Yihui Hu

Nanozymes in bionanotechnology: from sensing to therapeutics and beyond

In the past few decades, researchers have developed lots of artificial enzymes with various materials to mimic the structures and functions of natural enzymes. Recently, nanozymes, nanomaterials with enzyme-like characteristics, are emerging as novel artificial enzymes, and attracting researchers’ enormous interest. Remarkable advances have been made in the area of nanozymes due to their unique properties compared with natural enzymes and classic artificial enzymes. Until now, lots of nanomaterials have been studied to mimic various natural enzymes for wide applications. To highlight the recent progress of nanozymes (especially in bionanotechnology), here we discuss the diverse applications of nanozymes, which range from sensing, imaging, and therapeutics, to logic gates, pollutant removal, water treatment, etc. Finally, we address the current challenges facing nanozyme research as well as possible directions to fulfill their great potential in future.

Monitoring of Heparin Activity in Live Rats Using Metal–Organic Framework Nanosheets as Peroxidase Mimics

Metal-organic framework (MOF) nanosheets are a class of two-dimensional (2D) porous and crystalline materials that hold promise for catalysis and biodetection. Although 2D MOF nanosheets have been utilized for in vitro assays, ways of engineering them into diagnostic tools for live animals are much less explored. In this work, a series of MOF nanosheets are successfully engineered into a highly sensitive and selective diagnostic platform for in vivo monitoring of heparin (Hep) activity. The iron-porphyrin derivative is selected as a ligand to synthesize a series of archetypical MOF nanosheets with intrinsic heme-like catalytic sites, mimicking peroxidase. Hep-specific AG73 peptides as recognition motifs are physically adsorbed onto MOF nanosheets, blocking active sites from nonspecific substrate-catalyst interaction. Because of the highly specific interaction between Hep and AG73, the activity of AG73-MOF nanosheets is restored upon the binding of Hep, but not Hep analogues and other endogenous biomolecules. Furthermore, by taking advantages of biocompatibility and diagnostic property enabled by AG73-MOF nanosheets, the elimination process of Hep in live rats is quantitatively monitored by coupling with microdialysis technology. This work expands the biomedical applications of 2D MOF nanomaterials and provides access to a promising in vivo diagnostic platform.

Nanozymes: Next Wave of Artificial Enzymes

This book describes the fundamental concepts, the latest developments and the outlook of the field of nanozymes (i.e., the catalytic nanomaterials with enzymatic characteristics). As one of today s most exciting fields, nanozyme research lies at the interface of chemistry, biology, materials science and nanotechnology. Each of the book s six chapters explores advances in nanozymes. Following an introduction to the rise of nanozymes research in the course of research on natural enzymes and artificial enzymes in Chapter 1, Chapters 2 through 5 discuss different nanomaterials used to mimic various natural enzymes, from carbon-based and metal-based nanomaterials to metal oxide-based nanomaterials and other nanomaterials. In each of these chapters, the nanomaterials enzyme mimetic activities, catalytic mechanisms and key applications are covered. In closing, Chapter 6 addresses the current challenges and outlines further directions for nanozymes. Presenting extensive information on nanozymes and supplemented with a wealth of color illustrations and tables, the book offers an ideal guide for readers from disparate areas, including analytical chemistry, materials science, nanoscience and nanotechnology, biomedical and clinical engineering, environmental science and engineering, green chemistry, and novel catalysis

Modulating luminescence of Tb(3+) with biomolecules for sensing heparin and its contaminant OSCS.

The detection of heparin (Hep) and its contaminant oversulfated chondroitin sulfate (OSCS) is of great importance in clinics but remains challenging. Here, we report a sensitive and selective time-resolved luminescence (TRL) biosensing system for Hep by modulating the photoluminescence of Tb(3+) with guanine-rich ssDNA and Hep-specific AG73 peptide (RKRLQVQLSIRT). With the developed system, Hep including both unfractionated Hep (UFH) and the low molecular weight Hep (LMWH) has been successfully detected with a satisfactory detection limit. Owing to the highly specific interaction between Hep and AG73 peptide, major interfering substances in Hep detection, such as Hep analogs of chondrotin sulfate (Chs) and hyaluronic acid (HA), did not interfere with Hep detection. The established TRL sensing system was then successfully used for monitoring Hep metabolism in living rats by microdialysis. Moreover, the proposed TRL sensing system was further applied to analyze OSCS contaminant in Hep with heparinases treatment by exploring the inhibition effects of OSCS on the activity of heparinases. As low as 0.002% of OSCS in Hep was identified.

