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Review

Ag/Au Bimetallic Core–Shell Nanostructures: A Review of Synthesis and Applications

by
Shuyue He
*,
Ziyu Tang
,
Tianhang Huo
,
Di Wu
and
Jasper H. Tang
Department of Chemical Engineering and Materials Science, Stevens Institute of Technology, Hoboken, NJ 07030, USA
*
Author to whom correspondence should be addressed.
J. Manuf. Mater. Process. 2025, 9(4), 131; https://doi.org/10.3390/jmmp9040131
Submission received: 20 March 2025 / Revised: 12 April 2025 / Accepted: 14 April 2025 / Published: 15 April 2025
Browse Figures
Versions Notes

Abstract

:
Silver/gold (Ag/Au) core–shell nanostructures exhibit tunable plasmonic properties and enhanced catalytic performance, enabling applications across sensing, biomedicine, and environmental remediation. This review presents representative synthetic strategies for fabricating Ag/Au bimetallic core–shell nanostructures with three distinct morphologies: nanospheres, nanocubes, and nanowires. For each architecture, we cover the representative synthetic approaches, such as seed-mediated growth, one-pot synthesis, and evaporation deposition methods, along with their corresponding applications. This review provides discussions on the synthesis methods and applications through specific examples, offering researchers guidance for fabricating Ag/Au core–shell nanostructures with tailored morphologies while addressing major challenges in controlling bimetallic formation.

1. Introduction

Nanotechnology, a rapidly developing field, has revolutionized our ability to design and manipulate materials at the nanoscale, unlocking unprecedented properties and functionalities. Nanomaterials, defined by at least one dimension size below 100 nm, are of great interest due to their unique physical and chemical properties, which differ markedly from their bulk counterparts. Metal nanomaterials, particularly noble metals, exhibit a multitude of captivating and distinctive characteristics that enable their exploration for different applications due to their physiochemical properties. Among these nanomaterials, gold (Au) demonstrates fantastic properties that make versatile scaffolds for the fabrication of catalysts [1,2,3,4] photodynamic therapeutic platforms [5], optical applications [6,7] and bio-sensors [8,9,10]. Silver (Ag), another excellent noble metal, exhibits unique characteristics in terms of antimicrobial activity [11], surface-enhanced Raman spectroscopy (SERS) sensitivity [12,13,14,15], chemical sensing capabilities [16,17,18,19,20,21] and biomedical applications [22]. However, monometallic systems face inherent limitations in practical implementation that cannot be ignored, such as lack of enhanced catalytic properties [23,24], synergistic effects [25], chemical stability [26] and functionalization [27].
Compared to monometallic nanostructures, bimetallic nanostructures have become a focus of research due to their unique and diversified properties [28,29,30]. The combination of two different metals in nanostructure synthesis creates opportunities for expanded properties through compositional variations and synergistic interactions between the metals, which produce critical enhancements in surface area, electrocatalytic activity, biocompatibility, electron transfer rates and resistance to intermediate species. Among bimetallic structures, core–shell architectures have emerged as the most widely studied, thanks to established synthetic protocols and the ability to fine-tune their properties by modifying shell thickness and architecture [31].
Among the various core–shell systems, silver/gold (Ag/Au) bimetallic core–shell nanostructures stand out as especially promising candidates. These materials combine the superior electrical conductivity and plasmonic properties of the Ag core with the exceptional chemical stability of the Au shell. The synergistic properties of Ag/Au core–shell nanostructures enable detailed studies of catalytic reaction kinetics and mechanistic pathways [32], while their exceptional biocompatibility makes them ideal for the creation of porous electrodes in bioelectronic devices [33]. Additionally, their corrosion resistance benefits energy applications, showing effectiveness in multiple electrochemical systems [34]. Optimal synergistic effects require sufficiently thin Au shells to maintain the influence of the Ag core at the surface.
Generally, there are three main methods that exist for Ag/Au core–shell nanostructure synthesis: seed-mediated growth, one-pot synthesis and evaporation deposition. Each of these has specific advantages and challenges. Seed-mediated growth offers unmatched control by isolating core formation from shell growth. However, it presents challenges when the seed material undergoes galvanic replacement with the shell metal precursor in solution, leading to unexpected alloy formation at the surface [35]. Specifically, for Ag/Au core–shell nanostructures, the two half-reactions occur through seed-mediated growth [36]:
Ag0 → Ag+(aq) + 1e−   ε01 = −0.8 V
AuCl4−(aq) + 3e− → Au0 + 4Cl−(aq)    ε02 = 1.0 V
which leads to the final balanced equation:
AuCl4−(aq) + 3Ag0 → 3Ag+(aq) + Au0 + 4Cl−(aq)   ε03 = 0.2 V
When a Ag nanoparticle is exposed to a AuCl4− solution, the Ag atoms on its surface are rapidly oxidized and dissolved by AuCl4− ions, releasing Ag+ ions into the reaction mixture. This process results in the creation of small cavities on the surface of the nanoparticle. Concurrently, Au atoms are deposited onto the nanoparticle surface through the reduction of AuCl4−. Given that Au and Ag are miscible at the nanoscale, both sharing a face-centered cubic (fcc) crystal structure and having similar lattice constants (αAu = 4.079 Å; αAg = 4.086 Å), the formation of a uniform Ag/Au alloy is generally anticipated. This issue can be effectively managed by employing strong reducing agents that drive the reduction reaction faster than the competing galvanic replacement process [37]. In one-pot synthesis, the careful regulation of reduction kinetics is critical as both metal precursors coexist in the reaction medium. This method enables sequential metal reduction, though concurrent precursor presence frequently causes unwanted surface alloying [38]. Evaporation deposition offers an alternative approach with precise shell formation control through physical vapor deposition [39]. Unlike solution-based methods, this technique produces uniform, dense shells while preventing interfacial core–shell reactions. Although the requirement for substrate fixation limits certain applications, this constraint can be advantageous for developing surface-integrated devices and sensing platforms.
This review provides an overview of the synthesis strategies employed to fabricate Ag/Au bimetallic core–shell nanostructures with diverse morphologies, including nanospheres, nanocubes, and nanowires. We introduce and discuss representative synthetic approaches for each geometry, highlighting successful preparation methods and their corresponding applications. By exploring recent advancements in synthesis techniques, structural variations, and functional applications, this review aims to serve as a practical guide for researchers seeking to synthesize Ag/Au core–shell nanostructures with tailored properties for specific applications. The examination of synthetic strategies and resulting applications in catalysis, sensing, and biomedical sciences highlights the potential of Ag/Au core–shell nanostructures for addressing challenges in scientific and industrial territories.

