Metal Nanoclusters: Molecular-like Hybrids for Biosensing, Diagnostics and Pharmaceutics

The use of proteins as biomolecular templates to synthesize atomically precise metal nanoclusters has been gaining traction due to their appealing properties such as photoluminescence, good colloidal- and photostability and biocompatibility. The synergistic effect of using a protein scaffold and metal nanoclusters makes it especially attractive for biomedical applications. Unlike other reviews, we focus on proteins in general as the protective ligand for various metal nanoclusters and highlight their applications in the biomedical field. We first introduce the approaches and underlined principles in synthesizing protein-templated metal nanoclusters and summarize some of the typical proteins that have been used thus far. Afterwards, we highlight the key physicochemical properties and the characterization techniques commonly used for the size, structure and optical properties of protein-templated metal nanoclusters. We feature two case studies to illustrate the importance of combining these characterization techniques to elucidate the formation process of protein-templated metal nanoclusters. Lastly, we highlight the promising applications of protein-templated metal nanoclusters in three areas-biosensing, diagnostics and therapeutics.

Stepwise-Enhanced Tumor Targeting of Near-Infrared Emissive Au Nanoclusters with High Quantum Yields and Long-Term Stability

We developed an in situ coordination-driven spatially confined strategy for preparing near-infrared emissive gold nanoclusters encapsulated by fluorinated polymers (AuNCs@PF, λ_max = 810 nm) with good stability and high quantum yields (27.7%), far higher than those previously reported for NIR AuNCs (>800 nm). Based on the stepwise enhancements including long blood circulation-induced passive tumor targeting, fluoro-enhanced tumor permeation, and tumor microenvironment (weak acid)-induced aggregation retention in cells, these AuNCs demonstrated bright and stable NIR fluorescence imaging ability in tumors. Additionally, the AuNCs@PF were capable of fluorine magnetic resonance imaging and computed tomographic imaging. The multimodal imaging of tumor-bearing mice clearly implied the potential of AuNCs@PF in biomedical fields.

Tailoring the NIR-II Photoluminescence of Single Thiolated Au25 Nanoclusters by Selective Binding to Proteins

Atomically precise gold nanoclusters are a fascinating class of nanomaterials that exhibit molecule-like properties and have outstanding photoluminescence (PL). Their ultrasmall size, molecular chemistry, and biocompatibility make them extremely appealing for selective biomolecule labeling in investigations of biological mechanisms at the cellular and anatomical levels. In this work, we report a simple route to incorporate a preformed Au₂₅ nanocluster into a model bovine serum albumin (BSA) protein. A new approach combining small-angle X-ray scattering and molecular modeling provides a clear localization of a single Au₂₅ within the protein to a cysteine residue on the gold nanocluster surface. Attaching Au₂₅ to BSA strikingly modifies the PL properties with enhancement and a redshift in the second near-infrared (NIR-II) window. This study paves the way to conrol the design of selective sensitive probes in biomolecules through a ligand-based strategy to enable the optical detection of biomolecules in a cellular environment by live imaging.

Influence of Pt alloying on the fluorescence of fully inorganic, colloidal gold nanoclusters

Noble metal alloy nanoclusters (NCs) are interesting systems as the properties of two or more elements can be combined in one particle, leading to interesting fluorescence phenomena. However, previous studies have been exclusively performed on ligand‐capped NCs from wet chemical synthesis. This makes it difficult to differentiate to which extent the fluorescence is affected by ligand‐induced effects or the elemental composition of the metal core. In this work, we used laser fragmentation in liquids (LFL) to fabricate colloidal gold‐rich bi‐metallic AuPt NCs in the absence of organic ligands and demonstrate the suitability of this technique to produce molar fraction series of 1nm alloy NC. We found that photoluminescence of ligand‐free NCs is not a phenomenon limited to Au. However, even minute amounts of Pt atoms in the AuPt NCs lead to quenching and red‐shift of the fluorescence, which may be attributed to the altered surface charge density.

Accelerated optimization of pure metal and ligand compositions for light-driven hydrogen production

Data-driven optimization of hydrogen production.

