Flavoenzymes are ubiquitous in biological systems and catalyze a diverse range of chemical transformations.

Target-induced differences in the electrostatic interactions between methylene blue (MB) and indium tin oxide (ITO) electrode surface was firstly employed to develop a homogeneous electrochemical biosensor for flap endonuclease 1 (FEN1) detection. In the absence of FEN1, the positively charged methylene blue (MB) is free in the solution and can diffuse onto the negatively charged ITO electrode surface easily, resulting in an obvious electrochemical signal. Conversely, with the presence of FEN1, a 5′-flap is cleaved from the well-designed flapped dumbbell DNA probe (FDP). The remained DNA fragment forms a closed dumbbell DNA probe to trigger hyperbranched rolling circle amplification (HRCA) reaction, generating plentiful dsDNA sequences. A large amount of MB could be inserted into the produced dsDNA sequences to form MB-dsDNA complexes, which contain a large number of negative charges. Due to the strong electrostatic repulsion between MB-dsDNA complexes and the ITO electrode surface, a significant signal drop occurs. The signal change (ΔCurrent) shows a linear relationship with the logarithm of FEN1 concentration from 0.04 to 80.0 U/L with a low detection limit of 0.003 U/L (S/N = 3). This study provides a label-free and homogeneous electrochemical platform for evaluating FEN1 activity.

A chemical investigation of Streptomyces sp. SCSIO 40069 resulted in the isolation of a series of aromatic polyketides with rare skeletons, including five new compounds RM18c–RM18g (1–5) and three known ones (6–8). Their structures and absolute configurations were determined by diverse methods, including HRMS and NMR spectra, chemical reaction, Snatzke’s method, quantum mechanical–nuclear magnetic resonance (QM-NMR), and X-ray crystallographic analysis. Compounds 1, 2, 4b, and 8 displayed moderate or weak antibacterial activities.