In-Tae Hwang

Efficient immobilization and patterning of biomolecules on poly(ethylene terephthalate) films functionalized by ion irradiation for biosensor applications.

The surface of a poly(ethylene terephthalate) (PET) film was selectively irradiated with proton beams at various fluences to generate carboxylic acid groups on the surface; the resulting functionalized PET surface was then characterized in terms of its wettability, chemical structure, and chemical composition. The results revealed that (i) carboxylic acid groups were successfully generated in the irradiated regions of the PET surface, and (ii) their relative amounts were dependent on the fluence. A capture biomolecule, anthrax toxin probe DNA, was selectively immobilized on the irradiated regions on the PET surface. Cy3-labeled DNA as a target biomolecule was then hybridized with the probe DNA immobilized on the PET surface. Liver-cancer-specific α-fetoprotein (AFP) antigen, as a target biomolecule, was also selectively immobilized on the irradiated regions on the PET surface. Texas Red-labeled secondary antibody was then reacted with an AFP-specific primary antibody prebound to the AFP antigen on the PET surface for the detection of the target antigen, using an indirect immunoassay method. The results revealed that (i) well-defined micropatterns of biomolecules were successfully formed on the functionalized PET surfaces and (ii) the fluorescence intensity of the micropatterns was dependent mainly on the concentrations of the target DNA hybridized to the probe DNA and the target AFP antigen immobilized on the PET films. The lowest detectable concentrations of the target DNA and target AFP antigen in this study were determined to be 4 and 16 ng/mL, respectively, with the PET film prepared at a fluence of 5 × 10(14) ions/cm(2).

Surface Morphology Control of Polymer Films by Electron Irradiation and Its Application to Superhydrophobic Surfaces

A simple and controllable one-step method to fabricate superhydrophobic surfaces on poly(tetrafluoroethylene) (PTFE) films is developed on the base of electron irradiation. When the thickness of PTFE films is higher than the penetration depth of electron beams, electrical charging occurs at the surface of the films because of the imbalance between the accumulation of incident electrons and the emission of secondary electrons. Local inhomogeneity of charge distribution due to this electrical charging results in the nonuniform decomposition of PTFE molecular bonds. As electron fluence increases, surface morphology and surface roughness of the films are dramatically changed. An extremely rough surface with micrometer-sized pores is produced on the surface of PTFE films by electron irradiation at a fluence higher than 2.5 × 10(17) cm(-2).Because of high surface roughness, the irradiated PTFE films exhibit superhydrophobic property with a water contact angle (CA) greater than 150° at fluences ranging from 4 × 10(17) to 1 × 10(18) cm(-2). The surface morphology and corresponding water CA can be controlled by simply changing the electron fluence. This electron irradiation method can be applicable to the fabrication of superhydrophobic surfaces using other low-surface-energy materials including various fluoropolymers.

Poly(acrylic acid)-Grafted Fluoropolymer Films for Highly Sensitive Fluorescent Bioassays

In this study, a facile and effective method for the surface functionalization of inert fluoropolymer substrates using surface grafting was demonstrated for the preparation of a new platform for fluorescence-based bioassays. The surface of perfluorinated poly(ethylene-co-propylene) (FEP) films was functionalized using a 150 keV ion implantation, followed by the graft polymerization of acrylic acid, to generate a high density of carboxylic acid groups on the implanted surface. The resulting functionalized surface was investigated in terms of the surface density of carboxylic acid, wettability, chemical structure, surface morphology, and surface chemical composition. These results revealed that poly(acrylic acid) (PAA) was successfully grafted onto the implanted FEP surface and its relative amount depended on the fluence. To demonstrate the usefulness of this method for the fabrication of bioassays, the PAA-grafted FEP films were utilized for the immobilization of probe DNA for anthrax toxin, followed by hybridization with Cy3-labeled target DNA. Liver cancer-specific α-feto-protein (AFP) antigen was also immobilized on the PAA-grafted FEP films. Texas Red-labeled secondary antibody was reacted with AFP-specific primary antibody prebound to the AFP antigen using an immunoassay method. The results revealed that the fluorescence intensity clearly depended on the concentration of the target DNA hybridized to the probe DNA and the AFP antigen immobilized on the FEP films. The lowest detectable concentrations of the target DNA and the AFP antigen were 10 fg/mL and 10 pg/mL, respectively, with the FEP films prepared at a fluence of 3 × 10(14) ions/cm(2).

Patterning of biomolecules on a poly(ɛ-caprolactone) film surface functionalized by ion implantation

Biomolecule patterning is important due to its potential applications in biodevices, tissue engineering, and drug delivery. In this study, we developed a new method for a biomolecular patterning on poly(epsilon-caprolactone) (PCL) films based on ion implantation. Ion implantation on a PCL film surface resulted in the formation of carboxylic acid groups. The generated carboxylic acid groups were used for the covalent immobilization of amine-functionalized p-DNA, followed by hybridization with fluorescently tagged c-DNA. Biotin-amine was also covalently immobilized on the carboxylic acid generated PCL surfaces. Successful biotin-specific binding of streptavidin further confirmed the potential of this strategy for patterning of various biomolecules.

