Femtosecond laser disruption of mitochondria in living cells

Selective induction of targeted cell death and elimination by near-infrared femtosecond laser ablation

The techniques for inducing the death of specific cells in tissue has attracted attention as new methodologies for studying cell function and tissue regeneration. In this study, we show that a sequential process of targeted cell death and removal can be triggered by short-term exposure of near-infrared femtosecond laser pulses. Kinetic analysis of the intracellular accumulation of trypan blue and the assay of caspase activity revealed that femtosecond laser pulses induced immediate disturbance of plasma membrane integrity followed by apoptosis-like cell death. Yet, adjacent cells showed no sign of membrane damage and no increased caspase activity. The laser-exposed cells eventually detached from the substrate after a delay of >54 min while adjacent cells remained intact. On the base of in vitro experiments, we applied the same approach to ablate targeted single cardiac cells of a live zebrafish heart. The ability of inducing targeted cell death with femtosecond laser pulses should find broad applications that benefit from precise cellular manipulation at the level of single cells in vivo and in vitro.

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Cell level dissection for studying cell function and tissue regeneration is proposed.

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Femtosecond laser induces apoptosis-like cell death at single cell level immediately.

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The dead culture cells shrank and eventually detach from a substrate over 1 h delay.

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Femtosecond laser ablates selected cells in translucent organs like zebra fish larva.

Live cell imaging of mitochondria following targeted irradiation in situ reveals rapid and highly localized loss of membrane potential

The reliance of all cell types on the mitochondrial function for survival makes mitochondria an interesting target when trying to understand their role in the cellular response to ionizing radiation. By harnessing highly focused carbon ions and protons using microbeams, we have performed in situ live cell imaging of the targeted irradiation of individual mitochondria stained with Tetramethyl rhodamine ethyl ester (TMRE), a cationic fluorophore which accumulates electrophoretically in polarized mitochondria. Targeted irradiation with both carbon ions and protons down to beam spots of <1 μm induced a near instant loss of mitochondrial TMRE fluorescence signal in the targeted area. The loss of TMRE after targeted irradiation represents a radiation induced change in mitochondrial membrane potential. This is the first time such mitochondrial responses have been documented in situ after targeted microbeam irradiation. The methods developed and the results obtained have the ability to shed new light on not just mitochondria's response to radiation but to further elucidate a putative mechanism of radiation induced depolarization and mitochondrial response.

Nanosurgery of cells and chromosomes using near-infrared twelve-femtosecond laser pulses

ABSTRACT. Laser-assisted surgery based on multiphoton absorption of near-infrared laser light has great potential for high precision surgery at various depths within the cells and tissues. Clinical applications include refractive surgery (fs-LASIK). The non-contact laser method also supports contamination-free cell nanosurgery. In this paper we describe usage of an ultrashort femtosecond laser scanning microscope for sub-100 nm surgery of human cells and metaphase chromosomes. A mode-locked 85 MHz Ti:Sapphire laser with an M-shaped ultrabroad band spectrum (maxima: 770  nm/830  nm) and an in situ pulse duration at the target ranging from 12 fs up to 3 ps was employed. The effects of laser nanoprocessing in cells and chromosomes have been quantified by atomic force microscopy. These studies demonstrate the potential of extreme ultrashort femtosecond laser pulses at low mean milliwatt powers for sub-100 nm surgery of cells and cellular organelles.

Fiber laser-microscope system for femtosecond photodisruption of biological samples

We report on the development of a ultrafast fiber laser-microscope system for femtosecond photodisruption of biological targets. A mode-locked Yb-fiber laser oscillator generates few-nJ pulses at 32.7 MHz repetition rate, amplified up to ∼125 nJ at 1030 nm. Following dechirping in a grating compressor, ∼240 fs-long pulses are delivered to the sample through a diffraction-limited microscope, which allows real-time imaging and control. The laser can generate arbitrary pulse patterns, formed by two acousto-optic modulators (AOM) controlled by a custom-developed field-programmable gate array (FPGA) controller. This capability opens the route to fine optimization of the ablation processes and management of thermal effects. Sample position, exposure time and imaging are all computerized. The capability of the system to perform femtosecond photodisruption is demonstrated through experiments on tissue and individual cells.

