In order to meet the requirements of high sensitivity and specificity of clinical diagnosis, the effects of magnetic nanoparticles (MNPs) on the transmission performance of optical nanofiber are studied, as well as the possibility of MNPs functioned as labels to enhance the sensitivity of bio-chemical detection and the purificaiton of the determinand. The fabrication process of tapered optical nanofiber sensors, functionalization of optical nanofiber biosensors and MNPs are presented. Experiments are designed, the amplication function of MNPs is verified, and single MNP with the diameter from 200 nm to 300 nm is successfully resolved by optical nanofiber biosensor. The results of experiments demonstrate that the project of using MNPs as separation, purification and enhancing of sensitivity, can work well on optical nanofibers.