Laser scissors and tweezers

Laser Scissors and Tweezers to Study Chromosomes: A Review

Starting in 1969 laser scissors have been used to study and manipulate chromosomes in mitotic animal cells. Key studies demonstrated that using the “hot spot” in the center of a focused Gaussian laser beam it was possible to delete the ribosomal genes (secondary constriction), and this deficiency was maintained in clonal daughter cells. It wasn’t until 2020 that it was demonstrated that cells with focal-point damaged chromosomes could replicate due to the cell’s DNA damage repair molecular machinery. A series of studies leading up to this conclusion involved using cells expressing different GFP DNA damage recognition and repair molecules. With the advent of optical tweezers in 1987, laser tweezers have been used to study the behavior and forces on chromosomes in mitotic and meiotic cells. The combination of laser scissors and tweezers were employed since 1991 to study various aspects of chromosome behavior during cell division. These studies involved holding chromosomes in an optical while gradually reducing the laser power until the chromosome recovered their movement toward the cell pole. It was determined in collaborative studies with Prof. Arthur Forer from York University, Toronto, Canada, cells from diverse group vertebrate and invertebrates, that forces necessary to move chromosomes to cell poles during cell division were between 2 and 17pN, orders of magnitude below the 700 pN generally found in the literature.

Particle Manipulation by Optical Forces in Microfluidic Devices

Since the pioneering work of Ashkin and coworkers, back in 1970, optical manipulation gained an increasing interest among the scientific community. Indeed, the advantages and the possibilities of this technique are unsubtle, allowing for the manipulation of small particles with a broad spectrum of dimensions (nanometers to micrometers size), with no physical contact and without affecting the sample viability. Thus, optical manipulation rapidly found a large set of applications in different fields, such as cell biology, biophysics, and genetics. Moreover, large benefits followed the combination of optical manipulation and microfluidic channels, adding to optical manipulation the advantages of microfluidics, such as a continuous sample replacement and therefore high throughput and automatic sample processing. In this work, we will discuss the state of the art of these optofluidic devices, where optical manipulation is used in combination with microfluidic devices. We will distinguish on the optical method implemented and three main categories will be presented and explored: (i) a single highly focused beam used to manipulate the sample, (ii) one or more diverging beams imping on the sample, or (iii) evanescent wave based manipulation.

Injection Guidance System for Cellular Microinjections

In this paper we present a novel injection guidance system that assists an operator in the microinjection of living adherent cells. The system includes a micromanipulator, an injection system, an impedance measurement device and control software. The impedance measurement system detects changes in the resistance of an injection capillary during cell injections. From the measurement signal, the software determines parameters that can be used to detect several injection events such as cell—capillary contact, capillary breakage and capillary clogging, which are all unavailable in the current microinjection systems. Real cell injection experiments indicate that injection success rates can be significantly increased: from 30—40% without the system to 65% with the system.

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.

Light forces the pace: optical manipulation for biophotonics

The biomedical sciences have benefited immensely from photonics technologies in the last 50 years. This includes the application of minute forces that enable the trapping and manipulation of cells and single molecules. In terms of the area of biophotonics, optical manipulation has made a seminal contribution to our understanding of the dynamics of single molecules and the microrheology of cells. Here we present a review of optical manipulation, emphasizing its impact on the areas of single-molecule studies and single-cell biology, and indicating some of the key experiments in the fields.

Optical tweezers for single cells

Optical tweezers (OT) have emerged as an essential tool for manipulating single biological cells and performing sophisticated biophysical/biomechanical characterizations. Distinct advantages of using tweezers for these characterizations include non-contact force for cell manipulation, force resolution as accurate as 100aN and amiability to liquid medium environments. Their wide range of applications, such as transporting foreign materials into single cells, delivering cells to specific locations and sorting cells in microfluidic systems, are reviewed in this article. Recent developments of OT for nanomechanical characterization of various biological cells are discussed in terms of both their theoretical and experimental advancements. The future trends of employing OT in single cells, especially in stem cell delivery, tissue engineering and regenerative medicine, are prospected. More importantly, current limitations and future challenges of OT for these new paradigms are also highlighted in this review.

