A novel potentiometric detection strategy based on functionalized magnetic nanoparticles has been developed for rapid and sensitive sensing of polyions.Highly dispersed magnetic nanoparticles coated with ion exchanger and plasticizer could promote an in situ cooperative ion-pairing interaction between the ion exchanger and the polyion analyte in sample solution by dramatically reducing the mass-transfer distance.With applying a magnetic field,the nanoparticles can be attached to the surface of ion exchanger free polymeric membrane.The observed potential signals are related to the polyion concentrations.The proposed polymeric membrane electrode exhibits a linear relationship between the greatest potential response slope(dE/dt) and the logarithm of protamine concentration in the range of 0.05-5μg/mL with a lower detection limit of 0.033μg/mL. A novel potentiometric detection strategy based on functionalized magnetic nanoparticles has been developed for rapid and sensitive sensing of polyions. Highly dispersed magnetic nanoparticles coated with ion exchanger and plasticizer could promote an in situ cooperative ion-pairing interaction between the ion exchanger and the polyion analyze The solution to dramatically reducing the mass-transfer distance. Applying a magnetic field, the nanoparticles can be attached to the surface of ion exchanger free polymeric membrane. The observed potential signals are related to the polyion concentrations. The proposed polymeric membrane electrode exhibits linear relationship between the greatest potential response slope (dE / dt) and the logarithm of protamine concentration in the range of 0.05-5 μg / mL with a lower detection limit of 0.033 μg / mL.