Two-dimensional materials such as graphene and oxide nanosheets have emerged as promising nanozymes capable of mimicking peroxidase and oxidase-like activity. These materials offer distinct advantages over natural enzymes, including high stability, tunable catalytic properties, and ease of fabrication. Their unique surface chemistry and electronic structure allow for precise modulation of enzymatic activity, enabling applications in biomedical sensing, environmental monitoring, and therapeutic interventions.

The catalytic activity of 2D materials as nanozymes stems from their abundant active sites, high surface-to-volume ratio, and defect-rich surfaces. Graphene oxide (GO), for instance, exhibits peroxidase-like activity due to its oxygen-containing functional groups, such as carboxyl, epoxy, and hydroxyl groups, which facilitate electron transfer reactions. Similarly, transition metal oxide nanosheets, including MnO2 and CeO2, demonstrate oxidase-like behavior by leveraging metal redox centers to catalyze substrate oxidation. The catalytic efficiency of these materials can be further enhanced through doping, defect engineering, and surface functionalization.

Surface chemistry plays a critical role in determining the enzymatic behavior of 2D nanozymes. For example, the peroxidase-like activity of graphene-based materials is highly dependent on the degree of oxidation. Partially reduced GO shows higher catalytic activity than fully oxidized GO due to an optimal balance between conductive sp2 domains and reactive oxygen moieties. Similarly, the oxidase-like activity of MnO2 nanosheets can be tuned by controlling the oxidation state of manganese (Mn3+/Mn4+ ratio), which directly influences the material’s ability to activate molecular oxygen. Chemical modifications, such as nitrogen doping in graphene or vacancy engineering in metal oxides, further enhance substrate binding and catalytic turnover rates.

Substrate specificity is another key aspect where 2D nanozymes differ from natural enzymes. While natural enzymes exhibit high selectivity toward specific substrates due to their well-defined active sites, nanozymes often display broader reactivity. However, recent advances in surface functionalization have enabled improved selectivity. For instance, aptamer-conjugated graphene oxide can selectively catalyze the oxidation of target molecules, mimicking the lock-and-key mechanism of natural enzymes. Similarly, molecularly imprinted polymers on oxide nanosheets enhance specificity by creating tailored binding pockets for substrates such as glucose or dopamine.

In biomedical sensing, 2D nanozymes have been widely employed for detecting biomarkers, pathogens, and small molecules. Graphene-based peroxidase mimics are commonly used in colorimetric assays, where they catalyze the oxidation of chromogenic substrates like 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide. This reaction produces a visible color change, enabling rapid and sensitive detection of targets such as nucleic acids, proteins, and metal ions. Oxide nanosheets, on the other hand, are utilized in electrochemical sensors due to their excellent electron transfer properties. For example, CeO2 nanosheets have been integrated into biosensors for detecting reactive oxygen species (ROS) in cellular environments, offering real-time monitoring of oxidative stress.

Compared to natural enzymes, 2D nanozymes exhibit superior stability under harsh conditions, including extreme pH, high temperatures, and long-term storage. Natural enzymes like horseradish peroxidase (HRP) are prone to denaturation and degradation, limiting their practical utility. In contrast, graphene and oxide nanosheets retain their catalytic activity across a wide range of environmental conditions, making them suitable for industrial and point-of-care applications. Additionally, nanozymes can be mass-produced at a lower cost than purified enzymes, further enhancing their commercial viability.

Despite these advantages, toxicity concerns remain a critical consideration for biomedical applications. Graphene-based materials, particularly those with sharp edges or high oxidation levels, have been reported to induce cellular membrane damage and oxidative stress. Similarly, certain metal oxide nanosheets may release toxic ions under physiological conditions. To mitigate these risks, researchers have developed surface passivation strategies, such as PEGylation or biocompatible polymer coatings, which reduce cytotoxicity while preserving catalytic activity. Rigorous in vitro and in vivo studies are necessary to ensure the safe deployment of these materials in clinical settings.

Future research directions include the development of multifunctional nanozymes that combine peroxidase and oxidase activities within a single platform. Hybrid structures, such as graphene-metal oxide composites, offer synergistic effects by integrating the unique properties of both components. Additionally, machine learning approaches are being explored to predict optimal surface modifications for desired catalytic outcomes, accelerating the design of next-generation nanozymes.

In summary, 2D materials represent a versatile class of nanozymes with tunable catalytic properties, robust stability, and broad applicability in biomedical sensing. While challenges related to substrate specificity and toxicity persist, ongoing advancements in surface engineering and biocompatibility are paving the way for their widespread adoption in diagnostics and therapeutics.