This article may be too technical for most readers to understand.(June 2009) |
Optical transfection is a biomedical technique that entails introducing nucleic acids (i.e. genetic material such as DNA) into cells using light. All cells are surrounded by a plasma membrane, which prevents many substances from entering or exiting the cell. Lasers can be used to burn a tiny hole in this membrane, allowing substances to enter. This is tremendously useful to biologists who are studying disease, as a common experimental requirement is to put things (such as DNA) into cells.
Typically, a laser is focussed to a diffraction limited spot (~1 μm diameter) using a high numerical aperture microscope objective. The plasma membrane of a cell is then exposed to this highly focussed light for a small amount of time (typically tens of milliseconds to seconds), generating a transient pore on the membrane. The generation of a photopore[ check spelling ] allows exogenous plasmid DNA, RNA, organic fluorophores, or larger objects such as semiconductor quantum nanodots to enter the cell. In this technique, one cell at a time is treated, making it particularly useful for single cell analysis.
This technique was first demonstrated in 1984 by Tsukakoshi et al., who used a frequency tripled Nd:YAG to generate stable and transient transfection of normal rat kidney cells. [1] Since this time, the optical transfection of a host of mammalian cell types has been demonstrated using a variety of laser sources, including the 405 nm continuous wave (cw), [2] 488 nm cw, [3] or pulsed sources such as the 800 nm femtosecond pulsed Ti:Sapphire [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] or 1064 nm nanosecond pulsed Nd:YAG. [14] [15]
The meaning of the term transfection has evolved. [16] The original meaning of transfection was "infection by transformation", i.e. introduction of DNA (or RNA) from a prokaryote-infecting virus or bacteriophage into cells, resulting in an infection. Because the term transformation had another sense in animal cell biology (a genetic change allowing long-term propagation in culture, or acquisition of properties typical of cancer cells), the term transfection acquired, for animal cells, its present meaning of a change in cell properties caused by introduction of DNA (or other nucleic acid species such as RNA or SiRNA).
Because of this strict definition of transfection, optical transfection also refers only to the introduction of nucleic acid species. The introduction of other impermeable compounds into a cell, such as organic fluorophores or semiconductor quantum nanodots is not strictly speaking "transfection," and is therefore referred to as "optical injection" or one of the many other terms now outlined.
The lack of a unified name for this technology makes reviewing the literature on the subject very difficult. [17] Optical injection has been described using over a dozen different names or phrases (see bulleted lists below). Some trends in the literature are clear. The first term of the technique is invariably a derivation of word laser, optical, or photo, and the second term is usually in reference to injection, transfection, poration, perforation or puncture. Like many cellular perturbations, when a single cell or group of cells is treated with a laser, three things can happen: the cell dies (overdose), the cell membrane is permeabilised, substances enter, and the cell recovers (therapeutic dose), or nothing happens (underdose). There have been suggestions in the literature to reserve the term optoinjection for when a therapeutic dose is delivered upon a single cell, [18] [19] [20] and the term optoporation for when a laser generated shockwave treats a cluster of many (10s to 100s) cells. [18] [19] [14] [20] The first definition of optoinjection is uncontroversial. The definition of optoporation, however, has failed to be adopted, with a similar number of references using the term to denote the dosing of single cells [3] [5] [15] [21] as those using the term to denote the simultaneous dosing of clusters of many cells [18] [19] [14] [20]
As the field stands, it is the opinion of the authors of a review article on the subject [17] that the term optoinjection always be included as a keyword in future publications, regardless of their own naming preferences.
Terms agreed by consensus
Terms under deliberation
Some of the above was reproduced with permission from. [17]
A typical optical transfection protocol is as follows: [11] 1) Build an optical tweezers system with a high NA objective 2) Culture cells to 50-60% confluency 3) Expose cells to at least 10 μg/mL of plasmid DNA 4) Dose the plasma membrane of each cell with 10-40 ms of focussed laser, at a power of <100 mW at focus 5) Observe transient transfection 24-96h later 6) Add selective medium if the generation of stable colonies is desired
A spatial light modulator (SLM) is a device that can control the intensity, phase, or polarization of light in a spatially varying manner. A simple example is an overhead projector transparency. Usually when the term SLM is used, it means that the transparency can be controlled by a computer.
Transfection is the process of deliberately introducing naked or purified nucleic acids into eukaryotic cells. It may also refer to other methods and cell types, although other terms are often preferred: "transformation" is typically used to describe non-viral DNA transfer in bacteria and non-animal eukaryotic cells, including plant cells. In animal cells, transfection is the preferred term as transformation is also used to refer to progression to a cancerous state (carcinogenesis) in these cells. Transduction is often used to describe virus-mediated gene transfer into eukaryotic cells.