Polysorbate- and DNA-Mediated Synthesis and Strong, Stable, and Tunable Near-Infrared Photoluminescence of Plasmonic Long-Body Nanosnowmen

Direct photoluminescence (PL) from metal nanoparticles (NPs) without chemical dyes is promising for sensing and imaging applications since this offers a highly tunable platform for controlling and enhancing the signals in various conditions and does not suffer from photobleaching or photoblinking. It is, however, difficult to synthesize metal NPs with a high quantum yield (QY), particularly in the near-infrared (NIR) region where deep penetration and reduced light scattering are advantageous for bioimaging. Herein, we designed and synthesized Au-Ag long-body nanosnowman structures (LNSs), facilitated by polysorbate 20 (Tween 20). The DNA-engineered conductive junction between the head and body parts results in a charge transfer plasmon (CTP) mode in the NIR region. The junction morphology can be controlled by the DNA sequence on the Au core, and polythymine and polyadenine induced thick and thin junctions, respectively. We found that the LNSs with a thicker conductive junction generates the stronger CTP peak and PL signal than the LNSs with a thinner junction. The Au-Ag LNSs showed much higher intensities in both PL and QY than widely studied Au nanorods with similar localized surface plasmon resonance wavelengths, and notably, the LNSs displayed high photostability and robust, sustainable PL signals under continuous laser exposure for >15 h. Moreover, the PL emission from Au-Ag LNSs could be imaged in a deeper scattering medium than fluorescent silica NPs. Finally, highly robust PL-based cell images can be obtained using Au-Ag LNSs without significant signal change while repetitively imaging cells. The results offer the insights in plasmonic NIR probe design, and show that chemical dye-free LNSs can be a very promising candidate with a high QY and a robust, reliable NIR PL signal for NIR sensing and imaging applications.

Near-Infrared Inorganic Nanomaterials for Precise Diagnosis and Therapy

Traditional wavelengths (400–700 nm) have made tremendous inroads in vivo fluorescence imaging. However, the ability of visible light photon penetration hampered the bio-applications. With reduced photon scattering, minimal tissue absorption and negligible autofluorescence properties, near-infrared light (NIR 700–1700 nm) demonstrates better resolution, high signal-to-background ratios, and deep tissue penetration capability, which will be of great significance for in-vivo determination in deep tissue. In this review, we summarized the latest novel NIR inorganic nanomaterials and the emission mechanism including single-walled carbon nanotubes, rare-earth nanoparticles, quantum dots, metal nanomaterials. Subsequently, the recent progress of precise noninvasive diagnosis in biomedicine and cancer therapy utilizing near-infrared inorganic nanomaterials are discussed. In addition, this review will highlight the concerns, challenges and future directions of near-infrared light utilization.

Recent Advances in Second Near-Infrared Region (NIR-II) Fluorophores and Biomedical Applications

Fluorescence imaging technique, characterized by high sensitivity, non-invasiveness and no radiation hazard, has been widely applicated in the biomedical field. However, the depth of tissue penetration is limited in the traditional (400-700 nm) and NIR-I (the first near-infrared region, 700-900 nm) imaging, which urges researchers to explore novel bioimaging modalities with high imaging performance. Prominent progress in the second near-infrared region (NIR-II, 1000-1700 nm) has greatly promoted the development of biomedical imaging. The NIR-II fluorescence imaging significantly overcomes the strong tissue absorption, auto-fluorescence as well as photon scattering, and has deep tissue penetration, micron-level spatial resolution, and high signal-to-background ratio. NIR-II bioimaging has been regarded as the most promising in vivo fluorescence imaging technology. High brightness and biocompatible fluorescent probes are crucial important for NIR-II in vivo imaging. Herein, we focus on the recently developed NIR-II fluorescent cores and their applications in the field of biomedicine, especially in tumor delineation and image-guided surgery, vascular imaging, NIR-II-based photothermal therapy and photodynamic therapy, drug delivery. Besides, the challenges and potential future developments of NIR-II fluorescence imaging are further discussed. It is expected that our review will lay a foundation for clinical translation of NIR-II biological imaging, and inspire new ideas and more researches in this field.

