In recent years, magnetic particle spectroscopy (MPS) has emerged as a new technology for immunoassay applications. In MPS, alternating magnetic fields are applied to magnetic nanoparticles (MNPs). The magnetic responses of these nanoparticles are collected and recorded by a pair of specially designed pick-up coils. These magnetic responses contain higher harmonics that are specific to the physical changes of the nanoparticles such as the binding events of target analytes to nanoparticles. This volumetric-based bioassay method analyses the response signal from the whole nanoparticle suspension, thus, allows one step and wash-free immunoassay with minimum technical requirements. In this work, we developed a handheld MPS system as a future highly sensitive, cheap, in vitro, and easy-to-use point-of-care (POC) detection kit.