2. Ag/Au Bimetallic Core–Shell Nanostructures with Diverse Morphologies and Applications

Within the diverse family of bimetallic nanostructures, Ag/Au composites have been engineered in various architectural configurations. This section examines the synthesis and applications of distinct Ag/Au core–shell morphologies, namely, nanospheres, nanocubes and nanowires. Table 1 summarizes these different nanostructures along with their applications. The uniform and isotropic nanospheres provide consistent optical responses and catalytic performance, making them suitable for applications requiring uniformity and reliability [40]. Nanocubes, on the other hand, with flat facets and sharp edges, deliver higher active site densities. Their unique geometry also modulates localized surface plasmon resonance, yielding tunable optical properties [41]. Nanowires, with their high aspect ratio and marked anisotropy, facilitate superior electron transport and directional current conduction, while their distinctive light scattering and absorption behaviors provide significant advantages in optoelectronic applications [42]. For each geometry, we discuss both the synthetic strategies and their potential applications.

2.1. Nanospheres

Ag/Au bimetallic core–shell nanospheres demonstrate significant application potential in catalysis, sensing, environmental monitoring and biomedicine. Synthesis methods including pH-controlled reduction, one-pot synthesis, and thermal evaporation deposition enable precise control over core–shell morphology, shell thickness and interfacial properties, effectively addressing challenges such as galvanic replacement and unwanted alloying.

