Continuous-wave Thulium Laser for Heating Cultured Cells to Investigate Cellular Thermal Effects

Abstract

An original method to heat cultured cells using a 1.94 µm continuous-wave thulium laser for biological assessment is introduced here. Thulium laser radiation is strongly absorbed by water, and the cells at the bottom of the culture dish are heated through thermal diffusion. A laser fiber with a diameter of 365 µm is set about 12 cm above the culture dish, without any optics, such that the laser beam diameter is almost equivalent to the inner diameter of the culture dish (30 mm). By keeping a consistent amount of culture medium in each experiment, it is possible to irradiate the cells with a highly reproducible temperature increase. To calibrate the temperature increase and its distribution in one cell culture dish for each power setting, the temperature was measured during 10 s of irradiation at different positions and at the cellular level. The temperature distribution was represented using a mathematical graphics software program, and its pattern across the culture dish was in Gaussian form. After laser irradiation, different biological experiments could be performed to assess temperature-dependent cell responses. In this manuscript, viability staining (i.e., distinguishing live, apoptotic, and dead cells) is introduced to help determine the threshold temperatures for cell apoptosis and death after different points in time. The advantages of this method are the preciseness of the temperature and the time of heating, as well as its high efficiency in heating cells in a whole cell culture dish. Furthermore, it allows for study with a wide variety of temperatures and time durations, which can be well-controlled by a computerized operating system.

Real-time optoacoustic temperature determination on cell cultures during heat exposure: a feasibility study

“…We have recently reported an experimental irradiation setup to heat adherent cells in a culture dish by heating the culture medium with a thulium laser (wavelength 1.94 mm) for 10 s [4]. In that study, temperatures at different positions over a culture plate without cells were measured using small thermocouples.…”

Mode-locked near-infrared thulium doped fibre laser using evanescent field effect with Bi2O3 saturable absorber

“…Near-to mid-infrared fibre lasers are highly desired for various applications ranging from eye-safe LIDAR, free space communications, material processing, environ mental sensing and in medical surgery [1][2][3][4][5]. Of the many lasers capable of operating in this spectral range, the thulium-doped fibre laser (TDFL) is a very promising light source capable of generating powerful and stable ultra-short pulses in the two micron wavelength region [6][7][8].…”