Analysis of the competitive adsorption and mass transfer influence on equilibrium mass fluctuations in affinity-based biosensors

We analyze the fluctuations of the equilibrium adsorbed mass in affinity-based biosensors, considering adsorption–desorption and mass transfer processes of two molecular species which compete for binding to the same probe molecules immobilized on the sensing surface. The analytical expression for the fluctuations spectral density is derived. The calculations show the significant influence of both the competitive adsorption and the mass transfer on the fluctuations spectrum, and also of their combined effect. The dependences of the fluctuations on association and dissociation rate constants of both adsorbing species, their concentrations, molecular masses and mass transfer coefficients and also on the density of capturing probes can be examined by using the presented model. The model is applicable for biosensors in which the spatial distribution of adsorbates concentrations in the reaction chamber can be approximated using the two-compartment model. The theory provides a more realistic estimation of the biosensors’ limiting performance, and is useful for their improvement.