This study mainly employs magnetic nanoparticles (MNPs) for an amazing variety of engineering and biomedical applications. Herein MNPs are fabricated from fine ferromagnetic particles of iron ferrite by chemical co-precipitation technique, and their average size is about 27 nm via HR-TEM micrograph and XRD analysis to investigate. In this study, MNPs have been demonstrated their excellent properties of heat transfer, electric conductivity, magnetism within the applications for multi-loop pulsating heat pipe (MLPHP), switch-based nanodevice, microfluidic on-chip system and nanogap-based DNA sensor. Based on the effect of magnetic field for MNPs, MLPHP can enhance thermal performance itself at different heating power. In addition, the switch-based nanodevice with MNPs can efficiently add and remove an electrical function of electron charging with current shift. Furthermore, the microfluidic chip utilizing MNPs is demonstrated that can be suited for drug delivery. Finally, we use MNPs to develop an electrical approach to detect femtomolar DNA that can amplify the low target DNA concentration for a clinical gene diagnostic system.