Although physical and chemical methods have successfully produced high-purity nanoparticles of desired sizes, these processes often incur high costs and involve toxic chemicals. Hence, the toxicity issues in the preparation process become particularly critical. One of the primary goals of nanotechnology is to establish an ecologically friendly production process. To achieve this, some researchers have focused on biological methods for synthesizing metal nanoparticles due to their advantages, such as rapidity, cost-effectiveness, and environmental friendliness (Ghosh S. et al., 2021).

Nanoparticles (NPs) biosynthesis is fundamentally a bottom-up process involving the reduction of ions in aqueous solutions. In these studies, proteins and enzymes secreted by organisms like plants, bacteria, fungi, and yeast play a crucial role as reducing agents in NP synthesis. Although NPs synthesized through biological routes are enveloped by proteins and enzymes, making them excellent candidates for biological applications like drug delivery, this encapsulation may hinder their application in the field of electronics (Nyabadza et al., 2023).

However, research on the green synthesis of Ag-Cu NPs is relatively scarce. Recently, Hamouda et al. conducted a study evaluating the antibacterial activity of Ag-Cu NPs extracted from the seaweed Ulva lactuca against both Gram-positive and Gram-negative bacteria, as well as their impact on antibiofilm formation. The synthesized nanoparticles exhibited significant antibacterial activity against multidrug-resistant strains, highlighting their potential as alternative antibacterial agents (Hamouda et al., 2023). Simultaneously, Kumar et al. successfully prepared Ag-Cu NPs from wastewater extract of Prosopis cineraria pods (commonly known as “Sangri”), confirming the promising application prospects of this synthesis method (Kumar et al., 2023). Other plant extraction methods, such as Artemisia haussknechtii leaf extract, (Alavi and Karimi, 2018b), Salvia officinalis, (Malik et al., 2023), and Aegle marmelos and Citrus limetta fruit peel extract (Kushwah et al., 2019) have also been reported. The majority of these studies have focused on research in the field of antibacterial properties.

In addition to the common methods for synthesizing Ag-Cu NPs mentioned above, there is widespread interest in various bottom-up synthesis approaches, such as galvanic deposition, (Mahara et al., 2016), galvanic displacement, (Muzikansky et al., 2013; Lee et al., 2015), and one-pot synthesis (Giorgetti et al., 2013; Delsante et al., 2015). In contrast, top-down synthesis methods have received relatively less attention in the research.

Extensively studied for their geometric control and exceptional physical properties, core-shell nanoparticles (CS NPs) exhibit synergistic attributes (Tao et al., 2017). Ferrando’s research revealed that components with higher REDOX potential in the reduction process tend to assume the core role, while the second component has a propensity to deposit onto this core, forming a core-shell structure. Furthermore, he observed that the introduction of surfactants can alter the deposition sequence, leading to the formation of an antinuclear shell arrangement (Ferrando et al., 2008). Numerous studies focus on Ag-Cu CS NPs, with concentric spherical CS NPs being most explored (Yang Z. et al., 2019). Ghosh outlines two synthesis methods for diverse CS NPs: using distinct core shapes for physical control or employing capping agents, polymers, or reagents to govern growth direction and size (Ghosh Chaudhuri and Paria, 2012). Although generally less biologically active than singular nanoparticles, CS NPs exhibit prolonged metal ion release for extended bactericidal efficacy (Feng et al., 2021). Ag-Cu CS NPs exhibit broad-spectrum antibacterial activity and negligible genetic toxicity, highlighting their potential in antimicrobial applications (Długosz et al., 2021).

Ghosh discovered that different core shapes can lead to distinct Ag-Cu NPs, and the antibacterial effectiveness and toxicity of CS NPs are intimately linked to the core shape and shell thickness (Ghosh Chaudhuri and Paria, 2012). Gan’s findings reveal that triangular CS NPs, compared to spherical and cubic counterparts, possess larger specific surface areas and porosity, thereby enhancing their antibacterial activity (Gan et al., 2018). Caruso and colleagues have observed that shell materials not only enhance core stability and dispersion through surface charge modification but also shield the core from external stimuli by adjusting shell thickness at the nanoscale (Caruso, 2001). This synergistic mechanism imparts excellent antibacterial properties to Ag-Cu NPs while effectively preventing nanoparticle aggregation and inhibiting the genetic toxicity of BNPs.