2.1.1. Synthesis Methods of Nanospheres

Zhao et al. [43] developed a method to synthesize SERS-labeled Ag/Au bimetallic core–shell nanospheres while preventing galvanic replacement. Their approach involved depositing HAuCl4 solution onto Ag nanoparticles under carefully controlled pH conditions. By adjusting the solution pH to 9.5, the galvanic replacement reaction that typically produces hollow Ag/Au structures (E0(Ag+/Ag) = 0.8 V, E0(Au3+/Au) = 1.5 V [49]) was successfully suppressed. Under these basic pH conditions, ascorbic acid becomes a strong reducing agent, driving the rapid reduction of HAuCl4 and preventing its galvanic interaction with Ag nanoparticles [37]. The synthesis procedure involved first preparing a mixture of PVP (poly(N-vinyl-2-pyrrolidone), stabilizer) and ascorbic acid, followed by adding NaOH for pH adjustment. SERS-labeled Ag nanoparticles and HAuCl4 solution were then introduced to this mixture under constant stirring in dark conditions. The resulting nanostructures were isolated via centrifugation and dispersed in ultrapure water for storage. This method produced core–shell particles consisting of 15 ± 3 nm Ag cores encased in Au shells of 4.5 ± 1.0 nm thickness. Figure 1 shows the schematic of the synthesis process of SERS-labeled Ag/Au core–shell nanostructures and the TEM and HAADF-STEM images of the nanostructures.
Zhang et al. [44] described a one-pot synthesis approach for producing small-sized Ag/Au bimetallic core–shell nanoparticles. The method used PVP as a stabilizing agent, which weakly bound to and protected the core–shell nanostructures during the rapid reduction process initiated by NaBH4 injection into AuCl4−/Ag+/PVP aqueous solutions. The synthesis procedure involved several sequential steps. First, HAuCl4 and PVP solutions were combined and stirred at low temperature. AgClO4 solution was then introduced to this mixture and stirred under the same temperature conditions. The reduction was initiated when NaBH4 solution was swiftly injected into the vigorously stirred mixture. The resulting colloidal dispersion underwent purification through ultrafiltration, followed by washing with water and ethanol under inert conditions to remove excess reagents and byproducts. To eliminate residual ethanol from the PVP-protected colloid, the mixture was processed using a rotary evaporator at an elevated temperature. The final Ag/Au core–shell nanoparticles, obtained after vacuum drying, exhibited sizes below 2 nm. Figure 2 depicts the synthesis process and the TEM image of PVP-protected Ag/Au core–shell nanoparticles.
He et al. [32] reported a straightforward method for producing Au-coated Ag (AOA) nanospheres using thermal evaporation deposition (TVD). This technique allowed precise control over the Au shell thickness, which is difficult to achieve using traditional solution-based chemical methods due to galvanic replacement. The process involved two main steps. First, silver nanospheres were synthesized by using a modified version of the Lee and Meisel method [50]—sodium citrate mixed with AgNO3 solution, which was then exposed to UV light while stirring gently. This produced uniform Ag nanospheres with a size of 43 ± 6 nm. Second, Ag nanospheres were deposited onto a silicon surface, followed by the use of thermal evaporation to coat them with a 7 nm layer of Au. This was performed by heating a Au source in a thermal evaporator until it vaporized and condensed on the Ag nanospheres, as shown in Figure 3. The resulting AOA nanostructures were then stored in an inert gas environment to prevent degradation.

2.1.2. Applications of Nanospheres

Ag/Au bimetallic core–shell nanospheres demonstrate versatility in their applications, which include water treatment and catalytic applications. In a notable study, Li et al. [45] developed these nanostructures as colorimetric probes for cyanide detection in aqueous solutions. Their research revealed a systematic color transition from purple through orange and yellow to colorless with increasing cyanide concentrations. The underlying detection mechanism exploits cyanide’s ability to progressively etch the Au shell through the formation of [Au(CN)2]−, a thermodynamically stable complex. This etching process alters the dimensional ratio of the Au shell to the Ag core in the bimetallic nanoparticles, manifesting in distinct spectral and colorimetric changes. In drinking water analysis, the system achieved remarkable sensitivity with a limit of detection of 0.16 µM and a visual detection limit of 0.4 µM, as shown in Figure 4a. Furthermore, by employing polysorbate 40 as a stabilizer, they successfully extended the application to sewage water analysis, achieving a visual detection limit of 4 µM. This achievement demonstrates the robustness of Ag/Au bimetallic core–shell nanoparticles as analytical tools even in complex environmental matrices.
Omar et al. [46] evaluated the photocatalytic performance of Ag/Au bimetallic core–shell nanospheres using methylene blue degradation under solar irradiation. Their UV–Vis spectroscopic analysis revealed a progressive decrease in methylene blue’s absorption peak with increasing exposure time, eventually reaching a minimum value that indicated complete dye degradation, as illustrated in Figure 4b. The core–shell nanostructures achieved a superior degradation efficiency of 96.3%, outperforming pure Ag nanoparticles (88%). This enhanced photocatalytic activity can be attributed to two key mechanisms. First, photo-generated excited electrons interact with oxygen molecules to form oxygen radicals and hydroxyl ions, which facilitate dye molecule degradation. Second, the Au shell exhibits dual absorption capabilities: it absorbs UV light through inter-band electron transitions from 5d to 6sp states, and visible light through the excitation of 6sp electrons, which are redistributed to energy levels above the Fermi level via a continuous electron band. Notably, these excited energetic electrons maintain their state for up to 1 ps, providing sufficient time to interact with reactant molecules and initiate chemical reactions.

