An optical tweezer is a scientific instrument that uses a focused laser beam to provide an attractive or repulsive force, depending on the index mismatch (typically on the order of piconewtons) to physically hold and move microscopic dielectric objects. Optical tweezers have been particularly successful in studying a variety of biological systems in recent years. For other uses, see Laser (disambiguation). ... A dielectric is a physical model commonly used to describe how an electric field behaves inside a material. ...

History and development

Professor Steven Chu giving a seminar at The Chinese University of Hong Kong

The detection of optical scattering and gradient forces on micrometer sized particles was first reported in 1970 by Arthur Ashkin^[1], a scientist working at Bell Labs. Years later, Ashkin and colleagues reported the first observation^[2] of what is now commonly referred to as an optical trap: a tightly focused beam of light capable of holding microscopic particles stable in three dimensions. Image File history File links Dr. Steven Chu giving a seminar at the Chinese University of Hong Kong. ... Image File history File links Dr. Steven Chu giving a seminar at the Chinese University of Hong Kong. ... CUHK Science Building, commonly known as the rice cooker The Chinese University of Hong Kong, commonly referred to as CUHK, is the second oldest university in Hong Kong; it is also the only collegiate university in the city. ... Arthur Ashkin, father of the optical tweezers Arthur Ashkin is a retired scientist who worked at Bell Laboratories and Lucent Technologies. ... Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) was the main research and development arm of the United States Bell System. ...

One of the authors of this seminal 1986 paper, Steven Chu, would go on to use optical tweezing in his work on cooling and trapping atoms. This research earned Chu the 1997 Nobel Prize in Physics.^[3]. In an interview^[4], Steven Chu described how Askhin had first envisioned optical tweezing as a method for trapping atoms. Ashkin was able to trap larger particles (10 to 10,000 nanometers in diameter) but it fell to Chu to extend these techniques to the trapping of atoms (0.1 nanometers in diameter). Steven Chu (Chinese: ; pinyin: ), born 1948 in St. ... Laser cooling is a technique that uses light to cool atoms to a very low temperature. ... See also: Other events of 1997 List of years in science . ...

In the late 1980s, Arthur Ashkin and his colleagues first applied the technology to the biological sciences, using it to trap an individual tobacco mosaic virus and Escherichia coli bacterium^[5]. Throughout the 1990s and afterwards, researchers like Carlos Bustamante, James Spudich, and Steven Block pioneered the use of optical trap force spectroscopy to characterize molecular-scale biological motors. These molecular motors are ubiquitous in biology, and are responsible for locomotion and mechanical action within the cell. Optical traps allowed these biophysicists to observe the forces and dynamics of nanoscale motors at the single-molecule level; optical trap force-spectroscopy has since led to greater understanding of the stochastic nature of these force-generating molecules. Arthur Ashkin, father of the optical tweezers Arthur Ashkin is a retired scientist who worked at Bell Laboratories and Lucent Technologies. ... This article does not cite any references or sources. ... E. coli redirects here. ... Carlos José Bustamante (born 1951 in Lima, Peru) is an American scientist. ... Steve Block Dr. Steven M. Block (born 1952) is a professor at Stanford University with a joint appointment in the departments of Biological Sciences and Applied Physics. ... This article or section seems not to be written in the formal tone expected of an encyclopedia entry. ... Molecular motors are biological nanomachines and are the essential agents of movement in living organisms. ... One single-molecule, an individual molecule that can be isolated or distinguished for propose of an experiment or analysis. ...

Optical tweezers have proven useful in other areas of biology as well. For instance, in 2003 the techniques of optical tweezers were applied in the field of cell sorting; By creating a large optical intensity over the sample area filled with micro-biological sample, the cell can be sorted by its intrinsic optical characteristics.^{[6] [7]}. In 2004 Optical tweezers made the leap from large, complicated, expensive machines to much simpler, smaller, inexpensive and ultimately portable systems with the introduction of DLBT (Diode Laser Bar Trapping) pioneered by Applegate et al. at the Colorado School of Mines^[8]. Optical tweezers have also been used to probe the cytoskeleton, measure the visco-elastic properties of biopolymers, and study cell motility. The eukaryotic cytoskeleton. ... A viscoelastic material is one in which: hysteresis is seen in the stress-strain curve. ... A biopolymer is a polymer found in nature. ... Motility is a biological term which refers to the ability to move spontaneously and independently. ...

The physics of optical tweezers

Dielectric objects are attracted to the center of the beam, slightly above the beam waist, as described in the text. The force applied on the object depends linearly on its displacement from the trap center just as with a simple spring system.

Image File history File links Download high-resolution version (1204x723, 166 KB)Diagram of an optical trap. ... Image File history File links Download high-resolution version (1204x723, 166 KB)Diagram of an optical trap. ...

