Glucose-induced decomposition of layer-by-layer films composed of phenylboronic acid-bearing poly(allylamine) and poly(vinyl alcohol) under physiological conditions

Multilayer thin films prepared via layer-by-layer (LbL) deposition of phenylboronic acid-bearing poly(allylamine hydrochloride) (PBA-PAH) and poly(vinyl alcohol) (PVA) were combined with glucose oxidase (GOx) to develop LbL films that can be decomposed in response to glucose. LbL deposition of PBA-PAH and PVA on a GOx-modified quartz slide afforded GOx/(PBA-PAH/PVA)_n films, in which PBA-PAH and PVA layers were connected to each other through boronate ester bonds, while GOx was immobilized electrostatically. The GOx/(PBA-PAH/PVA)_n films were stable in glucose-free solutions under physiological conditions. In contrast, films decomposed in the presence of glucose, depending on the concentration of glucose and solution pH. The GOx/(PBA-PAH/PVA)₁₀ film decomposed almost completely in 60 min in the presence of 10 mM glucose at pH 7.4, while it took 120 min in 0.1 mM glucose solution. Film decomposition was accelerated at pH 5.0-7.4, whereas it was suppressed in acidic and basic media (pH 3.0 and 9.0, respectively) due to the lower catalytic activity of GOx. Glucose-induced decomposition of the film can be rationalized based on the scission of the carbon-boron bonds of PBA in the film by hydrogen peroxide (H₂O₂), which is produced through a GOx-catalyzed oxidation reaction of glucose.