Search

In this article, synthesis of white-light-emitting, highly stable carbon dots (CDs) using a colloidal synthesis technique is reported. It has been observed that the use of a non-coordinating solvent plays a vital role in the successful fabrication of highly stable CDs. Dilution-independent emissive behavior in CDs is achieved. Excitation-energy-dependent emissive behavior is observed in CDs. However, by surface passivating the CD core by using hexadecylamine (HDA), excitation wavelength dependence of emission is successfully minimized. Surface-functionalized CDs (SFCDs) show blue to green light tunable emission with the change in synthesis conditions. HDA also plays an important role in achieving dilution-independent emission in SFCDs. Furthermore, the carbon dots synthesized are highly inert, and their emission spectra are unaffected on exposure to an open atmosphere for as long as 9 days. A new class of highly crystalline carbon dots called ``carbon onion rings'' is reported.

Thin film transistor (TFT) active matrix backplanes are used in large area electronic systems, such as displays and image sensors. With backplanes being fabricated on wearable and flexible substrates, the possibilities of operational faults in backplanes have increased. These faults could either be hard faults, such as line opens or shorts or could be softer faults, such as time dependent variations in the TFT transfer characteristics. Real time diagnosis of these faults require built-in-self-test systems. While many such systems have been demonstrated to diagnose hard faults, an easily realizable system to identify soft faults, such as variations in transistor transconductance remain an open challenge. In this paper, we discuss a system that extracts the transconductance by charging and then discharging the pixel capacitor at various gate voltages for an active matrix liquid crystal display backplane. This permits a plot of the time averaged current versus the gate voltage from which the spatial variation of transconductance can be extracted. The details of the design are discussed and a proof of concept with a $3\times 4$ amorphous silicon backplane is demonstrated.

The pumping of fluids into microfluidic channels has become almost an unavoidable operation in all microfluidic applications. Such a need has seen an outburst of several techniques for pumping, out of which the majority of techniques involve complicated fabrication, as they require the introduction of electrodes, valves, piezoelectric materials, acoustic transducers, etc., into the microfluidic device. In addition to the complexity, this also escalates the cost incurred per device. Further, the use of stable external power supplies to produce such a pumping action adds to the bulkiness of the pumps, making them unsuitable for point-of-care diagnostic (POCD) applications. This paper reports a technique of pumping that is simple to realize and does not require external electric/magnetic power, but exploits the elastic properties of materials to achieve the pumping action. This mechanism of pumping ensured the cost per pump to less than 4 USD and can be used for at least 500 times. Several simulations, validation, and characterization experiments were performed on the developed pump to establish its functionality and suitability for use in POCD applications.

Graphical abstract, Highlights • FBGET is novel, non-invasive, and easy to mount eye tracking methodology. • FBGET can be utilized as a point of care device. • FBGs are electrically and chemically inert, hence suitable for biomedical sensing. • FBGET tracks both eyes simultaneously eliminating time synchronization complexity. • FBGET can facilitate diagnosis of ophthalmological/neurological disorders., Eye movement evaluation is vital for diagnosis of various ophthalmological and neurological disorders. The present study proposes a novel, noninvasive, wearable device to acquire the eye movement based on a Fiber Bragg Grating (FBG) Sensor. The proposed Fiber Bragg Grating Eye Tracker (FBGET) can capture the displacement of the eyeball during its movements in the form of strain variations on a cantilever. The muscular displacement generated by the eyeball over the lower eyelid, by its swiveling action while moving the gaze on a target object, is converted into strain variations on a cantilever. The developed FBGET is investigated for dynamic tracking of the eye-gaze movement for various actions of the eye such as fixations, saccades and main sequence. This approach was validated by recording the eye movement using the developed FBGET as well as conventional camera-based eye tracker methodology simultaneously. The experimental results demonstrate the feasibility and the real-time applicability of the proposed FBGET as an eye tracking device. In conclusion, the present study illustrates a novel methodology involving displacement of lower eyelid for eye tracking application along with the employment of FBG sensors to carry out the same. The proposed FBGET can be utilized in both clinical and hospital environment for diagnostic purposes owing to its advantages of wear-ability and ease of implementation making it a point of care device.

A highly sensitive, selective, and rapid interference green synthesis based determination of potential milk adulterant melamine has been reported here. Melamine is a nitrogenous compound added to milk for mimicking proteins, consumption of which leads to kidney stones and renal failures. Melamine interacts with ascorbic acid (AA) through strong hydrogen-bonding interactions, thus resulting in an interference/interruption in the formation of silver (Ag) nanoparticles which was confirmed by UV-Vis spectroscopy and Transmission Electron Microscopy (TEM). The corresponding benchmark validations for melamine spiked milk samples were performed using High Performance Liquid Chromatography (HPLC). This interference in the formation of Ag nanoparticles resulted in color change that varies with concentration of melamine, thereby enabling in-situ rapid sensing of melamine from milk to a lower limit of 0.1 ppm with a linear correlation coefficient of 0.9908. (C) 2016 Elsevier B.V. All rights reserved.

Multi-scan waveguides have been inscribed in GeS2 glass sample with different pulse energies and translation speeds. Mechanical and structural changes on GeS2 binary glass in response to irradiation to 1047 nm femto-second laser pulses have been investigated. The optical characterization of these waveguides has been done at 1550 nm of laser wavelength and the material response to laser exposure is characterized by both nanoindentation studies and micro-Raman spectroscopy. Nanoindentation investigations show a decrease in hardness (H) and elastic modulus (E) upon laser irradiation. The change in E and H are found to be varying with the translational speed, pulse energy and hence the net-fluence at the sample. These changes are correlated with variations in the Raman response of photo-exposed glass which is interpreted in terms of structural modifications made by the laser inscriptions to the glassy network. The mechanical behavior and local structural changes on waveguide writing is found to be dependent on net-fluence and it is correlated with the preparation conditions like melt temperature and cooling rate. (C) 2017 Elsevier B.V. All rights reserved.

