A 20-fold enhancement in sensitivity of absorption based labeled fiber-optic biosensor was achieved using nanogold as reporter compared to conventional fluorescent dyes. This is due to high extinction coefficient and LSPR property of nanogold. © 2014 OSA.

Jitendra Satija

Centre for Nanobiotechnology

Vellore Campus

Punjabi N

Mukherji S.

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Advanced Photonics

Convergence of localized surface plasmon resonance of metal nanoparticles with classical ELISA has emerged as a new class of immunoassays, i.e. plasmonic ELISA, enabling biocatalysis mediated ultrasensitive naked-eye detection of disease biomarkers.

RSC Advances

Plasmonic-ELISA: Expanding horizons

Noble metals in their 'nano' dimensions show unique electromagnetic phenomena, localised surface plasmon resonance, in response to optical excitation. This phenomenon was reported long ago by Michael Faraday in 1850, but applications of these towards sensors and biosensors have occurred only after efforts towards functionalising these nanoparticles with receptor molecules have been successful. The use of nanoparticles and structures has been further invigorated with the increasing interest in surface enhanced Raman scattering. To optimally exploit these electromagnetic effects for optical biosensing, various morphologies of gold, namely rods, stars, core shell, have been tried. This short review traces the recent developments in this area, highlighting a small section of significant reports in this vibrant field of research. © 2015 W. S. Maney & Son Ltd.

Materials Technology

Gold nanoparticles and nanostructures in optical biosensors

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.

Plasmonics

Optimal design for U-bent fiber-optic LSPR sensor probes

In this study, design and fabrication of a novel bent-tapered optical fiber sensor for enhanced Evanescent Wave Absorption (EWA) based sensing application is demonstrated. A combination of bending and tapering acts as a mode converter, which results in high penetration depth of evanescent field. In addition, tapered region of the probe increases the coupling efficiency at the detector end by V-number matching and thus helps in improving the signal to noise ratio significantly. Effect of taper ratios (ranging from 0.17 to 1) was investigated using fluorescein isothiocyanate (FITC) dye as a model analyte, binding directly to the functionalize fiber. Taper ratio of 0.37 showed the highest sensitivity towards FITC, and was found to be 2.4-fold better compared to untapered bent probe of similar length. The larger penetration depth coupled with higher sensitivity will be beneficial for sensing application involving larger analytes e.g. bacteria and virus. © 2013 IEEE.

Proceedings of the International Conference on Sensing Technology, ICST

Novel bent-tapered mode converting multimode optical fiber sensor based on evanescent wave absorption

Integrated optical waveguide sensors are usually fabricated using materials like silicon, silica, SU-8, etc. Their fabrication requires clean room processes which are expensive and time-consuming. We demonstrated the fabrication of PDMS(polydimethylsiloxane) based optical waveguide in non-cleanroom environment using soft lithography technique. A master-mold was fabricated using acralyn. PDMS polymer was chosen for waveguide fabrication, as it provides low refractive index contrast in the sensing region compared to SU-8 for various biosensing application. These PDMS waveguides were found to be five-fold more sensitive than SU-8 waveguides. High sensitivity along with mechanical robustness and ease of fabrication of PDMS waveguides provides a promising and versatile platform for biosensor application. © 2013 SPIE.

Proceedings of SPIE - The International Society for Optical Engineering

Micromolded U-shaped PDMS optical waveguide for biosensing applications

The localized surface plasmon resonance (LSPR) property of gold nanoparticles (GNP) has been exploited in a variety of optical sensor configurations including solution-based bioassays, paper-based colorimetric detection, surface-confined nanoparticle film/array-based sensing, etc. Amongst these, gold nanostructured films are of great interest because of their high stability, good reproducibility, robustness, and cost-effectiveness. The inherent optical characteristics of GNP, are attributed to parameters like size and shape (eg, nanospheres, nanorods, nanostars), eg, LSPR spectral location sensitivity to the local environment, composition (eg, gold-silver or silica-gold nanoshells), sensing volume, mesospacing, and multiplexing. These properties allow sensor tunability, enabling enhanced sensitivity and better performance of these biosensors. Ultrasensitive biosensor designs were realized using gold nanostructured films fabricated by bottom-up as well as top-down approaches. In this review, we describe the past, present, and future trends in the development of GNP-LSPR-based sensors, concentrating on both design (fabrication) and application. In the process, we have discussed various combinations of GNP size and shape, substrate, and application domains. © 2010 Satija et al, publisher and licensee Dove Medical Press Ltd.

Fulltext

Nanotechnology, Science and Applications

Emerging use of nanostructure films containing capped gold nanoparticles in biosensors

The aim of this study is to develop an optical absorbance based biosensor suitable for wide scale use in resource-poor locales. A sensor for sensitive measurement of refractive index (RI) with the help of optical absorbance properties of gold nanoparticles (GNP) coupled to an efficient optical transducer in the form of a U-bent fiber optic probe is described. A U-bent probe was fabricated by a simple procedure. The absorbance due to the localized surface plasmon resonance (LSPR) of fiber-bound GNP was found to be linear to refractive index changes between 1.33 and 1.35. A U-bent probe of 200 μm diameter with a bend radius of 0.75 mm gave rise to a sensitivity of 35 ΔA/RIU at 540 nm. The resolution of the sensor probe was 3.8 × 10-5 RIU. Label-free biosensing was demonstrated using these probes with the help of IgG-anti IgG as bioreceptor-analyte pair. © 2009 Elsevier B.V. All rights reserved.

Journal	Advanced Photonics
Publisher	OSA
Open Access	0