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

In vivo femtosecond laser nanosurgery of the cell wall enabling patch-clamp measurements on filamentous fungi

Studying the membrane physiology of filamentous fungi is key to understanding their interactions with the environment and crucial for developing new therapeutic strategies for disease-causing pathogens. However, their plasma membrane has been inaccessible for a micron-sized patch-clamp pipette for pA current recordings due to the rigid chitinous cell wall. Here, we report the first femtosecond IR laser nanosurgery of the cell wall of the filamentous fungi, which enabled patch-clamp measurements on protoplasts released from hyphae. A reproducible and highly precise (diffraction-limited, submicron resolution) method for obtaining viable released protoplasts was developed. Protoplast release from the nanosurgery-generated incisions in the cell wall was achieved from different regions of the hyphae. The plasma membrane of the obtained protoplasts formed tight and high-resistance (GΩ) contacts with the recording pipette. The entire nanosurgical procedure followed by the patch-clamp technique could be completed in less than 1 hour. Compared to previous studies using heterologously expressed channels, this technique provides the opportunity to identify new ionic currents and to study the properties of the ion channels in the protoplasts of filamentous fungi in their native environment.

Advanced tools and methods for single-cell surgery

Highly precise micromanipulation tools that can manipulate and interrogate cell organelles and components must be developed to support the rapid development of new cell-based medical therapies, thereby facilitating in-depth understanding of cell dynamics, cell component functions, and disease mechanisms. This paper presents a literature review on micro/nanomanipulation tools and their control methods for single-cell surgery. Micromanipulation methods specifically based on laser, microneedle, and untethered micro/nanotools are presented in detail. The limitations of these techniques are also discussed. The biological significance and clinical applications of single-cell surgery are also addressed in this paper.

Femtosecond laser oocyte enucleation as a low-invasive and effective method of recipient cytoplast preparation

Recipient cytoplast preparation, commonly performed by DNA aspiration with a needle, inevitably leads to the loss of reprogramming factors. As an alternative to the traditional enucleation technique, femtosecond laser enucleation can eliminate DNA effectively without loss of reprogramming factors and without oocyte puncturing. In this work we have performed oocyte enucleation by destructing the metaphase plate using a 795 nm femtosecond laser. The disability of the enucleated oocytes to develop after the parthenogenetic activation, as well as the lack of DNA staining luminescence, strongly confirms the efficiency of the femtosecond laser enucleation. The parthenogenetic development of oocytes after the cytoplasm treatment suggests a low-invasive effect of the laser enucleation technique.

Nanosurgical Manipulation of Titin and Its M-Complex

Titin is a multifunctional filamentous protein anchored in the M-band, a hexagonally organized supramolecular lattice in the middle of the muscle sarcomere. Functionally, the M-band is a framework that cross-links myosin thick filaments, organizes associated proteins, and maintains sarcomeric symmetry via its structural and putative mechanical properties. Part of the M-band appears at the C-terminal end of isolated titin molecules in the form of a globular head, named here the “M-complex”, which also serves as the point of head-to-head attachment of titin. We used high-resolution atomic force microscopy and nanosurgical manipulation to investigate the topographical and internal structure and local mechanical properties of the M-complex and its associated titin molecules. We find that the M-complex is a stable structure that corresponds to the transverse unit of the M-band organized around the myosin thick filament. M-complexes may be interlinked into an M-complex array that reflects the local structural and mechanical status of the transversal M-band lattice. Local segments of titin and the M-complex could be nanosurgically manipulated to achieve extension and domain unfolding. Long threads could be pulled out of the M-complex, suggesting that it is a compact supramolecular reservoir of extensible filaments. Nanosurgery evoked an unexpected volume increment in the M-complex, which may be related to its function as a mechanical spacer. The M-complex thus displays both elastic and plastic properties which support the idea that the M-band may be involved in mechanical functions within the muscle sarcomere.

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.

