This PDF file contains the front matter associated with SPIE Proceedings Volume 8097, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Holographic optical tweezers are fast becoming an established tool in micro- and nano-science. We present developments in both the interface and the underlying technology as used in our lab, along with some of the uses we have put them to. Real time particle tracking from stereoscopic video images enables us to determine position to nanometre precision in 3D. This can be performed in real time at several kHz, allowing us to positionclamp trapped objects in 3D and measure positions and forces with optically controlled tools. Our multi-touch iPad interface gives interactive control over multiple traps at the same time, which opens new possibilities for controlling tools, structures and other dynamic processes.

Various products have been miniaturized in recent years. And, the measurement technology for surface profile of micro components is highly demanded. Then, we proposed a new measurement technique for surface profile using the standing wave trapping. The high-accuracy scale and the high-sensitive sensor are required in the profile measurement. In our measurement system, the optical trapping particle is used as the sensor. The standing wave pattern is used as the measurement scale, which has wavelength-determined intensity pitch of interference field (λ/2). Therefore, this measurement technique is expected to perform the high-accuracy measurement. It was experimentally found that the vertical measurement range is about 250 μm. The uncertainty of the sensor is ±λ/100. Thus, this technique is capable of measuring large objects in height. When measuring the continuous surface, the sensor particle is scanned in the horizontal direction above the measured surface. The trapped sensor particle in the standing wave field axially moves to follow the measured surface topography. The particle jumps when the surface profile exceeds the pitch of the standing wave pattern. Therefore, the surface profile can be calculated based on the measurement of the particle motional variation. As pre-measurement, the dependency of the scale pitch on measured surface angles was investigated. A microlens was measured with the angle dependency correction. This shows the improvement of the measurement accuracy.

We present an imaging technique using an optically trapped silica microrod probe controlled using holographic optical tweezers. The probe is raster scanned over a surface, allowing an image to be recorded in a manner analogous to scanning probe microscopy (SPM), with closed loop feedback control provided by high-speed CMOS camera image tracking. We demonstrate a proof of principle of this technique by imaging the surface of an oil droplet. We estimate the normal force exerted on the sample during imaging to be 1 pN. The resolution is limited by the diameter of the microrod tip, thermal motion of the probe and the tracking accuracy. As our technique is not diraction limited, there is scope for signicant improvement by reducing the tip diameter, and position clamping to reduce unwanted thermal motion.

We recently showed that force measurements through the detection of beam momentum changes can be implemented in single-beam gradient traps. We thereby achieved a method that renders force measurements insensitive to sample's geometrical and optical properties. Our instrument could be calibrated by a parameter that remained constant within a 4% error when, under comparable conditions, the traditional approach based on position detection could change by a factor of two or more. The setup required for these measurements was but a modified version of the apparatus used for position detection with back-focal-plane interferometry (BFPI). Despite the apparent difference between both techniques, we show here that they are not independent and we explicitly indicate the connection between them. The results suggest that our changes in the position detection instrument could have some important advantages and improve the technique when this is used to ultimately determine optical forces.

A limited range of instruments are available which allow the controlled injection of sub-picolitre volumes; microfluidic devices and commercially produced mechanical microinjection systems accounting for the majority. We present an optically controlled microsyringe capable of dispensing femtolitres of liquid. Triple beam optical tweezers are used to manipulate hollow glass microneedles and also polymer microspheres which were used as 'handles' to assist the manipulation of microneedles and 'plungers' to dispense liquid from the microneedle. Standard optical tweezers were used with the addition of a Ronchi ruling (250 lines per inch) mounted in the image relay telescope. The diffraction pattern generated by the Ronchi ruling produced three optical traps in the sample chamber. Trap spacing was controlled by translating the ruling along the axis of beam propagation within the image relay telescope. Utilizing the three-beam trap, it was possible to manipulate pulled, borosilicate capillaries (5-150μm in length, 1-10μm in diameter) both perpendicular and parallel to the axis of the capillary. Rolled SiO/SiO2 microtubes (4μm diameter, 50μm long) were also manipulated, however in this case polymer microspheres were used as 'handles'. In both cases the microneedles did not align vertically along the propagation axis; an advantage over using a single beam optical trap. Tweezing a microsphere within a microneedle dispenses femtolitres of liquid from the needle. The force exerted on microneedles is calculated to be in the order of picoNewtons so may have applications where femtolitre volumes must be controllably delivered beyond a barrier, such as single cell microinjection.

For collections of particles in a thermal bath interacting with an asymmetric substrate, it is possible for a ratchet effect to occur where the particles undergo a net dc motion in response to an ac forcing. Ratchet effects have been demonstrated in a variety of systems including colloids as well as magnetic vortices in type-II superconductors. Here we examine the case of active matter or self-driven particles interacting with asymmetric substrates. Active matter systems include self-motile colloidal particles undergoing catalysis, swimming bacteria, artificial swimmers, crawling cells, and motor proteins. We show that a ratchet effect can arise in this type of system even in the absence of ac forcing. The directed motion occurs for certain particle-substrate interaction rules and its magnitude depends on the amount of time the particles spend swimming in one direction before turning and swimming in a new direction. For strictly Brownian particles there is no ratchet effect. If the particles reflect off the barriers or scatter from the barriers according to Snell's law there is no ratchet effect; however, if the particles can align with the barriers or move along the barriers, directed motion arises. We also find that under certain motion rules, particles accumulate along the walls of the container in agreement with experiment. We also examine pattern formation for synchronized particle motion. We discuss possible applications of this system for self-assembly, extracting work, and sorting as well as future directions such as considering collective interactions and flocking models.

