Specific glucose-to-SPR signal transduction at physiological pH by molecularly imprinted responsive hybrid microgels.

We design a class of imprinted hybrid microgels that can optically monitor glucose levels with high sensitivity and selectivity in complex media at physiological pH, acting like a "glucose-indicator". Such imprinted hybrid microgels were made of Ag nanoparticles (NPs) in situ immobilized in molecularly imprinted glucose-responsive polymeric microgel templates containing phenylboronic acids in such a way that the Ag NPs were confined in the immediate vicinity to each other, thus enabling their efficient plasmon coupling. The glucose-responsive gel-actuated tunable plasmon coupling effects among the Ag NPs immobilized inside the microgels were investigated in both phosphate buffer solution and artificial tear fluid. The visually evident color shift from yellow to red of the hybrid microgel dispersion in response to a glucose concentration change from 0 to 20.0 mm allows one to see the glucose levels without instrumental aid. The surface plasmon resonance (SPR) response of the imprinted hybrid microgels at appropriate loading amount of Ag NPs is free of the significant interferences from the major non-glucose constituents, enabling the optical glucose sensing in artificial tear fluids with the achieved root-mean-squared error of predication (RMSEC) as low as 13.7 μM (~0.2 mg/dL) over a clinically relevant glucose concentration range of 0.1-20 mm (1.8-360 mg/dL). The highly versatile imprinted hybrid microgels could potentially be used for continuous glucose monitoring in clinical diagnostic and bioprocess applications.