From prevention to diagnosis and treatment: Biomedical applications of metal nanoparticle-hydrogel composites

Recent advances in biomaterials integrate metal nanoparticles with hydrogels to generate composite materials that exhibit new or improved properties. By precisely controlling the composition, arrangement and interactions of their constituents, these hybrid materials facilitate biomedical applications through myriad approaches. In this work we seek to highlight three popular frameworks for designing metal nanoparticle-hydrogel hybrid materials for biomedical applications. In the first approach, the properties of metal nanoparticles are incorporated into a hydrogel matrix such that the composite is selectively responsive to stimuli such as light and magnetic flux, enabling precisely activated therapeutics and self-healing biomaterials. The second approach mediates the dynamic reorganization of metal nanoparticles based on environment-directed changes in hydrogel structure, leading to chemosensing, microbial and viral detection, and drug-delivery capabilities. In the third approach, the hydrogel matrix spatially arranges metal nanoparticles to produce metamaterials or passively enhance nanoparticle properties to generate improved substrates for biomedical applications including tissue engineering and wound healing. This article reviews the construction, properties and biomedical applications of metal nanoparticle-hydrogel composites, with a focus on how they help to prevent, diagnose and treat diseases. Discussion includes how the composites lead to new or improved properties, how current biomedical research leverages these properties and the emerging directions in this growing field.

Visualizing Ligand-Mediated Bimetallic Nanocrystal Formation Pathways with in Situ Liquid-Phase Transmission Electron Microscopy Synthesis

Colloidal synthesis of alloyed multimetallic nanocrystals with precise composition control remains a challenge and a critical missing link in theory-driven rational design of functional nanomaterials. Liquid-phase transmission electron microscopy (LP-TEM) enables direct visualization of nanocrystal formation mechanisms that can inform discovery of design rules for nanocrystal synthesis, but it remains unclear whether the salient flask synthesis chemistry is preserved under electron beam irradiation during LP-TEM. Here, we demonstrate controlled in situ LP-TEM synthesis of alloyed AuCu nanocrystals while maintaining the molecular structure of electron beam sensitive metal thiolate precursor complexes. Ex situ flask synthesis experiments formed alloyed nanocrystals containing on average 70 atomic% Au using heteronuclear metal thiolate complexes as a precursor, while gold-rich alloys with nearly no copper formed in their absence. Systematic dose rate-controlled in situ LP-TEM synthesis experiments established a range of electron beam synthesis conditions that formed alloyed AuCu nanocrystals that had statistically indistinguishable alloy composition, aggregation state, and particle size distribution shape compared to ex situ flask synthesis, indicating the flask synthesis chemistry was preserved under these conditions. Reaction kinetic simulations of radical-ligand reactions revealed that polymer capping ligands acted as effective hydroxyl radical scavengers during LP-TEM synthesis and prevented oxidation of metal thiolate complexes at low dose rates. Our results revealed a key role of the capping ligands aside from their well-known functions, which was to prevent copper oxidation and facilitate formation of prenucleation cluster intermediates via formation of metal thiolate complexes. This work demonstrates that complex ion precursor chemistry can be maintained during LP-TEM imaging, enabling probing nonclassical nanocrystal formation mechanisms with LP-TEM under reaction conditions representative of ex situ flask synthesis.

Ultrasmall Au nanoclusters for bioanalytical and biomedical applications: the undisclosed and neglected roles of ligands in determining the nanoclusters' catalytic activities

Significantly different from conventional Au nanoparticles, ultrasmall Au nanoclusters (NCs) consisting of several to about a hundred Au atoms with a size below 2 nm exhibit a strong quantum confinement effect, and possess an intriguing molecular-like highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) transition, quantized charging, intrinsic chirality, and special fluorescence properties, as well as high catalytic activities. In virtue of their unique molecular-like electronic structure, remarkable physicochemical properties, mild preparation conditions and good biocompatibility, Au NCs have been having a profound impact on bioanalytical and biomedical applications, such as biosensing, biological imaging, cell markers, drug delivery, photodynamic/photothermal therapy, and biomedical toxicology. As an indispensable part of Au NCs, shell ligands not only stabilize and protect the structure of Au NCs, but also have an important influence on the structure and biocatalytic activities of Au NCs. Nevertheless, the effect of shell ligands on the biocatalytic activities of Au NCs has not been paid much attention or even ignored. In this Focus article, thus, the structure and biocatalytic activities of Au NCs are discussed from the perspective of the shell ligands. Particular emphasis is directed to the discussion and exploration of the undisclosed and neglected roles of shell ligands in the biocatalytic activities of Au NCs, which are of fundamental importance to the unraveling of charge transfer behaviors and biocatalytic processes of Au NCs. In addition, the future directions to explore the mechanism of shell ligands affecting the biocatalytic activities of Au NCs, such as surface ligand engineering of Au NCs, advanced surface/interface in situ characterization techniques, theoretical analysis, and the nanobiology of Au NCs, are also put forward.

