Track-etched magnetic micropore (TEMPO) filter for the rapid isolation of rare cells (D. Issadore)

a) Schematic of a single TEMPO micropore, coated with permalloy (Ni20Fe80) and a gold passivation layer. Cells flow vertically through the pore. In an applied field Bo, the TEMPO and the magnetically labeled cells are magnetized. The magnetically labeled cells (green) are trapped and unlabeled cells (red) pass through. b) A cross section of the microfluidic chip and external NdFeB permanent magnet. c) Exploded view of the laminate sheet microfluidics. d) SEM images of a TEMPO filter and stereoscope image of the “shower head” microfluidics. The scale bars are 2 µm, 25 µm, and 800 µm.

a) Schematic of a single TEMPO micropore, coated with permalloy (Ni20Fe80) and a gold passivation layer. Cells flow vertically through the pore. In an applied field Bo, the TEMPO and the magnetically labeled cells are magnetized. The magnetically labeled cells (green) are trapped and unlabeled cells (red) pass through. b) A cross section of the microfluidic chip and external NdFeB permanent magnet. c) Exploded view of the laminate sheet microfluidics. d) SEM images of a TEMPO filter and stereoscope image of the “shower head” microfluidics. The scale bars are 2 µm, 25 µm, and 800 µm.

Purpose: Rapid and accurate isolation of rare cells in fluid samples is a major challenge in medical diagnostics. There is a crucial need to isolate small numbers of cells from large populations, thus requiring high throughput techniques. The Issadore group at Penn has recently developed a new separation system to selectively sort magnetically labeled cells from heterogeneous suspensions, the Track-Etched Magnetic micro-POre (TEMPO) filter (Muluneh, submitted).

Method of Fabrication/Use: The TEMPO filter consists of an ion track-etched polycarbonate membrane coated with a soft magnetic film (Ni20Fe80). In the presence of an applied field, provided by a small external NdFeB magnet, the filter becomes magnetized and strong magnetic traps are created within the micropores to isolate targeted cells. In contrast to conventional microfluidic devices, fluid flows vertically through the porous membrane allowing large flow rates to be obtained while keeping efficiency high and the chip compact. By utilizing track-etching, micropores can be fabricated with pore sizes from 100 nm – 100 µm at little cost (< 5 ₵/cm2), enabling this approach to be optimally applied to a wide range of biological targets.  The low cost fabrication technique also facilitates fabrication and delivery of these devices via our center.

Results: We utilized a microfluidic chip with a 5 µm pore size TEMPO to demonstrate efficient enrichment (ξ > 104) of magnetic vs. non-magnetic 1 µm diameter polystyrene beads at large flow rates (Φ > 10 mL/hr). Furthermore, taking advantage of the easy integration of TEMPO filters into microfluidic chips, we placed multiple filters in series with an observed exponential increase in sorting efficiency for each additional layer.  This approach can be applied to cells and bacteria by functionalizing magnetic particles and attaching them to the cells. To demonstrate the biomedical utility of this platform, E. Coli were efficiently isolated from a background of similarly sized bacteria for subsequent downstream analysis.

References

Muluneh M, Wu S, Issadore D. Track-etched magnetic micropores for rapid and highly efficient immunomagnetic isolation. Lab on a Chip, submitted;

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