Karen S. L. Chong

In situ formation of anti-bacterial silver nanoparticles on cotton textiles

The efficiency of chemical biocides as anti-bacterial agents is well documented and there are various methods to incorporate these bactericidal agents onto commonly used substrates, such as textile materials. Silver is known for its excellent inhibitory properties due to its direct action on the morphology of the cellular membrane of the bacteria. The use of silver is, however, limited due to its cost and challenges to incorporate silver into relevant products and materials with minimal loss of efficiency. In this article, we present an ‘in situ’ (one-pot) process for the formation of silver nanoparticles onto cotton fabrics in an aqueous media. Silver nanoparticles are bonded onto the cotton fibers via a surface modification that involves the use of 3-aminopropyltriethoxysilane. This enables the improved bonding of silver nanoparticles onto the textiles, thus mitigating the challenges associated with the leaching of silver into eluents and wash-offs. Anti-bacterial efficiency testing was also carried out on the textiles with more than 99% reduction of bacterial growth within 1 h of contact. Additionally, the textiles have also demonstrated continued anti-bacterial efficiency after prolonged period of washing. Thus, our method can potentially be applied to large-scale manufacturing of anti-bacterial textiles with potential uses in biomedical and consumer clothing industries.

Patterned microcontainers as novel functional elements for µTAS and LOC

Using nanoimprint lithography, arrays of highly ordered patterns of polyelectrolyte multilayer microcapsules consisting of alternating layers of poly(allylamine hydrochloride) and poly(sodium 4-styrene sulfonate) have been achieved. Anchoring the capsules on a pre-patterned substrate facilitates the utilization of their various capabilities in lab-on-a chip devices. In this paper we have demonstrated a very effective method to entrap soft capsules into surface cavities. Supported microcapsules were applied as the depots for loading and storage of macromolecular cargo (glucose oxidase and peroxidase) and as preserved microvessels for the cascade of enzymatic reactions. The loading of capsules was achieved under a pre-determined pH environment. This development is potentially useful for the realization of novel multianalytical systems for catalytic, bio-affinity and pH detection with protected sensing molecules.

Fabrication of Self-Cleaning, Reusable Titania Templates for Nanometer and Micrometer Scale Protein Patterning

The photocatalytic self-cleaning characteristics of titania facilitate the fabrication of reuseable templates for protein nanopatterning. Titania nanostructures were fabricated over square centimeter areas by interferometric lithography (IL) and nanoimprint lithography (NIL). With the use of a Lloyds mirror two-beam interferometer, self-assembled monolayers of alkylphosphonates adsorbed on the native oxide of a Ti film were patterned by photocatalytic nanolithography. In regions exposed to a maximum in the interferogram, the monolayer was removed by photocatalytic oxidation. In regions exposed to an intensity minimum, the monolayer remained intact. After exposure, the sample was etched in piranha solution to yield Ti nanostructures with widths as small as 30 nm. NIL was performed by using a silicon stamp to imprint a spin-cast film of titanium dioxide resin; after calcination and reactive ion etching, TiO2 nanopillars were formed. For both fabrication techniques, subsequent adsorption of an oligo(ethylene glycol) functionalized trichlorosilane yielded an entirely passive, protein-resistant surface. Near-UV exposure caused removal of this protein-resistant film from the titania regions by photocatalytic degradation, leaving the passivating silane film intact on the silicon dioxide regions. Proteins labeled with fluorescent dyes were adsorbed to the titanium dioxide regions, yielding nanopatterns with bright fluorescence. Subsequent near-UV irradiation of the samples removed the protein from the titanium dioxide nanostructures by photocatalytic degradation facilitating the adsorption of a different protein. The process was repeated multiple times. These simple methods appear to yield durable, reuseable samples that may be of value to laboratories that require nanostructured biological interfaces but do not have access to the infrastructure required for nanofabrication.

