Co3O4/CuO hollow nanocage hybrids with high oxidase-like activity for biosensing of dopamine.

Here, we report the synthesis, characterization, and oxidase-like activity of Co3O4/CuO hollow nanocage (HNC) nanocomposites. The Co3O4/CuO HNCs were successfully prepared by hydrothermal treatment of ZIF-67 in copper nitrate solution, followed by carbonization in air. The obtained nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The Co3O4/CuO HNCs possess enhanced oxidase-like activity compared with pure Co3O4 and CuO, and they can catalytically oxidize the 3,3',5,5'-tetramethylbenzidine (TMB) substrate in the absence of H2O2 to produce an intense blue product. Reactive oxygen species (ROS) measurements indicate that 1O2 and O2- radicals are the major ROS in catalytic oxidation of TMB by dissolved oxygen in the TMB-Co3O4/CuO HNC system. We then developed a simple, sensitive, visual, and colorimetric biosensing method for dopamine (DA) based on its inhibiting effect on TMB oxidation. The proposed method allows for DA detection with a limit of detection of 0.027 µM and a dynamic range of 0.05-8 µM. This new colorimetric method was successfully used to detect DA in biological samples. The present work demonstrates a simple strategy to fabricate an efficient oxidase mimic with potential applications in bioanalysis and clinical diagnosis.

Preparation of the chitosan grafted poly (quaternary ammonium)/Fe3O4 nanoparticles and its adsorption performance for food yellow 3.

Chitosan and its derivatives can be used to modify magnetic materials to promote the adsorption properties of the magnetic materials and avoid the weakness of chitosan and its derivatives. In the present study, chitosan grafted poly(trimethyl allyl ammonium chloride) (CTS-g-PTMAAC) was prepared by graft copolymerization; then it was coated on the surfaces of the sodium citrate coated Fe3O4 nanoparticles (SC-Fe3O4) to prepare a novel composite CTS-g-PTMAAC/SC-Fe3O4 magnetic nanoparticles, with which possesses abundant surface positive charges. The structure and properties of the CTS-g-PTMAAC/SC-Fe3O4 composite magnetic nanoparticles were characterized by FTIR, TEM, VSM, and zeta potential. The dye adsorption characteristics of the CTS-g-PTMAAC/SC-Fe3O4 nanoparticles were determined using the food yellow 3 aqueous solutions as a model food effluent. Effect of pH of the dye solution on the adsorption of food yellow 3 was determined and compared with N-2-hydroxylpropyl trimethyl ammonium chloride chitosan coated sodium citrate-Fe3O4 (CTS-g-HTCC/SC-Fe3O4) composite magnetic nanoparticles. The adsorption kinetics, adsorption isotherms, adsorption thermodynamics, and desorption and reusability of the magnetic nanoparticles were investigated.