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Filter membrane sample after filtration of solution with latex beads: (a) PAN with 2 µm latex beads at ×270 magnification; (b) PAN with 2 µm latex beads at ×800 magnification; (c) PAN with 50 nm latex beads at ×800 magnification; (d) PAN with 50 nm latex beads at ×27,000 magnification.