General description

Optical tweezers are capable of manipulating nanometer and micrometer-sized dielectric particles by exerting extremely small forces via a highly focused laser beam. The beam is typically focused by sending it through a microscope objective. The narrowest point of the focused beam, known as the beam waist, contains a very strong electric field gradient. It turns out that dielectric particles are attracted along the gradient to the region of strongest electric field, which is the center of the beam. The laser light also tends to apply a force on particles in the beam along the direction of beam propagation. It is easy to understand why if you imagine light to be a group of tiny particles, each impinging on the tiny dielectric particle in its path. This is known as the scattering force and results in the particle being displaced slightly downstream from the exact position of the beam waist, as seen in the figure. A dielectric is a physical model commonly used to describe how an electric field behaves inside a material. ... For other uses, see Laser (disambiguation). ... Several objective lenses on a microscope. ... In optics, a Gaussian beam is a beam of electromagnetic radiation whose transverse electric field and intensity (irradiance) distributions are described by Gaussian functions. ... In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. ...

Optical traps are very sensitive instruments and are capable of the manipulation and detection of sub-nanometer displacements for sub-micrometre dielectric particles.^[9] For this reason, they are often used to manipulate and study single molecules by interacting with a bead that has been attached to that molecule. DNA and the proteins and enzymes that interact with it are commonly studied in this way. The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Neuraminidase ribbon diagram An enzyme (in Greek en = in and zyme = blend) is a protein, or protein complex, that catalyzes a chemical reaction and also controls the 3D orientation of the catalyzed substrates. ...

For quantitative scientific measurements, most optical traps are operated in such a way that the dielectric particle rarely moves far from the trap center. The reason for this is that the force applied to the particle is linear with respect to its displacement from the center of the trap as long as the displacement is small. In this way, an optical trap can be compared to a simple spring, which follows Hooke's law. Hookes law accurately models the physical properties of common mechanical springs for small changes in length. ...

Detailed view of optical tweezers

Proper explanation of optical trapping behavior depends upon the size of the trapped particle relative to the wavelength of light used to trap it. In cases where the dimensions of the particle are greater than this wavelength, a simple ray optics treatment is sufficient. On the other hand, if the wavelength of light exceeds the particle dimensions, then the particles must be treated as tiny electric dipoles in an electric field.

The ray optics approach

Ray optics explanation. When the bead is displaced from the beam center, as in (a), the larger momentum change of the more intense rays cause a net force to be applied back toward the center of the trap. When the bead is laterally centered on the beam, as in (b), the net force points toward the beam waist.

In cases where the diameter of a trapped particle is significantly greater than the wavelength of light, the trapping phenomenon can be explained using ray optics. As shown in the figure, individual rays of light emitted from the laser will be refracted as it enters and exits the dielectric bead. As a result, the ray will exit in a direction different from which it originated. Since light has a momentum associated with it, this change in direction indicates that its momentum has changed. Due to Newton's third law, there should be an equal and opposite momentum change on the particle. Image File history File links Download high-resolution version (1136x748, 227 KB)Ray optics explanation as to how optical tweezers work. ... Image File history File links Download high-resolution version (1136x748, 227 KB)Ray optics explanation as to how optical tweezers work. ... For the property of metals, see refraction (metallurgy). ... This article is about momentum in physics. ... Newtons First and Second laws, in Latin, from the original 1687 edition of the Principia Mathematica. ...

Most optical traps operate with a Gaussian beam (TEM₀₀ mode) profile intensity. In this case, if the particle is displaced from the center of the beam, as in (a) in the figure, the particle has a net force returning it to the center of the trap because more intense beams impart a larger momentum change towards the center of the trap than less intense beams, which impart a smaller momentum change away from the trap center. The net momentum change, or force, returns the particle to the trap center. In optics, a Gaussian beam is a beam of electromagnetic radiation whose transverse electric field and intensity (irradiance) distributions are described by Gaussian functions. ...

If the particle is located at the center of the beam, then individual rays of light are refracting through the particle symmetrically, resulting in no net lateral force. The net force in this case is along the axial direction of the trap, which cancels out the scattering force of the laser light. The cancellation of this axial gradient force with the scattering force is what causes the bead to be stably trapped slightly downstream of the beam waist.

The electric dipole approximation

In cases where the diameter of a trapped particle is significantly smaller than the wavelength of light, the conditions for Rayleigh scattering are satisfied and the particle can be treated as a point dipole in an inhomogenous electromagnetic field. The force applied on a dipole in an electromagnetic field is known as the Lorentz force, Rayleigh scattering causing the blue hue of the sky and the reddening at sunset Rayleigh scattering (named after Lord Rayleigh) is the scattering of light, or other electromagnetic radiation, by particles much smaller than the wavelength of the light. ... The Earths magnetic field, which is approximately a dipole. ... The electromagnetic field is a physical field that is produced by electrically charged objects and which affects the behaviour of charged objects in the vicinity of the field. ... Lorentz force. ...

