A computational reaction-diffusion model for the analysis of transport-limited kinetics

Optical, evanescent wave biosensors have become popular tools for quantitatively characterizing the kinetic properties of biomolecular interactions. Analyzing data from biosensor experiments, however, is often complicated when mass-transfer influences the detection kinetics. We present a computational, transport-kinetic model that can be used to analyze transport-limited biosensor data. This model describes a typical biosensor experiment in which a soluble analyte diffuses through a flow chamber and binds to a receptor immobilized on the transducer surface. Analyte transport in the flow chamber is described by the diffusion equation while the kinetics of analyte-surface association and dissociation are captured by a reactive boundary condition at the sensor surface. Numerical integration of the model equations and nonlinear least-squares fitting are used to compare model kinetic data to experimental results and generate estimates for the rate constants that describe analyte detection. To demonstrate the feasibility of this model, we use it to analyze data collected for the binding of fluorescently labeled trinitrobenzene to immobilized monoclonal anti-TNT antibodies. A successful analysis of this antigen-antibody interaction is presented for data collected with a fluorescence-based fiber-optic immunoassay. The results of this analysis are compared with the results obtained with existing methods for analyzing diffusion-limited kinetic data.