We present measurements on single and multiple DNA molecules inside a nanocapillary. Nanocapillaries are single molecule sensors with similar properties as standard solid-state nanopores made from silicon nitride. For stalling of DNA in the nanocapillaries, we apply optical fiber illumination in combination with video detection for real-time tracking of optically trapped colloids on a microsecond time scale. Using a cross-correlation based algorithm after image acquisition from a CMOS camera we are able to measure the position of a colloid at rates up to 40,000 frames per second over hours. A full understanding of electrokinetic transport of polyelectrolytes in strongly confined environments is still elusive. In order to shed new light on this process we perform electrophoretic force and ionic-current measurements on single and multiple DNA molecules inside nanocapillaries attached to an optically trapped colloid. The hydrodynamic interaction between single DNA molecules was investigated by capturing multiple strands inside the tip of a capillary. We find that the capture force depends linearly on the number of DNA molecules.

We have used constant force axial optical tweezers to understand the subtle eects of sequence variations on the mechanical properties of DNA. Using designed sequences of DNA with nearly identical curvatures, but varied AT content, we have shown the persistence length to be highly dependent on the elasticity of DNA. The persistence length varies by almost thirty percent between sequences containing 61% AT and 45% AT. The biological implications of this can be substantial, as the need to bend DNA is involved in a host of regulatory schemes, ranging from nucleosome positioning to the formation of protein-mediated repressor and enhancer loops.

Kinetic studies on double strand DNA damages induced by a laser microbeam have allowed a precise definition of the temporal order of recruitment of repair molecules. The order is KU70 / KU80 - XRCC4 --NBS1 -- RAD51. These kinetic studies are now complemented by studies on molecular structures of the repair proteins, using the program YASARA which does not only give molecular structures but also physicochemical details on forces involved in binding processes. It turns out that the earliest of these repair proteins, the KU70 / KU80 heterodimer, has a hole with high DNA affinity. The next molecule, XRCC4, has a body with two arms, the latter with extremely high DNA affinity at their ends and a binding site for Ligase 4. Together with the laser microbeam results this provides a detailed view on the early steps of DNA double strand break repair. The sequence of DNA repair events is presented as a movie.

The ability to identify and characterize microorganisms (algae, bacteria, eukaryotic cells) from minute sample volumes in a rapid and reliable way is the crucial first step in their classification and characterization. In the light of this challenge related to microorganisms exploitation Raman spectroscopy can be used as a powerful tool for chemical analysis. Raman spectroscopy can elucidate fundamental questions about the metabolic processes and intercellular variability on a single cell level. Moreover, Raman spectroscopy can be combined with optical tweezers and with microfluidic chips to measure nutrient dynamics and metabolism in vivo, in real-time, and label free. We demonstrate the feasibility to employ Raman spectroscopy-based sensor to sort microorganisms (bacteria, algae) according to the Raman spectra. It is now quite feasible to sort algal cells according to the degree of unsaturation (iodine value) in lipid storage bodies.

Zera® technology offers the possibility to artificially induce the formation of spherical organelles in different kinds of cells. Their large size and high density, compared to the native organelles of the cell, make them good candidates to be used as a handles for the realization of biophysical experiments inside living cells. Furthermore, they present a high signal-to-noise ratio in fluorescence microscopy and small photobleaching. This work focuses mainly on the nature of protein body motion in Nicotiana Benthamiana (tobacco) cells. The high-speed tracking of these structures reveals that they move in a stepwise mode, suggesting that myosin XI motors directly pull these organelles through the cytosol. Our results indicate that these artificially-induced structures are well integrated into the natural processes of the cell so that the technique may be advantageous for the study of the intracellular transport mechanisms. Large forces can be exerted with optical tweezers to mechanically interact with the moving organelles.

We present results demonstrating for the first time that an optically trapped bead can be used as a local probe to measure the variation in the viscoelastic properties of the vitreous humor of a rabbit eye. The Brownian motion of the optically trapped bead was monitored on a fast CCD camera on the millisecond timescale. Analysis of the bead trajectory provides local information about the viscoelastic properties of the medium surrounding the particle. Previous, bulk, methods for measuring the viscoelastic properties of the vitreous destroy the sample and allow only a single averaged measurement to be taken per eye. Whereas, with our approach, we were able to observe local behaviour typical of non-Newtonian and gel-like materials, along with the homogenous and in-homogeneous nature of different regions of the dissected vitreous humor. The motivation behind these measurements is to gain a better understanding of the structure of the vitreous humor in order to design effective drug delivery techniques. In particular, we are interested in methods for delivering drug to the retina of the eye in order to treat sight threatening diseases such as age related macular degeneration.

The interactions between T cells and antigen-presenting cells (APCs) are crucial in triggering a successful antigenspecific, adaptive immune response leading to protection against a particular pathogen or disease. At present very little is known about the magnitudes of the forces involved in these interactions. We present results showing for the first time that optical tweezers can be used to measure these cell-cell interaction forces. We were able to see a significant difference in the force distributions taken with and without antigen, as evidenced by a Mann-Whitney U-test. The T cells of interest were trapped directly and no exogenous beads were added to the sample. Interaction forces between T cells and APCs in the presence of specific antigen ranged from 0-6.5 pN, whereas, when the specific antigen was absent the interaction forces ranged from 0-1.5 pN. The accuracy of the system will be discussed in terms of how we tracked the position of the optically trapped cell and the methods we used to minimise cell roll.

We present a viability study of optically trapped live T cell hybridomas. T cells form an important part of the adaptive immune response system which is responsible for fighting particular pathogens or diseases. The cells of interest were directly trapped by a laser operating at a wavelength of 1064 nm and their viability measured as a function of time. Cell death was monitored using an inverted fluorescent microscope to observe the uptake by the cell of the fluorescent dye propidium iodide. Studies were undertaken at various laser powers and beam profiles. There is a growing interest in optically trapping immune cells and this is the first study that investigates the viability of a T cell when trapped using a conventional optical trapping system. In such experiments it is crucial that the T cell remains viable and trapping the cell directly means that any artefacts due to a cell-bead interface are removed. Our motivation behind this experiment is to use optical tweezers to gain a greater understanding of the interaction forces between T cells and antigen presenting cells. Measuring these interactions has become important due to recent theories which indicate that the strength of this interaction may underlie the activation of the T-cell and subsequent immune response.

