The utilization of iron-based nanomaterials has attracted significant attention in the field of biomedical applications, primarily due to their distinct paramagnetic or superparamagnetic magnetization characteristics. A Fe₃O₄@MoS₂-Ag nanozyme with an abundant defect rough surface was prepared using a simple hydrothermal method and in situ photo deposition method, demonstrating a good bacteriostatic effect (~69.4%) against Escherichia coli. Additionally, the magnetic recovery of Fe₃O₄ provides power for efficient disinfection of the nanozyme ^[1][173]. Drums et al. developed a cost-effective and versatile approach by utilizing paramagnetic iron oxide particles (SPION) conjugated with fructose metabolites, which effectively enhanced the uptake and therapeutic efficacy of SPION against both Gram-positive MRSA and Gram-negative biofilms (e.g., E. coli and Pseudomonas aeruginosa) ^[2][174]. These materials have demonstrated immense potential in various biomedical domains, including bio-separation, targeted drug delivery, magnetic resonance imaging, biosensors, and hyperthermia therapy ^[1][3][4][173,175,176]. In 2007, Gao and Yan presented pioneering evidence that magnetite (Fe₃O₄) nanoparticles possess inherent peroxidase-like enzymatic activity due to the substantial presence of Fe²⁺ and Fe³⁺ ions on their surface ^[5][53]. This pioneering research has served as a catalyst for the exploration and subsequent implementation of iron-based nanozymes in diverse biological domains, encompassing bioassays, tumor therapy, and antibacterial interventions ^[6][7][8][177,178,179]. The research conducted by Sun’s group has involved developing an enzymatic antibacterial approach centered around thermogenic nanozymes, which aims to achieve synergistic bacterial inhibition by enhancing the activity of nanozymes while simultaneously reducing the activity of natural enzymes in bacteria ^[9][29]. Specifically, yolk-shell structured Fe₂C@Fe₃O₄ NPs with a uniform size of approximately 20 nm were synthesized as the thermogenic nanozymes, exhibiting exceptional magnetothermal efficiency and escalated peroxidase-like activities facilitated by thermal enhancements ^[9][29]. Furthermore, in order to achieve an elevated level of nanozyme activity, a Fe,N co-doped ultrathin hollow carbon framework (Fe,N-UHCF) was synthesized and characterized by the substantial presence of Fe-Nx bonding as well as its distinct morphology. The Fe,N-UHCF framework exhibits exceptional peroxidase-like activity, surpassing that of nearly all previously reported nanozymes ^[10][180]. Ali and his colleagues conducted a study on the fabrication of Fe-doped MoS₂ (Fe@MoS₂) nanomaterials, which exhibited an enhanced peroxidase-like activity through a co-catalytic mechanism. The remarkable improvement can be attributed to the synergistic effect resulting from the concurrent co-catalytic activities of Fe and MoS₂, as well as the inherent characteristics of MoS₂ layers ^[7][178]. Furthermore, Liao and colleagues have achieved a significant breakthrough by engineering FePO₄-hydrogel (FePO₄-HG) as an exceptionally effective antibacterial therapeutic approach. The FePO₄ nanoparticles (NPs) were synthesized using the hydrothermal growth method and subsequently modified with L-cysteine to produce FePO₄-Cys. These were then covalently linked to the hydrogel (HG) through an amidation reaction, resulting in the fabrication of FePO₄-HG. This novel construct exhibits notable trienzyme-like functionality, eradicating bacteria through peroxidase-like catalytic capabilities while safeguarding normal cells from exogenous H₂O₂-induced damage via synergistic antioxidant effects stemming from the superoxide dismutase- and catalase-like activities of FePO₄-HG ^[11][181]. A multifunctional GGFzyme was successfully synthesized using a one-pot method, effectively and promptly combining glucose oxidase (GOx), gallic acid (GA), and ferrous ions (Fe²⁺). This innovative GGFzyme utilizes endogenous glucose molecules in the local environment to generate a controlled cascade of ROS, acting as a cytotoxic agent against MRSA commonly found in wound surroundings with high mortality rates. Notably, this approach eliminates the need for exogenous H₂O₂ administration. By efficiently reducing glucose concentration, GGFzyme promotes simultaneous elimination of pathogenic bacteria and wound healing, offering a promising therapeutic strategy for hyperglycemic wound treatment ^[12][182]. In summary, these investigations highlight the vast potential of iron-based nanozymes in various biomedical fields, offering innovative solutions for bioassays, tumor therapy, antibacterial interventions, and other emerging biomedical challenges.

