Stimuli-Responsive Microgel-Based Surface Plasmon Resonance Transducer for Glucose Detection Using a Competitive Assay with Concanavalin A

Glucose responsive microgels composed of poly­(N-isopropylacrylamide-co-glycosyloxyethyl methacrylate) (p­(NIPAm-co-GEMA)) were synthesized by free radical precipitation polymerization. The resultant microgels were shown to collapse upon addition of Concanavalin A (ConA) owing to its ability to bind up to four GEMA molecules. We showed that the microgel could reswell upon addition of free glucose due to the competitive binding of GEMA and glucose with ConA, effectively breaking the cross-links responsible for the collapse. Thus, by monitoring the contraction/expansion process of the p­(NIPAm-co-GEMA) microgels bound to a Au surface via surface plasmon resonance (SPR), the concentration of glucose in solution can be quantified. We go on to show that there is a ninefold SPR signal enhancement compared to exposure of bare Au to glucose and a similar enhancement compared to microgels without GEMA. Finally, we showed that the p­(NIPAm-co-GEMA) microgel-based SPR sensor surfaces were not responsive to other interfering species. Taken together, the results show that the competitive binding concept can be useful for detecting small biologically relevant molecules that are usually difficult to detect via SPR. Therefore, this concept can be expanded upon to detect other small molecules of interest in the future.