Different theoretical models have been developed to understand light propagation in biological media and to facilitate the analysis of experimental data, both at the cellular level and in bulk tissues. Optical tweezers, combined with a light scattering measurement facility, enable the measurement of elastic light scattering distributions from single particles and cells. The aim of this paper is to present elastic light scattering measurement results from several red blood cells (RBCs) held in elliptical optical tweezers and to compare these results with theoretical predictions found in literature. Both faceon and rim-on incidence of He-Ne laser light (vertical polarization) in relation to the measured RBCs was considered. In the face-on case, light scattering intensity was larger from two RBCs than from one, but almost no difference was found when using three RBCs instead of two. In rim-on incidence, clear changes in the shape of the scattering light intensity field were found when the number of RBCs was increased from one to two. These results are supported by modelling results from literature.

Low viscosity fluids with tunable optical properties can be processed to manufacture thin film and interfaces for molecular detection, light trapping in photovoltaics and reconfigurable optofluidic devices. In this work, self-assembly in wormlike micelle solutions is used to uniformly distribute various metallic nanoparticles to produce stable suspensions with localized, multiple wavelength or broad-band optical properties. Their spectral response can be robustly modified by varying the species, concentration, size and/or shape of the nanoparticles. Structure, rheology and optical properties of these plasmonic nanogels as well as their potential applications to efficient photovoltaics design are discussed.

Many marine organisms have evolved complex optical mechanisms of dynamic skin color control that allow them to drastically change their visual appearance. In particular, cephalopods have developed especially effective dynamic color control mechanism based on the mechanical actuation of the micro-scale optical structures, which produce either variable degrees of area coverage by a given color (chromatophores) or variations in spatial orientation of the reflective and diffractive surfaces (iridophores). In this work we describe the design, fabrication and characterization of electrowetting-controlled bio-inspired artificial iridophores. The developed iridophores geometrically resemble microflowers with flexible reflective petals. The microflowers are fabricated on a silicon substrate using surface micromachining techniques. After fabrication a small droplet of conductive liquid is deposited at the center of each microflower. This causes the flower petals to partially wrap around the droplet forming a structure similar to capillary origami. The dynamic control over the degree of wrapping is achieved by applying a voltage differential between the conductive core of the petals and the droplet. The applied voltage causes dynamic contact angle change between the droplet and each of the petals due to the electrowetting effect. We have characterized mechanical and optical properties of the microstructures and discuss their electrowetting-based actuation. These experimental results are in good agreement with a 3D theoretical model based on electrocapillarity and elasticity theory. This work forms the basis for a broad range of novel optical devices.

We present a thiol-ene/methacrylate-based polymer capable of creating both physical fluidic features and optical index features via a series of three UV mask-lithography steps. The process of creating the two types of features are addressed independently by control of the polymerization and diffusion rates within the polymer system. The rapidly curing methacrylate creates a gelled, rubbery scaffold structure that allows for the creation of physical features and also monomer diffusion within the structure. The thiol-ene is a high-index polymer that cures more slowly in the presence of the methacrylate and is used to create the index structures via diffusion of replacement monomer into exposed regions. We demonstrate low-loss, multi-mode optical waveguides coupled to a fluidic channel to implement a refractometer. Waveguide loss at 635 nm for a 12.5 mm x 63.5 micron x 63.5 micron waveguide-only sample is 0.57 dB. A waveguide plus fluidic-channel device acts as a refractometer whose optical throughput is dependent on the index of refraction of the fluid in the channel.

We present experimental evidence of hydrodynamic assisted escape from a potential well. Holographic optical tweezers are used to landscape a bistable system composed of two optical traps, separated by 400nm as seen by a Si colloid of radius 400nm. We observe thermally activated transitions between the two metastable states in the system with transition rates that are in agreement with Kramers theory. Introducing a second bistable system into our experiment allows us to study the behaviour of thermally activated transitions in the presence of hydrodynamic interactions. The two bistable systems are placed in a line separated by a few micrometers. Using camera tracking technologies we track each of the two beads as they hop back and forth within their respective system. The escape events are recorded and any correlation between the two systems are then computed. We consistently find that the number of observed correlations are as expected and that the number of correlations having a positive coefficient are greater than the number of correlations having a negative coefficient. The hydrodynamic interactions assist in the escape from a metastable potential. Our results are particularly relevant in the context of concentrated colloidal suspensions where hydrodynamic interactions could lead to the formation of higher mobility paths along which it is easier to overcome barriers to structural rearrangement.

We report on dynamic modifications of the size of micro-structures self-arranged in counter-propagating laser beams by means of beams width changing. In contrast to previous published results, where the optically bound structures were kept stationary without dynamic control, here we present a method that allows dynamic modification of the self-arranged structure employing shrinking or enlargement of the "optical cage" where the particles are kept. We show the full potential of this method and demonstrate tunable optical self-arrangement of particles in one-dimension using a pair of counter-propagating Bessel beams or Gaussian beams, in two-dimensions far from the surface using a pair of counter-propagating elliptical Gaussian beams, in three-dimensions using three pairs of counter-propagating Gaussian beams arranged in space. Moreover, we present the first demonstration of optically bound revolving structure size of which can be tuned in a pair of counter-propagating Laguerre-Gaussian beams.

