The refractive index (RI) sensitivity of a localized surface plasmon resonance (LSPR)-based fiber-optic probes is dependent on surface coverage of gold nanoparticles (GNP), fiber core diameter, and probe geometry. For U-bent LSPR fiber-optic probes, which demonstrated an order higher absorption sensitivity over straight probes, bend diameter and probe length may also have a significant influence on the sensitivity. This study on U-bent fiber-optic LSPR probes is aimed at optimizing these parameters to obtain highest possible RI sensitivity. RI sensitivity increases linearly as a function of surface coverage of GNP in the range of 2–22%. U-bent fiber-optic probes made of 200-, 400-, and 600-μm fiber core diameter show optimum bend diameter value as ∼1.4 mm. In addition, RI sensitivity is almost the same irrespective of fiber core diameter demonstrating flexibility in choice of the fiber and ease in optical coupling. The length of the probe preceding and succeeding the bend region has significantly less influence on RI sensitivity allowing miniaturization of these probes. In addition to these experimental studies, we present a theoretical analysis to understand the relative contribution of evanescent wave absorbance of GNP and refractive losses in the fiber due to GNP, towards the RI sensitivity. © Springer Science+Business Media New York 2013.

Sai V V Raghavendra

Department of Applied Mechanics

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Plasmonics

This study presents an in situ growth technique to develop highly sensitive plasmonic fiber optic sensors with an excellent control over the plasmonic properties of gold (AuNPs) and silver nanoparticles (AgNPs). Here, we exploit the dual functionality of the U-bent fiber optic sensor (FOS) probes, where the probe acts as, firstly, the substrate for nanoparticles’ growth and, secondly, an invaluable tool to monitor as well as control the gold and silver seed binding to the surface amine groups and subsequently their growth in real time by means of the evanescent wave absorbance (EWA) spectral response. Au and Ag seeds (&lt; 5&nbsp;nm) with a peak absorbance at 510 and 390&nbsp;nm, respectively, were used. The NP growth kinetics from the probes for different seed densities with a peak EWA response of 0.05, 0.1, and 0.15&nbsp;optical density (OD) were observed in the presence of the respective metal precursor, cetyltrimethylammonium bromide (CTAB), and ascorbic acid. In comparison with AuNP grown FOS, a significant anisotropic growth was observed for AgNP with a redshift and spectral width as high as 215&nbsp;nm and 425&nbsp;nm, respectively, for a peak EWA response of 2.0&nbsp;OD. The localized surface plasmon resonance (LSPR) activity of the AuNPs and AgNP grown FOS probes was evaluated for seed density of 0.1&nbsp;OD. These proof-of-the-concept studies show significantly high RI sensitivity and surface-enhanced Raman scattering (SERS) enhancement factor for AgNP probes at 15.8 ΔA/RIU (for 22 AgNPs/μm2) and 1.3 × 107, respectively, in comparison with 18.9 ΔA/RIU (for 1424 AuNPs/μm2) and 1.1 × 106, respectively, for AuNP FOS probes. In addition, these plasmonic probes were stable in organic solvent (hexane) but its stability was deteriorated in alkaline solution (1&nbsp;M NaOH). © 2019, Springer Science+Business Media, LLC, part of Springer Nature.

Controlled In Situ Seed-Mediated Growth of Gold and Silver Nanoparticles on an Optical Fiber Platform for Plasmonic Sensing Applications

This study presents design and development of evanescent wave absorbance based U-bent plastic optical fiber (POF) probe with high sensitivity and its applications to refractive index (RI) sensing. The probes were fabricated by a controlled decladding procedure to remove the fluorinated polymer without damaging the poly methyl methacrylate (PMMA) core and a simple and scalable fabrication technique to obtain POF U-bent probes of desired geometry. U-bent probes of fiber diameter from 250 to 1000 μm were fabricated and optimum bend diameter for each fiber diameter was investigated. The sensitivity was found to be maximum when the bend diameter of the probe varies from 2 to 3 times the fiber diameter. Probes with 500 μm core and 1.25 mm bend diameter showed highest sensitivity (5.57ΔA560 nm/ΔRIU) in the visible region to RI changes from 1.33 to 1.47 with a resolution better than 1 milli RI units. Furthermore, U-bent probes were amine functionalized and coated with gold nanoparticles to obtain a localized surface plasmon resonance (LSPR) based RI sensor that has an 8-fold improvement in RI sensitivity, hence extending their applicability to plasmonic biosensing. © 2016 Elsevier B.V. All rights reserved.