Metal-Based Nanomaterials for Nanozymes

The use of metal nanomaterials for mimicking natural enzymes is discussed in this chapter. These nanozymes are roughly classified into two types: for type I, the nanozymes’ activities are entirely from the assembled monolayer onto a metallic core rather than the core itself; for type II, the nanozymes’ activities are originated from the metal nanomaterials themselves. For both of them, their enzyme mimetic activities (such as RNase mimics, DNase mimics, superoxide dismutase mimics, peroxidase mimics, catalase mimics, etc.) are discussed. The catalytic mechanisms for the multiple enzyme mimicking activities of metal nanomaterials are elucidated by combing computational studies with experimental results. Representative examples for applications, from biosensing and immunoassays to bioimaging and therapeutics, are covered.

Metal Oxide-Based Nanomaterials for Nanozymes

Metal oxide-based nanomaterials have been extensively studied to mimic various natural enzymes due to their unique properties. In this chapter, several metal oxide-based nanozymes are discussed. First, the use of cerium oxide nanomaterials for mimicking natural enzymes (such as superoxide dismutase, catalase, oxidase, peroxidase, phosphatase, etc.) is discussed. Second, the use of iron oxide nanomaterials for peroxidase mimics and other mimics is covered. Third, the enzyme mimicking activities of other metal oxides (such as vanadium oxide, cobalt oxide, copper oxide, etc.) are discussed. The catalytic mechanisms are also discussed if they have been elucidated. Selected examples for broad applications are discussed, which cover from glucose detection, DNA detection, immunoassay, and immunostaining, to neuroprotection, cardioprotection, cancer therapy, and tissue engineering.

Carbon-Based Nanomaterials for Nanozymes

Carbon-based nanomaterials, such as fullerene, graphene, carbon nanotubes, and their derivatives, have been extensively studied to mimic various natural enzymes owing to their fascinating catalytic activities. In this chapter, their enzyme mimetic activities (such as nuclease mimics, superoxide dismutase mimics, peroxidase mimics, etc.) are discussed. The catalytic mechanisms are also discussed if they have been elucidated. Representative examples for applications, from biosensing to therapeutics, are covered.

Other Nanomaterials for Nanozymes

The use of other nanomaterials beyond carbon-based nanomaterials, metal-based nanomaterials, and metal oxide-based nanomaterials for mimicking natural enzymes is discussed in this chapter. Prussian blue, metal-organic frameworks, metal chalcogenides, metal hydroxides, etc., have been selected as representative nanomaterials for mimicking peroxidase, superoxide dismutase, catalase, etc. The catalytic mechanisms are also discussed if they have been elucidated. Selected examples for in vitro biosensing, in vivo bioanalysis, and therapeutics are discussed to highlight the broad applications of these nanozymes.

Introduction to Nanozymes

Natural enzymes play vital roles in biological reactions in living systems. However, some intrinsic drawbacks, such as ease of denaturation, laborious preparation, high cost, and difficulty of recycling, have limited their practical applications. To tackle these problems, intensive efforts have been devoted to developing natural enzymes’ alternatives called “artificial enzymes.” As an emerging research area of artificial enzymes, nanozymes, the catalytic nanomaterials with enzyme-like characteristics, have attracted researchers’ enormous attentions. In this chapter, after the brief description of the history of nanozymes research in the course of natural enzymes and artificial enzymes research, a comparison between nanozymes and natural enzymes as well as artificial enzymes is made. Such a comparison highlights the unique characteristics of nanozymes, such as their size-(shape-, structure-, composition-)tunable catalytic activities, large surface area for modification and bioconjugation, multiple functions besides catalysis, smart response to external stimuli, etc.