Tojo proposed that the morphology of CS NPs can be finely tuned by adjusting the proportions and introduction sequence of metal precursors (Tojo and Vila-Romeu, 2014). Notably, Osowiecki et al. discovered an intriguing phenomenon during the synthesis of Ag-Cu core-shell NPs: varying the atomic fraction of Ag leads to distinct structures, ranging from nano crescent to complete core-shell configurations with enhanced surface coverage, a novel finding (Osowiecki et al., 2018). Jang et al. demonstrated that successful formation of Ag-Cu CS NPs requires sequential reduction of Cu and Ag precursors, while simultaneous introduction or initial reduction of Ag precursors impedes the formation of Cu-Ag CS NPs. This phenomenon might be attributed to the underlying chemical reactions: 2 A g + + C u → 2 A g + C u 2 +

Jang et al. (2020) Moreover, the inclusion of appropriate capping agents, surfactants, and coordination compounds has been demonstrated to have a substantial impact on the structure, shape, size, and characteristics of CS NPs (Zhao et al., 2022; Boas et al., 2023).

Several specific core-shell structures of Ag-Cu nanoparticles have been reported, including core-shell-shell particles (Bouazizi et al., 2018), metal Ag-Cu core-shell clusters with incomplete fractional phases (Benetti et al., 2019), cluster-within-cluster structures, triple onion-like core-shell structures, (Ferrando et al., 2008), multiple core-shell microspheres, and hollow core-shell structures (Ghosh Chaudhuri and Paria, 2012). These structures frequently exhibit outstanding antibacterial properties, concurrently mitigating the adverse reactions attributed to nanocomposites.

Hybrid structures can adopt either ordered or random arrangements. When the atomic sizes of the two elements closely resemble each other, the resulting alloy tends to exhibit a random configuration. Conversely, when there is a significant disparity in the sizes of the metal atoms, and the molar ratio of the two elements is simple enough, an intermetallic compound forms, resulting in a distinct structure (Zaleska-Medynska et al., 2016).

Much like the intricate factors governing CS nanostructures, those shaping alloy nanostructures are equally diverse. An array of synthesis conditions, encompassing variations in reduction potential (Tojo and Vila-Romeu, 2014), precise control of calcination temperature (Cybula et al., 2014), modulation of radiation dose (Treguer et al., 1998), and meticulous management of precursor concentration and sequence (Tojo and Vila-Romeu, 2014), collectively contribute to the diversity observed in bimetallic alloy nanoparticle structures.

The physicochemical attributes of BNPs are governed by a diverse array of factors, spanning from precursor concentration and sequential introduction to the chosen synthesis modality, bimetallic composition, and the utilization of surfactants and terminal agents. Furthermore, extraneous parameters like variance in reduction potential, temperature, and radiation dosage throughout the synthesis procedure significantly impact the eventual nanoparticle attributes.

Bimetallic nanoparticles are highly prized for their significant potential across various fields. A multitude of studies has consistently demonstrated that BNPs inhibit bacterial growth through the following mechanisms: i) Adhesion to the cell membrane: BNPs can change the structure of the membrane, leading to altered permeability and deficiencies in cell functions such as ATP secretion and transport activity. ii) Penetration inside the cell and nucleus: BNPs can disrupt mitochondrial function, destabilize and denature proteins, destabilize ribosomes, and interact with DNA. iii) Cellular toxicity and ROS generation: BNPs have the ability to induce cellular toxicity and generate reactive oxygen species (ROS), which can oxidize proteins, lipids, and DNA bases. iv) Modulation of cellular signaling: BNPs can modify the phosphotyrosine profile, thereby influencing cellular signaling pathways (Abbasi et al., 2018; Kushwah et al., 2019; Fanoro and Oluwafemi, 2020; Medina-Cruz et al., 2020).