This paper presents a method to construct Mathieu stability plot for any arbitrary toroidal ion trap mass analyser. The proposed method is demonstrated on two toroidal ion trap mass analyser geometries. Two additional studies have also been carried out. These include prediction of ion secular frequency and ion trajectories at resonances in these traps. In this numerical study, toroidal multipole coefficients of the respective traps are first evaluated and these are used for computing Mathieu parameters, a and q. These Mathieu parameters are used for constructing the stability plot, predicting secular frequency of ion motion and evaluating nonlinear resonances. The stability regions of both the traps considered in this paper are qualitatively similar to the corresponding plot of the linear ion trap mass analyser. There are, however two significant differences. First, the stability plots for toroidal ion trap mass analysers have prominent resonances. Second the apices of the stability plots of the toroidal ion trap mass analysers are different from those of the linear ion trap mass analyser. The secular frequency obtained using the Mathieu parameters in this paper agrees well with those obtained numerically, except close to the stability boundaries. Finally, the prominent nonlinear resonances have been identified as beta(r) = 2/3 and beta(r) = 2/3 in both the traps. In one of the two traps there is an additional prominent nonlinear resonance at beta(r) + beta(z) =1. (C) 2016 Elsevier B.V. All rights reserved.

In this article, we report on the development of indicator-impregnated agarose sensor films for colorimetric estimation of the pH of different standard buffer solutions and urine samples. In contrast to the conventional paper-based dipstick method, the presented method employs dried agarose that was infused with a chemical indicator, which when exposed to the test sample results in an appropriate chromogenic outcome. The color change was then quantified by the smart camera system. The divulged instrument has been calibrated with standard buffers and also tested with clinical urine samples. The systematic study was conducted to characterize the performance of the presented technique, such as interplate variations, time variations, volume variations, and shelf life study of agarose sensor films for the commercial viability of such a technique. The employed method is competent enough to bring a change in the paradigm of dipstick method from being qualitative estimation to quantitative, manual detection to automated, and a subjective approach of diagnosis to an objective one. The technique presented here has potential application in the field of point-of-care diagnostics with high fidelity, multiplexing, and robust quantitative estimation.

Portable microfluidic diagnostic devices, including flow cytometers, are being developed for point-of-care settings, especially in conjunction with inexpensive imaging devices such as mobile phone cameras. However, two pervasive drawbacks of these have been the lack of automated sample preparation processes and cells settling out of sample suspensions, leading to inaccurate results. We report an automated blood sample preparation unit (ABSPU) to prevent blood samples from settling in a reservoir during loading of samples in flow cytometers. This apparatus automates the preanalytical steps of dilution and staining of blood cells prior to microfluidic loading. It employs an assembly with a miniature vibration motor to drive turbulence in a sample reservoir. To validate performance of this system, we present experimental evidence demonstrating prevention of blood cell settling, cell integrity, and staining of cells prior to flow cytometric analysis. This setup is further integrated with a microfluidic imaging flow cytometer to investigate cell count variability. With no need for prior sample preparation, a drop of whole blood can be directly introduced to the setup without premixing with buffers manually. Our results show that integration of this assembly with microfluidic analysis provides a competent automation tool for low-cost point-of-care blood-based diagnostics.

In this paper, we present the fabrication and characterization of molybdenum microheaters for high-temperature gas sensing applications. The surface morphology of dc magnetron sputtered molybdenum thin films was characterized by scanning electron microscopy and atomic force microscopy. The suspended membrane microheater consumed 104 mW to reach a maximum temperature of 800 degrees C and showed an absolute thermal resistance of 7.2 degrees C/mW. Thermal distribution patterns over the active heating area were recorded using FLIR camera. It showed a temperature gradient of 1.18 % from the center of the microheater to its periphery. The thermal and mechanical stabilities of the microheater were analyzed, and its membrane failure at higher operating temperatures was prevented. The microheater membrane deformation at different temperatures was characterized using optical profilometer, and its maximum value was found to be 16.25 mu m at 800 degrees C. The microheater response to a pulse, continuous pulse train, and constant dc voltages was characterized. Its response and recovery times are in the order of 19 and 34 ms, respectively. It showed a stable temperature with a negligible resistance drift (0.96%) over a period of 600 h. The TiO2 thin film integrated molybdenum microhotplate-based MEMS gas sensor response for CO (5000 ppb) was measured at different operating temperatures (300 degrees C-700 degrees C).

Separating the particles from the liquid component of sample solutions is important for several microfluidic-based sample preparations and/or sample handling techniques, such as plasma separation from whole blood, sheath-free flow focusing, particle enrichment etc. This paper presents a microfluidic in-flow decantation technique that provides the separation of particles from particle-free fluid while in-flow. The design involves the expansion of sample fluid channel in lateral and depth directions, thereby producing a particle-free layer towards the walls of the channel, followed by gradual extraction of this particle-free fluid through a series of tiny openings located towards one-end of the depth-direction. The latter part of this design is quite crucial in the functionality of this decantation technique and is based on the principle called wee-extraction. The design, theory, and simulations were presented to explain the principle-of-operation. To demonstrate the proof-of-principle, the experimental characterization was performed on beads, platelets, and blood samples at various hematocrits (2.5%&ndash, 45%). The experiments revealed clog-free separation of particle-free fluid for at least an hour of operation of the device and demonstrated purities close to 100% and yields as high as 14%. The avenues to improve the yield are discussed along with several potential applications.

We demonstrate room temperature nitrogen dioxide (NO2) sensing at parts per billion level (ppb) using a chemiresistive sensor based on strontium nanoparticles decorated reduced graphene oxide. Among the various functional materials used for NO2 sensing, it is a unique study reported for the first time using hybrid of reduced graphene oxide with a low work function alkaline earth metal. An increase of nearly 222% in sensing response is observed in the hybrid device over reduced graphene oxide alone at a concentration of 1 ppm. Moreover, the hybrid device exhibits a good sensitivity to NO2 over a wide concentration range from 500 ppb to 104 ppm. Additionally, the hybrid device is highly selective to NO2 amongst other pollutants. The integration of strontium nanoparticles onto reduced graphene oxide imparts excellent performance to the hybrid sensor due to their high adsorption energy for NO2. Further, strontium nanoparticle, being a low work function material, raises the fermi level of reduced graphene oxide and populate it with more electrons thus facilitating rapid charge transfer to electrophilic nitrogen dioxide. Hence, strontium nanoparticles attribute to an important role in fast and selective adsorption of nitrogen dioxide at room temperature with underlying graphene helping in rapid charge transfer.

