Yazdankhah et al. (1999) used the magnetic beads to collect the thermostable nuclease (TNase) of S. aureus in composite milk and subsequently employed ELISA to detect as low as 1 ng of TNase, which corresponds to approximately 105 cells/ml. Although this LOD is superior to that of the nanocomposites-based colorimetric sensor, the ELISA combined with the IMS had the total assay time of 3 h, requiring much more time than the selective filtration system to generate the test results.