The force on the dipole can be calculated by substituting two terms for the electric field in the equation above, one for each charge. The polarization of a dipole is where is the distance between the two charges. For a point dipole, the distance is infinitesimal, Taking into account that the two charges have opposite signs, the force takes the form In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ... Infinitesimals have been used to express the idea of objects so small that there is no way to see them or to measure them. ...

Notice that the cancel out. Multiplying through by the charge, q, converts position, , into polarization, ,

where in the second equality, it has been assumed that the dielectric particle is linear (i.e. ).

In the final steps, two equalities will be used: (1) A Vector Analysis Equality, (2) One of Maxwell's Equations. The following identities are important in vector calculus: // This section explicitly lists what some symbols mean for clarity. ... Faradays law of induction (more generally, the law of electromagnetic induction) states that the induced emf (electromotive force) in a closed loop equals the negative of the time rate of change of magnetic flux through the loop. ...

First, the vector equality will be inserted for the first term in the force equation above. Maxwell's equation will be substituted in for the second term in the vector equality. Then the two terms which contain time derivatives can be combined into a single term.^[10]

The second term in the last equality is the time derivative of a quantity that is related through a multiplicative constant to the Poynting vector, which describes the power per unit area passing through a surface. Since the power of the laser is constant when sampling over frequencies much shorter than the frequency of the laser's light ~10¹³ Hz, the derivative of this term averages to zero and the force can be written as The Poynting vector describes the energy flux (J·m−2·s−1) of an electromagnetic field. ...

The square of the magnitude of the electric field is equal to the intensity of the beam as a function of position. Therefore, the result indicates that the force on the dielectric particle, when treated as a point dipole, is proportional to the gradient along the intensity of the beam. In other words, the gradient force described here tends to attract the particle to the region of highest intensity. In reality, the scattering force of the light works against the gradient force in the axial direction of the trap, resuling in an equilibrium position that is displaced slightly downstream of the intensity maximum. The scattering force depends linearly on the intensity of the beam, the cross section of the particle and the index of refraction of the trapping medium (e.g. water).^{[citation needed]}

Experimental design, construction and operation

A generic optical tweezer diagram with only the most basic components.

The most basic optical tweezer setup will likely include the following components: a laser (usually Nd:YAG), a beam expander, some optics used to steer the beam location in the sample plane, a microscope objective and condenser to create the trap in the sample plane, a position detector (e.g. quadrant photodiode) to measure beam displacements and a microscope illumination source coupled to a CCD camera. Image File history File links Download high-resolution version (869x830, 139 KB)This is a generic and most basic optical tweezer setup. ... Image File history File links Download high-resolution version (869x830, 139 KB)This is a generic and most basic optical tweezer setup. ... Several objective lenses on a microscope. ... Look up condenser in Wiktionary, the free dictionary. ... Photodiode closeup A photodiode A photodiode is a semiconductor diode that functions as a photodetector. ... A charge-coupled device (CCD), is an integrated circuit containing an array of linked, or coupled, capacitors. ...

The Nd:YAG laser (1064 nm wavelength) is the most common laser choice because biological specimens are most transparent to laser wavelengths around 1000 nm. This assures as low an absorption coefficient as possible, minimizing damage to the specimen, sometimes referred to as opticution. Perhaps the most important consideration in optical tweezer design is the choice of the objective. A stable trap requires that the gradient force, which depends upon the numerical aperture (NA) of the objective, be greater than the scattering force. Suitable objectives typically have a NA between 1.2 and 1.4.^[11] The absorption coefficient is a property of a material. ... Opticution is the term given to the damaging beyond viability of biological samples that are manipulated via optical traps, most commonly optical tweezers. ... Numerical aperture is a technical term of multiple uses: Numerical aperture of optical telecommunication fiber Numerical aperture in microscopy This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...

While alternatives are available, perhaps the simplest method for position detection involves imaging the trapping laser exiting the sample chamber onto a quadrant photodiode. Lateral deflections of the beam are measured similarly to how its done using atomic force microscopy (AFM). Topographic scan of a glass surface The atomic force microscope (AFM) is a very high-resolution type of scanning probe microscope, with demonstrated resolution of fractions of a nanometer, more than 1000 times better than the optical diffraction limit. ...

