Nanozymes-based biosensors for food quality and safety

Highlights

• Nanozymes are used for biosensing of analytes relevant to food quality and safety.

• Metallic, non-metallic, and organomettalic nanozymes are discussed.

• Mechanisms of peroxidase and oxidase enzymes mimicking of nanozymes described.

• Color-change signaling is the most popular nanozyme detection mechanism.

• Nanozymes structure should be improved to enhance their catalytic ability and specificity.

Abstract

Nanozymes are nanomaterials, both metallic and non-metallic, that have the ability to catalyze biochemical reactions just as natural enzymes do. Since their discovery in 2007, nanozymes are exploited as nanoscale enzymatic mimics, which are now at the forefront for various biosensing applications. Compared with natural enzymes, nanozymes offer several advantages such as relatively higher stability, lower cost, easier modification, and inherently more efficient. Past research on the structure and catalytic principles of nanozymes has brought into focus various developments of nanozyme-based biosensors. Herein we introduce several typical nanozymes, primarily those belonging to the peroxidase and oxidase families. The enzyme mimicking mechanisms of these nanozymes are presented, which primarily result in colorimetric signals suitable for simple and easy biosensing. Emphasis is placed on nanozyme-based biosensors for detecting chemical contaminants, such as ions and pesticide residues, and biological contaminants, such as pathogens and biotoxins, that can compromise food quality and safety. In the future, more optimizations and improvements could be in the structure of nanozymes to enhance their catalysis ability and specificity. Overall, nanozymes possess great potential for biosensing in food and non-food applications.

Introduction

Natural enzymes are powerful biocatalysts for substrate conversion due to their specific recognition abilities and relatively high catalytic activities under mild environmental conditions in most cases. These enzymes find ubiquitous uses in myriad of laboratories and industries for performing biochemical reactions [1]. However, the use of natural enzymes is beset with such drawbacks as insufferable price, unstable structure, high sensitivity to external conditions, low reusability etc. [2,3]. Therefore, numerous researches have been focused on finding appropriate substitutes for enzymes with similar active site and catalytic properties. Some enzyme mimics include catalytic cyclodextrins, polymers, supramolecules, porphyrins, and dendrimers [[4], [5], [6], [7]].

In 2007, Yan et al. reported peroxidase enzyme-like activity of ferromagnetic nanoparticles (Fe₃O₄ NPs) and pointed out that with catalytic activity similar to that of protein/RNA which specifically acts as peroxidase enzyme in nature, inorganic NPs could directly trigger and accelerate oxidation of peroxidase substrates in the presence of hydrogen peroxide (H₂O₂) [8]. Since then, several other NPs have been identified to have biocatalytic activity either alone or as hybrids in conjunction with other biomolecular ligands [9]. Wei and Wang coined the term ‘nanozyme’ to describe NPs that possess the ability to mimic enzymatic action [10]. In addition to good recognition and biocatalytic activity, nanozymes offer prolonged life and high stability all at a cost lower than that of natural enzymes [11]. Consequently, nanozymes are increasingly employed in a number of applications such as biosensing, cancer therapy, environmental protection, and antibacterial treatment [[12], [13], [14], [15]].

Nanozyme-based biosensors (NBs) are popular in different areas, food quality safety evaluation, clinical disease diagnosis, biological metabolite measurement, and environmental pollutant monitoring (Fig. 1). To date, there has been only limited review of information on NBs, especially focusing on food quality and safety [16,17]. To fill this gap, herein we present a more comprehensive review of NBs in food analysis, along with discussion on major catalytic mechanisms of nanozymes for biosensing.