Chemical Fusion of Gold Nanorods into Continuous Ring Nanostructures

Abstract

The synthesis of continuous non-linear metal nanostructures at the micro and nanoscale remains a challenging frontier in nanotechnology due to inherent synthetic constraints. This study introduces an innovative chemical methodology for fabricating continuous rings and diverse geometries via the chemical fusion of gold nanorods (AuNRs) on a solid substrate. Initially, aqueous solutions of cetyltrimethylammonium bromide (CTAB)-coated AuNRs were deposited and dried on a solid substrate, resulting in the self-assembly of ring-like arrays. Subsequent chemical growth of the AuNRs in all dimensions was achieved using an aqueous solution of Au(I)/CTAB/Ascorbic Acid (AA), enabling their fusion into continuous structures. This approach permits the formation of arbitrary shapes by pre-arranging AuNRs, thereby opening new avenues for the exploration of non-linear nanostructures with potentially novel plasmonic and electronic properties. The capability to engineer such complex nanostructures is pivotal for advancing fields such as photonics, electronics, and sensing, where the unique optical and electronic properties of gold nanostructures can be exploited for cutting-edge applications. Furthermore, this technique shows a significant promise for the fabrication of various micro- and nanodevices and the seamless interconnection of components in integrated electronic circuits, potentially leading to more efficient and miniaturized electronic systems. The broader implications of this research are significant, offering a potential pathway to the development of nanomaterials and devices that could benefit various industries and technological processes.

1. Introduction

The formation of novel nanostructures is crucial for discovering previously unseen physical and chemical properties, which can significantly impact various fields of science and technology. These unique properties often arise from the intricate geometries and dimensions at the nanoscale, where quantum effects become pronounced. Over the past two decades, there has been extensive exploration of gold nanostructures—both spherical and anisotropic—due to their intriguing optical properties, such as localized surface plasmon resonance, which can be finely tuned by altering their shape and size.

Chen et al. have reported techniques for the growth, morphological tuning, functionalization, and assembly of gold nanorodsAuNRs, as well as the preparation of their hybrid structures [1]. A detailed discussion on the synthesis of three types of AuNRs—single-crystalline, pentahedrally twinned, and polycrystalline—along with strategies for their functionalization, drug delivery, and photothermal therapy has also been presented [2,3]. Furthermore, a comprehensive synthetic strategy for AuNRs that integrates substrate-based techniques with colloidal chemistry to develop functional nanomaterials, utilizing substrate-immobilized templates for precise control over nanostructure formation, has been previously reported [4,5]. Research has not only concentrated on the synthesis, purification, and surface functionalization of these gold nanostructures but has also emphasized self-assembly in both 2D [6,7] and 3D [8] configurations, including linear and non-linear arrangements.

The self-assembly of AuNRs into ring-like superstructures [9], vertical arrays [10,11], and macroscopic colloidal superlattices has been documented [12,13]. This self-assembly is essential for uncovering new physical properties that can be leveraged in applications ranging from optics to drug delivery to sensing technologies.

The ability to manipulate nanostructures at this scale allows for the design of materials with tailored functionalities, which can lead to breakthroughs in areas such as catalysis, where increased surface area and active sites can enhance reaction rates. Moreover, the integration of these nanostructures into composite materials can improve mechanical, thermal, and electrical properties, thereby expanding their applicability in advanced manufacturing and nanomedicine. The exploration of these novel nanostructures is not merely an academic pursuit; it holds the potential to drive innovation in nanoelectronics, sensing, and biotechnology.

Despite these advancements, the formation of non-linear continuous metallic nanostructures remains a significant challenge. Colloidal lithography has been employed to fabricate periodic gold nanocups [14,15] while three-dimensional lithography techniques have been utilized to create mesostructured semiconductors [16]. Additionally, electron beam lithography has been applied to produce gold nanoring cavities and various other types of arrays [17,18,19]. The fabrication and characterization of gold nanocrescents on silicon substrates have been achieved by depositing a gold film at oblique angles using nanosphere lithography, followed by etching and dissolution of the nanospheres [20,21,22]. It is reported in the literature that these nanorings support both bright and dark plasmon modes, enabling enhanced light–matter interactions that are useful for sensing and nanophotonic applications [23]. Moreover, detailed electron energy loss spectroscopy (EELS) studies have provided deep insight into the complex plasmonic behaviors of nanorings, demonstrating their potential for finely tuning optical responses at the nanoscale [24]. In contrast to solid gold particles of similar size, the nanorings exhibit a redshifted localized surface plasmon that can be finely tuned by adjusting the ratio of the ring’s thickness to its radius [25]. Furthermore, studies investigating surface-enhanced Raman scattering (SERS) using gold nanoring substrates have reported enhancement factors for arrays of single nanorings and nanoring dimers, revealing an average enhancement factor of 4.2 × 10⁶ for the single nanorings [26].

