10 May 1996 Two-photon excitation in living cells induced by low-power cw laser beams
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We demonstrate multi-photon excitation in optically-trapped living cells. Intracellular non-resonant two-photon excitation of endogenous and exogenous chromophores was induced by CW near infrared (NIR) trapping beams of 105 mW power. In the case of fluorescent chromophores, detection of NIR-excited visible fluorescence was achieved by imaging and spectroscopy methods. Trap-induced, two-photon excited fluorescence was employed as a novel diagnostic method to monitor intracellular redox state and cell vitality of single motile spermatozoa and Chinese hamster ovary cells. We found, that nonlinear absorption of NIR photons <800 nm may lead to oxidative stress and severe cell damage. Biological response was amplified in multimode CW lasers due to longitudinal mode-beating and partial mode- locking. As a result, we recommend the use of longwavelength-NIR, single-frequency traps ("optical tweezers") for micromanipulation of vital cells.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Karsten Koenig, Tatjana B. Krasieva, Yagang Liu, Michael W. Berns, Bruce J. Tromberg, "Two-photon excitation in living cells induced by low-power cw laser beams", Proc. SPIE 2678, Optical Diagnostics of Living Cells and Biofluids, (10 May 1996); doi: 10.1117/12.239503; https://doi.org/10.1117/12.239503

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