HAuCl4-mediated green synthesis of highly stable Au NPs from natural active polysaccharides: Synthetic mechanism and antioxidant property.

Polysaccharide-functionalized gold nanoparticles (Polysaccharide-Au NPs) with high stability were successfully prepared by a straightforward method. Notably, the Au (III) ion acts as a strong Lewis acid to facilitate glycosidic bond breaking. Subsequently, the polysaccharide conformation was transformed to an open-chain form, exposing highly reduced aldehyde or ketone groups that reduce Au (III) to Au (0) crystal species, further growing into Au NPs. As-prepared Au NPs displayed excellent stability over a longer storage period (more than 70 days), a wide range of temperatures (25-60 °C), and pH range (3-11), varying concentrations (0-200 mM) and types of salt ions (Na+, K+, Ca2+, Mg2+), and glutathione solutions (5 mM). More interestingly, polysaccharide-Au NPs retained the antioxidant activity of polysaccharides and reduced oxidative damage at the cellular level through decreased reactive oxygen species (ROS) production. The intracellular levels of ROS pretreated with polysaccharide and polysaccharide-Au NPs were decreased 53.12-75.85 % compared to the H2O2 group, respectively. Therefore, the green synthesized Au NPs from natural active polysaccharides exhibit potential applications in biomedical fields.

Simple fluorescence "turn-off" assay for Congo red using commercial 2-aminophthalic acid.

In this work, the fluorescence properties of 2-aminophthalic acid (NH2-BDC) were studied. NH2-BDC possessed excellent optical properties including bright blue emission with maximum emission at 425 nm, a high quantum yield of 38.49% and excellent photostability. And the fluorescence of NH2-BDC could be selectively quenched by Congo red, which was ascribed to the inner filter effect. Accordingly, NH2-BDC was further employed for fluorescence "turn-off" assay of Congo red with a linear range of 0.05-50 µM and a limit of detection of 1.72 µM. And the sensor was used for the detection of Congo red in real water samples with acceptable results.