# Polymer-Stabilized Silver (Gold)-Zinc Oxide Nanoheterodimer Structures as Antimicrobials
## 1 Introduction  
Due to their unique physicochemical properties, nanotechnological products are widely used in biotechnology [1; 2; 3; 4]. In the antibiotics-resistant era, nano-antibiotics are potential nano-weapons in the fight against multidrug-resistant pathogens and even biofilms [5; 6; 7; 8; 9]. The results of using metal nanoparticles, their compounds, and their various combinations as antibacterial agents are very encouraging, since such structures are active against protozoa, fungi, bacteria, and viruses. Materials with antispetic properties containing nanoparticles of silver or cations of copper, zinc, iron, manganese, etc., are known and widely used. Silver nanoparticles (AgNPs), known for their antimicrobial properties, are used as food additives (E 174). Silver, unlike conventional antibiotics, practically does not cause resistance to a wide range of pathogens [10]. Numerous reviews have been published on the production and use of AgNPs [11; 12; 13; 14; 15]. As for the mechanism of the toxic effect of AgNPs on microorganisms, a number of researchers believe that this occurs due to the release of silver ions from nanoparticles depositing corresponding cations [16; 17]. Silver ions may bind to the phosphorous-containing groups of nucleic acids in microorganism cell nuclei or the sulfhydryl and carboxylic groups of bacterial enzymes. They can produce reactive oxygen species (ROSs) inside the pathogen cell, while disrupting the activity of the electrontransport chain inside the cell. These factors are the cause of the suppression of vital activity and the colonization of bacteria [18; 19; 20]. Unlike silver nanoparticles, gold nanoparticles (AuNPs) are much less often used as bactericides. For example, AuNPs were found to have an almost negligible effect on _E. coli_, _S. aureus_, _B. subtilis_, and _A. tumefaciens_[21; 22]. Greater bactericidal activity was observed for silver nanoparticles than for AuNPs [23; 24; 25; 26; 27]. Gold NPs exert their antibacterial activities in two predominant ways: one is to collapse the membrane potential, inhibiting ATPase activities to decrease the ATP level; the other is to inhibit the subunit of ribosome from binding to tRNA. Gold NPs enhance chemotaxis in an early-phase reaction. The actions of gold NPs do not include a reactive oxygen species (ROS)-related mechanism, which is the cause for cellular death induced by most bactericidal antibiotics and nanomaterials [28]. The disruption of the cell membrane of the _P. aurgenosa_ and the uncontrolled leakage of cell DNA was reported after interacting with 4,6-dihydroxy-2-pyrimidin-functionalized cationic 3 nm AuNPs [29]. Gold nanoparticles were also tested against pathogenic microorganisms in combination with antibiotics. It was shown, for example, that vancomycin hybrid AuNPs showed better antibacterial activity than free vancomycin [30]. As for the toxicity of silver and gold nanoparticles, a comparative assessment was carried out on the adverse bioactivity of virtually equidimensional gold and silver nanoparticles that were administered to rats either intratracheally or intraperitoneally at equal mass doses. It was demonstrated that AgNPs were more toxic than AuNPs, notwithstanding the latter's higher accumulation in RES-abundant organs [31]. In addition, gold has a low toxicity to biological systems, followed by silver, whether the systems are bacterial, animal, or human [32]. In other words, although silver nanoparticles have been shown to be more toxic than AuNPs, AgNPs have a relatively low toxicity to human cells in comparison with lower forms of life [33; 34; 35; 33]. Zinc oxide NPs (ZnO NPs) and zinc cations are also among the most studied antibacterial agents. It is believed that ZnO NPs are biocompatible and nontoxic [36]. ZnO NPs are more active against _S. epidermidis_, _S. pyogenes_, _S. aureus_, and _B. subtilis_ than MgO, TiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), CuO, and CeO\({}_{2}\) NPs [37].