Development of gold enhanced surface plasmon resonance polymer and nanowire waveguides for optical sensing

The recent advances in nanotechnology have created the need for the development of materials and devices with unique properties, suitable for applications in related areas such as nano-electronics, nano-photonics and high sensitivity optical sensing. Nanowires are becoming good candidates for such applications, however, most of the ongoing research is still at the early stage and therefore all the effort in this field is to improve the fabrication techniques, as well as to increase the performance of such devices, by optimizing their key parameters, in order to bring them into the production line. Ormocomp and silicon nanowire waveguides (NWs) are studied and developed as optical waveguides intended to be used in optical sensing applications. The NWs are designed and developed as part of integrated optical devices by having tapered and feed waveguides connected at both the ends. The ormocomp and the silicon NWs are theoretically investigated using a full-vectorial H-field Finite Element Method (FEM). The aim is to obtain high power confinement in the sensing area, which is considered to be the core/cladding interface for the ormocomp NWs and the slot region (low-index area) for the silicon NWs. The modal field and the power confinement of the guided modes that contribute to the enhancement of the sensitivity in the corresponding sensing area of the NWs are studied, with respect to the variation of the refractive index of the cladding material and the operating wavelength. The structure parameters including the width and the height of the NWs are optimized to achieve the maximum possible sensitivity. A biosensor structure incorporating the silicon NWs with horizontal slot structure is also studied theoretically using the full-vectorial H-field FEM. It is designed to detect DNA hybridisation through the change of the effective index of the NW structure. The key parameters, such as power confinement, power density, change in effective index and sensitivity of the fundamental guided optical modes are presented, by optimizing the device parameters of the slot waveguide. Experimental characterisation of the integrated ormocomp NWs is also demonstrated. The integrated optical ormocomp NWs are used to measure the change of effective index when there is a change of refractive index of the material. An evanescent wave coupling technique is exploited for the ormocomp NW to be used as optical sensors. The evanescent field that exists at the core/cladding interface of the NWs can be enhanced by introducing surface plasmon resonance (SPR). The SPR is introduced by coating the integrated ormocomp NWs with a thin gold layer with a thickness of around 50-100 nm. The optical power at the output, the attenuation coefficient of the NWs, the SPR peak wavelengths and their shifts are experimentally extracted over three different cladding materials. The redshift of the supermode coupling between the dielectric mode and the anti-symmetric supermode is observed with higher cladding index and larger metal thickness. The power confinement in the sensing region with the SPR effect is improved by a factor of ten compared to the performance obtained by the un-coated ormocomp NWs

Demonstration of Polarization-Independent Surface Plasmon Resonance Polymer Waveguide for Refractive Index Sensing

The effect of the variation of the refractive index in a gold-coated ormocomp waveguide for sensing application is studied in this paper. The ormocomp waveguide is fabricated by using the nanoimprint method. A waveguide with width and height both equal to 10 μm is coated with 100 nm thick gold using the sputtering technique in order to introduce surface plasmon resonance at the vertical sides and also at the top of the structure. Here, polarization-independent waveguide is achieved by supporting both the plasmonic TE and TM modes and the light confinement in these modes are studied. Supermodes forming from coupling between the fundamental dielectric mode and the plasmonic supermode at the resonance peak are also investigated. This paper presents the numerical simulated results and also their experimental validations. For this structure, there are two dielectric-plasmon supermodes with two resonance peaks separated by 50 nm. A red shift is observed when the refractive index of the cladding material increases. The cladding material includes water (n = 1.333) and iso-propanol solutions with refractive indices of 1.344, 1.351, and 1.365. The gold-coated ormocomp waveguide has sensitivity of about 544.55 nm/RIU with a resolution of 5.3 × 10⁻³ RIU

Realization of a polymer nanowire optical transducer by using the nanoimprint technique

An optical transducer using an integrated optics polymer nanowire is proposed. The nanoimprint technique is used to fabricate an OrmoComp nanowire with 1.0 μm width and 0.5 μm height, but the resulting sidewalls are not perfectly vertical. Maximum sensitivity is achieved by enhancing the evanescent field in the cladding region. The possible mode fields and power confinement of the nanowire are studied with respect to their structural dimensions, the operating wavelength, and the cladding material by using th