Expanding the beam emitted from the laser to fill the aperture of the objective will result in a tighter, diffraction-limited spot.^[12] While lateral translation of the trap relative to the sample can be accomplished by translation of the microscope slide, most tweezer setups have additional optics designed to translate the beam to give an extra degree of translational freedom. This can be done by translating the first of the two lenses labelled as "Beam Steering" in the figure. For example, translation of that lens in the lateral plane will result in a laterally deflected beam from what is drawn in the figure. If the distance between the beam steering lenses and the objective are chosen properly, this will correspond to a similar deflection before entering the objective and a resulting lateral translation in the sample plane. The position of the beam waist, that is the focus of the optical trap, can be adjusted by an axial displacement of the initial lens. Such an axial displacement causes the beam to diverge or converse slightly, the end result of which is an axially displaced position of the beam waist in the sample chamber. A very clear explanation has been presented by Joshua W. Shaevitz a former graduate student in the Block Lab at Stanford University.^[13] a big (1) and a small (2) aperture For other uses, see Aperture (disambiguation). ...

Visualization of the sample plane is usually accomplished through illumination via a separate light source coupled into the optical path in the opposite direction using dichroic mirrors. This light is incident on a CCD camera and can be viewed on an external monitor or used for tracking the trapped particle position via video tracking. Dichroic filters A dichroic filter or thin-film filter is a very-accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. ... Video tracking is the process of following movable objects in time using a camera. ...

Descriptions of various optical tweezer setups

Optical tweezers based on alternate laser beam modes

The majority of optical tweezers make use of conventional TEM₀₀ Gaussian beams. However a number of other beam types have been used to trap particles, including high order laser beams i.e Hermite Gaussian beam (TEM_xy), Laguerre-Gaussian (LG) beams (TEM_pl) and Bessel beams. A transverse mode of a beam of electromagnetic radiation is a particular intensity pattern of radiation measured in a plane perpendicular (i. ... A Bessel beam is a beam of electromagnetic radiation whose intensity is described by a Bessel function. ...

Optical tweezers based on Laguerre Gaussian beam have the unique capability of trapping particles that are optically reflective and absorptive. Laguerre-Gaussian beams also possess a well-defined orbital angular momentum that can rotate particles.^[14][15] This is accomplished without external mechanical or electrical steering of the beam. The Azimuthal quantum number (or orbital angular momentum quantum number) l is a quantum number for an atomic orbital which determines its orbital angular momentum. ...

Both zeroth and higher Bessel Beams also possess a unique tweezing ability. They can trap and rotate multiple particles that are millimeters apart and even around obstacles. ^[16]

Micromachines can be driven by these unique optical beams due to their intrinsic rotating mechanism due to the spin and orbital angular momentum of light.^{[citation needed]} Micromachines are mechanical objects that are fabricated in the same general manner as integrated circuits. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... In physics, orbital motion is the either a motion of a planet in a planetary orbit, or a motion of an electron around the nucleus of an atom, or any other motion of parts of a bound system. ... This gyroscope remains upright while spinning due to its angular momentum. ...

Multiplexed optical tweezers

A typical setup uses one laser to create one or two traps. More complex optical tweezing operations can be achieved either by time-sharing a single laser beam among several optical tweezers or by diffractively splitting the beam into multiple traps. With acousto-optic deflectors or galvanometer-driven mirrors, a single laser beam can be shared among hundreds of optical tweezers in the focal plane, or else spread into an extended one-dimensional trap. Specially designed diffractive optical elements can divide a single input beam into hundreds of continuously illuminated traps in arbitrary three-dimensional configurations. The trap-forming hologram also can specify the mode structure of each trap individually, thereby creating arrays of optical vortices, optical tweezers, and holographic line traps, for example. When implemented with a spatial light modulator, such holographic optical traps also can move objects in three dimensions. Wire carrying current to be measured Restoring spring N and S are poles of magnet A galvanometer is a type of ammeter — an instrument for detecting and measuring electric current. ... A spatial light modulator (SLM) is an object that imposes some form of spatially-varying modulation on a beam of light. ...

Optical tweezers based on optical fibers

The fiber optical trap relies on the same principle as the optical trapping, but with the laser delivered through an Optical fiber. If one end of the optical fiber tip is moulded into a lens-like facet, that lens tip will act as a focusing (converging) point for the high optical gradient trap to be formed.^[17] Optical fibers An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length. ... This article is about the optical device. ...

