Department of Applied Mechanics

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

IIT Madras

Chikungunya is a mosquito-borne infectious disease, which causes acute fever and joint pain, and can trigger long term arthritis. In the present study, we demonstrate a label-free detection of chikungunya virus non-structural protein 3 (CHIKV-nsP3), which is responsible for alphavirus replication, using electrochemical impedance spectroscopy (EIS). This is hitherto, the first work addressing the detection of CHIKV-nsP3 using biosensors. The immunosensors were developed by modifying a gold surface using self-assembled monolayer of 11-mercaptoundecanoic acid and 6-mercaptohexanol. Anti-CHIKV-nsP3 antibodies were attached to the sensor surface via cabodiimide coupling reaction. The impedance spectra were fit to an equivalent circuit, and the percentage change in charge transfer resistance was correlated to the antigen concentration, and a linear working range from 25 ng/ml to 1 μg/ml of CHIKV-nsP3 was obtained. The limit of detection was 8 ng/ml and the limit of quantification was 17 ng/ml. The biosensor was also found to be highly specific to CHIKV-nsP3. The sensor was further tested for matrix effect from human serum, and appreciable recoveries ranging from 97% to 106% was observed. The results illustrate the potential of EIS based immunosensors with CHIKV-nsP3 as a suitable biomarker for direct and sensitive detection of chikungunya. © The Author(s) 2019.

GENERAL

Department Of Chemical Engineering

Journal of the Electrochemical Society

Label-free detection of chikungunya non-structural protein 3 using electrochemical impedance spectroscopy

The stability of a cylindrical interface separating two incompressible, inviscid and immiscible fluids under the action of radial motion is studied. Linear stability analysis is employed to understand the destabilization characteristics of the two fluid interface.Three-dimensional as well as two-dimensional (axisymmetric and azimuthal) disturbances are separately considered in the presence of surface tension. A dispersion relation governing this problem is taken from literature and analyzed. The relevant dimensionless parameters governing this study are Bond number, radial Weber number and density ratio. This dispersion relation permits the consideration of two different scenarios: (1) density of the inner fluid being greater than the outer fluid and (2) density of the inner fluid being lesser than the outer fluid. It is found out that the surface tension restricts and aids the destabilization for the former and latter case, respectively. It is also observed that the interface is unstable when even at a constant radial velocity. This is contrary to our common understanding of Rayleigh–Taylor instability where acceleration is required. Three destabilization modes are identified namely Taylor (axial) mode, flute (azimuthal) mode and helical (three-dimensional) mode for a range of parameters. It is found that three-dimensional modes are more susceptible to destabilization than the two-dimensional modes when the radial Weber number is close to zero. Regime maps are created in the Bond number, radial Weber number and density ratio space to establish the regimes where different modes occur. For a given density ratio, the destabilization starts from one mode to another two-dimensional disturbance through three-dimensional disturbances. The second and utmost finding of this study reveals that radial Weber number alone (albeit the Bond number) is sufficient to destabilize a cylindrical interface. © 2019, Springer Nature B.V.

Meccanica

Destabilization characteristics of three dimensional Rayleigh–Taylor mechanism on a cylindrical interface

Using a dynamic variant of the Vicsek model, we show that the emergence of disorder from an orderly moving human crowd is a nonequilibrium first-order phase transition. We also show that this transition can be reversed by modifying the dynamics of a few agents, deemed as game changers. Surprisingly, the optimal placement of these game changers is found to be in regions of maximum local crowd speed. The presence of such game changers is effective owing to the discontinuous nature of the underlying phase transition. Thus our generic approach provides strategies to (i) delay crowd crush and (ii) design safe evacuation procedures, two aspects that are of paramount importance in maintaining safety of mass gatherings of people. © 2019 American Physical Society.