Monitoring of Anthracene Using Nanoscale Au-Cu Bimetallic Alloy Nanoparticles Synthesized with Various Compositions

Bimetallic alloy Au-Cu nanoparticles (Au-Cu alloy NPs) were synthesized using a chemical reduction method for sensing applications. Electronic absorption spectroscopy (UV-visible spectroscopy), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used for the confirmation and morphological studies of the synthesized nanoparticles. The composition of Au-Cu alloy NPs was studied by energy-dispersive spectroscopy (EDS). The high crystallinity of Au-Cu alloy NPs was demonstrated by XRD analysis. Both XRD and SEM analyses revealed that the nanoparticles' size ranges from 15 to 25 nm. Pyrrole was polymerized into polypyrrole (PPy) over a neat and clean glassy carbon electrode (GCE) by potentiodynamic polymerization. The sensitivity of GCE was improved by modifying it into a composite electrode. The composite electrode was developed by coating GCE with an overoxidized PPy polymer followed by Au-Cu alloy NPs. The ratio of Au and Cu was carefully controlled. The composite electrode (PPyox/Au-Cu/GCE) successfully detected an environmental toxin anthracene with a detection limit of 0.15 μM, as evidenced by cyclic voltammetry (CV), square-wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS).

Recent Progress in NIR-II Contrast Agent for Biological Imaging

Fluorescence imaging technology has gradually become a new and promising tool for in vivo visualization detection. Because it can provide real-time sub-cellular resolution imaging results, it can be widely used in the field of biological detection and medical detection and treatment. However, due to the limited imaging depth (1-2 mm) and self-fluorescence background of tissue emitted in the visible region (400-700 nm), it fails to reveal biological complexity in deep tissues. The traditional near infrared wavelength (NIR-I, 650-950 nm) is considered as the first biological window, because it reduces the NIR absorption and scattering from blood and water in organisms. NIR fluorescence bioimaging's penetration is larger than that of visible light. In fact, NIR-I fluorescence bioimaging is still interfered by tissue autofluorescence (background noise), and the existence of photon scattering, which limits the depth of tissue penetration. Recent experimental and simulation results show that the signal-to-noise ratio (SNR) of bioimaging can be significantly improved at the second region near infrared (NIR-II, 1,000-1,700 nm), also known as the second biological window. NIR-II bioimaging is able to explore deep-tissues information in the range of centimeter, and to obtain micron-level resolution at the millimeter depth, which surpass the performance of NIR-I fluorescence imaging. The key of fluorescence bioimaging is to achieve highly selective imaging thanks to the functional/targeting contrast agent (probe). However, the progress of NIR-II probes is very limited. To date, there are a few reports about NIR-II fluorescence probes, such as carbon nanotubes, Ag2S quantum dots, and organic small molecular dyes. In this paper, we surveyed the development of NIR-II imaging contrast agents and their application in cancer imaging, medical detection, vascular bioimaging, and cancer diagnosis. In addition, the hotspots and challenges of NIR-II bioimaging are discussed. It is expected that our findings will lay a foundation for further theoretical research and practical application of NIR-II bioimaging, as well as the inspiration of new ideas in this field.

Engineering ultrasmall metal nanoclusters for photocatalytic and electrocatalytic applications

In view of many of the fundamental properties of ultrasmall noble metal nanoclusters progressively being uncovered, it has become increasingly clear that this class of materials has enormous potential for photocatalytic and electrocatalytic applications due to their unique electronic and optical properties. In this Minireview, we highlight the key electronic and optical properties of metal nanoclusters which are essential to photocatalysis and electrocatalysis. We further use these properties as the basis for our discussion to map out directions or principles for the rational design of high performance photocatalysts and electrocatalysts, highlighting several successful attempts along this direction.

Surface Chemistry-Mediated Near-Infrared Emission of Small Coinage Metal Nanoparticles