Van Hengel et al. discovered that in Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) experiments, the synergistic effect of Ag-Cu NPs was significantly enhanced, with a respective increase of 2 and 10 times (van Hengel et al., 2020). The underlying mechanisms involve the production of more endogenous ROS, leading to a stronger oxidative stress response and reduced bacterial cell activity (Xie et al., 2022). Furthermore, Ag-Cu NPs release higher quantities of metal ions (Zhou et al., 2022), display a more dispersed structure (Pourjafari et al., 2022), diverse morphologies and sizes (Gu et al., 2018), enhance cellular permeability in prokaryotes (Garza-Cervantes et al., 2017), and the charge transfer effect further amplifies their antibacterial activity (Yang L. et al., 2019). In the review, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were utilized as crucial parameters for evaluating the bactericidal activity of bimetallic nanoparticles (BNPs), and Table 2 presents the antibacterial effect of Ag-Cu NPs in the retrieved articles.

The fundamental mechanisms underlying NPS (nanoparticle) toxicity encompass oxidative stress, inflammatory response, immunotoxicity, with genotoxicity being the primary factor impacting human host cells (Magdolenova et al., 2014). The mechanisms underlying nanoparticle-induced genotoxicity remain a subject of intrigue, with the degree of their impact on DNA specificity remaining unclear. Barnes et al. put forward the hypothesis that genotoxicity may arise from interactions between nanoparticles and genetic material or result from damage induced by reactive oxygen species (ROS) generated by nanoparticles or the release of toxic ions from soluble NPs (Barnes et al., 2008). Agnihotri et al. propose that nanoparticle-induced inflammation may give rise to secondary genotoxicity. In this process, activated phagocytes like neutrophils and macrophages release reactive oxygen species (ROS) that initiate oxidative damage to host cell DNA (Magdolenova et al., 2014; Agnihotri et al., 2020).

Ag NPs and Cu NPs exhibit potent antibacterial potential and have been extensively studied. The most widely accepted genotoxic mechanisms currently encompass direct DNA interactions, protein engagement, and the induction of oxidative stress, potentially resulting in host DNA damage and cellular dysfunction (Magdolenova et al., 2014). Ag NPs might enter mammalian cells via Ag ⁺ release, generating reactive oxygen species and disrupting redox systems, leading to cellular toxicity in cells (Yin et al., 2020). Saifi discovered that exposure pathways to Ag NPs can lead to the accumulation of toxic concentrations in the body, possibly resulting in organ toxicity, including impacts on the brain, liver, spleen, lymph nodes, and other organs (Saifi et al., 2018). Research into the toxicity of Cu NPs is currently limited. Carmona et al. reported a variety of adverse effects from Cu-NPs on mouse kidneys, livers, and spleens, both in vitro and in vivo experiments (Carmona et al., 2018). Sadiq et al. detected DNA strand breaks and oxidative DNA damage induced by Cu NPs, correlating cellular toxicity with released Cu ions (Sadiq et al., 2015). The low stability and aggregation of Cu NPs in aqueous solutions should be considered when interpreting their nanotoxicological effects.

Emerging research confirms that Ag-Cu NPs exhibit not only synergistically enhanced antibacterial efficacy but also a reduced potential for nanoparticle-induced bodily toxicity (Yin et al., 2020). Van Hengel believes that the synergistic effect of Ag-Cu NPs boosts antibacterial effectiveness while minimizing cytotoxicity by reducing the required Ag NPs (van Hengel et al., 2020). Długosz et al. contend that the reduced toxicity of Ag-Cu NPs primarily stems from their synergistic capacity to generate larger, less mobile nanoparticles. This inhibits the formation of detrimental free radicals and the binding process with -SH groups (Długosz et al., 2021). Further research has highlighted that in conventionally synthesized nanoparticles, aggregation serves as the primary source of toxicity. In Ag-Cu NPs, Ghadiri observed a more uniformly dispersed single nanoparticle, providing strong evidence of the safety performance of BNPs (Ghadiri et al., 2020). Furthermore, the genotoxicity of BNPs can be affected by various factors, encompassing aspects like their shape, surface characteristics, physicochemical parameters (such as pH and temperature), solubility, in addition to variables like the dosage of nanoparticles, duration of exposure, and the type of cells involved (Magdolenova et al., 2014). These findings hold significant implications for the future development of antimicrobial products.

