Graphene-based sensors have a great potential for applications in public and personal health protection, including defense and security fields. However, sensitivity and selectivity of such sensors are inherently dependent on adsorption properties of the graphene sensing layer, which is typically of heterogeneous morphology and/or of heterogeneous chemical composition due to intentionally introduced functionalizing elements or spontaneously adsorbed molecules during sensor fabrication or operation. Therefore, characterization and optimization of sensing layers is extremely important for achieving high sensing performance. In this work, we present a method for characterization of the heterogeneous sensing layer by using the frequency domain analysis of the sensor output signal. The method is based on the mathematical model we devised. Here, the model is presented in detail for the case of a surface with three types of adsorption sites, and then the method is applied for extraction of parameters that characterize adsorption properties of a graphene sensing layer
