Integrated waveguide and nanostructured sensor platform for surface-enhanced Raman spectroscopy

Limitations of current sensors include large dimensions, sometimes limited sensitivity and inherent single-parameter measurement capability. Surface-enhanced Raman spectroscopy can be utilized for environment and pharmaceutical applications with the intensity of the Raman scattering enhanced by a factor of 106. By fabricating and characterizing an integrated optical waveguide beneath a nanostructured precious metal coated surface a new surface-enhanced Raman spectroscopy sensing arrangement can be achieved. Nanostructured sensors can provide both multiparameter and high-resolution sensing. Using the slab waveguide core to interrogate the nanostructures at the base allows for the emission to reach discrete sensing areas effectively and should provide ideal parameters for maximum Raman interactions. Thin slab waveguide films of silicon oxynitride were etched and gold coated to create localized nanostructured sensing areas of various pitch, diameter, and shape. These were interrogated using a Ti:Sapphire laser tuned to 785-nm end coupled into the slab waveguide. The nanostructured sensors vertically projected a Raman signal, which was used to actively detect a thin layer of benzyl mercaptan attached to the sensors

Low-loss slot waveguides with silicon (111) surfaces realized using anisotropic wet etching

We demonstrate low-loss slot waveguides on silicon-on-insulator (SOI) platform. Waveguides oriented along the (11-2) direction on the Si (110) plane were first fabricated by a standard e-beam lithography and dry etching process. A TMAH based anisotropic wet etching technique was then used to remove any residual side wall roughness. Using this fabrication technique propagation loss as low as 3.7dB/cm was realized in silicon slot waveguide for wavelengths near 1550nm. We also realized low propagation loss of 1dB/cm for silicon strip waveguides

Design, fabrication and optimization of large area chemical sensor based on Surface-enhanced Raman Scattering (SERS) mechanism

In recent years there has been an increasing interest in analysis and identification of complex molecules for the medical diagnostics, pharmaceutical research and homeland security applications. If these molecules are present in high concentration, a technique known as Raman spectroscopy can be utilized. Unfortunately, only one in every 1012 photon incidence on molecule undergoes Raman scattering resulting in weak Raman absorption. An efficient technique to overcome this limitation is to utilize surface-enhanced Raman scattering (SERS) whereby molecules are placed on the surface of nanostructured metallic substrate which performs the function of transducting photons into and out of the molecules. SERS extends the scope of Raman scattering to detect molecules at low concentrations to few/single molecule level. Previously the ‘KlariteTM’ substrate consisting of an inverted array of square based pyramidal nanostructures patterned onto a Silicon substrate has been demonstrated to afford highly reproducible SERS signals with approximately 107 enhancement factor.In this report, the effect of geometrical parameters associated with the inverted pyramidal array on SERS effect for sensing applications was investigated. Geometrical parameters studied include pitch length, pit size, aspect ratio of the base of pyramid and fill factor. 3D computational modelling based on Rigorous Coupled Wave Analysis (RCWA) is used to bridge with theory. From these observations, the geometrical parameters of inverted pyramid nanostructures have been optimized for better sensing ability. A test chip is fabricated for the purpose of performing a matrix experiment, allowing deconvolution of geometrical variables: lattice pitch (1000nm-3000nm), pit size (500nm-2500nm), pit aspect ratio [width to length]. Fabrication steps include electron-beam lithography, anisotropic wet etching and metallization.Computational and experimental reflectometry systems were applied to enable the identification and analysis of a variety of dispersive features including propagating surface plasmons, localized surface plasmons and diffraction dispersion. From the study of inverted pyramid, plasmonic behaviors are observed: 1. the surface plasmon polariton depends strongly on polarization. 2. Highly dispersive features arising from simple surface diffraction effects appear insensitive to polarization state. 3. As the pit size gets bigger, the diffraction efficiency decreases but the wavelength/angular position remain the same. 4. Diffractive features are relatively sharp and clearly defined (narrow bandwidth), and are highly dependent on lattice pitch. Hence they move in wavelength and angle (e.g. highly dispersive) as pitch is varied. These features relate to the coupling of light into or out of the sensor chip. 5. Localized surface plasmons have characteristic of small wavelength shift over wide angular range (low dispersion), and are generally broader in bandwidth. Plasmon features can conclusively be identified over diffractive features by making comparisons between simulations ‘with’ and ‘without’ the top metal coating.In order to derive the optimal geometry for SERS sensor, a highly stable test molecule which is known to form a monolayer coating on gold is required. For this purpose benzenethiol was used as standard in this work. Devices were tested using a Renishaw Invia Raman system. The main wavelength of interest here is 785nm where this laser is readily available and compatible with the end user Raman system. Full details of the optical and Raman measurements are carried out on the silicon test platform. Results show that the averaged SERS enhancement factor was only slightly dependent upon lattice pitch, but was highly dependent on pit size and aspect ratio. Density of the pits plays a further role simply by increasing the number of pits/unit area and so provides extra increase in SERS signal. The experimental data shows this is not simply a surface area dependent effect, but the optimal SERS signal can be obtained by close packing as tightly as possible pits of the optimal size. Minimum spacing (between adjacent pits) of 250nm is found to give the highest SERS enhancement. The optimal aspect ratio was found to be 1:1.2 and the optimal pit size determined to be 1000nm. This new optimized design shows 10-fold improvement in sensitivity compared to current available benchmark Klarite. The study has also explored the possibility of replicating the optimized design to a cost effective and disposable polymer for the purpose of mass production. This was carried out using nanoimprint lithography. The replicated plastic sensor is comparable to the benchmark silicon Klarite. As a proof of principle, the qualitative performance in two demonstrator molecules such as ibuprofen and melamine has been carried out. The disposable plastic sensor was demonstrated for the possibility of dual sensing mechanisms such as surface plasmon resonance (SPR) and surface-enhanced Raman scattering (SERS). The sensitivity of plastic sensor using SPR mechanism is 225.83nm/RIU on thiol molecule. The work has also been carried out for an alternative SERS sensor design by changing the sidewall profile to 90º angle from (100) silicon etched plane. Changing the sidewall profile makes impact on the plasmonic behaviour. The straight sidewalls are favourable to the localized plasmon mode. The structures with slope sidewalls are favourable to both localized and propagating plasmons inside the cavities. This work was conducted as part of the FP7 "PHOTOSENSE" consortium project