Silver nanoparticles (AgNPs) and copper nanoparticles (CuNPs) exhibit excellent antibacterial activity, along with higher safety and longer activity cycles compared to organic nanomaterials, even at low concentrations. Additionally, the susceptibility of CuNPs to oxidation in ambient aerobic conditions leads to the formation of irregularly shaped, often spherical, agglomerated particles during the preparation process, potentially compromising their physicochemical and antimicrobial performance (Dlugosz and Banach, 2020).

Relevant studies suggest that the incorporation of silver components significantly reduces the oxidation tendencies of CuNPs. The formation of Ag-Cu NPs reduces oxygen ingress, resulting in a more stable structure compared to monometallic conditions, allowing for slow ion release, both favorable for synergistic interactions between the two metals (Cruces et al., 2022). Ahmadinejad et al. investigated the aging of synthesized Ag-Cu alloy nanoparticles and found them to be more stable than pure Cu nanoparticles, attributing this stability to the protective effect of a thin Ag shell (Ahmadinejad and Mahdieh, 2022). Similarly, Tsai demonstrated, through experiments, that the formation temperature of Cu oxide in Ag-Cu NPs is at least 150°C higher than in similarly sized pure Cu nanoparticles, owing to the protective role of the thin Ag shell (Tsai et al., 2013).

The stability of nanoparticles is closely linked to their high surface-to-volume ratio and rapid, uncontrolled release characteristics. Ongoing research in the quest for long-term stable NPs includes Dlugosz et al.'s suggestion that the addition of higher concentrations of tannic acid during CuNPs synthesis favors the generation of more stable CuNPs products (Dlugosz and Banach, 2020). Cruces emphasizes the importance of carriers, suggesting that negatively charged surfaces of zeolite (Zeo) and montmorillonite (Mtt) facilitate a more uniform loading and even release of Ag-Cu NPs, significantly enhancing their stability (Cruces et al., 2022). Recently, Ahmadinejad discovered a correlation between the presence and intensity of an applied electric field and the size and stability of Ag-Cu alloy NPs. Under appropriate field strength, Ag-Cu NPs become increasingly stable with increasing field intensity, providing theoretical support for new development strategies (Ahmadinejad and Mahdieh, 2022). Furthermore, studies on the addition of stabilizers such as polyvinyl pyrrolidone (PVP)polyvinyl alcohol (PVA) have been reported to enhance stability (Zhu et al., 2021).

Numerous studies have substantiated the superior antibacterial capabilities of nanomaterials compared to their larger counterparts, attributed to their smaller size and higher dispersion. Nevertheless, the challenge of nanoparticle aggregation persists during synthesis. Kalinska attributes the aggregation tendency of Ag-Cu NPs to nanoparticle size heterogeneity (Kalińska et al., 2019), while Manikam and colleagues propose that high surface energy and thermodynamic instability are the primary aggregation causes (Manikam et al., 2011). Ghadiri argues that nanoparticle aggregation is an inherent outcome of their synthetic pathways. He posits that conventional methods of nanoparticle synthesis might induce substantial particle aggregation, consequently significantly enhancing their toxicity (Ghadiri et al., 2020). To maximize the antibacterial efficacy of Ag-Cu NPs and mitigate toxicity, it is crucial to employ diverse strategies to reduce nanoparticle aggregation.