In this paper, long range surface plasmon devices using metallic subwavelength gratings are experimentally demonstrated. Subwavelength gold gratings are fabricated with deep UV interference lithography. Long range surface plasmon device using these subwavelength gold gratings is characterized by measuring the surface plasmon resonance reflectance curve in an attenuated total reflection setup. Surface plasmon resonance curve with approximately ten times narrower angular width than that from long range surface plasmon propagating along metallic thin films has been observed experimentally.

This paper reports on some new results from the analyses of the video microscopy data obtained in a prior experiment on two-dimensional (2D) colloidal crystals. It was reported previously that optical tweezers can be used to create mono- and di-vacancies in a 2D colloidal crystal. Here we report the results on the creation of a vacancyinterstitial pair, as well as tri-vacancies. It is found the vacancy-interstitial pair can be long-lived, but they do annihilate each other. The behavior of tri-vacancies is most intriguing, as it fluctuates between a configuration of bound pairs of dislocations and that of a locally amorphous state. The relevance of this observation to the issue of the nature of 2D melting is discussed.

Aerosols play a crucial role in many areas of science, ranging from atmospheric chemistry and physics, to drug delivery to the lungs, combustion science and spray drying. The development of new methods to characterise the properties and dynamics of aerosol particles is of crucial importance if the complex role that particles play is to be more fully understood. Optical tweezers provide a valuable new tool to address fundamental questions in aerosol science. Single or multiple particles 1-15 μm in diameter can be manipulated over indefinite timescales using optical tweezing. Linear and non-linear Raman and fluorescence spectroscopies can be used to probe a particle's composition and size. In this paper we will report on the latest developments in the use of holographic optical trapping (HOT) to study aerosols. Although widely used to trap and manipulate arrays of particles in the condensed phase, the application of HOT to aerosols is still in its infancy. We will explore the opportunities provided by the formation of complex optical landscapes for controlling aerosol flow, for comparing the properties of multiple particles, for performing the first ever digital microfluidic operations in the aerosol phase and for examining interparticle interactions that can lead to coalescence/coagulation. Although aerosol coagulation is the primary process driving the evolution of particle size distributions, it remains very poorly understood. Using HOT, we can resolve the time-dependent motion of trapped particles and the light scattering from particles during the coalescence process.

When using single microfluidic droplets as isolated biological/chemical micro-reactors or arrays of droplets as 2D assaying tools, control over droplet placement is crucial to successful device implementation. Here we demonstrate a combined mechanical and optical approach to generate highly controllable arrays of droplets in pre-determined 'rails and anchors' patterns on a two-dimensional plane. The technique combines passive mechanical forcing with selective laser action. Passive mechanical forcing provides a vehicle for droplet transport and storage and laser induced optical forcing is employed for stopping, guiding or derailing droplets as they pass through the chip. In this way intelligent operations can be performed upon arrays of droplets such as sorting, merging to initiate chemical reactions or selective removal of droplets from a predefined array. The usergenerated array may then be held static against a mean flow for prolonged observation.

We study the rotation of photo-driven Archimedes screw with multiple blades. The micron-sized Archimedes screws are readily made by the two-photon polymerization technique. Free-floating screws that are trapped by optical tweezers align in the laser irradiation direction, and rotate spontaneously. In this study we demonstrate that the rotation speeds of two-blade-screws is twice the rotation speed of one-blade-screw. However, more complex 3-blade-screws rotate slower than 2-blade-screws due to their limited geometry resolution at this micron scale.

Conventional optical trapping or tweezing is often limited in the achievable trapping range because of high numerical aperture and imaging requirements. To circumvent this, we are developing a next generation BioPhotonics Workstation platform that supports extension modules through a long working distance geometry. This geometry provides three dimensional and real time manipulation of a plurality of traps facilitating precise control and a rapid response in all sorts of optical manipulation undertakings. We present ongoing research and development activities for constructing a compact next generation BioPhotonics Workstation to be applied in three-dimensional studies on regulated microbial cell growth including their underlying physiological mechanisms, in vivo characterization of cell constituents and manufacturing of nanostructures and new materials.

Microrheology, the study of flow at the microscopic scale, has benefited immensely from a variety of optical micromanipulation techniques developed over the past two decades. However, very few present procedures allow the rapid measurement of the viscoelastic properties of fluid samples with volumes on the order of tens of picolitres over a wide frequency range. We detail preliminary construction and analysis of an active rotational microrheological method which promises to achieve this. Rotational microrheology was performed by optically trapping a birefringent probe particle in a linearly polarised dual-beam trap and rapidly rotating the polarisation direction through a xed angle. This provides measurements of the low-frequency fluid response, whilst passive monitoring of thermal motion is used to determine high-frequency components. Our method is less sensitive to boundary effects and probe particle asphericity than analogous translational microrheological techniques, so will be ideal for microfluidic applications and analysis of fluids which are generally available in volumes which preclude the use of existing experimental techniques.

In a recent paper we explored the novel reflection properties of several conical optical elements using numerical simulations based on Maxwell's equations. For example, in the case of a hollow metallic cone having an apex angle of 90°, a circularly-polarized incident beam acquires, upon reflection, the opposite spin angular momentum in addition to an orbital angular momentum twice as large as the spin, whereas a 90° cone made of a transparent material in which the incident light suffers two total internal reflections before returning, may be designed to endow the retro-reflected beam with different mixtures of orbital and spin angular momenta. In the present paper we introduce an approximate analysis based on the Jones calculus to elucidate the physics underlying the reflection properties, and we point to the strengths and weaknesses of the approach.

