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

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Abstract

We have applied photothermal bending of a cantilever induced by an intensity-modulated infrared laser to control the tip-surface distance in atomic force microscopy. The slow response of the photothermal expansion effect is eliminated by inverse transfer function compensation. By regulating the laser power and regulating the cantilever deflection, the tip-sample distance is controlled; this enables much faster imaging than that in the conventional piezoactuator-based z scanners because of the considerably higher resonant frequency of small cantilevers. Using this control together with other devices optimized for high-speed scanning, video-rate imaging of protein molecules in liquids is achieved.

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Tapping mode atomic force microscopy in liquids

P. Hansma, J. P. Cleveland, M Radmacher … (1994)

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Evidence for localized cell heating induced by infrared optical tweezers.

Y. LIU, D.K. Cheng, G.J. Sonek … (1995)

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.