A smart temperature and magnetic-responsive gating carbon nanotube membrane for ion and protein transportation

Abstract

Carbon nanotube (CNT) nanoporous membranes based on pre-aligned CNTs have superior nano-transportation properties in biological science. Herein, we report a smart temperature- and temperature-magnetic-responsive CNT nanoporous membrane (CNM) by grafting thermal-sensitive poly(N-isopropylacrylamide) (PNIPAM) and Fe3O4 nanoparticles (Fe3O4-NPs) on the open ends of pre-aligned CNTs with a diameter around 15 nm via surface-initiated atom transfer radical polymerization (SI-ATRP) method. The inner cavity of the modified CNTs in the membrane is designed to be the only path for ion and protein transportation, and its effective diameter with a variation from ~5.7 nm to ~12.4 nm can be reversible tuned by temperature and magnetic field. The PNIPAM modified CNM (PNIPAM-CNM) and PNIPAM magnetic nanoparticles modified CNM (PNIPAM-MAG-CNM) exhibit excellent temperature- or temperature-magnetic-responsive gating property to separate proteins of different sizes. The PNIPAM-CNMs and PNIPAM-MAG-CNMs have potential applications in making artificial cells, biosensors, bioseparation and purification filters.

Figure 1

Schematic (a) and chemical (b) illustration of the fabrication process of PNIPAM-MAG-CNM.

Figure 2

Images of the obtained CNM: (a) optical photo, (b) top surface of membrane by SEM, (c) cross section surface of membrane by SEM, (d) TEM image of CNTs in membrane.

Figure 3. UV-Vis spectra of Au-NPs feed suspension (red curve) and the permeate solution (black curve) after diffusion for 48 hours in the obtained CNM.

Figure 4

EDS spectra of pure CNM (a), PNIPAM-CNM (b) and PNIPAM-MAG-CNM (c).

Figure 5

Ion transportation properties of (a) the pure CNM at 20 °C and 40 °C, and (b) PNIPAM-CNM at 20 °C and 40 °C measured through conductivity variation in the downstream.

Figure 6. Reversible temperature-responsive property of the PNIPAM-CNM for ion transportation measured through conductivity variation in the downstream.

Figure 7

Ion transportation properties of the (a) pure CNM at 20 °C and 40 °C without magnetic field, (b) pure CNM at 20 °C and 40 °C with magnetic field, (c) PNIPAM-MAG-CNM at 20 °C and 40 °C without magnetic field, and (d) PNIPAM-MAG-CNM at 20 °C and 40 °C with magnetic field measured through conductivity variation in the downstream.

Figure 8

Dimension figures of Lys (a), BSA (b), Mb (c), and CE detection of filtrated proteins by PNIPAM-CNM at (d) T = 20 °C, (e) T = 40 °C, and by PNIPAM-MAG-CNM at (f) T = 20 °C without magnetic field, (g) T = 20 °C with magnetic field. Separation conditions: buffer, 40 mM phosphate (pH = 3.0); injection, 20 s with a height difference of 20 cm; applied voltage, +15 kV; UV detection, 214 nm; sample, 0.5 mg·mL⁻¹ for each protein; capillary, 75 μm id × 50 cm (40 cm effective); capillary temperature, 25 °C. Peak identification: (1) Lys; (2) BSA; (3) Mb.