技術論文とプレゼンテーション

Tyrosinase-based biosensors offer a promising way to detect L-DOPA, a key drug in Parkinson's disease management¹. But getting a reliable signal depends heavily on how the enzyme is immobilized². Glutaraldehyde is commonly used to cross-link the enzyme in place², and BSA is added alongside it to protect the enzyme from denaturing². Too much of either, though, creates a dense matrix that blocks diffusion and slows the sensor's response³,⁴ while excess glutaraldehyde also distorts the enzyme's structure and reduces its activity⁵. This project uses a 1D COMSOL Multiphysics model to explore that trade-off. By coupling species transport, enzyme kinetics, and electrode kinetics, we map how peak current changes across a range of BSA and glutaraldehyde ratios (relative to the enzyme), validating simulation results against experimental data to optimize the immobilization layer for our SensUs 2026 biosensor. The tyrosinase biosensor is modeled as two coupled domains (Figure 1): an enzyme layer (BSA/glutaraldehyde/tyrosinase) and a diffusion layer extending to the bulk solution. Species transport follows the Electroanalysis interface, with L-DOPA diffusivity reduced inside the gel through a Mackie–Meares effective diffusion coefficient dependent on porosity and BSA tortuosity. Enzymatic conversion of L-DOPA is described by Michaelis–Menten kinetics, with the catalytic rate constant scaled by factors accounting for GA-induced denaturation, enzyme retention, and BSA's scaffolding role. Electrode kinetics follow Butler–Volmer theory, with parameters derived from EIS and CV characterization of the bare electrode. A full-factorial sweep over BSA and glutaraldehyde ratios was run to identify the formulation maximizing peak current. The parametric sweep identified an optimal formulation of a glutaraldehyde ratio of 0.5, combined with a BSA ratio of 2, consistent with excess glutaraldehyde restricting diffusion and denaturing the enzyme. The diffusion mechanism was supported experimentally: EIS diffusion measurements showed a much higher diffusion rate at a glutaraldehyde ratio of 0.5 compared to 1, confirming that lower cross-linking density improves mass transport through the enzyme layer.