In optics, an ultrashort pulse, also known as an ultrafast event, is an electromagnetic pulse whose time duration is of the order of a picosecond or less. Such pulses have a broadband optical spectrum, and can be created by mode-locked oscillators. Amplification of ultrashort pulses almost always requires the technique of chirped pulse amplification, in order to avoid damage to the gain medium of the amplifier.
A fiber laser is a laser in which the active gain medium is an optical fiber doped with rare-earth elements such as erbium, ytterbium, neodymium, dysprosium, praseodymium, thulium and holmium. They are related to doped fiber amplifiers, which provide light amplification without lasing.
Silicon photonics is the study and application of photonic systems which use silicon as an optical medium. The silicon is usually patterned with sub-micrometre precision, into microphotonic components. These operate in the infrared, most commonly at the 1.55 micrometre wavelength used by most fiber optic telecommunication systems. The silicon typically lies on top of a layer of silica in what is known as silicon on insulator (SOI).
In optics, a supercontinuum is formed when a collection of nonlinear processes act together upon a pump beam in order to cause severe spectral broadening of the original pump beam, for example using a microstructured optical fiber. The result is a smooth spectral continuum. There is no consensus on how much broadening constitutes a supercontinuum; however researchers have published work claiming as little as 60 nm of broadening as a supercontinuum. There is also no agreement on the spectral flatness required to define the bandwidth of the source, with authors using anything from 5 dB to 40 dB or more. In addition the term supercontinuum itself did not gain widespread acceptance until this century, with many authors using alternative phrases to describe their continua during the 1970s, 1980s and 1990s.
Black silicon is a semiconductor material, a surface modification of silicon with very low reflectivity and correspondingly high absorption of visible light.
A subwavelength-diameter optical fibre is an optical fibre whose diameter is less than the wavelength of the light being propagated through it. An SDF usually consists of long thick parts at both ends, transition regions (tapers) where the fibre diameter gradually decreases down to the subwavelength value, and a subwavelength-diameter waist, which is the main acting part. Due to such a strong geometrical confinement, the guided electromagnetic field in an SDF is restricted to a single mode called fundamental. In usual optical fibres, light both excites and feels shear and longitudinal bulk elastic waves, giving rise to forward-guided acoustic wave Brillouin scattering and backward-stimulated Brillouin scattering. In a subwavelength-diameter optical fibre, the situation changes dramatically.
The Mamyshev 2R regenerator is an all-optical regenerator used in optical communications. In 1998, Pavel V. Mamyshev of Bell Labs proposed and patented the use of the self-phase modulation (SPM) for single channel optical pulse reshaping and re-amplification. More recent applications target the field of ultrashort high peak-power pulse generation.
The Raman microscope is a laser-based microscopic device used to perform Raman spectroscopy. The term MOLE is used to refer to the Raman-based microprobe. The technique used is named after C. V. Raman, who discovered the scattering properties in liquids.
Gas in scattering media absorption spectroscopy (GASMAS) is an optical technique for sensing and analysis of gas located within porous and highly scattering solids, e.g. powders, ceramics, wood, fruit, translucent packages, pharmaceutical tablets, foams, human paranasal sinuses etc. It was introduced in 2001 by Prof. Sune Svanberg and co-workers at Lund University (Sweden). The technique is related to conventional high-resolution laser spectroscopy for sensing and spectroscopy of gas, but the fact that the gas here is "hidden" inside solid materials give rise to important differences.
Light sheet fluorescence microscopy (LSFM) is a fluorescence microscopy technique with an intermediate-to-high optical resolution, but good optical sectioning capabilities and high speed. In contrast to epifluorescence microscopy only a thin slice of the sample is illuminated perpendicularly to the direction of observation. For illumination, a laser light-sheet is used, i.e. a laser beam which is focused only in one direction. A second method uses a circular beam scanned in one direction to create the lightsheet. As only the actually observed section is illuminated, this method reduces the photodamage and stress induced on a living sample. Also the good optical sectioning capability reduces the background signal and thus creates images with higher contrast, comparable to confocal microscopy. Because light sheet fluorescence microscopy scans samples by using a plane of light instead of a point, it can acquire images at speeds 100 to 1,000 times faster than those offered by point-scanning methods.