Fulltext

Physical Review Letters

Sparse Game Changers Restore Collective Motion in Panicked Human Crowds

In this paper, we investigate the coupled behvior of the acoustic field in the confinement and the unsteady flame dynamics in a laboratory scale spray combustor. We study this interaction during the intermittency route to thermoacoustic instability when the location of the flame is varied inside the combustor. As the flame location is changed, the synchronization properties of the coupled acoustic pressure and heat release rate signals change from desynchronized aperiodicity (combustion noise) to phase synchronized periodicity (thermoacoustic instability) through intermittent phase synchronization (intermittency). We also characterize the collective interaction between the multiple flamelets anchored at the flame holder and the acoustic field in the system, during different dynamical states observed in the combustor operation. When the signals are desynchronized, we notice that the flamelets exhibit a steady combustion without the exhibition of a prominent feedback with the acoustic field. In a state of intermittent phase synchronization, we observe the existence of a short-term coupling between the heat release rate and the acoustic field. We notice that the onset of collective synchronization in the oscillations of multiple flamelets and the acoustic field leads to the simultaneous emergence of periodicity in the global dynamics of the system. This collective periodicity in both the subsystems causes enhancement of oscillations during epochs of amplitude growth in the intermittency signal. On the contrary, the weakening of the coupling induces suppression of periodic oscillations during epochs of amplitude decay in the intermittency signal. During phase synchronization, we notice a sustained synchronized movement of all flamelets with the periodicity of the acoustic cycle in the system. © 2018 The Combustion Institute.

Department of Aerospace Engineering

Proceedings of the Combustion Institute

Phase synchronization and collective interaction of multiple flamelets in a laboratory scale spray combustor

Bacterial endotoxins such as lipopolysaccharides (LPS) are major contaminants of most pharmaceutical and consumer products. We report an antibiotic-mediated plasmonic biosensor for LPS detection based on a facile U-bent fiber optic probe (UFOP) technology. Biomimetic self-assembled layer of octadecyltrichlorosilanes (OTS) were functionalized on the surface of optical fiber probes to hydrophobically entrap LPS from aqueous solutions. The binding of LPS molecules was monitored in real-time by measuring the change in refractive index (RI) in the evanescent layer. To add specificity and signal amplification, the bound LPS molecules were further tagged with antimicrobial polymyxin-B conjugated gold nanoparticles (PMB-AuNPs) in a sandwich format. The assay was extensively optimized by investigating the role of experimental parameters like OTS concentration, incubation time and addition of a silver reduction step at the end of the assay. The lower limit of detection (LOD) for LPS was found to be 0.4 ng/mL with a 36-fold improved sensitivity upon silver enhancement. The total assay time was 1 h. The assay was also found to be highly specific in the presence of common biopharmaceutical components and could thus serve as an efficient endotoxin detection platform for quality control testing during therapeutic development. © 2019 Elsevier B.V.

Biosensors and Bioelectronics

Plasmonic biosensors for bacterial endotoxin detection on biomimetic C-18 supported fiber optic probes

We report a novel one-step polyamidoamine (PAMAM) dendrimer based polymethyl methacrylate (PMMA) surface functionalization strategy for the development of polymeric optical fiber (POF) based plasmonic sensors utilizing gold nanoparticles (AuNP). Simple contact angle measurements over PMMA sheets reveal the ability of the dendrimers to strongly bind to PMMA surface without additional acid/alkali pretreatment, unlike the conventional hexamethylene diamine (HMDA) based surface modification. Subsequently, U-bent POF probes with high evanescent wave absorbance sensitivity were exploited for relative quantification of the surface amine groups using fluorescein isothiocyanate (FITC) binding and efficient chemisorption of gold nanoparticles (AuNP) in order to identify the optimum conditions viz. dendrimer concentration, incubation time and dendrimer generation. While FITC binding showed a proportional increase in amine functional density with PAMAM concentration and time, interestingly the AuNP (40 nm) binding studies revealed the formation of loose PAMAM multilayers and their desorption. PAMAM (G4) concentration as low as 5 mM and incubation time of 24 h provide faster binding rate with densely packed AuNP and the RI sensitivity of ∼15 (A546 nm/RIU). This simpler and inexpensive strategy could also be exploited for the development of functional PMMA substrates for various applications including nanotechnology, bio-imaging, drug delivery and analytical separations. © 2019 Wiley-VCH Verlag GmbH &amp; Co. KGaA, Weinheim

ChemNanoMat

Self-Assembled Polyamidoamine Dendrimer on Poly (methyl meth- acrylate) for Plasmonic Fiber Optic Sensors

Sex-selective abortions, based on ultrasound foetal scanning of pregnant women, is a rampant problem in developing countries like India. Although prenatal gender screening has been outlawed, poor enforcement of it has abetted a steady rise in their number. Currently, the B-scans are displayed on the screen in real-time and the operator can make out the gender from the displayed image. Therefore, enforcement of the secrecy has not been effective and has only led to limitations on the usage of the technology. Hence, it may be useful to develop a method that can identify frames containing gender-indicative features in real-time and block it out automatically from the display, thus, preventing unauthorized viewing. In this work, deep learning-based techniques have been explored to detect images containing the gender-defining features among the entire set of images in cine-loop, with a conforming accuracy averaging above 80%. © 2019 IEEE.

