Dynamics of a Shock Wave in Laser-Induced Surface Air Breakdown

The amplitude and the time of arrival of a shock wave have been measured experimentally and calculated numerically at different distances from the region of the surface air breakdown by the radiation of a single-pulse YAG:Nd³⁺ laser for energy densities of 2.5–570 J/cm². Good agreement between the experimental and calculated values of the shock-wave amplitude beyond the breakdown region has been established. A more rapid propagation of the actual shock wave as compared to the calculated shock wave has been revealed for low energies of laser pulses, whereas a retarded propagation of the actual shock wave as compared to the calculated one has been revealed for high energies.     

Raman spectroscopy of primary bovine aortic endothelial cells: a comparison of single cell and cell cluster analysis

There are many techniques that allow in vitro interactions among cells and their environment to be monitored, including molecular, biochemical and immunochemical techniques. Traditional techniques for the analysis of cells often require fixation or lysis from substrates; however, use of such destructive methods is not feasible where the expanded cell cultures are required to be used for clinical implantation. Several studies have previously highlighted the potential of Raman spectroscopy to provide useful information on key biochemical markers within cells. As such, we highlight the capability of Raman spectroscopy with different laser spot sizes for use as a non-invasive, rapid, and specific method to perform in situ analysis of primary bovine aortic endothelial cells (BAECs). Raman spectra were collected from both individual live cells cultured on fused silica substrates and on clusters of live cells placed on fused silica substrates, measured at 532 and 785 nm. The results obtained show notable spectral differences in DNA/RNA region indicative of the relative cytoplasm and nucleus contributions. Raman spectra of cell clusters show slight variations in the intensity of the phenylalanine peak (1004 cm⁻¹) indicating variations in protein contribution. These spectra also highlight contributions from other cellular components such as, proteins, lipids, nucleic acids and carbohydrates, respectively.     

Impact of release dynamics of laser-irradiated polymer micropallets on the viability of selected adherent cells

We use time-resolved interferometry, fluorescence assays and computational fluid dynamics (CFD) simulations to examine the viability of confluent adherent cell monolayers to selection via laser microbeam release of photoresist polymer micropallets. We demonstrate the importance of laser microbeam pulse energy and focal volume position relative to the glass–pallet interface in governing the threshold energies for pallet release as well as the pallet release dynamics. Measurements using time-resolved interferometry show that increases in laser pulse energy result in increasing pallet release velocities that can approach 10 m s⁻¹ through aqueous media. CFD simulations reveal that the pallet motion results in cellular exposure to transient hydrodynamic shear stress amplitudes that can exceed 100 kPa on microsecond timescales, and which produces reduced cell viability. Moreover, CFD simulation results show that the maximum shear stress on the pallet surface varies spatially, with the largest shear stresses occurring on the pallet periphery. Cell viability of confluent cell monolayers on the pallet surface confirms that the use of larger pulse energies results in increased rates of necrosis for those cells situated away from the pallet centre, while cells situated at the pallet centre remain viable. Nevertheless, experiments that examine the viability of these cell monolayers following pallet release show that proper choices for laser microbeam pulse energy and focal volume position lead to the routine achievement of cell viability in excess of 90 per cent. These laser microbeam parameters result in maximum pallet release velocities below 6 m s⁻¹ and cellular exposure of transient hydrodynamic shear stresses below 20 kPa. Collectively, these results provide a mechanistic understanding that relates pallet release dynamics and associated transient shear stresses with subsequent cellular viability. This provides a quantitative, mechanistic basis for determining optimal operating conditions for laser microbeam-based pallet release systems for the isolation and selection of adherent cells.     

Pulsed UV Laser-Induced Stationary Capillary Vibration for Highly Sensitive and Direct Detection of Capillary Electrophoresis

A stationary wave of the capillary vibration effect was successfully induced by a series of short laser pulses. This wave could be applied to highly sensitive detection of capillary electrophoresis as well as the already reported capillary vibration induced by an intensity-modulated CW laser (CVL effect). Generally, pulses with much shorter width than the period of the natural frequency of the vibrating system cannot induce a standing vibration. However, utilizing the time constant of CVL determined by heat dissipation time, we found conditions which could induce a stable stationary wave of the capillary by a series of nanosecond light pulses. We used the KrF excimer laser operated at 248 nm with a pulse width of 60 ns and output of ～10 μJ/pulse as the CVL excitation source and applied it to highly sensitive detection of nonderivatized amino acids at the femtomole level. The sensitivity was at least 2 orders of magnitude superior to that of a commercially available UV absorbance detector. This technique extends the CVL's spectral regions. For example, in the UV region, where many biological materials have significant absorption bands, this technique will extend analytical applications in capillary electrophoresis by eliminating the need for a derivatization process.     

