Atomic layer deposition-based functionalization of materials for medical and environmental health applications

Abstract

Nanoporous alumina membranes exhibit high pore densities, well-controlled and uniform pore sizes, as well as straight pores. Owing to these unusual properties, nanoporous alumina membranes are currently being considered for use in implantable sensor membranes and water purification membranes. Atomic layer deposition is a thin-film growth process that may be used to modify the pore size in a nanoporous alumina membrane while retaining a narrow pore distribution. In addition, films deposited by means of atomic layer deposition may impart improved biological functionality to nanoporous alumina membranes. In this study, zinc oxide coatings and platinum coatings were deposited on nanoporous alumina membranes by means of atomic layer deposition. PEGylated nanoporous alumina membranes were prepared by self-assembly of 1-mercaptoundec-11-yl hexa(ethylene glycol) on platinum-coated nanoporous alumina membranes. The pores of the PEGylated nanoporous alumina membranes remained free of fouling after exposure to human platelet-rich plasma; protein adsorption, fibrin networks and platelet aggregation were not observed on the coated membrane surface. Zinc oxide-coated nanoporous alumina membranes demonstrated activity against two waterborne pathogens, Escherichia coli and Staphylococcus aureus. The results of this work indicate that nanoporous alumina membranes may be modified using atomic layer deposition for use in a variety of medical and environmental health applications.

Figure 1.

Plan-view scanning electron micrograph of a nanoporous alumina membrane following atomic layer deposition of 8 nm platinum coating. Images were obtained from (a) the large pore side of the membrane and (b) the small pore side of the membrane.

Figure 2.

(a) Cross-sectional scanning electron micrograph obtained from a cleaved specimen of a nanoporous alumina membrane following atomic layer deposition of an 8 nm platinum coating. (b) High-resolution scanning electron micrograph at the middle of the pore shows a partially continuous platinum coating. (c) High-resolution scanning electron micrograph near the large pore edge shows a continuous platinum coating.

Figure 3.

High-resolution scanning electron micrograph at the middle of the pore shows the island structure of the partially continuous platinum coating.

Figure 4.

Plan-view scanning electron micrograph of a PEGylated, platinum-coated (coating=8 nm) 20 nm pore size nanoporous alumina membrane.

Figure 5.

Fourier transform infrared spectrum of a PEGylated, platinum-coated, titanium-coated silicon wafer. Scale bar, 500 nm.

Figure 6.

The 24 h MTT viability assay data for the PEGylated, platinum-coated (coating=8 nm) 20 nm pore size nanoporous alumina membrane, the platinum-coated (coating=8 nm) 20 nm pore size nanoporous alumina membrane and the uncoated 20 nm pore size nanoporous alumina membrane. Data were standardized to the uncoated membrane control. The PEGylated, platinum-coated membrane and the platinum-coated membrane demonstrated lower viability than the uncoated membrane.

Figure 7.

(a) Plan-view scanning electron micrograph of a PEGylated, platinum-coated (coating=8 nm) 20 nm pore size nanoporous alumina membrane after treatment with human platelet-rich plasma. (b) Energy-dispersive X-ray analysis spectrum for the PEGylated, platinum-coated nanoporous alumina membrane after treatment with human platelet-rich plasma. Protein adsorption, fibrin networks and platelet aggregation were not observed on the surface of the platelet-rich plasma-exposed membrane. The pores largely remain free of fouling. (Reproduced with kind permission from Adiga et al. (2008), fig. 2. Copyright Springer Science+Business Media.)

Figure 8.

(a) Plan-view scanning electron micrograph of a platinum-coated (coating=9 nm) 20 nm pore size nanoporous alumina membrane after treatment with human platelet-rich plasma. (b) Energy-dispersive X-ray analysis spectrum for the platinum-coated nanoporous alumina membrane after treatment with human platelet-rich plasma. Protein adsorption and pore fouling were observed on the surface of the platelet-rich plasma-exposed membrane. Sodium chloride crystals were identified on the scanning electron micrograph; sodium and chlorine were noted on the energy-dispersive X-ray spectrum.

Figure 9.

(a) Plan-view scanning electron micrograph of an uncoated 20 nm pore size nanoporous alumina membrane after treatment with human platelet-rich plasma. (b) Energy-dispersive X-ray analysis spectrum for the uncoated nanoporous alumina membrane after treatment with human platelet-rich plasma. Protein adsorption and pore fouling were observed on the surface of the platelet-rich plasma-exposed membrane. Sodium chloride crystals were identified on the scanning electron micrograph; sodium and chlorine were noted on the energy-dispersive X-ray spectrum.

Figure 10.

Plan-view scanning electron micrograph of a zinc oxide-coated (coating= 5 nm) 100 nm pore size nanoporous alumina membrane.

Figure 11.

Cross-sectional scanning electron micrographs obtained from a cleaved specimen of a nanoporous alumina membrane following atomic layer deposition of a 5 nm zinc oxide coating.

Figure 12.

X-ray diffraction pattern for a zinc oxide-coated (coating= 5 nm) nanoporous alumina membrane, which contains peaks that correspond to hexagonal zincite.

Figure 13.

(a) X-ray photoelectron spectrum of an uncoated 100 nm pore size nanoporous alumina membrane. (b) X-ray photoelectron spectrum of a zinc oxide-coated (coating=5 nm) 100 nm pore size nanoporous alumina membrane.

Figure 14.

The 24 h MTT viability assay data for the uncoated 100 nm pore size nanoporous alumina membrane and the zinc oxide-coated (coating=5 nm) 100 nm pore size nanoporous alumina membrane. Data were standardized by the uncoated membrane control. The zinc oxide-coated membranes demonstrated higher viability than the uncoated membrane.

Figure 15.

Light microscopy images of agar plating assay results after 24 h of incubation. Materials were examined on Luria–Bertani agar plates, which were inoculated with E. coli. (a) Uncoated 100 nm pore size nanoporous alumina membrane without light exposure. (b) Zinc oxide-coated (coating= 5 nm) 100 nm pore size nanoporous alumina membrane without light exposure. (c) Uncoated 100 nm pore size nanoporous alumina membrane under continuous light exposure. (d) Zinc oxide-coated (coating= 5 nm) 100 nm pore size nanoporous alumina membrane under continuous light exposure.

Figure 16.

Light microscopy images of agar plating assay results after 24 h of incubation. Materials were examined on tryptic soy agar plates, which were inoculated with S. aureus. (a) Uncoated 100 nm pore size nanoporous alumina membrane without light exposure. (b) Zinc oxide-coated (coating= 5 nm) 100 nm pore size nanoporous alumina membrane without light exposure. (c) Uncoated 100 nm pore size nanoporous alumina membrane under continuous light exposure. (d) Zinc oxide-coated (coating= 5 nm) 100 nm pore size nanoporous alumina membrane under continuous light exposure.