From size-dependent luminescence to localized surface plasmon resonances, the optical properties that emerge from common materials with nanoscale dimensions have been revolutionary. As nanomaterials get smaller, they approach molecular electronic structures, and this transition from bulk to molecular electronic properties is a subject of far-reaching impact. One class of nanomaterials that exhibit particularly interesting optoelectronic features at this size transition are coinage metal (i.e., group 11 elements copper, silver, and gold) nanoparticles with core diameters between approximately 1 to 3 nm (∼25-200 atoms). Coinage metal nanoparticles can exhibit red or near-infrared photoluminescence features that are not seen in either their molecular or larger nanoscale counterparts. This emission has been exploited both as a probe of electronic behavior at the nanoscale as well as in critical applications such as biological imaging and chemical sensing. Interestingly, it has been demonstrated that their photoluminescence figures of merit such as emission quantum yield, energy, and lifetime are largely independent of particle diameter. Instead, emission from particles at this size range depends heavily on the particle surface chemistry, which includes both its metallic composition and the capping ligand architecture. The strong influence of surface chemistry on these emergent optoelectronic phenomena has powerful implications for both the study and use of these particles, primarily due to the theoretically limitless possible surface ligand architectures and metallic compositions. In this Account, we highlight recent work that studies and uses surface chemistry-mediated photoluminescence from coinage metal nanoparticles. Specifically, we emphasize the distinct, as well as synergistic, roles of the nanoparticle capping ligand and the nanoparticle core for controlling and/or enhancing their near-infrared photoluminescence. We then discuss the implications of surface chemistry-mediated photoluminescence as it relates to downstream applications such as energy transfer, sensing, and biological imaging. We conclude by discussing current challenges that remain in the field, including opportunities to develop new particle synthetic routes, analytical tools, and physical frameworks with which to understand small nanoparticle emission. Taken together, we anticipate that these materials will be foundational both in understanding the unique transition from molecular to bulk electronic structures and in the development of nanomaterials that leverage this transition.

Growth and optical properties of Ag-Ti composite nanorods based on oblique angle co-deposition technique

Ag-Ti composite nanorod structures with various Ag compositions were fabricated by the oblique angle co-deposition technique, and their optical transmission spectra are tuned by composition ratios of Ag and Ti, polarization directions, and deposition angles. Such tunable optical properties have potential applications in optoelectronics. Specially, for the Ag80 composite nanorod structures, there exists a wavelength, where it is isotropic. We also show that the transmission spectra of the Ag80 composite nanorod structure for the deposition angle of 87.5° are greater than 90%, while the transmission spectra for the 75° deposition angle are lower than 20%. Utilizing such a property, high or low transmission lenses can be designed.

d-Penicillamine-coated Cu/Ag alloy nanocluster superstructures: aggregation-induced emission and tunable photoluminescence from red to orange

The aggregation-induced emission (AIE) behavior of metal nanoclusters has attracted much attention owing to their extensive application prospects in bio-imaging and chemical sensors. However, the intrinsic mechanism of metal nanoclusters' aggregation-induced emission is still not very clear. Herein, Cu nanoclusters S1 and Ag(i)-doped Cu/Ag nanoclusters S2 and S3 coated with d-penicillamine are designed and synthesized by a self-assembly strategy. S1-S3 show strong luminescence properties with luminescence quantum yields as high as 11.4%-14.2%. Moreover, their luminescence peak position shows an obvious hypsochromic shift from 615 (S1) to 570 nm (S3). With the introduction of Ag(i) ions, the assembly morphology also shows clear changes from the irregular assembly structure (S1) to large spherical particles with the average size of 0.18 μm for S2 and 0.47 μm for S3. A detailed investigation of high-resolution transmission electron microscopy (HRTEM) images, X-ray diffraction (XRD) patterns, ESI-TOF-mass spectra, UV-vis absorption spectra, photoluminescence spectra and luminescence lifetimes of Cu/Ag nanoclusters S2 and S3 indicates that Cu/Ag nanoclusters are actually a Cu/Ag alloy nanocluster superstructure and the microscopic arrangement of S2 and S3 is more compact and ordered relative to S1. The more compact and ordered Cu/Ag alloy nanocluster superstructure enhances the metal-metal interaction of inter-nanoclusters and intra-nanoclusters and facilitates the radiative transition of ligand-to-metal charge transfer (LMCT) and/or ligand-to-metal-metal charge transfer (LMMCT), which results in the aggregation-induced emission phenomenon. In addition, an enhanced metal-metal interaction increases the average metal-metal distance of the Cu/Ag nanocluster superstructure, leading to a hypsochromic shift of emission spectra. Furthermore, the Cu/Ag alloy nanoclusters show good stability and reversibility on pH cycling between pH = 3 and 7 and temperature cycling between 5 °C and 48 °C. The Cu/Ag alloy nanoclusters can be used as probes for Ag(i) ion and halide anion detection in real water samples by the ratiometric PL method (I₅₇₀/I₆₁₅).

