Stress Response in Caenorhabditis elegans Caused by Optical Tweezers: Wavelength, Power, and Time Dependence

Abstract

Optical tweezers have emerged as a powerful technique for micromanipulation of living cells. Although the technique often has been claimed to be nonintrusive, evidence has appeared that this is not always the case. This work presents evidence that near-infrared continuous-wave laser light from optical tweezers can produce stress in Caenorhabditis elegans. A transgenic strain of C. elegans, carrying an integrated heat-shock-responsive reporter gene, has been exposed to laser light under a variety of illumination conditions. It was found that gene expression was most often induced by light of 760 nm, and least by 810 nm. The stress response increased with laser power and irradiation time. At 810 nm, significant gene expression could be observed at 360 mW of illumination, which is more than one order of magnitude above that normally used in optical tweezers. In the 700-760-nm range, the results show that the stress response is caused by photochemical processes, whereas at 810 nm, it mainly has a photothermal origin. These results give further evidence that the 700-760-nm wavelength region is unsuitable for optical tweezers and suggest that work at 810 nm at normal laser powers does not cause stress at the cellular level.

Raman spectroscopy: techniques and applications in the life sciences

“…The results at single cell level in vitro have been supported by experiments on a transgenic strain of Caenorhabditis elegans that carried an integrated heat-shock-responsive reporter gene [189]. The experimental data showed that expression of the heat-shock gene was most often induced by exposure to 760 nm laser light, and least expressed at 810 nm laser wavelength.…”

“…The linear relationship between the damage and the irradiation energy dose in the 700-760 nm range indicated that the stress response is caused by photochemical processes. In contrast, for 810 nm laser wavelength, the stress depended linearly with the laser power, indicating a photothermal effect caused by single photon absorption, although calculations indicated an expected temperature rise only on the order of 1 • C per 100 mW of laser light (the simulations considered a diffraction limited spot obtained with a microscope objective with 100x/1.35 NA and assumed that all absorbed light is converted to heat) [189].…”

Optical tweezers for single cells

“…Shorter wavelengths below 800 nm can also bring great damage to biological cells that were observed by Konig et al (1996a,b) and Leitz et al (2002). Leitz et al (2002) systematically investigated effects of illumination from OT by using different laser powers, irradiation time and wavelength on cell damage.…”

Low-level (gallium-aluminum-arsenide) laser irradiation of Par-C10 cells and acinar cells of rat parotid gland

“…Laser irradiation can be considered a stress signal for cells [24]. The most obvious feature of response to stress is that it leads to an increase in synthesis of HSPs [25,26], which are believed to function in the protection and recovery of cells from environmental or pathological stress [25,26].…”