Debjit Roy

Postdoctoral Research Associate, Washington University in St. Louis

Education / Work History

Postdoctoral Research Associate, Washington University in St. Louis (2018-present)
Ph.D. Scholar, IIT Kanpur (2016)

Thesis Abstract

Control and application of two photon fluorescence in microscopy and optical tweezers

The broad two photon absorption spectra of fluorophores along with the large spectral width of excitation laser pulses lead to the simultaneous excitation of different fluorophores. Control using selective excitation of chromophores is required to overcome such a problem. I performed such a control of TPF in microscopy using a single laser beam. Precise control of the delay between pairs of ultrafast laser pulses can effectively serve such a purpose by exploiting both the coherent vibrational wavepacket interferometry as well as the selective suppression of fluorescence by stimulated emission depletion. I also explored the effect of 20–50 GHz pulse-train on selective TPF suppression and a compared with the pulse-pair case. Optical trapping of tiny Rayleigh particles using high repetition rate femtosecond laser pulses occurs at a much lower average power as compared to that of a continuous wave laser. In this regard, I have shown the optical trapping of fluorophore coated latex bead spheres (diameter 100 nm) and fluorescent quantum dots at average powers of only a few tens of milliwatts. The gigantic peak power of the femtosecond laser pulses even at a very low average power enables such optical tweezing events. The TPF generated from the optically trapped Rayleigh particles by the trapping femtosecond laser pulses serves as a detection scheme for these Rayleigh particles. This is fortunate as they cannot be otherwise visualized easily under the conventional bright field imaging techniques because their sizes are below the diffraction limited spot size. I have also explored the effectiveness of TPF detection scheme in optical traps. Rather than just being a good background free detection scheme, I showed that TPF generated from the trapped objects can be used as their position marker. Extending on this, the optical tweezers system has been calibrated by measuring the trap stiffness using power spectrum method. When the sizes of the optically trapped objects are more than the laser beam focal spot size, partial illumination of the trapped objects occur. If the trapped objects are fluorophore coated, then the fluorophore molecules present only on the illuminated surface of the optically trapped objects undergo laser induced two photon absorption processes. Fluorescence energy transfer occurs from the fluorophore molecules present on the illuminated zone to those present on the non-illuminated zone of the trapped object surface. This leads to a counterintuitive decay of the two photon fluorescence signal with time. I have shown this phenomenon by optically trapping fluorophore coated polystyrene microspheres of diameters 1 μm, 2 μm and 4μm, respectively. A simple model that matches these experimental results has been proposed to explain this fact. The high gradient force of the optical tweezers arising from the tight focusing of the transverse Gaussian laser beam drags the particle towards the center of the optical trap. For the trapping of smaller particles, this would result in multiple particle trapping and as a consequence, an optically bound cluster would form. I have studied the structure and dynamics of such optically bound clusters formed by the optical trapping of multiple 0.5 μm diameter polystyrene microspheres that are fluorophore coated. This has been determined from the fluorescence resonance energy transfer process occurring between the fluorophores present on the illuminated and non-illuminated surface of the trapped microspheres using linearly versus circularly polarized trapping laser beams.

Research Topic / Interest

Contact me to know my current interests.

Publications

These include only those published in our lab.

‪Control of Selective Two-Photon Fluorescence Suppression by One-Color Pulse-Pair Excitation‬. D. Roy, A. K. De, and D. Goswami, Asian Journal of Physics 31(3-5), 475–478 (2022)

BibTeX: @article{royControlSelectiveTwophoton2022,
  title = {‪{{Control}} of Selective Two-Photon Fluorescence Suppression by One-Color Pulse-Pair Excitation‬},
  author = {Roy, Debjit and De, Arijit K. and Goswami, Debabrata},
  year = {2022},
  journal = {Asian Journal of Physics},
  volume = {31},
  number = {3-5},
  pages = {475--478},
  urldate = {2022-12-31},
  annotation = {GSCC: 0000000}
}

Two-Photon Fluorescence Tracking of Colloidal Clusters. D. Roy, D. Mondal, and D. Goswami, Journal of Fluorescence 26(4), 1271–1277 (2016)

