Laser cavitation

Because removing a cell from its growth substrate alters many of the biological processes occurring in the cell, its detachment increases the difficulty in analyzing the cell and the variation from its normal function. Thus, in order to obtain the most accurate portrait of the cell s internal environment, it must be sampled quickly after removal from the substrate. Two innovative techniques, laser cavitation and fast electrical lysis, allow for rapid sampling of substrate-bound cells. 

Sims et al." have exploited the production of a shockwave created by a laser beam for then-laser cavitation scheme (Figure 14.1b). The shockwave generated by laser pulse is focused in close proximity to the cell to be analyzed, forming plasma at the focal point. A cavitation bubble is produced that subsequently collapses and causes a shockwave that ruptures the cell s membrane. Cellular contents can then be loaded rapidly after lysis, reducing the time available for deviation from standard cell function to occur. 

FIGURE 14.1 Recently developed whole cell sampling schemes, (a) Continuous cell introduction. (From Chen, S. andLillard, S.J., AnaZ. Chem., 73, 111, 2001. With permission.) (b) Laser cavitation. (From Sims, C.E. et al.. Anal. Chem., 70, 4570, 1998. With permission.) (c) Fast electrical lysis. (From Han, R, et al.. Anal. Chem., 75, 3688, 2003. With permission.)... 

A second problem in these studies concerns cavitation dynamics on the nanometer length scale [86]. If sufficiently energetic, the ultrafast laser excitation of a gold nanoparticle causes strong nonequilibrium heating of the particle lattice and of the water shell close to the particle surface. Above a threshold in the laser power, which defines the onset of homogeneous nucleation, nanoscale water bubbles develop around the particles, expand, and collapse again within the first nanosecond after excitation (Fig. 9). The size of the bubbles may be examined in this way. 

Ohl CD, Arora M, Dijkink R, Janve V, Lohse D (2006) Surface cleaning from laser-induced cavitation bubbles. Appl Phys Lett 89 074102 (3 pages)... 

Optic cavitation It is produced by photons of high intensity light (laser) rupturing the liquid continuum. 

The dynamic process of bubble collapse has been observed by Lauter-born and others by ultrahigh speed photography (105 frames/second) of laser generated cavitation (41). As seen in Fig. 4, the comparison between theory and experiment is remarkably good. These results were obtained in silicone oil, whose high viscosity is responsible for the spherical rebound of the collapsed cavities. The agreement between theoretical predictions and the experimental observations of bubble radius as a function of time are particularly striking. 

Fig. 4. Dynamics of bubble motion. Laser-induced cavitation in silicone oil upper portion is the experimental observations at 75,000 frames/second lower curve compares the experimentally observed radius versus theory. [W. Lauterborn (47).]...

Fig. 6. Cavitation near a surface. Jet formation from laser-induced cavitation in water at 75,000 frames/second. Sequence is from left to right, top to bottom the solid boundary is at the bottom of each frame. From Ref. 66.

A number of terms in this area will be unfamiliar to most chemists. Cavitation is the formation of gas bubbles in a liquid and occurs when the pressure within the liquid drops significantly below the vapor pressure of the liquid. Cavitation can occur from a variety of causes turbulent flow, laser heating, electrical discharge, boiling, radiolysis, or acoustic irradiation. We will be concerned... 

More recent light-scattering studies (ref. 26,59,60) of microbubble populations in fresh water, using laser-light sources, have yielded very similar results. For example, Keller s laser-scattered-light technique (ref. 26) provided precise measurements of the size and number of freestream gas nuclei (i.e., long-lived microbubbles) in a cavitation tunnel from microbubble spectra... 

Wray, W. O., Aida, T., and Dyer, R. B. (2002). Photoacoustic cavitation and heat transfer effects in the laser-induced temperature jump in water. Appl. Phys. B 74, 57—66. 

Liquid carbon dioxide (purity 99, 95 Vol %) was undercooled (W2) to avoid cavitation in the membran pump (P). After the compression to pre-expansion pressure, the fluid is heated to the extraction temperature (W3). The supercritical fluid loaded with anthracene leaves the extractor (V = 0,6 1). With a additional heat exchanger (W4), the solution is heated to pre-expansion temperature. In the separation vessel, the supercritical solution is expanded through a nozzle. The expanded gas will be condensed (Wl) and recompressed or let off. After the experiment, the separation vessel is opened and the particles were collected. The particle size is measured by laser diffraction spectroscopy (Malvern Master Sizer X). 

A schematic illustration of the laser tsunami and laser power dependence of shockwave generation, plasma emission, and cavitation bubbling is given in Figure 28.2. It is noticeable that the threshold of the shockwave is lowest and that of the bubbling is highest [35]. Of course this tendency is rather qualitative, as direct... 

Figure 28.2 A schematic representation of the laser tsunami and laser energy necessary to induced shockwave, emission, and cavitation.

Laser tsunami comprising, shockwaves, emission, cavitation bubble, and convection flows... 

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