In 2023, Pulsar Timing Array (PTA) collaborations reported the first detection of a stochastic background of nanohertz gravitational waves. If this signal is of primordial origin, its amplitude would require violent early-Universe phenomena likely accompanied by other signatures. One possible counterpart is the formation of solar-mass primordial black holes, already the subject of intense study following the ∼300 merger events observed by LIGO–Virgo–KAGRA. Another, less explored — but promising — signature could be the presence of ultra-compact dark-matter minihalos (UCMHs). This project aims to investigate how UCMHs could be detected through gravitational microlensing. Detecting or constraining such objects could provide a decisive test for the primordial origin of the PTA signal.