BibTeX: @article{royTwoPhotonFluorescenceTracking2016,
  title = {Two-{{Photon Fluorescence Tracking}} of {{Colloidal Clusters}}},
  author = {Roy, Debjit and Mondal, Dipankar and Goswami, Debabrata},
  year = {2016},
  month = jul,
  journal = {Journal of Fluorescence},
  volume = {26},
  number = {4},
  pages = {1271--1277},
  issn = {1573-4994},
  doi = {10/f82fs3},
  urldate = {2019-08-01},
  langid = {english},
  annotation = {GSCC: 0000003 \\
  2 citations (Crossref) [2024-05-28]\\
  00000}
}

Structure and Dynamics of Optically Directed Self-Assembly of Nanoparticles. D. Roy, D. Mondal, and D. Goswami, Scientific Reports 6, 23318 (2016)

BibTeX: @article{royStructureDynamicsOptically2016,
  title = {Structure and Dynamics of Optically Directed Self-Assembly of Nanoparticles},
  author = {Roy, Debjit and Mondal, Dipankar and Goswami, Debabrata},
  year = {2016},
  month = mar,
  journal = {Scientific Reports},
  volume = {6},
  pages = {23318},
  issn = {2045-2322},
  doi = {10/f8fjqk},
  urldate = {2019-08-01},
  copyright = {2016 Nature Publishing Group},
  langid = {english},
  annotation = {GSCC: 0000016 \\
  11 citations (Crossref) [2024-05-28]\\
  00000}
}

Elucidating Two Photon FRET and Its Application through Femtosecond Optical Tweezers. D. Mondal, D. Roy, S. Dinda, A. Singh, and D. Goswami, in Advanced Photonics 2016 (IPR, NOMA, Sensors, Networks, SPPCom, SOF) (OSA, 2016), p. NoTu2D.4

BibTeX: @inproceedings{mondalElucidatingTwoPhoton2016,
  title = {Elucidating {{Two Photon FRET}} and Its Application through Femtosecond Optical Tweezers},
  booktitle = {Advanced {{Photonics}} 2016 ({{IPR}}, {{NOMA}}, {{Sensors}}, {{Networks}}, {{SPPCom}}, {{SOF}})},
  author = {Mondal, Dipankar and Roy, Debjit and Dinda, Sirshendu and Singh, Ajitesh and Goswami, Debabrata},
  year = {2016},
  pages = {NoTu2D.4},
  publisher = {OSA},
  address = {Vancouver},
  doi = {10/gf5mr4},
  urldate = {2019-08-01},
  isbn = {978-1-943580-14-9},
  langid = {english},
  annotation = {GSCC: 0000000 \\
  0 citations (Crossref) [2024-05-28]\\
  00000}
}

Exploring the Physics of Efficient Optical Trapping of Dielectric Nanoparticles with Ultrafast Pulsed Excitation. D. Roy, D. Goswami, and A. K. De, Applied Optics 54(23), 7002 (2015)

BibTeX: @article{royExploringPhysicsEfficient2015,
  title = {Exploring the Physics of Efficient Optical Trapping of Dielectric Nanoparticles with Ultrafast Pulsed Excitation},
  author = {Roy, Debjit and Goswami, Debabrata and De, Arijit K.},
  year = {2015},
  month = aug,
  journal = {Applied Optics},
  volume = {54},
  number = {23},
  pages = {7002},
  issn = {0003-6935, 1539-4522},
  doi = {10/gf5msm},
  urldate = {2019-08-01},
  langid = {english},
  annotation = {GSCC: 0000035 \\
  27 citations (Crossref) [2024-05-28]\\
  00000}
}

Enhanced Detection of Tissue Auto-Fluorescence by One-Photon Ultrafast Pulsed Illumination. A. De, D. Roy, V. Bansal, A. Gupta, and D. Goswami, Current Science 109(1), 21–22 (2015)

BibTeX: @article{deEnhancedDetectionTissue2015,
  title = {Enhanced Detection of Tissue Auto-Fluorescence by One-Photon Ultrafast Pulsed Illumination},
  author = {De, Arijit and Roy, Debjit and Bansal, Vivek and Gupta, Aditya and Goswami, Debabrata},
  year = {2015},
  month = jul,
  journal = {Current Science},
  volume = {109},
  number = {1},
  pages = {21--22},
  annotation = {GSCC: 0000000}
}

Elucidating Microscopic Structure and Dynamics in Optically Tweezed Environments. D. Roy, D. Mondal, and D. Goswami, Chemical Physics Letters 621, 203–208 (2015)

