Ying Liu

The efficiency of dielectric particle confinement with 790-nm AlGaAs laser diode optical traps is investigated as a function of beam magnification and polarization state. When an anamorphic prism pair is used to correct for diode beam ellipticity, trapping efficiencies of nearly 0.37 are achieved with a magnification factor of 3X, laser powers of 4-18 mW, and an overfilled microscope objective entrance aperture. Results are compared for diodes having small and large astigmatisms, but comparable far-field divergence angles. © 1994 IEEE.

We report the results of microfluorometric measurements of physiological changes in optically trapped immotile Chinese hamster ovary cells and motile human sperm cells under continuous-wave and pulsed-mode trapping conditions at 1064 nm. The fluorescence spectra derived from the exogenous fluorescent probes laurdan, acridine orange, propidium iodide, and Snarf are used to assess the effects of optical confinement with respect to temperature, DNA structure, cell viability, and intracellular pH, respectively. In the latter three cases, fluorescence is excited via a two- photon process, using a CW laser trap as the fluorescence excitation source. An average temperature increase of < 1.0 ± 0.30°C/100 mW is measured for cells when held stationary with CW optical tweezers at powers of up to 400 mW. The same trapping conditions do not appear to alter DNA structure or cellular pH. In contrast, a pulsed 1064-nm laser trap produced significant fluorescence spectral alterations in acridine orange, perhaps because of thermally induced DNA structural changes or laser-induced multiphoton processes. The techniques and results presented herein demonstrate the ability to perform in situ monitoring of cellular physiology during CW and pulsed laser trapping, and should prove useful in studying mechanisms by which optical tweezers and microbeams perturb metabolic function and cellular viability.

The confinement of liposomes and Chinese hamster ovary cells by infrared 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, a temperature rise of ~1.45 ± 0.15°C/100 mW is observed when the vesicles are held stationary with a 1.064 μm optical tweezers having a power density of ~10 7 W/cm 2 and a focused spot size of ~0.8 μm. 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°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 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.

We describe a novel microfluorometric technique, based on the temperature-dependent fluorescence emission from single dye-labeled phospholipid vesicles, for the determination of localized heating effects. An increase in sample temperature results in a red shifting of the probe fluorescence spectrum. As individually calibrated microthermometers, fluorescent liposomes exhibit a temperature sensitivity of ∼0.1°C in the vicinity of the bilayer phase transition temperature. Through modification of the bilayer components, both the sensitivity and operating temperature range of these microthermometers can be controlled. Micron spatial resolution is achieved at a signal-to-noise ratio in excess of 103:1. We use the above technique, for the first time, to determine localized heating effects induced by a laser beam focused to its near-diffraction limited spot size. At the laser wavelength of λ=1.064 μm, a temperature change of 1.1°C/100mW in 10-μm-diam organic liposomes is reported. Implications for the real-time optical monitoring of temperature in biological systems are discussed.

In the 1990s, have long been into the "limbo" of literary criticism and ethics scholars quietly occupied the United States. In the post-modern context, the literary criticism of the ethical shift is not a simple return to tradition, but was given a new meaning and carry a new mission. Engaged in literary criticism of the construction of ethical theorists because of their different starting points and strategies basically two camps: the new humanism and deconstruction were sent, who together constitute a post-modern context of the ethical criticism of American literature the landscape. Ethic criticism dominated American literary criticism once again in 1990's, though for a long time it was marginized. However, the ethics turn of literary criticism in the post modern context is not simply a returning to tradition, instead, it was endowed with new connotation therefore equipped with new missions. Varied in starting points and strategies, critics devoted to ethic criticism could roughly be divided into two parts: that of ness humanism and of deconstruction. The work together and form a postmodern brilliant ethic landscape in American criticism