Transport Control in GPTMS-Crosslinked Chitosan/PDMS Membranes for Glucose Sensing

First-generation glucose oxidase (GOx) biosensors require control over the coupled transport of glucose and oxygen to the enzyme layer. Without an effective membrane, the amperometric current approaches a plateau below the physiological maximum; an excessively restrictive membrane, however, decreases current and slows the response. Here, a stepwise membrane-design strategy was evaluated using chitosan–3-glycidyloxypropyltrimethoxysilane (GPTMS) and polydimethylsiloxane (PDMS)-containing chitosan–GPTMS coatings. Crosslinked chitosan–GPTMS alone remained highly permeable to glucose: the current approached its plateau already at 20 mM. Introduction of PDMS resulted in a heterophase membrane with a distributed hydrophobic siloxane-containing phase. At a comparable thickness the amperometric response remained concentration-dependent beyond 100 mM glucose, while thicker membranes produced an approximately proportional response up to at least 200 mM. The PDMS-containing membranes also supported substantially higher attainable currents, consistent with an altered coupled transport–reaction environment. Increasing membrane thickness from 6 to 31 µm decreased sensitivity from 11.35 to 3.34 nA/mM and increased the response time constant from 13.8 to 159 s. Thus, the crosslinked chitosan matrix provides a stable hydrated continuous phase, whereas a distributed hydrophobic phase imposes the additional glucose-transport resistance required for high-range sensing.