High speed in-plane (X-Y) nanopositioners are of central importance in scanning probe microscopy for performing fast imaging and manipulation. Reducing the size of the nanopositioning stage improves the response speed of the positioner but also introduces challenges in integration of conventional motion sensors. This paper presents the design and development of a novel high speed flexure-guided, piezo-electrically actuated nanopositioner with integrated optical beam deflection-based motion sensing. The sensing strategy eliminates spatial constraints even for small stages. A simple lumped-parameter model is proposed for the nanopositioner. Subsequently, the model is used to design and fabricate the nanopositioner. The measurement system is integrated with the nanopositioning stage and is employed to characterize the quasi-static and dynamic response of the stage. Finally, the in-plane motion measurements are employed to control the stage when it is commanded to track both slow- and fast-varying position signals. In both cases, the use of control is shown to significantly improve the tracking accuracy. © 2019 Author(s).

The smartphone-based human activity recognition (HAR) systems are not capable to deliver high-end performance for challenging applications. We propose a dedicated hardware-based HAR system for smart military wearables, which uses a multilayer perceptron (MLP) algorithm to perform activity classification. To achieve the flexible and efficient hardware design, the inherent MLP architecture with parallel computation is implemented on FPGA. The system performance has been evaluated using the UCI human activity dataset with 7767 feature samples of 20 subjects. The three combinations of a dataset are trained, validated, and tested on ten different MLP models with distinct topologies. The MLP design with the 7-6-5 topology is finalized from the classification accuracy and cross entropy performance. The five versions of the final MLP design (7-6-5) with different data precision are implemented on FPGA. The analysis shows that the MLP designed with 16-bit fixed-point data precision is the most efficient MLP implementation in the context of classification accuracy, resource utilization, and power consumption. The proposed MLP design requires only 270 ns for classification and consumes 120 mW of power. The recognition accuracy and hardware results performance achieved are better than many of the recently reported works. © 2013 IEEE.

Pulmonary function tests (PFTs) are noninvasive diagnostic tests that evaluate the functionality of the lungs. Spirometry is an established diagnostic tool for the evaluation and management of lung disorders. Pulmonary function testing carried out using a spirometer provides vital information about the functional status of the respiratory system. In this study, a spirometer based on a fiber Bragg grating (FBG) sensor for PFT has been proposed. The proposed fiber Bragg grating spirometer (FBGS) is a novel, noninvasive device that has the ability to convert the rate of air flow into strain variations using an FBG sensor bonded on a cantilever. The FBGS dynamically acquires in real time, the complete breath sequence comprising of inhalation phase, pause phase, and exhalation phase, in terms of the air flow rate along with the time duration of each phase. Fundamental pulmonary parameters such as forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), the FEV1/FVC ratio, and peak expiratory flow are evaluated from the data obtained from the FBGS, which will aid greatly during clinical tests. The results from the FBGS developed are compared with a standard hospital grade pneumotachograph-based spirometer for a sample size of 16 subjects to prove the efficacy of the proposed device.

Polycrystalline copper indium gallium diselenide (CIGS) thin film is a favourable candidate for solar cell applications. In the present work the effect of post-deposition annealing on the structure, surface morphology, optical and electrical properties are discussed. Initially, gallium rich CIG thin films were deposited by RF magnetron sputtering followed by an indium rich CIG layer and subjected to selenization to realize CIGS stoichiometry. X-ray diffraction (XRD) results revealed the polycrystalline nature of the films with chalcopyrite structure having preferential orientation along direction normal to the substrate. Optical properties of CIGS thin films were studied using UV-vis spectrophotometry and the band gap of CIGS was found to be around 1.15 eV. Hall Effect studies carried out on the CIGS thin films showed a linear dependence of conductivity with post deposition annealing. The elemental composition of the films was quantified using X-ray photoelectron spectroscopy (XPS) and the results are discussed. (C) 2016 Elsevier B.V. All rights reserved.

Lithium-sulfur batteries mostly suffer from the low utilization of sulfur, poor cycle life, and low rate performances. The prime factors that affect the performance are enormous volume change of the electrode, soluble intermediate product formation, poor electronic and ionic conductivity of S, and end discharge products (i.e., Li2S2 and Li2S). The attractive way to mitigate these challenges underlying in the fabrication of a sulfur nanocomposite electrode consisting of different nanoparticles with distinct properties of lithium storage capability, mechanical reinforcement, and ionic as well as electronic conductivity leading to a mechanically robust and mixed conductive (ionic and electronic conductive) sulfur electrode. Herein, we report a novel bottom-up approach to synthesize a unique freestanding, flexible cathode scaffold made of porous reduced graphene oxide, nanosized sulfur, and Mn3O4 nanoparticles, and all are three-dimensionally interconnected to each other by hybrid polyaniline/sodium alginate (PANI-SA) matrix to serve individual purposes. A capacity of 1098 mAh g(-1) is achieved against lithium after 200 cycles at a current rate of 2 A g-1 with 97.6% of initial capacity at a same current rate, suggesting the extreme stability and cycling performance of such electrode. Interestingly, with the higher current density of 5 A g(-1), the composite electrode exhibited an initial capacity of 1015 mA h g(-1) and retained 71% of the original capacity after 500 cycles. The in situ Raman study confirms the polysulfide absorption capability of Mn3O4. This work provides a new strategy to design a mechanically robust, mixed conductive nanocomposite electrode for high-performance lithium sulfur batteries and a strategy that can be used to develop flexible large power storage devices.

