Conghua Lu

Fabrication of ultrathin films based on chitosan and bovine serum albumin and their stability studied with the radio-labeled method

Chitosan (CS)/bovine serum albumin (BSA) ultrathin films were fabricated on the modified quartz wafer through the layer-by-layer deposition technique. The effects of the experimental conditions, such as pH, molecular weight (MW), ionic strength and the coexistence of the additional polyanions on the fabrication and the stability of assembly films were investigated with a radio-labeled method. The results show that the amount of adsorbed BSA is proportional to the number of assembly cycle except the first two cycles and CS/BSA films fabricated in CS acetic acid aqueous solution (aq. AcOH) at pH 5.2 are more favorable compared with at pH 1.0. When two different MW CS were used (M η≈1.2×105, M η≈1.0×106), the lower MW CS adsorbs more BSA, but the films formed are less stable. The same trend is observed, i.e. the amount of adsorbed BSA in deionized water is higher but the films fabricated are less stable than in phosphate-buffered saline (PBS). The adsorption of BSA in the presence of poly(sodium styrene-sulfonate) (PSS) decreases severely due to existence of the strong interaction between BSA and PSS, which has been confirmed by the fluorescence spectrometry. The morphology of CS/BSA assembly films was visualized with atomic force microscopy (AFM) and shows that some aggregates of BSA occur and are eluted first in 1% sodium dodecyl sulfate (SDS) aqueous solution.

Micropatterns constructed from Au nanoparticles

Covalently linked Au-NPs micropatterns have been successfully fabricated from the self-assembly film composed of 4-mercaptophenol-capped Au nanoparticles (Au-NPs) and -N2+ containing polymers of nitro-diazoresin (NDR) by selective exposure to UV light and development in sodium dodecyl sulfate (SDS) aqueous solution. The resultant well-defined micropatterns were characterized with AFM and XPS.

Self-assembly of a covalently attached magnetic film from diazoresin and Fe3O4 nanoparticles

On different substrates, such as the quartz wafer, mica and silicon, a stable magnetic ultrathin film was fabricated layer-by-layer using the self-assembly method, through the electrostatic interaction between the polycations of diazoresin (DR) and negatively charged Fe3O4 nanoparticles. The results of UV–Vis spectra, magnetization measurements and AFM for DR–Fe3O4 films show that the assembly is very successful. After UV irradiation, the ionic bonds of the film convert to covalent ones and the stability of the magnetic film against etching by the polar solvents or salting liquids increases dramatically.

Stable multilayer ultrathin film containing covalently attached colloidal Ag nanoparticles

Stable multilayer ultrathin films were constructed by alternate deposition of nitro-diazoresin (NDR) and Ag nanoparticles (Ag-NPs) followed by UV irradiation. The absorbance of the un-irradiated film at 385 and 412 nm, which is the characteristic absorption of –N2+ of NDR and Ag-NPs respectively, increases linearly with the fabrication cycle. This result shows that the layer-by-layer electrostatic deposition of NDR and Ag-NPs is successful and uniform. An atomic force microscopy image of the film with four deposition cycles demonstrates the presence of the close-packed Ag-NPs with the average roughness of 1.5 nm. Furthermore, the stability of the irradiated film toward polar solvents and salty liquids increases significantly, due to the formation of covalent bonds between the layers of the assembled film upon exposure to UV light.