Large Area Directed Self-Assembly of Sub-10 nm Particles with Single Particle Positioning Resolution

Directed self-assembly of nanoparticles (DSA-n) holds great potential for device miniaturization in providing patterning resolution and throughput that exceed existing lithographic capabilities. Although nanoparticles excel at assembling into regular close-packed arrays, actual devices on the other hand are often laid out in sparse and complex configurations. Hence, the deterministic positioning of single or few particles at specific positions with low defect density is imperative. Here, we report an approach of DSA-n that satisfies these requirements with less than 1% defect density over micrometer-scale areas and at technologically relevant sub-10 nm dimensions. This technique involves a simple and robust process where a solvent film containing sub-10 nm gold nanoparticles climbs against gravity to coat a prepatterned template. Particles are placed individually into nanoscale cavities, or between nanoposts arranged in varying degrees of geometric complexity. Brownian dynamics simulations suggest a mechanism in which the particles are pushed into the template by a nanomeniscus at the drying front. This process enables particle-based self-assembly to access the sub-10 nm dimension, and for device fabrication to benefit from the wealth of chemically synthesized nanoparticles with unique material properties.

Directed self-assembly of sub-10 nm particle clusters using topographical templates

Directed self-assembly of nanoparticles (DSA-n) is an approach that creates suitable conditions to capture nanoparticles randomly dispersed in a liquid and position them into predefined locations on a solid template. Although DSA-n is emerging as a potential bottom-up patterning technique to build nanostructures using nanoparticles of various sizes, geometries and material compositions, there are still several outstanding challenges. In this paper, we focus on the DSA-n of sub-10 nm particles using topographical templates to guide them into 1D and 2D ordered arrays. The process mechanism leading DSA-n at sub-10 nm size scale has been reviewed and experimental evidence of the impact of the template on the positioning both individual and clusters of particles with low level of structure defects have also been demonstrated. Furthermore, by controlling the drying direction of the liquid within polygonal traps, we are also able to tune the spacing between the trapped nanoparticle clusters. This self-structuring phenomenon is of crucial importance for various applications such as plasmonics and charge transport within quantum circuits, whereby the coupling effects are highly dependent on the size of the nanoparticles and their separation.

Scalable nanoimprint patterning of thin graphitic oxide sheets and in situ reduction

This article presents a scalable technique to precisely deposit and pattern graphitic oxide (GO) flakes onto a SiO2/Si or glass substrate. A blanket coating of GO was first applied from a colloidal solution onto an amine-functionalized SiO2/Si substrate. The amine termination was used to enhance the adhesion of GO sheets to the substrate. A poly(methyl methacrylate) (PMMA) etch mask was patterned via nanoimprint lithography on top of the GO coating. An oxygen plasma etch was then used to remove GO from areas unprotected by the PMMA mask. The PMMA mask was then dissolved by solvent lift-off technique leaving behind GO lines. GO lines down to 250 nm have been demonstrated. Reduction in hydrazine, followed by annealing in hydrogen ambient, increases the conductivity of the patterned GO lines. This technique can enable large-scale fabrication of electronic devices and sensors based on patterned GO sheets.

Recessed area patterning via nanoimprint lithography

Three-dimensional structures in the channels of a patterned substrate are typically fabricated via a variety of approaches that include a combination of soft lithography and multiple photolithographic steps which can be complex and time consuming. Moreover, the design of a three-dimensional hierarchical template to carry out the direct recessed imprinting of polymers at the recessed area would be complicated and costly. To overcome this shortcoming, we report a method to fabricate a three-dimensional template that is capable of carrying out a direct recessed area imprint via the use of a polymer material. A sequential nanoimprinting process was used to first fabricate the template. A primary imprint was carried out to emboss micron-sized primary features onto a polymer template after which a secondary imprinting process was then carried out to imprint smaller nanoscale features onto the primary features thereby creating three-dimensional or hierarchical features on the polymer template. The template with ...

High-resolution, high-aspect-ratio iridium–nickel composite nanoimprint molds

Nanoimprint molds are traditionally made from silicon. Silicon molds suffer from distinct disadvantages as they are brittle, prone to damage, scratch easily, and can only be used in a planar format. This has limited their use in higher throughput systems where flexible molds are required such as in roll-to-roll and roll-to-plate systems. Nickel (Ni) molds, which are now de-rigueur in both batch and roller nanoimprint processes, can be used to address these problems, but fabrication and durability issues limit their availability and effectiveness in production. In this report, the authors introduce a fabrication route that has the potential to overcome the fabrication, quality, and wear problems of Ni molds. The new process relies on atomic layer deposition to form a smooth and high-aspect ratio patterned layer of iridium (Ir) on a Ni substrate. A large area nanohole array mold was fabricated using displacement Talbot lithography to demonstrate this process. The authors show the use of such composite molds...