Fluorescence Boost in Polyelectrolyte Multilayer Architectures

Polyelectrolyte multilayer coated colloids were fabricated by means of layer-by-layer (LbL) deposition of poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) in alternating order. The top layer consisted of PAH fluorescently labeled with one of the following dyes: succinimidyl 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4yl)amino) hexanoate, fluorescein isothiocyanate, or rhodamine B isothiocyanate. For all three PAH−dye conjugates, a manifold increase in fluorescence intensity was observed upon adsorption of a PSS layer on top of the labeled PAH layer. The degree of fluorescence increase varied for each of the fluorescent dyes and depended on the polyelectrolyte concentration, revealing the existence of different modes of adsorption of the incoming polyelectrolyte molecules. Dequenching as well as changes in the local environment following polyelectrolyte adsorption were identified as the possible causes for the fluorescence enhancement. These findings prove that the top layer has a distinct physicochemical quality that makes it intrinsically responsive toward polyelectrolyte interactions, opening the way for the design of new sensing devices.