Automated single-cell sorting system based on optical trapping.

We provide a basis for automated single-cell sorting based on optical trapping and manipulation using human peripheral blood as a model system. A counterpropagating dual-beam optical-trapping configuration is shown theoretically and experimentally to be preferred due to a greater ability to manipulate cells in three dimensions. Theoretical analysis performed by simulating the propagation of rays through the region containing an erythrocyte (red blood cell) divided into numerous elements confirms experimental results showing that a trapped erythrocyte orients with its longest axis in the direction of propagation of the beam. The single-cell sorting system includes an image-processing system using thresholding, background subtraction, and edge-enhancement algorithms, which allows for the identification of single cells. Erythrocytes have been identified and manipulated into designated volumes using the automated dual-beam trap. Potential applications of automated single-cell sorting, including the incorporation of molecular biology techniques, are discussed.

Optical selection, manipulation, trapping, and activation of a microgear structure for applications in micro-optical-electromechanical systems.

The optical processes involved in laser trapping and optical manipulation are explored theoretically and experimentally as a means of activating a micrometer-size gear structure. We modeled the structure by using an enhanced ray-optics technique, and results indicate that the torque present on the gear can induce the gear to rotate about the gear-arm plane center with light as the driving energy source. We confirmed these findings experimentally by using gears manufactured with conventional semiconductor techniques and from a layer of polyimide. It is expected that such a simple gear design activated by use of light could lead to an entire new class of micro-optical-electromechanical systems.

Optical levitation and trapping of a micro-optic inclined end-surface cylindrical spinner.

Cylindrical micro-objects with inclined end surfaces have been observed to be optically trapped in a focused laser beam and to rotate about the beam's propagation direction. A simplified vector model is developed that accounts for the observed effect; the enhanced ray-optics model is used to simulate the behavior of time evolution for the cylindrical object in the beam. Experimental laser trap configurations are presented, along with a video image sequence of the cylinder's precession.

Optical levitation particle delivery system for a dual beam fiber optic trap.

We combine a radiation-pressure-based levitation system with a dual fiber, laser trapping system to demonstrate the potential of delivering single particles into the fiber trap. The forces versus position and the trajectory of the particle subjected to the laser beams are examined with an enhanced ray optics model. A sequence of video images taken from the experimental apparatus demonstrates the principle of particle delivery, trapping, and further manipulation.

Theoretical investigation of the optical trapping properties of a micro-optic cubic glass structure.

An enhanced ray optics model is applied to the study of the optical levitation and trapping properties of a glass cubic object. It is found that for certain highly symmetric orientations simultaneous force and torque equilibrium can exist in the lowest-order TEM00 laser beam profile. For analytical purposes, the square surfaces of the cube are divided into two identical triangular surfaces, and the interaction of the rays with these triangular surfaces simplifies the computation of the total force and torque on the cube. The technique developed can easily be extended to the study of other regular or complex structures.

Radiation-pressure-based cylindrically shaped microactuator capable of smooth, continuous, reversible, and stepped rotation.

Long cylindrical objects have been observed to align their central axis with the propagation axis of the illuminating laser beam through the action of radiation-pressure-generated force and torque. A cylindrically shaped microactuator based on this principle and suitable for micromachine applications is examined theoretically. When four in-plane laser beams converging at a common point centered on the cylinder are used, the cylinder can be made to rotate about a pivot point. In one mode, smooth, continuous, and reversible rotation is possible, whereas the other cylinder can be step rotated and locked, similar to the operation of conventional stepping motors. The properties of the device are analyzed based on obtaining either a constant rotation rate with variable beam power levels or a quasi-constant rotation rate with constant beam power levels or on using a fixed beam sequence rate that matches the system parameters and produces smooth or stepped operation.

Experimental confirmation of the optical-trapping properties of cylindrical objects.

A sophisticated modeling program was used recently to predict the trapping and the manipulation properties of elongated cylindrical objects in the focal region of a high-intensity laser beam. On the basis of the model, the cylinders should align their longest diagonal dimension with the propagation axis of the laser beam and follow the beam when it is displaced transverse to the cylinder's central axis. Experimental confirmation of the cylinder's behavior is presented and confirms the suitability of the enhanced ray-optics approach to modeling micrometer-scale objects in optical-trap environments.

Simulated dynamic behavior of single and multiple spheres in the trap region of focused laser beams.

An enhanced photon propagation method is used to calculate the forces and torque present on each sphere of a system of particles located in the vicinity of focused laser-trapping beams. Infinitesimal trajectory displacements are computed through classical mechanics and the new particle position used to define the next trapping system geometry considered. Repeated applications of the process, implemented as a computer program, enables full trajectory plotting and the dynamic behavior of the systems to be explored as a function of time.

Theoretical and experimental considerations for a single-mode fiber-optic bend-type sensor.

A novel single-mode bend fiber-optic sensing principle is presented. The design makes use of the translucent protective sheath that encases a typical fiber as a means of locating the position of a small bend present on an otherwise straight fiber. We can simultaneously determine bend magnitude by measuring the reduction in the fiber's core light. The theoretical model presented and the experimental results obtained are in excellent agreement, suggesting that a single-point sensor system is feasible with the proposed technique.

Analysis of a birefringent sensor's dependence on the blocking properties of linear polarizers and the input laser beam's polarization state.

The performance of birefringent fiber-optic sensors is examined theoretically, based on the extinction properties and leakage of the linear polarizers and the initial light beam's polarization state. Results indicate that polarizers with leakage factors as large as 0.01 can still be part of high-quality sensing systems. It is also shown that in certain input-beam polarization conditions, the presence of a leaky polarizer in the sensing system acts similarly to a perturbation point on the fiber, causing polarization mixing and signal degradation.

Polarization-maintaining distributed fiber-optic sensor: software elimination of second-order (ghost) coupling points.

A distributed polarization-maintaining sensor is theoretically analyzed when the applied perturbations are large enough to generate second-order effects. A software algorithm has been developed that identifies the real perturbation points and returns the magnitude of the perturbations distributed along the fiber.