MODELING OF PARTICLE-ENHANCED SENSITIVITY OF THE SURFACE-PLASMON-RESONANCE BIOSENSOR

A theoretical model is presented for a surface-plasmon-resonance (SPR) biosensor, used to sense particle-enhanced antigen-antibody binding. The particles used in this technique, such as colloidal gold, are generally of high optical refractive index. We propose a two-dimensional fractal-cluster model to study the effect of coalescence of these particles and compare our results with those obtained from the Maxwell-Garnett model. This latter model ignores coalescence and assumes that the particles disperse randomly throughout the binding layer. Our results show that the comparison depends critically on the fractal dimension, which is a measure of the clustering among the particles. The conclusion is that for colloidal gold, clustering among particles will likely lead to greater signal enhancement, while for other particles, such as polystyrene and titanium dioxide, the enhancement is less certain due to their smaller refractive indices as well as the uncertainty in their fractal dimensions. In addition, our results indicate that analysis of the SPR signal using the Maxwell-Garnett model could lead to an overestimate of the binding in this technique.