BibTeX: @article{royElucidatingMicroscopicStructure2015,
  title = {Elucidating Microscopic Structure and Dynamics in Optically Tweezed Environments},
  author = {Roy, Debjit and Mondal, Dipankar and Goswami, Debabrata},
  year = {2015},
  month = feb,
  journal = {Chemical Physics Letters},
  volume = {621},
  pages = {203--208},
  issn = {0009-2614},
  doi = {10/f6zd8x},
  urldate = {2019-08-01},
  annotation = {GSCC: 0000007 \\
  7 citations (Crossref) [2024-05-28]\\
  00000}
}

Fluorescence Advantages with Microscopic Spatiotemporal Control. D. Goswami, D. Roy, and A. K. De, in Design and Quality for Biomedical Technologies VI (International Society for Optics and Photonics, 2013), 8573, p. 857302

BibTeX: @inproceedings{goswamiFluorescenceAdvantagesMicroscopic2013,
  title = {Fluorescence Advantages with Microscopic Spatiotemporal Control},
  booktitle = {Design and {{Quality}} for {{Biomedical Technologies VI}}},
  author = {Goswami, Debabrata and Roy, Debjit and De, Arijit K.},
  year = {2013},
  month = mar,
  volume = {8573},
  pages = {857302},
  publisher = {{International Society for Optics and Photonics}},
  doi = {10/gf5npw},
  urldate = {2019-08-02},
  annotation = {GSCC: 0000059 \\
  0 citations (Crossref) [2024-05-28]\\
  00002}
}

Selective Two-Photon Fluorescence Suppression by Ultrafast Pulse-Pair Excitation: Control by Selective One-Color Stimulated Emission. A. K. De, D. Roy, and D. Goswami, Journal of Biomedical Optics 16(10), 100505 (2011)

BibTeX: @article{deSelectiveTwophotonFluorescence2011,
  title = {Selective Two-Photon Fluorescence Suppression by Ultrafast Pulse-Pair Excitation: Control by Selective One-Color Stimulated Emission},
  shorttitle = {Selective Two-Photon Fluorescence Suppression by Ultrafast Pulse-Pair Excitation},
  author = {De, Arijit K. and Roy, Debjit and Goswami, Debabrata},
  year = {2011},
  month = oct,
  journal = {Journal of Biomedical Optics},
  volume = {16},
  number = {10},
  pages = {100505},
  issn = {1083-3668, 1560-2281},
  doi = {10/fqkzpp},
  urldate = {2019-08-02},
  annotation = {GSCC: 0000008 \\
  3 citations (Crossref) [2024-05-28]\\
  00000}
}

Fluorophore Discrimination by Tracing Quantum Interference in Fluorescence Microscopy. A. K. De, D. Roy, and D. Goswami, Physical Review A 83(1), 015402 (2011)

BibTeX: @article{deFluorophoreDiscriminationTracing2011,
  title = {Fluorophore Discrimination by Tracing Quantum Interference in Fluorescence Microscopy},
  author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
  year = {2011},
  month = jan,
  journal = {Physical Review A},
  volume = {83},
  number = {1},
  pages = {015402},
  doi = {10/c73nhs},
  urldate = {2019-08-14},
  annotation = {GSCC: 0000006 \\
  4 citations (Crossref) [2024-05-28]\\
  00006}
}

Two-Photon Fluorescence Diagnostics of Femtosecond Laser Tweezers. A. K. De, D. Roy, and D. Goswami, CURRENT SCIENCE 101(7), 4 (2011)

BibTeX: @article{deTwophotonFluorescenceDiagnostics2011,
  title = {Two-Photon Fluorescence Diagnostics of Femtosecond Laser Tweezers},
  author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
  year = {2011},
  journal = {CURRENT SCIENCE},
  volume = {101},
  number = {7},
  pages = {4},
  langid = {english},
  annotation = {GSCC: 0000009 \\
  00000}
}

Polarization Modulated Ultrafast Pulse-Pair Control in Two-Photon Fluorescence Microscopy. D. Roy, A. K. De, and D. Goswami, in Frontiers in Optics 2011/Laser Science XXVII (OSA, 2011), p. JWA3

BibTeX: @inproceedings{royPolarizationModulatedUltrafast2011,
  title = {Polarization Modulated {{Ultrafast Pulse-Pair Control}} in {{Two-Photon Fluorescence Microscopy}}},
  booktitle = {Frontiers in {{Optics}} 2011/{{Laser Science XXVII}}},
  author = {Roy, Debjit and De, Arijit Kumar and Goswami, Debabrata},
  year = {2011},
  pages = {JWA3},
  publisher = {OSA},
  address = {San Jose, California},
  doi = {10/gf5nqh},
  urldate = {2019-08-02},
  isbn = {978-1-55752-917-6},
  langid = {english},
  annotation = {GSCC: 0000000 \\
  0 citations (Crossref) [2024-05-28]\\
  00000}
}