Copper (Cu), a crucial microelement in living organisms, plays a significant role in the redox processes of native enzymes, as demonstrated by Cu-Zn superoxide dismutase and tyrosinase ^[13][14][183,184]. In parallel, although Cu ions have demonstrated commendable antibacterial efficacy, their significant toxicity limits direct utilization within living organisms ^[15][37]. Currently, investigations have confirmed the more favorable applicability of Cu-based nanomaterials as nanozymes due to their broader catalytic activity pH range compared to their Fe-based counterparts ^[15][37]. Drawing inspiration from natural enzymes’ active site structure, Liang and colleagues used Cu²⁺ to functionalize melanin nanoparticles (NMPs) in cuttlefish-ink-derived ink. This approach produced a highly stable and active SOD-like nanozyme (Cu-NMPs) with strong free radical scavenging capabilities. Subsequently, the simulated enzyme was incorporated into carrageenan films for food packaging purposes. Results showed that at a concentration of 10 μg/mL, Cu-NMPs generated over 80% •O⁻₂ and exceeded natural SOD enzyme activity by reaching 60 U/mL ^[16][185]. The research group, led by He, developed a versatile nanozyme called polydopamine (PDA)-modified copper oxide (Cu_xO-PDA). Cu_xO-PDA demonstrated peroxidase-like behavior, which was further enhanced under near-infrared (NIR) irradiation. Under neutral or alkaline conditions, Cu_xO-PDA had a negative surface charge and showed minimal peroxidase activity. However, under acidic conditions, the surface charge of Cu_xO-PDA can become positive, allowing for specific targeting of negatively charged bacteria. Interestingly, well-dispersed Cu_xO-PDA quickly aggregates upon NIR irradiation, trapping bacteria and nanozymes in close proximity. The study revealed that a decrease in the distance between the nanozyme and bacteria led to an increase in antibacterial efficacy. The conducted experiments demonstrated that the Cu_xO-PDA nanozyme induced DNA degradation, lipid peroxidation, and eradication of biofilm formations ^[17][170]. Liu et al. developed and synthesized biodegradable Cu-doped phosphate glass (Cu-PBG) nanozymes, which exhibit potent antibacterial activity against both Gram-positive and Gram-negative bacteria. The antimicrobial mechanism of Cu-PBG involves the generation of ROS and copper release. In wounds, it functions akin to peroxidase by inducing lethal oxidative stress on bacteria by catalyzing the decomposition of H₂O₂ into •OH. Additionally, Cu-PBG possesses inherent degradability attributed to its phosphate glass properties ^[18][186]. These studies emphasize the potential of Cu-based nanomaterials as nanozymes, providing a promising alternative for various applications such as food preservation and antibacterial interventions. Their unique characteristics, including a wide pH range and enhanced catalytic efficacy under specific circumstances, make them invaluable tools in both biomedical and environmental fields.

Due to their notable surface metal atom ratios, various noble metal-based nanozymes, including Au ^[19][167], silver ^[20][169], platinum ^[21][187], and palladium ^[4][176], exhibit substantial catalytic activity. As a consequence, these nanozymes have found widespread utilization in the realm of biomedical applications, specifically in biosensing ventures ^[22][188]. Previous studies have predominantly observed monometallic compositions at the branch ends of dendritic structures. It is well-established that the peroxidase-like activity exhibited by monometallic nanozymes consistently falls short compared to their multimetallic counterparts ^[23][24][189,190]. According to the Sabatier principle, it is hypothesized that maintaining an optimal level of catalyst–intermediate interaction is crucial for achieving a balanced and moderate interaction between the catalyst and intermediate species ^[25][26][191,192]. Alloying is a suitable strategy for finely tuning the interaction between the catalyst’s surface and intermediate species. Pd nanocrystals have been shown to exhibit facet-dependent oxidase and peroxidase-like activities, endowing them with exceptional antibacterial efficacy through the generation of reactive oxygen species (ROS) ^[27][193]. Sun’s research group successfully developed a nanoplatform, designated as Pd@Pt-T790, which was easily synthesized by conjugating enzyme-catalytic Pd@Pt nanoplates with the organic sonosensitizer meso-tetra(4-carboxyphenyl) porphine (T790). Notably, it was observed that the incorporation of T790 onto Pd@Pt resulted in a significant suppression of the catalase-like activity exhibited by Pd@Pt. Under ultrasonic irradiation, the nanozyme activity was effectively restored, facilitating the catalytic decomposition of endogenous H₂O₂ into O₂. This “blocking and activating” phenomenon is crucial in mitigating potential toxicity and adverse effects of nanozymes on normal tissues, while also offering significant potential for achieving active, controllable, and disease-targeted nanozyme catalysis ^[22][188]. The development of ultrasonic (US)-switchable nanozyme systems represents a highly promising avenue for enhancing the active, controlled, and precise eradication of deeply entrenched bacterial infections through sonodynamic modalities. This innovative strategy demonstrates remarkable potential for future prospects in the realms of biomedical research and clinical therapeutics, laying the foundation for transformative applications.

