In order to characterize and control the adhesive behaviors of nanometer scaled stimuli-responsible gel particles designed for oral peptide delivery, their interaction with artificial mucin layer in the small intestinal solutions was determined by the colloid probe atomic force microscope method. The prepared nanometer scaled gel particles with a core-shell structure were designed to exhibit behaviors responsive to temperature and pH in solutions, consequently protect the incorporated peptide drug under harsh acidic conditions in the stomach, adhere and penetrate to the mucin layer in the small intestine, and thereafter release the drugs. Spherical agglomerates of the nano-gel particles with several micron meters in diameter were prepared by the spray freeze drying method and adhered on the top of tip of commercial atomic force microscope. The interaction between the artificial mucin layer and nano-gel surface determined by the colloid probe method depended on pH of the solution. Based on the possible transition of the surface-microstructure of nano-gel particles following the pH change and the measured results from the colloid probe AFM method, the relationship between surface interaction and microstructure of nano-gel was discussed.

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