Assembling of gold nanorods on P(NIPAM–AAPBA) microgels: a large shift in the plasmon band and colorimetric glucose sensing

Abstract

Amine modified gold nanorods (GNR) were assembled onto the surface of poly(N-isopropylacrylamide-co-3-acrylamidophenylboronic acid) (P(NIPAM–AAPBA)) microgel particles via electrostatic interactions. The effects of pH and GNR/microgel ratio on the self-assembly were studied. It was revealed that GNRs can be sequestered more effectively at a higher pH because the surface charge density of the microgel particles increases with increasing pH. In addition, the surface coverage of the GNRs increases with increasing GNR/microgel ratio. Based on these observations hybrid microgels were prepared at pH 8.5 and 9.0 using a high GNR/microgel ratio. Upon heating these hybrid microgels exhibit a redshift of over 100 nm in their plasmon band, which is much larger than those reported in the literature. At the same time, the color of the microgel dispersion gradually changes from blue to grey. The hybrid microgel can be regarded to have a core/shell-like structure, as the radius increase of the hybrid microgel, either at a fully swollen state or a fully collapsed state, is comparable to the diameter of the GNRs. The thermal phase transition of the hybrid microgel starts at the same temperature as that of the bare microgel, but ends at a much higher temperature. The widened phase transition is attributed to the restriction of the non-thermosensitive GNR shell on the deswelling of the core. Similarly glucose-induced swelling is also retarded, resulting in a reduced glucose-sensitivity. The glucose-induced swelling also results in the blueshift of the plasmon band and color change of the sample. The new hybrid microgel can be used as a dual colorimetric sensor for temperature and glucose.