## 1 Introduction  
The synthesis and properties of metallic nanoparticles (NPs) has been extensively studied over decades, not only because of their unique properties, but also because of their potential applications in catalysis, electronics, optoelectronics, information storage, biosensors, and surface-enhanced Raman spectroscopy (SERS) [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]. Nanoparticles can exist as common structural elements or composites, and they have a wide functional diversity compared to bulk materials. The physical and chemical properties of metallic nanoparticles are mostly determined by the following parameters: size, shape, and composition [11; 12]. Therefore, controlling these parameters is extremely important in tailoring the properties of the nanoparticles. Particular emphasis has recently been placed on controlling the shape because it allows the fine-tuning of optical properties with a greater versatility than can be achieved otherwise. Only recently has it become possible to control the shape of metal nanoparticles synthesized in solution, leading to the development of numerous synthetic methods [13; 14; 15; 16]. For example, [PERSON] et al. developed a seed-mediated growth method to prepare gold nanorods and nanowires with controllable aspect ratios; these nanomaterials offer potential applications in optical sensing and as interconnects in nanoelectronics [17]. [PERSON] and co-workers demonstrated a hot solution approach based on the polyol process for the large-scale synthesis of silver nanobars and nanorice particles, where the surface plasmon resonance can be tuned from the visible to near-infrared (NIR) spectral regions [18]. Additionally, [PERSON] et al. prepared bimetallic, magnetic Ni-Co (core-shell) nanoparticles under microwave irradiation [19]. Currently, procedures to fabricate various types of metal nanoparticles with excellent control over their size and shape are well-established [20]. However, the applicability of single-component metal nanoparticles is restricted by their limited properties. To overcome these limitations, metal nanoparticles can be modified through the construction of bimetallic architectures consisting of two distinct metals. These composite bimetallic nanoparticles exhibit fascinating properties that can be dramatically different from those of the corresponding single-component particles; these properties include the enhancement of plasmonic properties in Au-based alloy nanoparticles, enhanced magnetic properties in magnetic materials, or enhanced optical and magnetic properties in multifunctional nanoparticles, such as AuFe. These properties arise from both the electronic and structural effects of the bimetallic structures [21; 22; 23]. Bimetallic nanoparticles have played an important role in tuning the surface plasmon band, enhancing the stability and dispersion of nanoparticles, and regulating the magnetic and optical properties. Since these properties are strongly dependent on the structure and composition of the nanomaterials, the synthesis of bimetallic nanoparticles with accurately controlled structures and compositions is a worthwhile objective. For example, it has been demonstrated that the surface plasmon resonance of hollow bimetallic Au@Ag core-shell nanoparticles can be readily tuned by controlling the Ag:Au ratio in the replacement reaction [24]. In addition, AuCu nanoparticles have been used to prepare atomically ordered intermetallic nanocrystals by controlling the diffusion of Cu into Au; this strategy provides a new avenue to fabricate unique bimetallic nanoparticles [25]. Separate studies have demonstrated the synthesis of CoAu bimetallic nanoparticles via chemical reduction, offering enhanced magnetic performance with little or no surface oxidation, which can lead to applications in magnetic resonance imaging [26].