Magnetic nanoparticles have attracted much attention in biomedical areas due to their excellent biological compatibility,easy coupling with other molecules and great manipulability through magnetic fields.Interaction between the nanoparticles and the biomolecules has been a hot topic and deserves great efforts for better application of these materials [1-2].In our work,the interaction of citric acid dispersed Fe3O4 nanoparticles (Fe3O4-NPs) with three common proteins,bovine serum albumin(BSA) 、bovine hemoglobin(BHB)、trypsin(TRY) was evaluated by pulsed streaming potential over fused silica capillaries.The evaluation relied on the change of streaming potential caused by the flushing of solutions of proteins,nanoparticles and their mixtures.The interaction of a protein with the nanoparticles was deducted through the streaming potential differences obtained with pure protein solutions and the mixtures of proteins and nanoparticles.The results demonstrated that the presence of Fe3O4-NPs significantly changed the streaming potential values,which indicated possible interactions between Fe3O4-NPs and the proteins (Figure 1,Figure 2).The acidity of the solution exhibited profound influence on the process and the highest changes of streaming potential were obtained at pH of 8.2,8.3 and 5.6 for BSA,BHB and TRY,respectively.Similar results were obtained within microchannels of cyclic olefin copolymer (COC) chips.Based on these results,it can be concluded that pulsed streaming potential might be a way to study the interaction between proteins and nanoparticles.