On the other hand, if the ends of the fiber are not moulded, the laser exiting the fiber will be diverging and thus a stable optical trap can only be realised by balancing the gradient and the scattering force from two opposing ends of the fiber. The gradient force will trap the particles the transverse direction, while the axial optical force comes from the scattering force of the two counter propagating beams emerging from the two fibers. The equilibrium z-position of such a trapped bead is where the two scattering forces equal each other. This work was pioneered by A. Constable et al., Opt. Lett. 18,1867 (1993), and followed by J.Guck et al., Phys. Rev. Lett. 84, 5451 (2000), who made use of this technique to stretch microparticles. By manipulating the input power into the two ends of the fiber, there will be an increase of a "optical stretching" that can be used to measure viscoelastic properties of cells, with sensitivity sufficient to distinguish between different individual cytoskeletal phenotypes. i.e. human erythrocytes and mouse fibroblasts. A recent test has seen great success in differentiating cancerous cells from non-cancerous ones from the two opposed, non-focused laser beams. ^[18] The term transverse means side-to-side, as opposed to longitudinal, which means front-to-back. In automotive engineering, the term transverse refers to an engine in which the crankshaft is oriented side-to-side relative to the wheels of the vehicle. ... Axial has different meanings: In geometry it means: along the same line as an axis (coaxial) or centerline: parallel (geometry), contrary to radial or perpendicular In anatomy it relates to an anatomical direction of animals and humans. ...

Optical tweezers in a 'landscape' (cell sorting)

One of the more common cell sorting systems make use of flow cytometry through fluorescent imaging. In this method, a suspension of biologic cells is sorted into two or more containers, based upon specific fluorescent characteristics of each cell during an assisted flow. By using an electrical charge that the cell is "trapped" in, the cell are then sorted based on the fluorescence intensity measurements. The sorting process is undertaking by an electrostatic deflection system that diverts cell into containers based upon their charge. Fluorescent-activated cell sorting is a type of flow cytometry, a method for sorting a suspension of biologic cells into two or more containers, one cell at a time, based upon specific light scattering and fluorescent characteristics of each cell. ...

In the optically actuated sorting process, the cell are flowed through into an optical landscape i.e 2D or 3D optical lattices. Without any induce electrical charge, the cell would sorting based on their intrinsic refractive index properties and can be re-configurability for dynamic sorting. Mike MacDonald, Gabe Spalding and Kishan Dholakia, Nature 426, 421-424 (2003)[1] made use of diffractive optics and optical elements to create the optical lattice. An automated cell sorter was described at the University of Toronto in 2001, but made use of mechanical parameters as opposed to spatial light modulation ^[19] Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... The University of Toronto (U of T) is a public research university in the city of Toronto, Ontario, Canada. ... For other uses, see Light (disambiguation). ...

On the other hand, K. Ladavac, K. Kasza and D. G. Grier, Physical Review E 70, 010901(R) (2004)[2] made use of the spatial light modulator to project an intensity pattern to enable the optical sorting process.

The main mechanism for sorting is the arrangement of the optical lattice points. As the cell flow through the optical lattice, there are forces due to the particles drag force that is competing directly with the optical gradient force(See Physics of an Optical Tweezers) from the optical lattice point. By shifting the arrangement of the optical lattice point, there is a preferred optical path where the optical forces are dominate and biased. With the aid of the flow of the cells, there is a resultant forces that is directed along that preferred optical path. Hence, there is a relationship of the flow rate with the optical gradient force. By adjusted the two forces, one will be able to obtain a good optical sorting efficiency. For a solid object moving through a fluid or gas, drag is the sum of all the aerodynamic or hydrodynamic forces in the direction of the external fluid flow. ...

Competition of the forces in the sorting environment need fine tuning to succeed in high efficient optical sorting. The need is mainly with regards to the balanced of the forces; drag force due to fluid flow and optical gradient force due to arrangement of intensity spot.

Scientists at the University of St. Andrews have received considerable funding from the UK Engineering and Physical Sciences Research Council (EPSRC) for an optical sorting machine. This new technology could rival the conventional fluorescence-activated cell sorting.^[20] The Engineering and Physical Sciences Research Council (EPSRC) is a British Research Council that provides government funding for grants to undertake research and postgraduate degrees in engineering and the physical sciences (including mathematics, Artificial Intelligence and computer science), mainly to universities in the United Kingdom. ... The Engineering and Physical Sciences Research Council (EPSRC) is a British Research Council that provides government funding for grants to undertake engineering and science research, mainly to universities in the United Kingdom. ...

Optical tweezers based on evanescent fields

An evanescent field [3] [4] is a residue optical field that "leaks" during total internal reflection. This "leaking" of light fades off at an exponential rate. The evanescent field has found a number of applications in nanometer resolution imaging (microscopy); optical micromanipulation (optical tweezers) are becoming ever more relevant in research. Evanescent is an adjective which means vanishing or disappearing. In the context of electromagnetic fields, evanescent refers to an exponential decay. ... The optical field is a term used in physics and vector calculus to designate the electric field shown as E in the electromagnetic wave equation which can be derived from Maxwells Equations. ... The larger the angle to the normal, the smaller is the fraction of light transmitted, until the angle when total internal reflection occurs. ...