Selective Suppression of Two-Photon Fluorescence in Laser Scanning Microscopy by Ultrafast Pulse-Train Excitation. A. K. De, D. Roy, and D. Goswami, Journal of Biomedical Optics 15(6), 060502 (2010)

BibTeX: @article{deSelectiveSuppressionTwophoton2010,
  title = {Selective Suppression of Two-Photon Fluorescence in Laser Scanning Microscopy by Ultrafast Pulse-Train Excitation},
  author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
  year = {2010},
  month = nov,
  journal = {Journal of Biomedical Optics},
  volume = {15},
  number = {6},
  pages = {060502},
  issn = {1083-3668, 1560-2281},
  doi = {10/cp9rx2},
  urldate = {2019-08-14},
  annotation = {GSCC: 0000010 \\
  6 citations (Crossref) [2024-05-28]\\
  00007}
}

Towards Stable Trapping of Single Macromolecules in Solution. A. K. De, D. Roy, and D. Goswami, in Optical Trapping and Optical Micromanipulation VII (International Society for Optics and Photonics, 2010), 7762, p. 776203

BibTeX: @inproceedings{deStableTrappingSingle2010,
  title = {Towards Stable Trapping of Single Macromolecules in Solution},
  booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation VII}}},
  author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
  year = {2010},
  month = aug,
  volume = {7762},
  pages = {776203},
  publisher = {{International Society for Optics and Photonics}},
  doi = {10/ckqvtz},
  urldate = {2019-08-14},
  annotation = {GSCC: 0000228 \\
  4 citations (Crossref) [2024-05-28]\\
  00009}
}

Spatio-Temporal Control in Multiphoton Fluorescence Laser-Scanning Microscopy. A. K. De, D. Roy, and D. Goswami, in Multiphoton Microscopy in the Biomedical Sciences X (International Society for Optics and Photonics, 2010), 7569, p. 756929

BibTeX: @inproceedings{deSpatiotemporalControlMultiphoton2010,
  title = {Spatio-Temporal Control in Multiphoton Fluorescence Laser-Scanning Microscopy},
  booktitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences X}}},
  author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
  year = {2010},
  month = feb,
  volume = {7569},
  pages = {756929},
  publisher = {{International Society for Optics and Photonics}},
  doi = {10/c529hw},
  urldate = {2019-08-14},
  annotation = {GSCC: 0000004 \\
  3 citations (Crossref) [2024-05-28]\\
  00004}
}

Stable Optical Trapping of Latex Nanoparticles with Ultrashort Pulsed Illumination. A. K. De, D. Roy, A. Dutta, and D. Goswami, Applied Optics 48(31), G33–G37 (2009)

BibTeX: @article{deStableOpticalTrapping2009,
  title = {Stable Optical Trapping of Latex Nanoparticles with Ultrashort Pulsed Illumination},
  author = {De, Arijit Kumar and Roy, Debjit and Dutta, Aveek and Goswami, Debabrata},
  year = {2009},
  month = nov,
  journal = {Applied Optics},
  volume = {48},
  number = {31},
  pages = {G33-G37},
  issn = {2155-3165},
  doi = {10/b9sxj4},
  urldate = {2019-08-14},
  copyright = {\&\#169; 2009 Optical Society of America},
  langid = {english},
  annotation = {GSCC: 0000080 \\
  49 citations (Crossref) [2024-05-28]}
}

Towards Spatio-Temporal Control in Optical Trapping. D. Roy, A. K. De, and D. Goswami, in Optical Trapping and Optical Micromanipulation VI (International Society for Optics and Photonics, 2009), 7400, p. 74000G

BibTeX: @inproceedings{roySpatiotemporalControlOptical2009,
  title = {Towards Spatio-Temporal Control in Optical Trapping},
  booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation VI}}},
  author = {Roy, Debjit and De, Arijit Kumar and Goswami, Debabrata},
  year = {2009},
  month = aug,
  volume = {7400},
  pages = {74000G},
  publisher = {{International Society for Optics and Photonics}},
  doi = {10/fpdhxs},
  urldate = {2019-08-14},
  annotation = {GSCC: 0000003 \\
  1 citations (Crossref) [2024-05-28]\\
  00003}
}