Fabricating Cost-Effective Nanostructures for Biomedical Applications

In this thesis we described inexpensive alternatives to fabricate nanostructures on planar substrates and provided example applications to discuss the efficiency of fabricated nanostructures. The first method we described is forming large area systematically changing multi-shape nanoscale structures on a chip by laser interference lithography. We analyzed the fabricated structures at different substrate positions with respect to exposure time, exposure angle and associated light intensity profile. We presented experimental details related to the fabrication of symmetric and biaxial periodic nanostructures on photoresist, silicon surfaces, and ion-milled glass substrates. Behavior of osteoblasts and osteoclasts on the nanostructures was investigated. These results suggest that laser interference lithography is an easy and inexpensive method to fabricate systematically changing nanostructures for cell adhesion studies. We also used laser interference lithography to fabricate plasmonic structures. Fabrication details of gold nanodisk arrays were described. Experimental and simulation results show that those structures are suitable to develop highly sensitive plasmonic sensors. As a second fabrication method we described the growth of surface immobilized gold nanoparticles with organometallic chemical vapor deposition (OMCVD) on amine terminated surfaces. Samples fabricated using different deposition times were characterized by UV-Vis spectroscopy and scanning electron microscopy. Particle stability on the samples was tested by washing and rinsing treatments with various organic solvents. The size, interparticle distance, and shape of the gold nanoparticles demonstrated that OMCVD is a simple, economical, and fast way to fabricate surface-bonded and stable gold nanoparticles. The plasmonic properties, the stability of the particles and the biotin-streptavidin test showed that these OMCVD-grown gold nanoparticles are suitable for reproducible, low noise and highly sensitive biosensing applications. We further investigated the similar-to-real-life biosensing capabilities of the OMCVD-grown nanoparticles. Conventional antibody immobilization methods using biotin-streptavidin affinity, introduces additional chemistry and distance between the surface and the recognition sites and decreases the sensitivity. With the new recognition chemistry, epidermal growth factor receptor (EGFR) antibody recognition sites were directly immobilized on AuNP surfaces to decrease the distance between the sensor surface and the recognition sites for detecting EGFR antigens. In comparison with the literature, we obtained increased signal response with further optimization possibilities

Laser Nano-Filament Explosion for Enabling Open-Grating Sensing in Optical Fibre

Embedding strong photonic stopbands into traditional optical fibre that can directly access and sense the outside environment is challenging, relying on tedious nanoprocessing steps that result in fragile thinned fibre. Ultrashort pulsed laser filaments have recently provided a non contact means of opening high aspect ratio nanoholes inside of bulk transparent glasses. This method has been extended here to optical fibre, resulting in high density arrays of laser filamented holes penetrating transversely through the silica cladding and guiding core to provide high refractive index contrast Bragg gratings in the telecommunication band. The point by point fabrication was combined with post-chemical etching to engineer strong photonic stopbands directly inside of the compact and flexible fibre. Fibre Bragg gratings with sharply resolved pi-shifts are presented for high resolution refractive index sensing from n = 1 to 1.67 as the nano-holes were readily wetted and filled with various solvents and oils through an intact fibre cladding.Comment: 21 pages, 12 figure

Surface Plasmon Resonance Sensing Properties of a 3D Nanostructure Consisting of Aligned Nanohole and Nanocone Arrays

Molecular surface plasmon resonance (SPR) sensing is one of the most common applications of an array of periodic nanoholes in a metal film. However, metallic nanohole arrays (NHAs) with low-hole count have lower resolution and SPR sensing performance compared to NHAs with high-hole count. In this paper, we present a compact three-dimensional (3D) plasmonic nanostructure with extraordinary optical transmission properties benefiting from surface plasmon matching and enhanced localized surface plasmon coupling. The 3D nanostructure consisted of a gold film containing a NHA with an underlying cavity and a gold nanocone array (NCA) at the bottom of the cavity. Each nanocone was aligned with the nanohole above and the truncated apex of each nanocone was in close proximity (100 nm) to the gold film. The NHA-NCA structures outperformed conventional NHA structures in terms of bulk sensitivity and Figure of Merit (FOM). Furthermore, the NHA-NCA structure with 525-nm periodicity was capable of sensing streptavidin down to 2 nM exhibiting a 10-fold increase in streptavidin sensitivity compared to conventional NHA structures. The sensitivity and performance of the 3D nanostructure can be further improved by exploiting multiplexing methods in combination with stable light sources and detection systems

A Biosensor based on Periodic Arrays of Gold Nanodisks under Normal Transmission

We present a biosensor based on periodic arrays of gold nanodisks patterned on top of a glass substrate. The sensor’s resonance wavelength, peak linewidth and figure of merit were studied both in experiments and in simulations. We analyzed the dependence of the sensor’s resolution on the inherent figure of merit of the sensor structure and the signal to noise ratio of the detection system. The best achieved refractive index resolution is 1.5×10-4 RIU and the detection limit on and antigen-antibody binding is better than 1 ng/mL