•

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

•

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

•

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

•

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

Genetic Material Manipulation and Modification by Optical Trapping and Nanosurgery-A Perspective

Light can be employed as a tool to alter and manipulate matter in many ways. An example has been the implementation of optical trapping, the so called optical tweezers, in which light can hold and move small objects with 3D control. Of interest for the Life Sciences and Biotechnology is the fact that biological objects in the size range from tens of nanometers to hundreds of microns can be precisely manipulated through this technology. In particular, it has been shown possible to optically trap and move genetic material (DNA and chromatin) using optical tweezers. Also, these biological entities can be severed, rearranged and reconstructed by the combined use of laser scissors and optical tweezers. In this review, the background, current state and future possibilities of optical tweezers and laser scissors to manipulate, rearrange and alter genetic material (DNA, chromatin and chromosomes) will be presented. Sources of undesirable effects by the optical procedure and measures to avoid them will be discussed. In addition, first tentative approaches at cellular-level genetic and organelle surgery, in which genetic material or DNA-carrying organelles are extracted out or introduced into cells, will be presented.

CARS-imaging guidance for fs-laser ablation precision surgery

Due to ageing populations the number of tumors is increasing worldwide. Successful surgical treatment requires complete resection of tumors to reduce recurrence rates. To reach this goal, novel methods combining in vivo tumor and tumor margin detection with low invasive precision surgical tools are needed. Coherent anti-Stokes Raman scattering (CARS) imaging is a highly promising optical tool for visualizing tumors based on characteristic changes in tissue morphology and molecular composition, while fs-laser ablation is to date the most precise surgical tool established in ophthalmology. In this contribution, CARS imaging has been combined with fs-laser ablation as a new approach for image-guided precision surgery for the first time. CARS guided fs-ablation has been applied to ablate brain, liver, skin, muscular and vascular tissues with μm-precision using sub-100 fs pulses of μJ level. We demonstrate superior imaging performance and contrast as well as detection of tissue margins by coherent Raman microscopy in comparison to laser reflectance imaging. The combination of CARS-image-guided tissue ablation is a promising tool for minimally invasive surgeries particularly in the vicinity of functional structures in the future.

Induction of neuronal activation by femtosecond-pulsed laser irradiation and its potential application for amyloid-β-induced toxicity assessment

Manipulating neural activity is crucial for studying the neural connectivity and the pathophysiology of neurodegenerative disease. Among various techniques for neural activation, direct optical stimulation method with femtosecond-pulsed laser is simple and can be specifically applied on a single neuron. Brief irradiation of femtosecond laser pulses on a neuron elevates intracellular calcium, and it propagates to adjacent neurons. However, the mechanisms of laser-induced neural activation are still unclear. In this report, we have elucidated the mechanism of laser-induced neural activation which could be mediated by superoxide, specifically blocked by diphenyleneiodonium chloride, and depletion in intracellular calcium storage. Furthermore, we also showed that the propagation of calcium initiated by laser stimulation is dependent on the presence of extracellular calcium as well as electrical and chemical synapses. We verified the applicability of such mechanism for the assessment of neuronal functionality, by measuring calcium elevation, intracellular calcium propagation, ROS increase, and performing cell death assay in vehicle and Aβ-treated neurons. This work suggests promising applications of the potential for implementing such laser-induced neural activation for rapid and reliable drug screening.

Laser-based technique for controlled damage of mesenchymal cell spheroids: a first step in studying reparation in vitro

Modern techniques of laser microsurgery of cell spheroids were used to develop a new simple reproducible model for studying repair and regeneration in vitro. Nanosecond laser pulses (wavelength 355 nm, frequency 100 Hz, pulse duration 2 ns) were applied to perform a microdissection of the outer and the inner zones of human bone marrow multipotent mesenchymal stromal cells (BM MMSC) spheroids. To achieve effective dissection and preservation of spheroid viability, the energy of laser pulses was optimized and adjusted in the range 7-9 μJ. After microdissection, the edges of the wound surface opened and the angular opening reached a value of more than 180°. The destruction of the initial spheroid structure was observed in the wound area, with surviving cells changing their shape into a round one. Partial restoration of a spheroid form took place in the first six hours. The complete structure restoration accompanying the reparative processes occurred gradually over seven days due to remodelling of surviving cells.

Summary: The technique of precise nanosecond laser microsurgery of mesenchymal cell spheroids was used to develop a new simple reproducible model for studying repair and regeneration in vitro.

