The Design and Synthesis of Nanozymes with Controllable Specificity

Abstract

Nanozymes, a class of catalytic nanomaterials engineered to mimic enzymatic activity, have emerged as a transformative alternative to natural enzymes owing to their cost-effectiveness, tunable catalytic properties, and enhanced stability. Recent advancements in nanotechnology have propelled the rapid expansion of this field, attracting considerable interdisciplinary interest. CeO₂, particularly in the shape of rod, has recently gained considerable attention for its ability to mimic peroxidase (POD) and haloperoxidase (HPO). However, this multi-enzyme activities unavoidably compete for H₂O₂ affecting its performance in relevant applications. The lack of consensus on facet distribution in rod-shaped CeO₂ further complicates the establishment of structure-activity correlations, presenting challenges for progress in the field. In the first study, the HPO-like activity of rod-shaped CeO₂ is successfully enhanced while maintaining its POD-like activity through a facile post-calcination method. By studying the spatial distribution of these two activities and their exclusive H₂O₂ activation pathways on CeO₂ surfaces, this study finds that the increased HPO-like activity originated from the newly exposed (111) surface at the tip of the shortened rods after calcination, while the unchanged POD-like activity is attributed to the retained (110) surface in their lateral area. These findings not only address facet distribution discrepancies commonly reported in the literature for rod-shaped CeO₂ but also offer a simple approach to enhance its antibacterial performance. This work aims at providing atomic insights into catalytic correlations and guide the design of nanozymes with improved activity and reaction specificity.

According to the understanding in H₂O₂ activation over rod-shaped CeO₂, we further address the challenges in simultaneously achieving controlled specificity and scaling up production over CeO₂-based nanozymes. In the second work, a simple method was developed for the mass production of CeO2-based nanozymes with controlled specificity. By regulating the preparation atmospheres, the electron density of Ce sites and hence H₂O₂ activation pathway can be precisely tuned, enabling nearly 100% mimicry of POD or bromoperoxidase (BPO) activities. This approach eliminates the need for labor-intensive purification, making it more cost-effective than natural enzymes and suitable for large-scale implementation. The optimized samples further demonstrate the importance of specificity control in boosting performances for glucose detection and antibacterial applications. This work is anticipated to inform the future design of scalable, cost-effective nanozymes with enhanced specificity.

Besides H₂O₂, O₂ is another common substrate in reactions related to bioassays. Therefore, controlling O₂ activation—and thus O₂ reaction specificity—is crucial. In the light of tuning the chemical state of cerium to enable control over H₂O₂ activation pathways for tunable POD/BPO-like activities in the second work, the control of O₂ activation on an element in oxidase/laccase nanozymes and the impact of its chemical state on these activities over Fe-based nanozymes was explored in the third work. In this work, a facile one-pot method was presented for the gram-scale synthesis of Fe-based nanozymes with tunable compositions of Fe₃O₄ and Fe₃C by adjusting preparation temperatures. The Fe₃O₄-containing samples exhibit superior laccase-like activity, while the Fe₃C-containing counterparts demonstrate better oxidase-like activity. This divergent O₂ activation behavior is linked to their surface Fe species: the abundant reactive Fe²⁺ in Fe₃O₄ promotes laccase-like activity via Fe³⁺-superoxo formation, whereas metallic Fe in Fe₃C facilitates OH radical generation for oxidase-like activity. Controlled O₂ activation pathways in these Fe-based nanozymes demonstrate improved sensitivity in the corresponding biomolecule detection, which should inform the design of nanozymes with enhanced activity and specificity.

Date of Award	7 Aug 2025
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Yung-kang PENG (Supervisor)