These findings motivate further development of reliable synthesis methods to fabricate continuous gold nanorings with controlled morphology and plasmonic functionality. The ability to fabricate complex nanostructures with precision could benefit various fields such as optoelectronics, where enhanced light-matter interactions can lead to more efficient solar cells and sensors. Furthermore, the integration of these continuous structures into nanodevices may facilitate the development of advanced electronic circuits, paving the way for smaller, faster, and more efficient components. However, to the best of our knowledge, there are currently no reported studies on the formation of continuous gold nanorings and their optical properties due to synthetic limitations. In this report, we present a straightforward and effective wet chemistry method for the formation of nanometer-sized continuous gold rings and other non-linear nanoobjects. To create these continuous rings of AuNRs, we synthesized cetyltrimethylammonium bromide CTAB-coated AuNRs using a seed- mediated growth technique [27,28]. These nanorods are self-assembled into ring like array on a solid substrate. When the pre-formed rings of nanorods were exposed to a growth solution of Au(I)/AA/CTAB, the overgrowth of nanorods from all directions was initiated, resulting in the fusion of the nanorods to form continuous rings as they expanded in both length and width. The resulting continuous rings were characterized using transmission electron microscopy (TEM) to confirm their morphology. A schematic in Figure 1 illustrates the process of formation of a continuous ring of gold by the chemical fusion of AuNRs. By overcoming the synthetic limitations of continuous gold nanorings, our findings pave the way for the exploration of previously unseen optical properties and their innovative applications. The simplicity and cost-effectiveness of this method make it accessible for widespread use, enabling researchers to explore a broader range of nanostructures and their applications. This method holds the potential to transform the fabrication of nanodevices, driving advancements in quantum computing, sensing technologies, and next-generation electronic materials.

Figure 1.

Schematic illustrating the process of forming continuous rings of gold through the chemical fusion of AuNRs. Initially, CTAB-coated AuNRs self-assemble into a ring-like array. This is followed by exposure to a growth solution containing Au(I), AA, and CTAB, which facilitates the continuous reduction in Au(I) on the surface of the pre-formed AuNRs. As a result, the AuNRs grow from all directions, ultimately leading to their fusion when they converge at various dimensions, thereby forming continuous gold rings. This process highlights the transformation from discrete nanorods to interconnected structures through chemical fusion.

2. Experimental Procedure

2.1. General

All chemicals were used as received without additional purification. Cetyltrimethylammonium bromide (CTAB, 98%, Acros Organics, Geel, Belgium), hydrogen tetrachloroaurate(III) trihydrate (HAuCl₄·3H₂O, 99%), L-ascorbic acid (99%), sodium borohydride (NaBH₄, 98%), and sodium citrate (99%) were obtained from Sigma-Aldrich (St. Louis, MO, USA). Deionized (DI) water was used in all experiments.

Transmission electron microscopy (TEM) characterization was conducted using JEOL 1200EX (operated at 100 kV) and JEOL 2010 (operated at 120 kV) instruments from JEOL Ltd., Akishima, Tokyo, Japan. Samples were prepared by drop-casting dispersions onto carbon-coated copper or gold grids (Electron Microscopy Sciences, Hatfield, PA, USA) and drying under ambient conditions prior to analysis.

2.2. Synthesis of Gold Nanorods

2.2.1. Preparation of Seed Particles

Pentahedrally twinned Au nanorods were synthesized through a seed-mediated method based on the procedure of Murphy et al. [27]. Subsequent purification and isolation steps were performed according to our previously reported method [28].

The seed solution was prepared by dissolving HAuCl₄·3H₂O (1.97 mg) and sodium citrate (1.47 mg) in 20 mL of deionized water under vigorous magnetic stirring (1200 rpm). Reduction was initiated by rapid addition of freshly prepared, ice-cold NaBH₄ (0.6 mL, 0.1 M). The solution immediately developed a reddish-brown color, consistent with the formation of ~3–4 nm citrate-stabilized gold nanoparticles. The freshly generated seeds were used within 10 min.

