Mr. Yit Lung Khung Profile

Yit Lung Khung

at Flinders Univ

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Publications (3)

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Proceedings Article | 27 December 2007 Paper

Control over wettability via surface modification of porous gradients

Y. Khung, M. Cole, S. McInnes, N. Voelcker

Proceedings Volume 6799, 679909 (2007) https://doi.org/10.1117/12.759377

KEYWORDS: Electrodes, Silicon, Chemistry, Scanning electron microscopy, Etching, Atomic force microscopy, Infrared spectroscopy, Ozone, Platinum, Semiconducting wafers

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The control over surface wettability is of concern for a number of important applications including chromatography, microfluidics, biomaterials, low-fouling coatings and sensing devices. Here, we report the ability to tailor wettability across a surface using lateral porous silicon (pSi) gradients. Lateral gradients made by anodisation of silicon using an asymmetric electrode configuration showed a lateral distribution of pore sizes, which decreased with increasing distance from the electrode. Pore sizes were characterised using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Pore diameters ranged from micrometres down to less than 10 nanometres. Chemical surface modification of the pSi gradients was employed in order to produce gradients with different wetting or non-wetting properties. Surface modifications were achieved via silanisation of oxidised pSi surfaces introducing functionalities including polyethylene glycol, terminal amine and fluorinated hydrocarbon chains. Surface modifications were characterised using infrared spectroscopy. Sessile drop water contact angle measurements were used to probe the wettability in regions of different pore size across the gradient. For the fluorinated gradients, a comparison of equilibrium and dynamic contact angle measurement was undertaken. The fluorinated surface chemistry produced gradients with wettabilities ranging from hydrophobic to near super-hydrophobic whereas pSi gradients functionalised with polyethylene glycol showed graded hydrophilicity. In all cases investigated here, changes in pore size across the gradient had a significant effect on wettability.

Proceedings Article | 27 December 2007 Paper

Preparation of two-directional gradient surfaces for the analysis of cell-surface interactions

Lauren Clements, Yit-Lung Khung, Helmut Thissen, Nicolas Voelcker

Proceedings Volume 6799, 67990W (2007) https://doi.org/10.1117/12.759351

KEYWORDS: Silicon, Polymers, Electrodes, Plasma, Scanning electron microscopy, Chemistry, Atomic force microscopy, Etching, Glasses, Coating

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The ability to evaluate and control the cellular response to substrate materials is the key to a wide range of biomedical applications ranging from diagnostic tools to regenerative medicine. Gradient surfaces provide a simple and fast method for investigating optimal surface conditions for cellular responses such as attachment and growth. By using two orthogonal gradients on the same substrate, a large space of possible combinations can be screened simultaneously. Here, we have investigated the combination of a porous silicon (pSi) based topography gradient with a plasma polymer based thickness gradient. pSi was laterally anodised on a 1.5 × 2.5cm² silicon surface using hydrofluoric acid to form a pore size gradient along a single direction. The resulting pSi was characterised by SEM and AFM and pore sizes ranging from macro to mesoporous were found along the surface. Plasma polymerisation was used to form a thickness gradient orthogonal to the porous silicon gradient. Here, allylamine was chosen as the monomer and a mask placed over the substrate was used to achieve the thickness gradient. The analysis of this chemistry based gradient was carried out using profilometry and XPS. It is expected that orthogonal gradient substrates will be used increasingly for the in vitro screening of materials used in biomedical applications.

Proceedings Article | 19 January 2006 Paper

Porous silicon microparticles as an alternative support for solid phase DNA synthesis

Steven McInnes, Sean Graney, Yit-lung Khung, Nicolas Voelcker

Proceedings Volume 6036, 60361W (2006) https://doi.org/10.1117/12.659972

KEYWORDS: Solids, Silicon, Scanning electron microscopy, Particles, Glasses, Infrared spectroscopy, UV-Vis spectroscopy, Diffuse reflectance spectroscopy, Etching, Sodium

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Current methods to produce short DNA strands (oligonucleotides) involve the stepwise coupling of phosphoramidites onto a solid support, typically controlled pore glass. The full-length oligonucleotide is then cleaved from the solid support using a suitable aqueous or organic base and the oligonucleotide is subsequently separated from the spent support. This final step, albeit seemingly easy, invariably leads to increased production costs due to increased synthesis time and reduced yields. This paper describes the preparation of a dissolvable support for DNA synthesis based on porous silicon (pSi). Initially it was thought that the pSi support would undergo dissolution by hydrolysis upon cleavage of the freshly synthesised oligonucleotide strands with ammonium hydroxide. The ability to dissolve the solid support after completion of the synthesis cycle would eliminate the separation step required in current DNA synthesis protocols, leading to simpler and faster synthesis as well as increased yields, however it was found that the functionalisation of the pSi imparted a stability that impeded the dissolution. This strategy may also find applications for drug delivery where the controlled release of carrier-immobilised short antisense DNA is desired. The approach taken involves the fabrication of porous silicon (pSi) microparticles and films. Subsequently, the pSi is oxidised and functionalised with a dimethoxytrityl protected propanediol to facilitate the stepwise solid phase synthesis of DNA oligonucleotides. The functionalisation of the pSi is monitored by diffuse reflectance infrared spectroscopy and the successful trityl labelling of the pSi is detected by UV-Vis spectroscopy after release of the dimethoxytrityl cation in the presence of trichloroacetic acid (TCA). Oligonucleotide yields can be quantified by UV-Vis spectroscopy.

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