2.2. Nanocubes

Ag/Au bimetallic core–shell nanocubes with flat crystal {100} facets and sharp edges provide enhanced catalytic efficiency and tunable optical properties suitable for photothermal therapy, surface-enhanced Raman scattering and biomedical imaging. Synthesis strategies including seed-growth methods enable precise control over shell thickness and uniformity.

2.2.1. Synthesis Methods of Nanocubes

Yang et al. [37] developed a robust method to synthesize Ag/Au bimetallic core–shell nanocubes through direct Au deposition on Ag nanocubes’ surfaces. Their strategy employed a strong reducing agent to suppress galvanic replacement between Ag and HAuCl4. The synthesis involved mixing PVP with ascorbic acid (AA) and NaOH, followed by adding Ag nanocubes and titrating HAuCl4 into the mixture. In this system, HAuCl4 reduction occurs through two competing pathways: galvanic replacement with Ag, which creates hollow structures, and AA-mediated reduction, which forms Au shells on Ag nanocubes. By increasing the pH to enhance AA’s reducing power, HAuCl4 reduction by AA was prioritized over galvanic replacement [51,52], resulting in conformal Au deposition on Ag nanocubes’ surfaces. Figure 5a illustrates these possible reaction pathways, while Figure 5b,c presents the high-angle annular dark-field scanning TEM (HAADF-STEM) images of the core–shell nanocubes with varying Au shell thicknesses.
Despite the successful fabrication of Ag/Au bimetallic core–shell nanocubes, two challenges arise from using NaOH: Ag2O formation at cube corners due to Ag+ reacting with OH− and decreasing pH during HAuCl4 titration. Under acidic conditions, these Ag2O patches dissolve, exposing Ag to galvanic replacement with HAuCl4 when using weak reducing agents such as H2Asc [53]. Thus, producing Ag/Au bimetallic core–shell nanocubes with Au shells remains challenging.
Therefore, Zhang et al. [54] developed a defect-assisted approach to synthesize Ag/Au bimetallic core–shell nanocubes with controlled thin shells. Their synthetic strategy employed ethylene glycol (EG) as both solvent and reducing agent, eliminating the need for H2Asc, NaOH, and water, thereby preventing Ag2O formation on Ag nanocubes. The synthesis involved dispersing Ag nanocubes in a heated ethylene glycol solution containing PVP, followed by controlled titration of aqueous HAuCl4. Upon completion of titration, the reaction mixture was rapidly cooled in an ice bath. Figure 6a displays the synthesis process and Figure 6b,c show the HAADF-STEM images of Ag/Au bimetallic core–shell nanocubes. The product was then purified through acetone and water washing steps, with the final core–shell nanostructures being redispersed in water. The synthesis of Ag/Au core–shell nanocubes proceeded through several distinct stages. Initially, galvanic replacement between HAuCl4 and Ag created defects on the nanocubes’ {100} facets while simultaneously depositing Au. These defect sites, possessing high surface energy, became preferential locations for the co-deposition of Ag and Au atoms reduced from their ionic states by ethylene glycol. The defects were subsequently filled, followed by the rapid surface diffusion of additional atoms to form a thin Ag/Au alloy shell. Once galvanic replacement terminated, the continued reduction of HAuCl4 by ethylene glycol deposited pure Au atoms, ultimately producing Ag/Au core–shell nanocubes with thin Au shells.