2.2.2. Preparation of the Growth Solution

CTAB (64.06 g) was dissolved in 880 mL DI water at approximately 35 °C to ensure complete dissolution. In a separate vessel, HAuCl₄·3H₂O (173.4 mg) was dissolved in 880 mL DI water and then combined with the CTAB solution to produce the growth solution stock.

The resulting solution was distributed into three flasks containing 45 mL (flask A), 140 mL (flask B), and 1575 mL (flask C), respectively, and kept at 27 °C. A freshly prepared ascorbic acid solution (0.1 M; 176 mg dissolved in 10 mL DI water) was added to flasks A, B, and C in volumes of 0.25, 0.77, and 8.75 mL, respectively. Gentle mixing resulted in complete decolorization of each solution.

Nanorod growth was initiated by introducing 4 mL of seed solution into flask A with mild mixing. After 3 s, 12.4 mL of the resulting mixture was transferred to flask B and briefly homogenized. Immediately thereafter, the entire contents of flask B were transferred to flask C within 3 s and rapidly mixed by manual shaking. The final reaction mixture was maintained undisturbed at 27 °C. A color transition from purple (within 2–3 min) to deep red (~30 min) was observed. The reaction was allowed to proceed under quiescent conditions for an additional 14 h.

A thin precipitated layer consisting of gold nanorods and faceted two-dimensional platelets formed at the bottom of the flask. The supernatant, enriched in spherical nanoparticles, was carefully decanted. The precipitate was redispersed in 10 mL of 0.1 M CTAB via brief sonication (30 s).

2.2.3. Separation of Nanorods via Oxidative Etching and Gravitational Precipitation

An oxidative Au(III)/CTAB solution was prepared separately by dissolving CTAB (364 mg) and HAuCl₄·3H₂O (1.97 mg) in 10 mL DI water. One milliliter of this solution was added to the nanorod/platelet dispersion under stirring and allowed to stand undisturbed for 14 h. Following sedimentation, the greenish-blue supernatant containing small nanodisks was removed. The precipitated material was redispersed in 10 mL of 0.1 M CTAB, and an additional 1 mL aliquot of the oxidative solution was introduced.

This oxidative treatment was repeated three to four times until TEM analysis confirmed complete removal of platelet byproducts and isolation of morphologically uniform gold nanorods.

2.3. Formation of Rings of AuNRs

1.5 mL of pure AuNRs solution was centrifuged at 8000 rpm for 7 min. The supernatant, which mainly contained dissolved CTAB, was discarded. The precipitate was re-dispersed in 30 µL of DI water (light sonication was applied, if necessary). On a carbon-coated copper/gold TEM grid, 3 µL of AuNRs solution was cast carefully and air-dried at room temperature. Careful attention was given to the drying solvent. It is very important to dry all 3 µL of solution on the TEM grid since there is a strong possibility that the drop may flow inside the TEM tweezers. After complete drying, the TEM grid was carefully examined by TEM.

2.4. Fusion of Nanorods to Obtain Continuous Rings of Gold

For the formation of continuous rings of gold, AuNRs in the rings were fused by amplifying them in all dimensions. Carbon-coated gold TEM grids were employed in place of standard copper grids to prevent the galvanic corrosion of copper mesh when immersed into Au growth solution. The growth solution was prepared by dissolving CTAB (364 mg) and HAuCl₄·3H₂O (10 mL of 0.001 M aqueous solution) in deionized water. To this mixture, 0.25 mL of 0.1 M ascorbic acid was gently added, resulting in a mildly reducing environment.

For the fusion process, 3 mL of the growth solution was transferred to a watch glass, and the TEM grid was immersed for 10 min using TEM tweezers. Following incubation, the grid was carefully rinsed with hot water (35–40 °C) to remove residual Au(I), ascorbic acid, and excess of CTAB. The fused nanorods forming continuous rings were subsequently characterized by TEM.

