JaeJong Lee

Highly Sensitive Biosensing Using Arrays of Plasmonic Au Nanodisks Realized by Nanoimprint Lithography

We describe the fabrication of elliptical Au nanodisk arrays as a localized surface plasmon resonance (LSPR) sensing substrate for clinical immunoassay via thermal nanoimprint lithography (NIL) and enhancement in the sensitivity of the detection of the prostate-specific antigen (PSA) using the precipitation of 5-bromo-4-chloro-3-indolyl phosphate p-toluidine/nitro blue tetrazolium (BCIP/NBT), catalyzed by alkaline phosphatase. Au nanodisks were fabricated on glass through an unconventional tilted evaporation, which could preserve the thickness of imprinted resists and create an undercut beneficial to the subsequent lift-off process without any damage to pattern dimension and the glass while removing the residual polymers. To investigate the optically anisotropic property of the LSPR sensors, a probe light with linear polarization parallel to and perpendicular to the long axis of the elliptical nanodisk array was utilized, and their sensitivity to the bulk refractive index (RI) was measured as 327 and 167 nm/RIU, respectively. To our knowledge, this is the first application of enzyme-substrate reaction to sandwich immunoassay-based LSPR biosensors that previously suffered from a low sensitivity due to the short penetration depth of the plasmon field, especially when large-sized antibodies were used as bioreceptors. As a result, a large change in local refractive index because of the precipitation on the Au nanodisks amplified the wavelength shift of the LSPR peak in the vis-NIR spectrum, resulting in femtomolar detection limits, which was ∼10(5)-fold lower than the label-free detection without the enzyme precipitation. This method can be extended easily to the other clinical diagnostics with a high sensitivity.

Simulation study on stress and deformation of polymeric patterns during the demolding process in thermal imprint lithography

Thermal imprint lithography or hot embossing is a processing technique using molding to produce surface patterns in polymer resist at micro- and nanoscales. While fast molding is important to improve the yield of the process, the process step that determines the success of imprinting high aspect ratio structures is demolding, a process to separate the mold insert from the patterned resist after conformal molding. In this paper the authors studied the stress and deformation behavior in polymer resist during the cooling and demolding process of thermal imprint lithography via finite element method. A simple model structure of the Si stamp/poly(methyl methacrylate) (PMMA) resist/Si substrate was used for the simulation, assuming that PMMA is viscoelastic. As demolding proceeds, Von Mises stress in the PMMA layer is highly localized in two locations, one at the transition corner zone between the residual layer and the replicated PMMA pattern and the other close to the contact region with the moving stamp edge...

3D molding of hierarchical micro- and nanostructures

We show a simple and effective process to produce large area, hierarchical 3D micro- and nanostructures via a modified hot embossing process, which we name 3D molding. The 3D molding process takes advantage of both a hard mold from hot embossing and the flexibility of a thin, elastomeric intermediate stamp from soft lithography. Using this method, we have demonstrated the formation of various micro- and nanostructures in non-planar microscale structures including microchannels and step surfaces. The ability to produce micro/nanopatterns within microchannels will have potential applications in bioanalytic micro/nanofluidic devices by allowing for the manipulation of a broader range of surface properties and thus control over surface interactions with biomaterials flowing through the microfluidic channels.

Human alpha-fetal protein immunoassay using fluorescence suppression with fluorescent-bead/antibody conjugate and enzymatic reaction.

The aim of the study was to develop a simple and rapid immunoassay using fluorescent microbeads and enzyme-substrate reactions to measure alpha-fetal protein (AFP) concentrations. We demonstrated the functionality of the fluorescent immunosensor using antibody-conjugated fluorescent latex beads (AB-FLBs) and horseradish peroxidase (HRP) to catalyze a reaction, where the products would precipitate and suppress the fluorescence of AB-FLBs. First, the AB-FLBs were incubated with antigen, biotinylated antibodies (bABs), and streptavidin-HRP (SAv-HRP) to form a sandwich-type immunoreaction. The mixture was then filtered through a membrane to concentrate the beads on a small area. After washing to remove unbound bABs and SAv-HRP, a chromogenic HRP substrate and H2O2 were added to form precipitates on the FLB surface. The suppression of the fluorescence was measured with a fluorescent image analyzer system. Under optimized conditions, AFP could be measured at concentrations as low as 1 pg mL(-1) with a dynamic range up to 100 ng mL(-1).

