Phototransistor-based Optoelectronic Tweezers (Ph-OET) enables optical manipulation of microscopic particles in physiological buffer solutions by creating electrical field gradients around them. A spatial light pattern is created by a DMD based projector focused through a microscope objective onto the phototransistor. In this paper we look into what differences there are in the trap stiffness profiles of HeLa cells trapped by Ph-OET compared to previous a-Si based OET devices. We find that the minimum trap size for a HeLa cell using a phototransistor with pixel pitch 10.35μm is 24.06μm in diameter which can move cells at 20μms-1 giving a trap stiffness of 8.38 x 10-7 Nm-1.
Optoelectronic Tweezers (OET) creates patterned electrical fields by selectively illuminating a photoconductive layer
sandwiched between two electrodes. The resulting electrical gradients are used to manipulate microscopic particles,
including biological cells, using the dielectrophoresis (DEP) force. Previously it has been shown that up to 15,000 traps
can be created with just 1 mW of optical power1, and that OET traps are 470 times stiffer than traps created with optical
tweezers of the same power2. In this paper we explore the use of OET for trapping HeLa cells. First, experiments are
performed using glass beads as a model particle, and the results are compared with numerical simulations to confirm our
ability to model the electrical field gradients in the OET device. We then track trapped HeLa cells in different sizes of
traps, showing maximum cell velocities of 60 μm s-1 using an illumination intensity of just 2.5 W cm-2. We measure the
electrical properties of the cell's membrane by analyzing the cell's DEP frequency response and use this information to
model the forces on the cell. We find that it is possible to create a trap with a stiffness of 3×10-6 N m-1 that does not vary
with position within the trap.
Optofluidics is the process of integrating the capabilities of optical and fluidic systems to achieve novel
functionalities that can benefit from both. Among the novel capabilities that an optical system can bring to the table is
the ability to manipulate objects of interest in a liquid media. In the case of biological samples, the objects of interest
consist mainly of cells and viruses, whereas in applications such as nanoelectronics, manipulation of nanoparticles is of
interest. In recent years, optoelectronic tweezers (OET) has emerged as a powerful technique for manipulation of
microscopic particles such as polystyrene beads, cells, and other biological samples and nanoscopic objects such as
In this paper, we will focus mostly on recent advances in the optoelectronic tweezers technology, including
characterization of optoelectronic tweezers operational regimes, manipulation of biological samples such as cells in highconductivity
physiological solutions with translation speeds higher than 30 μm/s, manipulation of air bubbles in
silicone oil media with speeds up to 1.5 mm/s, and exploring the limits on the smallest particle that OET is capable of
trapping. These advances all contribute immensely to the functionalities of OET as an optofluidic system.
Optoelectronic tweezers (OET) provides a non-invasive, low-power, optical manipulation tool for trapping, transporting, and separating microparticles, cells, and other bioparticles. The OET device uses a photosensitive layer to form "virtual electrodes" upon exposure to light, creating non-uniformities in an applied electric field. The electric field gives rise to a force known as dielectrophoresis: microparticles move as a result of the non-uniformities in the electric field imparting unequal forces on the induced dipoles of the particles. These virtual electrodes can be actuated with low optical intensities, enabling the use of incoherent light sources and direct imaging techniques to create optical manipulation patterns in real-time. In this paper, we demonstrate OET operation on live cells, including the trapping and manipulation of red and white blood cells, and the automated collection of HeLa cells. Automated size-based sorting is performed on a mixture of 15- and 20-μm-diameter polystyrene beads, and dielectric property-based separation is used to differentiate between live and dead white blood cells.
To achieve all-optical-lab-on-a-chip systems, it requires optical manipulation tools for both microparticles and microfluids. Optical tweezers have attracted a great deal of interests in manipulating cells or particles. However, it is not effective in handling microfluid. Its high optical power requirement also limits its application in high throughput bio-analysis system. In this paper, we demonstrate two novel mechanisms, optoelectrowetting (OEW) for handling microdroplets, and optoelectronic tweezers (OET) for optical manipulation of microscopic particles with low optical power actuation. Instead of using direct optical force, both mechanisms rely on light induced electrical force for optical manipulation.
Optoelectrowetting (OEW) enables control of microfluids in droplet form by optical beams. It is based on light induced electrowetting, which changes surface tension at solid-liquid interface at illuminated area. It is realized by integrating a layer of photoconductive material with electrowetting electrodes. By programming the illumination pattern, we have successfully demonstrated various functions for droplet, such as moving, splitting, and merging. A 100 pico-liter droplet was transported at a speed of 785um/sec by an optical beam with an optical power of 100mW.
Optoelectronic tweezers (OET) manipulate cells or particles based on light induced dielectrophoresis (DEP). Trapping or repelling of microscopic particles is achieved with a light intensity of 2W/cm^2, which is 5 orders of magnitudes lower than that required by optical tweezers (10^5~ 10^7 W/cm^2). The liquid containing cells or particles is sandwiched between a photosensitive surface and a transparent ITO glass, with an ac bias between them.. When the laser beam is focused on the photosensitive layer, it creates a virtual electrode on the illuminated area, resulting a non-uniform electric field at the aqueous layer. Cells or particles in the liquid layer are polarized by this non-uniform electric field and driven by the DEP force. The force could be attractive or repulsive, depending on the dielectric properties of the particles and the bias frequency. Using OET, we have demonstrated concentration of polystyrene particles and live E.coli cells using an optical power less than 10uW.