V. V. R. Sai

Bio: V. V. R. Sai is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topic(s): Optical fiber & Fiber optic sensor. The author has an hindex of 16, co-authored 29 publication(s) receiving 916 citation(s). Previous affiliations of V. V. R. Sai include Indian Institute of Technology Bombay.

Novel U-bent fiber optic probe for localized surface plasmon resonance based biosensor.

Abstract: 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 microm diameter with a bend radius of 0.75 mm gave rise to a sensitivity of 35 DeltaA/RIU at 540 nm. The resolution of the sensor probe was 3.8x10(-5) RIU. Label-free biosensing was demonstrated using these probes with the help of IgG-anti IgG as bioreceptor-analyte pair.

Development of LSPR based U-bent plastic optical fiber sensors

Abstract: 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 (5.57Δ A 560 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.

Evanescent wave absorbance based fiber optic biosensor for label-free detection of E. coli at 280 nm wavelength.

Abstract: A novel label-free technique for the detection of pathogens based on evanescent wave absorbance (EWA) changes at 280 nm from a U-bent optical fiber sensor is demonstrated. Bending a decladded fiber into a U-shaped structure enhances the penetration depth of evanescent waves and hence sensitivity of the probe. We show that the enhanced EWA response from such U-bent probes, caused by the inherent optical absorbance properties of bacterial cells or biomolecules specifically bound to the sensor surface, can be exploited for the detection of pathogens. A portable optical set-up with a UV light emitting diode, a spectrometer and U-bent fiber optic probe of 200 μm core diameter, 0.75 mm bend radius and effective probe length of 1cm demonstrated an ability to detect less than 1000 cfu/ml.

Immobilization of Antibodies on Polyaniline Films and Its Application in a Piezoelectric Immunosensor

Abstract: Conducting polymers, especially polyaniline (PAni), have been extensively used in biosensor applications. A protocol for covalent immobilization of human IgG on polyaniline using glutaraldehyde as the cross-linker is described in this report and utilized in development of a piezoelectric immunosensor. Here, PAni was used as the substrate for immobilization. The electropolymerization parameters were optimized to get suitable thickness and surface morphology of the PAni for obtaining high density and uniformity of immobilized antibodies on the surface of our films. Possible reaction between PAni thin films and glutaraldehyde was explored using FT-IR characterization in grazing angle mode and XPS. The protocol has been characterized with the help of quartz crystal microbalance analysis. An antibody surface density of 4.86 ng/mm2 was obtained. A piezoelectric biosensor developed for detection of IgG with the proposed protocol was capable of differentiating the target analyte concentrations between 500 ng/mL a...

Optimal Design for U-bent Fiber-optic LSPR Sensor Probes

Abstract: 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.

Drug Discovery Today

Abstract: In recent years, tools for the development of new drugs have been dramatically improved. These include genomic and proteomic research, numerous biophysical methods, combinatorial chemistry and screening technologies. In addition, early ADMET studies are employed in order to significantly reduce the failure rate in the development of drug candidates. As a consequence, the lead finding, lead optimization and development process has gained marked enhancement in speed and efficiency. In parallel to this development, major pharma companies are increasingly outsourcing many components of drug discovery research to biotech companies. All these measures are designed to address the need for a faster time to market. New screening methodologies have contributed significantly to the efficiency of the drug discovery process. The conventional screening of single compounds or compound libraries has been dramatically accelerated by high throughput screening methods. In addition, in silico screening methods allow the evaluation of virtual compounds. A wide range of new lead finding and lead optimization opportunities result from novel screening methods by NMR, which are the topic of this review article.

Gold nanorod-based localized surface plasmon resonance biosensors: A review

Abstract: Noble metal nanoparticle-based localized surface plasmon resonance (LSPR) is an advanced and powerful label-free biosensing technique which is well-known for its high sensitivity to the surrounding refractive index change in the local environment caused by the biomolecular interactions around the sensing area. The characteristics of the LSPR effect in such sensors are highly dependent on the size, shape and nature of the material properties of the metallic nanoparticles considered. Among the various types of metallic nanoparticles used in studies employing the LSPR technique, the use of gold nanorods (GNRs) has attracted particular attention for the development of sensitive LSPR biosensors, this arising from the unique and intriguing optical properties of the material. This paper provides a detailed review of the key underpinning science for such systems and of recent progress in the development of a number of LSPR-based biosensors which use GNR as the active element, including an overview of the sensing principle, the synthesis of GNRs, the fabrication of a number of biosensors, techniques for surface modification of GNRs and finally their performance in several biosensing applications. The review ends with a consideration of key advances in GNR-based LSPR sensing and prospects for future research and advances for the development of the GNR-based LSPR biosensors.

Review of plasmonic fiber optic biochemical sensors: improving the limit of detection.

Abstract: This paper presents a brief overview of the technologies used to implement surface plasmon resonance (SPR) effects into fiber-optic sensors for chemical and biochemical applications and a survey of results reported over the last ten years. The performance indicators that are relevant for such systems, such as refractometric sensitivity, operating wavelength, and figure of merit (FOM), are discussed and listed in table form. A list of experimental results with reported limits of detection (LOD) for proteins, toxins, viruses, DNA, bacteria, glucose, and various chemicals is also provided for the same time period. Configurations discussed include fiber-optic analogues of the Kretschmann–Raether prism SPR platforms, made from geometry-modified multimode and single-mode optical fibers (unclad, side-polished, tapered, and U-shaped), long period fiber gratings (LPFG), tilted fiber Bragg gratings (TFBG), and specialty fibers (plastic or polymer, microstructured, and photonic crystal fibers). Configurations involving the excitation of surface plasmon polaritons (SPP) on continuous thin metal layers as well as those involving localized SPR (LSPR) phenomena in nanoparticle metal coatings of gold, silver, and other metals at visible and near-infrared wavelengths are described and compared quantitatively.

Recent advances in polyaniline based biosensors

Abstract: The present paper contains a detailed overview of recent advances relating to polyaniline (PANI) as a transducer material for biosensor applications. This conducting polymer provides enormous opportunities for binding biomolecules, tuning their bio-catalytic properties, rapid electron transfer and direct communication to produce a range of analytical signals and new analytical applications. Merging the specific nature of different biomolecules (enzymes, nucleic acids, antibodies, etc.) and the key properties of this modern conducting matrix, possible biosensor designs and their biosensing characteristics have been discussed. Efforts have been made to discuss and explore various characteristics of PANI responsible for direct electron transfer leading towards fabrication of mediator-less biosensors.

Fiber-Optic Chemical Sensors and Biosensors (2008–2012)

Abstract: ■ CONTENTS Books, Reviews, and Articles of General Interest 488 Sensors for (Dissolved) Gases and Vapors 489 Hydrogen 489 Hydrocarbons 490 Oxygen 491 Ammonia 493 Carbon Dioxide 494 Nitrogen Oxides 494 Vapors of Organic Solvents 495 Sensors for Humidity, Water Fractions, Hydrogen Peroxide, and Hydrazine 495 Humidity 495 Water Fractions 496 Hydrogen Peroxide and Hydrazine 496 Sensors for pH Values, Ions, and Salinity 496 pH Values 496 Ions 497 Salinity and Ionic Strength 499 Sensors for Organic Species 499 Biosensors 500 Immunosensors 500 PNA-Based Biosensors (DNA, Aptamers) 501 Other Affinity Sensors 501 Enzymatic Biosensors 502 Whole Cell Sensors 502 Advanced Optical Sensing Schemes and Materials 503 Author Information 505 Corresponding Author 505 Notes 505 Biographies 505 Acknowledgments 505 References 505