Optical bio-sensing devices based on etched fiber Bragg gratings coated with carbon nanotubes and graphene oxide along with a specific dendrimer

We demonstrate that etched fiber Bragg gratings (eFBGs) coated with single walled carbon nanotubes (SWNTs) and graphene oxide (GO) are highly sensitive and accurate biochemical sensors. Here, for detecting protein concanavalin A (Con A), mannose-functionalized poly(propyl ether imine) (PETIM) dendrimers (DMs) have been attached to the SWNTs (or GO) coated on the surface modified eFBG. The dendrimers act as multivalent ligands, having specificity to detect lectin Con A. The specificity of the sensor is shown by a much weaker response (factor of similar to 2500 for the SWNT and similar to 2000 for the GO coated eFBG) to detect non specific lectin peanut agglutinin. DM molecules functionalized GO coated eFBG sensors showed excellent specificity to Con A even in the presence of excess amount of an interfering protein bovine serum albumin. The shift in the Bragg wavelength (Delta lambda(B)) with respect to the lambda(B) values of SWNT (or GO)-DM coated eFBG for various concentrations of lectin follows Langmuir type adsorption isotherm, giving an affinity constant of similar to 4 x 10(7) M-1 for SWNTs coated eFBG and similar to 3 x 10(8) M-1 for the GO coated eFBG. (C) 2014 Elsevier B.V. All rights reserved.

Reversible and irreversible pH induced conformational changes in self-assembled weak polyelectrolyte multilayers probed using etched fiber Bragg grating sensors

Polyelectrolytes are charged polymer species which electrostatically adsorb onto surfaces in a layer by layer fashion leading to the sequential assembly of multilayer structures. It is known that the morphology of weak polyelectrolyte structures is strongly influenced by environmental variables such as pH. We created a weak polyelectrolyte multilayer structure (similar to 100 nm thick) of cationic polymer poly-allylamine hydrochloride (PAH) and an anionic polymer poly-acrylic acid (PAA) on an etched clad fiber Bragg grating (EFBG) to study the pH induced conformational transitions in the polymer multilayers brought about by the variation in charge density of weak polyelectrolyte groups as a function of pH. The conformational changes of the polyelectrolyte multilayer structure lead to changes in optical density of the adsorbed film which reflects in the shift of the Bragg wavelength from the EFBG. Using the EFBG system we were able to probe reversible and irreversible pH induced transitions in the PAH/PAA weak polyelectrolyte system. (C) 2014 Elsevier B.V. All rights reserved.

A Brief Overview of the Recent Bio-Medical Applications of Fiber Bragg Grating Sensors

Fiber Bragg Grating (FBG) sensors have become one of the most widely used sensors in the recent times for a variety of applications in the fields of aerospace, civil, automotive, etc. It has been recently realized that FBGs and etched FBGs can play an important role in biomedical applications. This article provides a brief overview of the recent advancements in the application of FBG sensors in bio-mechanical, bio-sensing and bio-medical fields.

Radial arterial compliance measurement by fiber Bragg grating pulse recorder

In the present work, we report a novel, in vivo, noninvasive technique to determine radial arterial compliance using the radial arterial pressure pulse waveform (RAPPW) acquired by fiber Bragg grating pulse recorder (FBGPR). The radial arterial compliance of the subject can be measured during sphygmomanometric examination by the unique signatures of arterial diametrical variations and the beat-to-beat pulse pressure acquired simultaneously from the RAPPW recorded using FBGPR. This proposed technique has been validated against the radial arterial diametrical measurements obtained from the color Doppler ultrasound. Two distinct trials have been illustrated in this work and the results from both techniques have been found to be in good agreement with each other.

Highly Sensitive Carbon Nanotubes Coated Etched Fiber Bragg Grating Sensor for Humidity Sensing

The sensing of relative humidity (RH) at room temperature has potential applications in several areas ranging from biomedical to horticulture, paper, and textile industries. In this paper, a highly sensitive humidity sensor based on carbon nanotubes (CNTs) coated on the surface of an etched fiber Bragg grating (EFBG) sensor has been demonstrated, for detecting RH over a wide range of 20%-90% at room temperature. When water molecules interact with the CNT coated EFBG, the effective refractive index of the fiber core changes, resulting in a shift in the Bragg wavelength. It has been possible to achieve a high sensitivity of similar to 31 pm/% RH, which is the highest compared with many of the existing FBG-based humidity sensors. The limit of detection in the CNT coated EFBG has been found to be similar to 0.03 RH. The experimental data shows a linear response of Bragg wavelength shift with increase in humidity. This novel method of incorporating CNTs on to the FBG sensor for humidity sensing has not been reported before.

