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

Abstract

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≈1.2×10 5, M η≈1.0×10 6), 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.