This paper presents a case study of the interaction between nanoelectrodes and dielectric nanoparticles possibly representative of biomolecules in a simple cylindrical capacitive biosensor. The small signal admittance change due to the insertion of the biomolecule in the biosensor electrolyte is studied as a function of the position, aspect ratio and charge of the biomolecule and of the signal frequency. Results suggest clear advantages in operating the biosensor beyond the electrolyte cutoff frequency.