E-Beam Patterned Gold Nanodot Arrays on Optical Fiber Tips for Localized Surface Plasmon Resonance Biochemical Sensing

Electron beam lithography (EBL) was used to directly pattern periodic gold nanodot arrays on optical fiber tips. Localized surface plasmon resonance of the E-beam patterned gold nanodot arrays on optical fiber tips was utilized for biochemical sensing. The advantage of the optical fiber based localized surface plasmon resonance (LSPR) sensors is the convenience to work with and work in harsh environments. An optical fiber tip LSPR refractive index sensor of 196 nm per refractive index unit (RIU) sensitivity has been demonstrated. The affinity sensing property of the fiber tip sensor was demonstrated using biotin/streptavidin as the receptor/analyte. The detection limit for streptavidin was determined to be 6 pM

A reflection-based localized surface plasmon resonance fiber-optic probe for biochemical sensing

We report the fabrication and characterization of an optical fiber biochemical sensing probe based on localized surface plasmon resonance (LSPR) and spectra reflection. Ordered array of gold nanodots was fabricated on the optical fiber end facet using electron-beam lithography (EBL). We experimentally demonstrated for the first time the blue shift of the LSPR scattering spectrum with respected to the LSPR extinction spectrum, which had been predicted theoretically. High sensitivity [195.72 nm/refractive index unit (RIU)] of this sensor for detecting changes in the bulk refractive indices has been demonstrated. The label-free affinity bio-molecules sensing capability has also been demonstrated using biotin and streptavidin as the receptor and the analyte

Nanotrimer enhanced optical fiber tips implemented by electron beam lithography

Here we present a novel fabrication approach that allows for the implementation of sophisticated planar nanostructures with deep subwavelength dimensions on fiber end faces by electron beam lithography. Specifically, we planarize the end faces of fiber bundles such that they are compatible with planar nanostructuring technology, with the result that fibers can be treated in the same way as typical wafers, opening up the entire field of nanotechnology for fiber optics. To demonstrate our approach, we have implemented densely-packed arrays of gold nanotrimers on the end face of 50 cm long standard single mode fibers, showing asymmetrical resonance lineshapes that arise due to the interplay of diffractive coupling of the individual timer response at infrared wavelengths that overlap with the single mode regime of typical telecommunication fibers. Refractive index sensing experiments suggest sensitivities of about 390 nm/RIU, representing the state-of-the-art for such a device type. Due to its unique capability of making optical fibers compatible with planar nanostructuring technology, we anticipate our approach to be applied in numerous fields including bioanalytics, telecommunications, nonlinear photonics, optical trapping and beam shaping

An enhanced LSPR fiber-optic nanoprobe for ultrasensitive detection of protein biomarkers

A miniaturized, localized surface plasmon resonance (LSPR)-coupled fiber-optic (FO) nanoprobe is reported as a biosensor that is capable of label-free, sensitive detection of a cancer protein biomarker, free prostate specific antigen (f-PSA). The biosensor is based on the LSPR at the reusable dielectric-metallic hybrid interface with a robust, gold nano-disk array at the fiber end facet that is directly fabricated using EBL and metal lift-off process. The f-PSA has been detected with a mouse anti-human PSA monoclonal antibody (mAb) as a specific receptor linked with a self-assembled monolayer at the LSPR-FO facet surfaces. Experimental investigation and data analysis found near field refractive index (RI) sensitivity at ~226 nm/RIU with current LSPR-FO nanoprobe, and demonstrated the lowest limit of detection (LOD) at 100 fg/mL (~3 fM) of f-PSA in PBS solutions. The control experimentation using 5 mg/mL bovine serum albumin in PBS and nonspecific surface test shows the excellent specificity and selectivity in the detection of f-PSA in PBS. These results present important progress towards a miniaturized, multifunctional fiber-optic technology that integrates informational communication and sensing function for developing a high performance, label-free, point-of-care (POC) device

Design, implementation and application of nanostructure-enhanced optical fibers

This thesis covers the research topic of nano-plasmonics as well as fiber optics with a studyf ocus on design and implementation of a functional optical fiber tip by integrating nanoscale resonance structure on its facet. Accordingly, the research back groundandstate of the art are generally discussed at the beginning. Since this work is highly related to two distinct optic areas, the fundamentals of both fields would begiven in the following sections.Diese Arbeit beschäftigt sich mit dem Forschungsthema Nanoplasmonik sowie Faseroptik mit einem Schwerpunkt auf dem Design und der Implementierung einer funktionalen Glasfaserspitze durch Integration der nanoskaligen Resonanzstruktur auf ihrer Facette. Dementsprechend werden der Forschungshintergrund und der Stand der Technik in der Regel zu Beginn diskutiert. Da diese Arbeit in hohem Maße mit zwei verschiedenen optischen Bereichen zusammenhängt, werden die Grundlagen beider Bereiche in den folgenden Abschnitten erläutert

Lab-on-fiber technology: a new avenue for optical nanosensors

The "lab-on-fiber" concept envisions novel and highly functionalized technological platforms completely integrated in a single optical fiber that would allow the development of advanced devices, components and sub-systems to be incorporated in modern optical systems for communication and sensing applications. The realization of integrated optical fiber devices requires that several structures and materials at nano- and micro-scale are constructed, embedded and connected all together to provide the necessary physical connections and light-matter interactions. This paper reviews the strategies, the main achievements and related devices in the lab-on-fiber roadmap discussing perspectives and challenges that lie ahead

