UC Irvine

Microthermometric measurements on optically-trapped Chinese Hamster Ovary (CHO) cells and sperms cells are reported, using a non-invasive microfluorometric detection technique. Within an optical tweezer system that has been outfitted with a spectral fluorescence excitation and detection capability, the changes in temperature induced by the process of sample confinement by a focused laser beam has been quantified over micron-sized spatial regions of both motile and immotile cells. Our measurement technique is based on the use of environmentally sensitive fluorophores that can be incorporated into the cell membrane and used to sense local changes in temperature when the cell membrane is perturbed optically or via other environmental stress factors. Using a cw 1 .064 tm Nd:YAG laser for trapping CHO and human sperm cells, a temperature increase of -4°C per 100 mW laser power was observed. At this infrared wavelength, cellular heating as result of laser confinement appears to be mainly due to radiation absorption by water.