We calculate optical forces on colloidal particles over a photonic crystal slab. We show numerically that exciting a guided resonance mode of the slab yields a resonantly-enhanced, attractive optical force. Optical forces in the lateral direction result in a two-dimensionally periodic pattern of stable trapping positions. Trapping patterns can be reconfigured by changing the wavelength or polarization of incident light. We study the dependence of optical forces on particle size, particle dielectric constant, and photonic-crystal slab parameters. Finally, we describe the fabrication and measurement of a photonic crystal slab with a Q ~ 370.

In a recent article [Swartzlander et al. Nature Photonics, 5, 4851 (2010)], the optical analogue of conventional, aerodynamic lift was experimentally demonstrated. When exposed to quasi-plane wave illumination, a dielectric hemicylinder rotates into a stable configuration in which its cylindrical axis is perpendicular to the direction of propagation and its flat surface angled to it. In this configuration the body forces experienced by the particle contain a component perpendicular to the momentum flux of the incident field. This phenomenon can be meaningfully termed "optical lift", and the hemicylinder acts as a "light foil". Here, we present rigorous, full wave vector simulations of this effect for light foils of varying dimensions and composition. We investigate the general form of the forces and torques experienced by light foils, as a function of their orientation. The influence of the linear dimensions and the refractive indices of the hemicylinders is also investigated.

We theoretically propose laser manipulation utilizing the resonant nonlinear optical response. We calculated the radiation force exerted on a single molecule in a focused laser beam by solving density matrix equations using the non-perturbative method, because the high laser power is necessary for single molecular trapping. As the result, we coherently elucidate certain recently reported puzzling phenomena that contradict the conventional understanding of laser manipulation. Further, we demonstrate unconventional forms of laser manipulation which drastically enhances the number of degrees of freedom to manipulate nano-sized objects. For example, we can pull objects by using traveling wave that usually pushes them along the direction of traveling wave.

By means of the extended discrete dipole approximation into which the microscopic nonlocal response is incorporated, we theoretically demonstrate the radiation force and torque exerted on single molecules near the metallic nanogap. In this theory, we consider the spatial interplay between the light electric field localized within a nanometer-sized region and molecular wavefunctions. The results show a strong enhancement of exerted force due to the plasmonic and electronic double resonances, and also show the possibility of selective control of molecular alignment and orientation near the nanogap by the resonance laser manipulation.

In the phenomenon known as optical binding, optical fields induce significant forces between microparticles of dielectric matter. Most experimental studies have centered on particles of spherical morphology, assumed to be isotropic and able to tumble freely in a fluid. However, when birefringent micro-crystals and anisotropic nanoparticles such as carbon nanotubes are held in an optical trap, it is essential to account for their orientation. These particles are susceptible not only to optical forces but also torques, and there is considerable interest in their response to light that conveys angular momentum - especially optical vortices. Before the full effects of such interactions can be fully understood, however, it is necessary to cultivate a thorough understanding of the rotational effects that operate in optical binding with conventional laser radiation. Here, the orienting effect of the radiation on each individual particle, as well as the orienting influences they exert on each other, need robust theory to account for partial alignment with the throughput radiation. The aim of this paper is to develop, from results based on quantum electrodynamics and perturbation theory, analytical expressions for the observables associated with pair-wise optical binding in anisotropic, non-polar particles. The intricacies of weighted rotational averaging and tensor analysis are tackled, deploying newly devised methods to resolve results into forms amenable to experimental application. Analyzing the resulting equations allows the identification of terms corresponding to specific properties of the considered particles, including terms reflecting the degree of anisotropy. It is then straightforward to recognize criteria for the validity of commonly held approximations.

We have implemented several algorithms for hologram generation, aimed for holographic optical tweezers applications, using the parallel computing architecture CUDA. We compare required computation time for different implementations of the Gerchberg-Saxton algorithm and provide guidelines for choosing the best suited version with respect to the application. We also show that additional calculations, compensating for limitations in the used spatial light modulator and optical system, can be included in the hologram generating software with little or no loss in computational speed.

Conical refraction produces the well-known ring profile when circularly polarised light is incident on a biaxial crystal. Conical diffraction of linearly polarised light in a biaxial crystal produces a beam with a crescent-shaped intensity profile. Rotation of the plane of polarisation of the incident light produces the unique effect of spatially moving the crescent-shaped beam around a ring. We use this effect to trap microspheres and white blood cells and to position them at any angular position on the ring. Continuous motion around the circle is also demonstrated by rotating the input linear polarisation. The ability to spatially locate a beam and an associated trapped object simply by varying the polarisation of light suggests that this optical process should find application in the manipulation and actuation of micro- and nano-scale physical and biological objects.

We present a novel implementation of Fourier optics along a single strand of hybrid optical fiber in a monolithic manner that can generate a highly efficient pseudo-Bessel beam. The incident fundamental mode of an optical fiber is adiabatically transformed to multiple ring modes by interference within a coreless silica fiber, which serves as a micro annulus apertures. A micro polymer lens was formed at the end face to complete the Fourier-transform providing a pseudo-Bessel beam at the output. Efficient multiple particle trapping experiments for both polystyrene beads were realized over 1 mm distance along the pseudo-Bessel beam. Furthermore all-optical transport of the trapped particles along a three dimensional optical route was demonstrated by spatially multiplexing pseudo-Bessel beams via multi mode interference (MMI) type Bessel beam generators. 1x3 pseudo-Bessel beam multiplexer was installed in the water based solution with 10mm(micro meter?) polystyrene beads. After a polystyrene particle was trapped by pseudo-Bessel beam, the initial acceleration was observed as 150μm/s². The final velocity of the trapped particle maintained about 300μm/s with 40μm/s undulation due to pseudo-Bessel beam crossing points. The spatial multiplexing of fiber optic pseudo- Bessel beam arrays could make a new building block to realize reconfigurable all-optical transportation of particles.

