DNA-induced assembly of biocatalytic nanocompartments for sensitive and selective aptasensing of aflatoxin B1.

Enzyme cascade with high specificity and catalytic efficiency has significant applications for developing efficient bioanalysis methods. In this work, a sensitive and selective aptasensor was constructed based on the DNA-induced assembly of biocatalytic nanocompartments. Different from the conventional co-immobilization in one pot, the cascade enzymes of glucose oxidase (GOX) and horseradish peroxidase (HRP) were separately encapsulated in ZIF-90 nanoparticles. After conjugating complementary DNA or aptermer on enzyme@ZIF-90, DNA hybridization drove enzyme@ZIF-90 connected into clusters or linked on other DNA modified biocatalytic nanocompartment (such as invertase loaded Fe3O4@SiO2). Owing to the shortened distance between enzymes, the catalytic efficiency of connected clusters was significantly enhanced. However, the specifically interaction between the substrate molecule and aptermer sequence would lead to the disassembly of DNA duplexes, resulting in the gradual "switching-off" of cascade reactions. With aflatoxin B1 (AFB1) as the model substrate, the compartmentalized three-enzyme nanoreactors showed good analytical performance in the linear range from 0.01 ng mL-1 to 50 ng mL-1 with a low detection limit (3.3 pg mL-1). In addition, the proposed aptasensor was applied to detect AFB1 in corn oil and wheat powder samples with total recoveries ranging from 94 % to 109 %. As a result, this DNA-induced strategy for enzyme cascade nanoreactors opens new avenues for stimuli-responsive applications in biosensing.

Antibacterial Activity and Components of the Methanol-Phase Extract from Rhizomes of Pharmacophagous Plant Alpinia officinarum Hance.

The rhizomes of Alpinia officinarum Hance (known as the smaller galangal) have been used as a traditional medicine for over 1000 years. Nevertheless, little research is available on the bacteriostatic activity of the herb rhizomes. In this study, we employed, for the first time, a chloroform and methanol extraction method to investigate the antibacterial activity and components of the rhizomes of A. officinarum Hance. The results showed that the growth of five species of pathogenic bacteria was significantly inhibited by the galangal methanol-phase extract (GMPE) (p < 0.05). The GMPE treatment changed the bacterial cell surface hydrophobicity, membrane fluidity and/or permeability. Comparative transcriptomic analyses revealed approximately eleven and ten significantly altered metabolic pathways in representative Gram-positive Staphylococcus aureus and Gram-negative Enterobacter sakazakii pathogens, respectively (p < 0.05), demonstrating different antibacterial action modes. The GMPE was separated further using a preparative high-performance liquid chromatography (Prep-HPLC) technique, and approximately 46 and 45 different compounds in two major component fractions (Fractions 1 and 4, respectively) were identified using ultra-HPLC combined with mass spectrometry (UHPLC-MS) techniques. o-Methoxy cinnamaldehyde (40.12%) and p-octopamine (62.64%) were the most abundant compounds in Fractions 1 and 4, respectively. The results of this study provide data for developing natural products from galangal rhizomes against common pathogenic bacteria.