2.2.2. Applications of Nanocubes

Ag/Au bimetallic core–shell nanocubes demonstrate significant potential in various fields, particularly in biological applications. Liu et al. [47] developed a novel approach using Ag nanocubes as cores with highly branched Au shells, encoded by L-cysteine (L-Cys) and D-cysteine (D-Cys), for photothermal tumor therapy. These three-dimensional bimetallic branched nanostructures exhibited exceptional photothermal conversion efficiency, demonstrating promising results in both in vitro and in vivo tumor therapy. Under laser irradiation, L-CAg/Au and D-CAg/Au nanocubes achieved photothermal conversion efficiencies of 74.11% and 87.28%, respectively. The in vitro photothermal antitumor efficacy of these core–shell nanostructures was evaluated using the MTT method [55,56] on B16, A549 and HeLa cell lines, confirming their effectiveness as photothermal therapy agents. Furthermore, in vivo studies using BALB/c mice implanted with A549 cells demonstrated both positive therapeutic effects and the biosafety of D-CAg/Au nanocubes. Figure 7 illustrates the therapeutic efficacy of these nanostructures: (a) shows the relative viabilities of A549 cells treated with Ag/Au core–shell nanostructures in vitro, while (b) presents the relative tumor volume changes in different treatment groups over a 16-day period.
Beyond biological applications, Ag/Au bimetallic core–shell nanocubes have shown promise in optical applications, particularly in surface-enhanced Raman scattering (SERS). Yang et al. [37] demonstrated enhanced SERS activity in their developed Ag/Au core–shell nanocubes. Using 1,4-benzenedithiol (1,4-BDT) as a probe molecule, they found that the SERS enhancement factor (EF) of Ag/Au nanocubes was 5.4-fold higher than that of pure Ag nanocubes. This superior SERS sensitivity can be attributed to two key factors: first, due to the thin Au shell, this nanostructure maintains electromagnetic enhancement comparable to pure Ag nanocubes, and second, the charge transfer between the Au surface and adsorbed molecules provides additional chemical enhancement, collectively resulting in the increased SERS enhancement factor of Ag/Au nanocubes.

2.3. Nanowires

Ag/Au bimetallic core–shell nanowires with high aspect ratio and anisotropy offer superior electron transport and distinctive optical properties applicable in bioelectrodes, catalysis, energy conversion, microbial fuel cells and CO₂ electrochemical reduction. Synthesis methods including cyan-free electroless plating and conformal epitaxial growth enable precise control over shell thickness and surface smoothness.

2.3.1. Synthesis Methods of Nanowires

Araki et al. [57] developed a direct method to synthesize Ag/Au nanowires through cyan-free Au electroless plating on Ag nanowire tracks. The process began with spraying Ag nanowire dispersion onto a Parylene substrate, followed by drying and applying a glass plate as a weight to enhance nanowire adhesion. The researchers then patterned the Ag nanowires using laser ablation before performing cyan-free Au electroless plating. This plating process consisted of three steps: dilute sulfuric acid pretreatment, palladium catalyst application, and immersion in Au trisodium disulfite solution at elevated temperature. The final nanostructures were protected with Parylene and PMC3A coatings. Figure 8 presents the structural characterization of the Ag/Au nanowires: SEM images at different magnifications (a,c), the corresponding energy dispersive X-ray spectrometry mapping (b) and a cross-sectional TEM image (d).
Zhu et al. [58] explored a strategy to grow a conformal epitaxial Au shell on Ag nanowires with precisely controlled coating thickness, enhancing both chemical stability and material properties. The resulting Ag/Au bimetallic core–shell nanowires exhibited atomically smooth surfaces, which minimized additional electron scattering and optical losses from the coating, resulting in superior performance with significantly improved lifetime and stability. The synthesis process involved dispersing Ag nanowires in H2O, followed by the addition of PVP, AA and diethylamine solution. The diethylamine played a crucial role by eliminating energy differences between different facets of Ag through non-selective adsorption on the nanowire surface without causing etching. Subsequently, a Au growth solution—prepared from HAuCl4, NaOH, Na2SO3 and H2O—was slowly introduced into the Ag solution. The thickness of the Au shell could be precisely controlled by adjusting the injection time. The final products were isolated through centrifugation, washed with water and stored in aqueous suspension. To prevent galvanic replacement during Au shell deposition, the reduction potential of the Au ion source was decreased by complexing Au3+ ions from the HAuCl4 precursor with SO32– to form the stable complex Au(SO3)22–. Figure 9 illustrates the synthesis process and characterization results: (a) shows a schematic of the two synthetic pathways for Ag/Au bimetallic core–shell nanowires, (b) presents an SEM image of the nanowires and (c–e) display the elemental mapping of Ag and Au in the core–shell structures.

