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Indocyanine Green: An U. S. FDA Approved Dye for Multiphoton Bioimaging

5 Apr | By Biophotonics.World
Indocyanine Green: An U. S. FDA Approved Dye for Multiphoton Bioimaging
The two-photon excitation property of the ICG to the S2 state and its direct emission for multiphoton bioimaging. Ex; Excitation, 1P; one photon, 2P; two-photon, S0; ground state, S1; first singlet excited state and S2; second singlet excited state.
By: Dr. Sharad Gupta

Biophysicists Dr. Sharad Gupta and his team from Indian Institute of Technology Indore, India are the first research group worldwide to demonstrate the application of indocyanine green (ICG) as an exogenous contrast agent for multiphoton bioimaging. Multiphoton imaging is a powerful non-invasive bioimaging technique that is used to assess the different aspects of healthy or diseased cells. According to the principle, multiple photons of near-infrared (NIR) wavelength are used to excite the endogenous or exogenous contrast agents in the sample. This technique provides the biochemical and morphological information of the live cells in real time. In the NIR wavelength range biological tissue has minimal absorption and scattering of the excitation photons, which enables to look deeper into the tissues. Additionally,  the use of an exogenous imaging probe that can be activated by the nonlinear process and gives emission, would further improve the contrast and signal-to-noise ratio of the multiphoton bioimaging.

In this direction, Ms. Anshu Kumari and Dr. Sharad Gupta have studied the non-linear excitation process of the only U. S. Food and Drug Administration (FDA) approved dye for the multiphoton bioimaging application. ICG has been used for various clinical applications since 1956, its nonlinear excitation to the second singlet excited state (S2) and its direct emission was never studied earlier for bioimaging. Recently they published a research letter in the Journal of Biophotonics, which discussed the nonlinear excitation behavior of the free ICG. The ICG molecules were excited to the S2state using NIR femtosecond laser followed by their direct relaxation to the S0 state causing visible emission. Due to this property ICG can be included in the list of the molecules that violate Kasha’s rule.

ICG is a biocompatible and safe dye for in-vivo clinical applications. The two-photon excitation to the S2 state of ICG was achieved with the 790 nm wavelength of a femtosecond laser, which lies in the well-known tissue-optical window. The photons of this wavelength penetrate much deeper in the turbid environment such as biological tissues and enable us to look deeper into the tissues. Thus, ICG could be used as the first FDA approved exogenous contrast agent for two-photon imaging. This study could be useful for the development of novel diagnostics technique that could be used to assess the tissue function during healthy and diseased development as well as in response to treatments. These findings would make a remarkable influence on preclinical and clinical multiphoton cellular imaging.


Related Journal Article: J. Biophotonics201912:e201800086


Author: Dr. Sharad Gupta


Area of application: Molecular diagnostics

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