Investigations on pressure and thickness profiles in carbon fiber-reinforced polymers during vacuum assisted resin transfer molding

Systematic experiments have been carried out by monitoring the in-situ pressure and thickness profiles for three different configurations, viz., flat plate, flat plate with a central circular hole, and an L-section using vacuum assisted resin transfer molding (VARTM) process. The effect of anisotropy on resin flow has been quantified by considering uni-directional carbon fiber preforms with 0 degrees and 90 degrees orientation to the flow direction for each configuration. A quasi-isotropic 45 degrees/0 degrees/-45 degrees/90 degrees](S) layup has also been included for flat plate case. Additionally, the study has been extended to understand the effect of using high permeability medium for each configuration. Fluid pressure profiles and thickness variation profiles have been obtained using an array of pressure sensors and linear variable differential transformers for each configuration. Experimental data reveal that anisotropy (due to changing fiber orientations), configuration, and gravity significantly change fluid pressure and displacement fields obtained during VARTM.

Effect of Anisotropy of Fibers on the Stress-Strain Response of Fiber-Reinforced Soil

Reinforcing soil with fibers is a useful method for improving the strength and settlement response of soil. The soil and fiber characteristics and their interaction are some of the major factors affecting the strength of reinforced soil. The fibers are usually randomly distributed in the soil, and their orientation has a significant effect on the behavior of the reinforced soil. In the paper, a study of the effect of anisotropic distribution of fibers on the stress-strain response is presented. Based on the concept of the modified Cam clay model, an analytical model was formulated for the fiber-reinforced soil, and the effect of fiber orientation on the stress-strain behavior of soil was studied in detail. The results show that, as the inclination of fibers with the horizontal plane increased, the contribution of fibers in improving the strength of fiber-reinforced soil decreased. The effect of fibers is maximum when they are in the direction of extension, and vice versa. (C) 2014 American Society of Civil Engineers.

Sensitive detection of C-reactive protein using optical fiber Bragg gratings

An accurate and highly sensitive sensor platform has been demonstrated for the detection of C-reactive protein (CRP) using optical fiber Bragg gratings (FBGs). The CRP detection has been carried out by monitoring the shift in Bragg wavelength (Delta lambda(B)) of an etched FBG (eFBG) coated with an anti-CRP antibody (aCRP)-graphene oxide (GO) complex. The complex is characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. A limit of detection of 0.01 mg/L has been achieved with a linear range of detection from 0.01 mg/L to 100 mg/L which includes clinical range of CRP. The eFBG sensor coated with only aCRP (without GO) show much less sensitivity than that of aCRP-GO complex coated eFBG. The eFBG sensors show high specificity to CRP even in the presence of other interfering factors such as urea, creatinine and glucose. The affinity constant of similar to 1.1 x 10(10) M-1 has been extracted from the data of normalized shift (Delta lambda(B)/lambda(B)) as a function of CRP concentration. (C) 2014 Elsevier B.V. All rights reserved.

Nanomaterials coated multiplexed fiber Bragg grating for multiparameter sensing

Fiber Bragg Grating (FBG) sensors have been extensively used for strain and temperature sensing. However, there is still a need to measure multiple environmental parameters with a single sensor system. We demonstrate a multiplexed FBG sensor with various nano materials (polyallylamine-amino-carbon-nanotube, carbon nanotubes, polyelectrolyte and metals) coated onto the surface of the core/cladding FBG for sensing multiple environmental parameters such as pH (64 pm/pH), protein concentration (5 pm/mu g/ml), temperature (15 pm/degrees C), humidity (31 pm/% RH), gas concentration (7 pm/1000 ppm), and light intensity (infrared: 33 pm/mW, visible: 12 pm/mW and UV: 1 pm/mW) utilizing the same FBG based platform.