Optical Fiber, Nanomaterial, and THz-Metasurface-Mediated Nano-Biosensors: A Review

The increasing use of nanomaterials and scalable, high-yield nanofabrication process are revolutionizing the development of novel biosensors. Over the past decades, researches on nanotechnology-mediated biosensing have been on the forefront due to their potential application in healthcare, pharmaceutical, cell diagnosis, drug delivery, and water and air quality monitoring. The advancement of nanoscale science relies on a better understanding of theory, manufacturing and fabrication practices, and the application specific methods. The topology and tunable properties of nanoparticles, a part of nanoscale science, can be changed by different manufacturing processes, which separate them from their bulk counterparts. In the recent past, different nanostructures, such as nanosphere, nanorods, nanofiber, core–shell nanoparticles, nanotubes, and thin films, have been exploited to enhance the detectability of labelled or label-free biological molecules with a high accuracy. Furthermore, these engineered-materials-associated transducing devices, e.g., optical waveguides and metasurface-based scattering media, widened the horizon of biosensors over a broad wavelength range from deep-ultraviolet to far-infrared. This review provides a comprehensive overview of the major scientific achievements in nano-biosensors based on optical fiber, nanomaterials and terahertz-domain metasurface-based refractometric, labelled and label-free nano-biosensors

Characterization of polymer nanowires fabricated using the nanoimprint method

In this paper, an ormocomp polymer nanowire with possible use in integrated-optics sensing applications is presented. We discuss the structure design, the fabrication process and present results of the simulation and characterization of the optical field profile. Since the nanowires are designed and intended to be used as integrated optics devices, they are attached to tapered and feed waveguides at their ends. The fabrication process in this work is based mainly on the nanoimprint technique. The method assumes a silicon nanowire as an original pattern, and polydimethylsiloxane (PDMS) as thesoft mold. The PDMS mold is directly imprinted on the ormocomp layer and then cured by UV light to form the polymer based nanowire. The ormocomp nanowires are fabricated to have various dimensions of width and length at a fixed 500nm thickness. The length of the nanowires is varied from 250 μm to 2 mm, whereas the width of the structures is varied between 500nm and 1μm. The possible optical mode field profile that occurs in the proposed polymer nanowire design is studied using the H-field finite element method (FEM). In the characterization part, the optical field profile and the intensity at the device output are the main focus of this paper. The various lengths of the nanowires show different characteristics in term of output intensity. An image processing is used to process the image to obtain the intensity of the output signal. A comparison of the optical field and output intensity for each polymer nanowire is also discussed

A Highly Sensitive SPR Refractive Index Sensor Based on Microfluidic Channel Assisted with Graphene-Ag Composite Nanowire

A highly sensitive refractive index (RI) sensor based on a microfluidic channel (MFC) incorporated in a single-mode fiber (SMF), filled with Ag-graphene composite nanowire is presented and analyzed here. The sensing performance and the coupling properties of designed sensor are numerically analyzed by using a full vectorial finite element method (FEM) incorporating amplitude and wavelength interrogation techniques in the detection range varied from ${n_a}$ = 1.330-1.350. The maximum wavelength and amplitude sensitivity are obtained of 13700 nm/RIU and 1026 RIU-1, respectively. Here, the Ag-graphene composite nanowire can not only solve the problem of oxidation but also enhances the sensitivity of the sensor. In addition of high sensitivity, it also provides better performance than other sensing devices based on similar technologies such as Ag nanowire-filled sensors. Moreover, the influences of polishing depth (D), nanowire radius (rn), graphene layer (Lg) and channel size (s) on the designed sensor, are also thoroughly investigated here. The present work can provide a base for designing a real-time, highly sensitivity, remote sensing, and distributed SPR based RI sensor

Recent Advances in Optical Hydrogen Sensor including Use of Metal and Metal Alloys: A Review

