Integrated magnetic sensors based on niobium dc SQUID (Superconducting Quantum Interference Device) for nanoparticle characterizations are presented. The SQUIDs consists of two Dayem bridges of 90 nm × 250 nm and loop area of 4, 1, and 0.55 μm2. The devices are realized by using an e-beam lithography nano-fabrication process which can directly pattern the devices in an electron-positive resist and then transferred to a 20 nm single niobium layer by a lift-off post-process. The SQUIDs were designed to have a hysteretic current–voltage characteristic in order to work as a magnetic flux-current transducer. The presence of an integrated niobium coil, tightly coupled to the SQUID, allows us to easily excite the SQUID and to flux bias the SQUID at its optimal working point. Current–voltage characteristics, critical current as a function of the external magnetic field and switching current distributions were …