Pulse transit time differential measurement by fiber Bragg grating pulse recorder

The present study reports a noninvasive technique for the measurement of the pulse transit time differential (PTTD) from the pulse pressure waveforms obtained at the carotid artery and radial artery using fiber Bragg grating pulse recorders (FBGPR). PTTD is defined as the time difference between the arrivals of a pulse pressure waveform at the carotid and radial arterial sites. The PTTD is investigated as an indicator of variation in the systolic blood pressure. The results are validated against blood pressure variation obtained from a Mindray Patient Monitor. Furthermore, the pulse wave velocity computed from the obtained PTTD is compared with the pulse wave velocity obtained from the color Doppler ultrasound system and is found to be in good agreement. The major advantage of the PTTD measurement via FBGPRs is that the data acquisition system employed can simultaneously acquire pulse pressure waveforms from both FBGPRs placed at carotid and radial arterial sites with a single time scale, which eliminates time synchronization complexity. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Study on effect of optical wavelength on photo induced strain sensitivity in carbon nanotubes using fiber Bragg grating

In this work, the role of optical wavelength on the photo induced strain in carbon nanotubes (CNT) is probed using a Fiber Bragg Grating (FBG), upon exposure to infrared (IR) (21 mu epsilon mW(-1)) and visible (9 mu epsilon mW(-1)) radiations. The strain sensitivity in CNT is monitored over a smaller range (10(-3) to 10(-9) epsilon) by exposing to a low optical power varying in the range 10(-3) to 10(-6) W. In addition, the wavelength dependent response and recovery periods of CNT under IR (tau(rise) = 150 ms, tau(fall) = 280 ms) and visible (tau(rise) = 1.07 s, tau(fall) = 1.18 s) radiations are evaluated in detail. This study can be further extended to measure the sensitivity of nano-scale photo induced strains in nano materials and opens avenues to control mechanical actuation using various optical wavelengths.

Non-invasive pressure monitoring by hoop strain using Fiber Bragg Grating sensor

Non-invasive, real-time dynamic monitoring of pressure inside a column with the aid of Fiber Bragg Grating (FBG) sensor is presented in the present work. A bare FBG sensor is adhered on the circumference of a pressure column normal to its axis, which has the ability to acquire the hoop strain induced by the pressure variation inside the column. Pressure induced hoop strain response obtained using FBG sensor is validated against the pressure measurements obtained from conventional pressure gauge. Further, a protrusion setup on the outer surface of the column has been proposed over which a secondary FBG sensor is bonded normal to its axis, in order to increase the gauge length of this FBG sensor. This is carried out in order to validate the variation in sensitivity of the protrusion bonded FBG sensor compared to the bare FBG sensor bonded over the surface. A comparative study is done between the two FBG sensors and a conventional pressure gauge in order to establish the capacity of FBG sensor obtained hoop strain response for pressure monitoring inside the column.

Ag+-induced reverse vesicle to helical fiber transformation in a self-assembly by adjusting the keto-enol equilibrium of a chiral salicylideneaniline

A new chiral amphiphilic salicylideneaniline bearing a terminal pyridine was synthesized. It formed reverse vesicles in toluene. The addition of Ag+, however, reversibly transforms these reverse vesicles into left-handed nanohelices accompanied by spontaneous gel formation at room temperature.

Ultra sensitive NO2 gas detection using the reduced graphene oxide coated etched fiber Bragg gratings

We report a simple and highly sensitive methodology for the room temperature NO2 gas sensing using reduced graphene oxide (RGO) coated clad etched fiber Bragg grating (eFBG). A significant shift (>10 pm) is observed in the reflected Bragg wavelength (lambda(B)) upon exposing RGO coated on the surface of eFBG to the NO2 gas molecules of concentration 0.5 ppm. The shift in Bragg wavelength is due to the change in the refractive index of RGO by charge transfer from the adsorbing NO2 molecules. The range of NO2 concentration is tested from 0.5 ppm to 3 ppm and the estimated time taken for 50% increase in Delta lambda(B) ranges from 20 min (for 0.5 ppm) to 6 min (for 3 ppm). (C) 2015 Elsevier B.V. All rights reserved.