Characterization of cellular optoporation with distance

We have developed and characterized cellular optoporation with visible wavelengths of light using standard uncoated glass cover slips as the absorptive media. A frequency-doubled Nd:YAG laser pulse was focused at the interface of the glass surface and aqueous buffer, creating a stress wave and transiently permeabilizing nearby cells. Following optoporation of adherent cells, three spatial zones were present which were distinguished by the viability of the cells and the loading efficiency (or number of extracellular molecules loaded). The loading efficiency also depended on the concentration of the extracellular molecules and the molecular weight of the molecules. In the zone farthest from the laser beam (> 60 microns under these conditions), nearly all cells were both successfully loaded and viable. To illustrate the wider applicability of this optoporation method, cells were loaded with a substrate for protein kinase C and the cellular contents then analyzed by capillary electrophoresis. In contrast to peptides loaded by microinjection, optoporated peptide showed little proteolytic degradation, suggesting that the cells were minimally perturbed. Also demonstrating the potential for future work, cells were optoporated and loaded with a fluorophore in the enclosed channels of microfluidic devices.     

透明材料中冲击波速度直接测量技术

本文提出了超高压条件下应用于透明材料中冲击波速度直接测量的成像型速度干涉仪技术.介绍了成像型速度干涉仪技术的光路结构和基本原理,给出全系统的光路图.分析了预热效应产生和冲击波到达时刻的时间顺序,发现方波驱动脉冲平台的前沿到达时刻和X光离化效应出现的时刻相同,冲击波信号到达时刻晚于X光离化时刻,验证了冲击波到达窗口材料时形成反射面的反射率会突然增高,可以通过该现象确认冲击波到达的时刻.给出了实验结果,分析了条纹间断是由于X光预热效应引起的,并且发现预热效应在激光脉冲平台期前沿进入靶腔后开始,平台期后沿结束后约400 ps减弱到不影响冲击波信号探测,通过理论分析和实验数据比对的方法,确认了蓝宝石当中的减速曲线.给出了加蓝宝石窗口后的测速公式,经过实验对比,确认了测速公式的正确性.     

Fast electrical lysis of cells for capillary electrophoresis

In the past decade, capillary electrophoresis has demonstrated increasing utility for the quantitative analysis of single cells. New applications for the analysis of dynamic cellular properties demand sampling methods with sufficient temporal resolution to accurately measure these processes. In particular, intracellular signaling pathways involving many enzymes can be modulated on subsecond time scales. We have developed a technique to rapidly lyse an adherent mammalian cell using a single electrical pulse followed by efficient loading of the cellular contents into a capillary. Microfabricated electrodes were designed to create a maximum voltage drop across the flattened cell's plasma membrane at a minimum interelectrode voltage. The influence of the interelectrode distance, pulse duration, and pulse strength on the rate of cell lysis was determined. The ability to rapidly lyse a cell and collect and separate the cellular contents was demonstrated by loading cells with Oregon Green and two isomers of carboxyfluorescein. All three fluorophores were detected with a separation efficiency comparable to that of standards. Parallel comparison of electrical lysis to that produced by a laser-based lysis system revealed that the sampling efficiencies of the two techniques were comparable. Rapid cell lysis by an electrical pulse may increase the application of capillary electrophoresis to the study of cellular dynamics requiring fast sampling times.     

Single-shot spatially resolved characterization of laser-induced shock waves in water

We have developed an optical method for single-shot spatially resolved shock-wave peak-pressure measurements. A schlieren technique and streak photography were used to follow the propagation of the shock wave. The shock position r as a function of time was extracted from the streak images by digital image-processing techniques. The resulting r(t) curves were differentiated with respect to time to yield shock-wave velocities that were converted to shock pressures with the aid of the equation of the state of the medium. Features and limitations of the technique are demonstrated and discussed on the basis of measurements of shock-wave amplitudes generated by laser-induced breakdown in water. For this purpose, laser pulses of 6-ns duration and pulse energies of 1 and 10 mJ were focused into a cuvette containing water. Complete p(t) curves were obtained with a temporal resolution in the subnanosecond range. The total acquisition and processing time for a single event is ~2 min. The shock-peak pressures at the source were found to be 8.4 ? 1.5 and 11.8 ? 1.6 GPa for pulse energies of 1 and 10 mJ, respectively. Within the first two source radii, the shock-wave pressure p(r) was found to decay on average in proportion to r(-1.3?0.2) for both pulse energies. Thereafter the pressure dropped in proportion to r(-2.2?0.1). In water the method can be used to measure shock-wave amplitudes exceeding 0.1 GPa. Because it is a single-shot technique, the method is especially suited for investigating events with large statistical variations.     