Local People Opinion on Urbanization and its impact for Lake Conservation: A Case Study of Aung Pin Le Lake, Mandalay, Myanmar

The research paper examines the Local Peoples Opinion on Urbanization and its impact for Lake Conservation. The study Area was renovated during last Myanmar Kingdom for the beautiful and green scenario and the area was 2.28 square kilometers. At that time the people from this area had not seen the “sea” naturally, so that the people named it “Aung Pin Le” (means sea of success). So, the natural environment is always chassis due to the activities human environment. Moreover, major agent for conserves environment always depends on the local people of that particular area. Applying our educational knowledge in real life, to improve our wisdom on environmental conservation, maintain the History of Aung Pin Le, conservation and protecting and preserving areas. From this research paper, many positive and negative outcomes have been obtained. But mostly were positive outcomes. It is realized that how much local wisdoms effect on environmental conservation. Moreover, it was clearly known that the usefulness of Aung Pin Le lake from its official historical background. It caused to improve the experiences, knowledge, skills of management, communication with people and it has been confident. There is a saying that “Unity is strength”, so it is well noticed the value of unity

3D analysis of surface Plasmon dispersion for SERS sensor based on inverted pyramid nanostructures

Surface enhanced Raman scattering (SERS) can be used to amplify the Raman cross-section of signals by several orders of magnitude, when a mixed photon-Plasmon mode (surface Plasmon polaritons) couples to molecules on a nano textured metallo-dielectric substrate. In this paper we demonstrate a comprehensive 3D computational model based on Rigorous coupled wave analysis (RCWA) for the purpose of analysing propagating and localised surface Plasmon polaritons supported by planar SERS substrates based on periodic array of metal coated inverted pyramidal nanostructures. Although studies [1, 2] have explored the optical properties of inverted square pyramidal pits using simulation and experimentation, there has yet been no investigation performed on rectangular inverted pyramidal pits. Here we perform 3D modelling and simulation on rectangular pit arrays with aspect ratio 1:1.2 over 400nm thick gold. We investigate the effect of incident polarisation and electric-field density within the pits and show that inverted rectangular pyramidal pit array can be used as highly effective SERS and Plasmonic substrates