Determination of beam incidence conditions based on the analysis of laser interference patterns

Beam incidence conditions in the formation of two-, three- and four-beam laser interference patterns are presented and studied in this paper. In a laser interference lithography (LIL) process, it is of importance to determine and control beam incidence conditions based on the analysis of laser interference patterns for system calibration as any slight change of incident angles or intensities of beams will introduce significant variations of periods and contrasts of interference patterns. In this work, interference patterns were captured by a He-Ne laser interference system under different incidence conditions, the pattern period measurement was achieved by cross-correlation with, and the pattern contrast was calculated by image processing. Subsequently, the incident angles and intensities of beams were determined based on the analysis of spatial distributions of interfering beams. As a consequence, the relationship between the beam incidence conditions and interference patterns is revealed. The proposed method is useful for the calibration of LIL processes and for reverse engineering applications

Large area periodic, systematically changing, multishape nanostructures by laser interference lithography and cell response to these topographies

The fabrication details to form large area systematically changing multishape nanoscale structures on a chip by laser interference lithography (LIL) are described. The feasibility of fabricating different geometries including dots, ellipses, holes, and elliptical holes in both x- and y- directions on a single substrate is shown by implementing a Lloyd\u27s interferometer. The fabricated structures at different substrate positions with respect to exposure time, exposure angle and associated light intensity profile are analyzed. Experimental details related to the fabrication of symmetric and biaxial periodic nanostructures on photoresist, silicon surfaces, and ion milled glass substrates are presented. Primary rat calvarial osteoblasts were grown on ion-milled glass substrates with nanotopography with a periodicity of 1200 nm. Fluorescent microscopy revealed that cells formed adhesions sites coincident with the nanotopography after 24 h of growth on the substrates. The results suggest that laser LIL is an easy and inexpensive method to fabricate systematically changing nanostructures for cell adhesion studies. The effect of the different periodicities and transition structures can be studied on a single substrate to reduce the number of samples significantly

Dye Distance Mapping using Waveguide Evanescent Field Fluorescence Microscopy and its Application to Cell Biology

Previous studies have measured the distance between cells and the substratum at sites of adhesion via the emission of a fluorescent dye and waveguide methods. Here, we demonstrate a novel approach to measure the position of fluorescent dyes above a waveguide surface in the 10-200 nm distance range throughout an entire area, yielding a 2D dye distance map or a 3D contour plot. The dye is located in a multilayered Langmuir Blodgett (LB) film or in the plasma membrane of a cell. Waveguide evanescent field fluorescence (WEFF) images obtained using two different waveguide modes are employed allowing, with a simple mathematical approach, the calculation of dye distance maps. Ultra-thin steps made using LB technology, adhesion distances and the bending of the plasma membrane between focal adhesions of osteoblastic cells are shown as examples. The errors are discussed

Fabrication of hierarchical moth-eye structures with durable superhydrophobic property for ultrabroadband visual and mid-infrared applications

Multifunctional antireflective coatings have practical applications as important optical components in many fields, particularly for optical devices and imaging systems. However, a good antireflection application in the visible region is often unsatisfactory for mid-infrared devices, and the difficulty in obtaining multiple capabilities simultaneously is one of the main factors limiting their applications. In this work, hierarchical moth-eye structures with superhydrophobicity were fabricated via inductively coupled plasma reactive ion etching (ICP-RIE) using nanodisk-array masks, which were formed by three-beam laser interference lithography (LIL), for improving the ultra-broadband optical properties. The uniform antireflection efficiency, which was close to 1% reflectivity covering over the visible and mid-infrared wavelength range, was exhibited by the moth-eye structures with high-quality pillar arrays. Additionally, irregular nanostructures were tailored onto the top of the pillars to generate hierarchical moth-eye structures for simultaneously obtaining both the superhydrophobic and anticorrosive properties. The fabricated antireflective structures, with the features of self-cleaning and durability, have the advantage of being for long-term use in harsh environments

The ATLAS Data Acquisition and High-Level Trigger: Concept, Design and Status

The Trigger and Data Acquisition system (TDAQ) of the ATLAS experiment at the CERN Large Hadron Collider is based on a multi-level selection process and a hierarchical acquisition tree. The system, consisting of a combination of custom electronics and commercial products from the computing and telecommunication industry, is required to provide an online selection power of 105 and a total throughput in the range of Terabit/sec. This paper introduces the basic system requirements and concepts, describes the architecture of the system, discusses the basic measurements supporting the validity of the design and reports on the actual status of construction and installation