Off-Axis Microsphere Photolithography Patterned Nanohole Array and Other Structures on an Optical Fiber Tip for Glucose Sensing

Microsphere photolithography (MPL) using off-axis UV exposure is a technique that uses a layer of self-assembled microspheres as an optical mask to project different periodic nanopatterns. This paper introduces MPL as an alternative fabrication technique to pattern complex metasurfaces on an optical single mode fiber tip as a sensor for measuring refractive index. Based on the hexagonal close packing microsphere array, complicated metasurfaces were successfully created by changing the UV illumination angle. Using the same self-assembled microspheres monolayer, multiple UV illumination jets were projected to create multiple hole group patterns. Fiber sensors with three-hole group and four-hole group patterns were fabricated and tested with different glucose concentrations in water. The different concentration solutions have various refractive indexes, which result in the shift of the metasurface resonant wavelength, represented as sensitivity. The testing results show that the three-hole group and four-hole group have the sensitivity of 906 nm per RIU and 675 nm per RIU, respectively. Finite element analysis was used to model the fiber sensor\u27s surrounding with different refractive index solutions. These new pattern metasurface coated fibers\u27 refractive index sensitivity has increased by 40% compared to our previous work, while the technique still provides a cost-effective, flexible, high-throughput fabrication of the fiber sensor

Selective ultrasensitive optical fiber nanosensors based on plasmon resonance energy transfer

The facet of optical fibers coated with nanostructures enable the development of ultraminiature and sensitive (bio)chemical sensors. The reported sensors until now lack of specificity and the fabrication methods offer poor reproducibility. Here, we demonstrate that by transforming the facet of conventional multimode optical fibers onto plasmon resonance energy transfer (PRET) antenna surfaces the specificity issues may be overcome. To do so, a low cost chemical approach was developed to immobilize gold nanoparticles on the optical fiber facet in a reproducible and controlled manner. Our nanosensors are highly selective as PRET is a nanospectroscopic effect that only occurs when the resonant wavelength of the nanoparticles matches that of the target parameter. As an example, we demonstrate the selective detection of picomolar concentrations of copper ions in water. Our sensor is 1,000 times more sensitive than state of the art technologies. An additional advantage of our nanosensors is their simple interrogation; it comprises of a low-power light emitting diode, a multimode optical fiber coupler, and a miniature spectrometer. We believe that the PRET-based fiber optic platform reported here may pave the way of the development of a new generation of ultra-miniature, portable, and hypersensitive and selective (bio)chemical sensors.Gobierno de España, Ministerio de Economia y Competitividad, with Grant No. BIO2016-80417-P. European Union funds: DNASURF (H2020-MSCA-RISE-778001). Departamento de Educación del Gobierno Vasco Grant No. IT1271-19. Fondo Europeo de Desarrollo Regional (FEDER) and the Ministerio de Economia y Competitividad (Spain) under projects PGC2018-101997-B-I00 and RTI2018-094669-B-C31. Departamento de Educación del Gobierno Vasco Grant No. IT933‐16. The authors thank for technical and human support provided by electronic microscopy and material microanalysis services from Advanced Research Facilities (SGIker) of the University of the Basque Country UPV/EHU

Plasmonic Optical Sensors: Performance Analysis and Engineering Towards Biosensing

Surface plasmon resonance (SPR) sensing for quantitative analysis of chemical reactions and biological interactions has become one of the most promising applications of plasmonics. This thesis focuses on performance analysis for plasmonic sensors and implementation of plamonic optical sensors with novel nanofabrication techniques. A universal performance analysis model is established for general two-dimensional plasmonic sensors. This model is based on the fundamental facts of surface plasmon theory. The sensitivity only depends on excitation light wavelength as well as dielectric properties of metal and dielectrics. The expression involves no structure-specified parameters, which validates this formula in broad cases of periodic, quasiperiodic and aperiodic nanostructures. Further analysis reveals the intrinsic relationship between plamonic sensor performance and essential physics of surface plasmon. The analytical results are compared to the sensitivities of previously reported plasmonic sensors in the field. This universal model is a promising qualification criterion for plasmonic sensors. Plasmonic optical sensors are engineered into high-performance on-chip sensors, plasmonic optical fibers and freestanding nanomembranes. (1) Periodic nanohole arrays are patterned on chip by a simple and robust template-transfer approach. A spectral analysis approach is also developed for improving the sensor performance. This sensor is applied to demonstrate the on-chip detection of cardiac troponin-I. (2) Plasmonic optical fibers are constructed by transferring periodic metal nanostructures from patterned templates onto endfaces of optical fibers using an epoxy adhesive. Patterned metal structures are generally extended from nanohole arrays to nanoslit arrays. A special plasmonic fiber is designed to simultaneously implement multimode refractive index sensing with remarkably narrow linewidth and high figure of merit. A real-time immunoassay relying on plasmonic fiber is demonstrated. Plasmonic optical fibers also take advantages of consistent optical responses, excellent stability during fiber bending and capability of spectrum filtering. (3) Large-area freestanding metal nanomembranes are implemented using a novel fabrication approach. The formed transferrable membranes feature high-quality and uniform periodic nanohole arrays. The freestanding nanomembranes exhibit remarkably higher transmission intensity in comparison to the nanohole arrays with same features on the substrate. These three modalities of plasmonic sensors possess different applicability to fulfill various plasmonic sensing tasks in respective scenarios