Capillary electrophoretic separation of nuclei released from single cells

We report here the first capillary electrophoresis analysis of intact nuclei released on-column from single cells. Expression of the nuclear-targeted protein nuDsRed2 and the plasma membrane-bound farnesylated enhanced green fluorescent protein in cultured human DeltaH2-1 cells allowed fluorescent monitoring of the fate of these subcellular compartments upon injection of a single cell into the separation capillary. On-column treatment with digitonin allowed for the separation of the plasma membrane from the nucleus as indicated by their selective laser-induced fluorescence detection in two separate spectral regions. The data suggest that less than 0.1% of the plasma membrane remains bound to individually detected nuclei. In digitonin-treated cells, the electropherograms consisted of a prominent fluorescent peak attributed to nuDsRed2 localized to the nucleus and a collection of weakly fluorescent events (barely distinguishable from scattering) that seem to indicate additional localization of this protein to other subcellular regions. Taken together, this report points to the feasibility of studying intact organelles released from a single mammalian cell by capillary electrophoresis, which is a prerequisite to understanding the relevance of subcellular heterogeneity in biological systems.     

A study of explosive effects in close proximity to a submerged cylinder

Measurements of acceleration and pressure together with high-speed imaging have been used to study the interaction of an underwater explosion with a nearby steel cylinder. Variation of the initial separation between the cylinder and explosive charge generated different cases of interaction in which the response of the cylinder to the shock wave, the bubble pulse wave, water jetting and bubble collapse could be studied. Shock wave loading generated a significant response in all cases. The pressure wave from the pulsating bubble was a less significant load, generating a peak velocity about half that caused by the shock wave. However the collapse of the bubble onto the cylinder was found to be the most severe structural load, generating a peak velocity almost twice that caused by the shock wave and causing significant plastic deformation.     

Electron spectrum of atoms ionized by an ultrashort laser pulse of relativistic intensity

Energy transfer to electrons in atoms ionized by an ultrashort laser pulse of relativistic intensity (I > 10¹⁹ W/cm²) is considered. The ionization process is taken into account using the mechanism of direct suppression of the Coulomb barrier in a laser field. The acceleration of electrons in the laser wave field is described in terms of the classical relativistic equation of motion. Electron energies in the final state are determined as dependent on the average intensity of a laser pulse with a given shape. A distribution of the final energies of electrons upon multiple ionization of a complex atom is found.     

Shock-wave propagation and cavitation bubble oscillation by Nd:YAG laser ablation of a metal in water

A highly sensitive fiber-optic sensor based on optical beam deflection is applied for investigating the propagation of a laser-induced plasma shock wave, the oscillation of a cavitation bubble diameter, and the development of a bubble-collapse-induced shock wave when a Nd:YAG laser pulse is focused upon an aluminum surface in water. By the sequence of experimental waveforms detected at different distances, the attenuation properties of the plasma shock wave and of the bubble-collapse-induced shock wave are obtained. Besides, based on characteristic signals, both the maximum and the minimum bubble radii at each oscillation cycle are determined, as are the corresponding oscillating periods.     

Attenuation or enhancement—a one-dimensional analysis on shock transmission in the solid phase of a cellular material

The characteristics of compressive shock wave propagation in the solid phase of a cellular material are studied in the present paper using a one-dimensional mass-spring model. The unique compressive stress–strain relation of a cellular material leads to several interesting observations on the characteristic of one-dimensional stress wave transmission in a cellular material, which are important for understanding the blast and impact mitigation and attenuation through a cellular material. Generally, cellular material attenuates impact- or blast-induced loads by cell collapse mechanism at low impact velocities or low pulse pressure intensities when the stress transmission in a cellular material is limited by the plateau stress before the densification stage starts. This feature leads to wide applications of cellular materials in structural crashworthiness design where low speed impact is considered as potential survivable scenarios. However, scattered information has shown that stress enhancement in cellular material may occur when an intensive loading is applied, which, in contrast to the stress attenuation function of a cellular material, could produce more severe damage on the protected structures. This phenomenon is studied qualitatively in the present paper using a one-dimensional spring-mass model.     

Mass imaging of iron oxide nanoparticles inside cells for in vitro cytotoxicity

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging analysis was performed on murine macrophage cells treated with various concentrations of iron oxide (Fe3O4) nanoparticles, which are used as MRI contrast agents. First, murine macrophage cells were seeded on a slide glass for 24 hrs and treated with varying concentrations of Fe3O4 nanoparticles for 24 hrs. To expose a cross section of each cell and obtain a distribution of the nanoparticles inside the cells, the cells were sputtered using Bi ions after which the cross section of each cell was scanned and imaged using the focused cluster ion beam with a spatial resolution of 300 nm. Fe3O4 nanoparticles were found mainly in the cytoplasm region of the cells, not in the nucleus region of cells, suggesting that the uptake of the Fe3O4 nanoparticles were into the cytoplasm of cell, not into the nucleus of cell. Based on these observations, our protocol using mass imaging analysis would be a useful addition to the study of in vitro nanoparticle cytotoxicity.     

