Cell viability in optical tweezers: high power red laser diode versus Nd :YAG laser

Viability of cultivated Chinese hamster ovary cells in optical tweezers was measured after exposure: to various light doses of red high power laser di odes (lambda=670-680 nm) and a Nd:yttrium-aluminum-garnet laser (lambda=106 4 nm). When using a radiant exposure of 2.4 GJ/cm(2), a reduction of colony formation up to a factor 2 (670-680 nm) or 1.6 (1064 nm) as well as a dela y of cell growth were detected in comparison with nonirradiated controls. I n contrast, no cell damage was found at an exposure of 370 MJ/cm(2) for bot h wavelengths, and virtually no lethal damage at 1 GJ/cm(2) applied at 1064 nm. Cell viabilities were correlated with fluorescence excitation spectra and with literature data of wavelength dependent cloning efficiencies. Fluo rescence excitation maxima of the coenzymes NAD(P)H and flavins were detect ed at 365 and 450 nm, respectively. This is half of the wavelengths of the maxima of cell inactivation, suggesting that two-photon absorption by these coenzymes may contribute to cellular damage. Two-photon excitation of NAD( P)H and flavins may also affect cell viability after exposure to 670-680 nm , whereas one-photon excitation of water molecules seems to limit cell viab ility at 1064 nm. (C) 2000 society of Photo-Optical instrumentation Enginee rs. [S1083-3668(00)01001-7].