Nanoporous solid-state membranes modified with multi-wall carbon nanotubes with anti-biofouling property

Abstract

Purpose: Nanoporous membranes have been employing more than before in applications such as biomedical due to nanometer hexagonal pores array. Biofouling is one of the important problems in these applications that used nanoporous membranes and are in close contact with microorganisms. Surface modification of the membrane is one way to prevent biofilm formation; therefore, the membrane made in this work is modified with carbon nanotubes.

Methods: In this work, nanoporous solid-state membrane (NSSM) was made by a two-step anodization method, and then modified with carbon nanotubes (NSSM-multi-wall carbon nanotubes [MWCNT]) by a simple chemical reaction. Techniques such as atomic force microscopy (AFM), energy dispersive X-ray (EDAX), field emission scanning electron microscopy (FESEM), Fourier-transform infrared spectroscopy (FTIR), contact angle (CA), surface free energy (SFE), protein adsorption, flow cytometry, and MTT assay were used for membrane characterization.

Results: The BSA protein adsorption capacity reduced from 992.54 to 97.24 (μg mL^-1 cm^-2) after modification. The findings of flow cytometry and MTT assay confirmed that the number of dead bacteria was higher on the NSSM-MWCNT surface than that of control. Adsorption models of Freundlich and Langmuir and kinetics models were studied to understand the governing mechanism by which bacteria migrate to the membrane surface.

Conclusion: The cell viability of absorbed bacteria on the NSSM-MWCNT was disrupted in direct physical contact with carbon nanotubes. Then, the dead bacteria were desorbed from the surface of the hydrophilic membrane. The results of this research showed that NSSM-MWCNT containing carbon nanotubes have significant antimicrobial and self-cleaning property that can be used in many biomedical devices without facing the eminent problem of biofouling.

Keywords: alumina anodic membrane; anodizing; anti-biofilm; antibacterial.

Figure 1

FTIR spectrum of membranes: a: NSSM, b: NSSM-OH, c: NSSM-MWCNT. Abbreviations: FTIR, Fourier-transform infrared spectroscopy; MWCNT, multi-walled carbon nanotube; NSSM, nanoporous solid-state membrane.

Figure 2

EDAX point data and EDAX image of membrane (A, B) NSSM, (C, D) NSSM-MWCNT which were anodized in aqueous solutions of acid, 100 V and 25°C. Abbreviations: EDAX, energy dispersive X-ray; MWCNT, multi-walled carbon nanotube; NSSM, nanoporous solid-state membrane.

Figure 3

SEM image of surface and cross-section (A, B) of NSSM and (C, D) NSSM-MWCNT membranes which were anodized in aqueous solutions of acid, 100 V and 25°C. Abbreviations: MWCNT, multi-walled carbon nanotube; NSSM, nanoporous solid-state membrane; SEM, scanning electron microscopy.

Figure 4

AFM: two-dimensional (A and B) three-dimensional images of NSSM, (C) two-dimensional and (D) three-dimensional images of NSSM-MWCNT (500×500 nm), (E) three-dimensional images of NSSM and (F) NSSM-MWCNT (100×100 nm). Abbreviations: AFM, atomic force microscopy; MWCNT, multi-walled carbon nanotube; NSSM, nanoporous solid-state membrane.

Figure 5

WCA and SFE of NSSM and NSSM-MWCNT membranes. Abbreviations: MWCNT, multi-walled carbon nanotube; NSSM, nanoporous solid-state membrane; SFE, surface free energy; WCA, water contact angle.

Figure 6

Surface SEM image of NSSM (A) 5.00 kx, (B) 200 kx, and NSSM-MWCNT (C) 30.00 kx and (D) 50.00 kx after biofilm assay. Abbreviations: E. coli, Escherichia coli; MWCNT, multi-walled carbon nanotube; NSSM, nanoporous solid-state membrane; SEM, scanning electron microscopy; S. aureus, Staphylococcus aureus.

Figure 7

Results flow cytometry analysis (A) NSSM-E. coli, (B) NSSM-S. aureus, (C) NSSM-MWCNT-E. coli and (D) NSSM-MWCNT- S. aureus. Abbreviations: PI, propidium iodide; SSC-H, side scatter height.

Figure 8

Percentage of bacterial viability in membrane specimens. Abbreviations: MWCNT, multi-walled carbon nanotube; NSSM, nanoporous solid-state membrane.

Figure 9

FTIR spectrum of NSSM-MWCNT membrane, which is absorbed by bacteria (1.5×10⁸ CFU/mL). Abbreviations: FTIR, Fourier-transform infrared spectroscopy; MWCNT, multi-walled carbon nanotube; NSSM, nanoporous solid-state membrane.

Figure 10

SEM images of membrane modified with carbon nanotube before (A) and after coming into contact with bacteria (B) and normal E. coli (C). Abbreviations: E. coli, Escherichia coli; SEM, scanning electron microscopy.

Figure 11

Pesudo-first-order (A) and pesudo-second-order (B) kinetic models plot for the absorption of E. coli of 1.5×10⁸ CFU/mL. Abbreviation: E. coli, Escherichia coli.

Figure 12

Isotherm models plot (A) Freundlich and (B) Langmuir for the absorption of E. coli at concentrations of 1.5×10⁸, 10⁷, 10⁶, 10⁵, 10⁴, and 10³ CFU/mL, 13 minutes and flow rate of 0.05 mL/min.