LAUSR

Developing stable and cost-effective sensors and biosensors is one of the main goals of analytical chemists. Many biosensors rely on enzymes either for recognition of target analytes such as using glucose oxidase for detecting glucose, or for signal generation such as using horse radish peroxidase (HRP) in immunoassays. While these protein-based enzymes are highly efficient, they are susceptible to denaturation and some enzymes are quite costly. Using nanomaterials to mimic enzyme activities has attracted growing interest over the last 10 years or so. Many common metal oxides, metals, and carbon-based nanomaterials have oxidase, peroxidase and catalase like activities, and nanozyme was coined for describing them. The main difference between nanozymes and typical inorganic catalysts is the former focuses on biologically relevant reactions taking place at close to physiological conditions. Nanozymes, in general, have higher stability and lower cost compared to protein-based enzymes. For the analytical community, nanozymes have been used for both target recognition and for signal transduction. We are seeing more and more examples of nanozymes used in environmental monitoring, biomedical diagnosis and food safety applications. Journal of Analysis and Testing provides an international academic platform for the publication of original research papers, rapid communications, and critical reviews in all aspects of fundamental and applied analytical chemistry. To highlight the current developments and stimulate new thoughts of the nanozyme field, this Special Issue is focused on biologically and environmentally related nanozymebased analysis and testing. This Special Issue features two review papers and eight research articles. Professor Chang from National Taiwan University reviewed carbon dot (Cdot) based peroxidase mimics for analytical applications. Carbon dots are often produced by simple hydrothermal methods from cost-effective starting materials with interesting fluorescence and sometimes also phosphorescence properties. The importance of the oxidation state and surface residues of Cdots are highlighted, and their nanocomposites with metals, metal oxides, and metal sulfides are described. Examples of selective absorption, fluorescence, and electrochemical sensing systems are presented to show their potential analytical applications. Huang and coworkers from National Taiwan Ocean University reviewed nanozyme-based sensors for detection of heavy metal ions. Heavy metals are important analytes in the environment due to their bioaccumulative and non-degradable properties, posing adverse health effects. This paper articulates the importance of the surface properties of nanozymes, and metal binding can either promote or inhibit the activity of nanozymes, which is the basis of sensing. For the research papers, a few of them focused on the development of new nanozymes. Lopez and Liu from the University of Waterloo compared adenine and 2-aminopurine for forming coordination nanoparticles with various metal ions and Au3+ was found to form similar nanoparticles with both ligands. 2-Aminopurine is a fluorescent analog of adenine and its fluorescence allowed convenient monitoring of the formation and dissolution of the product. The products showed oxidase-like activity for oxidation of a chromogenic substrate. Alkaline phosphatase (ALP) is an important clinical biomarker for many diseases. Taking advantage of the strong oxidase-like activity of MnFe2O4, and its inhibition by pyrophosphate (PPi), Niu and coworkers from Jiangsu University developed a colorimetric sensor for detecting ALP. ALP can hydrolyze PPi and recover the activity of MnFe2O4 for signal-on detection of ALP down to 0.27 u/L. Most nanozymes collected in this Special Issue have peroxidase-like activity, where oxidation takes place in the presence of H2O2. Professor Yigit’s team from University at Albany, State University of New York studied the peroxidase-like activity of zirconium(IV) oxide nanoparticles. The effects of pH, temperature and H2O2 concentration have been systematically studied. This nanozyme was tested in different protein solutions and showed robust activity. * Juewen Liu [email protected]