Department of Engineering Design

IEEE International Ultrasonics Symposium, IUS

Deep-Learning based Identification of Frames Containing Foetal Gender Region during Early Second Trimester Ultrasound Scanning

Changes in tissue elasticity are generally correlated with pathological phenomena. For example, diffuse liver disease progressively reduces the elasticity of the liver. Quasi-static elastography is popular in clinical applications to visualize regions with different relative stiffness. However, the limitation of this technique is that it provides only qualitative information. To overcome this, we investigate the use of a calibrated reference layer, sandwiched between the transducer and the tissue surface, to quantitatively image the unknown modulus of the examined tissue. The performance of the method was studied through simulations and experiments on agar-gelatin phantoms having Young's modulus within a range appropriate for the liver application. Furthermore, we explored the translational capability of the proposed method to work with existing commercially-available ultrasound scanners having elastography option. The Young's modulus value of the phantom estimated from quantitative elastography in simulation and experiment was compared against the corresponding ground-truth modulus value obtained from COMSOL and Universal Testing Machine (UTM) results, respectively. The results obtained for the compressive elastic modulus of the underlying phantom using quasi-static ultrasound elastography was found to be within 6% and 11% in simulation and experiments, respectively, to the corresponding ground-truth values. © 2018 Elsevier B.V.

Ultrasonics

Towards quantitative quasi-static ultrasound elastography using a reference layer for liver imaging application: A preliminary assessment

In this paper, a technique combining Diverging Beam with Synthetic Aperture Technique (DB-SAT) is demonstrated that utilizes only limited number of active elements yet provides better quality images at higher frame rates than possible with Conventional Focused Beamforming (CFB). The DB-SAT has been investigated in simulations and experiments on wire and tissue-mimicking phantoms, and the results are compared with routinely used CFB with Linear Array (CFB-LA). The estimated lateral resolution at the focal point was 0.41 mm and 0.34 mm for CFB-LA and DB-SAT, respectively, in simulations. These were estimated to be 0.78 mm and 0.71 mm, respectively, in experiments. Experimentally computed contrast resolution (contrast-to-noise ratio) for the cyst located at 60 mm depth were 0.50 (1.31 dB) and 0.58 (2.33 dB) for CFB-LA and DB-SAT, respectively. The frame-rate achieved by DB-SAT was 8 times and 2 times higher than that achieved by CFB-LA when transmit sub-apertures had an overlap 0% and 75%, respectively. Therefore, it can be concluded from the results that DB-SAT using 8 active transmit elements and 64 active receive elements yields better quality images at higher frame-rates than those obtained using CFB-LA with 64 active elements in transmit and receive. Since there is a reduction in the number of active transmit elements in the case of DB-SAT, it leads to a reduction in the overall system complexity. © 2018 Elsevier B.V.

Diverging beam transmit through limited aperture: A method to reduce ultrasound system complexity and yet obtain better image quality at higher frame rates

In most cases, high energy solid state lasers such as Nd:YAG are used as source of illumination for Photoacoustic Tomography (PAT). However the bulkiness, high cost and low pulse repetition frequency (PRF) poses a challenge in translating this technology to an affordable clinical imaging option at bed-side. Pulsed Laser Diodes (PLD) on the other hand is portable, inexpensive and offers high PRF. However, the achievable depth of penetration using PLD is much lower than the solid state lasers. In this work, we demonstrate the feasibility of using sub-pitch translation approach on the receive-side ultrasound transducer to increase the depth sensitivity in PAT imaging system while using PLD as a source of illumination. The preliminary results obtained from experiments suggest that the higher density data obtained by augmenting raw RF lines from λ/2 positions of a linear array transducer provides better signal strength from deeper located targets and thereby increasing the depth of penetration by about 15% that reaches up to a depth of 14.3 mm. © 2019 IEEE.