Sensors and Actuators, B: Chemical

Development of LSPR based U-bent plastic optical fiber sensors

This study demonstrates a simple evanescent wave absorbance based sensing scheme for plasmonic sandwich immunoassay with the help of U-bent fiber probes as transducers. High absorbance sensitivity of the U-bent probes (200 μm core and 1.5 mm bend diameter) is exploited for sensitive detection of a small number of gold nanoparticles (AuNP) labels bound to the probe for the first time. Using 13 nm AuNP labels conjugated with recognition antibodies, picomolar detection limit (2 pM or 0.3 ng/ml) for human immunoglobulin (HIgG) is achieved. The absorbance sensitivity and dynamic range were 0.019 A530nm/log (ng/ml) and 1-105 ng/ml respectively. Nonspecific adsorption (NSA) of labels is minimized to less than 2% by PEGylation. The ease in U-bent probe fabrication and simple optoelectronic instrumentation consisting of an LED and a fiber optic spectrometer could facilitate extensive use of U-bent probes for several biosensing applications. © 2015 Elsevier B.V. All rights reserved.

Evanescent wave absorbance based U-bent fiber probe for immunobiosensor with gold nanoparticle labels

Journal of Nanoscience and Nanotechnology

Bimetallic Hollow Nanostructures for Colorimetric Detection of Picomolar Level of Mercury

Fluorescence microscopy is one of the important instruments used in research and clinical laboratories on an everyday basis due to its wide range of applications ranging from a diagnostic tool to a molecular imaging device. However, the high cost, complex instrumentation, and requirement of sophisticated facilities limit its availability to school and college students, especially in developing and underdeveloped countries. In this work, we report the design and development of a slide-like portable total internal reflection fluorescence (TIRF) adapter, which can be integrated easily with Foldscope (a paper microscope) to observe and capture the fluorescence images using any smartphone. The adapter consists of a battery-powered LED (light source), a small piece of multimode optical fiber, a slide-like 3-D printed waveguide platform to hold the optical fiber and light emitting diode (LED) at an appropriate position. The potential of the adaptor is validated by capturing the fluorescence images of two most commonly used dyes i.e. fluorescein isothiocyanate (FITC) and rhodamine-B, after being immobilized on amine-functionalized optical fiber probe. Further, this adaptor is successfully used to demonstrate (i) Förster resonance energy transfer phenomenon by employing FITC dye as donor and gold nanoparticles as quencher moiety and (ii) fluorescence bioassay by observing antigen-antibody interactions using human immunoglobulin G as the receptor and FITC-tagged goat anti-human immunoglobulin G as analyte. The inexpensive, portable and user-friendly TIRF adapter is a potential alternative to conventionally used fluorescence microscopes, especially for the school and college students and in resource-constrained clinical laboratories. © 2019 IEEE.

IEEE Sensors Journal

Total Internal Reflection Fluorescence Foldscope Adapter: Design, Fabrication and Applications

Sensors and Actuators B: Chemical

Wavelength-based localized surface plasmon resonance optical fiber biosensor

IEEE Photonics Technology Letters

Fiber Optic Refractometer Based on Cladding Excitation of Localized Surface Plasmon Resonance

Localized Surface Plasmon Resonance-Based Fiber Optic U-Shaped Biosensor for the Detection of Blood Glucose

U-bend optical fiber probes have been shown to be very responsive to refractive index variations around the core, which makes them ideally suited for biosensor applications. Similar U-shaped polymer waveguides have also been fabricated using standard micro-fabrication technology. In the present study, suitable bend radii for such U-shaped embedded polymer waveguide probes have been determined for bio/chemical sensing applications. Although the effect of bend radii have been studied earlier for U-bend optical fiber sensors, such an investigation has not yet been performed for embedded bent waveguides. A single step fabrication procedure was performed to pattern SU-8 photo resist into semicircular C-shaped waveguides (of various bending diameters) interfacing a microchannel network and ending in fiber-to-waveguide coupler structures. The refractive index (RI) sensitivity was found to double as the bending radius was reduced from 2 to 1 mm, however the interaction length did not have any effect on RI sensitivity. The evanescent absorbance per unit length was also found to double, when the bend radius was reduced from 2 to 1 mm. Finally, the efficacy of these 1 mm bending diameter embedded waveguides as evanescent wave absorbance based immuno-biosensors was studied by immobilizing HIgG molecules on the waveguides and allowing FITC tagged GaHIgG molecules to interact with them. © 2012 Elsevier B.V. All rights reserved.

Journal	Data powered by TypesetPlasmonics
Publisher	Data powered by TypesetSpringer New York LLC
ISSN	15571955
Open Access	No