Low-thermal-budget and selective relaxation of stress gradients in gold micro-cantilever beams using ion implantation

The stress gradient of gold micro-cantilever beams induced during dry-release in oxygen plasma is quantitatively studied, and the relaxation of the stress gradient by He and N2 ion implantation is investigated. An analytic model considering the finite anchor stiffness of a step-up anchor and the geometry of the beam cross-section is constructed to evaluate the induced stress gradient. Various measurements are carried out to verify the effectiveness of ion implantation in relaxing the stress gradient.

Electrochemical DNA biosensor with nanometer scale using nano-patterning lithography machine

Major challenges in the field of electrochemical DNA hybridization biosensors are the immobilization of DNA and the detection of hybridization signals. The method of DNA immobilization using the nano-patterning machine and detection for DNA hybridization signals has been proposed. Here, two gold electrodes were deposited on SiO2 layer and the gap between the electrodes was fabricated by electron beam lithography. 3-aminopropyltriethoxysilane (APTES) solution was selectively treated to immobilize the amino-modified oligonucleotides onto the SiO2 layer between the electrodes. The recognition of DNA hybridization was accomplished by metallic aggregation of nano-particles. The results showed that DNA is immobilized with nanometer scales and the method for detecting hybridization signals is useful. The experimental results were verified by I-V curves. The conductance between two electrodes changed with the density of the Au-nanoparticles immobilized onto the oxide layer. These results can be applied to the DNA chip and the multi-functional sensors which will be researched in the further study.

The fabrication scheme of a high resolution and high aspect ratio UV-nanoimprint mold

We propose a new scheme of fabricating molds for UV-nanoimprint lithography (UV-NIL) that is both high resolution and has a high aspect ratio. The scheme involves the utilization of a hydrogen silsesquioxane (HSQ) electron beam resist for high resolution patterning and the sputter-deposited alpha-Si layer that defines the high-aspect-ratio mold pattern obtained from the high etch selectivity between the HSQ and the alpha-Si. We obtained high resolution line patterns and dot patterns with feature sizes of 40 nm and 25 nm, respectively. The aspect ratio of the patterns was about 3.5 for line patterns and about 5 for dot patterns. These molds also demonstrate successful UV-nanoimprint patterning.

The UV-Nanoimprint Lithography with Multi-head Nanoimprinting Unit for Sub-50nm Half-pitch Patterns

Nanoimprint lithography is a promising technology to produce sub-50nm half-pitch features on silicon chips. The contact-based nano lithography, such as thermal and/or UV nano-imprint, is well-known as the next generation lithography. Especially, the UV nano-imprint lithography technology has advantages of the simple process, low cost, high replication fidelity, and relatively high throughput. To achieve nano-imprinting process, nano-imprinting lithography equipment must have required some multi-functional units which are imprinting head, self-alignment wafer stage, overlay and alignment system for multi-layer process, master with sub-50nm half-pitch patterns, and anti-vibration unit, etc

3-D Integration of Micro-Gratings Into Bio-Analytical Devices

The ability to produce three-dimensional micro- and nanoscale features at low cost is desirable for many applications such as microfluidic devices, micro and nanomechanical systems, photonic crystals and diffractive optics. For example, micro and nanostructures patterned on the sidewalls of microfluidic devices allow better control over the wetting behavior of fluids flowing through the microchannel. In this study we report on a simple and effective process that allows direct integration of microstructures into a microfluidic device via a modified molding process. The key for the process is to use a thin poly(dimethylsiloxane) layer having microgratings as an intermediate stamp which was placed between a brass mold insert with microfluidic features and a PMMA sheet, which was followed by hot embossing. Using this method, we have demonstrated the formation of micropatterns on non-planar surfaces and at the sidewalls of microfluidic devices, as confirmed using scanning electron microscopy. The designed process will fill the gap in current micro- and nanofabrication technologies in that most of the technologies allow for patterning only on planar substrates.Copyright

Nanoimprint lithography with a focused laser beam for the fabrication of nanopatterned microchannel molds

We present a process based on nanoimprint lithography for the fabrication of a microchannel mold having nanopatterns formed at the bottoms of its microchannels. A focused laser beam selectively cures the resist in the micrometer scale during nanoimprint lithography. Nanopatterns within the microchannels may be used to control microfluidic behavior.