Synthesis of Positively Charged Photoluminescent Bimetallic Au-Ag Nanoclusters by Double-Target Sputtering Method on a Biocompatible Polymer Matrix

Herein, we report a novel positively charged photoluminescent Au-Ag bimetallic nanocluster synthesized using 11-mercaptoundecyl-N,N,N-trimethylammonium bromide as the capping ligand by means of "green" double-target sputtering method on a biocompatible polymer matrix. The photoluminescent Au-Ag bimetallic cluster showed emission tunability from blue to near infrared (NIR) regions with respect to change in the composition.

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.

Ag-Cu mixed phase plasmonic nanostructures fabricated by shadow nanosphere lithography and glancing angle co-deposition

By combining shadow nanosphere lithography with a glancing angle co-deposition technique, mixed-phase Ag-Cu triangular nanopatterns and films were fabricated. They were prepared at different compositions with respect to Ag from 100% to 0% by changing the relative deposition ratio of each metal. Characterizations by ellipsometry, energy dispersive x-ray spectroscopy, and x-ray diffraction revealed that the thin films and nanopatterns were composed of small, well-mixed Ag and Cu nano-grains with a diameter less than 20 nm, and their optical properties could be described by an effective medium theory. All compositions of the nanopattern had the same shape, but showed tunable localized surface plasmon resonance (LSPR) properties. In general, the LSPR of the nanopatterns redshifted with decreasing composition. Such a relation could be fitted by an empirical model based on the bulk theory of alloy plasmonics. By changing the colloidal template and the material deposited, this fabrication technique can be used to produce other alloy plasmonic nanostructures with predicted LSPR wavelengths.

Single plasmonic nanoparticles as ultrasensitive sensors

In this mini review, we will provide a brief introduction focusing on the current applications of single plasmonic nanoparticle-based sensors using DFM, including the detection of molecules, the real-time monitoring of chemical/electrochemical reactions and the imaging of living cells.

Synergistic effect of Au–Ag nano-alloying: intense SEIRA and enhanced catalysis

The mild reducing agent, PVP, synergistically decreases the diffusion activation energy of the metal precursors, facilitating the formation of homogenous AuAg alloy nanohybrid system; their structure-property functional relationship and enhanced applications are duly established.

Terbium ion-coordinated carbon dots for fluorescent aptasensing of adenosine 5'-triphosphate with unmodified gold nanoparticles

This work reports on a novel time-resolved fluorescent aptasensing platform for the quantitative monitoring of adenosine 5'-triphosphate (ATP) by interaction of dispersive/agglomerate gold nanoparticles (AuNPs) with terbium ion-coordinated carbon dots (Tb-CDs). To construct such a fluorescent nanoprobe, Tb-CDs with high-efficient fluorescent intensity are first synthesized by the microwave method with terbium ions (Tb(3+)). The aptasensing system consists of ATP aptamer, AuNP and Tb-CD. The dispersive/agglomerate gold nanoparticles are acquired through the reaction of the aptamer with target ATP. Upon target ATP introduction, the aptamers bind with the analytes to form new aptamer-ATP complexes and coat on the surface of AuNPs to inhibit their aggregation in the high salt solution. In this case, the fluorescent signal of Tb-CDs is quenched by the dispersive AuNPs on the basis of the fluorescence resonance energy transfer (FRET). At the absence of target analyte, gold nanoparticles tend to aggregate in the high salt state even if the aptamers are present. Thus, the added Tb-CDs maintain their intrinsic fluorescent intensity. Experimental results indicated that the aptasensing system exhibited good fluorescent responses toward ATP in the dynamic range from 40nM to 4.0μM with a detection limit of 8.5nM at 3sblank criterion. The repeatability and intermediate precision is less than 9.5% at three concentrations including 0.04, 0.4 and 2.0μM ATP. The selectivity was acceptable toward guanosine 5'-triphosphate, uridine 5'-triphosphate and cytidine 5'-triphosphate. The methodology was applied to evaluate the blank human serum spiked with target ATP, and the recoveries (at 3 concentration levels) ranged between 97.0% and 103.7%. Importantly, this detection scheme is rapid, simple, cost-effective, and does not require extensive sample preparation or separation.