3. Results and Discussion

The quest to fabricate continuous non-linear nanostructures has been driven by the potential to uncover novel physical and chemical properties that can impact various scientific and technological fields. In our laboratory, we have been inspired by three major experimental findings—(1) fully controlled tip-selective growth of AuNRs in solution to form nanowires [29,30], (2) formation of microrods through overgrowth amplification of AuNRs [31], and (3) self-assembly of AuNRs into ring-like superstructures [9,28]. These observations have provided critical insights into the growth dynamics and self-assembly behaviors of AuNRs, which we integrated to achieve the formation of continuous nanometer-sized gold rings. Based on our observations, we hypothesized that fixing the position of the AuNRs on a solid substrate, followed by the overgrowth, would lead to fusion at the points of physical contact, thereby forming a continuous nanostructure. This hypothesis suggests that by controlling the spatial arrangement of AuNRs on a substrate and promoting the overgrowth, it is possible to engineer complex nanoobjects inaccessible by conventional wet chemistry. This approach leverages the inherent growth characteristics of AuNRs to achieve precise and controlled fusion, potentially enabling the creation of a wide variety of nanostructures with tailored properties for specific applications. In principle, any desired continuous shape—such as triangles, squares, pentagons, and rings—can be achieved by pre-arranging the AuNRs in defined configurations on a solid substrate.

However, a fundamental difference exists between the three approaches and the hypothesis mentioned above. The tip- and side-selective growth was achieved on CTAB-coated AuNRs through a continuous supply of Au(I)/CTAB/AA growth solution [30,31]. In contrast, self-assembly into ring-like superstructures was accomplished using polystyrene-functionalized AuNRs from highly volatile organic solvents [9,30]. Our experiments revealed that, unlike CTAB-coated AuNRs in aqueous solution, AuNRs covalently functionalized with long-chain polymers could not be further grown from their tips or sides using Au(I)/CTAB/AA solutions. This limitation is likely due to the complete removal of CTAB from the AuNR surface, caused by the covalent attachment of thiol-terminated polystyrene, which renders the surface atoms inaccessible for further crystal growth. This finding underscores the critical role of surface chemistry in the growth process and the necessity of maintaining an appropriate surface coating to facilitate further growth. Therefore, it was essential to self-assemble aqueous CTAB-coated AuNRs into rings and other desired shapes, followed by attempts to grow from their tips and sides to form continuous nanostructures. It is also very important to emphasize that the tip-selective growth was only possible on pentahedrally twinned AuNRs but not on single-crystalline gold nanorods [29,30,31].

Therefore, we employed a three-step seed-mediated method for the synthesis of pentahedrally twinned AuNRs [27], followed by purification through gravitational precipitation and partial dissolution techniques [28]. Excess CTAB was removed via centrifugation, while retaining the CTAB bilayer on the AuNRs to ensure their solubility in aqueous media. The nanorods, which had formed a dense pellet at the bottom of the centrifuge tube after centrifugation, were redispersed in approximately 2 drops (~20 µL) of DI water by brief sonication (5–10 s) to achieve a homogeneous suspension. Immediately, a small volume (~3 µL) of this aqueous AuNR solution was cast onto a carbon-coated TEM grid and allowed to air dry, resulting predominantly in parallel packing of AuNRs, along with a few ring and other assembled shapes (Figure 2). The precise mechanism driving the self-assembly of CTAB-coated AuNRs into ring-like and other anisotropic structures remains unclear. We hypothesize that transient microbubbles generated during sonication may act as soft, dynamic templates for this assembly process. These microbubbles are likely stabilized by a monolayer of CTAB, with the hydrophobic tails oriented toward the air interface, forming a surface that can attract and organize AuNRs during solvent evaporation.

Figure 2.

Low magnification TEM images of rings of AuNRs prepared by self-assembly of CTAB-coated AuNRs. The images show the formation of well-defined ring-like structures, with AuNRs arranged end-to-end and side-to-side.

Once adsorbed at the bubble interface, AuNRs may experience a combination of capillary forces, surfactant-mediated interactions, and local concentration gradients that facilitate their lateral reorganization into closed or open-loop structures. Prior work has shown that CTAB can mediate the self-assembly of gold nanostructures by influencing surface energy and interfacial tension, contributing to ordered spatial arrangements of nanorods and nanospheres. Additionally, microbubble-assisted nanoparticle delivery studies further support the idea that microbubbles can enhance the localization and arrangement of nanoparticles at interfaces.

Unlike the near-quantitative yield of rings from polystyrene-coated AuNRs, the yield of ring formation from CTAB-coated AuNRs was fairly low (~15–20 rings per TEM grid, Figure 2). The majority of nanorods were observed to assemble either in parallel-packed arrangements or in random orientations. Careful TEM examination of the ring-like assemblies revealed that their sizes were not uniform but exhibited considerable variability. This variability in ring dimensions provided a diverse set of structures for subsequent growth experiments, allowing us to explore the formation of continuous nanostructures with different geometries and properties. Additionally, the packing density of nanorods within each ring also varied from one structure to another, which we attribute to local fluctuations in AuNR concentration during the drying process. This randomness in both size and structural density proved advantageous for our objectives, as our goal was to fabricate continuous ring structures and other non-linear assemblies spanning a range of dimensions.

