The mesoscopic effect on label-free biosensors based on localized surface plasmon resonance of immobilized colloidal gold

The mesoscopic effect of arrangement of monodisperse immobilized colloidal gold was studied with the aim of exploring sensor applicability of localized surface plasmon resonance (LSPR). In our experiments using our original LSPR sensor devices with various immobilization densities of nanometric colloidal gold, we demonstrated that the particle arrangement in the mesoscopic scale is significant for precise control of sensing characteristics, such as sensitivity. The interparticle distance between particles needs to be larger in order to achieve higher sensitivity of sensor devices. With our devices, we observed a 50% increase in sensor response measured by the spectral shift in the model immunoassay as well as in the refractive index sensing. The results indicated that LSPR is dependent on the average interparticle spacing in the measurement area, i.e., this mesoscopic scale averaged interparticle spacing is important in controlling LSPR sensor properties. To explain our experimental results, we also provided an illustration of a theoretical view of the electrophysical properties of LSPR obtained by computational electrodynamics simulation using the finite difference time domain (FDTD) method. This suggested that targeted analyte bindings are effectively detectable within the intensified electric field around colloidal gold with a sparse arrangement. Our results amount to a simple and effective method of designing and controlling the properties of nanoparticle-based LSPR sensor devices.