Noncontact laser microdissection and catapulting for pure sample capture

The understanding of the molecular mechanisms of cellular function, growth, and proliferation is based on the accurate identification, isolation, and finally characterization of a specific single cell or a population of cells and its subsets of biomolecules. For the simultaneous analysis of thousands of molecular parameters within one single experiment as realized by DNA, RNA, and protein microarray technologies, a defined number of homogeneous cells derived from a distinct morphological origin are required. Sample preparation is therefore a very crucial step preceding the functional characterization of specific cell populations. Laser microdissection and laser pressure catapulting (LMPC) enables pure and homogeneous sample preparation resulting in an increased specificity of molecular analyses. With LMPC, the force of focused laser light is utilized to excise selected cells or large tissue areas from object slides down to individual single cells and subcellular components like organelles or chromosomes. After microdissection, the sample is directly catapulted into an appropriate collection vial. As this process works entirely without mechanical contact, it enables pure sample retrieval from morphologically defined origin without cross-contamination. LMPC has been successfully applied to isolate and catapult cells from, for example, histological tissue sections, from forensic evidence material, and also from tough plant matter, supporting biomedical research, forensic science, and plant physiology studies. Even delicate living cells like stem cells have been captured for recultivation without affecting their viability or stem cell character, an important feature influencing stem cell research, regenerative medicine, and drug development. The combination of LMPC with microinjection to inject drugs or genetic material into individual cells and to capture them for molecular analyses bears great potential for efficient patient-tailored medication.

Optical Micromanipulation Methods for Controlled Rotation, Transportation, and Microinjection of Biological Objects

The use of laser microtools for rotation and controlled transport of microscopic biological objects and for microinjection of exogenous material in cells is discussed. We first provide a brief overview of the laser tweezers-based methods for rotation or orientation of microscopic objects. Particular emphasis is placed on the methods that are more suitable for the manipulation of biological objects, and the use of these for two-dimensional (2D) and 3D rotations/orientations of intracellular objects is discussed. We also discuss how a change in the shape of a red blood cell (RBC) suspended in hypertonic buffer leads to its rotation when it is optically tweezed. The potential use of this approach for the diagnosis of malaria is also illustrated. The use of a line tweezers having an asymmetric intensity distribution about the center of its major axis for simultaneous transport of microscopic objects, and the successful use of this approach for induction, enhancement, and guidance of neuronal growth cones is presented next. Finally, we describe laser microbeam-assisted microinjection of impermeable drugs into cells and also briefly discuss possible adverse effects of the laser trap or microbeams on cells.

Dynamically adjustable annular laser trapping based on axicons

To study the chemotactic response of sperm to an egg and to characterize sperm motility, an annular laser trap based on axicons is designed, simulated with the ray-tracing tool, and implemented. The diameter of the trapping ring can be adjusted dynamically for a range of over 400 microm by simply translating one axicon along the optical axis. Trapping experiments with microspheres and dog sperm demonstrate the feasibility of the system, and the power requirement agrees with theoretical expectation. This new type of laser trapping could provide a prototype of a parallel, objective, and quantitative tool for animal fertility and biotropism study.

Tails of histones in DNA double-strand break repair

DNA double-strand breaks (DSBs) are, arguably, the most deleterious form of DNA damage. An increasing body of evidence points to the inaccurate or inefficient repair of DSBs as a key step in tumorigenesis. Therefore, it is of great importance to understand the processes by which DSBs are detected and repaired. Clearly, these events must take place in the context of chromatin in vivo, and recently, a great deal of progress has been made in understanding the dynamic and active role that histone proteins and chromatin modifying activities play in DNA DSB repair. Here, we briefly review some of the most common techniques in studying DNA DSB responses in vivo, and focus on the contributions of covalent modifications of core histone proteins to these DNA DSB responses.

Hollow spheres as individual movable micromirrors in optical tweezers

We introduce the use of hollow micron-sized spheres with a finite-thickness glass shell as individual micromirrors operating by total internal reflection (TIR) when illuminated off-axis. We also demonstrated that this kind of spheres can be optically trapped and manipulated in two dimensions using a Gaussian beam in a conventional optical tweezers setup, which allows the precise positioning of the micromirrors at specific locations within a sample cell. This mirrors constitutes a new micro-tool in the context of the so called lab-on-a-chip.

Optical forces for noninvasive cellular analysis

A novel, noninvasive measurement technique for quantitative cellular analysis is presented that utilizes the forces generated by an optical beam to evaluate the physical properties of live cells in suspension. In this analysis, a focused, near-infrared laser line with a high cross-sectional intensity gradient is rapidly scanned across a field of cells, and the interaction of those cells with the beam is monitored. The response of each cell to the laser depends on its size, structure, morphology, composition, and surface membrane properties; therefore, with this technique, cell populations of different type, treatment, or biological state can be compared. To demonstrate the utility of this cell analysis platform, we evaluated the early stages of apoptosis induced in the U937 cancer cell line by the drug camptothecin and compared the results with established reference assays. Measurements on our platform show detection of cellular changes earlier than either of the fluorescence-based Annexin V or caspase assays. Because no labeling or additional cell processing is required and because accurate assays can be performed with a small number of cells, this measurement technique may find suitable applications in cell research, medical diagnostics, and drug discovery.