The influence of coatings on subsurface mechanical properties of laser peened 2011-T3 aluminum

High power Q-switched laser systems are currently being developed for use in a process known as laser shock processing or laser peening which results in significantly improved fatigue properties in aluminum components. An ablative, sacrificial coating such as paint or metal foil is used to protect the aluminum component from surface melting by the laser pulse, which adversely affects fatigue life. This paper, using nano-indentation, analyzes the effect of the paint and foil coatings on the shock wave propagation into the aluminum specimen and the resulting change in mechanical properties versus depth. Near the surface, hardness was found to be increased by the laser peening, however this process decreased the measured elastic modulus. The laser pulse energy density and properties of the foil including its adhesion to the aluminum alloy were found to influence the change in surface mechanical properties.     

Noncontact, Nondestructive Evaluation of Realistic Cracks with Surface Acoustic Waves by Scanning Excitation and Detection Lasers

Nondestructive evaluation of surface-breaking cracks with a scanning laser source, a scanning laser probe, or a scanning laser pump–probe setup is discussed. Multimode scattering of laser-excited surface acoustic wave pulses by artificial slots, realistic fatigue, or impulsive cracks is considered. This includes measuring the size of cracks in the micrometer-to-millimeter range by optical recording of the complete displacement or velocity field around the crack. Results obtained with a scanning pump–probe setup for a partially closed microcrack, generated by an elastic shock pulse in silica, are compared with those achieved with a scanning source or scanning probe for machined open notches. Crack size analysis based on the frequency spectrum of the reflected Rayleigh wave and the time lag of the transmitted Rayleigh wave is discussed. Signal enhancement effects observed in the displacement and velocity field near the crack are studied.     

Hot-nanoparticle-mediated fusion of selected cells

Complete fusion of two selected cells allows for the creation of novel hybrid cells with inherited genetic properties from both original cells.Alternatively,via fusion of a selected cell with a selected vesicle,chemicals or genes can be directly delivered into the cell of interest,to control cellular reactions or gene expression.Here,we demonstrate how to perform an optically controlled fusion of two selected cells or of one cell and one vesicle.Fusion is mediated by laser irradiating plasmonic gold nanoparticles optically trapped between two cells (or a vesicle and a cell) of interest.This hot-particle-mediated fusion causes total mixing of the two cytoplasms and the two cell membranes resulting in formation of a new hybrid cell with an intact cell membrane and enzymatic activity following fusion.Similarly,fusion between a vesicle and a cell results in delivery of the vesicle cargo to the cytoplasm,and after fusion,the cell shows signs of viability.The method is an implementation of targeted drug delivery at the single-cell level and has a great potential for cellular control and design.     

Optical micromanipulations inside yeast cells

We present a combination of nonlinear microscopy and optical trapping applied to three-dimensional imaging and manipulation of intracellular structures in living cells. We use Titanium-sapphire laser pulses for nonlinear microscopy of the nuclear envelope and the microtubules marked with green fluorescent protein in fission yeast. The same laser source is also used to trap small lipid granules naturally present in the cell. The trapped granule is used as a handle to exert a pushing force on the cell nucleus. The granule is moved in a raster-scanning fashion to cover the area of the nucleus and hence displace the nucleus away from its normal position in the center of the cell. Such indirect manipulations of an organelle (e.g., nucleus) can be useful when direct trapping of the chosen organelle is disadvantageous or inefficient. We show that nonlinear microscopy and optical manipulation can be performed without substantial damage or heating of the cell. We present this method as an important tool in cell biology for manipulation of specific structures, as an alternative to genetic and biochemical methods. This technique can be applied to several fundamental problems in cell biology, including the mechanism of nuclear positioning and the spatial coordination of nuclear and cell division.     

Features of the Time Shape of the Pressure Pulses of Optical Air Breakdown

The time shape and amplitude of pressure pulses initiated by surface laser air breakdown for different energies of laser pulses (1–180 mJ) has been compared to the results of numerical gasdynamic calculations of unsteady explosive motions with allowance for counterpressure at distances of 0.2 to 30 cm from the breakdown region. It has been established that the experimental pressure pulse has the character of slowly damped quasiperiodic vibrations, whereas the calculated pulse is a bipolar single pulse of a much shorter duration. Good agreement between the experimental and calculated amplitudes of a positive pressure phase has been found throughout the investigated range, whereas the agreement between the corresponding amplitudes and durations of a negative pressure phase is limited in character. The differences observed in the experimental and calculated data have been attributed to the transformation of the shockwave motion to acoustic radiation.