Numerous strategies exist to enhance Ag-Cu NPs dispersion. Research findings highlight that precursor type, proportion, and addition order impact complex formation and nanoparticle dispersion. Furthermore, Ghorbi’s suggestion to moderate the acceleration rate of silver precursors has been shown to notably improve the dispersion of silver cores in CS NPs, effectively preventing aggregation in the resulting Ag-Cu NPs; however, surpassing an optimal precursor concentration may reduce nanoparticle dispersion and lead to increased cluster formation, adversely affecting overall performance (Ghorbi et al., 2019). Researchers stress the vital role of surfactants as essential stabilizers to prevent nanoparticle aggregation, while capping agents are emphasized for their potential to boost the antibacterial performance of nanoparticles and avert particle aggregation (Manikam et al., 2011; Joel T and Shobini, 2018). In addition to these points, Perdikaki’s research indicates that a significant increase in the surface area ratio of Ag-Cu NPs often reduces aggregation, enhancing antibacterial effects while lowering genetic toxicity (Perdikaki et al., 2016). Długosz further highlights that an increased proportion of Cu NPs results in Ag-Cu NPs with noticeably larger sizes than Ag NPs, effectively improving stability and dispersion while mitigating aggregation-related risks (Długosz et al., 2021).

Based on their geometric shapes, BNPs can be categorized into zero-dimensional NPs, one-dimensional NPs, and two-dimensional NPs. Zero-dimensional nanoparticles, such as nanospheres and polyhedra, are predominantly synthesized using wet-chemical methods. One-dimensional nanoparticles consist of nanowires, nanorods, and nanotubes, while two-dimensional nanoparticles are composed of nanoplates, nanosheets, and nanobelts. These BNPs exhibit distinct properties and catalytic performance depending on the available active sites (Duan and Wang, 2013).

Some researchers emphasize that the higher surface area ratio of BNPs is inherently linked to their smaller nano size. Smaller nanoparticle sizes are more favorable for the release of metal ions from regions rich in low-coordination atoms (Ghasemi et al., 2017; Sabira et al., 2020). S Simultaneously, the reduction in size significantly enhances the generation of reactive oxygen species (ROS), resulting in a more potent oxidative stress damage during the antimicrobial action of Ag-Cu NPs (Manke et al., 2013). These two synergistic mechanisms collectively enhance their antibacterial efficacy.

The study conducted by Dulgosz indicates that enhancing the ratio of Cu NPs leads to the formation of larger Ag-Cu NPs. This results in the creation of nanocomplexes characterized by improved stability and reduced toxicity (Długosz et al., 2021). Consequently, a substantial enhancement in bactericidal efficiency occurs, propelled by the advantageous interplay of synergistic effects—an insightful finding within their research (Długosz et al., 2021). However, Zhang presents a differing viewpoint, suggesting that the miscibility and orderliness of the bimetallic structure can be affected, potentially resulting in smaller BNPs compared to their individual NP counterparts. This increase in surface-to-volume ratio, accompanied by a higher number of active sites and lower energy barriers, significantly enhances the catalytic activity of BNPs (Zhang and Zhang, 2018). Furthermore, it is important to note that the presence of Ag-Cu NPs has a synergistic effect, reducing the requirement for Ag NPs and effectively mitigating the genotoxicity associated with BNPs (van Hengel et al., 2020).

As a significant constituent within loaded nanoparticles, the carrier has been extensively examined by numerous scholars. Montmorillonite (Roy et al., 2018), sepiolite (Li et al., 2020), nanofibers (Liu et al., 2018), carbon nanotubes (Jiang et al., 2022), carbon nanospheres (Li et al., 2016)), nano-SiO ₂ (Ermini and Voliani, 2021), and biopolymeric materials (Arfat et al., 2017b) have garnered attention as carriers (Table 3). Based on their functionality, Yang et al. categorized carriers into two main types: biocompatible (Figure 4A) and absorptive (Figure 4B). Among the biocompatible carriers are hydroxyapatite and bioactive glass, which mitigate immune responses upon introduction into organisms. Zeolite and clay minerals, classified as absorptive carriers, offer conducive environments for the loading and dispersion of inorganic nanometals (Yang et al., 2022). Yang et al. ascribed the antibacterial mechanism of the carriers to their sturdy pore structure and expansive specific surface area. These attributes facilitated the efficient absorption and release of active ingredients through diverse mechanisms, simultaneously playing a pivotal role in averting the agglomeration of high-surface-energy nanoparticles (Yang et al., 2022).