Local small airway epithelial injury induces global smooth muscle contraction and airway constriction

Small airway epithelial cells form a continuous sheet lining the conducting airways, which serves many functions including a physical barrier to protect the underlying tissue. In asthma, injury to epithelial cells can occur during bronchoconstriction, which may exacerbate airway hyperreactivity. To investigate the role of epithelial cell rupture in airway constriction, laser ablation was used to precisely rupture individual airway epithelial cells of small airways (<300-μm diameter) in rat lung slices (∼250-μm thick). Laser ablation of single epithelial cells using a femtosecond laser reproducibly induced airway contraction to ∼70% of the original cross-sectional area within several seconds, and the contraction lasted for up to 40 s. The airway constriction could be mimicked by mechanical rupture of a single epithelial cell using a sharp glass micropipette but not with a blunt glass pipette. These results suggest that soluble mediators released from the wounded epithelial cell induce global airway contraction. To confirm this hypothesis, the lysate of primary human small airway epithelial cells stimulated a similar airway contraction. Laser ablation of single epithelial cells triggered a single instantaneous Ca(2+) wave in the epithelium, and multiple Ca(2+) waves in smooth muscle cells, which were delayed by several seconds. Removal of extracellular Ca(2+) or decreasing intracellular Ca(2+) both blocked laser-induced airway contraction. We conclude that local epithelial cell rupture induces rapid and global airway constriction through release of soluble mediators and subsequent Ca(2+)-dependent smooth muscle shortening.

Optical knock out of stem cells with extremely ultrashort femtosecond laser pulses

Novel ultracompact multiphoton sub-20 femtosecond near infrared 85 MHz laser scanning microscopes and conventional 250 fs laser microscopes have been used to perform high spatial resolution two-photon imaging of stem cell clusters as well as selective intracellular nanoprocessing and knock out of living single stem cells within an 3D microenvironment without any collateral damage. Also lethal cell exposure of large parts of cell clusters was successfully probed while maintaining single cells of interest alive. The mean power could be kept in the milliwatt range for 3D nanoprocessing and even in the microwatt range for two-photon imaging. Ultracompact low power sub-20 fs laser systems may become interesting tools for optical nanobiotechnology such as optical cleaning of stem cell clusters as well as optical transfection.

Targeted transfection of stem cells with sub-20 femtosecond laser pulses

Multiphoton microscopes have become important tools for non-contact sub-wavelength three-dimensional nanoprocessing of living biological specimens based on multiphoton ionization and plasma formation. Ultrashort laser pulses are required, however, dispersive effects limit the shortest pulse duration achievable at the focal plane. We report on a compact nonlinear laser scanning microscope with sub-20 femtosecond 75 MHz near infrared laser pulses for nanosurgery of human stem cells and two-photon high-resolution imaging. Single point illumination of the cell membrane was performed to induce a transient nanopore for the delivery of extracellular green fluorescent protein plasmids. Mean powers of less than 7 mW (<93 pJ) and low millisecond exposure times were found to be sufficient to transfect human pancreatic and salivary gland stem cells in these preliminary studies. Ultracompact sub-20 femtosecond laser microscopes may become optical tools for nanobiotechnology and nanomedicine including optical stem cell manipulation.

In vivo manipulation of fluorescently labeled organelles in living cells by multiphoton excitation

Femtosecond laser pulses in the near-infrared region have potential applications in the imaging and manipulation of intracellular organelles. We report on the manipulation of intracellular organelles by two-photon excitation. The dynamics of green fluorescent protein (GFP)-histone are investigated by two-photon fluorescence recovery after photobleaching (FRAP). Intracellular ablation of fluorescently labeled organelles in living cells is performed by focusing femtosecond laser pulses. We report on the selective marking of individual organelles by using two-photon conversion of a photoconvertible fluorescent protein.