Papers by Sarbari Bhattacharya
Orientational dynamics of human red blood cells in an optical trap
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We present an optical tweezer based study of rotation of microscopic objects with shape asymmetry... more We present an optical tweezer based study of rotation of microscopic objects with shape asymmetry. Thermal fluctuations and rotations are simultaneously monitored through laser back scattering. The rotation results in a modulation in intensity of the back scattered light incident on a quadrant photo detector. This results in the manifestation of peaks at a fundamental rotational frequency and at integer harmonics, superimposed on a modified Lorentzian in the power spectrum. The multiple peaks indicate that the rotations are periodic but with varying angular velocity. We demonstrate the use of video microscopy for characterization of low reflectivity rotors, such as biological cells. The methods also enable a measurement of the average torque on the rotor, and in principle, can reveal information about its principal moments of inertia, and the role of hydrodynamics at micron levels
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Magnetic Nanoparticles (MNPs) have been proposed as therapeutic agents for treatment of medical c... more Magnetic Nanoparticles (MNPs) have been proposed as therapeutic agents for treatment of medical conditions like cancer by using them either as drug carriers to specific locations in the body or as agents for localized heating. For these treatments to be effective, a substantial quantity of MNPs need to reach the target site from the site of injection. However, this may not be the case if blood flow alone is relied on to transport the MNPs as losses to branching blood vessels that lead to transport in directions away from the target site can occur. We have carried out numerical simulations on the flow of a dilute concentration of magnetic particles (MPs), where inter particle interactions can be ignored, in channels that mimic human vasculature like conditions. This has been done using Open Field Operation And Manipulation (OpenFOAM). Blood has been treated as a Newtonian fluid and only laminar flows are considered. The size of channels and direction of flow, which is always towards ...
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Macromolecular Symposia, 2017
The dynamics of trapped entities in an Optical Trap (OT) can yield information with regards to th... more The dynamics of trapped entities in an Optical Trap (OT) can yield information with regards to their viscoelastic response as well as optical anisotropy, if any. Detailed analysis of such dynamics correlated with parameters which affect the response can yield additional clues to the exact effect of these on the trapped entities. In this work, we illustrate this point by showing how the altered behavior of Red Blood Cells (RBC) treated with Bovine Serum Albumin (BSA) yields information about the nature of action of BSA, on which there is no current consensus in literature. We conclude from our studies that BSA treatment leads to a change in the birefringence of the RBCs, a conclusion arrived at from the altered optomechanical response of such cells in a linearly polarized Gaussian beam OT. Furthermore, we argue that the observed changes in cellular optical anisotropy may be thought of as due to changes in the curvature of the RBC membrane. We also note that BSA action could help mimi...
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Journal of Biological Physics
We investigate through simulations the phenomena of magnetoreception to enable an understanding o... more We investigate through simulations the phenomena of magnetoreception to enable an understanding of the minimum requirements of a fail-safe mechanism, operational at the cellular level, to sense a weak magnetic field at ambient temperature in a biologically active environment. To do this, we use magnetotactic bacteria (MTB) as our model system. The magnetic field sensing ability of these bacteria is due to the presence of magnetosomes, which are internal membrane-bound organelles that contain an iron-based magnetic mineral crystal. These magnetosomes are usually found arranged in a chain aligned with the long axis of the bacterial body. This arrangement yields an overall magnetic dipole moment to the bacterial cell. To simulate this orientation process, we set up a rotational Langevin stochastic differential equation and solve it repeatedly over appropriate time steps for isolated spherical shaped MTB as well as for a more realistic model of spheroidal MTB with flagella. The orientation process appears to depend on shape parameters with spheroidal MTB showing a slower response time compared to spherical MTB. Further, our simulation also reveals that the alignment to the external magnetic field is more robust for an MTB when compared to single magnetosome. For the simulation involving magnetosomes, we include an extra torque that arises from the twisting of an attachment tether and enhance the viscosity of the surrounding medium to mimic intracellular conditions in the governing Langevin equation. The response time of alignment is found to be substantially reduced when one includes a dipole interaction term with a neighboring magnetosome and the alignment becomes less robust with increase in inter dipole distance. The alignment process can thereby be said to be very sensitively dependent on the distance between magnetosomes. Simulating the process of alignment between two neighboring magnetosomes, both in the absence and presence of an ambient magnetic field, we conclude that alignment between these dipoles at the distances typical in an MTB is highly probable and it would be the locked unit that responds to changes in the external magnetic field.
