Evidence for localized cell heating induced by infrared optical tweezers

Abstract

The confinement of liposomes and Chinese hamster ovary (CHO) cells by infrared (IR) optical tweezers is shown to result in sample heating and temperature increases by several degrees centigrade, as measured by a noninvasive, spatially resolved fluorescence detection technique. For micron-sized spherical liposome vesicles having bilayer membranes composed of the phospholipid 1,2-diacyl-pentadecanoyl-glycero-phosphocholine (15-OPC), a temperature rise of approximately 1.45 +/- 0.15 degrees C/100 mW is observed when the vesicles are held stationary with a 1.064 microns optical tweezers having a power density of approximately 10(7) W/cm2 and a focused spot size of approximately 0.8 micron. The increase in sample temperature is found to scale linearly with applied optical power in the 40 to 250 mW range. Under the same trapping conditions, CHO cells exhibit an average temperature rise of nearly 1.15 +/- 0.25 degrees C/100 mW. The extent of cell heating induced by infrared tweezers confinement can be described by a heat conduction model that accounts for the absorption of infrared (IR) laser radiation in the aqueous cell core and membrane regions, respectively. The observed results are relevant to the assessment of the noninvasive nature of infrared trapping beams in micromanipulation applications and cell physiological studies.

Analysis of laser-induced heating in optical neuronal guidance

“…This magnitude of heating is in agreement with experimentally observed laser-induced heating of vesicles by infrared optical tweezers (Liu et al, 1995), of DNA in an infrared optical trap (Braun and Libchaber, 2002), of micron-sized silica and polystyrene beads in a optical traps (Peterman et al, 2003), and temperature sensitive dyes in buffer suspension in an infrared dual-beam laser trap (Ebert et al, 2007). We find that for spot sizes with w s = 1-2 m, we have d hm = 32.7 m, which is comparable to the diameter of a neuronal growth cone.…”

Tip-sample distance control using photothermal actuation of a small cantilever for high-speed atomic force microscopy

“…20 Liu et al have reported that the temperature rise of a lipid directly irradiated by the IR laser with 100 mW and a focused spot size of 0.8 m in water is about 1.5°C. 21 In our system, the spot size is larger ͑Ͼ1 m͒ for 100 mW and most of the laser illuminates the cantilever, which is separated from the surface about 1 m. Therefore it is expected that the IR laser does not rise sample temperature so much. In fact, obvious structural alterations of proteins were not observed when an IR laser was used.…”

Exploitation of physical and chemical constraints for three-dimensional microtissue construction in microfluidics

“…The temperature increases as much as 10, 11.5, and 14.5°C / W, respectively. 139,140 Local heating is a serious issue in trapping cells as heat adversely affects enzyme activity and other sensitive cellular functions; also, steep thermal gradient might cause a convection current that disrupts laminar flow in the microfluidic channel. Therefore, there is much room to improve and potentially in combination with other physical and chemical trapping techniques.…”