Current study relates to the development of an electrical power-free, handheld microfluidic nanoparticle synthesizer for synthesis of uniform sized silver nanoparticles at room temperature. The synthesizer module consists of a custom designed microreactor and employs negative pressure based pumping mechanism for the electrical power free synthesis of metal nanoparticles. In order to realize a microreactor capable of on-site synthesis of monodisperse nanoparticles, optimization studies by bulk biosynthesis at varying ratios of the precursor and the reducing agent followed by UV-VIS absorption studies were performed to determine the appropriate mixing ratio. Later, a custom designed microfluidic micromixer was used to perform volumetric flow rate optimizations at the desired ratio using syringe pumps. From the knowledge of the precursor and reducing agent ratio and the flow rates, we modified the hydraulic resistance of micro-mixer inlets by varying the channel geometry to meet the optimized specifications leading to effective synthesis. The synthesized nanoparticles were characterized by UV-VIS spectroscopy, XPS, FTIR, EDS, HRTEM and SAED. The crystal lattice planes of 111] and 220] from the SAED pattern confirms the presence of silver nanoparticles. HRTEM study elucidates that the size of the synthesized nanoparticles is between 2 and 10 nm.

In this paper, we present methods to determine multipole coefficients for describing the potential in toroidal ion trap mass analysers. Three different methods have been presented to compute the toroidal multipole coefficients. The first method uses at least square fit (LS) and is useful when we have ability to compute potential at a set of points in the trapping region. In the second method we use the Discrete Fourier Transform (DFT) of potentials on a circle in the trapping region. The third method uses surface charge distribution obtained from the Boundary Element Method (BEM) to compute these coefficients. Using these multipole coefficients we have presented (1) equations of ion motion in toroidal ion traps, (2) the Mathieu parameters in terms of multipole coefficients and (3) the secular frequency of ion motion in these traps. It has been shown that the secular frequency obtained from our method has a good match with that obtained from numerical trajectory simulation. (C) 2016 Elsevier B.V. All rights reserved.

The present work demonstrates the superhydrophobic and Surface Enhanced Raman Spectroscopy (SERS) active substrate performance of silver coated copper oxide (Ag@CuO) nanostructured thin films prepared by the SILAR process. Super hydrophobic substrates that combine super hydrophobic condensation effect and high enhancement ability of Ag@CuO nanoflowers are investigated for SERS studies. The possible growth mechanism for the formation of nanoflower arrays from nanospindles has been discussed. Morphology and crystallinity of the Ag@CuO thin films are confirmed using FESEM and XRD. The results obtained in the present study indicate that the as-deposited hydrophobic nanospindles structure converts to super hydrophobic nanoflower arrays on annealing at 200 degrees C. The Ag@CuO super hydrophobic nanoflowers thin film based SERS substrates show highly enhanced Raman spectra with an EF value of 2.0 x 10(7) for (Rhodamine 6G) R6G, allowing a detection limit from a 10(-10) mol L-1 solution. The present study may provide a new perception in fabricating efficient super hydrophobic substrates for SERS, suggesting that the fabricated substrates are promising candidates for trace analysis of R6G dye and are expected to be widely used as highly sensitive SERS active substrates for various toxic dyes in the future. (C) 2016 Elsevier Inc. All rights reserved.

Light absorption efficiency and doping induced charge carrier density play a vital role in self-powered optoelectronic devices. Unique vanadium-doped zinc oxide nanoflake array (VZnO NFs) is fabricated for self-powered ultraviolet (UV) photodetection. The light harvesting efficiency drastically improved from 84% in ZnO NRs to 98% in VZnO NFs. Moreover, the hydrogenation of as-synthesized VZnO (H:VZnO) NFs displayed an outstanding increase in response current as compared to pristine structures. The H:VZnO NFs device presents an extraordinary photoelastic behavior with faster photodetection speed in the order of ms under a low UV illumination signal. Excellent responsivity and external quantum efficiency with larger value of specific detectivity of H:VZnO NFs device promises an outstanding sensitivity for UV signal and self-powered high-performance visible-blind photodetector.

In the present study synthesis of BaTi1-xCrxO3 nanocatalysts (x = 0.0

We discuss the potential application of high dc voltage sensing using thin-film transistors (TFTs) on flexible substrates. High voltage sensing has potential applications for power transmission instrumentation. For this, we consider a gate metal-substrate-semiconductor architecture for TFTs. In this architecture, the flexible substrate not only provides mechanical support but also plays the role of the gate dielectric of the TFT. Hence, the thickness of the substrate needs to be optimized for maximizing transconductance, minimizing mechanical stress, and minimizing gate leakage currents. We discuss this optimization, and develop n-type and p-type organic TFTs using polyvinyldene fluoride as the substrate-gate insulator. Circuits are also realized to achieve level shifting, amplification, and high drain voltage operation.

An electroactive poly(3,4-(2,2-dimethylpropylenedioxy)thiophene) (PProDOT-Me-2) thin film was electropolymerized by cyclic voltammetry technique, and its electrochemical and electrochromic properties were systematically studied. The prepared PProDOT-Me-2 thin film was electrochemically reversible, and it showed a linear relation between peak current with scan rates. The electrochemical impedance spectrum also indicated the diffusion limitation of the film during charge/discharge process. The film showed a good color contrast (60 %) with a low applying potential of 1.2 V. The electrochromic window (ECW) based on PPro-DOT-Me-2 film was fabricated and studied for its electrochromic performance. The color contrast of the device was achieved as 36 % at lambda(max) of 560 nm. The switching speed of fabricated ECW for coloring and bleaching were almost 0.7 s in a range of +1.5 to -1.5 V. The fabricated device showed better cyclic current response and remarkable switching stability over 100 cycles. The novelty of the electrochromic window based on PProDOT-Me-2 is the maximum absorbance at photopic wavelength that would be highly sensitive to human eyes.