Simultaneously, Yang et al. employed Cu,I-doped carbon dots (Cu, i-CDs) as a reducing agent in conjunction with nanozymes to fabricate an Au-based nanozyme composite material (AuNPs/Cu,I). The AuNPs/Cu,I nanozymes not only emulate the intrinsic activities of superoxide dismutase, peroxidase, and catalase under diverse conditions but also serve as surface-enhanced Raman spectroscopy (SERS) enhancers. The integration of Cu, I-CDs, and AuNPs enhances electron transferability, leading to augmented peroxidase-like activity and superoxide-like activity. The multi-enzyme-like functionality of AuNPs/Cu,I nanozymes can be precisely modulated by altering the composition of Cu⁰/Cu⁺ and Au ^[28][194]. In addition, Prasad’s team synthesized bimetallic Cu-M nanoparticles (M = Au, Ag, Pt, or Pd) using an electrical substitution (GR) reaction. The catalytic activity of the bimetallic system was compared with that of Cu nanozymes, and the Cu-Pt nanozymes showed the highest catalytic efficiency ^[29][195]. The combination of both materials takes advantage of the two properties of the redox processes of native enzymes of Cu and the significant catalytic activity of novel metal for applications of nanozymes in antibacterial mechanisms.

Apart from the previously mentioned nanozymes based on Fe, Cu, and noble metals, vanadium (V)- and cerium (Ce)-based nanomaterials, possessing intrinsic mimic enzyme catalytic properties, are commonly denoted as vanadium-based nanozymes ^[15][37]. The exceptional capacity of vanadium (V)-based nanomaterials to mimic multiple enzymatic activities has been well-documented, demonstrating their efficacy in combating bacterial infections. These nanomaterials exhibit remarkable potential for addressing such infections due to their superior multienzyme-mimicking properties ^[30][196]. Ma et al. successfully developed a highly efficient bienzyme system, which demonstrated potent synergistic antibacterial activity. Vanadium oxide nanodots (VO_xNDs) were synthesized using a streamlined ethanol–thermal strategy with vanadium (III) trichloride (VCl₃) as the precursor. The as-synthesized VO_xNDs exhibited remarkable peroxidase- and oxidase-like activities, mimicking natural enzymes’ functions. This antibacterial system showed exceptional efficacy against both non-resistant bacteria, including Gram-positive S. aureus and Gram-negative E. coli, and drug-resistant strains such as ESBL-producing E. coli, MRSA, and kanamycin-resistant E. coli. Importantly, due to their nanoscale dimensions, the VO_xNDs displayed favorable biosafety as confirmed with various assessments including MTT assays, examination of physiological indices, and H&E staining ^[30][196]. Hu’s research team successfully synthesized a targeted nanozyme, Co^IITBPP(bpy), using meticulous supramolecular self-assembly techniques. This unique nanozyme possesses peroxidase-like properties and can generate •OH radicals without light, showing exceptional production of ROS under irradiation. This causes bacterial membrane disruption and the release of intracellular contents, resulting in synergistic antibacterial effects. Co^IITBPP(bpy) also efficiently decomposes excess H₂O₂ into O₂, thanks to its outstanding catalase-like activity. The catalytic process improves PDT efficacy, and reduces tissue hypoxia and excessive H₂O₂ levels. The synthesized nanozyme shows good biocompatibility and achieves over 95% antibacterial efficiency in vitro. The supramolecular self-assembly of these multi-porphyrin structures offers great potential for use in antibacterial treatments and wound healing ^[31][150]. Furthermore, vanadium- and cerium-based nanomaterials have emerged as promising candidates for mimicking haloperoxidase activity to address the challenge of low stability in natural enzymes. These nanomaterials possess the capability to mitigate biofouling and enable the development of materials with prolonged stability even in demanding environments ^[32][197]. Hu’s research group developed free-standing nanofibrous mats using electrospinning PVA with CeO_2−x NRs. After cross-linking, the resulting PVA mats incorporated CeO_2−x NRs and exhibited haloperoxidase-like activity in water environments. The CeO_2−x activity within the PVA fibers was quantitatively assessed with bromination of phenol red, confirming that the nanozyme remained active even after being processed in the polymer matrix. These mechanically robust hybrid mats exhibited catalytic oxidation of Br⁻ and H₂O₂ to HOBr, similar to natural haloperoxidases. Leveraging the haloperoxidase-like activity of ceria NRs in PVA mats, along with their easy production, these PVA/CeO_2−x hybrid fibrous networks show promise for robust anti-biofouling coatings on surfaces exposed to humid and marine environments ^[33][160]. The present study elucidates the inherent potential exhibited by nanomaterials derived from vanadium and cerium as nanozymes, thereby offering a wide range of applications including antibacterial therapies, wound healing, and the fabrication of durable materials tailored for demanding conditions. The unique catalytic properties and excellent compatibility with biological systems make these nanomaterials highly promising candidates for future biomedical advancements and environmental initiatives.

