Lasers Laser trapping

Gould P L, Lett P D, Julienne P S, Phillips W D, Thorsheim H R and Weiner J 1988 Observation of assooiative ionization of ultraoold laser-trapped sodium atoms Phys.Rev.Lett. 60 788-91... 

Ashkin, A. (1992) Forces of a single-beam gradient laser trap on a dielectric sphere in... 

We have applied FCS to the measurement of local temperature in a small area in solution under laser trapping conditions. The translational diffusion coefficient of a solute molecule is dependent on the temperature of the solution. The diffusion coefficient determined by FCS can provide the temperature in the small area. This method needs no contact of the solution and the extremely dilute concentration of dye does not disturb the sample. In addition, the FCS optical set-up allows spatial resolution less than 400 nm in a plane orthogonal to the optical axis. In the following, we will present the experimental set-up, principle of the measurement, and one of the applications of this method to the quantitative evaluation of temperature elevation accompanying optical tweezers. 

Laser trapping is a technique to manipulate small sized materials, which was developed by Ashkin in 1970 [20, 21]. In this experiment, a laser beam is tightly focused by an objective lens with high numerical aperture (NA), and a dielectric... 

Won, J., Inaba, T., Masuhara, H., Fujiwara, H., Sasaki, K, Miyawaki, S. and Sato, S. (1999) Photofhermal fixation of laser-trapped polymer microparticles on polymer substrates. Appl. Phys. Lett., 75, 1506-1508. 

Hosokawa, Y, Matsumura, S., Masuhara, H., Ikeda, K., Shimo-oka, A. and Mori, H. (2004) Laser trapping and patterning of protein microcrystals Toward highly integrated protein microarrays. J. Appl. Phys., 96, 2945-2948. 

Kim, H.-B., Hayashi, M., Nakatani, K., Kitamura, N., Sasaki, K., Hotta, J.-I., and Masuhara, H., In situ measurements of ion exchange processes in single polymer particles laser trapping microspectroscopy and confocal fluorescence microspectroscopy, Anal. Chem., 68, 409, 1996. 

Laser Trapping-Spectroscopy-Electrochemistry of Individual Microdroplets in Solution (Nakatoni, Chikami, and Kitamura). 

In the first example, we describe time-resolved fluorescence measurements of a fluorescent bead (Fujino and Tahara 2004). Figure 3.6a shows the CCD image of a commercial fluorescent bead that has a diameter of -4.85 pm (Mag Sphere). This bead was laser trapped near the focus point by the excitation pulse. In fact, when the irradiation... 

FIGURE 3.6 The CCD image of a fluorescent bead under (a) laser trapping, and (b) without laser trapping, (c) The femtosecond time-resolved fluorescence at 520 nm observed with lOOx objective lens. (Form, Fujino, T. and Tahara, T.,Appl. Phys. B 79 145-151, 2004.)... 

J. Greenleaf, T. Woodside, A. Abbondanzieri, and S. Block. Passive all-optical clamp for high-resolution laser trapping. Phys. Rev. Lett. 95, 208102 (2005). 

The radiation pressure exerted by light is very weak. A bright laser beam of several milliwatts of power can exert only a few piconewtons (pN) of force. However, a force of 10 pN is enough to pull a cell of E. coli through water ten times faster than it can swim.213 In about 1986, it was found that a laser beam focused down to a spot of - one K ( 1 pm for an infrared laser) can trap and hold in its focus a retractile bead of 1 pm diameter. This "optical tweezers" has become an important experimental tool with many uses.213 214 For example, see Fig. 19-19. Not only are optical tweezers of utility in studying biological motors but also mechanical properties of all sorts of macromolecules can be examined. For example, DNA can be stretched and its extensibility measured.215 Actin filaments have even been tied into knots 216... 

In this review, we describe a laser trapping-spectroscopy-electrochemistry technique as a novel methodology for studying single microdroplets in solution and, demonstrate recent progress in the research on electron transfer and mass transfer across a microdroplet/solution interface in special reference to a droplet size dependence of the process. 

Figure 3. Block diagram of a laser trapping-spectroscopy-electrochemistry system.

The laser trapping-spectroscopy-electrochemistry technique is unique in that simultaneous three-dimensional manipulation and spectroscopic/elec-trochemical measurements can be conducted for individual microdroplets in solution. Although the technique is highly useful for studying single microdroplets, its applicability and limitations have not been well documented until now. Therefore, before discussing detailed chemistry of single droplets in solution, we describe briefly the characteristics of the technique. 

Figure 4. Laser trapping of a single DBP microdroplet in the vicinity of an Au microelectrode. Laser power under the microscope was 300mW.

Figure 5. Fluorescence spectrum of Pe (0.5 mM) in a single laser-trapped TBP droplet (r = 1.5 /im) in water.

Figure 6. Fluorescence decay curves of Pe (5 mM, >440 nm) in the absence and presence of FeCp-H (0.05 M) in single laser-trapped TBP droplets (r = 8 /xm) in water.

Figure 7. Absorption spectra of C-Dye (18.5 mM) in single laser-trapped DBP droplets with r = 4.4, 13.6, and 19.0 /im.

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