Photoassisted photoluminescence fine-tuning of gold nanodots through free radical-mediated ligand-assembly

In this study, we have developed a simple photoassisted ligand assembly to fine-tune the photoluminescence (PL) of (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide-capped gold nanodots (11-MUTAB-Au NDs). The 11-MUTAB-Au NDs (size: ca. 1.8 nm), obtained from the reaction of gold nanoparticles (ca. 3 nm) and 11-MUTAB, exhibited weak, near-infrared (NIR) PL at 700 nm with a quantum yield (QY) of 0.37% upon excitation at 365 nm. The PL QY of the Au NDs increased to 11.43% after reaction with 11-mercaptoundecanoic acid (11-MUA) for 30 min under ultraviolet (UV) light, which was accompanied by a PL wavelength shift to the green region (∼520 nm). UV-light irradiation accelerates 11-MUA assembly on the 11-MUTABAu NDs (11-MUA/11-MUTAB-Au NDs) through a radical-mediated reaction. Furthermore, the PL wavelength of the 11-MUA/11-MUTAB-Au NDs can be switched to 640 nm via cysteamine under UV-light irradiation. We propose that the PL of the Au NDs with NIR and visible emissions was originally from the surface thiol-Au complexes and the Au core, respectively. These dramatically different optical properties of the Au NDs were due to variation in the surface ligands, as well as the densities and surface oxidant states of the surface Au atoms/ions. These effects can be controlled by assembling surface thiol ligands and accelerated by UV irradiation.

Luminescent Metal Nanoclusters with Aggregation-Induced Emission

Thiolate-protected metal nanoclusters (or thiolated metal NCs) have recently emerged as a promising class of functional materials because of their well-defined molecular structures and intriguing molecular-like properties. Recent developments in the NC field have aimed at exploring metal NCs as novel luminescent materials in the biomedical field because of their inherent biocompatibility and good photoluminescence (PL) properties. From the fundamental perspective, recent advances in the field have also aimed at addressing the fundamental aspects of PL properties of metal NCs, shedding some light on developing efficient strategies to prepare highly luminescent metal NCs. In this Perspective, we discuss the physical chemistry of a recently discovered aggregation-induced emission (AIE) phenomenon and show the significance of AIE in understanding the PL properties of thiolated metal NCs. We then explore the unique physicochemical properties of thiolated metal NCs with AIE characteristics and highlight some recent developments in synthesizing the AIE-type luminescent metal NCs. We finally discuss perspectives and directions for future development of the AIE-type luminescent metal NCs.

Production of Oxidation-Resistant Cu-Based Nanoparticles by Wire Explosion

The low performance or high cost of commercially available conductive inks limits the advancement of printed electronics. This article studies the explosion of metal wires in aqueous solutions as a simple, low-cost, and environmentally friendly method to prepare metallic nanoparticles consisting of Cu and Cu alloys for use in affordable, highly conductive inks. Addition of 0.2 M ascorbic acid to an aqueous explosion medium prevented the formation of Cu₂O shells around Cu nanoparticles, and allowed for the printing of conductive lines directly from these nanoparticles with no post-treatment. Cu alloy nanoparticles were generated from metal wires that were alloyed as purchased, or from two wires of different metals that were twisted together. Cu nanoparticles alloyed with 1% Sn, 5% Ag, 5% Ni and 30% Ni had electrical conductivities similar to Cu but unlike Cu, remained conductive after 24 hrs at 85 °C and 85% RH.

Description and Role of Bimetallic Prenucleation Species in the Formation of Small Nanoparticle Alloys

We report the identification, description, and role of multinuclear metal-thiolate complexes in aqueous Au-Cu nanoparticle syntheses. The structure of these species was characterized by nuclear magnetic resonance spectroscopy, mass spectrometry, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy techniques. The observed structures were found to be in good agreement with thermodynamic growth trends predicted by first-principles calculations. The presence of metal-thiolate complexes is then shown to be critical for the formation of alloyed Au-Cu architectures in the small nanoparticle regime (diameter ∼2 nm). In the absence of mixed metal-thiolate precursors, nanoparticles form with a Cu-S shell and a Au-rich interior. Taken together, these results demonstrate that prenucleation species, which are discrete molecular precursors distinct from both initial reagents and final particle products, may provide an important new synthetic route to control final metal nanoparticle composition and composition architectures.