To proceed with our experiments, it was crucial to accurately identify and locate the pre-formed rings on the TEM grid. The exact location of pre-formed rings on the TEM grid was determined by counting the grid mesh from the center. Figure 3a shows a TEM image of a ring of AuNRs before treatment with the aqueous Au(I)/CTAB/AA solution. Most AuNRs in this ring were arranged end-to-end and side-to-side, creating ideal conditions for fusion through tip and side selective growth. The TEM grid was then exposed to the aqueous Au(I)/CTAB/AA solution for 10 min to promote growth from the sides and tips of the AuNRs, aiming to form a continuous solid ring-like structure. However, as shown in Figure 3b, there was minimal growth from the tips or sides of the nanorods; instead, we observed random nucleation followed by overgrowth and partial fusion of the nanorods. This unintended nucleation likely resulted from uncontrolled deposition of gold atoms, which did not preferentially adhere to the tips or sides of the AuNRs. Further exposure to the Au(I)/CTAB/AA solution did not enhance the quality of fusion, leading to the formation of irregularly shaped particles and excessive deposition on some parts of the ring (Figure 3c). This overgrowth not only compromised the structural integrity of the rings but also introduced significant variability in the final nanostructures, highlighting the challenges in achieving controlled growth under these conditions.

Figure 3.

TEM images of rings of AuNRs (a) before, (b) after the first treatment, and (c) after the second treatment with Au(I)/ascorbic acid solution. The electron beam from the TEM damaged the CTAB on the surface of the AuNRs, therefore, no directional growth was observed. Instead, certain random locations showed uncontrolled overgrowth.

Two major challenges arose under the experimental conditions described. First, unlike the expected growth from the tips and sides of the AuNRs, virtually no growth was observed when the TEM grid with AuNR rings was exposed to the aqueous Au(I)/CTAB/AA solution. This lack of growth suggests that the conditions were not conducive to the selective deposition of gold atoms on the AuNR surfaces. Second, partial to complete dissolution of the copper mesh due to galvanic replacement with Au(I) rendered the use of copper TEM grids impractical for this experiment. This dissolution compromised the structural integrity of the TEM grids, making it difficult to maintain a stable platform for the AuNRs. We believe that the CTAB bilayer coating on the AuNR surface is essential for their growth from their sides and tips. The exposure of CTAB-coated AuNRs to high-energy electron beams while locating and imaging the self-assembling rings resulted in the complete degradation of CTAB from the AuNR surfaces, preventing any growth when the pre-formed rings were subsequently exposed to the aqueous Au(I)/CTAB/AA solution. This e-beam-induced degradation likely stripped the CTAB bilayer from the AuNR surface, making the surface atoms essentially inactive for further crystal growth. Therefore, it was crucial to form the rings of AuNRs and achieve their growth from tips and sides without prior exposure to the electron beam. To address these issues, we replaced the copper TEM grids with gold TEM grids, which effectively mitigated the issue of corrosion due to galvanic replacement. The substitution of copper TEM grids with gold TEM grids preserved the integrity of the TEM grids, ensuring a stable platform for the AuNRs. In order to avoid the degradation of the CTAB bilayer from AuNR surfaces due to electron beam exposure, we decided not to pre-examine the TEM grid for rings and their location. Instead, we conducted experiments without pre-imaging of the self-assembled rings under the electron microscope. This approach allowed us to keep the CTAB bilayer intact, thereby creating a more stable environment for the formation and growth of continuous nanostructures. By avoiding prior electron beam exposure and using gold TEM grids, we were able to successfully overgrow and fuse AuNRs into continuous ring-like and other complex nanostructures.

A small amount of aqueous CTAB-coated AuNRs was cast onto a gold TEM grid and dried at ambient conditions. After complete drying, the TEM grid was not examined under the electron beam but was directly exposed to the aqueous Au(I)/CTAB/AA solution for 10 min, followed by TEM examination. Under these conditions, we observed a uniform overgrowth of AuNRs leading to complete fusion into continuous rings and other nanostructures of various shapes.