Optical lining of multiple dielectric beads was experimentally demonstrated using two counter- propagating Bessel-like beam generated by multimode interference in optical fibers embedded in polydimethylsiloxane (PDMS) channel. All Fiber Bessel-like beam (AFB) generator was composed of a single mode fiber concatenated with a segment of coreless silica fiber of 1600 μm length and a fiberized focusing lens. A Bessel-like beam was achieved by multimode interference along the coreless silica fiber, and it maintained an average center beam diameter of 3.7 μm over an axial length of 300 μm, having a nearly uniform output power within a variation of ±0.11%. AFB generator was designed to be compatible with a continuous wave Yb-doped fiber laser oscillating at the wavelength of 1084nm in order to provide all-fiber solution. A micro-fluidic system of cross-channel was fabricated using PDMS to embed two counter-propagating fiber probes, which provided an accurate beam alignment and stable delivery of sample. One dimensional optical potential well was generated along the counter propagating beams, where samples were trapped, and then self-optical line of them was formed along longitudinal axis. This results from self-reconstruction, which is property of Bessel beam and it was confirmed in not only dielectric particles but also biological sample. This AFB generator paves the way for novel integration of microfluidic system as optical filter or chromatography.

Orbital angular momentum (OAM), as nature of optical field, has attracted considerable attention, due to its academic interest and potential applications such as quantum information, atomic manipulation, micromanipulation and the biosciences. The well-known OAM carried by an optical field originates from the azimuthal phase gradient of an optical vortex field with a helical phase structure. Here we predict a novel optical OAM, which is induced by curl of polarization. To demonstrate experimentally the above prediction, we present an idea for creating a kind of radial-variant vector fields, which could have all local linear polarization and hybrid states of polarization (SoPs). By specifically arranging the SoPs of the vector fields, new effects and phenomena can be anticipated that can expand the functionality and enhance the capability of optical system. The generated vector fields with the radial-variant hybrid SoPs can carry such a novel OAM. Optical trapping experiments validate that the focused vector fields without any additional phase vortex, as the ring optical tweezers, exert torques to drive the orbital motion of the trapped isotropic microspheres.

When samples of interest are small enough, even the relatively weak forces and torques associated with light can be sufficient for mechanical manipulation, can offer extraordinary position control, and can measure interactions with three orders of magnitude better resolution than atomic force microscopy. However, as the components of interest grow to slightly larger length scales (which may yet be of interest for microfluidic, "lab-on-a-chip" technologies and for research involving biomedical imaging), other approaches gain strength. This paper includes discussion of the angular momentum carried by sonic beams that we have implemented both to levitate and controllably rotate disks as large as four inches across. Discussion of such acoustic beams complements the discussion of the angular momentum carried by light and, by further analogy, how we view stationary states discussed in quantum mechanics. Hence, a primary use of the sonic screwdriver is as a model system, although these beams are useful for a variety of other reasons as well (not least for aberration correction for ultrasonic array systems). Methods, including the use of holographically structured fields, are discussed.

In this work, we propose a unique plasmonic substrate that combine the strength of localized and extended surface plasmons for optical trapping, spectroscopy and biosensing, all in the same platform. The system is based on periodic arrays of gold nanopillars fabricated on a thin gold sheet. The proposed periodic structure exhibits high refractive index sensitivities, as large as 675 nm/RIU which is highly desirable for biosensing applications. The spectrally sharp resonances, we determine a figure of merit, as large as 112.5. The nanopillar array also supports easily accessible high near-field enhancements, as large as 10.000 times, for surface enhanced spectroscopy. The plasmonic hot spots with high intensity enhancement lead to large gradient forces, 350 pN/W/μm², needed for optical trapping applications.

Plasmonic dipole antennas are powerful optical devices for many applications since they combine a high field enhancement with outstanding tunability of their resonance frequency. The field enhancement, which is mainly localized inside the nanogap between both arms, is strong enough to generate attractive forces for trapping extremely small objects flowing nearby. Furthermore it dramatically enhances their Raman scattering cross-section generating SERS emission. In this publication, we demonstrate how plasmonic antennas provide unique means for bringing analyte directly into hotspots by merely controlling the optical force generated by the plasmon resonance. This technique is very suitable for immobilizing objects smaller that the diffraction limit and requires a very little power density. In this work, 20nm gold nanoparticles functionalized with Rhodamine 6G are trapped in the gap of nanoantennas fabricated with e-beam lithography on glass substrate. The entire system is integrated into a microfluidic chip with valves and pumps for driving the analyte. The field enhancement is generated by a near-IR laser (λ=808nm) that provides the trapping energy. It is focused on the sample through a total internal reflection (TIRF) objective in dark field configuration with a white light source. The scattered light is collected through the same objective and the spectrum of one single antenna spectrum is recorded and analyzed every second. A trapping event is characterized by a sudden red-shift of the antenna resonance. This way, it is possible to detect the trapping of extremely small objects. The SERS signal produced by a trapped analyte can then be studied by switching from the white light source to a second laser for Raman spectroscopy, while keeping the trapping laser on. The trapping and detection limit of this approach will be discussed in detail.

We present a holographic tweezers workstation to optically trap and spectroscopically characterise metal nanoparticles. The versatility of the holographic tweezers allows us to create multiple traps manipulating several metal nanoparticles simultaneously. We developed an imaging system to view the nanoparticles in a transmission darkfield configuration without compromising the high numerical aperture of our trapping and viewing objective. In addition we implemented single particle spectroscopy to interrogate the trapped particles' properties with the ability to directly monitor the plasmonics coupling between particles while changing the distance between them. We also demonstrate a laser based method to generate fixed arrays of nanoparticles.