2.3.2. Applications of Nanowires

Ag/Au bimetallic core–shell nanowires exhibit significant application potential, particularly as bioelectrode materials, as explored by Choi et al. [34]. Their investigation yielded three-dimensional Ag/Au bimetallic core–shell nanowire foam combining high porosity, electrical conductivity, biocompatibility, and chemical stability. This structure was designed to enable microbes to harness their electrochemical activity in microbial fuel cells. As Figure 10a depicts, the microbe–nanowire composite served as the anode, facilitating electron emission alongside H+ through biochemical reactions. Meanwhile, a carbon paper–Pt/C Nafion composite functioned as the air cathode, converting H+ to water in the presence of O2. The study demonstrated the exceptional power density performance of bioelectrodes based on Ag/Au core–shell nanowires.
Liu et al. [48] developed Ag/Au bimetallic core–shell nanowires as catalysts for CO2 electrochemical reduction, achieving nearly 100% conversion to CO. The catalyst’s effectiveness resulted from complementary metal properties: the Au shell provided selectivity, while the Ag core facilitated intermediate adsorption. The catalyst efficacy stemmed from metal property complementarity: the Au shell contributed selectivity while the Ag core enhanced intermediate adsorption. Ag demonstrated binding energy for reaction intermediates similar to Au [59], facilitating CO production selectivity and hydrogen evolution suppression. This intermetallic synergy optimized intermediate binding energy, resulting in enhanced Faradaic efficiency. Through precise control of the Ag-to-Au molar ratio, the researchers produced core–shell nanowires with superior CO selectivity in the KCl electrolyte. Figure 10b,c confirmed the catalyst’s electrochemical performance. The Ag/Au bimetallic core–shell nanowires maintained structural and chemical stability throughout the electrochemical reduction process.

3. Concluding Remarks

This review examines Ag/Au bimetallic core–shell nanostructures through three principal architectures: nanospheres, nanocubes and nanowires. The analysis addresses specific synthetic methodologies and applications for each morphology, providing researchers with methodological guidance for this complex field.
For nanospheres, we illustrated three synthetic strategies—seed-mediated growth, one-pot synthesis and evaporation deposition—with demonstrated applications in water treatment and catalysis. Nanocubes synthesized via seed-mediated methods have shown promise in biological applications and optical applications, including surface-enhanced Raman spectroscopy measurement. Nanowires prepared through plating and seed-mediated growth have demonstrated utility as bioelectrode materials and in electrochemical reduction reactions.
These examples highlight the versatility of Ag/Au bimetallic core–shell nanostructures but represent only a limited subset of potential synthetic methodologies and applications. The field’s principal challenge remains in achieving precise core–shell formation control, particularly given the inherent silver–gold reactivity. This review provides strategic methodological approaches for overcoming synthetic obstacles and obtaining morphologically tailored structures for targeted applications.
The discussed applications demonstrate the integration of the chemical stability of Au with the sensing properties of Ag in various cases. Despite synthesis and application advancements, further research remains essential to develop reproducible synthetic protocols. The ongoing investigation of these methodological challenges positions Ag/Au bimetallic core–shell nanostructures as potentially significant contributors to multiple technological areas [60,61].

Author Contributions

S.H.: conceptualization, writing—original draft, writing—review and editing, supervision. Z.T.: writing—review and editing. T.H.: writing—review and editing. D.W.: conceptualization, investigation. J.H.T.: project administration. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Conflicts of Interest

There are no conflicts to declare.

