High-Resolution Separation of Nanoparticles Using a Negative Magnetophoretic Microfluidic System

Abstract

The separation and purification of a sample of interest is essential for subsequent detection and analysis procedures, but there is a lack of effective separation methods with which to purify nano-sized particles from the sample media. In this paper, a microfluidic system based on negative magnetophoresis is presented for the high-resolution separation of nanoparticles. The system includes on-chip magnetic pole arrays and permalloys that symmetrically distribute on both sides of the separation channel and four permanent magnets that provide strong magnetic fields. The microfluidic system can separate 200 nm particles with a high purity from the mixture (1000 nm and 200 nm particles) due to a magnetic field gradient as high as 10,000 T/m being generated inside the separation channel, which can provide a negative magnetophoretic force of up to 10 pN to the 1000 nm particle. The overall recovery rate of the particles reaches 99%, the recovery rate of 200 nm particles is 84.2%, and the purity reaches 98.2%. Compared with the existing negative magnetophoretic separation methods, our system not only exhibits high resolution on particle sizes (800 nm), but also improves the sample processing throughput, which reaches 2.5 μL/min. The microfluidic system is expected to provide a new solution for the high-purity separation of nanoparticles, as well as nanobiological samples.

Keywords: microfluidic chip; nanoparticles; negative magnetophoresis; separation.

Figure 1

Design and image of the microfluidic system: (a) Overall structure of the system; (b) Schematic illustration on the system design; (c) Microscopic image on the separation area.

Figure 2

Simulation results of the magnetic field and particle trajectories: (a) The force analysis of the particle in separation channel; (b) The magnetic field distribution of separation area; (c) The magnetic field and its gradient in separation area along x-axis; (d) The magnetic field and its gradient in separation area along y-axis.

Figure 3

Calculated negative magnetophoretic force and particle trajectories based on the simulation results: (a) Negative magnetophoretic force acting on 1000 nm particles in the separation area along x-axis and (b) along y-axis; (c) The trajectories of 200 nm and 1000 nm particles in the simulation.

Figure 4

The trajectories of 200 nm and 1000 nm particles at different flow rates in the experiments.

Figure 5

Comparison between simulation results and experimental results on particle distribution along y-axis at the outlet area under different flow rates of the sample flow.

Figure 6

Flow cytometry test results obtained from: (a) Sample inlet; (b) Outlet A; (c) Outlet B; (d) The proportion of the two kinds of particles at inlet and outlets; (e) The number distribution of the two kinds of particles at both outlets.