Simple geometries which are possible alternatives for the Orbitrap are studied in this paper. We have taken up for numerical investigation two segmented-electrode structures, ORB1 and ORB2, to mimic the electric field of the Orbitrap. In the ORB1, the inner spindle-like electrode and the outer barrel-like electrode of the Orbitrap have been replaced by 35 rings and 35 discs of fixed radii, respectively. In this structure two segmented end cap electrodes have been added. In this geometry, different potentials are applied to the different electrodes keeping top-bottom symmetry intact. In the second geometry, ORB2, the inner and outer electrodes of the Orbitrap were replaced by an approximate step structure which follows the profile of the Orbitrap electrodes. In the present study 45 steps have been used. In the ORB2, like the Orbitrap, the inner electrode is held at a negative potential and the outer electrode is at ground potential. For the purpose of comparing the performance of ORB1 and ORB2 with that of the Orbitrap, the following studies have been undertaken: (1) variation of electric potential, (2) computation of ion trajectories, (3) simulation of image currents. These studies have been carried out using both 2D and 3D Boundary Element Method (BEM), the 3D BEM was developed specifically for this study. It has been seen in these investigations that ORB1 and ORB2 have performance similar to that of the Orbitrap, with the performance of the ORB1 being seen to be marginally superior to that of the ORB2. It has been shown that with proper optimization, geometries containing far fewer electrodes can be used as mass analyzers. A novel technique of optimization of the electric field has been proposed with the objective of minimizing the dependence of axial frequency of ion motion on the initial position of an ion. The results on the optimization of 9 and 15 segmented-electrode traps having the same design as ORB1 show that it can provide accurate mass analysis. (C) 2015 Elsevier B.V. All rights reserved.

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.

SU8-based micromechanical structures are widely used as thermal actuators in the development of compliant micromanipulation tools. This paper reports the design, nonlinear thermomechanical analysis, fabrication, and thermal actuation of SU8 actuators. The thermomechanical analysis of the actuator incorporates nonlinear temperature-dependent properties of SU8 polymer to accurately model its thermal response during actuation. The designed SU8 thermal actuators are fabricated using surface micromachining techniques and the electrical interconnects are made to them using flip-chip bonding. The issues due to thermal stress during fabrication are discussed and a novel strategy is proposed to release the thermal stress in the fabricated actuators. Subsequent characterization of the actuator using an optical profilometer reveals excellent thermal response, good repeatability, and low hysteresis. The average deflection is $\sim 8.5~\mu \text{m}$ for an actuation current of $\sim 5$ mA. The experimentally obtained deflection profile and the tip deflection at different currents are both shown to be in good agreement with the predictions of the nonlinear thermomechanical model. This underscores the need to consider nonlinearities when modeling the response of SU8 thermal actuators. [2015-0087]

In this article, we present a novel approach to throughput enhancement in miniaturized microfluidic microscopy systems. Using the presented approach, we demonstrate an inexpensive yet high-throughput analytical instrument. Using the high-throughput analytical instrument, we have been able to achieve about 125,880 cells per minute (more than one hundred and twenty five thousand cells per minute), even while employing cost-effective low frame rate cameras (120 fps). The throughput achieved here is a notable progression in the field of diagnostics as it enables rapid quantitative testing and analysis. We demonstrate the applicability of the instrument to point-of-care diagnostics, by performing blood cell counting. We report a comparative analysis between the counts (in cells per mu l) obtained from our instrument, with that of a commercially available hematology analyzer.

A binder-free novel three-dimensional assembly comprising graphene, carbon nanoparticles and nickel hydroxide is presented as a supercapacitor electrode. The combined effect of three-dimensional graphene for excellent charge conduction and nickel hydroxide coating on carbon nanoparticles for high surface area was exploited to obtain excellent supercapacitance. The resulting structure presented an ultrahigh 4667 F g(-1) specific capacitance at a 2 A g(-1) discharge rate with 98.6% high charge retention for more than 1000 charge-discharge cycles. In addition, the presented assembly demonstrated very high power and energy densities.

Superhydrophobic surfaces have attracted due to their potential applications such as self-cleaning surfaces etc. Many techniques have demonstrated in fabricating the artificial superhydrophobic surfaces such as CVD, Organic coatings etc. In this paper we present simple approach to fabricate non wettable superhydrobic surface on silicon Nanowires (Si NW) surface by H-2 ion etching technique through ECR device which is very efficient in producing the high ion density plasma at low pressure and at moderate energy. Large area high density (Si NW) were fabricated by two step Metal assisted chemical etching (MACE) of silicon using silver(Ag) as the catalyst along with pre immersion method. H-2 Plasma ion etching treatment was applied on the surface of the SiNW at the constant microwave power. The morphology of Si NWs is changed with the application of plasma which was revealed by Scanning electron microscopy. Water contact angles have been systematically measured for SiNWs& H-2 plasma treated SiNWs by increasing the etching time. It was observed that in H-2 ion plasma treated SiNWs, the water contact angle changed dramatically from 22.6 degrees to 146 degrees almost near to super hydrophobic nature. And these result suggest that the hydrogen plasma condition must be carefully regulated to achieve the superhydrophobic surface on silicon which is essential for many applications like Biosensors and Microfluidic surfaces. (C) 2015Elsevier Ltd. All rights reserved.

Potassium tetratitanate (K2Ti4O9) has been synthesized by solid state method using K2CO3 and TiO2, and studied as an anode material for potassium ion batteries for the first time. A discharge capacity of 80 mAh g(-1) has been obtained at a current density of 100 mA g(-1) (0.8 C rate) and 97 mAh g(-1) at 30 mA g(-1) (0.2 C rate), initially. The discharge capacity is stable at low rates of cycling. The uptake of K+ on charging K2Ti4O9 electrodes is quantitatively studied. The proposed mechanism of charging involves reduction of two Ti ions from 4+ oxidation state to 3+ oxidation state, which facilitates insertion of two K+ ions per formula unit. The rate capability experiments suggest that K2Ti4O9 is capable of undergoing charge-discharge cycling at high rates (up to 15 C rate), but with a low discharge capacity. Thus K2Ti4O9 is a promising anode material for future K-ion batteries. (C) 2016 The Electrochemical Society. All rights reserved.

