Numerical and Analytical Modeling to Determine Performance Tradeoffs in Hydrogel-Based pH Sensors

Hydrogel-based pH sensors are promising candidates for implantable sensors due to their low cost and biocompatibility. Despite their commercial potential and numerous theoretical/experimental reports, the tradeoffs between different performance parameters are not well understood and explicitly stated. In this work, we develop a numerical and analytical framework to show that there is a fundamental tradeoff between the performance parameters, i.e., sensitivity/dynamic range versus response-time/response-asymmetry in hydrogel sensors under constrained swelling conditions. Specifically, we consider the effect of the gel parameters, such as the ionizable group density (N-f) and its dissociation constant (K-a), on the sensor performance. We show that improvement in sensitivity/dynamic range leads to degradation in response time/symmetry and, therefore, a compromise must be made to optimize device performance.