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Applied Optics
We report an enhancement in the corner frequency of an optically trapped non-magnetic microsphere... more We report an enhancement in the corner frequency of an optically trapped non-magnetic microsphere in the plane perpendicular to the laser propagation direction on addition of ferrofluid to the suspension medium. We conjecture that a directed motion of the nanoparticles toward the trap in this plane is responsible for the augmentation. Changes in the corner frequency in the presence of external magnetic field gradients lend credence to this conjecture. Corner frequency augmentation is also observed when zinc oxide nanoparticles are used. Here, however, no further changes are seen in the presence of magnetic field gradients.
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DAE SOLID STATE PHYSICS SYMPOSIUM 2019
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PLOS ONE
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PLOS ONE
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Journal of Magnetism and Magnetic Materials
Abstract Bi(1−x)TbxFeO3 (x = 0, 0.03, 0.04, 0.06, 0.09, 0.12) nanoparticles are prepared by sol-g... more Abstract Bi(1−x)TbxFeO3 (x = 0, 0.03, 0.04, 0.06, 0.09, 0.12) nanoparticles are prepared by sol-gel method. X-ray diffraction analysis shows the formation of perovskite structure in the synthesized samples and crystallite sizes in the range of 15 nm. The perovskite structure together with the presence of a strong absorption peak observed at 545 cm−1 in the Fourier Transform Infrared Spectroscopy measurements, characteristic of FeO6 octahedral, confirms the formation of single phase BiFeO3 structure. The cycloidal spin nature of BiFeO3 is said to be suppressed in particles that are less than 62 nm across enhancing the ferromagnetic signature. The magnetic behaviour of the Bi(1−x)TbxFeO3 nanoparticles is found to change anomalously with change in Tb doping. Vibrating-sample magnetometer studies reveal a maximum in the magnetic moment for a Tb doping concentration of x = 0.03 with clear ferromagnetic order at room temperature. With increase in x beyond 0.03, magnetization decreases, while a further increase beyond x = 0.04 once again increases the magnetization. Room temperature Mossbauer spectroscopy reveals the presence of a paramagnetic doublet and a sextet, the variation of whose relative ratios is in corroboration with the magnetization studies.
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IOP Conference Series: Materials Science and Engineering
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Nanophotonics VI, 2016
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Optical Trapping and Optical Micromanipulation XIII, 2016
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Applied optics, Jan 20, 2016
We have studied in detail the situation wherein two microbeads are trapped axially in a single-be... more We have studied in detail the situation wherein two microbeads are trapped axially in a single-beam Gaussian intensity profile optical trap. We find that the corner frequency extracted from a power spectral density analysis of intensity fluctuations recorded on a quadrant photodetector (QPD) is dependent on the detection scheme. Using forward- and backscattering detection schemes with single and two laser wavelengths along with computer simulations, we conclude that fluctuations detected in backscattering bear true position information of the bead encountered first in the beam propagation direction. Forward scattering, on the other hand, carries position information of both beads with substantial contribution from the bead encountered first along the beam propagation direction. Mie scattering analysis further reveals that the interference term from the scattering of the two beads contributes significantly to the signal, precluding the ability to resolve the positions of the individu...