In optical tweezers, a continuous evanescent field can be created when light is propagating through an optical waveguide (multiple total internal reflection). The resulting evanescent field has a directional sense and will propel microparticles along its propagating path. This work was first pioneered by S. Kawata and T. Sugiura, in 1992 (Opt. Lett. 17 (11), 772 (1992)). Kawata showed that the field can be coupled to the particles in proximity on the order of 100 nanometers. An optical waveguide is a form of a dielectric waveguide, that is capable of guiding an optical signal. ... The larger the angle to the normal, the smaller is the fraction of light transmitted, until the angle when total internal reflection occurs. ...

This direct coupling of the field is treated as a type of photon tunnelling across the gap from prism to microparticles. The result is a directional optical propelling force.

A recent updated version of the evanescent field optical tweezers make use of extended optical landscape patterns to simultaneously guide a large number of particles into a preferred direction without using a waveguide. It is termed as Lensless Optical Trapping (“LOT”) [5]. The orderly movement of the particles is aided by the introduction of Ronchi Ruling that creates well-defined optical potential wells (replacing the waveguide). This means that particles are propelled by the evanescent field while being trapped by the linear bright fringes. At the moment, there are scientists working on focused evanescent fields as well. Look up waveguide in Wiktionary, the free dictionary. ...

Optical tweezers: an indirect approach

Ming Wu, a UC Berkeley Professor of electrical engineering and computer sciences invented the new optoelectronic tweezers. Sather tower (the Campanile) looking out over the San Francisco Bay and Mount Tamalpais. ...

Wu transformed the optical energy from low powered light emitting diodes (LED) into electrical energy via a photoconductive surface. The ideas is to allow the LED to switch on and off the photoconductive material via its fine projection. As the optical pattern can be easily transformable through optical projection, this method allow a high flexibility of switching different optical landscapes.

The manipulation/tweezing process is done by the variations between the electric field actuated by the light pattern. As the particles will be either attracted or repelled from the actuated point due to the its induced electrical dipole. Particles being suspended in a liquid will be susceptible to electrical field gradient, this is known as dielectrophoresis. Dielectrophoresis (or DEP) is a phenomenon in which a force is exerted on a dielectric particle when it is subjected to a non-uniform electric field. ...

One clear advantage is that the electrical conductivity between a different cells. Living cells have a lower conductive medium while the dead ones have minimum or no conductive medium. The system may be able to manipulate roughly 10,000 cells or particles at the same time.

See comments by Professor Kishan Dholakia on this new technique, K. Dholakia, Nature Materials 4, 579-580 (01 Aug 2005) News and Views.

"The system was able to move live E. coli bacteria and 20-micrometre-wide particles, using an optical power output of less than 10 microwatts. This is one-hundred-thousandth of the power needed for [direct] optical tweezers"[6].

Optical binding

When a cluster of microparticles are trapped within a monochromatic laser beam, the organization of the microparticles within the optical trapping is heavily dependent on the redistributing of the optical trapping forces amongst the microparticles. This redistribution of light forces amongst the cluster microparticles provides a new force equilibrium on the cluster as a whole. As such we can say that the cluster of microparticles are somewhat bounded together by light. One of the first evidence of optical binding was reported by Michael M. Burns, Jean-Marc Fournier, and Jene A. Golovchenko [7].

Research goups using optical tweezers

Here is a list of research groups using optical tweezers and the type of research they perform.

• ATOM3D is a joint project comprising 7 European optics group with optical tweezing expertise
• Block Laboratory at Stanford University, USA

DNA Properties, Instrument Design, Kinesin, RNA polymerase

• Bustamante Laboratory at the University of California, Berkeley, USA

DNA Properties, DNA gyrase, Instrument Design, HCV NS3 Helicase, RNA Folding, RNA polymerase

• Chiu Lab at University of Washington, USA
• COSMIC at University of Edinburgh, UK
• Crocker Laboratory at the University of Pennsylvania, USA
• Dufresne Lab at Yale University, USA
• Forde Lab at Simon Fraser University, Canada
• Furst Lab at University of Delaware, USA
• Glückstad Lab: Programmable Phase Optics at Risø National Laboratory, Denmark
• Grier Lab at New York University, USA
• Gross Laboratory at University of California, Irvine, USA

Dynein

• Glasgow Optical Trapping at the University of Glasgow, Scotland
• Lang Laboratory at MIT, USA
• Meiners Laboratory at The University of Michigan, USA
• Nanosystems Measurement & Controls Lab at The University of Pittsburgh, USA
• Oddershede Lab at the Niels Bohr Institute, University of Copenhagen, Denmark

Instrument Design

• Optical trapping Group in University of St Andrews, Scotland, UK
• Optical Tweezers Group in ICFO
• Optical Tweezers at Umeå University, Sweden
• Optical trapping Group in University of Queensland, Australia
• OMITEC group in Institute of Scientific Instruments, Czech Republic
• Perkins Lab at University of Colorado at Boulder, USA