Recently, carbon-based nanomaterials have emerged as highly promising entities in the field of biomedicine due to their exceptional physicochemical properties, commendable biocompatibility, cost effectiveness, and versatile mimicry of multiple enzyme functionalities ^[15][37]. Numerous efforts have been dedicated to exploring the antibacterial potential of carbon-based nanomaterials. Fang et al. successfully synthesized and modified a variety of oxygenated nanodiamonds (O-NDs) with different oxidation degrees using a simple yet efficient mixed acid-assisted reflux method, giving them remarkable peroxidase mimicking capabilities. A thorough spectroscopy analysis and chemical structure characterizations conclusively revealed the presence of carbonyl, carboxyl, and nominal hydroxyl groups in these O-NDs. Consequently, these nanomaterials exhibited enhanced enzymatic activity across a wide pH range. Importantly, spectroscopic observations and structural investigations suggested a significant increase in enzymatic activity during prolonged experimental durations. Furthermore, the addition of trace amounts of H₂O₂ resulted in exceptional antibacterial efficacy demonstrated by O-NDs, effectively eliminating periodontal bacteria and disrupting biofilms under physiologically relevant conditions both in vitro and in vivo ^[34][198]. Carbon-based nanomaterials, particularly oxygenated nanodiamonds, have shown great potential in the field of biomedicine due to their exceptional properties and surface modifications that enhance enzymatic activity and potent antibacterial effects. These significant advancements offer promising avenues for exploring novel antibacterial strategies and therapeutic interventions in biomedicine.

Transition metal nanomaterials have attracted significant attention due to their exceptional photo-thermal and electronic properties, as well as their commendable biosafety profile. These characteristics make them highly valuable and extensively utilized in various domains including sensing, imaging, catalysis, and biomedicine ^[35][36][199,200]. Bai’s research team developed a new heterostructure called ZnO@GDY NR, which consists of zinc oxide nanorods layered with graphdiyne nanosheets. This innovative configuration acts as a piezocatalytic nanozyme, where the graphdiyne layer provides electrical conductivity, adsorption, and catalytic nanozyme activity, while the zinc oxide layer is responsible for piezo catalysis and catalytic nanozyme activity. The resulting piezocatalytic nanozyme shows impressive antibacterial efficacy, with nearly 100% effectiveness against drug-resistant pathogens such as methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa in both in vitro and in vivo settings ^[37][153]. The present investigation not only demonstrates the exceptional antibacterial efficacy of the ZnO@GDY NR heterostructure as a nanozyme but also highlights its commendable biocompatibility characteristics. These valuable observations not only contribute essential knowledge but also serve as a pivotal reference for the conceptualization and advancement of forthcoming antibacterial nanozymes that prioritize enhanced biocompatibility, thereby fostering their potential in biomedical applications.

