Graphene@Poly(phenylboronic acid)s Microgels with Selectively Glucose-Responsive Volume Phase Transition Behavior at a Physiological pH

The selective response to glucose is possible by using a poly­(phenylboronic acid) microgel under a rational design. Such a microgel is made of graphene covalently immobilized in a microgel of poly­(4-vinylphenylboronic acid) cross-linked with <i>N</i>,<i>N</i>′-methylenebis­(acrylamide). Unlike the microgels reported in previous arts that would undergo volume phase transition in response to both glucose and other monosaccharides, the proposed microgels shrink upon adding glucose, whereas keep unchanged in the size upon adding other monosaccharides (with fructose, galactose, and mannose as models). Although the polysaccharides/glycoproteins (with dextran and Ribonuclease B as models) that contain many glycosyl residues can slightly absorb on the microgel surface and lead to a small impact on glucose-response, it can be addressed by further coating the microgel as a core with a thin nonglucose-responsive poly­(<i>N</i>-isopropylacrylamide) gel shell. This selectively glucose-responsive volume phase transition behavior enables “turn-on” photoluminescence detection of glucose in blood serum (a model for complex biosystems)

Synthesis and Characterization of Dextran–Tyramine-Based H₂O₂‑Sensitive Microgels

We report a type of polymer microgel that can undergo a rapid and highly sensitive volume change upon adding H₂O₂. Such a H₂O₂-sensitive microgel is made of dextran–tyramine and horseradish peroxidase (HRP), which are interpenetrated in chemically cross-linked gel networks of poly­(oligo­(ethylene glycol) methacrylates). Unlike the H₂O₂-sensitive microgels reported in previous arts that typically involve degradation processes related to H₂O₂-induced cleavability of specific bonds, the proposed microgels can shrink upon adding H₂O₂ owing to the HRP-catalyzed coupling reaction of tyramine residues via decomposition of H₂O₂. While a fast (<10 s) and stable shrinkage of the microgels can be reached upon adding H₂O₂ over a concentration range 50.0 μM–1.0 mM, the response time can be modulated by the dispersion temperature in a nonmonotonous way over 10–38 °C. With the microgels as probes, the H₂O₂ detection limit was approximately 6.8 μM. In a combined use of the microgels with glucose oxidase for glucose detection, the glucose detection limit was approximately 83.1 μM