Sugar response of layer-by-layer films composed of poly(vinyl alcohol) and poly(amidoamine) dendrimer bearing 4-carboxyphenylboronic acid

Multilayered thin films composed of poly(vinyl alcohol) (PVA) and 4-carboxyphenylboronic acid-modified poly(amidoamine) dendrimer (4-PBA-PAMAM) were prepared by a layer-by-layer (LbL) deposition of PVA and 4-PBA-PAMAM on the surface of a quartz plate to study the response of the multilayered films to sugars. PVA/4-PBA-PAMAM films were constructed successfully at pH 7.0–9.0 through the formation of boronate ester bonds between the boronic acid moiety in 4-PBA-PAMAM and 1,3-diol units in PVA, while the film deposition was unsuccessful at pH 6.0 probably owing to weaker affinity between 4-PBA-PAMAM and PVA in the weakly acidic medium. The films were stable in aqueous solutions at pH 7.5 or higher whereas the films decomposed in neutral and acidic solutions, which can be ascribed to lower affinity of neutral trigonal PBA derivatives than that of negatively charged tetragonal PBAs. PVA/4-PBA-PAMAM films decomposed in response to glucose and fructose depending on the concentration as a result of competitive binding of the sugars to 4-PBA-PAMAM in the film. The degree of glucose-induced decomposition of the film was 20–25 % in the presence of 30 mM at pH 7.4 and 9.0. On the other hand, in 10 mM fructose solution, the degree of film decomposition was 90 and 60 % at pH 9.0 and 7.4, respectively. A possible application of the LbL films to sugar-sensitive delivery systems was discussed.