Controlling metal species at the atomic level is a highly effective strategy for enhancing both the efficiency of metal utilization and the catalytic performance of nanomaterials ^[38][201]. In 2011, Qiao and his research group introduced the innovative concept of single-atom catalysts (SACs), which has since revolutionized the field of catalysis ^[39][202]. Following their creation, SACs have gained significant attention in the field of catalysis due to their advantages including efficient atom utilization, high catalytic activity, exceptional stability, and remarkable selectivity ^[40][34]. Recently, a group of SACs have emerged as single-atom nanozymes (SAzymes), exhibiting atomically dispersed active sites and coordination environments comparable to those observed in natural metalloenzymes. This novel development not only provides valuable insights into the catalytic mechanisms of nanozymes but also establishes a crucial connection between natural enzymes and nanozymes ^[15][37]. SACs exhibit strong catalytic ability and allow for efficient use of metals, which is particularly important in cancer and antibacterial treatments. This capability ensures effective therapeutic outcomes even at low metal concentrations ^[41][42][203,204]. N-doped porous carbon (NPC) has gained widespread recognition as a specialized nanoplatform for constructing SACs, thanks to its commendable catalytic efficacy, outstanding biosafety profile, distinctive mesoporous structure, and substantial specific surface area. They present the synthesis of Cu single-atom sites/NPC (Cu SASs/NPC) via a PEAP strategy, which exhibits notable nanozyme properties for photothermal–catalytic antibacterial therapy. The Cu SASs/NPC composite demonstrates superior catalytic activity, glutathione-depleting capabilities, and photothermal effects compared to pure NPC without Cu doping. These Cu SASs/NPC specimens, being peroxidase-like nanozymes, efficiently catalyze the conversion of H₂O₂ into •OH, facilitating conspicuous antibacterial efficacy. Additionally, under laser irradiation, the photothermal effect of Cu SASs/NPC enhances the peroxidase-like catalytic function, driving increased production of ROS and consequently yielding enhanced in vitro antibacterial effects ^[43][205]. In addition, Wang’s research group successfully synthesized a Mo SA-N/C single-atom nanozyme with remarkable heterogeneous peroxalate (HPO)-mimicking activity and visible-light-responsive photothermal behavior, offering a promising approach to mitigate biofouling in seawater environments. As an HPO-like nanozyme, Mo SA-N/C effectively catalyzes the oxidation of bromide ions (Br⁻) to produce cytotoxic hypobromous acid (HOBr). Furthermore, the application of visible light irradiation significantly enhances the oxidation activity of Br⁻ on the surface of Mo SA-N/C through a pronounced photothermal effect.

MOFs are crystalline materials composed of metal ions and organic bridging linkers, characterized by diverse porous structures and exhibiting attributes of exceptionally high porosity (up to 90% free volume) and a significant surface area within the organic framework ^[44][207]. Due to their porous structures, MOFs have gained significant attention as protective matrices for immobilizing enzymes through chemical grafting or physical adsorption, effectively preventing denaturation caused by external stimuli ^[45][46][208,209]. Liu et al. proposed a novel approach combining cerium complexes (DNase mimics) and MOFs with peroxidase-like activity to create an artificial nanozyme with dual enzyme-mimetic capabilities. This integrated nanozyme effectively disperses biofilms and eliminates bacteria without the adverse effects commonly associated with antibiotics. The cerium (IV) complexes acted as DNase mimics, effectively breaking down eDNA and disrupting mature biofilms. Meanwhile, the MOF with peroxidase-like activity killed bacteria in dispersed biofilms by using H₂O₂. The combination of these two types of nanozymes effectively prevented bacterial recolonization and biofilm reoccurrence, which is a rational strategy for combating biofilms considering the challenges associated with using single-modal antibacterial agents ^[47][166]. Hu et al. successfully synthesized ultrasmall gold nanoparticles (UsAuNPs) on ultrathin two-dimensional MOFs through an in situ reduction process. The resulting hybrid material, UsAuNPs/MOFs, combines the advantages of both UsAuNPs and ultrathin 2D MOFs. This hybrid material shows remarkable peroxidase-like activity, efficiently decomposing H₂O₂ into •OH. The antibacterial efficacy of the UsAuNPs/MOFs nanozyme was evaluated against both Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive), achieving excellent antibacterial properties with low concentrations of H₂O₂. Animal experiments showed that the hybrid material effectively promotes wound healing and is biocompatible, indicating the potential of hybrid nanozymes in antibacterial therapy for future clinical applications ^[48][210]. These innovative methodologies highlight the potential of MOFs and nanozymes in tackling the challenge of biofilm eradication. By leveraging the unique characteristics and synergistic interplay of these materials, researchers are striving to advance strategies that offer enhanced efficacy in combating biofilms. This is particularly crucial, as biofilms represent a persistent obstacle that is notoriously resistant to eradication using conventional monotherapy antibacterial agents.

Additionally, the integration of MOFs with other nanomaterials can manifest supplementary functional attributes. Through the amalgamation of MOFs and diverse materials, the resultant composite systems can exhibit synergistic effects, thereby augmenting antibacterial activity and efficacy ^[49][211]. In addition, by incorporating antibacterial agents into MOFs or utilizing MOFs as carriers for other materials, the controlled release of antimicrobial agents can be achieved, thereby ensuring prolonged and effective antibacterial activity ^[50][212]. Moreover, the porous structures of MOFs can function as protective matrices for immobilizing anti-bacterial agents, thereby preventing their degradation or premature release. This safeguarding mechanism contributes to the preservation of stability and efficacy of antibacterial agents, ultimately enhancing their durability and performance in antibacterial applications ^[51][213]. The combination of MOFs with other materials in antibacterial applications can provide synergistic antimicrobial properties, controlled release of antibacterial agents, and preservation of their efficacy.