Multilayer films composed of phenylboronic acid-modified dendrimers sensitive to glucose under physiological conditions

Layer-by-layer (LbL) multilayer films were prepared using phenylboronic acid-modified poly(amidoamine) dendrimers and poly(vinyl alcohol) (PVA) in order to investigate the glucose sensitivity of the films. We used dendrimer derivatives modified with 3-carboxyphenylboronic acid (3CPBA-D) and 3-carboxy-5-nitrophenylboronic acid (3C5NPBA-D) to evaluate the effect of electron-withdrawing nitro groups on glucose sensitivity. PVA/3CPBA-D and PVA/3C5NPBA-D films were prepared on the surface of a quartz slide from PVA and 3CPBA-D or 3C5NPBA-D solutions at pH 7.0, 8.0, and 9.0 through boronate ester bonds. The dendrimer-based LbL films were stable at pH 7.0-9.0, whereas they decomposed in acidic media because of the instability of the boronate ester linkages. The pH threshold of decomposition was at pH 6.0-7.0 for both films. The PVA/3C5NPBA-D film was more stable than the PVA/3CPBA-D film in this range. Both films decomposed in response to glucose under physiological conditions (pH 7.4 buffer solution containing 150 mM NaCl at 37 degrees C), and the decomposition depended on the glucose concentration. The PVA/3C5NPBA-D film was more sensitive to glucose than the PVA/3CPBA-D film, probably due to the higher binding affinity of 3C5NPBA-D to glucose under physiological conditions. The higher response of the PVA/3C5NPBA-D film was explained by the electron-withdrawing effect of the nitro substituent on the phenylboronic acid ring. The results suggest that dendrimer-based LbL films could be used for glucose-triggered release systems.