Polymer waveguide grating couplers for low cost nanoimprinted integrated optics

Waveguide grating couplers permit efficient coupling to planar waveguides, complete with relaxed alignment tolerances and the possibility of wafer scale device testing without cleaving. To date, most solutions have been implemented as 1D gratings in high index contrast waveguides (typically SOI) with high coupling strengths and lateral mode converters. Here, we report the design and optimization of 1D grating couplers in polymer waveguides with much lower index cores (n = 1.8). Basic parameters from grating theory are used as the basis for FDTD simulations scanning over etch depth and grating period. Several optimizations are tested, including top claddings, buried dielectric mirrors, and buried metal mirrors. More than 80% coupling efficiency to air is predicted for a uniform symmetric grating, 20 periods long, with a carefully positioned buried metal reflector. The designs are intended for monolithic integration in polymeric planar lightwave circuits mass-produced by a roll-to-roll nanoimprint lithography process, where metallic mirrors can be safely and successfully incorporated

Integration of nanostructures and waveguide core for surface enhanced Raman spectroscopy: a novel excitation method

Surface Enhanced Raman Spectroscopy (SERS) allows the intensity of Raman scattering to be enhanced by a factor of 106 by placing molecules within a few nm of a rough metal surface. In this paper we investigate a completely different configuration for the excitation mechanism, incorporating an optical waveguide beneath a nano-structured precious metal surface. The pyramidal geometry projects the Plasmon field into free space, thus increasing the cross section of interaction between the analyte molecules and optical fields, thereby increasing device sensitivity. In this arrangement the excitation field comes from underneath and enters the nanostructures at the base. This allows the emission to reach the discrete sensing areas effectively and provides ideal parameters for maximum Raman interactions. Using FDTD modeling methods the waveguide coupled SERS nanostructures were analyzed and its performance at different gold thicknesses was determined. The model investigates efficiency of coupling between the waveguide and surface plasmons, but also investigates spatial localization around sharp features of the geometry. Thin films of aluminum oxide and silicon oxynitride were reactively sputtered and characterized to determine their suitability as the waveguide core material. It was found that silicon oxynitride slab waveguide losses were too high to be considered as the core. The 2D and 3D simulations were based on an aluminum oxide core

Nanostructured surface enhanced Raman scattering sensor platform with integrated waveguide core

We present a planar waveguide based sensor capable of simultaneous surface enhanced Raman scattering (SERS)/surface plasmon resonance (SPR) sensing methodologies. The sensor consists of a nanostructured area etched into a low loss planar waveguide fabricated from silicon oxynitride. The selective deposition of the 25 nm thick gold film on the nanostructured features was applied to create the SERS/SPR active sites. In this work, we adapt the SPR approach, coupling light propagating along the slab waveguide to the nano-textured area from underneath. The shapes of the nanostructures, thickness, and morphology of the gold coating are chosen to be suitable for SERS and SPR. Effects of geometric parameters associated with the nanostructured features such as diameters, length, and pitch were investigated. Detection of Benzyl Mercaptan was accomplished using a 785 nm laser in a SERS configuration excited from the underlying waveguide core. The detection of the analyte was confirmed by normal incident SERS measurements using an InVia Raman spectrometer. The surface enhanced Raman scattering signal from the 25nm thick Au coated nanostructures provided a maximum intensity signal of 104. Using the same device in the SPR sensing arrangement provided a wavelength shift of 25 nm and an average signal to noise ratio of 10 dB to Benzyl Mercaptan. The fabricated sensor can easily be fabricated using nano imprinting into cheap polymer substrates and would provide disposable real-world remote sensing capabilities

Pre-operative pseudothrombocytopenia: terrifying but innocuous

An isolated thrombocytopenia was found in a 47-year old man during pre-operative&nbsp;work-up for his closed radial bone fracture on left forearm after a fall. His platelet count&nbsp;was as low as 14 x 103/&mu;L, but there was no active bleeding and past history of bleeding&nbsp;disorder. The clue to true diagnosis started from careful blood film examination - platelet&nbsp;clumps in blood film. Repeat full blood count tests were requested not only with the usual&nbsp;anticoagulant EDTA (Ethylene diamine tetra-acetic acid) but also with heparin as well as with&nbsp;citrate. EDTA-dependent pseudothrombocytopenia was diagnosed which can be confused&nbsp;with other life-threatening platelet disorders. The operation was successfully done without&nbsp;unusual bleeding.</p