Optoelectronic tweezers (OET) have emerged in recent years as a powerful form of optically-induced dielectrophoresis
for addressing single cells and trapping individual nanostructures with DMD-based virtual-electrodes. In this technique
an alternating electric field is used to induce a dipole within structures of interest while very low-intensity optical images
are used to produce local electric field gradients that create dynamic trapping potentials. Addressing living cells,
particularly for heat-sensitive cell lines, with OET's optical virtual-electrodes requires an in-depth understanding of
heating profiles within OET devices. In this work we present quantitative measurements of the thermal characteristics of
single-crystalline-silicon phototransistor based optoelectronic tweezers (PhOET). Midwave infrared (3 - 5 micron)
thermographic imaging is used to determine relative heating in PhOET devices both with and without DMD-based
optical actuation. Temperature increases of approximately 2°C from electrolyte Joule-heating are observable in the
absence of DMD-illumination when glass is used as a support for PhOET devices. An additional temperature increase of
no more than 0.2°C is observed when DMD-illumination is used. Furthermore, significantly reduced heating can be
achieved when devices are fabricated in direct contact with a metallic heat-sink.
By switching between two tilt angles MEMS mirrors can be used to produce spatial light patterns. This enables the
Digital Micromirror Display (DMD, Texas Instruments) chip to produce the images found in some data projectors. In
this paper we will show how these images can be converted into electrical patterns. We use the electrical gradients in
these patterns to control the movement of particles through dielectrophoresis. We show how this can be used to move
cells within PBS solution and characterize our device. We also discuss possible ways to improve our optical setup
through Adaptive Optics (AO).
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.