Copper Induces a Core Plasmon in Intermetallic Au(144,145)-xCux(SR)60 Nanoclusters

The electronic structure and optical absorption spectra of intermetallic thiol-stabilized gold-copper clusters, having 144-145 metal atoms and 60 thiols, were studied by ab initio computations. The widely known icosahedral-based cluster model from the work of Lopez-Acevedo et al. (2009) was used, and clusters doped with one to 30 copper atoms were considered. When doped inside the metal core, copper induces dramatic changes in the optical spectrum as compared to the previously studied all-gold Au144(SR)60. An intense broad absorption peak develops in the range 535-587 nm depending on the amount of doping and doping sites. This result agrees very well with recent experiments by the Dass group for Au144-xCux(SR)60 (x ≤ 23). The analysis of the peaks shows a collective plasmon-like dipole oscillation of the electron density in the metal core. Internal charge transfer from copper to gold and an almost perfect alignment of the upper edges of Cu(3d) and Au(5d) bands are observed in the metal core, contributing to the plasmon-like absorption. The calculations also predict energetically preferable doping of the ligand layer by copper, but such clusters are nonplasmonic.

Composition-tunable synthesis of Pt–Cu octahedral alloy nanocrystals from PtCu to PtCu3via underpotential-deposition-like process and their electro-catalytic properties

Octahedral Pt–Cu alloy nanocrystals with tunable composition from PtCu to PtCu₃ was successfully synthesized via UPD-like process.

A solventless mix–bake–wash approach to the facile controlled synthesis of core–shell and alloy Ag–Cu bimetallic nanoparticles

A solventless mix–bake–wash method using salt powder was developed to fabricate uniform Ag–Cu core–shell and alloy bimetallic nanoparticles.

Metal nanoclusters: applications in environmental monitoring and cancer therapy

Metal nanoclusters (NCs), with dimensions between metal atoms and nanoparticles, have attracted more and more attention due to their unique physical and chemical properties. With their size approaching the Fermi wavelength of electrons, metal NCs possess molecule-like properties and excellent fluorescence emission. Owing to their ultrasmall size, strong fluorescence, and excellent biocompatibility, they have been widely studied in environmental and biological fields concerning their applications. In this review, we will introduce the properties of metal NCs, mainly focusing on the synthesis of metal alloy NCs and the recent progress in their applications in environmental monitoring and cancer therapy.

Facile synthesis, pharmacokinetic and systemic clearance evaluation, and positron emission tomography cancer imaging of ⁶⁴Cu-Au alloy nanoclusters

Gold nanoparticles have been widely used for oncological applications including diagnosis and therapy. However, the non-specific mononuclear phagocyte system accumulation and potential long-term toxicity have significantly limited clinical translation. One strategy to overcome these shortcomings is to reduce the size of gold nanoparticles to allow renal clearance. Herein, we report the preparation of (64)Cu alloyed gold nanoclusters ((64)CuAuNCs) for in vivo evaluation of pharmacokinetics, systemic clearance, and positron emission tomography (PET) imaging in a mouse prostate cancer model. The facile synthesis in acqueous solution allowed precisely controlled (64)Cu incorporation for high radiolabeling specific activity and stability for sensitive and accurate detection. Through surface pegylation with 350 Da polyethylene glycol (PEG), the (64)CuAuNCs-PEG350 afforded optimal biodistribution and significant renal and hepatobiliary excretion. PET imaging showed low non-specific tumor uptake, indicating its potential for active targeting of clinically relevant biomarkers in tumor and metastatic organs.

On-demand shape and size purification of nanoparticle based on surface area

In order to overcome the serious deficiencies of the traditional aqueous centrifugation method in on-demand purification of metal nanoparticles, we have theoretically and experimentally developed a simple purification method based on the nanoparticles' surface area discrepancy, which can separate particles with the same mass but different shapes. As an example, we apply this method to obtain on demand homogeneous Au triangular nanoplates, and tune the plasmon modes of Au nanoplates into resonance with the emission of quantum dots to achieve fluorescence resonance energy transfer (FRET) between them. Moreover, due to their high homogeneity, the purified Au triangular nanoplates exhibit an excellent sensitivity to refractive index, as high as 963 nm RIU(-1) (approaching the theoretical value of 982 nm RIU(-1)), which leads to high gauging accuracy, up to 80 ppb and 1.0 U, for sensing bovine serum albumin and DNA polymerase in solution, respectively. Our work introduces a facile, effective strategy for the separation of nanoparticles, which could obtain building blocks with scalable uniform nanosize, providing a path to precise control of metal nanoparticle's plasmon modes and efficient fabrication of nanodevices.