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International Conference on Optics and Photonics 2015, 2015
The phase of a negative axicon is combined with that of a Fresnel zone lens (FZL) to obtain an el... more The phase of a negative axicon is combined with that of a Fresnel zone lens (FZL) to obtain an element labelled as conical FZL, which can generate a focused ring pattern at the focal plane of the FZL. The phase integration is achieved by modifying the location and width of zones of FZL in accordance with the phase variation of the negative axicon. The element was designed for a high power laser with a wavelength of 1064 nm, focal length and diameter of conical FZL of 30 mm and 8 mm respectively and for a ring diameter of 50 μm. The element was fabricated using photolithography. The pattern was transferred from the resist layer to the borosilicate glass plates by dry etching to achieve an etch depth of 1064 nm. The etch depth measured using confocal microscope was 1034 nm at the central part and 930 nm for the outermost part of the device with a maximum error of 12.5% at the outermost part and 3% at the central part. The element was used in an optical trapping experiment. The ring pattern generated by the conical FZL was reimaged into the trapping plane using a tightly focusing microscopic objective. Polystyrene beads with diameters of 3 μm were suspended in deionized distilled water at the trapping plane. The element was found to trap multiple particles in to the same trap.
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Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues XII, 2014
A microscopic object finds an equilibrium orientation under a laser tweezer such that a maximum o... more A microscopic object finds an equilibrium orientation under a laser tweezer such that a maximum of its volume lies in the region of highest electric field. Furthermore, birefringent microscopic objects show no rotational diffusion after reorienting under a linearly polarized optical trap and also are seen to follow the plane of polarization when the latter is changed using a half wave plate. We observe that a healthy human Red Blood Cell (RBC) reproduces these observations in an optical tweezer, which confirms it to be birefringent. Polarization microscopy based measurements reveal that the birefringence is confined to the cell’s dimple region and the mean value of retardation for polarized green light (λ = 546nm) is 9 ± 1.5nm. We provide a simple geometrical model that attributes the birefringence to the nature of arrangement of the phospholipid molecules of the bilayer. This predicts the observed variation in the measured birefringence, from the dimple to the rim of the cell which we further show, can serve to demarcate the extent of the dimple region. This points to the value of birefringence measurements in revealing cell membrane contours. . We extend this technique to understand the birefringence of a chicken RBC, an oblate shaped cell, wherein the slow axis is identified to be coincident with the long axis of the cell. Further, we observe the birefringence to be confined to the edges of the cell. Experiments to probe the optomechanical response of the chicken RBC are in progress.
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Journal of Biomedical Optics, 2014
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International Journal of Nanoscience, 2011
A dual optical tweezer has been built around an inverted microscope with high numerical aperture ... more A dual optical tweezer has been built around an inverted microscope with high numerical aperture objective (N.A 1.4). The setup is versatile and can be used both as a single and a dual tweezer, and in the dual mode, enables us to optically trap two micron-sized latex beads within a few microns from each other in solution. Using this setup, we report measurements of the microrheological parameters of Pseudomonas fluorescens and Bacillus subtilis bacterial suspensions. We study the variation of viscoelastic moduli of these bacterial suspensions as a function of their cell count in solution. A comparison with inactive bacteria of corresponding cell count enables us to characterize the activity of the bacterial samples in terms of an average force that the bacteria exerts on the trapped bead. This work paves way for studies of interesting nonlinear rheological phenomena at small length scales.
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Lecture Notes in Physics, 2002
In tunneling magneto resistance (TMR) devices the electronic and magnetic properties of the inter... more In tunneling magneto resistance (TMR) devices the electronic and magnetic properties of the interfaces between the ferromagnetic metals and the insulating spacer layer influence the effective scattering potential for the conduction electrons. As this is especially relevant for ...
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12th International Conference on Fiber Optics and Photonics, 2014
We report the trapping characteristics of semi metallic micro beads in an optical trap. We observ... more We report the trapping characteristics of semi metallic micro beads in an optical trap. We observe that the semi metallic beads are trapped at the focus like dielectric beads but with reduced corner frequency.
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Papers by Sarbari Bhattacharya