Ferroelectricity in ZnO is an unlikely physical phenomenon. Here, we show ferroelectricity in undoped 001] ZnO nanorods due to zinc vacancies. Generation of ferroelectricity in a ZnO nanorod effectively increases its piezoelectricity and turns the ZnO nanorod into an ultrahigh-piezoelectric material. Here using piezoelectric force microscopy (PFM), it is observed that increasing the frequency of the AC excitation electric field decreases the effective d(33). Subsequently, the existence of a reversible permanent electric dipole is also found from the P-E hysteresis loop of the ZnO nanorods. Under a high resolution transmission electron microscope (HRTEM), we observe a zinc blende stacking in the wurtzite stacking of a single nanorod along the growth axis. The zinc blende nature of this defect is also supported by the X-ray diffraction (XRD) and Raman spectra. The presence of zinc vacancies in this basal stacking fault modulates p-d hybridization of the ZnO nanorod and produces a magnetic moment through the adjacent oxygen ions. This in turn induces a reversible electric dipole in the non-centrosymmetric nanostructure and is responsible for the ultrahigh-piezoelectric response in these undoped ZnO nanorods. We reveal that this defect engineered ZnO can be considered to be in the competitive class of ultrahigh-piezoelectric nanomaterials for energy harvesting and electromechanical device fabrication.

A Screen printed potentiometric urea biosensor is developed to monitor the blood urea level non-invasively using reverse iontophoresis (RI). The working electrode is screen printed using graphitic carbon paste, reference and RI electrodes are screen printed using silver/silver chloride (Ag/AgCl) paste. Urease enzyme is immobilized in the polypyrrole (PPy) matrix of the working electrode using optimized cyclic voltammetry parameters to obtain maximum sensor performance. Electrochemical and material characterizations conducted in the Screen Printed Reference Electrodes (SPRE) are examined to ensure their stability and retention of their properties. The developed screen printed sensors exhibited sensitivity of 35.07 mV/decade and showed liner response for the range, 10 mu M to 5 mM with a correlation co-efficient of 0.995. Interference studies with KCl, NaCl and MgCl2 solutions are performed and it was found that sensor performance is unaffected due to interference ions. The urea sensor is further validated by conducting clinical investigations on 15 human subjects. A correlation is established between blood urea level and transdermal extracted urea level and the correlation co-efficient is found to be 0.391. (C) 2016 The Electrochemical Society. All rights reserved.

The effects of optical and magnetic fields have a pronounced influence on the electrical performance of graphene quantum dots (GQDs). Nonlinear current-voltage hysteresis during a voltage sweep is revealed due to the charge traps by adsorbates present on the quantum dot (QD) surface. Hence, a polarization dependent variation in QDs even in the presence of the surrounding medium presented an interesting variation in the electrical conductivity. Furthermore, a study of capacitance with frequency revealed that the microwave heating time (MHT) during the preparation of GQDs greatly affected the capacitance value of the colloidal QDs owing to size variation where larger QDs arising from a greater MHT showed lower capacitance and vice versa.

Radiation is the standard therapy used for treating Glioblastoma (GBM), a grade IV brain cancer. Glioma Stem-like Cells (GSCs), an integral part of GBM, enforces resistance to radiation therapy of GBM. Studying the differential biomolecular composition of GSCs with varying levels of radiation sensitivity can aid in identifying the molecules and their associated pathways which impose resistance to cells thereby unraveling new targets which would serve as potential adjuvant therapy. Raman spectroscopy being a noninvasive, label free technique can determine the biomolecular constituent of cells under live conditions. In this study, we have deduced Raman spectral signatures to predict the radiosensitivity of any GSC accurately using the inherent and radiation induced biomolecular composition. Our study identified the differential regulation of several biomolecules which can be potential targets for adjuvant therapy. We radiosensitized the resistant GSCs using small molecule inhibitors specific to the metabolic pathways of these biomolecules. Efficient antitumor therapy can be attained with lower dosage of radiation along with these inhibitors and thus improving the survival rate of GBM patients with reduced side-effects from radiation.

This paper presents the development of a novel wavefront measuring camera capable of detecting both the amplitude and phase of the captured light wave simultaneously. The main objective of the present work is to develop a simple ``aim and shoot'' camera system for quantitative estimation of density variations in high-speed gas flow fields. The interrogating beam which is a plane wave used here gets distorted by flow induced change in refractive index gradients. Wavefront distortion is quantitatively measured by inspecting the projected pattern through the embedded mask of a modified CMOS image sensor, which samples the incoming wavefront space continuously. Post-processing of the captured images through Fourier-and wind owed Fourier transform schemes reveals the change in phase and amplitude of the captured wave. The captured phase of the wavefront is used in an iterative tomography scheme to estimate the density distribution of the flow field. The utility of the developed camera is demonstrated in the quantitative visualization of the high-speed flowfields around test objects subjected to hypersonic flows at Mach numbers 8.89 and 5.82 in hypersonic shock tunnel facility (HST2) and also to visualize the flow field generated at the exit of a convergent-divergent nozzle (Mach number 2.9). It is observed that the recovered quantitative density values from the experiments match well with the results obtained through computational fluid dynamic simulations demonstrating the proficiency of the proposed wavefront measuring camera for high-speed flow diagnostics. Published by AIP Publishing.

