Transport-kinetic processes and surface chemistry in biosensor design

Biosensors are analytical devices that detect a target analyte on the basis of biomolecular recognition. Detection occurs as the consequence of specific interactions between the analyte and complementary biomolecules immobilized on the transducer surface. Several physicochemical factors influence this detection process. This thesis examines the role of these factors in sensor operation and also evaluates specific methods to manipulate these factors and improve sensor performance.; We begin by investigating the kinetic and transport processes that underlie analyte recognition. A transport-kinetic model is developed to quantitatively relate these processes to sensor response in a typical biosensor measurement. Predictions from our model are compared with kinetic data from a fiber optic immunosensor. With these experimental comparisons, we demonstrate that our model provides a more physically rigorous description of analyte transport, and is thus better for data analysis and sensor design than competing models.; The role of surface effects in biosensor operation is also addressed. We examine how immobilization impacts the activity of the biomolecules on the transducer surface. Although these molecules display homogeneous binding characteristics in solution, they often exhibit heterogeneous binding properties after surface immobilization. We measure binding isotherms and the detection kinetics for several analyte-receptor systems constructed with various immobilization strategies. By comparing theoretical models with experimental data, we elucidate the relationship between protein immobilization chemistry and receptor heterogeneity, and identify methods for constructing more uniformly reactive protein films.; Finally, sample mixing is examined as a potential method to improve the performance of microfluidic biosensors. We attempt to mix sections of the sample solution where the analyte concentration is high with other sections where it is low, and thereby reduce the sensor response time when the detection kinetics are diffusion-limited. A serpentine micromixer, originally designed to mix two fluids in bulk solution via “chaotic advection,” is used to mix the sample as it passes through a surface plasmon resonance biosensor. These experiments indicate that such “solution-based” mixing strategies can be effective in microfluidic biosensors.