Dr. Vijayalakshmi Varadarajan Profile

Dr. Vijayalakshmi Varadarajan

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Publications (3)

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Proceedings Article | 22 February 2011 Paper

Photothermal mediated transformation of carbon nanoparticles

N. Ingle, V. Varadrajan, S. Mohanty, A. Koymen

Proceedings Volume 7922, 792208 (2011) https://doi.org/10.1117/12.875905

KEYWORDS: Nanoparticles, Carbon, Raman spectroscopy, Continuous wave operation, Laser irradiation, Near infrared, Atomic force microscopy, Transmission electron microscopy, Particles, Spectroscopy

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Irradiating carbon nanoparticles (CNPs) with near-infrared laser beam leads to generation of heat, therefore it has potential to be used in many applications including the destruction of cancer cells. Though pulsed laser beams have been used earlier to transform shapes of metallic and semiconductor nanoparticles, changing shape of CNPs required intense electron beam irradiation. In this paper, we report significant size reduction of CNPs under continuous-wave (cw) near-infrared (NIR) laser beam micro-irradiation which was attributed to melting and vaporization or fragmentation of the carbon nanoparticles. Further, we show that the spherical shape of the CNPs can be transformed into ellipsoidal, by exposure to cw NIR laser microbeam irradiation for a few seconds. In-situ measurements using atomic force microscopy (AFM) reveal the shape and size changes of the CNPs upon laser micro-irradiation. Most importantly, cw NIR laser microbeam irradiation led to ultra-structural phase transformation of CNPs as detected via Raman spectroscopic imaging. While the graphitic CNPs could be changed to diamond-like carbon (DLC), no phase change in DLC nanoparticles was observed. These transformations did not require presence of any special chemical (catalyst, functionalization) or physical (pressure, temperature) arrangement. In-situ control of CNP-size, shape and ultra-structural properties opens new possibilities in multiple nanotechnology adventures.

Proceedings Article | 18 February 2011 Paper

Photothermal therapy of cancer cells using magnetic carbon nanoparticles

V. Vardarajan, L. Gu, A. Kanneganti, S. Mohanty, A. Koymen

Proceedings Volume 7897, 78970Z (2011) https://doi.org/10.1117/12.875971

KEYWORDS: Magnetism, Nanoparticles, Carbon, Absorption, Laser therapeutics, Cancer, Near infrared, Continuous wave operation, Luminescence, Ultrasonics

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Photothermal therapy offers a solution for the destruction of cancer cells without significant collateral damage to otherwise healthy cells. Several attempts are underway in using carbon nanoparticles (CNPs) and nanotubes due to their excellent absorption properties in the near-infrared spectrum of biological window. However, minimizing the required number of injected nanoparticles, to ensure minimal cytotoxicity, is a major challenge. We report on the introduction of magnetic carbon nanoparticles (MCNPs) onto cancer cells, localizing them in a desired region by applying an external magnetic field and irradiating them with a near-infrared laser beam. The MCNPs were prepared in Benzene, using an electric plasma discharge, generated in the cavitation field of an ultrasonic horn. The CNPs were made ferromagnetic by use of Fe-electrodes to dope the CNPs, as confirmed by magnetometry. Transmission electron microscopy measurements showed the size distribution of these MCNPs to be in the range of 5-10 nm. For photothermal irradiation, a tunable continuous wave Ti: Sapphire laser beam was weakly focused on to the cell monolayer under an inverted fluorescence microscope. The response of different cell types to photothermal irradiation was investigated. Cell death in the presence of both MCNPs and laser beam was confirmed by morphological changes and propidium iodide fluorescence inclusion assay. The results of our study suggest that MCNP based photothermal therapy is a promising approach to remotely guide photothermal therapy.

Proceedings Article | 12 February 2011 Paper

Fluorescent carbon nanoparticles synthesized from benzene by electric plasma discharge

R. Chaudhary, V. Varadarajan, S. Mohanty, A. Koymen

Proceedings Volume 7908, 79080C (2011) https://doi.org/10.1117/12.876004

KEYWORDS: Carbon, Luminescence, Plasma, Electrodes, Spectroscopy, Nanoparticles, Raman spectroscopy, Iron, X-rays, Laser therapeutics

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Various allotropes of Carbon nanoparticles (CNP) are emerging as very important building blocks for nanotechnology and biomedical applications due to their unique electronic, optical, mechanical and thermal properties. We report synthesis of crystalline CNPs from benzene using electric plasma discharge method under controlled laboratory environment. With varied electric field, different allotropes of carbon were synthesized as observed under high resolution electron microscope and selected area electron diffraction, optical spectroscopic studies revealed distinct differences between these CNPs. Raman spectroscopy of these CNPs showed a distinct peak at 1330 cm^-1 (characteristic of defect band) and another peak at 1600 cm^-1 (graphitic band). The ratio of defect to graphitic band was found to increase with increasing voltage between Fe-electrodes. Further, the ratio was altered when CNPs were formed using graphite-electrodes. Fluorescence spectroscopic measurements showed evident blue fluorescence exhibited by CNPs formed at relatively higher voltage between two Fe-electrodes. This was attributed to the increasing Fe-content, as measured by Energy dispersive X-ray analysis (EDX) and vibrating sample magnetometer (VSM). Addition of exogenous dyes in benzene during synthesis of CNPs using electric plasma discharge led to formation of fluorescent nanotubes. These fluorescent CNPs can be functionalized to target cancer cells for both imaging and targeted photothermal therapy using near-IR laser beam.

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