Arterial pulse is an established source of information for the clinical assessment of cardiovascular health. The central aortic pressure is known to be a better predictor of cardiovascular status than the peripheral pressure. The carotid arterial pulse is considered to be the best indicator of the central aortic pressure. The present work deals with the development of a novel noninvasive probe based on fiber Bragg grating (FBG) sensor for the real-time acquisition of the pulse waveform in the carotid arterial site. The fiber Bragg grating pulse probe (FBGPP) developed is used to obtain the carotid arterial pulse waveform (CAPW) of individual subjects, in the form of beat-to-beat carotid pulse. The FBGPP developed comprises of an elastic rubber diaphragm that comes into contact with the skin below, which the carotid artery is pulsating, creating strain variations over it. Effectively, the carotid arterial pulse is tranduced into the strain variations over a rubber diaphragm, which is acquired by the FBG sensor bonded over it. The FBGPP is designed such that the positioning and the access for the device to the carotid arterial site can be carried out with ease. Furthermore, the recorded CAPW is subjected to the pulse wave analysis in order to evaluate vital cardiovascular parameters like heart rate, left ventricular ejection time, carotid augmentation index, and ejection duration index, which are indicators of the cardiac health of the subject and the performance of the heart. Also, the linearity between these cardiovascular parameters is explored for a sample size of 55.

Fiber Bragg Grating (FBG) sensors have become popular for applications related to structural health monitoring, biomedical engineering, and robotics. However, for successful large scale adoption, FBG interrogation systems are as important as sensor characteristics. Apart from accuracy, the required number of FBG sensors per fiber and the distance between the device in which the sensors are used and the interrogation system also influence the selection of the interrogation technique. For several measurement devices developed for applications in biomedical engineering and robotics, only a few sensors per fiber are required and the device is close to the interrogation system. For these applications, interrogation systems based on InGaAs linear detector arrays provide a good choice. However, their resolution is dependent on the algorithms used for curve fitting. In this work, a detailed analysis of the choice of algorithm using the Gaussian approximation for the FBG spectrum and the number of pixels used for curve fitting on the errors is provided. The points where the maximum errors occur have been identified. All comparisons for wavelength shift detection have been made against another interrogation system based on the tunable swept laser. It has been shown that maximum errors occur when the wavelength shift is such that one new pixel is included for curve fitting. It has also been shown that an algorithm with lower computation cost compared to the more popular methods using iterative non-linear least squares estimation can be used without leading to the loss of accuracy. The algorithm has been implemented on embedded hardware, and a speed-up of approximately six times has been observed. Published by AIP Publishing.

Background: Inversion of dual-energy computed tomography (DECT) data for obtaining the electron density and effective atomic number of substances has been a work in progress for the past forty years. It has been the practice to characterize the material in terms of Hounsfield Unit (HU) values obtained by two different energies. Objectives: Since HU values are equipment-dependent quantities, it is necessary to develop a method that characterizes the substance in terms of certain physical quantities that are equipment independent. Materials and Methods: The process that we adopt is to find a calibration method by which all equipment-dependent quantities are eliminated and we directly deal with quantities that are representative of the sample, namely its electron density and effective atomic number. We collect the DECT data from 21 samples of non-calcified coronary artery plaques in human cadavers. Results: With our standardized inversion method, we have obtained the electron density and effective atomic number of these samples. With physical models of lipids and proteins, it becomes possible to conclude that non-calcified plaque samples can have calcium dispersed in the lipid part of the plaque in trace amounts that cannot be observed by light based microscopy or by CT images alone. Conclusion: This characterization, may give a new insight in characterization of non-calcified coronary artery plaque and in medical diagnostics.

We demonstrate a non-invasive technique, based on the modal frequency shift of a region insonified by a dual-beam ultrasound (US) transducer (region of interest, ROI), to remotely assess the temperature of the region in a tissue-mimicking object. The application is in ultrasound hyperthermia systems for controlled maintenance of tumour temperature during chemotherapy. Towards this, we have characterised the variation of the storage modulus with the temperature of two tissue-mimicking visco-elastic materials. Due to this variation in tissue storage modulus (and viscosity), we have observed a shift in the resonant modes of the ROI, vibrated remotely with a dual-beam focussed ultrasound transducer. A modal analysis of the vibrating ROI is done to identify the modes captured by the detector. A variation in this modal frequency with temperature is computed and matches reasonably well with the experimental measurements. Through this, we demonstrate that an ultrasound hyperthermia system can have a remote temperature sensor without using an additional imaging modality.

Thin films of different thicknesses in the range of 200-720 nm have been deposited on glass substrates at room temperature using thermal evaporation technique. The structural investigations revealed that the as-deposited films are amorphous in nature. The surface roughness of the films shows an increasing trend at higher thickness of the films. The surface roughness of the films shows an increasing trend at higher thickness of the films. Interference fringes in the transmission spectra of these films suggest that the films are fairly smooth and uniform. The optical absorption in Sb2Se3 film is described using indirect transition and the variation in band gaps is explained on the basis of defects and disorders in the chalcogenide systems. Raman spectrum confirms the increase of orderliness with film thickness. From the I-V characteristics, a memory type switching is observed whose threshold voltage increases with film thickness. (C) 2015 Elsevier B.V. All rights reserved.

Power densities required to operate active-matrix organic-light-emitting diode (AMOLED) based displays for high luminance applications, lead to temperature rise due to self heating. Temperature rise leads to significant degradation and consequent reduction in life time. In this work numerical techniques based computational fluid dynamics (CFD) is used to determine the temperature rise and its distribution for an AMOLED based display for a given power density and size. Passive cooling option in form of protruded rectangular fins is implemented to reduce the display temperature.

Titania aerogels were synthesized by sol-gel route followed by ambient pressure subcritical drying technique. The aerogels synthesized in the present work possess a maximum surface area of 252 m(2)/g. The pore size distribution is between 2 and 30 nm which confirms their mesoporosity. The oxygen plasma treatment on titania aerogel thin films improved the surface area up to 273 m(2)/g and produced additional hydrophilic groups on the surface. It is confirmed by BET surface area, XPS and thermal analysis in conjunction with dye adsorption studies. After plasma treatment the dye adsorption capacity was increased 2.5 times higher than that of untreated aerogel film. The increased surface area and the hydrophilic groups generated on the titania aerogel surface during plasma treatment are responsible for enhanced dye adsorption. The overall nanoporous morphology of titania aerogel is preserved after plasma treatment. (C) 2015 Elsevier B.V. All rights reserved.

