Specific responses of surface plasmon resonance and quartz crystal microbalance techniques to the mass of adsorbates at solid-liquid interfaces

Abstract

Surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) techniques are become increasingly popular in probing behaviors and properties of adsorbates at solid-liquid interfaces. Despite the numerous studies focusing on revealing various relations between their output signals and adsorbed mass, however, the mechanics of these specific relations remains elusive. In this paper, we showed that the universality of a proportional relation between SPR signal and surface mass stems from the catholicity of a linear relation between surface refractive index and surface concentration, and a small refractive index shift. The partial validity of a proportional relation between QCM signal and surface mass is due to that a linear relation between surface viscosity and surface concentration, and a small viscosity shift are not always true. The ratio of SPR and QCM signals to the surface mass is dominated by the refractive index increment and intrinsic viscosity, respectively. The weak sensitivity of refractive index increment to conformation, architecture, etc., makes the mass estimation from SPR technique very convenient. The strong sensitivity of intrinsic viscosity to these factors makes the mass evaluation from QCM technique very difficult, whereas endowing a powerful method in quantitatively probing the conformation of adsorbates at solid-liquid interfaces.