Spatial mapping of optical force near the hot-spot of a metal-dielectric-metal bow-tie nanoantenna at a wavelength of 1550 nm is presented. Non contact mode atomic force microscopy is used with a lock-in method to produce the map. Maxwell's stress tensor method has also been used to simulate the force produced by the bow-tie and it agrees with the experimental data. If dual lock-in amplifiers are used, this method could potentially produce the near field intensity and optical force map simultaneously, both with high spatial resolution. Detailed mapping of the optical force is critical for many emerging applications such as plasmonic biosensing and optomechanical switching.

The rapid development of microfluidic devices in recent years has led to a huge number of applications in chemistry, biology and interdisciplinary areas. This is because they act as miniaturized platforms in which sorting, mixing, reaction and measurement can be achieved in a precise and rapid manner. Being able to both understand and measure the pressure of fluids inside these devices is very important, especially in the cases where multiphase flows are involved. For example, certain advanced micromixing technologies demand accurate evaluations of bubble-induced extra pressure, since the pressure contribution from one bubble is likely to impact the velocity and residence time of others, affecting the mixing efficiency and quality in a complicated manner. Similarly, in some microfluidics-based biochemical analysis, extra pressure brought about by droplets is a critical factor in the design of on-chip pumping, as high throughput experiments involving continuous supply of large numbers of droplets often require a considerable enhancement in the pumping pressure necessary to maintain the droplet flow3. Last, state-of-the-art microfluidic logic devices rely heavily on the pressure distribution inside the channels, which automatically controls the paths of each droplet in the microfluidic network and as a result determines the "on" and "off" of each switch. A few techniques to measure pressure change or pressure drop in microfluidic channels have been developed. Examples include connecting the device to commercially available pressure sensors and comparing pressures of different areas by analyzing the position of fluid-fluid interface. However, all of those methods have intrinsic drawbacks in one or more aspects that considerably limit their applications. A significant one is that they are primarily aiming at measuring or comparing pressures over relatively long channels (~10 mm), and are hence only designed to work in the highpressure range, i.e. to detect a pressure change on the order of tens or hundreds of Pascals. Moreover, the long channels make it rather challenging to look into the detailed dynamics of pressure variations caused by inhomogeneous emulsions, since such a long section invariably contains multiple elements, for instance droplets, of the emulsion flow, and the measurements average out the behavior of one single element. Consequently, to further reveal the characteristics of flows in microfluidics, it is highly desirable for a pressure measurement device to work in the low-pressure range, and to resolve pressure changes "locally", i.e. within small spatial regions.

High density micron sized aerosols from liquid surfaces were generated using surface acoustic wave (SAW) nebulisation. The SAWs are made from a set of interdigitated electrodes (IDT) deposited on a lithium niobate (LiNbO₃) substrate and are designed to operate around 10MHz. RF powers of ~235mW are used to achieve nebulisation. Power below this results in droplet motion across the substrate surface. The nebulisation process generated aerosols of a narrow size distribution with diameter ranging from 0.5-2 μm. We consider ways in which these aerosols can be loaded into optical traps for further study. In particular we look at how SAW nebulisation can be used to load particles into a trap in a far more robust manner than a conventional nebuliser device. We demonstrate trapping of a range of particle types and sizes and analyse the size distribution of particles as a function of the applied frequency to the SAW device. We show that it is simpler to load, in particular, solid particles into optical traps using this technique compared to conventional nebulisation. We also consider the possibilities for loading nanoparticles into aerosol optical tweezers.

In recent years, particle transport at microscopic level has become an important research topic which has led to the understanding of directed particle transport subjected to thermal fluctuations. Brownian motors (also called ratchet mechanism) are one of the most interesting phenomena of work generation in nonequilibrium systems under random external forces. In this work, we report Brownian movement rectification of 0.5 μm diameter latex particles using pulsating ratchets. In order to implement the ratchets, an asymmetric 2D potential saw tooth phase pattern is displayed on a spatial phase modulator and then transformed into an intensity pattern by using the phase contrast method. This pattern is focused down with a 100x microscope objective obtaining a pattern of ~40x40 μm² at the focal plane. The patterns parameters can be dynamically controlled: periodicity, asymmetry, and on/off rate, which allows optimization of directed transport. We found that there is an optimum value for the on/off rate and particle diameter/spatial period obtaining an average speed of 0.6 μm/s. The 2D pattern allow us to manipulate a large number of particles, in contrast to previous studies were only one particle has been studied, opening the opportunity to massive sorting of particles.

A study of optically induced Zn/ZnO nanoparticles selective deposition using a coherent light source on single-mode fiber optic end is presented. In the numerical studies, Zn/ZnO spherical nanoparticles are considered dissolved in isopropyl alcohol with different diameters under the influence of a Gaussian beam with fundamental mode and linear polarization. The results of this study show that the gradient force is not sufficient to move Zn nanoparticles toward optical fiber end face, but it is sufficient to move ZnO nanoparticles of a certain diameter. In the experimental studies, Zn/ZnO nanoparticles were mixed with isopropyl alcohol and subsequently deposited on the fiber end face using an infrared laser. The results obtained by atomic force and optical microscopy show a good uniform distribution of nanostructures deposited on the core of the fiber end face.

Applying Maxwell stress tensor and 3D FDTD methods, physical properties of nanoparticle trapping by evanescent wave near the NSOM probe, including trapping size, trapping position and role of other forces versus optical trapping force, are revealed. From the distribution of trapping force acted on a nanoparticle along three axis directions, it is found that the nanoparticle tends to be trapped to the aperture edge and center surface of the probe tip. In experiments 120 nm polystyrene particles are trapped in a multi-circular shape and two circles of polystyrene particles are arranged to different positions on the substrate. The results indicate that the NSOM probe is able to trap nanoparticles with lower laser intensity than that required by conventional optical manipulator.