Direct measurement of three-dimensional (3-D) forces between an atomic force microscope (AFM) probe and the sample benefits diverse applications of AFM, including force spectroscopy, nanometrology, and manipulation. This paper presents the design and evaluation of a measurement system, wherein the deflection of the AFM probe is obtained at two points to enable direct measurement of all the three components of 3-D tip-sample forces in real time. The optimal locations for measurement of deflection on the probe are derived for a conventional AFM probe. Further, a new optimal geometry is proposed for the probe that enables measurement of 3-D forces with identical sensitivity and nearly identical resolution along all three axes. Subsequently, the designed measurement system and the optimized AFM probe are both fabricated and evaluated. The evaluation demonstrates accurate measurement of tip-sample forces with minimal cross-sensitivities. Finally, the real-time measurement system is employed as part of a feedback control system to regulate the normal component of the interaction force, and to perform force-controlled scribing of a groove on the surface of polymethyl methacrylate.

Mechanical properties of thin films such as residual stress and hardness are of paramount importance from the device fabrication point of view. Intrinsic stress in sputtered films can be tensile or compressive as decided by the number density and the energy of the plasma species striking the growing film. In the presence of hydrogen we analyzed the applicability of idealized stress reversal curve for amorphous silicon thin films deposited by DC, pulsed DC (PDC) and RF sputtering. We are successfully able to correlate the microstructure with the stress reversal and hardness. We observed a stress reversal from compressive to tensile with hydrogen incorporation. It was found that unlike in idealized stress reversal curve case, though the energy of plasma species is less in DC plasma, DC deposited films exhibit more compressive stress, followed by PDC and RF deposited films. A tendency towards tensile stress from compressive stress was observed at similar to 13, 18 and 23 at%H for DC, PDC and RF deposited films respectively, which is in exact agreement with the vacancy to void transition in the films. Regardless of the sputtering power mode, the hardness of a-Si:H films is found to be maximum at C-H similar to 10 at%H. Enhancement in hardness with C-H (up to C-H similar to 10 at%H) is attributed to increase of Si-H bonds. Beyond C-H similar to 10 at%H, hardness starts falling. (C) 2015 Elsevier Ltd. All rights reserved.

Disease conditions like malaria, sickle cell anemia, diabetes mellitus, cancer, etc., are known to significantly alter the deformability of certain types of cells (red blood cells, white blood cells, circulating tumor cells, etc.). To determine the cellular deformability, techniques like micropipette aspiration, atomic force microscopy, optical tweezers, quantitative phase imaging have been developed. Many of these techniques have an advantage of determining the single cell deformability with ultrahigh precision. However, the suitability of these techniques for the realization of a deformability based diagnostic tool is questionable as they are expensive and extremely slow to operate on a huge population of cells. In this paper, we propose a technique for high-throughput (800 cells/s) determination of cellular deformability on a single cell basis. This technique involves capturing the image(s) of cells in flow that have undergone deformation under the influence of shear gradient generated by the fluid flowing through the microfluidic channels. Deformability indices of these cells can be computed by performing morphological operations on these images. We demonstrate the applicability of this technique for examining the deformability index on healthy, diabetic, and sphered red blood cells. We believe that this technique has a strong role to play in the realization of a potential tool that uses deformability as one of the important criteria in disease diagnosis.

Multifrequency atomic force microscopy is a powerful nanoscale imaging and characterization technique that involves excitation of the atomic force microscope (AFM) probe and measurement of its response at multiple frequencies. This paper reports the design, fabrication, and evaluation of AFM probes with a specified set of torsional eigen-frequencies that facilitate enhancement of sensitivity in multifrequency AFM. A general approach is proposed to design the probes, which includes the design of their generic geometry, adoption of a simple lumped-parameter model, guidelines for determination of the initial dimensions, and an iterative scheme to obtain a probe with the specified eigen-frequencies. The proposed approach is employed to design a harmonic probe wherein the second and the third eigen-frequencies are the corresponding harmonics of the first eigen-frequency. The probe is subsequently fabricated and evaluated. The experimentally evaluated eigen-frequencies and associated mode shapes are shown to closely match the theoretical results. Finally, a simulation study is performed to demonstrate significant improvements in sensitivity to the second- and the third-harmonic spectral components of the tip–sample interaction force with the harmonic probe compared to that of a conventional probe.

We investigated the effect of oxygen flow rate during the reactive magnetron sputtering on the compositional, structural, optical and electrical properties of HfO2 films. We also studied the influence of annealing temperature on the structural and electrical properties of optimized HfO2 films of 25 to 30 nm thick. X-ray photoelectron study reveals that the films deposited at 15 SCCM of oxygen flow rate are stoichiometric and have an optical band gap of 5.86 eV. X-ray diffraction indicates that films without oxygen flow are amorphous, and beyond an oxygen flow rate of 5 SCCM exhibit polycrystalline monoclinic structure. At an annealing temperature of 600 degrees C, tetragonal phase was observed besides the monoclinic phase. The dielectric constant of 11 and low leakage currents of 1 x 10(-7) A/cm(2) were achieved for the stoichiometric films. As-deposited films show significant frequency dispersion due to the presence of defect states at the HfO2/Si interface, and it reduces after annealing.

Electronic monitoring of perimeters plays vital roles in homeland security, management of traffic and of human-wildlife conflict. This paper reports the design and development of an optical beam-interruption-based ranging and profiling sensor for monitoring perimeters. The developed sensor system can determine the distance of the object from the sensing units and its temporal height profile as the object crosses the system. Together, these quantities can also be used to classify the object and to determine its speed. The sensor is designed, fabricated, and evaluated. The design enables compact construction, high sensitivity, and low measurement crosstalk. The evaluation demonstrates accuracy better than 98.5% in the determination of height and over 94% in determination of the distance of an object from the sensing units. Finally, a strategy is proposed to classify the objects based on the obtained height profiles. The strategy is demonstrated to correctly classify the objects despite differences in their speed and the location at which they cross the system.

The variation of normalized electrical resistivity in the system of glasses Ge15Te85-xSnx with (1