Colloidal gold and colloidal gold labelled wheat germ agglutinin as molecular probes for identification in mucin/chitosan complexes

Polyelectrolyte complex formation between pig gastric mucin and chitosan and its implications to mucoadhesion have recently been studied using techniques such as analytical ultracentrifugation, static light scattering and turbidimetry (Fiebrig, I., Harding, S.E. and Davis, S.S. (1994) Prog. Coll. Polym. Sci. 93, 66-73; Fiebrig, I., Harding, S.E., Rowe, A.J., Hyman, S.C. and Davies, S.S. (1995) Carbohyd. Polym. 28, 239-44). The findings suggested the formation of large complexes, which were then visualised using electron microscopy. The present investigation employed electron microscopy combined with colloidal gold conjugates in order to identify and localize chitosan within the mucin/chitosan complex. Images of apparently dispersed chitosan molecules could be obtained using an anionic dye molecule, Orange II, which is known to interact stoichiometrically with the cationic sites on chitosan. Once chitosan was complexed with mucin, the colloidal gold labelled techniques revealed that chitosan is concentrated in the centre of the complex, surrounded by a possibly more hydrophilic layer of mucin.