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Figure 1. (a) Schematic of the synthesis of Ag/Au core–shell nanoparticles with SERS labels. (b) TEM and (c) HAADF-STEM-EDS images of Ag/Au core–shell nanoparticles. Copyright: 2015 American Chemical Society.
Figure 1. (a) Schematic of the synthesis of Ag/Au core–shell nanoparticles with SERS labels. (b) TEM and (c) HAADF-STEM-EDS images of Ag/Au core–shell nanoparticles. Copyright: 2015 American Chemical Society.
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Figure 2. (a) Schematic of synthesis of Ag/Au core–shell bimetallic nanoparticles using the rapid injection of NaBH4. (b) TEM image of PVP-protected Ag/Au core–shell nanoparticles. Copyright: 2011 Elsevier.
Figure 2. (a) Schematic of synthesis of Ag/Au core–shell bimetallic nanoparticles using the rapid injection of NaBH4. (b) TEM image of PVP-protected Ag/Au core–shell nanoparticles. Copyright: 2011 Elsevier.
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Figure 3. (a) Schematic of fabrication steps for the AOA nanostructure. TEM images of (b) Ag nanospheres, (c) Au film and (d) AOA nanostructure; (e) is a zoomed-in image of (d), where the yellow circle shows the Ag nanosphere and the red circle represents the edge of the Au shell. Copyright: 2022 IOP Publishing.
Figure 3. (a) Schematic of fabrication steps for the AOA nanostructure. TEM images of (b) Ag nanospheres, (c) Au film and (d) AOA nanostructure; (e) is a zoomed-in image of (d), where the yellow circle shows the Ag nanosphere and the red circle represents the edge of the Au shell. Copyright: 2022 IOP Publishing.
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Figure 4. (a) Photographs and UV–Vis spectra showing the response of Ag/Au bimetallic core–shell nanospheres to various cyanide concentrations, with the inset displaying the relationship between ∆A520 and cyanide concentration. (b) UV–Vis absorption spectra illustrating the photocatalytic degradation of methylene blue mediated by Ag/Au bimetallic core–shell nanospheres. Copyright: 2016 Elsevier, 2024 Elsevier.
Figure 4. (a) Photographs and UV–Vis spectra showing the response of Ag/Au bimetallic core–shell nanospheres to various cyanide concentrations, with the inset displaying the relationship between ∆A520 and cyanide concentration. (b) UV–Vis absorption spectra illustrating the photocatalytic degradation of methylene blue mediated by Ag/Au bimetallic core–shell nanospheres. Copyright: 2016 Elsevier, 2024 Elsevier.
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Figure 5. (a) Schematic illustration of the two possible routes for Ag/Au bimetallic core–shell nanocube synthesis. (b,c) HAADF-STEM images of Ag/Au core–shell nanocubes with three and six atomic layers, respectively, in thicknesses of Au shells, marked as blue dots. Insets: zoomed-out images. Copyright: 2014 American Chemical Society.
Figure 5. (a) Schematic illustration of the two possible routes for Ag/Au bimetallic core–shell nanocube synthesis. (b,c) HAADF-STEM images of Ag/Au core–shell nanocubes with three and six atomic layers, respectively, in thicknesses of Au shells, marked as blue dots. Insets: zoomed-out images. Copyright: 2014 American Chemical Society.
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Figure 6. (a) Schematic illustration of the synthetic process for transforming Ag nanocubes into Ag/Au bimetallic core–shell nanocubes in EG/PVP solution. (b,c) HAADF-STEM images of samples with three and eight atomic layers, respectively, in different thickness of Au shells, marked with red dots, which were prepared using different volumes of aqueous HAuCl4 in PVP/EG solution. Insets: zoomed-out images, where the dotted black line in (b) represents the identified defects on the side faces of the Ag nanocubes. Copyright: 2019 American Chemical Society.
Figure 6. (a) Schematic illustration of the synthetic process for transforming Ag nanocubes into Ag/Au bimetallic core–shell nanocubes in EG/PVP solution. (b,c) HAADF-STEM images of samples with three and eight atomic layers, respectively, in different thickness of Au shells, marked with red dots, which were prepared using different volumes of aqueous HAuCl4 in PVP/EG solution. Insets: zoomed-out images, where the dotted black line in (b) represents the identified defects on the side faces of the Ag nanocubes. Copyright: 2019 American Chemical Society.
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Figure 7. (a) The in vitro results of relative viabilities of A549 cells with Ag/Au bimetallic core–shell nanostructures. (b) The in vivo results of relative tumor volume treated with different Ag/Au bimetallic core–shell nanostructures after 16 days. Copyright: 2023 American Chemical Society.
Figure 7. (a) The in vitro results of relative viabilities of A549 cells with Ag/Au bimetallic core–shell nanostructures. (b) The in vivo results of relative tumor volume treated with different Ag/Au bimetallic core–shell nanostructures after 16 days. Copyright: 2023 American Chemical Society.
