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The inhibitory mechanism of spermine on the laccase-mimicking activity of flower-shaped Mn 3 O 4 nanoparticles was revealed and applied for the colorimetric determination of spermine in food. [Display omitted] • The flower-like Mn 3 O 4 nanoparticles exhibit the laccase-mimicking activity. • The laccase-mimicking activity was first used to detect biogenic amine. • A rapid and highly selective sensor for on-site detection of spermine was developed. • Smartphone-integrated and visual detection of spermine was achieved. • The detection strategy displayed good selectivity and applicability in food samples. Colorimetric methods have the benefits of rapid detection and easy operation in the detection of spermine (SPM). However, the existing colorimetric sensor for detecting SPM still face challenges in terms of performance stability, result reliability and safety of sensing materials. Herein, it was first found that flower-like Mn 3 O 4 nanoparticles (Mnf) exhibit excellent laccase-mimicking activity. Since SPM can effectively inhibit this activity, a colorimetric sensor was developed to detect SPM in food. The addition of positive charged SPM will induce the aggregation of multiple Mnf with negative charge through electrostatic interactions. In this case, the specific surface area of Mnf is reduced, and some surface-active sites are occupied by SPM, leading to a decrease in the laccase-mimicking activity of Mnf. Consequently, the colorimetric sensor appears light pink. Furthermore, a smartphone was utilized to convert the color of the reaction solution into the corresponding G/B value, facilitating on-site and fast analysis of SPM quantity. The proposed colorimetric sensor exhibits outstanding sensitivity and selectivity, with a limit of detection (LOD) as low as 0.094 μg·mL−1. The colorimetric sensor also features stable performance, reliable results and environmentally friendly safety, all of which will provide strong support for the monitoring of SPM in the food industry. [ABSTRACT FROM AUTHOR]

Due to the excellent oxidation effect on phenolic compounds, the present copper-based laccase-mimics are mostly used for the degradation and detection of phenolic pollutants in environment. As the oxidation substrates of laccase are only limited to compounds containing specific phenolic hydroxyl groups, which makes the application of laccase mimetics to non-phenolic pollutants faces great challenges and bottlenecks. Herein, a non-copper-based laccase mimics like cubic Ag 2 O nanoparticles is prepared. The maximum reaction velocity and affinity of cubic Ag 2 O nanoparticles to substrates are significantly better than that of natural laccase and most artificial laccase mimetics. Cubic Ag 2 O nanoparticles also exhibits high stability under various conditions and has good tolerance to organic solvents. Moreover, it is found that the laccase-mimic activity of cubic Ag 2 O nanoparticles can be effectively inhibited by kanamycin, which enable us to construct a colorimetric sensor for rapid detection of kanamycin in environment. The sensor has excellent sensitivity with the limit of detection (LOD) of 1.3 nM for kanamycin, and has high selectivity for other competitive substances. Besides, a standard curve for rapidly detecting kanamycin by smartphones is established, which expect to provide a novel idea for on-site monitoring of other hazards in environment. [Display omitted] • Cubic Ag2O NPs exhibits high laccase catalytic stability under extreme conditions. • Laccase-mimic activity is used in a sensor for non-phenolic hazards analysis. • The inhibitory mechanism of kanamycin on laccase-mimic activity was revealed. • Smartphone-assisted sensor enables the result to be recognized by naked eye. • The colorimetric sensor has excellent sensitivity with a LOD as low as 1.3 nM. [ABSTRACT FROM AUTHOR]

Phytic acid (PA) can be adsorbed on the surface of Zr(IV)-Glu complex and inhibit its phosphatase-like activity, which enables to develop a novel and facile fluorescent sensor for PA detection in food. [Display omitted] • A novel, robust and green phosphatase mimetics was prepared. • Zr(IV)-Glu complex exhibited excellent phosphatase-like activity. • Phosphatase-like activity was used in a fluorescent sensor for phytic acid analysis. • The inhibitory mechanism of phytic acid on phosphatase-like activity was revealed. • The fluorescent sensor has excellent sensitivity with a LOD as low as 58 μg·L-1. Artificial enzymes have attracted much attention in food analysis because of their simple preparation, low cost, and strong stability. However, the most used artificial enzymes are based on oxidoreductases such as oxidase, peroxidase, catalase, and laccase. There are few reports on hydrolases like phosphatase for food analysis. Herein, a novel green zirconium-glutamic acid (Zr(IV)-Glu) complex was prepared using Zr ions and glutamic acid. The Zr(IV)-Glu complex was first found to possess excellent phosphatase-like activity, which was used to establish a fluorescent sensor for detecting phytic acid (PA). The Zr(IV)-Glu complex can catalyze the hydrolysis of 4-methylumbellione phosphate disodium salt (4-MUP) to produce blue fluorescent products with fluorescence emission peaks at 448 nm. PA with six phosphate groups can attach on the surface of Zr(IV)-Glu to form Zr-O-P bond and inhibit the catalytic activity of Zr(IV)-Glu, leading to the decrease of fluorescence in the system. The change of fluorescent intensity at 448 nm was positively correlated with the PA content, so that a fluorescent sensor using the phosphatase-like activity of Zr(IV)-Glu was proposed to detect PA. The established sensor has high sensitivity, low detection limit (LOD) of PA to 58 μg·L-1, strong anti-interference ability, and excellent selectivity. This work can provide a new method for PA detection in food and further expand the application of phosphatase mimics. [ABSTRACT FROM AUTHOR]