Optical reprogramming of human somatic cells using ultrashort Bessel-shaped near-infrared femtosecond laser pulses

We report a virus-free optical approach to human cell reprogramming into induced pluripotent stem cells with low-power nanoporation using ultrashort Bessel-shaped laser pulses. Picojoule near-infrared sub-20 fs laser pulses at a high 85 MHz repetition frequency are employed to generate transient nanopores in the membrane of dermal fibroblasts for the introduction of four transcription factors to induce the reprogramming process. In contrast to conventional approaches which utilize retro- or lentiviruses to deliver genes or transcription factors into the host genome, the laser method is virus-free; hence, the risk of virus-induced cancer generation limiting clinical application is avoided.

Femtosecond near-infrared laser microirradiation reveals a crucial role for PARP signaling on factor assemblies at DNA damage sites

Laser microirradiation is a powerful tool for real-time single-cell analysis of the DNA damage response (DDR). It is often found, however, that factor recruitment or modification profiles vary depending on the laser system employed. This is likely due to an incomplete understanding of how laser conditions/dosages affect the amounts and types of damage and the DDR. We compared different irradiation conditions using a femtosecond near-infrared laser and found distinct damage site recruitment thresholds for 53BP1 and TRF2 correlating with the dose-dependent increase of strand breaks and damage complexity. Low input-power microirradiation that induces relatively simple strand breaks led to robust recruitment of 53BP1 but not TRF2. In contrast, increased strand breaks with complex damage including crosslinking and base damage generated by high input-power microirradiation resulted in TRF2 recruitment to damage sites with no 53BP1 clustering. We found that poly(ADP-ribose) polymerase (PARP) activation distinguishes between the two damage states and that PARP activation is essential for rapid TRF2 recruitment while suppressing 53BP1 accumulation at damage sites. Thus, our results reveal that careful titration of laser irradiation conditions allows induction of varying amounts and complexities of DNA damage that are gauged by differential PARP activation regulating protein assembly at the damage site.

Portable, miniaturized, fibre delivered, multimodal CARS exoscope

We demonstrate for the first time, a portable multimodal coherent anti-Stokes Raman scattering microscope (exoscope) for minimally invasive in-vivo imaging of tissues. This device is based around a micro-electromechanical system scanning mirror and miniaturized optics with light delivery accomplished by a photonic crystal fibre. A single Ti:sapphire femtosecond pulsed laser is used as the light source to produce CARS, two photon excitation fluorescence and second harmonic generation images. The high resolution and distortion-free images obtained from various resolution and bio-samples, particularly in backward direction (epi) successfully demonstrate proof of concept, and pave the path towards future non or minimally-invasive in vivo imaging.

Femtosecond optical transfection of individual mammalian cells

Laser-mediated gene transfection into mammalian cells has recently emerged as a powerful alternative to more traditional transfection techniques. In particular, the use of a femtosecond-pulsed laser operating in the near-infrared (NIR) region has been proven to provide single-cell selectivity, localized delivery, low toxicity and consistent performance. This approach can easily be integrated with advanced multimodal live-cell microscopy and micromanipulation techniques. The efficiency of this technique depends on an understanding by the user of both biology and physics. Therefore, in this protocol we discuss the subtleties that apply to both fields, including sample preparation, alignment and calibration of laser optics and their integration into a microscopy platform. The entire protocol takes ~5 d to complete, from the initial setup of the femtosecond optical transfection system to the final stage of fluorescence imaging to assay for successful expression of the gene of interest.

Exploring the ultrashort pulse laser parameter space for membrane permeabilisation in mammalian cells

The use of ultrashort femtosecond pulsed lasers to effect membrane permeabilisation and initiate both optoinjection and transfection of cells has recently seen immense interest. We investigate femtosecond laser-induced membrane permeabilisation in mammalian cells as a function of pulse duration, pulse energy and number of pulses, by quantifying the efficiency of optoinjection for these parameters. Depending on pulse duration and pulse energy we identify two distinct membrane permeabilisation regimes. In the first regime a nonlinear dependence of order 3.4-9.6 is exhibited below a threshold peak power of at least 6 kW. Above this threshold peak power, the nonlinear dependence is saturated resulting in linear behaviour. This indicates that the membrane permeabilisation mechanism requires efficient multiphoton absorption to produce free electrons but once this process saturates, linear absorption dominates. Our experimental findings support a previously proposed theoretical model and provide a step towards the optimisation of laser-mediated gene delivery into mammalian cells.