Engineering glucose swelling responses in poly(N-isopropylacrylamide)-based microgels

Poly(N-isopropylacrylamide) (PNIPAM) microgels are functionalized with aminophenyboronic acid (APBA) to produce nanoparticles which swell in response to increases in the glucose concentration. A graft-to approach was used to synthesize a range of microgels with different physical properties from the same base microgel. Higher APBA graft yields are achieved as the -COOH groups in the platform microgel become more localized on the surface and more highly spaced within the subchains. The glucose swelling response of the graft microgels is enhanced as the PBA functional groups become more localized in the outer shell of the microgel and more randomly distributed within the gel network subchains. The glucose-induced VPTT shift observed in the PBA-microgel conjugates can be exploited to produce microgels that exhibit on-off glucose swelling as a function of temperature or enhanced swelling responses over specific glucose concentration ranges at a single, tunable temperature. The secondary thermal phase transition is thus applied to effect an order-of-magnitude enhancement or suppression of the primary glucose-induced phase transition. Both linear and nonlinear microgel glucose sensors are subsequently designed which are active within targeted glucose concentration ranges.