Simple and biocompatible micropatterning of multiple cell types on a polymer substrate by using ion implantation.

A noncytotoxic procedure for the spatial organization of multiple cell types remains as a major challenge in tissue engineering. In this study, a simple and biocompatible micropatterning method of multiple cell types on a polymer surface is developed by using ion implantation. The cell-resistant Pluronic surface can be converted into a cell-adhesive one by ion implantation. In addition, cells show different behaviors on the ion-implanted Pluronic surface. Thus this process enables the micropatterning of two different cell types on a polymer substrate. The micropatterns of the Pluronic were formed on a polystyrene surface. Primary cells adhered to the spaces of the bare polystyrene regions separated by the implanted Pluronic patterns. Secondary cells then adhered onto the implanted Pluronic patterns, resulting in micropatterns of two different cells on the polystyrene surface.

Photosensitive polymer brushes grafted onto PTFE film surface for micropatterning of proteins

Surface grafting of photosensitive polymer brushes on a flexible polymer surface was performed using Ar ion irradiation, which generated peroxides on the polymer surface upon exposure to air. These peroxides were utilized as initiators for graft polymerization of a photosensitive diazoketo-functionalized methacrylate monomer. Upon UV light exposure, the diazoketo group was converted into the carboxylic acid group which was used to covalently immobilize amine-functionalized biotin in a patterned fashion. Successful binding of streptavidin to the biotin-linked regions proved the potential of the platform for biomolecular patterning applications on commercial polymer substrates.

Surface modification of Nafion membranes by ion implantation to reduce methanol crossover in direct methanol fuel cells

The surface of Nafion membranes was modified to reduce methanol crossover by ion implantation with proton ions. The methanol crossover of ion-implanted Nafion membranes was reduced without influencing the other properties including the membrane properties. This simple process could offer advantages for direct methanol fuel cells at high methanol concentrations.

Preparation of sulfonated reduced graphene oxide by radiation- induced chemical reduction of sulfonated graphene oxide

We report the preparation of sulfonated reduced graphene oxide (SRGO) by the sulfonation of graphene oxide followed by radiation-induced chemical reduction. Graphene oxide prepared by the well-known modified Hummers method was sulfonated with the aryl diazonium salt of sulfanilic acid. Sulfonated graphene oxide (SGO) dispersed in ethanol was subsequently reduced by γ-ray irradiation at various absorbed doses to produce SRGO. The results of optical, chemical, and thermal analyses revealed that SRGO was successfully prepared by γ-ray irradiation-induced chemical reduction of the SGO suspension. Moreover, the electrical conductivity of SRGO was increased up to 2.94 S/cm with an increase of the absorbed dose.

Electron beam irradiation effects on green biodegradable poly(ϵ-caprolactone) films

To investigate the influence of electron beam irradiation on the properties of poly(ϵ-caprolactone) (PCL), PCL films prepared by solvent casting were irradiated with high-energy electron beams. The irradiated PCL films were investigated in terms of degree of cross-linking, mechanical properties, thermal properties, and biodegradability. The degree of cross-linking of the irradiated PCL films was found to be dependent on the absorption dose. The tensile strength of the irradiated PCL films increased with increasing absorption dose, while their elongation-at-break was reduced. The dynamic mechanical analysis results revealed that the irradiated PCL films had a higher glass transition temperature and a wider rubbery state plateau. The melting and thermal decomposition temperatures of the irradiated PCL films gradually decreased with increasing absorption dose. The results of the enzymatic degradation test revealed that the irradiated PCL films were more slowly degraded than the nonirradiated PCL film. These changes in the properties of the PCL film after irradiation could result from the occurrence of cross-linking and chain scission during electron beam irradiation.

The fabrication of patterned gold nanoparticle arrays via selective ion irradiation and plasma treatment.

A simple and facile method for the patterning of gold nanoparticles (GNPs) was described via selective ion irradiation and oxygen plasma etching. Thin Pluronic films containing HAuCI4 as the precursor of GNPs were selectively irradiated through a pattern mask with 200 keV proton ions to generate GNP-embedded Pluronic patterns. The Pluronic was then removed by an oxygen plasma etching process for the pattern formation of GNPs. Based on the results of the UV-Vis, FE-SEM, and EDX analyses, 50 μm negative-tone line patterns of the GNP-embedded Pluronic were successfully generated at a fluence of less than 1 x 10(16) ions/cm2. The changes in the morphology and elemental composition of the formed GNP-embedded Pluronic patterns with different time periods of oxygen plasma etching were investigated using an FE-SEM with an EDX. The experimental results demonstrated that the patterns of GNPs were effectively generated by the oxygen plasma etching of the formed GNP-embedded Pluronic patterns for 15 min. Furthermore, the XRD results revealed that GNPs in the patterns formed by ion irradiation were further grown during the subsequent oxygen plasma etching.