Instrument Design

• Wagner Group at Saarland University, Germany
• Wang Lab at Cornell University, USA

DNA Unzipping, Instrument Design, Nucleosomes, RNA polymerase, SWI/SNF

• Wuite Lab at The Vrije Universiteit Amsterdam, The Netherlands
• Chiou Lab at University of California, Los Angeles, USA
• Wu Lab at University of California, Berkeley, USA
• Rohrbach Group at Albert-Ludwigs-Universität, Freiburg, Deutschland
• Laser Spectroscopy and Optical Manipulation Group at University Federico II, Napoli, Italy

Stanford redirects here. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... The kinesin dimer attaches to, and moves along, microtubules. ... This article does not cite any references or sources. ... Sather tower (the Campanile) looking out over the San Francisco Bay and Mount Tamalpais. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Topoisomerases (Type I: EC 5. ... This article or section does not cite its references or sources. ... Left: An RNA strand, with its nitrogenous bases. ... This article does not cite any references or sources. ... The University of Washington, founded in 1861, is a public research university in Seattle, Washington. ... The University of Edinburgh (Scottish Gaelic: ), founded in 1582,[4] is a renowned centre for teaching and research in Edinburgh, Scotland. ... This article is about the private Ivy League university in Philadelphia. ... Yale redirects here. ... Simon Fraser University (SFU) is located on Burnaby Mountain in Burnaby, British Columbia, Canada, part of the metropolitan area of Vancouver, British Columbia. ... The University of Delaware (UD) is the largest university in the U.S. state of Delaware. ... Risø National Laboratory (Danish: Forskningscenter Risø) is a scientific research organization in Roskilde, Denmark. ... New York University (NYU) is a private, nonsectarian, coeducational research university in New York City. ... The University of California, Irvine is a public research university primarily situated in suburban Irvine, California, USA. Founded in 1965, it is one of ten University of California campuses and is commonly known as UCI or UC Irvine. ... Dynein is a motor protein (also called molecular motor or motor molecule) in cells which converts the chemical energy contained in ATP into the mechanical energy of movement. ... Master of Theology (MTh) Dentistry Nursing Affiliations Russell Group Universitas 21 Website http://www. ... Mapúa Institute of Technology (MIT, MapúaTech or simply Mapúa) is a private, non-sectarian, Filipino tertiary institute located in Intramuros, Manila. ... University of Michigan, Ann Arbor The University of Michigan, Ann Arbor (U-M or U of M) is a public coeducational university in Michigan, United States. ... The University of Pittsburgh, commonly referred to as Pitt, is an independent, state-related, doctoral/research university in Pittsburgh, Pennsylvania, United States. ... The Niels Bohr Institute is part of the Niels Bohr Institute for Astronomy, Physics and Geophysics of the University of Copenhagen. ... Main campus on Frue Plads. ... St Marys College Bute Medical School St Leonards College[5][6] Affiliations 1994 Group Website http://www. ... The Institut de Ciències Fotòniques (ICFO, see webpage webpage) is an independent, non-profit, permanent research foundation established by the Generalitat de Catalunya (Government of Catalonia, Spain), Department dUniversitats, Recerca i Societat de la Informació , and by the Universitat Politècnica de Catalunya. ... Umeå University Umeå Universitet : Umeå University (Swedish: Umeå universitet) is a university in Umeå in the Midnorth of Sweden. ... The University of Queensland (UQ) is the longest-established university in the state of Queensland, Australia, a member of Australias Group of Eight, and the Sandstone Universities. ... The University of Colorado at Boulder (CU-Boulder, UCB officially[3]; Colorado and CU colloquially) is the flagship university of the University of Colorado System in Boulder, Colorado. ... Saarland University (German Universität des Saarlandes) is a university located in Saarbrücken, the capital of the German state of Saarland. ... Cornell redirects here. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... A nucleosome is a unit made of DNA and histones. ... This article does not cite any references or sources. ... Diagram indicating location of the SNF2 Subfamily of proteins and their relative similarity with other proteins organized by their conservation of NTP-binding motifs. ... The University of California, Los Angeles (generally known as UCLA) is a public research university located in Los Angeles, California, United States. ... Sather tower (the Campanile) looking out over the San Francisco Bay and Mount Tamalpais. ...