Numerous studies have shown that Ag-Cu NPs with support have better activity than those without support (Ahmad et al., 2016). Perdikaki contends that the presence of carriers plays a crucial role in augmenting oxidative stress and cell membrane disruption by BNPs, while also ensuring the uniform distribution of nanoparticles on the surface (Perdikaki et al., 2016). Conversely, Targhi attributes the heightened antibacterial efficacy in the presence of carriers to the sustained-release effect exhibited by the nanoparticles. Carriers can ensure that nanoparticles maintain a more prolonged in vitro antibacterial and anti-biofilm effect at lower doses, thus eliciting a more enduring bactericidal action (Targhi et al., 2021). In addition, it has been well-documented that the partial carrier possesses intrinsic antibacterial capabilities and exhibits mechanisms that synergistically amplify oxidative stress damage in conjunction with nanoparticles, thereby enhancing their antibacterial effectiveness (Ahmad et al., 2016).

It is important to note that the application of most carrier materials is often constrained by various factors. These limitations include complex synthesis processes, unclear in vivo reaction mechanisms, and severe inflammation in vital organs such as the kidneys. Consequently, it is imperative to carefully evaluate the selection of carrier materials in future research, development, and application (Fan et al., 2020).

Teixeira posits that pH can directly modulate the surface charge and electron transfer properties of BNPs, consequently influencing their photocatalytic capabilities and antibacterial attributes (Teixeira et al., 2019). Pelgrift et al., in their observation, found that the antibacterial potential of nanoparticles becomes readily activated in acidic conditions at the infection site (Pelgrift and Friedman, 2013). Further confirming this effect, Yan et al. demonstrated that BNPs exhibit increased bactericidal efficacy in a low pH environment (pH 5.0) compared to a physiological environment (pH 7.4). This enhancement is likely attributed to the substantial release of Cu ²⁺ and Ag ⁺ ions at low pH conditions (Yan et al., 2020).

Existing research has demonstrated that Cu NPs, a common p-type semiconductor, have gained widespread application in the fields of photocatalysis and sterilization due to their cost-effectiveness, unique physicochemical properties, high surface area, and promising prospects (Noman et al., 2020). Similarly, as a well-known active photocatalyst, Ag NPs possess tunable plasmonic resonance effects that can significantly mitigate infections caused by numerous bacteria (Asgari et al., 2022). While both Ag NPs and Cu NPs have their individual advantages in the field of photocatalysis, research on harnessing their synergistic effects for the synthesis of BNPs to enhance their antibacterial performance is scarce.

Scholars suggest that the photocatalytic antibacterial mechanism of hybrid semiconductor–metal nanoparticles (Ag-CuNPs) relies on charge separation and transfer between the metal and semiconductor materials (Kushwah et al., 2019). This charge separation was substantiated by Waiskopf et al. through the observation of fluorescence quenching effects in HNPs (Waiskopf et al., 2018). Therefore, the heightened bactericidal effect of Ag-Cu nanoparticles may be linked to the charge transfer mechanism. Panchal discovered that HNPs exhibited higher hydroxyl radical concentrations under light, thanks to electrons transferring from semiconductors to metal nanoparticles (Panchal et al., 2020) Similarly, Ag NPs with surface plasmon resonance released electrons to interact with oxygen, producing additional ROS. These amplified free radicals and ROS bolstered the oxidative stress response of Ag-Cu NPs (Zhu M. et al., 2020).

Various factors influence charge separation and hole removal between HNPs particles. Ben-Shahar indicated that surface and chemical properties of the surroundings impact HNPs charge separation. They linked charge separation to HNPs size, with a denser state-of-states in metal compounds boosting transfer rates for larger metal domains (Ben-Shahar et al., 2016). Waiskopf suggested that the metal composition plays a role in influencing charge transfer kinetics and efficiency. It was observed that more efficient charge transfer occurs in semiconductor nanorods modified with multi-island structures (Waiskopf et al., 2018). Moreover, it has been documented in the literature that environmental variables, including the presence of organic ligands and highly alkaline conditions, significantly enhance the process of charge separation (Simon et al., 2014).

