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

Bolus tracking with nanofilter-based multispectral videography for capturing microvasculature hemodynamics

Multispectral imaging is a highly desirable modality for material-based analysis in diverse areas such as food production and processing, satellite-based reconnaissance, and biomedical imaging. Here, we present nanofilter-based multispectral videography (nMSV) in the 700 to 950â €...nm range made possible by the tunable extraordinary-optical- transmission properties of 3D metallic nanostructures. Measurements made with nMSV during a bolus injection of an intravascular tracer in the ear of a piglet resulted in spectral videos of the microvasculature. Analysis of the multispectral videos generated contrast measurements representative of arterial pulsation, the distribution of microvascular transit times, as well as a separation of the venous and arterial signals arising from within the tissue. Therefore, nMSV is capable of acquiring serial multispectral images relevant to tissue hemodynamics, which may have application to the detection and identification of skin cancer

Tunable 3D Plasmonic Cavity Nanosensors for Surface-enhanced Raman Spectroscopy with Sub Femtomolar Limit of Detection

Metallic nanohole arrays (NHAs) with a high hole density have emerged with potential applications for surface-enhanced Raman spectroscopy (SERS) including the detection of analytes at ultra-low concentrations. However, these NHA structures generally yield weak localized surface plasmon resonance (LSPR) which is a prerequisite for SERS measurements. In this work, a compact three-dimensional (3D) tunable plasmonic cavity with extraordinary optical transmission properties serves as a molecular sensor with sub-femtomolar detection. The 3D nanosensor consists of a gold film containing a NHA with an underlying cavity and a gold nanocone array at the bottom of the cavity. These nanosensors provide remarkable surface plasmon polariton (SPP) and LSPR coupling resulting in a significantly improved detection performance. The plasmonic tunability is evaluated both experimentally and theoretically. A SERS limit of detection of 10-16 M for 4-Nitrothiophenol (4-NTP) is obtained along with distribution mapping of the molecule on the 3D plasmonic nanosensor. This results in an improved SERS enhancement factor (EF) of 106 obtained from a femtolitre plasmonic cavity volume. The tunability of these sensors can give rise to a potential opportunity for use in optical trapping while providing SERS sensing of a molecule of interest

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

Development of 3D metallic nano-structures for sensing applications

The interaction of a light with an array of sub-wavelength holes in a thin metal film has given rise to a unique optical property, the so-called extraordinary optical transmission (EOT). Not only does EOT of a sub-wavelength hole array exceed the incident light on the holes, but also could surpass the diffraction limit of the light and provide an intensified electric field at vicinity of the holes. These phenomena have introduced many new possibilities in the field of photonic applications. Surface Plasmon Resonance (SPR) sensing is one of the most common applications of a metallic sub-wavelength hole array structure and it results from EOT spectral shifts due to changes in the refractive index of materials on the top or bottom of the structure. In this thesis, novel sub-wavelength hole array structures with a surface plasmon energy matching property between the top and bottom of the structure have been fabricated and tested in a bulk-SPR sensing application. The numerical and experimental results demonstrated improved SPR sensitivities and higher electric field intensity at the edges of the holes at the EOT wavelength for an energy-matched structure compared to a conventional sub-wavelength hole array structure. However, in order to fabricate the novel structure, two systematic studies were performed to elucidate the effects of various geometrical parameters and different composition and thickness of the adhesion layers on the EOT properties of sub-wavelength hole array structures. Many other applications of a sub-wavelength hole array could potentially benefit from these novel structures due to their enhanced EOT properties over conventional structures

Analysis of Internet Topologies: A Historical View

Abstract — Discovering properties of the Internet topology is important for evaluating performance of various network protocols and applications. The discovery of power-laws and the application of spectral analysis to the Internet topology data indicate a complex behavior of the underlying network infrastructure that carries a variety of the Internet applications. In this paper, we present analysis of datasets collected from the Route Views project. The analysis of collected data shows certain historical trends in the development of the Internet topology. While values of various power-laws exponents have not substantially changed over the recent years, spectral analysis of the normalized Laplacian matrix of the associated graphs reveals notable changes in the clustering of Autonomous System (AS) nodes and their connectivity. I