Other resources

Extensive link pages to other academic groups in optical tweezing

• Extensive links to the worldwide Optical trapping community, hosted at University of St. Andrews, Scotland. [8]

Professional papers reviewing optical tweezers

• A. Ashkin, "Optical trapping and manipulation of neutral particles using lasers"[9]
• Neuman, K.C., and Block S.M Review on Optical Trapping method[10]
• M. Lang and S. Block, A Resource Letter on Optical Tweezers[11]
• K.Dholakia on Recent review of state of the art tweezers[12]
• D. McGloin on Review of Bessel beam optical tweezers[13]
• David Grier on A revolution in optical manipulation[14]
• Special Edition of Journal of Modern Optics A selection of optical tweezers papers from some of the leading groups[15]
• A more detailed list of references can be obtained from the online manuscript written by Justin E Molloy [16] and Miles J Padgett[17] titled Lights, Action: Optical Tweezers[18]posted online

Web resources

• Tweezers for information on the mechanical device from which optical tweezers take their name
• What are optical tweezers [19]
• Recent Optical Tweezers Journal Papers [20]
• Open source software for computer generated hologram design [21]
• Using optical tweezers to play a game of Tetris... [22]

Tweezers are tools used for picking up small objects that are not easily handled with the human hands. ...

Multimedia links

• BBC Frontier covering the technique of Optical Tweezers 2003[23]
• Movies showing positioning and rotation controlled by optical tweezers [24]
• Videos of optical tweezers being used on bacteria.
• Videos of optical tweezers being used on fungi.
• Video of optical tweezers used to play the tiniest game of Tetris ever.

Commercial optical tweezer systems

Commercial suppliers of optical tweezer systems include (in alphabetical order)

• Arryx
• Cell Robotics
• Elliot Scientific
• MMI Molecular Machines & Industries
• PALM

References

1. ^ Ashkin, A. "Phys. Rev. Lett. 24, 156-159", (1970)
2. ^ A Ashkin, J M Dziedzic, J E Bjorkholm and S Chu, Opt. Lett. 11, 288-290, 1986.
3. ^ Hill, Murray (November 1987). "wrote the book on atom trapping". Retrieved June 25, 2005.
   Interview conducted for internal newsletter at Bell Labs. Contains confirmation of Ashkin as the inventor of optical trapping and provides information on the 1997 Nobel Prize in Physics.
4. ^ "Conversations with History: An Interview with Steven Chu" (2004), Institute of International Studies, UC Berkeley. Last accessed on September 2, 2006.
5. ^ Ashkin, A. et al "Science vol. 235, iss. 4795, pp. 1517" (1987)
6. ^ Macdonald MP, Spalding GC, Dholakia K, "Microfluidic sorting in an optical lattice., Nature (2003); 421: 421-424.
7. ^ Koss BA, Grier DG, "Optical Peristalsis"
8. ^ Applegate, Jr. R. W. et al Optics Express vol. 12, iss. 19, pp. 4390 (2004)
9. ^ Moffitt JR, Chemla YR, Izhaky D, Bustamante C, "Differential detection of dual traps improves the spatial resolution of optical tweezers", PNAS (2006); 103(24): 9006-9011.
10. ^ Gordon JP, "Radiation Forces and Momenta in Dielectric Media", Physical Review A (1973). 8(1): 14-21.
11. ^ Neuman KC, Block SM, "Optical trapping", Review of Scientific Instruments (2004); 75(9): 2787-2809.
12. ^ Svoboda K, Block SM, "Biological Application of Optical Forces", Annual Reviews of Biophysics and Biomolecular Structure (1994); 23:247-285.
13. ^ Shaevitz JW, "A Practical Guide to Optical Trapping" (August 22, 2006). Last accessed on September 12, 2006.
14. ^ Curtis JE, Grier DG, "Structure of Optical Vortices" (2003). Last accessed on September 3, 2006.
15. ^ Padgett M, "Optical Spanners". Last accessed on September 3, 2006.
16. ^ McGloin D, Garces-Chavez V, Paterson L, Carruthers T, Melvil H, Dholakia K, "Bessel Beams". Last accessed on September 3, 2006.
17. ^ Hu Z, Wang J, Liang J, "Manipulation and arrangement of biological and dielectric particles by a lensed fiber probe", Optics Express, 12 (17): 4123-4128 (2004).
18. ^ Jochen Guck, Stefan Schinkinger, Bryan Lincoln, Falk Wottawah, Susanne Ebert, Maren Romeyke, Dominik Lenz, Harold M. Erickson, Revathi Ananthakrishnan, Daniel Mitchell, Josef Käs, Sydney Ulvick and Curt Bilby, "Optical Deformability as an Inherent Cell Marker for Testing Malignant Transformation and Metastatic Competence", Biophys. J., 88:3689-3698 (2005)
19. ^ Grover SC et al., Automated single-cell sorting system based on optical trapping. J Biomed Opt. 2001 Jan;6(1):14-22.
20. ^ "Optical fractionation and sorting.", IRC Scotland. Last accessed on September 3, 2006.