UC San Diego

Blood lactate concentration has been used as an important diagnostic parameter for assessing patient health conditions for over four decades, yet its measurement is currently time consuming and inconvenient, and its roles in disease development and homeostasis are still poorly understood. While much effort has been focused on developing implantable biosensors to achieve continuous monitoring of lactate concentrations in both blood and tissue, systematic studies of sensor behavior using mathematical modeling techniques have rarely been done. Experimental results complemented with such models would be potentially helpful in understanding the underlying physics behind sensor operation. Therefore, in this thesis we use mathematical models to characterize an enzyme electrode sensor that has shown great promise as potential implantable device. This thesis will also demonstrate how these theoretical results can be utilized to formulate efficient strategies to improve sensor performance.Lactate specificity for the enzyme electrode sensor of interest is obtained by immobilizing lactate oxidase which catalyzes the reaction between lactate and oxygen, onto an electrochemical oxygen electrode. Lactate can then be quantitatively detected by measuring the resulting oxygen dependent current. Oxygen and lactate concentration profiles within the sensor were obtained by solving reaction coupled mass conservation equations using a finite element analysis (FEA) software called COMSOL Multiphysics and the currents were calculated from the oxygen flux at the electrode surface. The model is used to predict the roles of geometric, kinetic, and environmental factors on the steady-state and transient responses of these potentially implantable sensors