Optical sensing technologies for hydrogen monitoring are of increasing importance in connection with the development and expanded use of hydrogen and for transition to the hydrogen economy. The past decades have witnessed a rapid development of optical sensors for hydrogen monitoring due to their excellent features of being immune to electromagnetic interference, highly sensitive, and widely applicable to a broad range of applications including gas sensing at the sub-ppm range. However, the selection of hydrogen selective metal and metal alloy plays an important role. Considering the major advancements in the field of optical sensing technologies, this review aims to provide an overview of the recent progress in hydrogen monitoring. Additionally, this review highlights the sensing principles, advantages, limitations, and future development

Surface plasmon resonance-enhanced light interaction in an integrated ormocomp nanowire

An integrated ormocomp nanowire coated with gold metal layer is proposed and its optical characteristics with the effect of surface plasmon resonance (SPR) are studied. The integrated rib-like nanowire has a trapezoidal shape with sidewall angles of 75°. It is coated with 50 nm gold layer to introduce the SPR and enhance the evanescent field in the sensing region located at the dielectric/metal interface. The possible field modes, the normalized power confinement, and the SPR peak position of the nanowire are studied over the wavelength and the metal thickness by using the full-vectorial H-field FEM in quasi-TM mode. The attenuation coefficient of the nanowire, the SPR peak wavelength, and the wavelength shift is experimentally extracted for three different cladding materials. The redshift of the supermode coupling between the dielectric mode and the anti-symmetric supermode is observed with the higher cladding-index and larger metal thickness. The improvement of the power confinement in the sensing region with the SPR effect is ten times (10×) better than a previous similar study

Optical Fiber, Nanomaterial, and THz-Metasurface-Mediated Nano-Biosensors: A Review

The increasing use of nanomaterials and scalable, high-yield nanofabrication process are revolutionizing the development of novel biosensors. Over the past decades, researches on nanotechnology-mediated biosensing have been on the forefront due to their potential application in healthcare, pharmaceutical, cell diagnosis, drug delivery, and water and air quality monitoring. The advancement of nanoscale science relies on a better understanding of theory, manufacturing and fabrication practices, and the application specific methods. The topology and tunable properties of nanoparticles, a part of nanoscale science, can be changed by different manufacturing processes, which separate them from their bulk counterparts. In the recent past, different nanostructures, such as nanosphere, nanorods, nanofiber, core-shell nanoparticles, nanotubes, and thin films, have been exploited to enhance the detectability of labelled or label-free biological molecules with a high accuracy. Furthermore, these engineered-materials-associated transducing devices, e.g., optical waveguides and metasurface-based scattering media, widened the horizon of biosensors over a broad wavelength range from deep-ultraviolet to far-infrared. This review provides a comprehensive overview of the major scientific achievements in nano-biosensors based on optical fiber, nanomaterials and terahertz-domain metasurface-based refractometric, labelled and label-free nano-biosensors

Nanowire Embedded Micro-Drilled Dual-Channel Approach to Develop Highly Sensitive Biosensor

In this letter, we propose a novel approach to develop a highly sensitive surface plasmon resonance (SPR) based fiber optics biosensor. The sensor comprises a dual-drilled channel (DDC) with gold-nanowire (AuNW) contained in each channel to excite the plasmon modes. The SPR effect between the core guided mode and the surface plasmon polariton (SPP) modes of the DDC is used to evaluate the sensing response with respect to different analytes. The sensing performance, coupling characteristics, and the fabrication tolerance of the sensor are numerically analyzed and characterized by using a full-vectorial Finite Element Method (FEM). The designed sensor shows a minimum sensitivity of 3150 nm/RIU for refractive index (RI) = 1.310. While, the sensor exhibits an extremely high sensitivity varying from 10250 nm/RIU to 90500 nm/RIU for RI varied over the range of 1.370 to 1.400. Various structural parameters, e.g., separation of the channel from the core, the radius of the AuNW, the fabrication tolerance, etc., have been studied in this work. In addition, the possible fabrication steps of such a design have been discussed indicating its simple practical realization