The ability to hold and manipulate nanowires using optical beams opens up a range of applications from force sensing to directed assembly. For this reason, optical trapping of nanowires has received much recent interest. In the following article we present a detailed computational investigation of the stability and general behaviour of these systems. It is found that relatively high index wires can be trapped. Furthermore, the properties of the trap vary with the parameters of the nanowire in characteristic ways. For example, the trap stiffness in the direction parallel to the axes of the beam and the wire falls off with increasing length, and can be made arbitrarily small. At the same time the other translational stiffness coefficients attain a limit in which the stiffness perpendicular to the polarization direction is approximately one half of that in the parallel direction. Rotational stiffness coefficients are seen, conversely, to increase steadily with length. These observations are explained in terms of a simple analytical model that supports the numerical calculations.

In this work we present new results regarding the optical trapping of single gold nanoparticles with a radially polarized laser beam. Since a radially polarized laser beam possesses a strong longitudinal component of the electric field in the center of the focal area, it opens up new advantages for optical manipulation. We describe a procedure of coating the experimental chamber with a charged polymer and the gold nanoparticles with ligands carrying the same charge as the polymer, thus generating electrostatic repulsion which prevents the nanoparticles from depositing on the bottom surface of the experimental chamber. Our experimental results show that a radially polarized laser beam focused with a high numerical aperture objective lens forms a stable trap of a single gold nanoparticle in aqueous solution. By comparing the duration of the interaction of particles with the trapping laser, we found that the average duration of the interactions with a radial beam is two times longer than with a Gaussian beam. Thus, we demonstrate that a radially polarized laser beam exerts stronger forces on the nanoparticles than the Gaussian beam. These findings provide a new insight into the complex interaction of a nanoparticle with the electromagnetic field of optical tweezers.

We proposed a discrete complex amplitude filter to create a focused hollow field with ultra long depth of focus. As for a high numerical aperture lens (NA=0.95), the focused field in the focal region can be engineered into a field like a long "tube" with flat wall through manipulating the distribution of the transmitted amplitude and phase at the pupil plane. This complex amplitude filter at the pupil plane can be discretized into multiple annular zones with different radius, transmittances and phase delays. A focused tube field with long depth of focus(~9λ) has been created as an example through separating and averaging of the projected pupil radiation pattern of magnetic dipole array in the focal region. Imperfections of the designed filter will influence the quality of the generated optical tube field and tolerance deviation of the radius, transmittance and phase delay in each zone is discussed. For the optical trapping, this created tube field can expand the manipulated distance and increase the trapped particles' numbers.

Owing to their self renewal and pluripotency properties, stem cells can efficiently advance current therapies in tissue regeneration and/or engineering. Under appropriate culture conditions in vitro, pluripotent stem cells can be primed to differentiate into any cell type some examples including neural, cardiac and blood cells. However, there still remains a pressing necessity to answer the biological questions concerning how stem cell renewal and how differentiation programs are operated and regulated at the genetic level. In stem cell research, an urgent requirement on experimental procedures allowing non-invasive, marker-free observation of growth, proliferation and stability of living stem cells under physiological conditions exists. Femtosecond (fs) laser pulses have been reported to non-invasively deliver exogenous materials, including foreign genetic species into both multipotent and pluripotent stem cells successfully. Through this multi-photon facilitated technique, directly administering fs laser pulses onto the cell plasma membrane induces transient submicrometer holes, thereby promoting cytosolic uptake of the surrounding extracellular matter. To display a chemical-free cell transfection procedure that utilises micro-litre scale volumes of reagents, we report for the first time on 70 % transfection efficiency in ES-E14TG2a cells using the enhanced green fluorescing protein (EGFP) DNA plasmid. We also show how varying the average power output during optical transfection influences cell viability, proliferation and cytotoxicity in embryonic stem cells. The impact of utilizing objective lenses of different numerical aperture (NA) on the optical transfection efficiency in ES-E14TG2a cells is presented. Finally, we report on embryonic and mesenchymal stem cell differentiation. The produced specialized cell types could thereafter be characterized and used for cell based therapies.

Optical tweezers constitute a powerful technique with a wide range of applications in biological studies. Nevertheless, the response of living matter to the interaction with laser light still remains unclear. Photothermal and photochemical effects primarily due to laser absorption seem to be the major detrimental causes. This work aims at assessing the laser heating effects on NG108 cells by studying the induction of apoptosis and necrosis on these cells. Furthermore, quantification of the local temperature increase in the focus of the optical trap with the back-focal-plane interferometry technique is also one of the main goals.

The stall forces of processive molecular motors have been widely studied previously in vitro. Even so, in vivo experiments are required for determining the actual performance of each molecular motor in its natural environment. We report the direct measurement of light momentum changes in single beam optical tweezers as a suitable technique for measuring forces inside living cells, where few alternatives exist. The simplicity of this method, which does not require force calibration for each trapped object, makes it convenient for measuring the forces involved in fast dynamic biological processes such us intracellular traffic. Here we present some measurements of the stall force of processive molecular motors inside living Allium cepa cells.

In this work, we present a novel method of cavitation, thermocavitation, induced by CW low power laser radiation in a highly absorbing solution of copper nitrate (CuNO₄) dissolved in deionized water. The high absorption coefficient of the solution (α=135 cm^-1) produces an overheated region (~300cm^-1) followed by explosive phase transition and consequently the formation of an expanding vapor bubble, which later collapse very rapidly emitting intense acoustic shockwaves. We study the dynamic behavior of bubbles formed in contact with solid interface as a function of laser power using high speed video recording with rates of ~10⁵ fps. The bubble grows regularly without any significant modification of its halfhemisphere shape, it reaches its maximum radius, but it deforms in the final stage of the collapse, probably due to the bubble adhesion to the surface. We also show that the maximum bubble radius and the shock-wave energy scales are inversely with the beam intensity.