Fabrication of Polydopamine-Based Curcumin Nanoparticles for Chemical Stability and pH-Responsive Delivery.

Polydopamine (PDA) possesses high aqueous dispersibility, strong optical absorption, and a zwitterionic property, which give it multitudes of advantages to coat light-sensitive hydrophobic curcumin (Cur) for pH-responsive release. However, PDA is formed in alkaline conditions, which hinders its potential application for alkali-sensitive curcumin coating. Here, we developed a method to prepare PDA-coated Cur nanoparticles (NPs), which reduced chemical degradation of Cur in alkaline conditions. Encapsulation efficiency and loading capacity decreased to 73.69% and 51.80%, as the time for dopamine polymerization went on. PDA could protect Cur from light-induced degradation in powder and solution forms. Controlled release and pH-responsive delivery of PDA-coated Cur were observed under stomach and intestinal conditions compared to free Cur, which resulted from the coverage and thickness of the PDA shell and the electrostatic attraction between PDA and Cur. PDA-coated Cur NPs could be a promising way for the application of Cur in the beverage and food industry.

Preparation of novel silver nanoplates/graphene composite and their application in vanillin electrochemical detection.

Hexagonal Ag nanoplates (NPs) were synthesized by polyvinylpyrrolidone (PVP) and trisodium citrate (TSC) which selectively absorbed to Ag (100) and Ag (111) surfaces, then were anchored to graphene (GN) to form novel Ag NPs/GN composite. The thickness of Ag NPs is ~4 nm and the length is 18-66 nm. Transmission electron microscopy (TEM) image shows that the plates are f-c-c crystals containing {111} facets on their two planar surfaces. Zeta potential indicated that the surface of Ag NPs/GN is negatively charged while vanillin is positively charged. Thus Ag NPs/GN modified on glass carbon electrodes (GCE) allowed abundant adsorption for vanillin and electron transfer between vanillin and Ag NPs/GN/GCE. Square wave voltammetry (SWV) results indicated that the over potential on Ag NPs/GN/GCE negatively shifts 52 mV than that on Ag NPs/GCE. Ag NPs/GN with enhanced surface area and good conductivity exhibited an excellent electrocatalytic activity toward the oxidation of vanillin. The corresponding linear range was estimated to be from 2 to 100 µM (R(2)=0.998), and the detection limit is 3.32×10(-7) M (S/N=3). The as-prepared vanillin sensor exhibits good selectivity and potential application in practical vanillin determination.