Materials in the form of a superposition of thin dielectric layers with nanometric dimensions such as core-shell nanoparticles are used in different nanotechnology fields. Reliable methods are needed to characterize such systems at the nanoscale. In this work, we study the possibility of the electrostatic force microscope (EFM) in the DC force gradient detection method to detect alumina thin layers deposited on polystyrene nanoparticles and on silicon dioxide nanospheres. The dielectric permittivity of these materials is used as their fingerprint. We find that the EFM is sensitive to the thickness of a dielectric layer over studied nanoparticles and over bare substrates.