The genesis of neurosurgery and the evolution of the neurosurgical operative environment: part II--concepts for future development, 2003 and beyond

The future development of the neurosurgical operative environment is driven principally by concurrent development in science and technology. In the new millennium, these developments are taking on a Jules Verne quality, with the ability to construct and manipulate the human organism and its surroundings at the level of atoms and molecules seemingly at hand. Thus, an examination of currents in technology advancement from the neurosurgical perspective can provide insight into the evolution of the neurosurgical operative environment. In the future, the optimal design solution for the operative environment requirements of specialized neurosurgery may take the form of composites of venues that are currently mutually distinct. Advances in microfabrication technology and laser optical manipulators are expanding the scope and role of robotics, with novel opportunities for bionic integration. Assimilation of biosensor technology into the operative environment promises to provide neurosurgeons of the future with a vastly expanded set of physiological data, which will require concurrent simplification and optimization of analysis and presentation schemes to facilitate practical usefulness. Nanotechnology derivatives are shattering the maximum limits of resolution and magnification allowed by conventional microscopes. Furthermore, quantum computing and molecular electronics promise to greatly enhance computational power, allowing the emerging reality of simulation and virtual neurosurgery for rehearsal and training purposes. Progressive minimalism is evident throughout, leading ultimately to a paradigm shift as the nanoscale is approached. At the interface between the old and new technological paradigms, issues related to integration may dictate the ultimate emergence of the products of the new paradigm. Once initiated, however, history suggests that the process of change will proceed rapidly and dramatically, with the ultimate neurosurgical operative environment of the future being far more complex in functional capacity but strikingly simple in apparent form.

Laser trapping and Raman spectroscopy of single cellular organelles in the nanometer range

The laser trapping technique combined with near-infrared Raman (NIR) spectroscopy was used for the analysis of single cellular organelles in the nanometer range. The samples were synaptosomes, nerve-ending particles (about 500-700 nm in diameter) isolated from a neuron in a rat brain, dispersed in the phosphate buffer solution. The NIR laser Raman trapping (NIR-LRT) system trapped a single synaptosome without photochemical damage and provided a Raman spectrum of the sample with less fluorescence background. After the background subtraction from the Raman spectrum, two large peaks appeared, which are attributed to the peaks of the CH(2) deformation mode and the amide I mode. This indicates the laser-trapped synaptosomes include some types of lipids and proteins. The result demonstrates that the NIR-LRT system can determine biological molecules in single cellular organelles in the nanometer range. Further improvement of the detection sensitivity will enable us to get detailed information about the functions of single cellular organelles in the brain, which will be valuable for neuroscience.

Laser-guided direct writing of living cells

To perform their myriad functions, tissues use specific cell-cell interactions that depend on the spatial ordering of multiple cell types. Recapitulating this spatial order in vitro will facilitate our understanding of function and failure in native and engineered tissue. One approach to achieving such high placement precision is to use optical forces to deposit cells directly. Toward this end, recent work with optical forces has shown that a wide range of particulate materials can be guided and deposited on surfaces to form arbitrary spatial patterns. Here we report that, when we use the light from a near-infrared diode laser focused through a low numerical aperture lens, individual embryonic chick spinal cord cells can be guided through culture medium and deposited on a glass surface to form small clusters of cells. In addition, we found that the laser light could be coupled into hollow optical fibers and that the cells could be guided inside the fibers over millimeter distances. The demonstration of fiber-based guidance extends by 2 orders of magnitude the distance over which optical manipulation can be performed with living cells. Cells guided into the fiber remained viable, as evidenced by normal cell adhesion and neurite outgrowth after exposure to the laser light. The results indicate that this particle deposition process, which we call "laser-guided direct writing," can be used to construct patterned arrays of tens to hundreds of cells using arbitrary numbers of cell types placed at arbitrary positions with micrometer-scale precision.

Molecular laser biotechnology

Laser technology has developed to the point where it is possible to utilize lasers as a sophisticated but accessible tool in understanding and manipulating gene functioning. This review emphasizes some of the systems that employ lasers in the new and growing field of molecular laser biotechnology. Here the main emphasis is on the manipulation and understanding of bacterial and plant systems.

Laser-guided direct writing for applications in biotechnology

Laser-induced optical forces can be used to guide and deposit 100 nm - 10 microm-diameter particles onto solid surfaces in a process we call 'laser-guided direct writing'. Nearly any particulate material, including both biological and electronic materials, can be manipulated and deposited on surfaces with micrometer accuracy. Potential applications include three-dimensional cell patterning for tissue engineering, hybrid biological-electronic-device construction, and biochip-array fabrication.