Using either a continuous-wave NdYAG laser (1064 nm) or semiconductor diode laser (800 nm) to create optical tweezers, the properties of optically confined Chinese Hamster Ovarian cells (CHOs) and human sperm cells were studied under a variety of trapping parameters. Exogenous probe fluorescence was investigated for samples separately incubated with membrane and nucleic acid probes. These probes facilitated the study of specimen temperature, cell viability, DNA structure, and cellular pH. It was found that trapping at 1064 nm with powers of up to several hundred milliwatts produced cell heating on the order of -1.0- 1.5?/100 mW. Results also demonstrated that trapping conditions can be created with a Q-switched laser (e.g. pulsed laser trapping at 40 J/pulse and 100 ns pulses) that does cause structural damage to DNA. Our fluorescence studies further showed that cw laser traps can produce two-photon excited fluorescence as a result of the extremely high power densities and photon fluxes within the beam focus. This is an important result since an optical trap can not only be used to noninvasively confine a sample, but simultaneously excite sample fluorescence which can be used to physiologically monitor a biological sample during optical confinement and manipulation.
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