Reactive oxygen species (ROS) are highly active oxygen-containing molecules, including unstable radicals like superoxide anions, hydroxyl radicals, and hydrogen peroxide. Research has demonstrated that cells can generate reactive oxygen species (ROS) through both endogenous pathways, such as NADPH oxidase, and exogenous pathways, including metal-catalyzed Fenton reactions (Manke et al., 2013). After exposure to nanoparticles (NPs), Dharmaraja observed an elevation in reactive oxygen species (ROS) production within microbial cells, resulting in oxidative damage to biomacromolecules such as lipids, proteins, and nucleic acids (Dharmaraja, 2017). The generation mechanism and bactericidal action of ROS are illustrated in Figure 5.

Manke has advanced the idea that when faced with an overabundance of ROS generation, host cells employ a regulatory mechanism involving the expression of cytokines (MAPK, PTPs, Src, NF-𝜅B, AP-1) to mitigate oxidative stress-induced genotoxicity. This regulation is facilitated by the coordinated action of non-enzymatic antioxidants, including enzymes (SOD, CAT, PER), as well as other substances (Vc, VE, GSH, Cys) (Manke et al., 2013).

Previous studies have shown that compared to other metal nanoparticles, Ag NPs and Cu NPs tend to generate a richer pool of ROS, consequently leading to more pronounced oxidative stress damage (Długosz et al., 2021). Meghana discovered that under aerobic conditions, Cu NPs not only rapidly degrade cell membranes but also generate extremely high concentrations of ROS. This ROS-induced oxidative stress damage serves as one of the primary mechanisms behind the antibacterial properties of copper nanoparticles (Meghana et al., 2015). Liao et al. proposed that the oxidative stress bactericidal mechanism of Ag NPs is linked to the significant inhibition of redox-related enzymes in bacterial cells, such as CAT and POD (Liao et al., 2019). Recently, Bondarenko identified a relatively novel phenomenon. He observed a strong correlation between the dissolution rate of Ag NPs and their primary bactericidal mechanism and toxic effects. Ag NPs with a high dissolution rate tend to primarily employ the bactericidal mechanism through the release of Ag ⁺ . In contrast, Ag NPs with a low dissolution rate demonstrate a greater tendency to induce ROS-mediated damage and exhibit minimal genotoxicity (Bondarenko et al., 2018).

Emerging research highlights the potent synergistic effect of Ag-Cu NPs, significantly elevating ROS levels within microbial systems, influenced by a variety of factors. Długosz observed that BNPs can enhance their antibacterial performance by increasing their surface-to-volume ratio, accelerating ion release, and intensifying ROS content and oxidative stress reactions (Długosz et al., 2021). Ahmad et al. emphasized the significance of carriers in ROS generation within BNPs systems (Ahmad et al., 2016; Targhi et al., 2021). Additionally, Metryka suggested that the presence of transition metals (Cu NPs) on the surface of BNPs contributes to the generation of additional ROS through Fenton, Fenton-like reactions, and the Haber-Weiss reaction, broadening our understanding of the multifaceted antibacterial mechanisms of NPs (Metryka et al., 2021).

The impact of the external environment should not be underestimated. Moussa proposed that under illuminated conditions, photo-excited charge-carrier interactions in the Fenton reaction enhance ROS levels within bacterial cells, facilitating BNPs’ effective oxidative stress bactericidal activity (Moussa et al., 2016). Zhang et al. emphasized the indispensable role of oxygen in oxidative stress reactions within the BNPs system (Zhang et al., 2017). André suggested that the reduced activity of BNPs in anaerobic environments primarily stems from decreased macrophage and neutrophil activity (André et al., 2022). Additionally, the influence of pH levels and temperature conditions in the surrounding environment on the oxidative stress damage caused by Ag-Cu NPs has been substantiated by relevant scholars (Sun et al., 2021; Hosny et al., 2022), offering insights for optimizing the antibacterial effectiveness of NPs.