Figure 4 illustrates TEM images of continuous ring-like nanostructures of gold obtained through the fusion of pre-assembled AuNRs into ring-like arrays. The resulting rings exhibit outer diameters ranging from approximately 200 to 500 nm. It is evident that there is a fusion of gold nanorods to form continuous structures due to the overgrowth of nanorods. The seamless integration of the nanorods into a single continuous structure indicates that the growth conditions were optimal for achieving the uniform fusion. This controlled growth process ensures that the nanorods merge without leaving gaps or irregularities, resulting in smooth and homogeneous surfaces. No random nucleation growth was observed, which further confirms the precision of the growth method. The surface of the nanostructures after growth was found to be continuous, smooth, and uniform. This indicates that the growth process was well-controlled, resulting in high-quality nanostructures. The shape of the final continuous structures depended on the pre-formed shapes, such as triangles, squares, hexagons, and rings (Figure 4 and Figure 5). The size of the fused nanostructures varied from a few nanometers to micrometers, depending on the dimensions of the pre-formed assemblies.

Figure 4.

TEM images of continuous rings of gold obtained by the fusion of AuNRs. The fusion is carried out by the exposure of rings to Au(I)/CTAB/AA solution. The images show the successful formation of continuous gold rings, with the AuNRs fused together to create a seamless structure.

Figure 5.

TEM images of continuous rings of gold formed by the fusion of monolayer/thin rings of AuNRs. The images depict the successful transformation of monolayer and thin AuNR rings into continuous gold rings through the fusion process. The resulting structures exhibit smooth and uniform surfaces, indicating effective fusion of the individual nanorods.

Depending on the packing density of the nanorods in the pre-formed structures, we observed thin and dense rings (Figure 4 and Figure 5). This technique also enabled the formation of partial rings or linearly fused nanostructures, as shown in Figure 6, when the AuNRs were assembled in pre-formed partial rings or linear configurations. The formation of partial or incomplete rings is typically observed when the nanorod concentration is relatively low. This behavior arises under two main conditions: (i) local depletion of nanorods during the drying process, which can lead to inhomogeneous surface coverage across the TEM grid, and (ii) insufficient overall nanorod concentration in the aqueous dispersion. Because the fusion geometries were achieved by fully immersing the TEM grid into the growth solution, ensuring uniform exposure of all regions to identical environmental conditions, we did not observe any selectivity in the fusion process between partial and complete rings. Despite the presence of incomplete assemblies, we consistently observed effective chemical fusion of nanorods in both full and partial ring structures. This demonstrates the robustness and effectiveness of the fusion process in producing well-defined, continuous nanostructures across different assembly geometries and with controlled morphology. The ability to form such diverse nanostructures shows the potential of this method for various applications in nanotechnology, including the development of advanced materials and devices. This approach not only capitalizes on the unique growth characteristics of AuNRs but also demonstrates the importance of surface chemistry in nanostructure formation. The ability to control the growth dynamics through the manipulation of surface coatings allows for the precise engineering of nanostructures with tailored properties. The integration of these growth mechanisms can lead to the development of complex architectures that may exhibit synergistic effects, enhancing their functionality in applications such as nano and microelectronics, sensing devices, and photonics. By understanding the interplay between self-assembly and selective growth, we can unlock new possibilities for designing advanced materials that leverage the unique properties of gold nanostructures.

Figure 6.

TEM images of partial rings of AuNRs after amplification with Au(I)/CTAB/AA solution. The images show the partial rings of AuNRs that have undergone growth and fusion, resulting in amplified structures. The amplification process has led to the formation of thicker and more robust partial rings, with some areas showing significant fusion and growth.

4. Conclusions

In conclusion, we have demonstrated a unique and effective technique for the chemical synthesis of nano- and micrometer-sized fused structures of gold. Using controlled growth dynamics and self-assembly of CTAB-coated AuNRs, we achieved continuous ring-like structures with outer diameters of approximately 200–500 nm. This method allows for the synthesis of continuous structures in any desired shape, applicable for both linear and circular nano- and microstructures. The potential physical properties of such nanostructures are still under investigation, promising exciting developments in future applications. Furthermore, the versatility and precision of this method hold significant promise for advancing various technological fields, including photonics, nanoelectronics, and sensing.

Author Contributions

Conceptualization, B.P.K.; Methodology, B.P.K.; Validation, E.R.Z.; Writing—original draft, B.P.K.; Writing—review & editing, E.R.Z.; Supervision, E.R.Z.; Funding acquisition, E.R.Z. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

Funding Statement

This research was funded by the Robert A. Welch Foundation (C-1703), and the Alfred P. Sloan Foundation.