Absorption-type optical pH sensitive film based on immobilized purple cabbage pigment

摘要

A new absorption-type optical pH sensitive film was prepared by immobilizing purple cabbage pigment (PCP) in sol-gel film. For preparation of the pH sensitive film, PCP was entrapped in sol-gel film and then coated on glass slides by dip-coating method. The sensing properties of the PCP-pH sensitive film were examined by ultraviolet-visible spectrophotometer and p-polarized reflectance method. The results indicate that the film responds rapidly (within l-2min) over a wide pH range of 2-11 with linearly calibration. The relative standard deviation (R.S.D.) of its reproducibility is less than 0.3%. In addition, the refractive index n_f and the thickness d_f of the film are not changed with different pH values. However, the extinction coefficient k_f of the film changes regularly as pH changes, tendency of which is consistent with that of the film absorbance at 633 nm. Therefore, PCP-pH sensitive film is proved to be an absorption-type film, which is promising to design absorption-type pH sensor.