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Figure 8. (a,c) SEM images of Ag nanowires with Au layers at different magnifications. (b) The energy dispersive X-ray spectrometry mapping. (d) The TEM image of cross-section of Ag/Au nanowires. Copyright: 2019 Wiley-VCH.
Figure 8. (a,c) SEM images of Ag nanowires with Au layers at different magnifications. (b) The energy dispersive X-ray spectrometry mapping. (d) The TEM image of cross-section of Ag/Au nanowires. Copyright: 2019 Wiley-VCH.
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Figure 9. (a) The schematic illustration of the two pathways for Ag/Au bimetallic core–shell nanowires synthesis. (b) SEM image of Ag/Au bimetallic core–shell nanowires. Elemental mapping of (c) Ag, (d) Au and (e) Ag/Au nanowires. Copyright: 2021 Springer.
Figure 9. (a) The schematic illustration of the two pathways for Ag/Au bimetallic core–shell nanowires synthesis. (b) SEM image of Ag/Au bimetallic core–shell nanowires. Elemental mapping of (c) Ag, (d) Au and (e) Ag/Au nanowires. Copyright: 2021 Springer.
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Figure 10. (a) The schematic illustration of the operating mechanism of a single–chamber MFC using AACNF as an anode electrode. (b) The CO Faradaic efficiency of Ag/Au core–shell nanowires with different mole ratios at different potentials. (c) The CO Faradaic efficiency of Ag/Au (mole ratio 1:1) core–shell nanowire electrocatalyst in 0.1 M KCl and 0.1 M KHCO3. Copyright: 2023 American Chemical Society, 2020 Wiley-VCH.
Figure 10. (a) The schematic illustration of the operating mechanism of a single–chamber MFC using AACNF as an anode electrode. (b) The CO Faradaic efficiency of Ag/Au core–shell nanowires with different mole ratios at different potentials. (c) The CO Faradaic efficiency of Ag/Au (mole ratio 1:1) core–shell nanowire electrocatalyst in 0.1 M KCl and 0.1 M KHCO3. Copyright: 2023 American Chemical Society, 2020 Wiley-VCH.
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Table 1. A summary of different nanostructures with their applications and effects.
Table 1. A summary of different nanostructures with their applications and effects.
NanostructureSizeApplicationEffectReference
NanosphereAg Core: 15 ± 3 nm
Au Shell: 4.5 ± 1.0 nm 		Detection of Ochratoxin A (OTA) and aflatoxin B1 (AFB1).The LOD for OTA: 0.006 ng/mL.
The LOD for AFB1: 0.03 ng/mL.		[43]
Nanosphere2.0 nmCatalysts of aerobic oxidation of glucose in water.The catalytic activity is 3 times higher than that of pure Au nanoparticles.[44]
NanosphereAg Core: 43 ± 6 nm
Au Shell: 7 nm		Monitoring the 4-NTP to 4-ATP reaction while simultaneously acting as the catalyst to drive this conversion process.The SERS sensitivity is 37 times higher than that of pure Au nanoparticles.[32]
Nanosphere18.0 ± 5.9 nmColorimetric sensing for cyanide detection.The LOD for cyanide: 0.16 ug/mL.[45]
Nanosphere85 nmRemoval of methylene blue (MB) as a model dye pollutant under visible light.The removal efficiency reaches 96.3% for MB, outperforming pure Ag with its 88% efficiency.[46]
NanocubeAg Core: 38 nm in average edge length
Au Shell: 0.6 nm/1.2 nm		Surface-enhanced Raman scattering (SERS) sensitivity enhancement.The SERS sensitivity is 5.4 times higher than pure Ag nanocubes.[37]
NanocubeAg Core: 100 ± 10 nm
Au Shell: branched Au nanorods		Photothermal tumor therapy.The photothermal conversion efficiency reaches 87.28%.[47]
NanowirePorous surface (pore size ranging from 1 to 10 μm)3D porous electrodes.High electrical conductivity (99.33–753.04 S/m) and mechanical stability. [34]
NanowireDiameter of 130 nm and length of 2~3 umCatalysts for CO2 to CO electrochemical reduction reaction.Nearly 100% Faraday efficiency in 0.1 M KCl electrolyte at an overpotential of ca. −1.0 V.[48]
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He, S.; Tang, Z.; Huo, T.; Wu, D.; Tang, J.H. Ag/Au Bimetallic Core–Shell Nanostructures: A Review of Synthesis and Applications. J. Manuf. Mater. Process. 2025, 9, 131. https://doi.org/10.3390/jmmp9040131

AMA Style

He S, Tang Z, Huo T, Wu D, Tang JH. Ag/Au Bimetallic Core–Shell Nanostructures: A Review of Synthesis and Applications. Journal of Manufacturing and Materials Processing. 2025; 9(4):131. https://doi.org/10.3390/jmmp9040131

Chicago/Turabian Style

He, Shuyue, Ziyu Tang, Tianhang Huo, Di Wu, and Jasper H. Tang. 2025. "Ag/Au Bimetallic Core–Shell Nanostructures: A Review of Synthesis and Applications" Journal of Manufacturing and Materials Processing 9, no. 4: 131. https://doi.org/10.3390/jmmp9040131

APA Style

He, S., Tang, Z., Huo, T., Wu, D., & Tang, J. H. (2025). Ag/Au Bimetallic Core–Shell Nanostructures: A Review of Synthesis and Applications. Journal of Manufacturing and Materials Processing, 9(4), 131. https://doi.org/10.3390/jmmp9040131

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