Functional multilayer thin films have been prepared by layer-by-layer (LbL) deposition for the development of sensors, separators, and drug delivery systems. In particular, glucose-sensitive LbL films have been widely studied for use as glucose sensors and in glucose-triggered drug delivery systems. In this work, I report on glucose-sensitive LbL films that consist of concanavalin A (ConA), phenylboronic acid (PBA), and glucose oxidase (GOx). ConA/glycogen LbL films were prepared by LbL deposition of ConA and glycogen through a lectin-sugar interaction. Similarly, PBA-modified poly(amidoamine) dendrimer/poly(vinyl alcohol) (PVA) LbL films were prepared through cyclic boronate ester bonds. Both types of films decomposed in the presence of glucose, by the competitive binding of glucose, although these LbL films did not show a satisfactory response to millimolar concentrations of glucose under physiological conditions. PBA-modified poly(allylamine hydrochloride) and PVA films were prepared on a GOx-modified quartz slide. The LbL film was stable over a wide pH range, from 3.0 to 9.0, in the absence of glucose. In contrast, the film decomposed upon exposure to 0.1-10 mM glucose solutions for 60 min at pH 7.4. The glucose-induced decomposition of the film can be explained by the scission of the carbon-boron bond of the PBA residues by hydrogen peroxide, which was produced through the GOx-catalyzed oxidation of glucose. These results suggest this multilayer film may be useful for the development of glucose-sensitive drug delivery systems.
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