Optical rogue waves are rare pulses of light analogous to rogue or freak ocean waves. The term optical rogue waves was coined to describe rare pulses of broadband light arising during the process of supercontinuum generation—a noise-sensitive nonlinear process in which extremely broadband radiation is generated from a narrowband input waveform—in nonlinear optical fiber. In this context, optical rogue waves are characterized by an anomalous surplus in energy at particular wavelengths or an unexpected peak power. These anomalous events have been shown to follow heavy-tailed statistics, also known as L-shaped statistics, fat-tailed statistics, or extreme-value statistics. These probability distributions are characterized by long tails: large outliers occur rarely, yet much more frequently than expected from Gaussian statistics and intuition. Such distributions also describe the probabilities of freak ocean waves and various phenomena in both the man-made and natural worlds. Despite their infrequency, rare events wield significant influence in many systems. Aside from the statistical similarities, light waves traveling in optical fibers are known to obey the similar mathematics as water waves traveling in the open ocean, supporting the analogy between oceanic rogue waves and their optical counterparts. More generally, research has exposed a number of different analogies between extreme events in optics and hydrodynamic systems. A key practical difference is that most optical experiments can be done with a table-top apparatus, offer a high degree of experimental control, and allow data to be acquired extremely rapidly. Consequently, optical rogue waves are attractive for experimental and theoretical research and have become a highly studied phenomenon. The particulars of the analogy between extreme waves in optics and hydrodynamics may vary depending on the context, but the existence of rare events and extreme statistics in wave-related phenomena are common ground.
Coherent Raman scattering (CRS) microscopy is a multi-photon microscopy technique based on Raman-active vibrational modes of molecules. The two major techniques in CRS microscopy are stimulated Raman scattering (SRS) and coherent anti-Stokes Raman scattering (CARS). SRS and CARS were theoretically predicted and experimentally realized in the 1960s. In 1982 the first CARS microscope was demonstrated. In 1999, CARS microscopy using a collinear geometry and high numerical aperture objective were developed in Xiaoliang Sunney Xie's lab at Harvard University. This advancement made the technique more compatible with modern laser scanning microscopes. Since then, CRS's popularity in biomedical research started to grow. CRS is mainly used to image lipid, protein, and other bio-molecules in live or fixed cells or tissues without labeling or staining. CRS can also be used to image samples labeled with Raman tags, which can avoid interference from other molecules and normally allows for stronger CRS signals than would normally be obtained for common biomolecules. CRS also finds application in other fields, such as material science and environmental science.
A tapered double-clad fiber (T-DCF) is a double-clad optical fiber which is formed using a specialised fiber drawing process, in which temperature and pulling forces are controlled to form a taper along the length of the fiber. By using pre-clad fiber preforms both the fiber core and the inner and outer cladding layers vary in diameter and thickness along the full length of the fiber. This tapering of the fiber enables the combination of the characteristics of conventional 8–10 μm diameter double-clad single-mode fibers to propagate light in fundamental mode with those of larger diameter (50–100 μm) double-clad multi-mode fibers used for optical amplification and lasing. The result is improved maintenance of pulse fidelity compared to conventional consistent diameter fiber amplifiers. By virtue of the large cladding diameter T-DCF can be pumped by optical sources with very poor brightness factor such as laser diode bars or even VECSELs matrices, significantly reducing the cost of fiber lasers/amplifiers.
Debabrata Goswami FInstP FRSC, is an Indian chemist and the Prof. S. Sampath Chair Professor of Chemistry, at the Indian Institute of Technology Kanpur. He is also a professor of The Department of Chemistry and The Center for Lasers & Photonics at the same Institute. Goswami is an associate editor of the open-access journal Science Advances. He is also an Academic Editor for PLOS One and PeerJ Chemistry. He has contributed to the theory of Quantum Computing as well as nonlinear optical spectroscopy. His work is documented in more than 200 research publications. He is an elected Fellow of the Royal Society of Chemistry, Fellow of the Institute of Physics, the SPIE, and The Optical Society. He is also a Senior Member of the IEEE, has been awarded a Swarnajayanti Fellowship for Chemical Sciences, and has held a Wellcome Trust Senior Research Fellowship. He is the third Indian to be awarded the International Commission for Optics Galileo Galilei Medal for excellence in optics.
Debora M. Kane is a Professor of Physics at Macquarie University, where her research interests are in non-linear optics and laser physics. She is a Fellow of The Optical Society and has edited four books on nanotechnology, nanomaterials and semiconductor lasers.
Luc Thévenaz is a Swiss physicist who specializes in fibre optics. He is a professor of physics at EPFL and the head of the Group for Fibre Optics School of Engineering.
János Hebling is a Hungarian physicist, known for his preliminary works at Terahertz physics and spectroscopy. He was born at Zirc on 9 May 1954 and currently works as a professor at the Institute of Physics at University of Pécs and is an active researcher at the Hungarian Academy of Sciences and ELI.
Intracellular delivery is the process of introducing external materials into living cells. Materials that are delivered into cells include nucleic acids, proteins, peptides, impermeable small molecules, synthetic nanomaterials, organelles, and micron-scale tracers, devices and objects. Such molecules and materials can be used to investigate cellular behavior, engineer cell operations or correct a pathological function.
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