Building assemblies from high molecular weight polyelectrolytes

Bulky, open assemblies, prepared from the sequential adsorption of opposite ly charged polyelectrolytes (PE), could potentially be used as receptor mat rixes in biosensing devices. We have examined the building of such structur es onto gold surfaces from water-soluble cationic and anionic polyelectroly tes of different chemical structures, molecular weights (5 x 10(4) to 1.5 x 10(7)), and charge densities (20-100%) using quartz crystal microgravimetr y and atomic force microscopy. The effects of molecular weight were found t o be small compared with the effects of charge density. When the charge den sity on the cationic PE was decreased, the number of PE layers that could b e reliably deposited also decreased, bt the same time the film became much more open and heterogeneous. The integrity of film fabrication improved wit h increasing solution ionic strength, confirming the key role of counterion s.